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Full text of "Practical Electronics 1965 August"


ctical Electronics 



AUGUST 15 



PRICE 2'6 





NOT BUILD ONE OFOUR 
PORTABLE TRANSISTOR 
RADIOS... 



BACKED BY OUR SUPER AFTER SALES SERVICE 



ROAMER SEVEN Hk 



S WAVEBAND PORTABLE OR CAR RADIO 

Amazing performance and specification * Now with PHILCO MICRO-ALLOY R.F. TRANSISTORS 

9 stages — 7 transistors and 2 diodes 

Covers Medium and Long Waves, Trawler Band and two Short Waves to approx, 15 metres. 

Push-pull output for room filling volume from rich toned heavy duty " Celestion " speaker,_ Air spaced 

ganged tuning condenser. Ferrite rod aerial for M &. L Waves and telescopic aerial for 

S Waves. Real leather-look case with gilt trim and shoulder and hand straps. Size 9 X 7 x 4in, 

appro*. The perfect portahle and the ideal car radio. (Uses PP7 battery available anywhere.) 

Total cost of parts now only fC 10 6 ^ * '"' 





Parts Price List and easy build plans 3 

NEW TRANSONA 
FIVE 



5 6 



Total cost of all 
parts now only 



42/6 

POCKET FIVE 



Home, Light, A.F.N.,Lux. 
alt at good volume. 

C.P. Durham 
#7 stages— 5 transistors and 2 diodes 

Fully tunable over Medium and Long 
Waves and Trawler Rand. Incorporates 
Ferrite rod aerial, tuning condenser, 
volume control, new type fine lone 
super dynamic 2Jin. speaker, etc. 
Attractive case. Size 61- x 41 x l.iirt. 
(Uses 1289 battery available anywhere.) 
P. & P. Ports Price List and easy build 
3 6 plans 2/- 



MELODY 
SIX 




9 7 stages — 5 transistors and 2 diodes 

Covers Medium and Long Waves and Trawler 

Band, a feature usually found in only the most 

expensive radios. On test Home, Light, 

Luxembourg and many Continental stations 

were received loud and clear. Designed round 

supersensitive Ferrite rod aerial and fine 

tone 2£in. moving coil speaker, built into 

attractive black case with red speaker grille. 

Size 5i x IV x 3iin. (Uses 1289 battery available anywhere.) 

Ports Price List and Total cost of all AVJ II. P. & P 

easy build plans 16 parts now only "AyO j . 




3 6 




42/6 

SUPER SEVEN 

# 9 stages — 7 transistors and 2 diodes 



Covers Medium and Long Waves and 
Trawler Band. The ideal radio for home, 
car, or can be fitted with carrying strap 
for outdoor use. Completely portable — 
lias built-in Ferrite rod aerial for wonderful 
reception. Special circuit incorporating 
2 RF Stages, push-pull output, 3in, speaker 
(will drive large speaker). Size 7 i X 5± X 

l^in. (Uses 9v battery, available anywhere.) 

Total cost of all £7 I Q f. P. & P. Parts Price List and easy build 



"... amazed at volume and performance, 
has really come up to my expectations". 
S.G., Stockton-on-Tees. 
% 8 stages— 6 transistors and Z diodes 

Our latest completely portable transistor 
radio covering Medium and Long Waves. 
Incorporates pre-tagged circuit board, 3in. 
heavy duty speaker, top grade transistors, 
volume control, tuning condenser, wave 
change slide switch, sensitive 6in, Ferrite 
rod aerial. Push-pull output. Wonderful 
reception of B.B.C. Home and Light, 
208 and many Continental stations. 
Handsome leather-look pocket size case, 
only 6J x 3i x l^in. approx. with gilt 

speaker grille and supplied with hand and shoulder straps. 

Pons Price List and Total cost of all £~t Q f. P. & P. 

easy build plans 2,'- parts now only m*f*WvW 



TRANSONA SIX 

08 stages— 6 transistors and 2 diodes 



This is a lop performance receiver cover- 
ing full Medium and Long Waves and 
Trawler Band. Push pull output. High- 
grade Speaker makes listening a pleasure, 
Ferrite rod aerial. Many stations 
listed in one evening including Luxem- 
bourg loud and clear. Attractive case 
in grey with red grille. Size 6V '-: 4i x 
ijin. (Uses PP4 battery available any- 
where.) Carrying Strap 1/- extra. 

of all CO A P- & P. Parts Price List and easy build 
only 3 ~/° 3,6 plans 16 




Total cost 

p. ires now 



parts now only 



3 6 plans 2/ 



COMPONENT BARGAINS 



TRANSISTORS 

PHILCO MADT Type 2NI727 
Maximum 1'rcquencv of oscilla- 
tion 150 Mc/s . . 8/6 

PHILCO MADT Type 2N1728 
Maximum frequency of oscilla- 
tion 150 Mc/s 9/6 

PHILCO MADT (Micro Alloy 
Diffused) Type 2N503 Maxi- 
mum frequency of oscillation 
over 500 Mc/s .. ,. 15/- 

TUNING CONDENSERS 

Air spaced fine quality German 
manufacture with slow motion 
drive. 00005 with oscillator 
section . , . . 5.6 Post 1 - 



HEADPHONES 

High Fidelity miniature magnetic 
earpieces (2) on slim band with 
lead and plug. Easily converted 
to stereo. American manufac- 
ture. 100 ohms impedance. 
Transformers supplied free for 
higher impedances . . 13/6 

P & P 1/6 

CYLDON PERMEABILITY 
TUNERS 

Full M.W. coverage. Fitted 
coupling coil, oscillator coil, 
ferrite slugs and slow motion 
tunini; with cursor, etc. GIVE 
AWAY PRICE . . . . 10- 
P & P I - 



ROAMER SIX new u 

NOW WITH PHILCO MICRO-ALLOY R.F. TRANSISTORS 

• 6 WAVEBAND!! 

S stages— 6 transistors 

and 2 diodes 

Listen to stations half a world away 
with this 6 waveband portable. Tunable 
on Medium and Long Waves, Trawler 
band and three Short Waves, Push pull 
outpul. Sensitive Ferrite rod aerial and 
telescopic aerial for short waves. Top 
grade transistors. 3-inch speaker, hand- 
some case with gilt fittings. Size 
7± x 5t X 1-lin. 

-JC Extra band for easier tuning of 
LUX., etc. 

Total cost of all /? I A P- & P. 

parts now only *■**• I * •** 3^6 

(Carrying Strap 1/6 extra.) 

Ail components used in our receivers may be purchased 
separately if desired. Parts price lists and easy build plans 
available separately at fixed prices stated. 




Parts Price List and 
easy build plans 2/- 



RADIO EXCHANGE Ltd 

61a, HIGH STREET, BEDFORD. Phone: 2367 



Callers side entrance 
Borrotti Shoe Shop 
Open 9 — 5 p.m. 
Sats. 9 — 12.30 p.m. 



] 



< 



The NEW Stern-Clyne 
ELECTRONIC CONCERT ORGAN 

TO BUILD YOURSELF 

DESIGNED - 

— For the Electronic amateur seeking the most fascinating 
project. 

— For the discriminating organist seeking an instrument 
which DOES sound like a pipe organ. 

NEW - 

— Constructional methods introducing " sectional com- 
plete instrument" building. 

— Extended range of tone colours. Without unrealistic 
" Gimmick" effects. 

THE MOST COMPREHENSIVE KIT OF 
PARTS AVAILABLE IN THIS COUNTRY 

START BUILDING FOR AS LITTLE AS 

£75.15.0 approx. (H.P. Terms Available) 

Send 2/6 for data and information booklet (credited on initial 
purchase) to: Electronic Organ Dept., 162 Holloway Road, 
London, N.7. 




VISIT US AT 

162 HOLLOWAY ROAD, LONDON. NJ 
and hear this fabulous new Electronic Concert 
Organ demonstrated. 




-CLYNE 



GREAT BRITAIN'S GREATEST ELECTRONIC HOBBIES ORGANISATION 



HERE'S WHY THOUSANDS OF 
ELECTRONICS ENTHUSIASTS 
BUY WITH CONFIDENCE 
FROM STERN-CLYNE — 

A wide range of exclusive equipment 
available including our own speciality 
— MULLARD DESIGNS— for the home 
constructor or ready assembled. 

The finest selection of Hi-Fi and Audio 
equipment by all leading manufacturers. 

A comprehensive range of electronic 
components for the build it yourself 
enthusiast available at all branches. 

Retail shops, showrooms and demonstra- 
tion rooms throughout London and the 
provinces all carry extensive stocks. 

Finest Mail Order Service-geared to give 
prompt and efficient attention. 

Hire Purchase facilities available on 
orders of CI I ID, q and over. 

Hi-Fi advisory service to help you in 
choosing the right equipment. 

# After sales service — complete satisfac- 
tion guaranteed. 



CTE ™X Y £»^ 



H I I I I — 

18 Tottenham Court Rd., W.I. MUSeum 3929-0095. Half Day Sot. 

23 Tottenham Court Rd., W.I. MUSeum 3451-2. Half Day Thurs. 

30? Edgware Rd., W.2. PADdington 4963. Half Day Thvrs. 

109 Fleet St., E.C.4. FLEet St. 5612-3. Half Day Sot. 

162 Holloway Road. N.7. NORth 7941. Half Day Thurs. 

9 Camberwell Church St., S.E-5. RODney 2875. Half Day Thurs. 



' II I — 

26 Merchant Street, Bristol 



Bristol 20261. 

Now open 6 days a week. 



12 Suffolk House, George St. MUNicipal 3250. Half Day Wed. 

BBSBBBM 

52 Lord Street, Liverpool. Royal 7450. Open 6 days a week. 

ISMJUEIAHdJ 

20-22 Withy Grove, Manchester 4. BLAckfriars 5379-5246. 

Open 6 days a weed. 

aaaaEEM 

I2S The Moor, Sheffield. 



Sheffield 29993. Half Day Thurs. 

Dept. P.E., 3-5 Eden Grove, Holloway, London, N.7. NORth 8161-5. 



MAIL ORDERS AND ENQUIRIES TO: 



Gol 



Z & I AERO SERVICES LTD. 



JU-l.-iil Shop; 

85 TOTTERHAM COUST BOAD, LOHDOH, W.l 

Office and Warehouse: 44A WE STBOURNE GROVE, LONDON, W.2. ™' : ^TefffriRK 564112 J3 



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I OC200 10/6 

I OC202 15/- 

I OC203 14/- 

OC2H4 10/6 

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2S412 3/6 
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matched 
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licence rcijuiref!, oriiperpwIri.lnsi/Gp.p. Aloo iivalIiiUel2V Power Supply Vnils which 
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Pleue Md 2/6 in £ lor postage. Minimum charge 2 -. No CO.D, 6tden Accepted. 

Pleaae addreja all correipondence to the Head Office. 








The New Picture-Book' way of learning 

DACir ELECTRICITY (5 vols) 
DAA9IW ELECTRON I CS (6 vols) 



You'll find it easy to Jcarn with ihis ouistand- 
ingly successful new pictorial method— the 
essential facts are explained in the simplest 
language, one at a time; and each is Illustrated 
by an accurate, cartoon-type drawing. 



The books are based on the latest research into 
simplified learning techniques. This has proved 
that the Pictorial Approach lo learning is the 
quickest and soundest way of gaining mastery 
over these subjects. 



The scries will be of 

exceptional value in 

training mechanics and 

technicians in Electricity, 

Radio and Electronics. 

WHAT THIS MONTH'S 
ENTHUSIASTIC READERS SAY 



7' / ';"V'/"; i '' ,/ V" 1 ' atll " irati! >n for Producing a tong felt want in 
litejwld oj understanding Electronics." , . . S.B.J., London. 

a? 1 "' 2 , >a '" < ' ( ' S' a /f "' ish , to thank you for an excellent set of 
Manuals: they find the subject matter very easy to communicate." 

...S,L;B„ Coventry. 
A TECH-PRESS PUBLICATION 



POST A/OiV FOR 7WS OFFER // 



m 



To Selray Book Co. 
60 Hayes Hill, Hayes. Bromley, Kent 

Please send me Without Obligation to Purchase. Basic Electricitv Basic 

Electronics on 7 Days' Free Trial. I will either return set, carriage" paid, 

tn good condition within 8 days or send down pavment or 15/- (Basic 

Electricity) followed by 6 fortnightly payments of i0 .'-. Dovyn payment 

of 15/- (Basic Electronics) followed by 6 fortnightly payments of 12 6. 

Alternatively, I will send 68/. (Basic Electricity— 5 parts). 81 - (Basic 

Electronics— 6 parts) post free. This offer applies to United Kingdom 

only. 

Tick against set required (only one set allowed on free trial). 

BASIC ELECTRICITY Q BASIC ELECTRONICS Q 



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FULL POSTAL 

Address .. 



682 



4 



UNUSUAL 

SINGLE SPEAKER 
SYSTEM 




A 

CONCRETE 



An inexpensive column 
speaker constructed 
from a concrete pipe 
and fined with a good 
8* or 10' unit, has 
attracted much interest 
and admiration 
because of its clean, 
open sound. 

Complete kits oT 
wooden fixtures arc 
available, including 
absorbent wadding 
and diffusing cone. 



Price £3.15.0 for8" model, Recommended 8" unit 
—Super 8/RS/DD £6.14.2 including purchase tax. 
Price £4.18.0 for 10" model. Recommended 10" 
units — Super I0RS.DD £10.18.8; Golden 
lO'RS.'DD £7.17.5; 10' Bronze/RS/DD £4.12.9. 
Prices include purchase tax. 
Suitable concrete pipes can be purchased from 
builders' merchants at about 12/6 and 17/6. 

Descriptive leaflet free on request from: 




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■Hp 








wms% 


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WHARFEDALE WIRELESS WORKS LTD. 

Dept. E 
IDLE, BRADFORD, YORKSHIRE 

Grams : " Wharfdel " Bradford 
Telephone ; Idle 1235 6 





FIRST QUALITY PVC TAPE 

5r Sid. 850 ft. 91- 5"D.P. 850 ft. 10/6 



7* Sid. 1200ft. 11/6 
3* LP. 240 ft. 4/- 
5-rL-P. 1200 ft. 11/6 
7" L.P. 1800 ft. 186 



■3T.P. 600 ft. 8/- 
5*T.P. 1800 ft. 20/6 
5I"T.P.2400ft. 27/6 
T T.P. 3600 ft. 37/6 



Complete with 
McLaren Vari- 
able Thermosun 
90 3 to 180'F. 20 
amp. A.C. and 
GEC double pole 
20 amp, ma ins 
switch. IK". 27", 
30" and 3 6". 
State length re- 
quired. £2.0.0 
plus 5 - P. & P. 



P. & P, on each 1/6, 4 or more post tree. 



3lcW IMMERSION HEATER 




"PREMIER" KETTLE ELEMENT 

1000 w„ 8 6 - 3 - - P. & P. Retaining nut and 
flange 2, 6, switch plug lo suit 2 6. 



A.C. MAINS MOTOR 




3 to 4 WATT 
AMPLIFIER KIT 




transformer, output transformer, 
volume and tone controls, re- 
sistors, condensers, etc, 6VG, 
ECC8I and metal rectifier. 
Circuit 1/6 free with kit. 29/6 
plus 4,6 P. & P. 



40w. FLUORESCENT LIGHT 

KIT incorporating GEC Choke size 8i" 
X If* X l : i", 2 bi-pin holders, starter and 
starter holder, 11/6. P. & P. 4/6. 
Similar to above: 80 w. Fluorescent Light 
Kit incorporating GEC choke size 11-i";-, - 
if* X 1-J-", 2 bi-pin holders, starter and starter holder, 17 6. P. & P. 5/6. 




8-watt 5-valve PUSH-PULL 
AMPLIFIER* METAL RECTIFIER 

Size: 9 X 6 ■■: 1|" A.C. Mains 200-250v, 5 valves. 

For use with Std. or L,P. records, musical 

instruments, all makes of pick-ups and mikes. 

Output 8 walls at 5 per cent total distortion. 

Separate bass and trehle lift controls. Two 

inputs, with controls, for gram, and mike. Output Transformer 

tapped for 3 and 15 ohms speech coils. Built and tested. £3 19 6 

P. & P. 8, -. 





SPECIAL OFFER! 

"ELEGANTSEVENMUI" 

Combined Portable and Car Radio 
The Radio with the " Star " Featurei 
•k 7-transistor super het. Output 

350 mW. * m 

-£ Grey wooden cabinet, fitted K 

handle with silver-coloured 

fittings, size 12£ in. ;■: 8* In. 

X 3| in. 
+ Horizontal tuning scale, size 1lHn 

X 2{ in. in silver with black lettering' 
■fc All stations clearly marked. 
ir Ferrite-rod internal aerial, 
T*r Operated from PP9 battery. 
it l.F. neutralisation on each stage 

460 kc.'s. 

• D.C, coupled output stage with 
separate A.C. negative feed back. 

•fr All components.ferrite rod and tuning 
assembly mounted on printed board. 

* Fully comprehensive instructions and point-to-point wiring diagram 
4 = fl u te . d c,r ; uii fioard ' back-printed with all component vfluw 

# Fully tunable over medium and long waveband. 

• Car aerial socket. * Full after-sales service, 

4 in. SPEAKER. Parts list and circuit diagram 2/*. FREE with parts, 
Shop Hours 9 a.m. — 6 p.m. Early Closing Wednesday 

RADIO & T.V. COMPONENTS (ACTON) LTD. 

2ID, HIGH STREET, ACTON, LONDON, W.3 



ONLY 

£4.4.0 

Plus 6, 6 Post & Packing 



683 




^■■■■■■■■■> 

-llluj □ I HI 



wz^: 



mstep A wi 



SIZE 8i' 



SINC1 

20 WATT INTEGRATED 



20 WATTS R.M.S.! 



X 



11* 



x I 



WEIGHT 4k ozs. 



THE SINCLAIR X-20 enables you to enjoy, for 
the first time ever, the advantages of using a 
high power, high fidelity, audio amplifier truly in 
step with today's space age electronics. No 
longer does power mean problems of heat and 
size, for the X-20 requires neither heatsink nor 
special ventilation. It measures only 8$"x3i" ■: I ", 
weighs 4 A- ozs. and will deliver up to 20 watts 
R.M.S. into a 7i-8 ohms loudspeaker— 40 watts 
by U.S.A. standards! A 3-stage pre-amplifier of 
exceptional efficiency is included within the 
above dimensions to ensure an overall frequency 
response from 20 to 20,000 c/s well within — IdB 
from input to output. With greatly improved 
transient response, there is corresponding im- 
provement in the results obtained from other 
equipment used with the X-20 which itself has 
an energy conversion factor of better than 95% 
at the output stage. At no point in the circuitry 
of the X-20 are components over-run, so that 
the instrument is both stable and assured of 
indefinite working life — and it is easier to build 
and instal than any amplifier you have ever 
owned. Best of alt it costs far less and enables 
you to have stereo for very modest outlay. 



Complete kit of parts 

including transistors 

and X-20 manual in 

sealed carton 



£7.19.6 



Built and tested with X-20 manual 
in sealed carton 



£9.19.6 



X-20 Power Pack sufficient to drive £ A I Q f\ 
two X-20' s JtrT»l7»w 



FULL SERVICE FACILITIES ALWAYS AVAILABLE TO ALL 
SINCLAIR CUSTOMERS 



WA'WI 11:11 hllilMIHiMMimiiimimMiL 




MR X-20 

P.W.M. AMPLIFIER AND PRE-AMP 



nn^ 



AA 



SQUARE WAVE 
GENERATOR 



FEED BACK 
INTEGRATOR 



r\j* 



THREE STAGE 

P«E AMP 



CURRENT 
ADDER 



ElECTKONIC 
SWITCH 



OUTPUT 
STAGE 



WHY P.W.M. IS BETTER 

Illustration shows in block diagram form, the principal stages used in the 
Sinclair X-20 Pulse Width Modulated Amplifier. Use of the latest Hypes 
of transistors and high quality components combined with unique 
circuitry achieve outstanding performance whilst retaining all the 
operational features of conventional quality amplifier design. No other 
amplifier In the wortd can compare for efficiency in the amatingiy high energy conversion factor of the X-20 — 
only Pulse Width Modulation used in exclusive Sinclair circuitry elves you this wonderful performance! 

THE ONLY AMPLIFIER IN THE WORLD TO 
HAVE ALL THESE EXCITING FEATURES 



•jr: Easily built in an evening 

•Jc No. of transistors — 12 

-£- Special silicon epitaxial planar output 

transistors with a rise and fall time of 

less than 0.2 micro- seconds 

if Frequency response 20 to 20,000 c/s 1- 
IdB 

if Total harmonic distortion at 10 watts 
R.M.S. 0.1% 

if Input sensitivity— I mV into S-K ohms 
if Signal-to-noise ratio — better than 70dB 
■*■ 20 WATTS R.M.S. MUSIC POWER 
OR IS WATTS R.M.5. CONTIN- 
UOUS POWER INTO 7.5 OHMS 
it 15 WATTS R.M.S. MUSIC POWER 
OR 12 WATTS R.M.S. CONTIN- 
UOUS POWER INTO 15 OHMS 
•if For use with any type of pick-up, 
microphone, radio tuner,' tape pre- 
amp, etc. 



*jf Makes an ideal amplifier for guitar 
or other forms of P.A, 

if Built-in low pass fitter cutting off 
above 20 Kc/s makes the amplifier 
widely tolerant of the load to which it 
is connected 

if Power required 36 V dc at 700 mA 
preferably from the Sinclair X-20 
Power Pack 

if m% ENERGY CONVERSION 

FACTOR AT OUTPUT 

* SUPERB QUALITY AND RELIA- 
BILITY 

if The simplest ever system of installa- 
tion, mono or stereo 

•^ The opportunity to connect the 
tone and control system of your 
choice 



LISTENERS REQUIRING LESS POWER 



This is ideal combined hi-fi amplifier and pre-amp for use in 
more restricted listening conditions. The X-10 uses P.W.M. 
with integrated p re-amplifier and offers the same outstanding 
advantages as the X-20 but with 10 watts peak output. It 
measures only 6 in. x 3 in. Thousands of these units have been 
built and are in regular use. For 12-15 volts D.C. operation. 
Tone control system added to choice. 

SINCLAIR X-10 

P.W.M. AMPLIFIER AND PRE-AMP 

Complete kit £C IO - Rtody built £(. It) X X-10 power HMf) 
with It Iran- fcJ-17i« om j , rst cd tO.I7.U slJ pply unil ti. M.U 
si's tors and X-10 Manual 



GUARANTEE ORDER FORM 



jfV- 




Please send me 



NAME 

ADDRESS, 



BUILD IT YOURSELF! 

THE SMALLEST AND MOST 
EXCITING RADIO IN THE WORLD 




SINCLAIR 



Power 



MICRO 6 

• Range • Quality 



Smaller than a matchbox, this world-famous receiver 
brings in stations ail over the medium waveband with 
fantastically good quality and volume. Ic performs with 
amazing efficiency in cars, buses, trains and steel- 
framed buildings, yet measures only I|" X IfV X_ \" 
complete with self-contained aerial and batteries. 
Building this smart minute set is enjoyable for 
expert and beginner alike. Its per- 
formance is wonderful. 
Alt ports including 3 M.A.T. transis- 
tors, case, lightweight earpiece, and 
instructions come to 

Mallory Mercury Batteries (2 required) 

Type ZM 312, I /I I each. (6 in pack for 10/6) 



enjoyable for 



SINCLAIR TR750 POWER AMP 



MEASURES $$ 

only 

2" x 2" 




All parts and 
instructions 39/6 



IDEAL 
WITH 
THE 

M1CRO-6 

Read/ built and tested 45/- 
With built-in switch and volume control. Output 750mW 
for feeding into standard 25 to 35 ohm speaker. Input lOmV 
into 2kQ. Operates from 9V d.e. Designed principally for 
use with the Micro-6 with which ic can make a car, portable 
or indoor domestic radio. This amplifier will also make a 
record player, intercom., baby alarm, etc. Easily adaptable 
to stereo. 



LOOKING FOR TROUBLE? 

You'll find it more easily with a 

SINCLAIR 

MICRO-INJECTOR 

This ingeniously designed device 

generates and injects a test signal 

into any part of audio or radio 

equipment at any frequency from 

1 kc s to 30 Mc s by means of 

which it becomes easy to locate 

faults rapidly and accurately. 

Measures Ifx li s *XjIfi., excluding probe and is the 

smallest and most efficient device of its type ever made 

available to constructors, With full instructions. 




Paris and 

instructions 

come to 



27/6 



Ready built 
and tested 



32/6 



For which I enclose- Cash;Cheque!Money Order value 
£...- s d 



Should you not be completely 
satisfied with your purchase when you 
receive it from us, your money will be 
refunded in full and at once without 
question. It is important to quote Pr.E 8 
should you prefer to write your order 
instead of cutting out this coupon, 

685J 



DE LUXE RECORD PLAYER KITS 


4-Speed Players 2-tont gag 






Cabinets 17 15 B'.in. Hid> H 






sax jouaspeaner ana a watt tH 






2^-valve £ stase amplifier ready ^ 


.■ : .-.''-:. 




aoilt. Quality output. Vol- ' 






ame and Tone controls. All 






items tit together perfectly. 






Special instruc- 




k 


tions ennMft #t&$$m 






assemtiiy in 30 j-- 5 ' *4jrapP 






minii id. only 5 1|K£ ■'■■ '-'■'■ '-^ t 


'+ J? \''^^§ 




wires to join. W^ftfe^ 


... J? : jftMm 




18 months' ij: ^%t^ 
gnarantee. j|» ^%L, 




* 


^JSe 


COMPLETE ^%^ 


wsmi^' 




KITS ^^J 






As above with ^^ 






B.5.R, Monarch Autochange 


f 10/10/0 P.P. 


Bf- 


Garrard Autoslim Autochange 


£10.19 6 P.P. 


S' 


Garrard SRP10 Single Play 


£9/19 6 P,P 


5 - 


ALL AVAILABLE SEPARATELY 






Cabinet with board cot to choice 


£3 9 G P.P. 


a n 


Amplifier with speaker 


£2 12 8 P.P. 


3 9 


AUTOCHANGEKS Stereo Mono 15 


* extra; 




B.S.R. UA25 Superslim 


£5 19 6 P.P. 


a ; « 




£6 10, P.P. 


3.8 




£10.10 -P.P. 


3B 




£8,' 10;- P.P. 


3 6 


SINGLE PLAYERS 


Garrard SEP 10 auto, stop/start , 


S4/17/6 P,P. 


m 


E.M.I, Latest model auto, stop . . . 


£3. IB 8 P.P 


PR 


B.S.R. with separate P.1T 


£37 6 P.P 


2 9 



NEW ELEGTROLYTICS FAMOUS MAKES 

TUBULAR I TUBULAR | CAW TYPES 

8:- 

m- 

7/6 
5.8 



I 350 v, 
2350 ». 
4 350 v. 
8,'450 v. 
18/450 t. 
32 .'450 t. 
25/24 t. 
50/60 ¥. 



%>- I 10025 T. 
8/3 ! SS0.25 v. . 
2 3 50fl;13 v. . 
2 ; 3 1,000 12 v, 
S 8.450 ' 



Sh 8,'MO y. 

2/8 IB 600 t. 



3.. 



IS 16 500 v. 



31- I 32+32 350 v. 
3/6 I 33 + 33 450 v. 
3/9 I 8 - 18:450 v. 3/9 | 50 i- 50 '350 r. 1{- 

1/9 IS i- 1 ti ■'■150 ■;, 4/3 64 + 120 350 v. 11 16 
21- . 32 :-3S/3S0 v. 4/8 . 100-200/275 t. 12/6 



PAPER TUBULARS 
350v. 0.1 3d., 0.5 18; 1 mid. 3 -. 
500v. 0.001 to 0.05 9di 0,1 1'-; 0.25 1/6: 0.5 2/6. 
l.OOOv. 0.001, 0.002, 0.005. 0.01, 0.02, 1.6: 0.05, 0.1 2/-: 
0.25, 0.5 3/'-. 

2.000v. 0.005, 0.01, 0.02 2 8; 0.05 3 6. 
PAPER CQSDENSERS, O.OOImld.. 7kV., 8 8; 20kV„ 10,.' 8., 



CERAMIC. 500 v. 1 pF, to 0.01 mfd., 9d. Disc Ceramics 1— 
Pulse 15 pF. to 155 pF., 12 kV„ 2 6. 

SILVER MICA. Close tolerance [plus or minus 1 pF.), 2.2 to 
47 pF.,1/-: ditto 1 % SO to 815 pF. 1/-; 1,000 to 5,000 pF., 1/9. 
TWIN GANG. "O-O" 208 pF.-178 pF., 10/6; 365 pF„ minia- 
ture 10 ■'-: 500 pF. standard with trimmers. 9,.-; midget, 7/8; 
midget with trimmers. 9' ; 500 pF. slow motion, standard 9/-; 
small 3-gang 500 pF. 17 6, Single '■0" 365 pF. 76. 
SHORT WAVE, Single 10 pF., 25 pF., 50 pF.. 75 pF., 
100 pF., 160 pF., 5 6 each. Can be ganged. Couplers 9d. each. 
TUNING. Solid dielectric. 100pF„300pF„500pF.,3 6 each. 
TRIMMERS. Compression ceramic 30, 50, 70 pF., 9d.; 
100 pF„ 150 PF., 13: 250 pF., 1 6; 600 pF., 750 pF.. 1.9. 
BEST BRITISH P.V.C, RECORDING TAPES. LP 5in. 90011. 
11 6, DP 1200ft. 16 6: LP 5iin. 1200ft. 14 6, DP lSOOlt. 24 6; 
LP 7in. lSOOft. 19/6. DP 2400H. 29. S. 



BAKERS SELHURST LOUDSPEAKERS 

HI-FIDELITY MODELS 



5gns. 



12in., 15 W. Stalwart 3 01 15 
ohms, 45-13,000 
c.p.s., 12,000 lines 

12in. De Luxe Foam Suspens- 
ion .14,000 lines, 15 Qi-rnc 
w, 25-17,000 e.p.l, T g n> * 

12in, Bass 25 w. I? anc 
25-15,000 c.p.i. <*S"»> 



c.p.s 



Super 20 I Anne 
to 25 kes IwgnS. 



NEW GROUP MODELS 

FOR BASS, LEAD and 

RHYTHM GUITARS 

12in. diameter, 25 watt, 

12.000 lines 

12in. diameter, 35 watt, 

14.000 lines 

15in. diameter, 50 watt, 
17,000 lines 




Q MAX CHASSIS CUTTER 

Complete: a die, a punch, an Allen screw and key 



tin. 


14 4 


l-Ain. 


ia - 


IJin. 


22 6 


tin. 


14 6 


liin. 


18 - 


2in. 


34 3 


Jin. 


IS 6 


Uin. 


18 & 


2Ain, 


37 9 


sin. 


IS 9 


I|in. 


20 - 


2jin. 


44 9 


lin. 


is - 


Ifin. 


20 s 


1 in. sq. 


31 6 



CRYSTAL MIKE INSERTS. 1! X Ha 

CRYSTAL HIKE BM3 I-VSERTS. 1 Jin 

ACOS CRYSTAL MIKE INSERT 15 y jin 

ACOS CRYSTAL STICK MIKE 39-1 

PROFESSIONAL MAGNETIC GUITAR MIKE with 

Vol. and Tone Controls 

Moving Coil Mike with Switch 90 -. Floor Stand,,.... 

TANNOY CARBON MIKE with Switch 

BARGAIN XTAL PICK-UP ARM Complete with 

ACOS LP- 78 Turnover Head and Stylii 



MAINS TRANSFORMERS /.,;„ 

250-0-250, 80 mA, 6.3 v. 3,5 a. or 4 v. 4 a. Rectifier 6.3 v, 
la. or 5 v. or 4 v. 2 a. 22 6; Ditto 350-0-350, 29 6; 
30O-0-300 v. 120mA.. 6.3 v.CT 4 a. 0.5, 6.3 v. 2. a. 33 8 

MINIATURE 200 v. 20 mA.. 6.3 v. 1 a 10 6 

MIDGET 220 v. 45 mA., 6.3 v. 2 a 15-6 

SMALL. 30O-0-300 v. 70 mA., 6.3 v. 4 a 19/6 

HEATER TRANS. 6.3 v. 1! a., 7.6: 6.3 v. 4 a 10 B 

Ditto tapped sec. 1.4 v,. 2, 3, 4, 5, 6.3 v. 11 amp. . . 8 6 
GENERAL PURPOSE LOW VOLTAGE. Outputs 3, 4, 5, 

6, 8, 9, 10, 12, 15, 18. 24 and 30 v. at 2 a 22'8 

Ditto, 1 amp., 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 

60 29/B 

Sub-Min. Mains to 9 v. 80 mA. 1 X li >' liin 7'8 

AUTQ TRANS, 150 w.. 0. 115 v., 230 v., 22 6; 50Q w. 82 6 

GRAM AMPLIFIERS 

Valves: UY85 Rectifier and UCL82 Triode Pentode 
3! warts. 5,-C SI X2rn.de ep. Now and Tested. 3 ohm 
sucpuc, rone and volume on-off eonrrois. Ready for 
U se20O-250v.A.C. QNLy 37 / 6 p _ & p 2 fi 



LOUDSPEAKERS P.M. 3 OHMS. 2! in,, 3in„ 4in„ 5in % 
"in. x 4in., 16 '6 each; Sin. 17 6; 6 lin. 16,6; 12in. 30/-; 
(15 ohms 35.-); lOin. X 6in. 22,6; Sin. >; Sin. 21/-; 9in. xein. 
21.-. E.M.I. Double Cone 131 X Bin., 45/-. 
Stentorian lOin. HF1012.87 6; 8in.HF812 72 6, Crossover 
3,000 c.p.s. 30'-, Horn Tweeter 3Kc,'s. to 16 Kes. 28 '6. 
WAVE-CHAKGE SWITCHES WITH LOWS SPINDLES. 

2 p. 2-way, or 2 p. 8-way. or 3 p. 4-way or 1 p. 12-way; ea. 3/6 

4 p. 2-way, or 4 p. 3-way, 3 6; 8 p. 4-way. 2 wafer, 6 8 

Wavechange " MAKITS " 1 p. 12-way, 2 p. 6-way, 3 p. 4-way, 
4 p. 3-way, 6 p. 2-way, Prices include click spindles, 
adjustable stops, spaces, etc., 1 wafer, 8,8; 2 wafer, 12.6; 

3 wafer. 16,-; 4 wafer, 19,6; 5 water. 23 j exlra waters, 2/6, 
TOGGLE SWITCHES, 3. P., 2 -; d'p., 2/6; d.p.d.t., 4/-. 



BOOKS (Please Add Postal i 

" W-W." Radio Valve Data 7/6 

High Fidelity Speaker Enclosures 5,'- 

At a Glance Valves, CRT Equivalents 3 6 

TV Fault-Findin* 6'- 

Mnllard Audio Amplifier Manual 8.6 

Radio Valve Guide, U....k.i ], -j, :: .-.r 4 m 5/. 

Practical Radio Inside Out ; 3,6 

Transistor Audio Amplmer Manual 6 . 

Shortwave transistor Receivers 5'. 



RETURN OF POST DESPATCH Post I '6, List /,-, C.O.D, 2/6extro. (Export, Send remittance and extra postage, no C.O.D.) CALLERS WELCOME 

337 WHITEH0RSE ROAD, 
WEST CROYDON tho^s 



RADIO COMPONENT SPECIALISTS 



TAPE RECORDER COVERS 




Smart water-proof cover 
to give complete protec- 
tion to your tape recorder. 
Made from rubberised 
canvas in navy, wine, tan, 
grey and bottle green 
with white contrasting 
pipings, reinforced base, 
handy zip microphone 
pocket and name panel. 



8 TK 1 ... 49/6 


Grundif Cub 


., 35/-* 


TK 5 ... 55/- 


Telefunken 85 


.. 65/- 


TK6 ... 67;6 


75/15 


& 


TK8 ... 63.'- 


76K . 


.. 55/- 


TK 14, 18 


95 . 


.. 69/6 


&23 ... 59 o 


Philips 3108 


. S7/6 


TK14L, I7L, 


,, 354S 


.. 79,6 


I8L& 23L 6716 


„ 3534 


.. 87/- 


TK20 ... 52/6" 


„ 3459 


..,79/6 


TK24 ... 55/- 


„ EL3538 . 


J fi3/- 


TK 25 ... 55/- 


„ EL3542 , 


.. 63/- 


TK 30 ... 60/- 


„ EL353& . 


. I 70/- 


TK35 ... 63,'- 


„ EL3515 . 


.. S7/6 


TK 40 & 41 66/- 


„ EL3S4I/I5 


57/6 


TK46 ... 82/- 


,, 3S4I/H , 


. 72/. 


TKSS ...63/-* 


,, Starmaker 


66/- 


TK 60 ... 75/-* 


Cossor 1602 


, 57/61 



Cossor 1601 

-, 1604 

1605 

Stella ST455 

„ ST454 

„ ST458 ... 

., ST459 

Saba 230S , 

Elizabethan LZ29 
Breneil Mk. 5 

,, 3 scar 
Truvox R92 and 94 
Robuk RK3 
Ferrograph 

Sony 521 

Revox 

Optacord 414—412 



63/- 

79/'- 
84/- 
63/- 
57/6 
79,'- 
84 - 
63/. 
75/- 
77/. 
69/- 
99/- 
67/6 
88/- 
90/- 
84/- 
63/- 



* Without pocket 



A. BROWN & SONS LTD. 

24-28 GEORGE STREET, HULL. TEL.: 25413, 25412 




SAVBIT ALLOY 
saves wear on 
soldering iron bits 



The world-famous copper 
loaded alloy containing 5 
cores of non-corrosive 
flux, that saves the solder- 
ing iron bit. Erstn Multicore 
Solder is also available in 
high tin quality alloys. 60 40 
in 22 s.w.g. for printed 
circuits, transistors, etc. 



/THE HANDY DISPENSER 

Easy to find in the 
tool box— simple to 
use. Virtually a third 
hand for tricky sold- 
ering jobs. 12 feet 
5 core 18 s.w.g. 
ERSIN MULTICORE 
SAVBIT alloy in a 
continuous coil used 
direct from free- 
standing dispenser. 

2/6 each 



^zS£ 



SAVBIT SIZE 1 CARTON 

Contains approximately 30 
feet of 18 s.w.g. SAVBIT. 
It is also sup- 
plied in 14 s.w.g. 
and 16s. w.g. Ob- 
tainable from ra- 
dio and electrical 
stores. 

5/- each 




BIB WIRE STRIPPER 
AND CUTTER 



Strips insulation 
without nicking 
wire, cuts wire 
cleanly, adjust- 
able to most 
thicknesses. 
Splits extruded 
plastic twin flex. 

3/6 each 




MULTICORE SOLDERS LTD. 

MULTICORE WORKS • HEMEL HEMPSTEAD • HERTS • HEMEL HEMPSTEAD 363G 



686 



BRAND NEW AM/FM (V.H.F.) RADIO GRAM 
CHASSIS AT £13,13.0 (Carriage Paid) 

" rM 




Chassis size IS x Bj x 5Jin. Mgft. New manufacture. Dial 14 J x 4in. in 2 

roiours, predominantly cream. 200-250 v. a.c. on*;'. 

Pick-up. Ext. Speaker. Ac. E., and incite Sockets, l'ivo inmhli nitons— 

OFF, L.W., M.W., J'.Hf,, and (iraui. Aliened and tested 0.1'. Transformer. 

Tone control. 1000-1000 ST.: 20n-5i>u M.: »s-im Mew. Valves EZ30 rect.; 

ECH81, EF89. EABCflO. K !.«■!. ECC85, 3-otou speafcor required. 

10 X Gin. ELLIPTH'AL 8TBAKEB 25 - to pravhMen ol this chants, 

TEEMS: 'Chassis) €3.10.0 down and a monthly payments of £8.4.0. Cheap 

Room Dipoie for V.H.K.. 18,6. feeder 6d. per Taid. 

ALTERNATIVE DESIGS. EAV. 1000-lflOQ jr.; S.W. (0O3 Sti-.'s): SLAV. 

130-475 31.; V.II.E. 87-100 Jlo.'s.; GfjUn positiini. Othprwieu similar to above 

chassis. Fricc £15.15.0 (carr. paid). TERMS: £3.10.0 flown and 6 monthly 

payments of £8.4.0. Total lt.l". price £18.14,0. Circuit diagi'iiin 2 '>}, 



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MINIATURE PUSH-PULL 
AUDIO AMPLIFIER 
HIGH IMPEDANCE 

PRINTED CIRCUIT, 4in. x 2jiti. >; Itin. over transformers. Output for 3-ohm 
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The newly improved model of this famous AVO 
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It- is simple to use, one rotary switch for instant range selection, 
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RESISTANCE: 0-2M.fi, in 2 ranges, using 1.5V cell 

SENSITIVITY: lO.OOOJi/V on d.c. voltage ranges 

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7 J X 4 K /f ins. and 
weighs only 24 ozs. 



fflir 



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687 



YOU 



THE WORLD-FAMOUS KIT-SETS ANYONE CAN SUCCESSFULLY BUILD «~ 

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CAN SAVE £ £'s BY BUILDING ANY HEATHKIT 



lUcuthJaJL 



MODEL 




MALVERN 
CABINET 



FM TUNER 



"MALVERN" HI-FI ESU1PMENT CABINET. 

Will house all your Hi-fi equipment. Left "in the 

white." Size: 39| x 32 X2lfin. 

Kit £18.1.0 (inc. P.T.) 

A wide range of other cabinets. 

HI-FI FM TUNER. Range 86.108 Mc's. Avail- 
able in two units, sold separate)/. TUNER (FMT- 
4U) 10.7 Mc's IF £2.15.0 (inc. P.T.), IF AMPLIFIER 
(FMA-4U) power supply and valves £13,13.0. Total 
Kt £16.8.0. 

AM/FM TUNER. Covers FM 86-108 Me s, AM 
16-50. 2QO-S50. 900-2,000 M. Tuning heart (£4.13.6 
inc. P.T.) and IF Amp. Case. Total £27.5.0 Kit 

JUNIOR ELECTRONIC WORKSHOP, Model 
EW-I. 20 exciting experiments can be made. 
Spcci.il 3oiderless connections. Kit £7.13.6 (inc. P.T.) 





SCOPE. 10-12U POWERSUPPLY, IP-20U 





PORTABLE 
UXR-2 



SW RECEIVER 

RG-I 



"OXFORD" LUXURYTRANSISTOR PORT- 
ABLE, Model UXR-2. Beautiful solid leather case. 
LW and MVY Coverage. Kit £14.8.0 (inc. P.T.) 

GENERAL COVERAGE RECEIVER, Model 
RG-I. Frees, coverage 600 kc/s-1.5 Mc's, 1.7-32 
Mc/s in 6 switched bands. Many features tncl, 
4r lattice crystal filter. Kit £39.16.0. Assembled 
£53.0.0. 

6W STEREO AMPLIFIER. Model S-33H. Ad 
inexpensive stereo/mono amplifier. Ideal for use 
with the Decca Deram lightweight pickup. Modern 
attractive styling. K* M5l*£Q 

Assembled £21,7.6 

50W PUBLIC ADDRESS AMPLIFIER, Model. 

PA-I. A multi-purpose unit, suitable for vocal 
and instrumental groups. 4 inputs Tor guitars, 
mics. etc. 2 heavy duty speakers, vol, indicator, 
variable tremolo, modern cabinet. Kit £54.15.0. 
Assembled £74,0.0. Legs optional extra, 17/6. 





TRANSISTOR HARMONIC DIST, 

TESTER, IM-30U METER, IM-I2U 




STEREO AMPLIFIER 
S-99 



COTSWOLD 
SPEAKER 



9 + svv HI-FI STEREO AMPLIFIER, Model 
S-99. Ganged controls, Stereo/Mono Gram,, 
Radio, Tape inputs. P.C. board construction. 

Attractive presentation. Kit £28.9.6. Assembled 
£36.9.6. 

SW MONO AMPLIFIER. Model MA-S. A 
general purpose amplifier based on model S-Jj. 
Separate bass and treble controls, gram and radio 
inputs. Printed circuit. Kit £10.19.6. Assembled 
£15.10.0. 

"COTSWOLD" HI-FI SPEAKER SYSTEMS. 

Std.model. Size: 26 x 23 x 14 in. Kit £25.12.0. 
MFS "Cotswold" for the smaller room. Size: 
36 X 16* X 14 in. Kit £25.12.0 

SSU-I SPEAKER SYSTEM. A practical solution 

to the problem of a low-price speaker system. Two 

speakers. Without legs £1 1.17.6 Kit {inc. P.T., 

With legs £12.12.0 Kit (ii 



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VYM, IM-I3U TV GEN, HFW-I 



Send for the FREE British Catalogue of Heathkit range of models 

Deferred Terms over £10 in U.K. Extended Deferred Terms in U.K. over £75 Prices quoted include postage in U.K, 



5 in. FLAT-FACE 
OSCILLOSCOPE- 



GENERAL PURPOSE 
Model 10-I2U. An out- 
standing 'scope, "Y T1 sensitivity, 10 mV rms per 
cm at I fee's; Bandwidth 3 c/s to 4.5 Mc/s. T/B 
10 e's to 500 kc's in 5 steps. Kit £35.17.6. Assembled 
£45.15.0, 



2i SERVICE SCOPE, Model OS-1 Light (wt. 10* 
lb.), compact. 5 x 8 x I4i in. The ideal port- 
able for servicemen. Kit £22,18,0 Assembled 
£30.6.0. 



ELECTRONIC SWITCH, Model S-3U. Convert 
your 'scope to dual trace. Kit £12.18.0, Assembled 
£18,10.0. 



MULTIMETER. Mode! MM-1U. Ranges 0-1,5 v to 
1.500 v A.C. and D.C. 150 ft A to 15A D.C.; 0.2 to 
20 Mii. 41 in. SOU A meter. Kit £12.18.0 Assembled 
£16.11.6. 



TRANSISTOR TESTER, Model IM-30U, Un- 
matched in quality, performance and price. Pro- 
vides complete d.c. analysis of PNP, NPN transis- 
tors and diodes. Internal battery for tests up to 9 v. 
Kit £24.18.0. Assembled £35.10.0. 

HARMONIC DISTORTION METER, Model 
1M-I2U. Freq, eov.: 20 to 20,000 cycles. Meter 
calibrated in V r.m.s, % distortion, dBs. Kit 
£24,15,0, Assembled £14.0.0. 

R.F. SIGNAL GENERATOR, Model RF-IU. 
Freq. coverage from 100 kc's-100 Mc/s or six bands, 
on fundamentals and up to 200 Mc/s on calibrated 
harmonics. Kit £13,8.0. Assembled £19.18.0. 

DECADE RESISTANCE, Model DR-IU. Range 
!-99,999Q in 111 steps, Kit £10.8.0. Assembled 
£14,8.0. 

DECADE CAPACITOR, Model DC-IU range, 
iQO/ifiF to 0.1 1 1 /(F in 100 /(/iF steps. Kit £7,5.0. 
Assembled £10.8.0. 



REGULATED POWER SUPPLY, Model 1P-20U. 
Transistorised, compact unit. Current range: from 
50 niA to 1 .5 A f.s.d. Voltage ranees; from 5 to 50 
volts f.s.d. Kit £35.8.0. Assembled £47.8.0. 



INTERNATIONAL MAIL ORDER SCHEME I 

covering the American Heathkit range of 250,1 
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1 1 details can be obtained from us for I/- post paid, . 



6 in. DE LUXE VALVE VOLTMETER, Model 
IM-I3U. Measures ac and dc volts 0-1. S to 1,500 V in 

7 ranges. Res. to 1,000 M0 in 7 ranges. Modern 
styling, with gimbal mount. Kit £18.18,0. Assembled 
£26.18.0. 



VALVE VOLTMETER, Model V-7A. DC volts 
to 1 500 AC to 1 ,500 rms and 4,000 V pk, to pk. 
Res. 0.1-1,000 MO. Kit £13.18.6. Assembled 
£19,18.6. RF Probe 309-CU £1-13.6 kit. HT Probe 
HV.336 £2,19,6 kit. Will extend range of models 
V-7AorlM-l3U. 



TV ALIGNMENT GENERATOR, Model 
HFW-l. 3.6 to 220 Mc/s on fundamentals. Unique 
electronic sweep oscillator. Built-in fixed and 
variable marker generators (S Mc,'s crystal). Kit 
£17.18.0. Assembled £47,10.0. 



AMATEUR TRANSMITTER. Model DX-IOOU. 
With built-in V.F.O. Kit £79.10.0. Assembled 
£104.15.0. 

REFLECTED POWER METER, Model HM-11. 
Indicated TX/antenna match. Kit £8.5.0. Assembled 
£10.10.0. 



MANY OTHER MODELS 

For the home, Hi-Fi enthusiast, Home 
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FULL RANGE OF MODELS IN 

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SIMPLY SEND COUPON TO.— 



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American 

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(Yes/No) - - "l-r.? 1 ! 



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6SS 



VOL 1 No. 10 
AOGOST 1965 



Practical Electronics 



A BROAD OUTLOOK 

Three international exhibitions held in London, and 
running in part concurrently during the latter part of 
May and beginning of June, offered as diverse a choice of 
interests as one could wish for. 

The International Packaging Exhibition at Earls Court 
brought one the factory floor atmosphere with the food and 
confectionery industries perhaps predominating. The World 
Fishing Exhibition at Olympia provided a strong salty 
flavour of the open seas, and against this the Hospital 
Equipment Exhibition in the adjoining hall offered a contrast 
with its clinical setting. 

Quite different, yes— but yet there was a common link. 
It was soon plain to see that in all these fields extensive use 
is already being made of electronic instrumentation and 
automated systems,* and it was equally clear that future 
improvements in efficiency depend very much (and in some 
cases, entirely) upon the increased adoption of electronics. 
* • * 

Sea fishing is a highly competitive business, and the 
modem trawler relies upon electronics not only for naviga- 
tional aids and communications, but as a means for locating 
the fish. Some modern fish-recording echo sounders can 
detect a single fish at 200 fathoms, and new sector scanning 
techniques promise to give even better results over the con- 
ventional asdic or sonar systems. 

It was not surprising to see how heavily dependent upon 
automated equipment the food confectionery, cosmetics and 
other industries have become. For example, electronic 
checkweighers can weigh 3,000 packages per hour, rejecting 
over or under weights, while servo systems automatically 
correct the filler machine. Other electronic systems are 
employed to detect metal in foodstuffs, to sort peas, nuts, 
rice, etc., according to colour, and to count articles of 
irregular shapes. 

An automatic patient monitor that will measure and 
record the blood pressure, pulse rate, and temperature of 
up to ten patients simultaneously was seen at the Hospital 
Equipment Exhibition. An automated drip feed system for 
transfusions, and instruments for remote control temperature 
measurement were just two further indications that auto- 
mation is reaching into the hospital service. 
* * # 

Here we have merely touched upon a few of the current 
uses of electronics in just three fields. We think it has been 
made clear that the student of electronics has much to gain 
by visiting exhibitions such as these. In so doing, not only 
will he keep in touch with technical advances of immediate 
interest, but in the process he will acquire an insight into 
many other fascinating facets of the modern world. Nothing 
like an interest in electronics for broadening the mind! 



THIS MONTH 



CONSTRUCTIONAL PROJECTS 



SIMPLE ANALOGUE 

COMPUTER 690 

ELECTRON fC FLASH GUN 697 

TRANSISTOR AND DIODE 

TESTER 715 

LOW VOLTAGE BATTERY 

PACK 726] 



SPECIAL SERIES 



BUILDING BLOCKS— 5 709 

BEGINNERS START HERE— 10 724 



GENERAL FEATURES 



U.H.F. RECEPTION 706 

INGENUITY UNLIMITED 729 

THE DECIBEL 732 



NEWS AND COMMENT 



EDITORIAL 689 

COMPONENT DEVELOPMENTS 705 

THE 73 PAGE 714 

ELECTRONORAMA 722 

NEWS BRIEFS 736 

NEW PRODUCTS 739 

DETACHED PARTICLES 743 

READOUT 744 

Our September issue will be published on 
Thursday, August 12 



All correspondence intended tor the Editor should be addressed to: The Editor, PRACTICAL ELECTRONICS, George Newnes Ltd., Tower 
House, Southampton Street, London, W.C.2. Editorial and Advertisement Offices: PRACTICAL ELECTRONICS, George Newnes Ltd. 
Tower House, Southampton Street, London, W.C.2, Phone: Temple Bar 4363, Telegrams: Newnes Rand London. Subscription Rates 
House, Southampton Street, London, W.C.2. Editorial and Advertisement Offices: PRACTICAL ELECTRONICS, George Newnes Ltd. 
Including postage for one year, to any part of the world, 36s. © George Newnes Ltd., 1964. Copyright In all drawings, photographs and 
articles published In PRACTICAL ELECTRONICS Is specially reserved throughout the countries signatory to the Berne Convention and 
the L.S.A. Reproductions or imitations of any of these are therefore expressly forbidden. 



689 








?&, 

' **' 'a 

i AS?'* 
./fflfe. 




'■"■■ ' ". "■■■" 



J ^ 




* i ih I i id* 






This instrument is capable of 

carrying out the arithmetical 

operations of multiplication and 

division with reasonable accuracy. 

The evaluation of powers and roots 

with log. scales may also be achieved. 



640 



Although popularly associated with formidable 
arrays of electronic instruments capable of 
incredibly complex calculations, computers in one 
form or another have been with us for a very long 
time. We have only to recall the familiar abacus or 
bead bar of our childhood to realise that our acquain- 
tance with computers started at a very early age. 

Modern computers are of two major types: the 
digital, which depend on the way we use numbers, 
and the analogue, in which numbers are represented 
by physical quantities such as length and current. 
A simple example of a digital computer is the abacus 
while a good example of the analogue computer is 
the slide rule. 

Although elaborate computers are beyond the scope 
of the average constructor, quite simple instruments 
can be made using everyday components. The simple 
analogue computer described in this article was con- 
structed by the author for classroom demonstration 
purposes. Although no originality is claimed for 
the design it was felt that a description of the instru- 
ment would be of interest to other constructors, 
particularly those engaged in teaching. 

BASIC CIRCUIT 

The computer is based on the familiar Wheatstone 
bridge network shown in Fig. 1. Such a network is 
commonly employed in the determination of an 
unknown resistance. When the bridge is balanced, 
for example, when the current through the galvano- 
meter is zero, the following well known relationship 
holds, 



or transposing, 



Rl X R4 = R2 x R3 




£1 
R2 



R_3 
R4 



Fig. I. Basic Wheatstone bridge network on which the 
computer is based 

Generally, Rl and R2 form a calibrated resistance 
wire system, while R3 is a resistor of known value. 
R4 is the unknown resistor. When the system is 
balanced, the ratio R1;R2 is determined, and hence 
R4 can be calculated. By a reversal of this procedure, 
the operations of multiplication and division can be 
carried out. 




If the resistors constituting the arms of the bridge 
are made variable and are accurately calibrated, the 
two arithmetical operations are easily performed. 
To multiply two numbers, R4 is set to some power of 
ten, the multiplicand set on R2 and the multiplier on 
R3. The bridge is balanced with Rl and the answer 
automatically read off on the Rl scale. To perform 
the operation of division, R4 is again set to a power 
of ten, while the numerator and denominator are set 
on Rl and R2 respectively. The bridge is balanced 
with R3 and the answer taken from this scale. For 
both arithmetical operations it is of course necessary 
to find the decimal point by inspection. 

The scope of the bridge can be further extended by 
providing logarithmic scales for R3 and R4. Powers 
and roofs may then be evaluated. This application 
will be discussed at a later stage. 

PRACTICAL CONSIDERATIONS 

In common with all other analogue computers the 
accuracy is limited by the precision of the components 
employed in the circuit. The author found that 
ordinary wire wound variable resistors of the type 
normally employed in radio work were of sufficient 
precision to enable quite a high degree of accuracy 
to be achieved. 

In the original design the bridge was energised by a 
battery, the balance point being indicated by a sensitive 
galvanometer. However, since it was highly likely 
that the instrument would be subjected to somewhat 
indelicate handling, the fragile galvanometer was 
replaced by headphones and a simple but robust 
transistor audio oscillator used to energise the bridge. 



CONSTRUCTIONAL DETAILS 

The computer is mounted on an aluminium panel, 
the relevant drilling and mounting details being given 
in Fig. 3. Four 3£in diameter discs cut from stiff 
white cardboard, and on which are described 2^in 
diameter circles, are used as dials. 

The audio oscillator is mounted on a 6in X 4in 
etched wiring board as shown in Figs. 4 and 5. An 
alternative method using Veroboard may also be 
used by those constructors who wish to avoid the 
use of chemicals. For comprehensive examples of 
this method the reader is referred to the April 1965 
issue of Practical Electronics. 

ETCHED WIRING BOARD 

The copper laminate is polished with metal polish 
and then washed in warm soapy water. After rinsing 
and drying, the circuit pattern shown in Fig. 4 is drawn 
out with cellulose paint of the car "touch up" type. 
The paint is allowed to dry for approximately 30 
minutes and the laminate immersed in a 30 per cent 
w.v. solution of ferric chloride. This solution is 
prepared either by dissolving 75gm of the anhydrous 
salt or 92gm of the hydrated salt in 200ml of water 
containing 3ml of concentrated hydrochloric acid. 
The resulting solution is made up to 250ml. For 
complete dissolution of the unwanted copper a reaction 
time of roughly 30 minutes at 40 degrees C is required. 
The etching is done by gentle agitation of the solution. 

The prepared board is washed with water to remove 
all traces of the iron salt and the cellulose paint removed 
by swabbing with cotton wool soaked in acetone or 
other suitable solvents. 



Fig. 2. Circuit of the simple com- 
puter. Additional resistors for 
calibration (R5-RI0) are not 
shown here but are explained 
later in Figs. 6, 7, and 10 



AAA- AAAi 




CIRCUIT DESCRIPTION 

The circuit diagram of the computer is given in 
Fig. 2. Four 1,000 ohm wire wound potentiometers 
(VR1-4) form the arms of the bridge. The transistor 
oscillator is of the Hartley type. Oscillation is main- 
tained by feedback in the correct sense through the 
primary of the audio transformer Tl. Although the 
output of the oscillator may be taken via C2 from the 
emitter of TR1, an additional stage of amplification 
may be found advantageous, particularly where noisy 
background levels are encountered. 

692 



Holes are drilled at the points shown in Fig. 5. Wiring 
of the board is straightforward and the customary heat 
shunt precautions are observed when the transistors 
and other closely clipped components are soldered in 
position. 

The audio frequency transformer is temporarily 
connected to the appropriate points on the board and 
a check made on the correct functioning of the oscil- 
lator. It may be found that the leads to the primary 
of the transformer require reversal to ensure feed- 
back in the correct sense. 




MATERIAL: I8SWG ALUMINIUM 



Fig. 3 (above). Drifting details of the aluminium pane! to 
hold the potentiometers 



PRIMARY 71 



-O 4 5V 



fr ::: -ht 



o+ 





OUTPUT 
Fig. 4. Component layout on the printed circuit board 



Fig. 5. Plan of the printed circuit board shown half scale 

693 



Before the completed audio oscillator is mounted 
on the main potentiometer panel, the potentiometers 
are calibrated by the following procedure. 

CALIBRATION OF BRIDGE 

A careful calibration of the four potentiometers is 
essential if accurate results are to be obtained. Al- 
though calibration is simplified if a resistance box 
calibrated in 10 ohm and 100 ohm steps is available, 
it is possible to use close tolerance fixed resistors as 
calibration standards. The construction of such a 
standard is shown later in Fig. 10. 

Both calibration methods will be described, the 
resistance box method being dealt with first. 



VRI CALIBRATION 

Two close tolerance resistors, R9 and RIO, each of 
1,000 ohms, are wired with VRI and the decade 
resistance box as shown in Fig. 6. The audio oscillator 
and headphones are connected to the appropriate 
points. With the decade box set at 100 ohms, VRI 
is adjusted until the null point is observed. The dial 
of VRI is carefully marked with pencil at this point. 
Repetition of the process with the decade box set at 
200, 300, 400 ohm etc., followed by balancing with VRI 
gives a series of points separated by 100 ohm intervals 
up to 1,000 ohms. If the decade box is calibrated in 
10 ohm steps intermediate points may be filled in. 



-TO RESISTANCE 




I PHONES 





=p» TO 
__ OSCILLATOR 



Fig. 6. VRI calibration 



Fig. 8. VR3 calibration 





TO AUDIO 
•» OSCILLATOR = 



Fig. 7. VR2 calibration 



Fig. 9. VR4 calibration 



Figs. 6-8. Temporary wiring of the potentiometer panel for calibration. Fig. 9. The final wiring 



694 



VR2 CALIBRATION 

The decade box is disconnected and VR2 wired into 
circuit as shown in Fig, 7. 

VR1 is successively set at each of the previously 
determined points and VR2 balanced against each 
point. In this way VR2 can be accurately calibrated 
in terms of VR1. 

VR3 CALIBRATION 

The decade box is reintroduced and R9 and RIO 
deleted. VR1 and VR2 are each set at 500 ohms and 
VR3 calibrated in 10 or 100 ohm steps against the 
decade box. Wiring details are shown in Fig. 8. 

VR4 CALIBRATION 

Prior to this final calibration the complete panel is 
wired as shown in Fig. 9. The audio oscillator and 
transformer may also be permanently attached. 
Two 3in 4 B.A. bolts serve as stand-off supports 
for the oscillator panel. 

After completing the wiring VR4 is calibrated against 
VR3 with VR1 and VR2 each set at 500 ohms. 

CALIBRATION WITH FIXED RESISTORS 

A simple calibration standard is shown in Fig. 10. 
Four close tolerance resistors of 100, 200, 300 and 
400 ohms respectively, are wired together as shown. 
By shorting out the appropriate sections a selection 
of resistance values from 100 to 1,000 ohms may be 
made. Two leads which terminate in crocodUe clips 
are conveniently used as shorting links. Resistance 

TABLE I 



Resistance Q 


Short Out 


100 


3 &8 


200 


1 & 2, 6 & 8 


300 


6&8 


400 


1 & 5 


500 


3& 5 


600 


7&8 


700 


1 & 4 


800 


3&4 


900 


1 & 2 


1,000 


none 




Fig. 10. Assembly and wiring of the calibration resistors. 
Due to the accuracy required for these resistors, It may be 
necessary to select and measure to within I per cent 
tolerance of the quoted values from resistors of the nearest 
"preferred" value available 

values obtained when the appropriate sections are 
shorted are given in Table 1. 

Calibration of the bridge using this standard is 
carried out exactly as before, the standard taking 
the place of the decade box. 

When calibration is complete the dials may be 
numbered from to 10 and permanently marked with 
indian ink. If the calibration has been made in 100 
ohm steps the intervals may be divided into ten equal 
parts. No great loss of accuracy will occur since it 
was found that over small portions of the potentio- 
meter tracks the resistance per unit length was constant 
enough to warrant this procedure. 

OPERATION OF COMPUTER 

A discussion of the operations of multiplication and 
division was given in the introduction to this article. 
These operations are summarised at this point. 

MULTIPLICATION 

Set VR4 to 1 or 10. The multiplicand is set on 
VR2 and the multiplier on VR3. The bridge is 
balanced with VR1 and the answer taken from this 
scale. 

DIVISION 

Set VR4 to 1 or 10. The numerator is set on VR1 
and the denominator on VR2. The bridge is balanced 
with VR3 and the answer taken from this scale. 



COMPONENTS . . . 



Resistors 

Rl 220kQ 10% 

R2 2-7k£i 10% 

R3 47kQ 10% 

R4 4-7kO 10% 

R5 I00£i 1% 

R6 200O 1% 

R7 300fl 1% 

R8 400£3 1% 

R9 I.OOOH 1% 
RIO 1,0000 1% 

Potentiometers 

VRI.2,3, 4 tkO 

Capacitors 

CI 0-0V F paper 
C2 0-25fxF paper 
C3 0-25/tF paper 



see Fig. 2 



see Fig. 10 



see Figs. 6 and 7 



inear, wire wound 



Transformer 

Intervalve type, ratio 3; J 

Transistors 

TRI.TR2 OC7lorNKT272 

Switch 

SI Single pole on/off 

Battery 

BY I 4-5V battery 

Miscellaneous 

Aluminium panel. Copper laminate board. Four 
pointer knobs. Headphones. Terminals. P.V.C 
insulated connecting wire. 



695 





Fig. 12 (above). Example of the linear type of scale 
that will be produced when the four potentiometers 
are individually calibrated as described on page 694. 
This linear scale is used for multiplication and division 

Fig. II (left). Calibration scale for VR4 drawn on a 
logarithmic basis to full sixe. This scale is used for the 
evaluation of powers and roots 



EVALUATION OF POWERS AND ROOTS 

In addition to the operations of multiplication and 
division, further interesting evaluations may be made 
if the scales of VR3 and VR4 are calibrated logarith- 
mically. 

If we let /- 3 be the reading of VR3 such that log r 8 = 
VR3 and similarly r t the reading of VR4 so that 
log r t =s VR4, then at the balance point, and recalling 
that in the basic bridge of Fig. 1, Rl x R4 = R2 x R3, 
it follows that 

VR1 log/- 4 = VR21ogr 3 



or 



VR2/YRI 



In other words we can determine the value of r 3 to the 
power VR2/VR1. 

As a simple example consider the evaluation of 3 4 . 
The required power VR2/VR1, is conveniently obtained 
by setting VR2 to 8 and VR1 to 2. VR3 is set to 3 
and the bridge balanced with VR4. The answer is 
taken from this scale. 

Roots may be evaluated using a similar procedure. 
For example, suppose we wish to find 1/21 or, what 
is the same thing, 27*. VR2 is set to 1 and VR1 to 3. 
After setting VR3 to 27 the answer is read off the 
VR4 scale. 

LOGARITHMIC SCALES 

The logarithmic scales are prepared as follows. 
A 2£in diameter circle is inscribed on a disc. Two 
points are marked with pencil on the circumference 
of the circle such that the length of the arc is the same 
as that of the linear scales. The arc is then divided 
into three equal portions which in turn are sub- 
divided into tenths. This calibration represents the 
logarithms of numbers between I and 1,000. The 
resistance scale may now be calibrated by inserting 
the values whose logarithms correspond to the inner 

696 



scale. An illustrative example is given in Fig. 11. 
This scale can conveniently be used for VR4. 

The second logarithmic scale is prepared by calibrat- 
ing VR3 in terms of VR4. To do this VR1 and VR2 
are each set at a dial reading of 5 and VR3 then 
balanced against each point of VR4 by the usual 
method. Fig. 12 shows an example of this scale. 

Doubtless other evaluations will suggest themselves 
to the mathematically-minded constructor. Circuit 
variations are also possible, for example, the audio 
oscillator may be replaced by a buzzer with a cheapen- 
ing in the overall cost. As a point of interest the cost 
of the instrument excluding battery and phones was 
ust over £2. ^ 



Contributed Articles 

The Editor will be pleased to consider for publica- 
tion articles of a theoretical or practical nature. Con- 
structional articles are particularly welcome, and the 
projects described should be of proven design, feasible 
for amateur constructors and use currently available 
components. 

Intending contributors are requested to observe the 
style in our published articles with regard to com- 
ponent references on circuit diagrams and the arrange- 
ment of components list. 

The text should be written on one side of the paper 
only with double spacing between lines. If the manu- 
script is handwritten, ruled paper should be used, and 
care taken to ensure clarity, especially where figures 
and signs are concerned. 

Diagrams should be drawn on separate sheets and 
not incorporated in the text. Photographic prints 
should be of high quality suitable for reproduction; 
but wherever possible, negatives should be forwarded. 

The Editor cannot hold himself responsible for 
manuscripts, but every effort will be made to return 
them if a stamped and addressed envelope is enclosed. 





PART TWO 
FLASH HEAD 



BY B.J.CROWE 



ELECTRONIC 



FLASH GUN 



WARNING: High voltages are encountered in this flash gun. Care should be exercised in 

handling and it is essential that the components and wiring should not be touched until the 

capacitors are completely discharged (see text later). To avoid any risk of damage or shocks 

the whole units should be kept dry and carried in a waterproof carrying case. 



The design of the flash head posed a rather different 
problem from that of the power pack. In the 
latter the innovation was in the circuit design rather 
than in the hardware; in the flash head, the circuit 
is well known, but as far as the author is aware a 
compact mechanical design is not available. 

The greatest contribution to miniaturisation in 
electronic flash has been the introduction of a compact 
reflector. The author decided, therefore, to attempt 
the design of a compact flash head incorporating the 
trigger circuit and cable storage compartment. The 
construction of the flash head necessarily involves 
some metal work, but this is kept to a minimum, and 
alternative designs will be suggested later for those 
who do not wish to attempt the compact head. 

CIRCUIT 

The circuit diagram for the flash head is shown in 
Fig. 2.1. The output voltage of the power pack is 
applied across the xenon tube (V2) and a proportion 
of this voltage appears at the junction of Rl and R2 
to charge the capacitor CI to approximately 250 volts. 
When the camera shutter is operated CI is effectively 
placed in parallel with the primary of the trigger coil 
(Tl) producing a "ringing" circuit, the first spike of 
which, at about 6 kilovolts, triggers the xenon tube 
into its conducting state. A smaller portion of the 
supply voltage (about 70 volts) is tapped off from 
VR1 to ignite the wire-ended neon indicator VI 
when the main capacitors have reached about 90 
per cent of their charge voltage. Resistors R2 and 
R3 are not strictly necessary and may be dispensed 
with if VR1 is replaced with a 2-5MA preset, but 
some sensitivity will be lost in setting the ignition 
point of the neon. 



HOUSING DESIGN 

The size of the flash head was dictated primarily 
by the size of the FA 10 xenon tube, and secondly 
by the requirement that it should fit on top of the 
power pack and form a compact unit for transportation. 
The size of the trigger circuit board and the space 
required for cable storage were also influencing fac- 




Fig. 2,1 Circuit diagram of the flash head 



697 




Fig . 2.2 Exploded view of the complete flash head 



tors, A pleasing appearance and relatively simple 
construction is achieved by keeping the mechanical 
fastening to a minimum by the use of "Araldite" 
epoxy resin adhesive. 

An exploded view of the flash head is shown in 
Fig. 2.2. The main component is a simple shallow 
rectangular box of 20 s.w.g. sheet aluminium, open 
at each end, and carrying two horizontal rails at the 
back and two short vertical rails at the front. 

The front rails carry the lens and reflector, on which 
is mounted the xenon tube socket. The rear rails 
carry the backplate which in turn carries the trigger 
and charge indicating circuit. 

The right-hand front rail is set in approximately 
|in from the edge of the box, forming a space 
alongside the lens in which the synchronisation and 
power supply leads may be stored. Only six screws 
are used as fasteners on the main assembly; all other 
joints are glued. 

CASE CONSTRUCTION 

Since the finished appearance of the flash head is 
directly dependent upon the accuracy and neatness 
with which the box is folded, as much care as possible 
should be exercised at this stage. The box is folded 
from a sheet of 20 s.w.g. aluminium measuring 1 1 -56in 
x 2-10in (Fig. 2.3a) and should be obtained ready cut, 
or cut by a friend with access to a guillotine, if possible, 
as this produces neat straight edges. If it is possible 
to gain access to a folding machine, the task of folding 
the box is greatly simplified. The box may, however, 
be folded quite successfully in an ordinary bench 
vice using the block shown in Fig. 2.3b and protecting 
the aluminium from the vice jaws with soft jaws or 
suitable packing, such as wood, on both sides of the 
sheet. 

When the box has been squared up the chamfered 
edges are cleaned thoroughly with acetone, carbon 
tetrachloride or trichlorethylene and a small quantity 
of Araldite applied to each edge. The edges are then 
brought together and held in position with elastic 
bands or adhesive tape. A liberal fillet of Araldite is 
run into the corner as in Fig. 2.4 to ensure a sound 
joint. The box should now be left for 24 hours to 
set, preferably in a warm, dry atmosphere. 

698 




Fig. 2.3a. The main case of the flash head is made from 
aluminium alloy sheet 10 s.w.g. and folded . . . 



1-68 




Fig. 2.3b. . . i round this btock to form an open ended box 



FILLET OF ARALDITE 




Fig . 2.4. Front view of the completed box with the rails 
fitted in position 




LAFAYETTE HA-63 
COMMUNICATION RECEIVER 

7 valves plus Hec tiller. 4 Bands. 500 ke/te- 
31 llcii "9" Meter— BFO— AN!.— Band- 
spread Timing. 2OO,'250v, A.C. Brand Sew 
24 Bus. Carr. Paid. 



STAR SR.40 
COMMUNICATION RECEIVER 

4 Bands, -jut) kc r '.«— SI) Me,:s. "S"* Meters 

BFO — AX I -Bnndspread Tuning — Built-in 

speaker 20i)/2al'v. A.C, Brand New. 
18'. 'Gas. Carr. 10/-- 




OS 8BU [OSCILLOSCOPES 
High finality Portable American Oscillo- 
scope. 3' c.r.t. T/B ;) c/s-50 ke/s X Amp: 
0-500 kejs Y Amp: 0-2 Me/s. Power re- 
quirements 10fl-120v. A.C. Supplied In 
brand new condition, fulh- tented, £25. 
Carr. Ki,'-. Suitable 230,'llBv. Traits- 
tarmer 15/8. 




I NEW MODEL! LAFAYETTE 
HA-230 AMATEUR COMMUNICA- 
TIONS RECEIVER 

1 Supercedes model HE-'tii. fl valves + rectifier. 
Continuous coverage on 4 bands. 550 Kc/s - 
30 Mc/S. Incorporates 1 BK A 2 IF stages, Q 
Multiplier, B.F.O.. ANL, "8" meter. Electrical 
bandimreail, Aerial trimmer etc. Supplied brand 
new and guaranteed. 33 gna. 
S.A.K. for full details. 



ERSKINE TYPE !3 DOUBLE 
BEAM OSCILLOSCOPE 

Time base 2 c/a-756 br/s, (Calibrators at 100 kc/s and 1 Mc/s. 

Reparole VI anil Yi! amplifiers up lo 5.5 Mc/s. Operation 110/2.10 
vtilt A.C. Supplied in perfect 
working order. 827/10,'-. Carriage 
20/-. 







AIR- 



NEW MODEL! 
LAFAYETTE HA-55 
CRAFT RECEIVER 

108-136 Mc/s. Bigh selectivity anil 
sensitivity. Incorporates 2 RF stages 
including 6C1V4 Nuvistor, 8 tubes for 

II tube performance, solid state jiower 
supply, adjustable squelch control, slide 
nil':: tiial, built in 4in. speaker and front 
panel phone jack. 220/240V. A.C 
Supplied brand new and guaranteed. 
19 gns, Carr. 10/-. 



i TE21 SINE SQUARE WAVE AUDIO 
GENERATORS 



CLEAR PLASTIC PANEL METERS 

First grade quality. Moving Cod panel meters, available 
ex-stock. S>.A.K. inr illustrated leallel. Discount* lur 
quantity. Available as follows; Type MR. 383P, 1 2l/32!u. 
square fronts. 




M»A 

HKI/jA ... 
2WlfiA . . . 
AQIlfjA . . . 
OO-O-SOriA 

loii.n.iiiiifi.J 
ioli-n-Smijji 
1-u-liiiA .. 

1mA 

'Jin A 



i mm A . 



22 8 
22 6 
22/6 
22. 8 
22 6 
22.8 
22 6 
22 6 



1A BjtJ, 

ba i>.a 

5 A !».(.'. 
3 V D.C. 

loV ll.l'. 



22 '6 
22 IS 
22 8 
22 6 
22 8 
228 
22 8 
22 8 
22 8 



OliliV A 



20V D.C. 

BOV H.i '. 

limy J 1. U 

22 6 lBoVD.C 

TBOiuA 22,6 

POST EXTRA larger sizes available— sen il for tlsls, 
ILLtTMUfATED "S" METER. 1 j| in. square front. Cat in a 
units, liV. lamp. £9 6. 1*. * P. 1 •. Kitlu S S.ltiln. square 
33 6. F.ar. 1>. 




LAFAYETTE TE-46 RESISTANCE 
CAPACITY ANALYZER 

■2 PF— 2,000 JIFD. 2 ohms — 2011 Megohms. Alsoche 
impedance, lurns raliu, insulation 200/230V. A 
Brand New £15. Carr, J/6. 



LAFAYETTE TE-20A R.F. SIGNAL 
GENERATOR 

12n kc's — 390 Mc/s on B ranges. Variable 1CF. : 
outputs. Large clear scale. Size 7!".: HI'" .4 
23IIV. A.C. Operation. Brand New £12'19,B. i. 



STOCKISTS OF 

NOMBREX, CODAR, 

SINCLAIR AND ALL 

ELECTRONIC 

EQUIPMENT 

COMPONENTS 



ARMY FIELD TELEPHONES 
TYPE F 

i; eneratn 
Bell Ringing 

2 Line Con- I 
ii e c t i m n. 
With Wood 
Carryi n g 
Case, Fitted 
Batteries, 

3 u pp lied 
fully Tested. 




2-WAY RADIOS 

S transistor. Range up 

lolMll.E. £9/19/6 lier 

pair. Post estra, 

'J transistor. Range up 

to 5 miles, 185 per pair. 

Post extra, 

H.A.K. for full detail?. 



£4 IB 6 I 



MAGNA VOX 363 TAPE 
DECKS 

Kelt ;<-speed tape deck, supersedes old 
Collaro studio deck. 2- truck £10.10.0. 
4 - 1 rack £ 1 3 . 10.0. Can . .Paid . 



AVO METERS 

Supplied recon- 
i ditioned, guaran- 
teed perfect. 



Model D $8.19.6 
Model 7 £12.10.0 




Post and Ins. 5,'- 



MINE DETECTOR No. 4A 

Will detect all tyiies of metals. Fully 
port ;d ilc. Complete with instructions, 
39 6. Cirr. Hi.-. Battery 8/8 estra. 



SILICON RECTIFIERS 

200 v. P.l.V. 200mA 2 6 

400 v. P.l.V, 3 amp 7, 8 

2110 v. P.l.V. am] 58 

1,000 v. P.l.V. 650 inA 7.8 

Hoi) v. P.l.V. 000mA. . , B, 8 

400 v, P.l.V. 500mA 3/8 

05 V. P.l.V. 3 uuip. ., 5.8 

TO v. P.l.V, I amp , 3/8 

150 v. P.C.V, HiamA 1/- 

Discnunts for quantities. Fust cstra. 



AMERICAN TAPE 



VOLTAGE 

STABILIZER 

TRANSFORMERS 

Input ,H0-120v. 
and 160-240V. 
Constant output 
HOv. or 240v„ 
250 watts. Brand 
Sew fJnnrniiteed. 
II 0.1 0.0. Carr. 
»/* 




2.5 Aiiip 
5 Amp . 



31 



BEST BUY! 

Send 1 - P.O. for fall Catalogue aad Lists. 
Open 9 a.m. to 6 p.m. every day Monday 
to Saturday. Trade supplied. 



First. gr:oic quality An 
Brand new ami guarantee 
lor quantities.. 
Sin., 22flft. L.P. acetate . . 

, 600ft. T.P. mylar . . 

HOOft.std. plusik .. 
Bin., IHiiiFt. L.P. acetule , . 
Bin., 1,200ft, 1).P. mylar .. 
5in., l.WJOfl. T.P, mylar . . 
Bjin., l,*2tii)ft. L.l>. aeelaic 
SJij). , l.Mtmfl . Ji.!'. itivlar 
SJin. 2, 41111ft. T.P. mylar .. 

Tin., I.Suun. slit, mylar .. 

7iu., l.MBlft. L.P. acelale 
Tin., L t $00ft. UP. mylar .. 
Tin., 2,400it. Ji.P. mylar . , 
Tin. a.fiooii. T.P. mylar ., 
Poslage 2, -. Over t"i post ] 



I. 1'Ih 



10. 
88 

3D - 
18- 
35/- 
126 
226 
45/- 
126 
15- 
20 - 
2S .- 
53 8 



VARIABLE VOLTAGE 
TRANSFORMERS 

Brand Sew riuarnnlecd 

- I'll I h" .Shrouded, Input 

aativ. 00/60 c/b. output 

200 Volts. 

1 Amp £4.10.0 

£5.17.8 

£0.0.0 
£13.10.0 

10 Amp £17.0.0 

12 Ami £10.10,0 

20 Amp £32.10.0 

2,0 Amp Portable 
Metal Case with Mcter- 
ru ses, etc._£B/17/6. 

MODEL PV-S8 VALVE 
VOLTMETER 



11 meg. input. 7 I).C. 
vol I ranges. 1.0- 

1,500 v. T A.C. volt 
1.0-1,500 



TS-76 20,000 O.P.V. PUSH 
BUTTON MULTI-TESTER 

Simple operation. 
D.C. tieH* up to 
1.000 v. A.C. volte 

up lo 1,000 v, 
Resistance up to 
1 megnbtn. Current 
up to 200 uiA. 
Llecibels — 20 to 
— 36 db. £5.5.0. 
P. i P. 2/*. 

MODEL TE-12 

20,000 O.P.V, 0/0.<i/ 
6/30/120/600/1,200/ 
3,060/6.000 v. D.C. 
/ B / 30 / 1211 / S00 , 
1.200V. A.C. WHOfl A 
ii 1 SO I 800 MA, 
tl/HK/MOK/S Meg. 
lid Meg. fl. P.P. 
.2 MFU. £5/19/8, 
P. & P. 2/6. 






MODEL 500. 30,000 
o.p.v. 0/. 5/1/2. a/10/ 
25 / 100 / 250 / BOO / 

t.ooov. D.t;. 

/ 2.B / 10 / 25/ 
100. ' / 250 / 000/ 
l,000v. A.C*, 

/ 50/lA I S / 50 / 
oOOmA. 12 amp. 

1 i.e. 

/ H0K / II Meg. / 60. 
Keg ii. £8,17/8 
Post Paid. 



laiiKU) 1.5-1,500 v. 

1 4,000 Peak to Peak. 
Resistance .2 ohm to 
1.000 megohm. Itecl- 
betl Itkth to ! 66db. 
Hupplk-d brand new 
uitih instructiims. 

I leads anil proton. 

. £18/10/-. P. & P. a/n. 




TE-SI NEW 
20,000ii/VOLT 
MULTIMETER 

/ 6 / 60 / 120 / 

1,200V. A.C. 

I 3 / 30 / 60 / 300 I 

600 / 3,000V, D.t.'. 

/ 60/(A / 12 / 300 

MA. D.C. 

/ 60K / 6 Meg.£i 

85,'-. P. A P. 2,'fi. 





699 







Through this IGS 
3-way Training Method : 



t 




MASTER THE THEORETICAL SIDE 
From basic principles to advanced applications, 
you'll learn the theory of electronic engineering, 
quickly and easily through ICS. That's because 
each course is set out in easy-to-understand terms. 

MASTER THE PRACTICAL SIDE 
ICS show you how to develop your practical 
abilities in electronic engineering — alongside your 
theoretical studies. It's the only sure way to 
success. All training manuals are packed with 
easy-to-follow illustrations. 

MASTER THE MATHEMATICAL SIDE 
To many this aspect is a bitter problem, Even 
more so because no electronic engineer is complete 
without a sound working knowledge of maths, 
But new ICS teaching makes mathematics easier 
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Wide range of courses available include: 
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FOR FREE HANDBOOK POST THIS COUPON TODAY 

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Solid state semi-conductor mod- 
ule*— fully transistorised and 
completely wired and tested cir- 
cuits that only require a 6-voIc 
battery and connection to- input 
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types are shockproof and almost 
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instructions. 

PUBLIC ADDRESS AMPLI- 
FIER — needs only crystal 
microphone and any speaker. 
Frequency response designed to 
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With IS in, speaker sound covers 
hundreds of yards. Fully encap- 
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in. 35/-. P. & P. |/-. 
CODE PRACTICE OSCIL- 
LATOR — simply connect with 
morse key, any P.M. speaker and 
any U-6v battery. Fully tran- 
sistorised and assembled on rigid 
board size2xl$in. 12/6. P. & P. I/-. 
BURGLAR ALARM — needs 
only 8-ohm loudspeaker, switch 
and microswitch (or reed switch 
and magnet) to complete, 
Operation of sensing switch trig- 
ger upward screaming siren to 
give instant alarm. For home or 
motor car protection, 30/-. 
P. & P. I/-. 

FIRE ALARM — module con- 
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operates in conjunction with 8- 
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immediately triggers screaming 
siren alarm. 50/-. P. & P. I/-. 



PHOTO MULTIPLIER 
POWER TRANSISTOR-com- 
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AMPLIFIER MODULE— com- 
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requires only telephone pick-up 
coil to operate, 30/-. P. & P. I/-. 
MICROPHONE TRANS- 
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Construct Electronics with NEW 
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VEROBOARDS supplied by Proops Pr °f eSSIOr *ally 

Brothers Limited have been specially designed to meet the needs of the 
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quantity purchase with attendant saving; specially prepared design 
sheets are provided with each purchaseto simplify circuit layout: acces- 
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VEROBOARD SHEETS. 12/6 each. Post Free. 
Board sue overall: 17 in. long X 3| in. wide 0.03 12 in, thick. Each is 
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pierced in line at 0.156 in. intervals across width and 0.2 in. along length. 
Boards are treated with flux preservative to give protection and ensure 
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SPOT FACE CUTTER, 8/6. Post Free. 

Specially designed hand cutting tool with hole locating spigot, Light 
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TERMINAL PINS. SO for 3/6. Post Free. 

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MINIATURE MERCURY SWITCH 

Almost indettructiMe, Feathertight operation 

Encapsulated in copper-plated steel tube only -ft'dia.x J" 
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20 3 movement makes or breaks contact: vacuum sealing 
ensures unchanged contact resistance throughout life. Con- 
struction permits switch to be simply clipped into position. 
Rating 240v. AC mains operation at I amp,, may also be used 
with DC current from small torch battery. Can be installed 
almost anywhere to operate lights automatically or to provide 



Post free simple warning or safety devices. 



PROOPS 



BROTHERS LIMITED 



I 52 TOTTENHAM COURT ROA0, LONDON W I. 
PHOd!: LAKjhim 0141. mguis- « Jm - tp*. 

| IHUIS: Nm-lpm, 0PEK UL D»» CD iltUUDU 



700 



Ij 




TOP VIEW 



HWM««w, v w,y. 

60°- 
SECTION X 




Fig. 2.5, Construction and bending details 
of the right-hand front rail 



Fig. 2.7* This block Is used to 
form the reflector shape shown 
in Fig. 2 




Fig. 2.8. Dimensions of the 
xenon tube 



FLANGE 




BEND ON DOTTED LIKES 
TO PRODUCE SHAPE 
SHOWN IN FIG.2 



4 HOLES DRILLED %j' 
TO ASSIST BENDING 



Fig. 2.6. The reflector base Is cut from aluminium alloy 
sheet 20 s.w.g. and folded 



The rails may now be constructed while the joint 
is hardening. The two rear rails and the front left- 
hand rail are £in x £in angle sections bent in the 
vice from ^in strips of 20 s.w.g. aluminium and cut 
to the appropriate lengths to fit inside the case as 
shown in Figs. 2.2 and 2.4. The right-hand front rail 
is iin x Jin and is bent to form an acute angle of 
60 degrees (see Fig. 2.5) in order to prevent the cables 
charing when being withdrawn from the storage com- 
partment. Since it cannot be bonded along the edge 
like the other rails, the ends are turned over as shown 
to provide the anchorages. It should be made slightly 
longer than required and then, when the box is set 
hard, the ends may be filed until it is a sliding fit in 
the box. 

The surface to be bonded on each rail and the mating 
surfaces in the box are scored with a sharp point 
(such as a scriber or hacksaw blade) in a fine criss- 
cross pattern until the whole surface to be bonded 
is rough. The surfaces are then cleaned with one of 
the fluids previously mentioned, smeared lightly with 
Araldite and each rail offered up to its mating surface. 
It is better to tackle the rails in pairs and allow one 
pair to set before fixing the next. 

The rear rails may be spaced from the back using 
a scrap of 20 s.w.g. material to simulate the back- 
plate. 



The front rails are set back -&in from the front of 
the box, and the right-hand rail set £in in from the 
inside of the box (Fig, 2.4). A small card template 
facilitates the setting of these components. 

REFLECTOR 

The reflector base is made from 20 s.w.g. sheet and 
covered with reflecting material (see later), so that the 
surface need not be protected during the bending 
operation. Cut the blank to the template shown in 
Fig. 2.6, and make the block from a scrap of wood 
(Fig. 2.7). Bend the flanges down at approximately 
60 degrees, and then clamp the blank in the vice with 
the block, the holes in the blank lying at the corners 
of the block. The sides are then bent forward until 
the edges all fine up. Square up the flanges, bond 
the edge joints with Araldite and put on one side for 
24 hours to harden. 

The backplate is cut from 20 s.w.g. sheet and fitted 
into the back of the box on the rear rails. The lens 
is cut from a piece of acrylic sheet to 3-375in x 1 -65in. 
It may be plain or fluted (as in the author's gun) 
in which case the curves are placed so as to give a 
"condensing" effect to the light beam. Admittedly 
no tests have been carried out on this lens to assess 
its performance compared with a clear lens, but the 
fluted effect undoubtedly provides a more uniform and 
diffused light. 

The lens and reflector assembly may be fixed with 
self-tapping screws, or, if a more durable fastening 
system is required, small pieces (iin x iin) of 16 
s.w.g, mild steel may be glued to the back of the rail 
and tapped for 6 B.A. screws. 

When the necessary preparation has been done, 
lay the reflector and lens on the rails and drill carefully 
through all three with a small drill, and then enlarge 
and tap the holes as required. The backing plate may 
be glued permanently in position, but in the author's 
gun it was attached by screws to give greater access 
to the interior. 

XENON TUBE SOCKET 

The FA 10 xenon tube (Fig. 2.8) has two pins which 
are spaced so as to fit a standard two-pin 2 amp 
socket, but the latter is bulky, and no provision is 
made for a contact to the trigger strap. Amateur 

701 



'araldite' filling 



ACETATE FORMER 



TRIGGER CONTACT 




FIXING PLATE 



THIS AREA IS CUT AWAY 
AFTER ASSEMBLY 



SPRING CONTACTS FOR 
XENON TUBE PINS 



Fig. 2.9 The socket to hold the xenon tube. Note the 
trigger contact strip which makes contact with the strap 
across the tube shown in Fig 8 



%" 



T 



■S/8- 



--he- 



BEND ALONG 
DOTTED LINES 



MATERIAL-ZOSWG 
ALUMINIUM 




3 HOLES DRILL 
l/ 8 " FOR LEADS 



2 HOLES DRILL 

V32" TO ASSIST 

BENDING 



Fig 2.10. The casing for the xenon tube socket is cut 
to shape and bent to form the shape shown in Fig. 9 



flash-heads usually use a coil of stiff wire twisted 
around the pins, and flexible wire twisted round the 
trigger strap, but with this system the tube is neither 
rigidly held, nor easily removed. The author has 
designed a socket in which all three contacts are made 
and yet the tube may be removed using moderate force. 

A word of warning before going into the description 
— the xenon tube is extremely fragile and should be 
handled with great care. 

The socket (Fig. 2.9) is made from a small piece of 
celluloid or cellulose acetate and some thin (22 s.w.g. 
or 24 s.w.g.) beryllium copper or phosphor-bronze 
sheet (obtainable from any good engineers' suppliers 
and many model shops). 

Cut a piece of phosphor-bronze (or beryllium cop- 
per) about fin wide and 31n long, and wrap it round 
a nail or drill about fin diameter so that it looks like 
a clock-spring. When 2£ turns have been wound, 
cut off the surplus and solder the coil so that it is held 
closed. This can be removed from the nail and fitted 
over one of the pins of the tube. Repeat for the 
other pins and solder a 6in length of plastics-covered 
wire (7/ *0048) to each one, red and black. Cut a 
thin strip (about ^in wide) of phosphor-bronze about 
■Jin long and solder a 6in length of white covered wire 
to this. (Phosphor-bronze sheet of this thickness 
may be cut with ordinary household scissors or tins- 
man's shears.) 

Cut the socket box from 20 s.w.g. aluminium alloy 
sheet to the shape shown in Fig. 2.10 and fold up the 
edges. (This may be done by hand with the aid of a 
pair of pliers or in a small vice.) Cut a piece of 
celluloid or acetate sheet &in thick (obtainable from 
model shops) about 2£in x iin and drill and bend as 
shown in Fig. 2.1 1. Cement it to the box as shown in 
Fig. 2.9. 

Thread the wires of the three contacts through the 
appropriate holes in the box, and push the long thin 
bronze strip (which forms the trigger contact) through 
the centre hole in the acetate sheet. The spring 
contacts are held in position while the Araldite sets 
by the pins of the xenon tube (Fig. 2.12) so these must 
be lightly smeared with grease to prevent unwanted 
adhesion. 

Insert the tube pins through the outer holes in the 
acetate sheet and push the spring contacts gently 
on to them (observe polarity!). The box is then laid 
on a flat surface with the end overhanging to allow 
the three wires to clear it, and the xenon tube packed 
up until it lies parallel to the surface (Fig. 2.12). Mix 

702 




2 HOLES % 4 FOR 1/ 16 HOLE FOR TRIGGER 

XENON TUBE PINS CONTACT 

MATERIAL '/ 16 " ACETATE SHEET 

Fig. 2.1 i. The' front plate of the xenon tube socket is 
cut to the sizelshown, drilled and bent to the shape shown 
in Fig. 9 



XENON-TUBE 



PACKING 




SOCKET SELLOTAPED TO TABLE 



LEADS 



Fig. 2J2. Aligning the xenon tube with the socket by 
using packing and adhesive tape prior to filling the socket 
with araldite. The pins should be insetted in the socket. 



a good quantity of Araldite (about a third of each tube) 
on a piece of clean scrap metal or glass and warm it 
in front of the fire until it runs easily. The Araldite 
may now be poured round the contacts into the mould 
formed by the box and the acetate sheet until it is 
level with the top, and then allowed to set. 

After 24 hours, the xenon tube may gently be removed 
from the socket (the importance of ensuring that no 
Araldite comes into contact with the pins is obvious) 
and the shaded portion (Fig. 2.9) cut away with a junior 
hacksaw and sharp knife. The socket may then be 
cleaned up with a file and the trigger contact bent to 
shape as shown in Fig. 2.9, so that it bears on the trig- 
ger strap when the tube is inserted. 

A hole must now be cut in the reflector base to 
accept the socket (see Fig. 2.2), either by drilling a 
series of small holes or using an "Abrafile" saw blade 
which fits a standard hacksaw frame. The hole is 




The component parts of the flash head before assembly 



carefully enlarged with a file until the socket sits 
snugly against the back and side of the reflector base. 
Two holes are then drilled through the reflector base 
and socket plate to take 6 B.A. countersunk head 
nickel plated screws. 

The reflector base must now have its reflective 
coating applied. In the author's gun this was a piece 
of 00025in thick aluminised transparent plastic film 
(Melinex) fixed to the reflector base with clear adhesive, 
the aluminium side being glued down to leave the 



plastic film as a protective coating on the outside. 
Alternatively, the reflector base may be covered with 
kitchen foil, or simply polished as it stands, although 
neither of these surfaces will have as high a reflectivity 
or durability as the former method provides. 

CIRCUIT BOARD 

The circuit is built up on a piece of Veroboard 
3in x lin (matrix of 19 x 6 holes). The component 
layout is shown in Fig. 2. 1 3, and the component wiring 
points on the reverse of the board are shown in Fig. 2.14. 
Cut the board to size and make the breaks in the strips 
at A7, A9, and Ell. Drill |in clearance holes at 
A3 and CI 8 and cut the strip well back from the holes. 

The author used a preset (skeleton type) potentio- 
meter for VR1, which was modified for use in the 
horizontal position by bending down the tags and 
cutting short the centre one. The holes in the Vero- 
board must be enlarged slightly to take this component, 

TABLE I: 
COMPONENT CONNECTION POINTS 



Component 


Wiring Board Location 


R) 


D8, A8 & B8 


R2 


AS, E5 


R3 


Al, F2 


R4 


AIO, E9 


VRI 


A2, A4, wiper to C3 


CI 


A 13, El 3 




fCommon FI5 


Tl 


•s L.T. winding EI6 




LH.T. winding DI3 


VI 


C7, F6 


PL2 


BI9 (Power in +) 


PL2 


FI9 (Power in — ) 


V2 positive 


Bl 


V2 negative 


FI 


V2 trigger 


Dl 


PL3 


A!8 (Sync inner) 


PL3 


FI8 (Sync screen) 



COIL ATTACHED WITH LACING CORD 



POWER SUPPLY LEADS 

+ 




LEAD TO FLASHTUBE 
SOCKET 



VRI 



Fig. 2.13. Component layout of the wiring board. 

Is shown removed from Its position to indicate its con 

nections 



Fig. 2.14. Underside view of the wiring board showing 

the component connections and cut-outs 



703 



but miniature components intended for use on 015in 
matrix board are available and would be preferable 
here. 

The connection points of each component are shown 
in Table 1. The trigger coil should be strapped to the 
board using lacing card or p.v.c. covered wire passed 
through spare holes. Note that the lead of Rl is fed 
through position A8 and bent up and soldered to strip 
B at B8. (A miniature resistor could be connected 
direct to B8 and so avoid this strap.) If the preset 
potentiometer is used a hole must be drilled through 
it between the tags to take the mounting screw. 

The board is now fitted, components downward, 
on the inside of the backplate, and holes drilled in the 
backplate to correspond to holes A3 and CI 8 in the 
Veroboard (see Fig. 2.2). A piece of p.v.c. sleeving 
from coaxial cable serves as a spacer under the circuit 
board at position A3. Two 6 B.A. screws are pushed 
through the backplate and board, and secured with 
nuts. Nylon screws and nuts are obtainable from 
some component shops and are best used here to 
prevent shorting adjacent circuit strips. 

Mark the position of the neon and potentiometer, 
remove the circuit board, and cut the holes which allow 
the neon to be viewed and the preset to be adjusted 



COMPONENTS 



FLASH- HEAD UNIT 



Resistors 



Rl 720kD, 
R2 1 -2MQ 
All £ watt 10 per cent 



R3 330kQ 
R4 3MO 



Potentiometer 

VRI IMH skeleton preset (Radiospares) 

Capacitor 

CI 0-l/xF 250V Polyester (Radiospares) 

Transformer 

Tl Trigger coil (General Electronics, l29Portobello 
Road, London, W.I I) 

Gas-filled tubes 

VI NT2 Neon indicator (or similar) 
V2 FA 10 Xenon discharge tube (A.E.I.) 
(Available from General Electronics, London) 

Plugs 
PL2 

PL3 



Two-pin plug to fit SK2 on the power unit 
(see last month's article) 
4mm sync plug and cable for camera (Arrow- 
tabs) 

Miscellaneous 

Aluminium alloy sheet (half hard grade) 20 s.w.g., 
I2in X I2in 

Perspex acrylic sheet (clear) plain or fluted, 3£in X 
I fin X £in thick from Perspex stockists or Fresnal 
lens (Proops Bros. Ltd) 

Aluminised Melinex plastic film, 6in X 6in X 
00025in thick (Utilex Ltd., Mill Street, Kingston 
upon Thames, Surrey) 

Phosphor bronze or beryllium copper, 3in x I in x 
22 s.w.g. 

Wood blocks (see text) 

P.v.c. covered wire 7/ -0048 

Araldite adhesive (packet of two tubes) 



from the back (see Fig. 2.2). Attach the socket leads, 
power supply lead (4ft red and black 7/ 00481 n 
twisted together) and the synchronisation cable 
(4mm coaxial plug and coaxial cable, obtainable from 
photographic dealers) to the appropriate points on the 
board, and fit the board to the backplate. The copper 
strip side of the wiring board should be thoroughly 
cleaned and lightly smeared with a coat of silicon 
grease. This is very important to avoid the possibility 
of shorts if any damp is present. 

Pass the leads through the flash head box from the 
front, followed by the backplate and circuit board, 
until the reflector is in position. Place the lens in 
position and insert the screws. Feed the cables 
back through the box, through the cable storage 
compartment until the backplate is in position, and 
screw down. After fitting the Radiospares flex- 
connector plug PL2 to the power lead the cables can 
be coiled and inserted in the storage space. To com- 
plete the flashy head, make a T-piece from a scrap of 
al umini um to fit the camera accessory shoe and fix in 
place with Araldite or screws to the underside of the 
flash head case (see photograph on page 703). 

CALIBRATION 

Plug the power supply lead from the flash head 
into the power pack and connect the synchronisation 
cable to a camera or suitable shorting switch. Turn 
the preset potentiometer in the flash head completely 
clockwise and switch S2 on the power pack to half 
power. 
Interior view of the power pack described last month 





704 



Switch on the power pack, and wait for about one 
minute, then turn VR1, which controls the neon, 
gradually clockwise until the neon just strikes. Press 
the camera shutter release and the gun should fire. 
If still switched on, the gun will automatically re- 
charge and the neon should strike again after 6 or 7 
seconds. Repeat this operation with switch S2 on 
full power. The gun should now take about 12 to 
15 seconds to recharge. 

If for any reason the gun fails to fire, it is imperative 
that tbe capacitors should be discharged before the 
power pack is opened. This may be done with a short 
length of wire in the output socket, but it is better to 
short with a low value resistor (say 500ft) to avoid 
damaging C4 and C5. Touching the capacitor 
terminals whilst they are charged up will result in a 
severe shock and possible local burning of the fingers. 

USING THE FLASH GUN 

Having ascertained that the gun functions satis- 
factorily, it is necessary to determine the exact amount 
of light which the gun provides. This is usually 
expressed as a pure number called the guide number, 
and which has the value of the product of the camera 
aperture and the distance between the camera and the 
subject, which will give the correct exposure with the 
film used. A table showing the guide numbers 
obtained with various film speeds with the author's 
gun is shown below. 



TABLE 2: EXPOSURE GUIDE 



Film Speed A.S.A. 


Guide Number 




50 


56 




125 


88 




140 


94 




200 


112 




400 


158 





To determine a guide number, expose several frames 
at different apertures, and one known camera-to- 
subject distance. After processing decide from the 
prints (or transparencies) which aperture gave the 
best exposure. Multiplying this aperture value by the 
known distance gives the guide number for the film 
emulsion in use. 

After about 40-50 flashes, it will be found that the 
recycling time of the gun has increased to 30 seconds 
or more, and may not even light the neon without 
resetting the preset potentiometer in the flash head. 
This indicates that the accumulator needs recharging. 
If the circuit shown has been incorporated into the 
power pack, it is only necessary to plug in the mains 
lead and leave overnight. Alternatively the cell 
may be charged from any suitable source at 100-1 50mA 
for 8-10 hours, with care. \ 



References 

The author has found the following articles helpful in compiling this 
article : 

1 . Wakefield, G. Flash Techniques Nos. 6 and 7. Amateur Photographer, 
October 2 and 9, 1963. 

2. Sheiton, R. J. Novel Electronic Flash Unit. Amateur Photographer, 
October 24, J 962. 



Component Developments 

Improved washing machines, television sets (including 
' colour TV), research microscopes and hearing aids are 
foreshadowed by new electronic "bits and pieces" 
which were shown at the Radio and Electronic Com- 
ponent Show at Olympia, London in May. 

Among the new components shown by 300 members 
of the industry there was a new colour television tube 
which will enable bigger and brighter pictures to be 
shown on a smaller television set. 

A field ion microscope, the first to be developed 
commercially in Britain, has a magnification of more 
than one million times; for the first time it enables 
individual atoms to be "seen". 

One firm foreshadows the use of thyristors, already 
proving of great value in industrial control, for making 
domestic washing machines simpler, more reliable and 
possibly cheaper. By using a thyristor to control a 
single motor, gearing is eliminated and the "washing" 
and "spinning" speeds can be optimised. 



Try and Light the Candle 



"This working exhibit (shown below) on the Mullard 
1 stand at the Components Exhibition effectively 
demonstrates the very high input impedance (10 12 ohms) 
of the recently introduced metal-oxide semiconductor 
transistor, type 95BFY. 

The two bare rods are input connections to a high- 
gain d.c.-coupled amplifier with an m.o.s. transistor 
in the first stage. Attempts to light the candle fail 
because the hot gases produced in the gap by a lighted 
match are sufficient to reduce the impedance seen by 
the amplifier. The resulting increase in output current 
opens a shutter which releases air to extinguish the 
match before it can light the candle. 





by J. D. Benson 



With the rapid expansion of the BBC 2 television 
service throughout the United Kingdom, tele- 
vision engineers are being faced with an increasing 
quota of technical problems relating to the reception 
of these broadcasts in the home. Although this article 
has been written with service engineers in mind, a 
large proportion of viewers will probably find many 
answers to their own problems. To help to explain 
some of the finer points of u.h.f. reception let us 
briefly examine some of the fundamentals of radio wave 
propagation. 

TRANSMISSION 

Radio waves consist basically of two components: 
the electrical field and the magnetic field. These two 
fields are at right angles to one another and when 
transmitted are either horizontally or vertically 
polarised according to which field is parallel with the 
earth's surface. Irrespective of their frequency, the 
signals travel at the speed of light, i.e. 186,000 miles 
per second or 300,000,000 metres per second and from 
this we can derive the wavelength (A) of any particular 
transmission: 

3 00,000,000 (metres per second ) 
frequency (cycles per second) 

Transmissions in the lower frequency bands are 
usually referred to by wavelength, whilst those in the 
higher bands are quoted in frequencies. 

When transmitted, radio waves produce three types 
of waves: the ground wave, sky wave, and direct wave. 
The effectiveness of these waves depends largely on the 
frequency at which they are transmitted. The ground 
wave is produced by the electromagnetic component 
when the transmission is vertically polarised, that is 
when the electrical component is vertical to the earth's 
surface. 

The power of the ground wave is determined by the 
frequency of the transmission; this can be better 
understood if the earth over which the waves travel is 
considered as a large capacitor. At low frequencies 
the earth offers a high impedance and little power is 
lost; as the frequency increases the impedance offered 

706 



decreases until at very high frequencies the ground 
wave is practically non-existent. A practical case of 
ground waves transmitted at low frequencies is the 
BBC Light Programme on 1,500 metres, which can be 
received hundreds of miles away from its source. 

The sky wave is so called because it is reflected from 
the Kennelly-Heavyside and Appleton layers which 
exist from about 40 miles to several hundred miles 
above the earth's surface. These layers are electrically 
charged (ionised) by the sun's action and deflect radio 
waves. Unlike a mirror, the waves are not directly 
reflected, but according to the frequency and state of 
ionisation are bent (refracted) before reaching the 
earth again. 

It is due to this natural phenomenon that reception 
of certain frequencies is possible at great distances. 
It also explains why any change in these ionised layers 
(sun spots, etc.) results in a great variation in the 
results received at various times of the year. Very 
high frequency waves pass through these layers or are 
absorbed by them. 




Fig. I. Twin 'Yogi* array for fringe reception. The beam 
width is so narrow that very precise positioning must be 
carried out to obtain best results. 




Fig. , A typical commercial *Yagi' array by Belling & Lee 



The long and medium wave stations are therefore 
very reliable under all climatic conditions because of 
their powerful ground wave component. The sky wave 
produced by medium wave stations is greatly reduced 
in power during the hours of daylight and are very 
powerful at night, which accounts for the improved 
reception of the medium wave band Continental 
stations during the hours of darkness. 

SKIP DISTANCE 

The high frequency band which covers 100-10 
metres depends almost entirely on the sky waves for 
reception and results, according to climatic conditions 
can be very erratic. At these frequencies another 
effect called "skip distance" is present. It is the area 
between where ground waves are non-existent and 
where the shortest sky waves begin. In the skip 
distance area, no reception is possible. By the use of 
directional aerials and choice of frequency, great 
distances can be covered, but because of the adverse 
effect of climatic conditions this band is very prone to 
interference between stations. 

Stations transmitting at v.h.f. rely almost entirely 
on direct waves for communication, i.e. aerial to 
aerial or line of sight. There is also a small percentage 
of reflection from the earth. This band is used for 
f.rn. transmissions, television, radar and many other 
services. These bands, which extend from I to III, 
have now become so crowded that any new service 
had to be allocated a frequency on a new band, hence 
the choice of u.h.f. (ultra high frequency) for BBC 2 in 
Band IV (470-582Mc/s). 

SITING AN AERIAL 

At these ultra high frequencies communication is 
almost entirely dependent on direct waves, which 
necessitates the transmitting aerial being very high 
above ground (1,000ft or more) if a useful service 
area is to be covered. In spite of the high power 



(500kW) and high aerials, the BBC 2 transmitter will 
only cover a service area of about 25-30 miles radius 
from the transmitter and within that area there will be 
many locations where the signal strength will be 
greatly reduced due to the impeding effects of hills and 
tall buildings. 

In areas beyond the service limits the service engineer 
can estimate his chances of receiving a workable signal 
by studying the contours of the ground between his 
receiving site and the transmitter. These contours can 
be obtained from an Ordnance Survey map. By 
drawing a straight line on the map from the position 
of the receiving aerial to that of the transmitter, the 
various heights can be read off and compared with the 
height of the transmitting aerial. For example, if the 
viewer's site is, say, 40 miles from the transmitter 
and directly behind a hill 1,000ft high, then his chances 
of receiving a workable signal are very small indeed. 

U.H.F. waves follow closely the same rules 
which apply to light, i.e. they travel in straight lines 
from the source of origin. They are largely absorbed 
by buildings, so unless the site is very near the trans- 
mitter, the use of indoor aerials may be impracticable. 
In locations where an indoor aerial will give sufficient 
signal, it will have to be very carefully sited if inter- 
ference from nearby moving objects is to be avoided. 

Loft aerials are a better answer if the location is near 
the transmitter, but here the engineer must first ascertain 
whether the roof is lined with metal or not. In 
positioning the aerial, he must make sure that no 
piping, tanks, etc. are near the aerial, as at these 
extremely short wavelengths, they can produce per- 
manent ghosts and reflections which can ruin reception. 

FEEDER LOSS 

It is well to remember that the signal strength 
required for good reception at these frequencies is at 
least three times more than those required for Band III 
(IT A). One of the main contributory factors to 

707 



this is that, as frequency is increased, the noise 
generated within the receiver itself is greater. To 
suppress this self-generated noise, a much greater signal 
strength is required. The feeder to the receiver also 
adds to the loss, but by using standard low loss feeder 
it has been proved that very little improvement can be 
gained by fitting other types of cable if the installation 
is to be kept within practicable limits. 

Whilst dealing with the subject o feeder loss, it 
must not be forgotten that whilst the aerial is a balanced 
component, the coaxial feeder is not, since one side, 
the outer sheath, is normally connected to earth. The 
danger point is near the aerial where currents can be 
induced in the outer sheath. This will greatly detract 
from the performance of the aerial. Since it is 
imperative to avoid all possible losses it is advisable 
that the cable be joined to the aerial via a "balun", a 
fitting well-known to the engineer and needing no 
description here. The mismatch is much more 
noticeable with horizontal aerials than with vertical 
aerials by reason of the position of the feeder in 
relation to the incoming signal. 

ERECTION 

Because of the necessity for obtaining as large a 
signal as possible, the aerials used for u.h.f. reception 
wlU be multi-element arrays which will follow the 
well-known Yagi design. Since the elements of the 
aerial are physically small, it is possible to increase 
their number and so effectively boost both the total 
voltage picked up and their directive qualities. In 
view of the size of the elements, the aerials are light in 
weight and can be safely installed in exposed positions 
where heavier arrays could be unstable. However, it 
must be borne in mind that u.h.f. arrays must be 
rigidly constructed, as any inclination to sway in the 
air when subjected to strong winds can produce 
variations m the signal strength received. 

The erection and positioning of u.h.f. aerials 
especially in areas of low signal strength, calls for 
patience. Wherever possible the array should be 
moved about whilst results are being observed, 
remembering that at their critical frequencies a matter 
of inches can mean the difference between a good signal 
and a poor one. Beyond a certain point there is little 
to be gained by increasing the size of the array and 
much better results can be obtained by using a pre- 
amplifier. 



since these wavelengths are measured in inches. A 
point of warning when using transistors with very 
short leads, do not forget to use a heat shunt or your 
transistor may be ruined before it is put into service. 

SIGNAL STRENGTH 

The following is a list of the signal strengths 
required to give good results for each of the four 
television bands from results of research by the BBC. 

Band I Oil 5-0*1 70m V/metre 

Band HI 045mV/metre 

Band IV l-2mV/metre 

Band V 2-4m V/metre 

At a glance it will be seen that a much greater signal 
is required at u.h.f. to obtain comparable results 
with the other bands. Added to these requirements 
is the fact that the signal strength delivered to the 
receiver is only half the signal strength received by the 
aerial provided perfect matching conditions exist. 

From these facts it can be more readily understood 
why an efficient aerial is required even in areas of 
comparatively high signal strength. There is one 
more factor which must be remembered when dealing 
with u.h.f, signals. For every 5 miles from the 
transmitter the signal strength decreases more than 
three times as rapidly as Band I. 

AERIAL ARRAYS 

The long wire inverted L aerial is well known to 
all radio experimenters. As the frequency increases, 
so the wavelength decreases, until at u.h.f. the wave- 
lengths can be measured in inches. The dipole aerials 
for v.h.f. and u.h.f. are usually made half a wave- 
length long, which makes the dipole for the lowest 
channel in Band IV about \2\ inches and for the 
highest channel in Band V about 5in. 

Elements positioned behind the dipole are known 
as reflectors; elements in front of the dipole which 
are pointed towards the transmitter are called directors. 
The complete array is known as a Yagi (see Fig. 2). 

continued on page 713 

Fig. 3. Antiference 'Uniray* aerial for the Winter Hill area, 
comprising 3-etement Band III plus 9-element u.h.f. arrays 



PRE-AMPLIFIER 

With the recent advent of a transistor that is capable 
of handling the Band IV frequencies, it is now possible to 
build a pre-amplifier which will give an amplification 
of about 14dB at low cost. This should give sufficient 
gain in areas where the field strength is below lOOmV. 
The best position to fit such a pre-amplifier is at the 
mast head; the power to operate it can be fed via the 
feeder or it can have a self-contained battery. Ampli- 
fication of a weak signal in the u.h.f. range is more 
satisfactory than amplification at lower frequencies 
since these signals are free from man-made forms of 
impulsive interference. Although Bands IV and V are 
free from aircraft flutter, they are subject to disturbance 
by passing vehicles, so wherever possible the installation 
should be kept as far away from roads bearing heavy 
traffic as is possible. 

For engineers who construct their own pre-amplifiers 
it should be noted that at Band IV frequencies all 
connections should be kept to a minimum length, 

708 





PART FIVE 



It is not the intention in" this series to delve deeply 
into the theory of transistors; information on this 
aspect has been published recently. This series is 
mainly concerned with the application of transistors. 
It is assumed throughout that the reader already has 
some rough idea of how a transistor works. Where it 
is essential to the text, simplified terms are used to 
indicate certain characteristics of the transistor. 

It should be stressed at this point that it is not 
necessary to know all the finer points of transistor 
theory in order to be able to design complete, and often 
complex, circuits. 

The essential knowledge of transistors that is needed 
in order to understand this series can be summed up 
as follows : 

TRANSISTOR CONFIGURATIONS 

While it is true that the theory of operation of the 
valve and transistor are quite different, there are many 
similarities in their functional operation. In the 
triode valve, for example, a small grid-to-cathode 
voltage controls a large anode-to-cathode current 
flow, while in the transistor a small base-emitter 
current controls a larger collector-emitter current. 

These voltages and currents are illustrated in Fig. 
5.1. Note that only the conventional currents are 
indicated; no reference is made to the flow of electrons. 

There are three basic configurations in which the 
valve can be used : common grid, common cathode, and 
common anode. Similarly, three configurations are 



by R. A. DARLEY 



used in transistor circuits: common base, common 
emitter, and common collector. These last three 
circuits are shown in Fig. 5.2, together with details 
of gain and impedance, Pnp transistors are depicted 
in these, as these are the most widely used of the 
two main types. 

The three configurations are easily remembered if 
the word "grounded" is substituted for "common", 
i.e., in the common base circuit, the base is connected 
directly to "ground" (chassis), and is, therefore, com- 
mon to both the input and output circuits. A point 
that must be remembered is that, while the negative 
line and ground are at different d.c. potentials, they 
are effectively common as far as a.c. is concerned, 
due to the fact that the power supply has a very low 
internal impedance. Thus, in the common collector 
circuit, the collector is effectively shorted to ground, 
and the term "grounded collector" can be applied. 

PRACTICAL TRANSISTOR CIRCUITS 

The circuits shown in Fig. 5.2 are, of course, very 
much simplified. A practical example of the most 
widely used of these configurations, that of the common 
emitter, is shown in Fig. 5.3. Three additional 
resistors (Rl, R2, and R3) are shown. 

The working point of a transistor, relative to its 
characteristics curve, is determined by the amount of 
base-bias applied. This "bias" may be referred to 
either in terms of voltage or current, as the two quant- 
ities are interdependent. The working point may be 
set by a simple voltage divider chain, shown as Rl and 
R2 in Fig. 5.3. 




ANODE 

GRID 



+ 250V 



SHIP I I 

CATHODE ^^ 



^m\ 



CONTROL 
CURRENT 



TIIODE VALVE NPN TRANSISTOR FHP TRANSISTOR 

Fig . S.l. Comparison of current flow In a triode and the two types of transistors 



709 



The basic transistor is, unfortunately, notoriously 
unstable when subjected to termperature changes, and 
suffers from such ailments as thermal runaway, chang- 
ing input and output impedances, etc. No complete 
cure for these troubles exists, as yet, but they can, with 
careful design, be at least kept under control. 

By placing a resistor in series with the emitter (R3 
of Fig. 5.3), d.c. negative feedback is obtained; any 
increase in emitter current results in an increased 
voltage drop across the emitter resistor. If no corres- 
ponding increase in the input voltage to the base has 
been made, the base-emitter voltage is reduced, thereby 



tending to reduce the emitter current. To prevent 
this feedback acting on signals applied to the transistor 
input, a decoupling capacitor (C2) is connected in 
parallel with R3, thus preventing a.c. feedback. 

The larger the value of R3, the better will be the 
stability. A limit is set on the maximum value of R3 
by the amount of voltage drop that can be afforded 
across this resistor; this will depend on the current, 
and hence peak-to-peak output signal, needed at the 
collector. In practice, it is adequate to allow for a 
voltage drop of i to 1 volt across the emitter resistor. 

As mentioned above, the transistor input impedance 




-15V 



OUT 



OR GROUNDED 
30 - 700Q 
300 - 500kQ 
500- 1,500 
< 
20 - 30dB 



BASE 





COMMON OR GROUNDED EMITTER 



COMMON OR GROUNDED COLLECTOR 



7 ~ 

■*-out — 

<J . ~ 

"cam — 



•cam — 



500 - i .soon 

25 - 50k£l 
300- 1,000 
25- 50 
25 - 40dB 



7. ~ 

^in — 

i-oue — 
'gain 



20 - SOOkfi 
50- 1,0000 
< I 
25-50 
10-25dB 



Fig. 5.2, Three basic transistor configurations 




NEGATIVE FEEDBACK =^ Q OUTPUT VOLTAGE 



OUTPUT 



INPUT 



|0-5V 



0-5V 




Fig. 5.3, Common emitter single stage Fig. S.4o. Block diagram of the circuit shown in Fig. 5.3 and the 
transistor amplifier waveforms of input and output when no negative feedback is applied 







FEEDBACK EFFECTIVE INPUT OUTPUT 

The effect of applying negative feedback to the circuit shown in Fig. 5.4a 



may be subject to change with ambient temperature. 
The input impedance is effectively in parallel with R2 
of the voltage divider chain, and therefore shunts it, 
so that any changes in input impedance may result 
in a change in the base-bias voltage, resulting in 
instability. The current flowing through Rl is shared 
by R2 and the base and, by ensuring that the current 
drawn by R2 is about 10 times greater than that of the 
base, the effect of variations of base current on the bias 
voltage is considerably reduced and greatly improved 
stability is obtained. Generally, the lower the values 
of Rl and R2 for any given voltage divider network, 
the better the stability will be. 

SINGLE COMMON EMITTER STAGE 

When designing a single stage common emitter 
circuit decide from the manufacturer's literature on the 
transistors working point. For example, an OC7I 
transistor should be designed to work with an emitter 
current of about 1mA, in most cases. 

Refer to the manufacturer's literature to find the 
permissible collector current swing without undue 
distortion, and from this value select Rl to give the 
required output voltage swing. 

Now select the emitter resistor R3. Remembering 
that the recommended voltage drop across this resistor 
is between | and 1 volt, and that in the case of the OC71, 
the emitter current is 1mA, R3 will be between 500 and 
1,000 ohms. Leakage and base currents have been 
neglected since they are relatively small and in this 
calculation are insignificant. 

Connect a potentiometer (about 100 kilohms) 
between the positive and negative supply lines with 
the wiper connected to the transistor base. Monitor 
the emitter current and adjust the potentiometer 
until the emitter current is 1mA. Measure the base 
voltage between the wiper and chassis and then replace 
the variable resistor by two fixed value resistors, Rl 
and R2, with values calculated to give the same base 
voltage, but with the lower reistor (R2) taking ten 
times more current than the transistor base. Connect 
capacitor C2, with a value of about 100/fF, in parallel 
with R3, to eliminate a.c. negative feedback. 

This procedure applies ONLY to a single, unloaded 
stage. When designing the circuit to feed into a 
specific load, such as the input impedance of a follow- 
ing stage, the value of the collector load, Rl, is chosen 
to give an impedance match, since Rl is effectively 
in parallel, and shunted by, the output load. 

In some cases R2 may be omitted from the circuit, 
in which case Rl is regarded as a series base current 
control resistor. Again, it may be found that Rl is 
replaced by the collector load of a preceding transistor. 
Stability may be maintained in this case but it is de- 
pendent on the stable functioning of the previous stage. 

FREQUENCY RESPONSE 

Generally speaking, the frequency response of an 
RC-coupled transistor a.f. amplifier is limited by two 
factors. At the low frequency end of the response 
curve, the limit is set by the time constant of the input 
coupling capacitor and the base-to-ground impedance 
of the circuit. For a good low frequency response, a 
long time constant is required; the input impedance 
of a common emitter amplifier is generally fairly low, 
however, and the best way of obtaining a really good 
low frequency response is to use either a very large 
value of coupling capacitor, or d.c. coupling between 
the input and base. 



The high frequency response is limited mainly by the 
characteristics of the transistor. The cut-off frequency 
of a transistor is usually given in the manufacturer's 
literature. That of the OC45, for example, is given 
as about 6Mc/s. It should be noted, however, that 
this figure applies only to the common base mode of 
operation, and that in common emitter only a fraction 
of this figure will be obtained. 

NEGATIVE FEEDBACK 

The transistor is basically a n on- linear device and, 
although a practical circuit may be designed to work 
on the most linear part of the characteristic curve, 
some distortion of the signal at its output must in- 
variably result. By applying negative feedback over 
the circuit, both the noise and distortion may be kept 
low. Unfortunately, the gain is reduced also, so no 
improvement in signal/noise ratio results. The 
effective cut-off frequency of the circuit is, in the 
common emitter mode of operation, increased. 

If 6dB of negative feedback is applied over a common 
emitter stage the noise and distortion are halved and 
the effective cut-off frequency doubled. Negative 
feedback is feedback in antiphase to the input, and the 
action may be understood with reference to Fig. 5.4. 

To illustrate this let a sine wave of 1 volt peak-to- 
peak be fed to the input; the transistor has a mean 
gain of 10, but the distortion due to non-linearity is 
such that at the output the positive half-cycles rise 
to 7 volts peak and the negative ones to 3 volts peak. 
This is the output signal without feedback. 

Now suppose that one-twentieth of the output is 
fed back to the input, in antiphase. When the positive 
half-cycle, of 0-5 volts peak, is fed to the input, the 
output will be a negative half-cycle of 3 volts peak, 
the true gain at this point of the curve being 6. With 
one-twentieth of the output fed back to the input, the 
feedback signal will have an amplitude of 3/20 = 0-15 
volts, so the actual signal on the base will be 0-5 — 
0-15 = 0-35 volts. With a gain of 6 the output from 
an input of 0-35 volts will be 21 volts. 

Now consider what happens when the negative 
half-cycle of 0-5 volts peak is fed to the input. The 
output = 7 volts peak at a gain of 14, and the feed- 
back signal = 7/20 = 0-35. The actual signal on the 
base is therefore 0-5 —0-35 volts, which gives a base 
signal of 0-15 volts. The gain is 14, so the output 
signal = 2-1 volts, exactly the same as was obtained 
with the other half-cycle. The distortion is thus 
eliminated. 

This explanation of the action of negative feedback 
is a considerable over-simplification ; the gains with 
feedback would not be the same as those without it. 
The explanation does, however, serve to indicate the 
principles involved. 

In the case of a single stage common emitter transis- 
tor, negative feedback can be obtained by leaving the 
emitter resistor un bypassed, or by resistive coupling 
of the base and collector. 

PHASE CHANGERS 

It is sometimes required that a phase change of 180 
degrees be imposed on the signal in some part of a 
circuit. Such a phase change can be imparted by a 
conventional common emitter circuit, and it should be 
noted that, when reading circuit diagrams, what looks 
like a conventional amplifier may in fact be a mere 
phase changer, the stage gain of the circuit being of 
secondary importance, and quite often very low. 

711 




PHASE SPLITTERS 

It is sometimes required that two outputs, in anti- 
phase to each other, be made available from a single 
input. 

One circuit that fulfils this requirement is shown in 
Fig. 5.5. This circuit, sometimes known as the 
"balanced inverter", has equal loads on the emitter 
and collector outputs. Since the current flowing in 
the collector circuit is practically the same as that 
flowing in the emitter, the two outputs across the equal 
value loads will be, for practical purposes, of equal 
amplitude, but opposite phase. 

The unbypassed emitter load resistor introduces 
considerable negative feedback, and results in a gain 
of a little less than one at each output. 

A disadvantage of the circuit is that the two output 
impedances are not equal. The output impedance 
at the collector is roughly equal to the collector load, 
and is thus fairly high, while the output impedance 
at the emitter is low, approximating to the input 
source impedance divided by the transistor current 
gain. This disadvantage can be overcome by con- 
necting a resistor in series with the emitter output, 
of a value equal to the difference between the two 
impedances. When so modified, the circuit gives two 
outputs of opposite phase, equal magnitude, and with 
equal output impedances, from a single input signal. 

Such a circuit may be used for driving push-pull 
output stages of an amplifier, or to give symmetrical 
deflection on the plates of an oscilloscope from a 
single-ended input. 



THE "LONG-TAILED" PAIR 

Another circuit that can be used for phase-splitting 
is shown in Fig. 5.6a. This circuit is a member of 
the 'long-tailed pair" family, this particular version 
being known as the "paraphase amplifier". The 
long-tailed pair circuit is distinguished by the use of a 
common resistor shared by the two emitters of the 
circuit. 

Referring to the circuit diagram, two transistors are 
connected in the common emitter mode, each with its 
own base bias chain (R1-R2, and R3-R4), but the 
input is applied to the base of one transistor only 
(TR1). The base of the other transistor is shorted 
to a.c. by CI. With no signal applied, the two base 
potentials of the circuit are equal. 

Let it be assumed that the transistors TR1 and TR2 
have similar characteristics, and that the two collector 
load resistors, R6 and R7, are of equal value. The 
current flowing through the common emitter resistor 
(R5) is shared equally by the two transistors, under 
"no-signal" conditions. 

With an input signal applied to the base of TR1, 
the negative going part of the input waveform results 
in an increase of current through TR1 and, therefore, 
through the common emitter resistor R5. The volt- 
age developed across R5 increases and, consequently, 
the emitters of the two transistors also move in a 
negative direction; negative feedback is thus obtained 
over TR1. 

Now, the part of the input signal that really controls 
the emitter current in a transistor amplifier is the 
effective difference between the emitter and base 
potentials resulting from the input signals, i.e. if 
the emitter is at a potential of I -5 volts and the base 
potential is at 1-7 volts, the true control voltage is 
0-2 volts. Thus, in the circuit under consideration, 



712 



the effect of the negative-going movement of the 
emitter potentials on TR2 is to reduce the difference 
between the emitter and base potentials (remember- 
ing that the base of this transistor is held at a fixed 
potential and is short circuited to a.c); the emitter 
current of TR2 is therefore reduced. The output 
signals at the two collectors of the circuit are therefore 
in antiphase. 

An increase in collector current th rough one transis- 
tor of a long-tailed pair results in a decrease in the 
collector current of the other transistor; the total cur- 
rent through the common emitter resistor therefore 
tends to remain constant. The larger the value of this 
resistor, the more nearly constant will the current be. 
It therefore follows that, if the ultimate in stability 
is to be obtained, an increase of 1mA through TR1 
will result in a decrease of 7mA through TR2, and the 
two signals at the outputs will be of exactly equal 
magnitude. 

Such a circuit will give two output signals of equal 
magnitude, equal impedance, but in opposite phase, 
from a single input. 

In any common emitter circuit (using pup transistors), 
the emitter current can be increased either by applying 
a negative signal to the base, or a positive signal to the 
emitter. 



THE DIFFERENTIAL AMPLIFIER 

A variation of the paraphase amplifier, known as the 
"differential amplifier", is shown in Fig. 5.6b. The 
main difference between this and the earlier circuit 
is that two inputs are applied, and only one output 
signal is needed; in view of this last requirement, one 
of the collector loads can be dispensed with. 

The action of the circuit is very similar to that already 
described; the common emitter resistor results in 
interaction between the two transistors. 

When a negative-going signal is applied to the base 
of TR1, the emitter current of TR1 increases and that 
of TR2 decreases. If, simultaneously, a negative- 
going signal is also applied to the base of TR2, the 
emitter current of TR2 will increase and that of TR1 
will decrease. If the two inputs are of equal amplitude 
and phase, the increase in emitter current of one 
transistor due to one input signal will be cancelled 
by the decrease in emitter current due to the other 
input; there will be no change in currents and no out- 
put signal will result. If the two inputs are not of 
equal amplitude the currents will not cancel out, 
and a current that is directly proportional to the 
difference between the two in-puts will flow in each 
emitter. 

In the circuit shown in Fig. 5.6b, only one collector 
load has been shown, connected to TR2. If loads 
are connected to both collectors, the output of TR2 
will be in phase with the base of TR1, and the col- 
lector of TR1 will be in phase with the base of TR2. 
The collector loads can be connected to one or both 
transistors depending on the phase relationship that is 
required. 

The difference between input signals is dictated not 
only by amplitude, but also by phase. Thus, if the 
two inputs are of equal amplitude but opposite phase, 
the output signal will be proportional to twice the 
value of either of the inputs. 

Next month: Considerations of the effects of 
impedance in transistor circuits and some 
practical matching circuits 



UHF RECEPTION 



continued from page 708 

If a half wave dipole were used on its own, the 
signal strength would be the same from all directions. 
If the signal strengths from all directions were plotted 
on paper, the results would be a circle with the dipole 
as the centre. This kind of graph is known as a 
polar diagram (sec Fig. 4). 




(a) (left) Simple dipole; 
similar signal strengths 
from all directions 



(b) (centre) Dipole with direc- 
tor and reflector reduces un- 
wanted signals behind dipole 
and improves directivity 

(c) (right) Yagi array giving 
much greater directivity with 
greater reduction of un- 
wanted signals behind dipole 



































r 3 . "=? 






"^—gr-^ 






(d) (left) Tandem Yagi array 

Fig. 4. Polar diagrams of aerial arrays 



(e) (right) Polar 
diagram of tandem 
array 



The addition of reflector and directors has a pro- 
found effect on the performance of the aerial as can 
be seen from the polar diagrams in Figs. 4b and 4c. 
Broadly speaking, the addition of a reflector greatly 
reduces the effect of unwanted signals, including 
man-made interference, from behind the dipole and 
the addition of reflectors increases the gain of the 
aerial and also increases the directive qualities of the 
whole array. 

For fringe area reception where two or more arrays 
may be used to increase the signal strength (Fig. 4d), 
the directive qualities or beam width is so narrow that 
very precise positioning of the aerial must be carried 
out to obtain optimum results. The polar diagram 
display is shown in Fig. 4e for a twin array. An 
added characteristic of multi-arrays is excellent 
selectivity. 

Next month: Some practical guidance on con- 
structing aerial arrays for u.h.f. 

713 




p3DB byJack Hum 
' 65UM 



Competitive 



Perceptive readers who examined 
closely the log extracts reproduced 
here last time will have noticed two 
details of some significance: that 
the contacts logged had been coming 
thick and fast, and that each was 
accompanied by a code number. 

What in fact was being shown 
was a portion of a log kept during the 
course of a transmitting contest. 
This month we reproduce another 
such log, this time rather more fully, 
comprising one page from the 
written record of a radio club station 
participating in one of the big annual 
transmitting contests organised by 
the Radio Society of Great Britain. 
It is shown here not so much to 
illustrate how a log should be kept 
as to underline the intense activity 
which such contests produce. Here 
too, as will be seen, contacts were 
coming thick and fast. 

Transmitting contests today occupy 
such an important part of the amateur 
radio scene throughout the world that 
The 73 Page would be failing in its 
duty did it not invite the attention 
of its readers to them — if indeed they 
have not become aware of them 
already, for barely a weekend passes 
but one contest or another can be 
heard in progress somewhere or other 
in the world. 



Snappy Operating 

The immediate evidence by which 
the short-wave listener gathers that a 
contest is on is an aura of urgency 
that seems to dominate the amateur 
bands. Operators may be heard 
calling "CQ Contest", sometimes 
naming the actual event in which 
they are participating so that no 
answers will be sent by people who 
are not! Leisurely conversation is 
out during contest time: snappy 
operating is in. Contacts are dis- 
posed of in the quickest possible 
time. 

714 



The operator who collects the 
largest number of contacts, or winkles 
out the rarest or most distant 
countries (according to how the 
rules are framed), will find his call- 
sign at the top of the list when the 
results are eventually published. 



The Hard Slog 

To achieve this status is the result 
of sheer hard work. Success in 
contests calls for nothing less. Nor 
is a top place simply a brief moment 
of glory, to be basked in for a month 
or two before all is forgotten: what 
is remarkable is how the same call- 
signs appear time after time in the 
top positions of the world's com- 
petitive transmitting events. 



aid of a transmitter-and-aerial com- 
bination of hyper-efficiency and 
reliability used at the psychological 
moment— and as a rapier, not as a 
broadsword. 

" Is it worth it?" 

Well may the practical electronician 
enquire "whether it is all worth it", 
to which he will be inclined to reply 
"Yes" if he agrees that the develop- 
ment and exercise of a skill are useful 
ends in themselves. Most people 
believe that they are. 

This belief counterbalances the 
oft-heard criticisms that contests 
''clutter up the bands", that "there 
is no weekend free of them" and 
that the collecting of code numbers 
from a myriad of other stations is a 



JON MX, 



The station log can be either a self-prepared one ruled up to carry the informa- 
tion required by the G.P.O. licence, or ft con be one of the several commer- 
cially produced varieties which are on the market. The example shown is from 
a "G6DS logbook". The extract is from a period of contest-operating on the 
2 metre amateur band. 



There is an obvious reason for 
this. The operator who is deter- 
mined to do well in a contest knows 
he will be wasting his time if either 
his skill or his technical facilities are 
less than one hundred per cent 
efficient. 

He knows that if he can sort out 
that elusive signal from beneath a 
pile-up of perhaps half-a-hundred 
others which are almost zero-beat 
with it then he stands a fair chance 
of a top place in the final table. 

He knows that this will be possible 
only if his receiver is better than the 
next man's — and he knows that "the 
next man" knows it too! 

He knows also that simply to hear 
them is not enough: he must be 
able to work them as well, with the 



monotonous chore that could be 
conveniently consigned to a com- 
puter — and all of these comments 
carry some validity. 




Inexpensive 
Versatile 
Simple to 
build 




By B. Crank 

This instrument was designed to provide an inex- 
pensive unit capable of carrying out a series of 
d.c. tests on various transistors and diodes. It measures 
leakage current between collector and emitter (/ co ) 
and between collector and base (/ c & ). It also enables 
transfer and collector characteristics to be determined 
quickly for both pnp and npn transistors. Forward 
and reverse currents for diodes at various applied 
voltages can be measured; Zener voltage can be 
determined on silicon Zener diodes. 

Indication is by an internal 50>A meter which is 
provided with fourteen ranges between zero and 
50mA, and between zero and 25 volts. Collector 
voltage is available up to 18 volts in three ranges, 
i.e. zero to 1 volt, zero to 9 volts, and 9 to 18 volts. 
The circuit employed ensures that any value of col- 
lector voltage within the above ranges can be easily 
and accurately set. Base current is available in six 
continuously variable ranges from zero to 5mA. 
Collector currents up to 50mA can be accommodated. 

The unit is housed in a small case 8£in x 5^in x 
3|in; the whole unit costs about five pounds to make. 

CIRCUIT 

This is best started by looking into the power supply 
arrangements. As can be seen from Fig. 1 two 9 volt 
batteries are used these being connected in series 



and centre tapped. S6 is the "pnploffinpri" switch 
and is shown drawn in the pnp position. The negative 
terminal of BY1 is connected via position 1 of S6c 
to the top end of VR1. The lower end of VR1 is 
connected via position 1 of S5a, position 1 of S5d 
and position I of S6d to the positive terminal of B2. 
Thus VR1 has the full 18 volt supply across it. It 
will also be noticed that in position I of S6a and b 
that the negative side of the meter is connected to 
Sib and the positive side to Sla. With S6 in position 
2 the batteries are disconnected and a short circuit is 
placed across the meter to damp the movement of the 
needle due to its own self-generated current during 
transit. In the third position of S6, i.e. npn posi- 
tion, the battery and meter connections are reversed. 
For the rest of this description it will be assumed 
that S6 is in the pnp position, i.e. position 1. VR1 
as has already been shown has 18 volts across it, as 
long as the unit is switched on, regardless of other 
switch positions. VR1 forms a potential divider and 
is the base current fine control. The potential at the 
wiper of VR1 is fed, via a limiting resistor, selected 
by the base current coarse control S4, to the base of 
the transistor under test via Sle. The resistors 
selected by S4 (R14 to R19) provide the following 
ranges of base current: 0-10/tA, 0-50/* A, 0-100/tA, 
0-500M, 0-1 mA, 0-5mA. 

715 



The action of the collector voltage coarse control 
(S5) and fine control (VR2) will be discussed next. 
With S5 in position I the negative terminal of BY1, 
as far as VR2 is concerned, is out of circuit. The 
negative terminal of BY2 is connected via R20 to 
VR2; R20 allows about 1 volt to be dropped across 
VR2, the positive return being S5d and S6d to Bl. 
Therefore a potential of between and 1 volt is avail- 
able at the wiper of VR2. 

With S5 in position 2 the circuit is identical except 
that R20 is short-circuited. The full nine volts from 
BY2 is applied across VR2 so that the potential at 
VR2 wiper can be varied between and 9 volts. 

With S5 in position 3 trie positive terminal of BY2 
is connected via S5a to the earth line of the tester 
maintaining the 18 volts across VR1. The lower end 
of VR2 is connected via S5c and S5d to the battery 
centre-tap and is therefore at 9 volts negative with 
respect to earth. The upper end of VR2 is con- 
nected via S5b to the negative terminal of BYI. 
Although there is still only 9 volts across VR2 the 
potential at the wiper is between 9 and 18 volts with 
respect to battery positive. The extra complication 
involved in giving VR2 this range of 9-18 volts instead 
of the much more easily obtained 0-18 volts is well 
worthwhile as it means that the operator has a much 
finer control over collector voltage. 

The main disadvantage of the system used is that 
when heavy collector currents are being taken (i.e. 
over 10mA) and when the switch is in the 9-18 volt 
position, the collector voltage falls sharply for the first 
movement of the potentiometer but the voltage soon 
recovers and still results in finer control being obtained. 

S2 and S3 control the meter ranges, provided Sib 
is at any position except position four, giving eight 
current ranges with full scale deflections of 50/tA, 
100//A, 250/iA, 500/* A, 1mA, 5mA, 10mA and 50mA. 
With SI in position four the multiplier resistor selected 
by S3 is now in the meter circuit to provide up to 
0-1V, 0-5V, IV, 5V, 10V and 25V on each range 
respectively. 

The instrument functions by applying various 
potentials to the transistor under test and by switching 
the meter into various parts of the circuit with SI. 

SI IN POSITION I l c0 

In this position the meter is indicating collector to 
emitter leakage current; the basic test circuit is shown 
in Fig. 2a. The meter together with a shunt resistor 
selected by S2 is in series with the negative supply 
to the collector; the base is open circuit. 

Reference to Fig. 1 will show how this is achieved. 
The negative supply at the wiper of VR2 is fed via 
position 1 of Sic through the meter and its shunt 
(selected by S2) to the collector of the transistor under 
test, via SI a and the external meter socket. The 
purpose of this socket is to allow collector currents 
of greater than 50mA to be measured on a more 
suitable external meter. It also simplifies the process 
of plotting performance curves, although this can be 
done without the external meter. Normally this 
socket is short-circuited when no external meter is 
used. The emitter of the transistor is connected to 
the battery positive line via S5a, S5d and S6d. 



Fig. I (right). Circuit diagram of the complete transistor 
and diode tester. Alt switch positions are related to the 
annotations given in Fig. 7. For example: position I of SI is 
for measuring l co , and so on 

716 




y uJ w u j s 

at h* *— i/» 3 — * 

^ UJ t*J rf o o 

if X X co o o- 

^ w n T in <<> 

%fr \f\ if* UJ i/V y> 



TO VR2 WIPER 







, R (shunt) 



<S 



Fig. 2a. Position I, (t ro ) 
collector to emitter 
leakage current 



Fig. 2b. Position 2, (f c &oJ 
collector to base leak- 
age current 



H shunt 




T0VR2 
WIPER(-vc, 



R shunt 




TO VR 2 WIPER 



Fig. 2c. Position 3, (It,) base current 




TO VR2 WIPER 



fl (Multiplier, 



Fig. 2d. Position 4, (V C(i ) collector to emitter voltage 



TO VR2 WIPER 



R (shunt) 




Fig. 2e. Position 5, (l c ) collector current 



Fig. 2. Basic circuits for each position of SI 



SI IN POSITION 2 f eb <j 

The basic circuit is shown in Fig. 2b. Here the 
negative supply is fed direct to the collector. The 
meter and its selected shunt is connected between the 
base and earth to indicate collector to base leakage 
current. 

The negative supply at the wiper of VR2 is fed via 
position 2 of Sid direct to the collector. The meter 
complete with shunt is connected via position 2 of 
Sic and Sla between the base and emitter. 

SI IN POSITION 3 l h 

In this position a measured value of base current is 
allowed to flow in the transistor. This checks the 
continuity of the base emitter junction and enables 
any base current between and 5mA to be preset 
so that other checks can be earned out. The basic 
circuit is shown in Fig. 2c. The wiper of VR1 is 
connected via a limiting resistor selected by S4 to 
one side of the meter and shunt. The other side of 
the meter is connected to the base via S6a and Sla. 
The meter will register base current, the value of that 
base current being controlled by VR1 and S4. Also 
the negative supply is still connected to the collector. 

The negative supply at the wiper of S4 is fed via 
position 3 of Sle and Sic to the meter and shunt. 
The negative supply to the collector is maintained 
via Sid. 

SI IN POSITION 4 V ce 

In this position, the collector voltage being applied 
is measured and set to any value within the range of 
the instrument. Also the base current preset in the 
last operation is maintained. This is because varia- 
tions in base current alters the collector current flowing 
through the transistor; changes in collector current 
cause alteration in collector voltage due to the voltage 
dropped by VR2. In this instrument the value of 
collector volts required is set after the base current has 
been set. The basic circuit may be seen in Fig. 2d. 
The base current is still allowed to flow and the meter, 
now a voltmeter, is connected with its multiplier 
resistor, selected by S3, between the collector and 
earth. 

The base supply is maintained via position 4 of 
Sle and the collector supply by position 4 of Sid. 
The multiplier resistor selected by S3 is connected 
to the meter via position 4 of Sib, then to the emitter 
via Sla. 

SI IN POSITION 5 fc 

In this position the collector current is measured 
and hence the gain of the transistor can be calculated. 
The basic circuit is shown in Fig. 2e. The collector 
of the transistor is connected to the negative supply 
through the meter and its selected shunt, through 
position 5 of Sic and Sla. The previously set base 
current is still allowed to flow. The base current 
supply is maintained by position 5 of Sle. 

METER SWITCHING 

The use of separate range switches for voltage and 
current reduces the number of switching operations 
during the test of a transistor to a minimum. The 
voltage range can be preset to a suitable value before 
the tests commence. Then it is only necessary to 
alter the current range switch from a suitable range 

717 






for base current to one for collector current. If an 
external meter is employed this need is eliminated. 
The internal meter range switches can be set to suitable 
ranges to measure collector voltage and base current, 
the external meter being switched to a suitable range 
to measure collector current. If this method is used, 
collector current can be measured in either the h 
or V ce positions of SI, but not in the h position. 
The alteration of the internal meter to a voltmeter 
is carried out by the switch SI to prevent the possibility 
of too large a voltage being applied across it when 
on a current range. 

Another point worthy of mention is the possible 
alteration of base current caused by switching the 
meter in and out of the base current circuit. The 
actual alteration is very small as the resistance of the 
meter is very small compared with the series limiting 
resistance switched in by S4. Once again this pos- 
sibility is eliminated by using an external meter, as the 
collector current can be measured in the h position. 

CONSTRUCTION AND COMPONENTS 

The instrument was built in a metal case of the type 
used for sandwiches as shown in Fig. 3. The meter 
was a surplus item with a full-scale deflection of 50/*A 
and internal resistance of about 1,000 ohms. It is 
obtainable on the surplus market for about 25s. 
although any similar meter would be suitable. A new 
scale has to be fitted, this is reproduced in Fig. 4. 
To do this it is necessary to remove the four screws 
at the rear of the instrument and remove the case. 








Fig. 4. New scale to suit the ranges of the instrument. This 
is reproduced full size for the original meter. If a different 
size or shape of meter is used check that the new scale 
suitably fits for angle of deflection and length 



The scale can then be drawn on paper and glued over 
the original scale, care being taken to ensure that it 
is correctly aligned. It is a good plan to smear a 
little vaseline round the flanges of the case when 
refitting to prevent the ingress of dust. 

Due to the number of different contact arrangements 
used on the wafer switches it is impracticable to show 
a point to point wiring diagram, therefore the following 
constructional procedure is recommended. 




5 V HOLES Vb DIA. 
O'KOLESS/^DIA. 
I'C HOLE 5/^DiA. 
8 '0' HOLES tyg'DIA. 

Fig. 3, Drilling details of the metal case used in the prototype. Some adjustments may be necessary if a different shaped 

meter is used 

718 



Sketch each wafer switch used numbering the poles 
and tags as in Fig. 1. Redraw Fig. 1 in pencil on a 
separate piece of paper. Mount all switches as shown 
in Fig. 5 with the exception of SI. SI is now wired 
up; as each wire is soldered on it is inked in on the 
previously made pencil drawing. This method ensures 
that no wires are omitted. All leads that come from 
SI to other parts of the circuit are left about eight 
inches long and are labelled. When completely 
satisfied that SI is correctly wired it can be mounted 
into the case. The rest of the wiring can now be 
completed by connecting S 1 wires to their appropriate 
terminations and adding additional wires and com- 
ponents as necessary; mark the circuit diagram as 
before. 

The values of R14 to R20 are not critical and any 
near values can be used. Rll, R12 and R13 should 
be 1 per cent high stability types. The values given 
for the meter shunt resistors (Rl to R7) are for guid- 
ance only. These are adjusted to their exact value 
during the setting up procedure. They should be 
wound on a small piece of s.r.b.p. using suitable 
resistance wire to a value slightly higher than that 
specified. R8, R9 and RIO should be high stability 
types chosen to be slightly lower in value than specified. 

The transistor terminals and external meter con- 
nections are made up from 4B.A. brass screws and 
mounted on a paxolin or s.r.b.p. strip about |in 



thick as shown in Fig, 6. The front panel can be 
reproduced from that shown in Fig. 7. 

ADJUSTING THE METER MULTIPLIERS 

After the wiring has been completed and throughly 
checked set the switches to the following positions: 



SI 


Vce 


S2 


50mA 


S3 


25 volts 


S4 


iom 



S5 


0-9 volts 


S6 


off 


VR1 


minimum 


VR2 


minimum 



Connect an external voltmeter to the emitter and 
collector terminals with the negative meter lead to the 
collector. Ensure that there is a shorting link fitted 
across the external meter terminals. Set S6 to pnp. 
Slowly rotate VR2 to maximum when both meters 
should read 9 volts. Return VR2 to minimu m when 
both meters should indicate zero. Set S5 to "9-18 
volts". Both meters should indicate 9 volts. Rotate 
VR2 to maximum; both meters should indicate 18 
volts. Return VR2 to minimum and S5 to the "0-9 
volts" position. 

The 10 and 5 volt ranges of S3 can be checked in 
the same manner, the only difference in this case 
being that the "9-18 volt" position of S5 is not used. 
The 10, 0-5 and 01 volt ranges can now be checked 
for function only, because the internal meter should 
read high on these ranges. The appropriate multi- 



GROMMET TO 
TERMINAL BOARD 




BATTERY PACK 



Fig. 5. Interior view of the case with the components assembled. Complete detailed wiring has 
been omitted for clarity. It is recommended that the system of wiring described in the text is 
adopted. The wires should be laced into a cable form if possible as shown above 



719 



plier resistor is increased in value by careful scraping 
with a razor blade to reduce its diameter. When 
the meter is reading accurately on these ranges, the 
resistors arc protected by giving them a coat of clear 
varnish. 

ADJUSTING THE METER SHUNTS 

Set switches to the following positions: 

51 7 eo S5 0-9 volts 

52 50mA S6 off 

53 25 volts VR 1 minimum 

54 10/4 A VR2 minimum 

Connect an external milliammeter to the external 
meter sockets, the negative test lead going to the 
supply terminal and the positive to the terminal con- 
nected to the collector. Connect a 150 ohm resistor 
between the collector and emitter terminals. Set S6 
to "/>«p". Rotate VR2 slowly clockwise; both meters 
should indicate a current, the internal meter should 
read higher than the external meter. This error is 
corrected by reducing the value of the selected shunt 
resistor. 



COMPONENTS . . . 



Resistors 



Rl 


500Q 


R2 


200n 


R3 


100ft 


R4 


son 


R5 


ion 


R6 


sn 


R7 


in 


R8 


ikn 


R9 


9kn 


RIO 


I9kn 


Rl! 


lookn 


RI2 


200kli 


RI3 


500 kn 


RI4 


1 -8MI1 


RI5 


360 kQ 


RI6 


ISOkn 


RI7 


36kn 


RI8 


I8kn 


RI9 


3-6kn 


R20 


39kQ 



:» Wirewound (see text) 



^High stab, i watt carbon 
(see text) 

High stab. £ watt 
1% carbon 



>i watt 10% carbon 



Potent i o m eters 

VRI 10kn linear wirewound 
VR2 5kn linear wirewound 

Switches 

51 6 poles, 5 ways (3 wafers, 2 poles on each; one 

pole not used) 

52 I pole, 12 ways (I wafer; 4 ways not used) 

53 I pole, 6 ways (or 2 poles, 6 ways; I pole not 

used) 

54 I pole, 6 ways (or 2 poles, 6 ways; I pole not 

used) 

55 4 poles, 3 ways 

56 4 poles, 3 ways 

All switches are rotary wafer types. 

Batteries 

BY! and BY2 9 volts each (type PP7 or similar) 

Meters 

Ml 50^A I.OOOn Moving coil 

Miscellaneous 

Metal lunch box (Woolworth), eight pointer knobs, 
s.r.b.p. strip (see text), 4B.A. nuts and bolts 



This must not be done while the instrument is 
switched on. To reduce the resistance of the shunt 
shorten the length of wire with which it is wound. 
This should be done a little at a time. This process 
is repeated for all the other current ranges. For the 
lower ranges it is advisable to fit a larger resistor 



2% 



7-ysDiAHOLES 




f- (j) | -^--^-h® 



& 



%• 



¥ . , V r 



1 

X 



3J 



3 /8 



?tf 



3l 



Fig. 6a. Drilling details of the s.r.b.p. strip for mounting the 
screw terminals 



SLOT FOR TRANSISTOR 
-LEAD OUT WIRES 



NUT-; 



■-^rd™...^"" " 11 aHT 



^ y$~ 



SLOT FOR CONNECTING 
WIRE TO UNIT 




WASHER- 
MODIFIED 
48A SCREW 

Fig. 6b. The 4 B.A. screw is slotted and mounted as shown 
above. The transistor wires can be clamped between the 
two nuts when testing 



iv. 



,5V 



0-5V, 
0JV» 



o 

METER RAN6E 
(S3) 



10V 
•25V 



9 C EXT 

METER 



j\ 



* 



500pA # 
25CjjA« 



100/iA 



METER RANGE 
ImA 
•5mA 

•10 mA 




o 

(S2) 



V)mA 



BASE CURRENT 



lOOuA* •500uA 
50>iA ImA 

lOji* fj 5mA 

COARSE 

N 



(VRl) 




O 



\MAX 

FINE 



FUNCTION 



h 

Icb0« * •V c , 



d Q % 


. o 


(Si) 


COARSE 




(ss) 


OFF 
PNP. • #NPN 
FWD REV 


fVR2) 



o 

(56) 



COLLECTOR VOLTS 



0-9V 
0HV. • »9-i8V 



O 



MIK/ ^MAX 

FINE 



Fig. 7. Suggested design for a front panel made from stiff 
card and lettered with transfers. This one is reproduced 
approximately half scale 



720 



J-gmA 
5 










1 
































3 
2 






















































































20 



30 



SO 60 



70 



80 



90 100 



V 



Fig. 8. A typical graph of the transfer characteristic of a 
medium gain transistor 

between the collector and emitter terminals. This is 
a tedious job but care and patience will be rewarded 
in the end. Disconnect this resistor and set VR2 to 
minimu m when finished. 

OTHER TESTS 

Check that with S5 in the npn position the internal 
meter reads in the correct direction but now the col- 
lector terminal is positive with respect to the emitter. 
Connect a milliammeter between the base and emitter 
terminals, the negative test lead going to the base. 
Set S5 to pnp and S4 to 1mA. Rotate VR1 towards 
maximum; both meters should show a reading until 
1mA is indicated on both meters at maximum. Set 
SI to V ee and h in turn; the internal meter should not 
read but the external should still read 1mA. 

With a 150 ohm resistor in circuit between the base 
and collector terminals select I C b and ensure that the 
meter indicates a reading. If the resistor is discon- 
nected the meter reading should fall to zero. 

USING THE INSTRUMENT 

IMPORTANT NOTE: Care should be taken to ensure 

that during the following checks the maximum ratings 

for the transistor under test are not exceeded. The 

supply voltage should not be switched on until all 

switches and potentiometers are correctly set. 

Set the controls as before when setting up the meter 

shunts. Connect the transistor to be tested to the 

test terminals. If an external meter is not being used 

ensure that the link is in place across the external 

meter test terminals. Set pnp or npn as appropriate 

and switch on. Slowly increase the setting of VR2; 

if the meter reading climbs rapidly the transistor is 

short-circuited and the instrument should be switched 

off. If the meter does not indicate, or indicates very 

little, all is well. Reduce the meter range until the 

collector to emitter leakage current can be accurately 

measured. Increase the meter range. Set VR2 to 

minimum. Select htn on SI. Proceed as before 

only this time collector to base leakage current is 

being measured. 

Return VR2 to minimum. Set the meter to a high 
range. Set SI to h and with S4 and VR1 set for a 
200/tA base current. Select V ce on SI and set the 
collector to 9 volts. Switch to I c and the collector 
current can be measured. The d.c. gain is given by 
collector current . 

base current or lclib ' 
This represents the /? or a' of the transistor. 




V VOLTS 

ce 

Fig, 9. A typical graph of collector current against collector 
voltage for given base currents of a medium gain a.f. 

transistor 

TRANSFER CHARACTERISTIC 

The transfer characteristic is plotted easily using the 
instrument. This is done by drawing a graph as 
typified by Fig. 8, i.e., base current against collector 
current. 



COLLECTOR CHARACTERISTIC 

Plot the collector current against collector voltage 
for various preset values of base current as typified 
in Fig. 9. 

TESTING DIODES 

Diodes are tested by connecting them across the 
collector and emitter test terminals. They can then 
be checked at various forward and reverse potentials 
using the pnpjnpn switch. Voltages and currents 
flowing are measured in the Vee and I c switch positions. 

OTHER USES 

From experience the user may find this instrument 
invaluable in many other ways. Electrolytic capacitors 
of low voltage rating may be checked to determine 
leakage currents by connecting across the collector and 
emitter terminals and applying voltages and currents 
as with diodes. The rated working voltage of the 
capacitor should not be exceeded. 

Resistance can be measured by connecting the 
"unknown" across the collector and emitter terminals, 
applying a low voltage and measuring as for the 
colllector current condition. The resistance is then 
calculated by dividing the applied voltage by the 
measured current. 

Once the instrument has been calibrated against a 
known reliable meter, other meters can be calibrated 
by connecting to the collector and emitter terminals and 
following a procedure similar to that described pre- 
viously. 

The tester also becomes an excellent tool in experi- 
mental work, for example, when it is required to design 
a transistor amplifying stage. Various voltages and 
currents can be applied to find the most suitable 
working conditions of a transistor. 

Care should be exercised in all operations of this 
tester to avoid undue damage to transistors. One 
cannot over stress the necessity to watch for rapidly 
rising currents indicated on the meter. Switch off 
the instrument before such a current rises too high. ^- 

721 



(nfi 



"P 



mm 



D 



II 



n^ 



D 




HIGHLIGHTS FROM THE CONTEMPORARY SCENE 



Automatic Wiring 



Qne of the many interesting features at the 
v - / Components Show held at Oiympia in May 
was this completely automatic wiring machine 
developed by Aircraft- Marine Products. 

The rack of equipment on the left is a punched 
paper tape programme console, which provides 
the wiring machine with information to operate 
the moving head. Insulated wire is fed into the 
head from a manufacturer's reel. The insulation 
is stripped at the end; a gold plated phosphor 
bronze spring clip (like those shown inset below) 
is crimped to the wire. The head then locates 
the required tag post on a large matrix and 
forces the clip on to it. 

The head then finds the corresponding post 
elsewhere on the matrix to which the other end 
has to be attached. The wire is threaded 
between the posts on its way. At its destination 
the wire is cut, stripped, and again fitted with a 
clip which is forced on to the next tag post. 






Painless Activity Recorder 




A new idea in the measurement of body move- 
**ment is announced by Faraday Electronic 
Instruments, a company of the Pye Group. 
Called the "Animal Activity Recorder", it 
measures and records accurately and electroni- 
cally many important movements of animals 
(including humans) under observation. It does 
this without the use of tilting cages, photo- 
electric beams or wires attached to the subject. 

The sort of things which can now be measured 
electronically without the "patient" being aware 
of it include breath-rate and the precise move- 
ments of it in its enclosure; even a hiccup is 
registered. How often a baby moves in its cot 
and the twitching of the whisker of a rat under- 
going drug tests, can all be picked up. 

A high frequency low amplitude signal is 
generated and fed on to the bottom wire grille 
of the cage containing the animal or to the 
metal frame of a hospital cot or bed. There is 
absolutely no danger in this tiny signal and no 
fear of electric shock. The animal or baby then 
acts as a "transmitting aerial" within the radiated 
field deflecting the signals to receiving aerials 
fastened to the cage or cot. 

As the subject moves around, it causes 
fluctuations in field strength relative to its 
position. 



Count Down 



This machine (shown in the photograph on the 
right) counts pills; small pills, large pills, 
even chocolates, nuts and bolts, seeds, buttons 
and many other small items. Known as the 
"Mastercount random path detector," the 
electronics attached to the front have been 
developed by Decca Radar to count at the rate of 
1,500 to 6,000 per minute by using an OCP71 
photo transistor and a beam of light provided 
by a torch bulb. 

The equipment employs an 
aperture many times larger 
than the object to be detected, 
hence the need for a narrow 
light beam is eliminated. 



Automatic Descent 

Duplex automatic flight control systems are being 
fitted to B.E.A. Hawker Siddeley Trident airliners to 
provide "autoflare" or automatic touchdown. The 
execution of the difficult landing phase is shared between 
the pilot and the electronic equipment developed by 
Smiths Aviation Division. The equipment is capable of 
guiding the Trident to a more precise position than can be 
achieved by a pilot on his own. 

At a height of about 150 feet the autoflare equipment is 
brought into action until touchdown. Aircraft pitch 
movements and throttle adjustments are controlled 
automatically while the pilot keeps the aircraft in line with 
the runway. 

An S.T.C. altimeter, emitting a constant sweep frequency 




within the 4,200 and 4,400 Mc/s band, measures the height 
of the aircraft during descent. 

The picture below shows the flight deck with duplicated 
instruments including attitude directors, flight compass, 
airspeed indicators, altimeter, and vertical speed indicator. 
The automatic flight control panel is mounted at the front 
of the pedestal between the pilots* seats. 

The system has been approved by the Air Registration 
Board for use on normal passenger services. 






fc ; - « « -\ « m m ■ - V* 




BEGINNERS start here... 



An Instructional Series far the Newcomer to Electronics 




This month we complete our present look at inductors 
and transformers by considering two different 
aspects of energy. First we note how energy can be 
conserved or stored in a coil, and afterwards we examine 
the energy losses incurred in iron-cored components. 



STORED ENERGY 

One further interpretation of inductor action which 
is very interesting is the notion that energy is stored in 
the surrounding magnetic field (see Fig. 10.1). This 
energy is built up during the current growth: when 
the current is switched off, this energy is given back to 
the circuit, and tends to keep the current flowing. 

If, in fact, the coil is switched completely off, no 
current can flow, and the collapsing magnetic field 
gives rise to a giant voltage peak across the coil. This 
"inductive surge" is put to good use in high voltage 
generation for television cathode ray tubes, and in 
electronic circuits known as "ringing oscillators", 
"pulse generators" and "blocking oscillators". But, in 
some circuits, notably transistor designs, these inductive 
surges are destructive, and must be guarded against. 
Later on we shall discuss methods of doing this. The 
storage of energy mentioned above is very similar to a 
capacitor — except that in the capacitor the energy is 
stored in the electric field between the plates. 



LOSSES IN TRANSFORMERS 

There are some losses in a transformer. For instance, 
if an output power of 100 watts was being taken from 
the secondary of a certain specimen, it could easily be 
the case that 110 watts was being supplied to the pri- 
mary. Where are the additional 10 watts going? 



After some little while, the transformer would feel 
slightly warm, and this heat produced represents the 
loss. 

Some energy is lost in overcoming the resistance 
of the windings— this is known as the copper loss. 
Some is lost in eddy current heating of the iron core, 
even though this is reduced to a minimum by laminat- 
ing the core. 

But, this is not the whole story. It takes energy 
to continually magnetise and demagnetise the iron 
in the core. In fact, the magnetic flux in the core is a 
different value while increasing with the growth of 
current in the windings, compared with that while the 
current is decreasing. 

MAGNETIC HYSTERESIS 

This lag, or "backlash" effect is called magnetic 
hysteresis, and the characteristic "S" shaped loop is 
often seen in connection with discussions on this topic. 
Actually, the iron is magnetised by the field produced by 
the current. The magnetic flux density, set up by a 
magnetising force, we can call B to follow convention. 
The magnetising force is denoted by the letter H. 
These quantities are connected by a small equation: 

B = fiH 

This "ft" is called the permeability of the material 
being magnetised. For iron ft can be a very large 
number, meaning that B can be considerable even 
though H is small. Ferrite rods have a large ft, for 
instance. For iron, B is not proportional to H — we 
say the relation between them is non-linear, hence the 
distortion that can arise when using cored transformers 
in amplifiers. 



^feio- 



S^ 



FIELD BUILDING 
UP 







_, - Ti&RpsnpsU -'" ' 






FIELD ESTABLISHED 

V 

~< 


1 


f 



SPARK MADE AS 
SWITCH IS OPENED 



t 



FIELD COLLAPSING 
RAPIDLY 



J- 



/\ SWITCH A 



SWITCH ON (o) SWITCH ON ^ SWITCH ON 

Fig. 1 0.1. These diagrams show how energy is stored in the magnetic field, (a) The switch has just 
been closed and the magnetic field is commencing to build up. The almost instantaneous rise of 
current at this moment is Indicated in the graph, (b) The magnetic field has reached peak value, 
and the current has now fallen off. The final circuit (c) shows how the magnetic field collapses as 
the switch is opened. The energy is dissipated giving rise to a large voltage peak which appears 
across the coil 

724 



fc> 



INDUCTIVE 
'SPIKE' 



Fig. 10.2a, shows how B might grow with H, Notice 
how the curve flattens off at the top. This means 
that the iron has the maximum B, i.e. flux density, that 
it can take. We say it is saturated. This means that 
sufficient core area must be used in transformers so 
that this saturation is not reached while in operation. 

Back to hysteresis again. If we reduce the value of 
H, B will fall, but not so fast as expected. In fact 
the value of B will still be something, when H has been 
reduced to zero (no current). This means there is 
some residual magnetism in the core, or permanent 
magnetism as it is commonly known. In order to 
reduce the value of B to zero, H would have to be 
reversed. If a.c. flows in a winding, the core goes 
through a complete cycle as above, in step with the 
changing H produced by the a.c. 



HYSTERESIS LOOPS 

A typical hysteresis loop is shown in Fig. 10.2b, com- 
plete with saturation in the two directions. Permanent 
magnets have a high residual magnetism, as part of 
their design. The hysteresis loop for the steel in these 




Two iron cored audio frequency transformers. These are 
reproduced approximately life size and indicate the kind 
of miniature components now in common use 

the core (called the "window")- So, an amateur can 
fairly easily design and make his own transformers — 
but the last point above usually makes itself apparent 
after most of the turns have been put on! 




Fig. 1 0.2a. This shows how the magnetic 
flux density B grows as the magnetising 
force H increases 



Fig. /0.2b. The initial growth of mag- 
netisation goes from '0' to saturation, 
thereafter the rise and fall "cycles" in 
the direction shown 



Fig. 10 2c. Materials which tend to 
retain their magnetisation (permanent 
magnets) have a "flat" hysteresis loop 
as depicted here 



devices resembles Fig. 10.2c. The ferrite ring material, 
already mentioned in connection with computers in 
part 7, usually has a very square loop (it is called 
square loop material)— so that the switching over in 
direction is well defined and sudden. 

Now we finish up this discussion with a final point 
about transformer cores. 

Energy is required to go round and round the 
hysteresis loop, as it were, and this comprises some of 
the loss in transformers. It can be shown that the 
energy lost is proportional to the area of the loop, so 
iron for a.c. cores is chosen to keep the loop narrow 
and of small area. Thus the iron losses in a trans- 
former consist of two parts, the eddy current loss, and 
that produced by hysteresis. Transformers designed 
for use on the 50 cycles per second mains must have at 
least 1 square inch of core for every 50 watts input 
when operating at the correct load. A good rule is to 
assume 8 turns per volt for a core area of 1 square inch; 
2 square inches would require 4 turns per volt, and 
so on. 

The gauge of the wire is chosen to carry the resultant 
current. The last point to check is whether the amount 
of wire needed will go into the space available around 



A USE FOR INDUCTIVE KICKS 

We end this month with an example of the use of the 
voltage pulse produced when the current through a coil 
is changed rapidly. 

In order to set up the discharge in the gas contained 
inside a photographic flash tube, a very high voltage is 
required across the starting electrodes to ionise the gas. 
The main store of energy (contained in a large capacitor) 
then pours through the ionised gas causing a tremend- 
ous burst of light output. , 

The way to get a pulse of a few thousands of volts 
for this job is simple, if you remember the theory of 
inductors. A small charge is passed through the prim- 
ary winding of a transformer by operating the camera 
shutter switch contacts. This burst of current produces 
a rapidly changing magnetic field which links with the 
large number of turns on the secondary winding, and 
by Faraday's Law a large voltage (many thousands per- 
haps) is induced across this winding. Thus the tube is 
triggered in synchronism with the operation of the 
camera shutter. 

You should now be able to follow Mr. B. J. Crowe's 
article, using your theoretical knowledge to explain the 
circuit action. 

725 




This pack provides a convenient and portable source 
of power for experimental circuits using transistors, 
small motors, lamps, and other low voltage devices. 
It incorporates a fast acting current operated trip, 
which can be set to any value from 0-5 milliamp to 
3 amp. This trip circuit protects the meter, power 
supply, and any connected load. The actual power 
source comprises four inexpensive cycle lamp batteries, 
and these are tapped to provide 3, 6, 9, and 12 volts. 

If a moving coil meter is shunted to give a range of 
current readings, the voltage across the meter terminals 
will remain constant for any given deflection on any 
range. The prototype battery pack incorporates a 
5 milliamp f.s.d. meter movement with an internal 
resistance of 15 ohms which, by calculation, shows a 
terminal voltage of 75 millivolts at full-scale deflection. 
When this meter is shunted to read 3 amp, for instance, 
the voltage across shunt and terminals will still be 
75 millivolts. 

CIRCUIT DETAILS 

By reference to the circuit diagram (Fig. 1) it can be 
seen that the transistor TR1 is arranged to "read" the 
voltage developed across the meter, via R7, and pulls 
in the relay RLA when this voltage exceeds a level pre- 
determined by the setting of VR1. 

Under normal circumstances this trip circuit is set 
to operate at the full scale deflection of the meter, and 
will therefore cut out at the values set by the range 
switch S2, namely 6mA, 30mA, 300mA, and 3A. 
At the most sensitive setting of VR1, the trip functions 
at lower than 10 per cent of these values. 

The circuit is sufficiently flexible to admit other 
meter movements and the ranges can be altered to suit 
the existing meter calibration and power supply 
characteristics. The formula for calculating alter- 
native shunt values is 

where R m is the resistance of the meter and n is the 
desired multiple of its basic current reading. Shunts 
may, alternatively, be manufactured by the "cut and 
try" method using a wide range test meter for com- 
parison. Generally speaking, a very sensitive low 
internal resistance meter would not be suitable for 
this circuit. 

Almost any a.f. transistor could be used for TR1 
provided its maximum rated collector-emitter voltage 
is greater than 12. Variations in gain can be catered 



I 



W 11 

BY B . DOUGLAS 




[mwiw mm 



for by adjustment of the relay. R9 allows the relay 
to hold on after the trip operates by permitting a small 
residual current to pass through the connected load. 
The trip is automatically reset when the load is 
disconnected. Capacitor CI serves to "hold up" the 
voltage across TR1 and the relay long enough for the 
trip to function under severe short circuit conditions. 
The fifth position of S2 checks the battery potential by 
means of the multiplier resistor R8. 



726 



C-I2V 



C-9V 
-C-6V 



C-3V 




CHECK VCtTS 
Z) 6mA 

3) 30mA 

4) 300 mA 

5) 3A 



Fig. I. Complete circuit of the battery pack 



Using the relay specified, the cut out operates within 
2 £a of a second, thus giving, for most applications, 
virtually instantaneous protection. If, for example, a 
1*5V 0-3A lamp is connected across the 12V terminals, 
with the trip set at 300 mA, there will be no glow 
whatsoever before the supply is cut off, and the meter 
pointer barely kicks. 

CONSTRUCTION 

A generally available polystyrene lunch box measur- 
ing 12in x 4in x 3£in was found to be ideally suited 
to contain the batteries and components. It will also 
stand upright, at a slight angle, thus taking a minimum 
of bench space. The transparent lid can be painted 
matt black, or coloured if desired, on the outside. 
If the lid is painted on the inside minute imperfections 
in the plastic will tend to look unsightly. To avoid 
splitting the plastic it is best to make holes with a hot 
soldering iron, then enlarge them with a round file. 
Figs. 2, 3 and 4 show the layout of components and 
wiring inside the box. 

Thick wire should be used between batteries, sockets, 
and the main meter connections, to avoid inaccuracies, 
particularly on the high current range. 

A small tag strip, bolted to the + meter terminal, is 
used to mount TR1. The relay is fixed on the back 
of the box, and the batteries "sit" inside it. Because 
of their large current capacity it is unlikely that the 
batteries will need replacing frequently so they can be 
soldered directly into circuit with short lengths of wire. 




Fig. 2. Details of wiring the switch wafer. This can be a 
2 pole S way wafer with one pole left unused 

The good contact thus made also helps to maintain 
consistent performance. All resistors can be wired 
point-to-point directly on to the mounted components. 
Finally, the lid is secured to the box with small self- 
tapping screws. 

SETTING UP 

Check that R8 indicates the actual battery voltage 
when switched on by S2. Set S2 to one of the lower 
current ranges and VR1 to maximum resistance. 

727 



TOM 




COMPONENTS 



Fig. 3. Wiring details of the batteries to the ** negative 
sockets 



Ml Tftl 




Resistors 

Rl 470 a 



R2 
R3 
R4 
R5 
All 



9lkn 

0-025 £5 w-w 

0-25 Q w-w 

2-5ii w-w 

high stability, cracked carbon except where 



R6 
R7 
R8 
R9 



75 Q 
4-7k£3 
2-4k« 
lOkD 



otherwise indicated. 

Potentiometer 

VRI lOOkfl carbon preset 

Capacitor 

CI 1,000 [if 12V electrolytic 

Transistor 

TRI OC7lorNKT272 

Meter 

Ml 5mA f.s.d., I5£l, moving coil 

Relay 

RLA I.OOQfi coll, single pole changeover contacts, 
Siemens high speed 

Switches 

SI, S3 Double pole on/off 
S2 Single pole, 5 way 

Batteries 

BY I -4 Twin cell cycle lamp batteries 3V type (4 off) 

Miscellaneous 

Polystyrene lunch box I2in X 4ln x 3£tn 
Five wander plugs and sockets 



Fig. 4. Internal view of the completed unit 



Connect a suitable variable load resistor across the 
positive and one of the negative output sockets. The 
meter should show that a current is passing through the 
load. 

Increase the load until the meter reads full-scale, 
then advance VRI until the trip operates. A click 
will be heard from the relay and the meter pointer will 
drop to zero. If this does not happen, and there is no 
wiring fault, the relay should be set for greater sensi- 
tivity by adjustment of its armature spring tension 
screw until it pulls in with VRI set near maximum 
resistance. Then disconnect, reduce the value of the 
load resistor and reconnect. It should be found that 
the trip operates at full scale on all ranges, or at less 
than full scale, depending on the setting of VRI . 

When, say, a transistor receiver is powered by the 
pack, two points should be noted. If there are high 
value electrolytic capacitors in the receiver, the switch- 
on current surge will cause the trip to cut off the supply. 
This can be avoided by setting S2 to a higher current 
range initially, then dropping down again to the range 
consistent with the normal consumption of the receiver. 
Also, audio peaks, not Indicated by the meter, but 
many times greater than the mean standing current 
of the receiver, will tend to operate the trip. 

In use, the pack allows minor adjustments to be made 
to experimental circuits while they are functioning, 
and protects against slow thermal runaway when 
transistorised circuits are left on and unattended for 
long periods. This is especially useful in development 
work and for extended soak tests. ~fc 



728 




QjjK^DKftnmMLDS 



IN THIS feature we hope, from time to time, to be able to 
publish suggestions submitted by some of our readers on the 
possible improvement of projects previously described in PRAC- 
TICAL ELECTRONICS; short contributions on other subjects may 
be included. The aim is not to find fault or undermine the abilities 
or knowledge of our contributors. It may well be that the 
original article is par excellence but could be improved or adapted 
to suit individual requirements. The views expressed by readers 
are not necessarily those of the Editor, 



PULSE COUNTER 



Ri R2 

2-ZkH 3-3kft 

— V\A-t-AAA 



CI 



I 




METER AMPLIFIER 



As the output from my version of the pulse counter 
was only 50/iA, I left the Zener diode out and added 
a meter amplifier. This gives about 500/tA enabling 
a cheaper meter to be used. 

To guard against instability through temperature 
changes, and to obviate non-linearity or zeroing 
difficulties, a silicon transistor such as an OC205 can 
be used. If battery variations are troublesome, a 
simple Zener stabiliser (OAZ207) may be introduced 
as in the circuit diagram above. This should be 
effective over the range 11 to 17 volts. 



The extra components can be mounted on the 
sample piece of printed wiring board which was given 
with the April issue of the magazine. To accom- 
modate them the components to the right of the 
original Zener diode should be moved to the left by 
one hole and re-positioned according to the circuit 
above. 

R. L. Mustow, 
Ickenham, 
Middlesex. 



METER ECONOMY 




With reference to the "Pulse Counter" in the April 
issue I would recommend the following modification. 
In view of the relatively high cost and fragility of a 
100/fA meter compared with a 1mA meter I have 
modified the circuit as shown to give 1mA output 
for 200c/s input. The performance is very linear 
but any increase in the value of C4 above 0-5^F leads 
to non-linearity. 

F. M. Gray, 

Rugeley, 

Staffordshire. 

Two good ideas well worth considering. Incidentally 
a few readers noticed in the article that C4 on the 
original drawing and in the components list should be 
0'47/tF, and the polarity of the meter in Fig. 1 should 
be reversed. — Ed. 

729 



PARKING LIGHT 



SIX VOLT PARKING LIGHT 



With reference to the "Automatic Parking Light" 
the circuit shown in the March issue is not sensitive 
enough for operation on 6 volt car batteries. It 
may work with a high gain pair of transistors but 
not with those of low gain. 

This can be remedied by a change in the photo 
transistors. The OCP71 was originally chosen because 
of its small size, but its sensitive area is only about 
7 square millimetres. Light sensitive resistors (cad- 
mium sulphide cells) such as ORP12 have a con- 
siderably larger sensitive area and, therefore, give 
effectively greater output. I am enclosing an alter- 
native circuit which should operate from a 6 volt 
battery. The value of VR1 may need to be changed 
to suit different transistors. 

A. K. Stevenson, 

Fife, 

Scotland. 




MODULE SEVEN 



I used the piece of Veroboard, presented with the 
April issue, as the circuit board for the construction 
of the "Automatic Parking Light" described in the 
March issue. 

Specified components were used throughout except 
for the photo-transistor. Being unable to afford the 
cost of an OCP71 I used a new OC71 with the metal 
can removed. 

By gently squeezing at the base of the transistor 
with a pair of long nosed pliers, the glass to metal 
seal can be broken and the transistor drawn out of the 
case. 

Any glass should be removed (most of it wilt have 
powdered when the can was squeezed), and by using 
a pin the majority of the opaque fiJling can be cleaned 
from the transistor junction. 



To protect the transistor a small piece of plastic 
tubing (transparent ink-cartridges are ideal) is placed 
over the transistor and stuck with a small amount of 
plastics glue to the transistor lead-out wires. The 
plastic tubing can be painted black leaving a small 
area unpainted through which light can pass on to the 
collector-base junction of the transistor. 

An OC71 modified in this manner has been used in 
the "Parking Light" circuit with complete success. 
The writer has used the cheap "Red Spot" transistors 
in place of the OC71, the only difference being that the 
time delay between the light striking the junction and 
the operation of the relay is greater. 

Nigel Isle, 

Stourport-on-Severn, 

Worcestershire. 




SENSITIVE PARKING LIGHT 



I have been experimenting with the circuit from the 
article "Automatic Parking Light" in the March 
issue and would like to suggest the following circuit 
which will operate even a clumsy large relay. 

Two OCP71 photo transistors were connected in 
parallel as shown in the diagram. When VR1 is set 
to some value between 5 kilohms and 50 kilohms the 
relay will operate when light falls on the photo transis- 
tors. The push button switch (SI) is normally closed 
and is pressed to reset the required condition between 
each operation of the circuit. 

Battery current consumption is 2mA in the dark 
and 5 to 15mA in the light depending on its intensity. 

R. W. Marshall, 
Belmont, 
Harrow. 



730 



TESTING DIODES 



Further to the "Magic Boxes" articles in the March 
and April issues, the principle of a diode conducting 
in one direction only can be applied to a practical unit 
such as a diode tester. I have made an instrument 
which will indicate whether a given diode is faulty or 
not, or if it is open-circuit or short-circuit. The 
polarity of an unmarked diode can also be determined. 

The known diode to be tested is connected across 
the test terminals — cathode to red and anode to 
black as shown in the circuit below. Since the test 
diode and Dl will conduct in the same direction the 
green lamp LP1 wiH light. Diode D2 is connected 
in reverse; no current will flow through it or LP2. 

If the test diode is connected in reverse the red 
lamp (LP2) will light due to the current flowing in 
the reverse direction through D2. 

If the polarity of the test diode is unknown it can 
be easily determined from the above tests. 

If it is found that both lamps light together, this 
can only be due to a short-circuit in the test diode, 
which will allow current to flow in both directions. 
Since the supply is alternating both lamps will be 
illuminated. 

Conversely if both lamps fail to light, this must be 
due to the diode being open-circuit. Such a diode 
would not allow current to flow in either direction. 



LP1 

GREEN 




Most types of diodes and rectifiers can be tested 
with this instrument, e.g., germanium, silicon, selenium, 
etc., so long as these are above the power rating of this 
circuit. This is governed by the supply voltage and 
current rating of the lamps, and should be calculated 
to ensure low power diodes can be safely tested. 

A 6 volt 60mA lamp is most suitable here and gives 
a calculated power dissipation of 360mW. Clearly 
any diode rated at about \ watt or above could safely 
be tested. Other lamps and power supplies will work 
equally well providing this power dissipation does not 
exceed the rated power of the diode. 

A 6-3 volt heater transformer will be the one which 
is usually to hand and this may be readily employed. 
Mine had tappings at 3, 5 and 8 volts. The 5-volt 
tapping was used in conjunction with a 6 volt 60mA 
lamp, slightly under- running the lamp, and actually 
permitted diodes down to about 300mW rating to be 
tested. 

The internal diodes, Dl and D2 are not critical 
so long as they are above the rating of the circuit 
as mentioned before. Two OAIOs were used, since 
they were readily available, but ones with much lower 
ratings could have been used. 

B. J. McNaughton, 

Sutton Coldfield, 

Warwickshire. 




INTERESTING CONSTRUCTIONAL 
PROJECTS NEXT MONTH 



COMMENTARY SYNCHRONISER 
FOR AUTO SLIDE PROJECTORS 

Enables a twin track tape recorder to change 
slides in an automatic slide projector at the 
appropriate point in the recorded commentary. 

NOUGHTS AND CROSSES MACHINE 

You cannot win ! An amusing and instructive 
attraction for Fete, Club, or small Exhibition. 

A MOTORIST'S AID 

Audible warning device for the car, having a 
variety of uses. 



SEPTI 

"k 



ISSUE ON SALE AUGUST 12 



I 



Make sure of your copy by filling in and 
handing this order form to your newsagent 



To 

(NAME OF NEWSAGENT) 

Please reserve /deliver PRACTICAL ELEC- 
TRONICS (2/6) every month, until further notice. 

Name __ 



Address 



731 




mm 




BY J.R. BRADBURY 



Outside the communications field the decibel is 
somewhat unfamiliar, yet its value to the hi-fi 
enthusiast is of far greater significance than some of the 
more familiar units. 

This article sets out to explain the decibel and its 
practical applications, ending with an exposition of 
its subjective use in listening which explains its value 
in assessing fidelity. 

ORIGIN 

The decibel (or dB) was originally called the "trans- 
mission unit" (itself a development from the "Neper") 
and was the attenuation of a 886c/s signal in a mile of 
standard cable such that 



inpu t power P t EJ^ _ 
output power P % ~ I? 2 / a - 



10 o.i 



This ratio was easily expressed in common logarithms 
and, as it is easier to add or subtract rather than 
multiply or divide when calculating gains or losses, 
it was adopted as standard for all frequencies. 

Later the transmission unit became the "decibel" 
and expressed the change in power over a given network 
of equipment. 



and 



Pi 
P* 



= io°i^ 



P.i 



N= 10 logi us* decibels 



The somewhat large unit of the "bel" equals ten 
decibels and is the common logarithm of the power 
ratio; the term honouring the inventor of the tele- 
phone, Alexander Graham Bell, 

BASIC FORMULAE 

The decibel is a comparison ratio between two 
power levels, one of which is a reference or "zero" 
level. Zero level is sometimes arbitrary — a value 
regarded as unity power, of which the other level is 
either a multiple or sub-multiple, or can be the 
conventional zero level which, in Europe and the U.K., 
is a voltage of 0-775 volt r.m.s. across 600 ohms to 
give a dissipation of 1 milliwatt. In the U.S.A., 
zero power is regarded as 6 milliwatts. 

Amplifier gain, expressed in decibels, is 

P 
N = 10 toitfisr decibels (power ratio) 

"i 

P 1 being the input or zero reference level and P E the 
output or compared value. 

732 



POWER 
p 2/ p l 

10,000 ■ 
8,000- 

6,000- 
4,000 



+40 

— -90 
— -B0 

70 

h-60 

so 



VOLTAGE 

OR CURRENT 

V 2 /V t 

100 



3,000 — ' 
Z,000 



1,000 - 
800- 

600 — ~~ 



400 

300— h+25 — 



100- 
80- 



40 
30—1 



10- 
8- 
6- 



■+20- 



+10 - 



3-T 

2 

i—L— o — 1— 1 



■40 



-3 




0-1 
0-08 



0-04 
0-03 H 



0-01 

o-ooe 



0-004- 
0-003 

0-002 



0*001 
0-0008 

0-0006 — 

0-0004 
0-0003 

0*0002 



0-0001 



-10- 



_— 25- 



■0-2 



0-1 
- 0-0V 

— -0-08 

0-07 



-0-06 
0-05 

0-04 



0*02 



Conversion scales of decibels to 
power, voltage and current ratios 



In this, and other decibel formulae, if the ratio 
(i.e. P 2 /Pi in the case above) becomes fractional due 
to a power loss as opposed to a gain, calculations are 
simpUfied by inverting the ratio and prefixing the 
formula with a negative sign: 



iV(loss) •= 



101og 1( £dB 



Since the decibel is a power ratio it may be used to 
express voltage or current ratios. For instance 



p = yv/R and if two voltages are measured across 
identical impedance values Z, their decibel ratio is 

iV=10Iog 10 |^ 
= 101og 10 (^) 8 
= (2)i01og 10 ^ 

= 20 logiov dB (voltage ratio) 

V t being the zero or reference voltage and F a the 
output or compared value. Phase relationships have 
been ignored here since they would cancel out in the 
above equations. 

This only applies if the resistances or impedances 
across which V% and V % are measured are identical in 
both magnitude and phase. 

Because P = PR, the formulae may be similarly 
applied to current ratios across identical resistances or 
impedances. 

DISSIMILAR IMPEDANCES 

An allowance has to be made in the case where the 
two impedances, are not the same. Voltage ratios 
across pure, but dissimilar, resistances are: 

N = 20 logjoy* + lOlog^ 1 dB 

(Note that resistance ratios are always the inverse of 
the voltage ratios but are not so for current ratios.) 

When impedances differ and cannot be regarded 
as pure resistances then power = VI cos $ = PZ cos $ 
= V^/Z cos 0. Hence 

tf=20iog„£+101og u §^ dB 

where cos <j> is phase angle between a.c. voltage and 
current for each respective impedance. 



Conversely, the power ratio equivalent to N dB is 



and a voltage ratio 



p- = antilog 1Q 

y # 

-~ = antilog 2Q 



the decibel equation being transposed and the antilog 
found, instead of the logarithm, as part of the trans- 
position. 



COMMUNICATION NETWORKS 

The simplest network always comprises several 
components providing gains or losses. Fig. 1 shows 
a simple communication network between a micro- 
phone at A whose output is carried to a transmitter 
at B. 

The microphone level is 60dB below (— 60dB) 
"zero" level and raised to "zero" level by an amplifier 
having a gain of 60dB. This is followed by a power 
amplifier which increases the level to 4dB above zero 
(+ 4dB) to counteract the noise in the transmission fine 
carrying the signal to the transmitter. During its 
passage the signal level is distorted by the component 
quantities (inductance, capacitance and resistance) of 
the line. To restore the signal to its original quality, 
an equaliser network is inserted in the system to cut 
down the least attenuated frequencies to the level of 
those that have suffered maximum attenuation. 

In so doing the overall level of the signal is generally 
lower (up to about — 50dB). To overcome this the 
receiving amplifier (C) is inserted to raise the signal 
by 50dB to zero level. A power amplifier boosts the 
signal to the required level of +10dB to feed the 
transmitter. Adding the gains and losses in the chain: 



-60 + 60 + 4 - 54 + 50> 10 = + 



lOdB. 



STATION A 



STATION B 



MICROPHONE 



+10 




.-20 



-40 



Fig, I. A simple communications chain. Below ft is a graph showing typical levels (in decibels) 
throughout the chain. The shaded area shows the differences due to line losses between 50c js and fOfcc/s 



733 



These levels are used purely to illustrate a typical 
example but in practice there would be several other 
items in the circuit whose attenuations and gains 
would need to be taken into consideration. It is 
obvious from this example that adding and subtracting 
decibels is preferable to multiplying and dividing 
voltages; calculations can be astronomical, even 
for a simple chain. 

Knowing the decibel gains or losses of each item 
of equipment immensely simplifies the planning of a 
communications chain, not only to find the gain 
required in amplifiers but also to assess the power 
levels and signal/noise ratio anywhere in the chain. 

AMPLIFIER FREQUENCY RESPONSE 

The frequency response of an amplifier (or other 
apparatus) is frequently expressed in decibels which 
are related to a "zero" reference level at a given 
frequency (often l,000c/s) at which the amplifier 
gain has first been found. The relationship between 
the power at two different frequencies is 



N 



lOlog^dB 

*f2 



where P n is the power at l,000c/s and P n is the power 
at some other given frequency. 

In this case if P n is greater than P n the answer would 
be negative and is prefixed by a minus sign. If P f2 
is greater than P n the answer is positive and is pre- 
fixed by a plus sign. 

In practice it is easier to work in voltages, 
the relationship would then be 

N = 20 logjo^ 1 dB 

r to 



Hence 



assuming that the input voltage is constant at all 
relevant frequencies. The signs apply as for power. 

Some measuring instruments are calibrated in 
decibels and read the values of level direct in 
decibels. In such a case the voltage at the reference 
frequency (say l.OOOc/s) is set so that the meter reads 
OdB. Hence the relative levels at other frequencies 
can be read direct in terms of ±M1B relative to the 
level at l,000c/s. 

Frequency responses can be plotted with the y-axis 
on a linear scale for voltage and decibels, and fre- 
quency on the three-cycle log x-axis. The decibel 
curve is broadly similar to the voltage curve but 
always flatter, as shown in Fig, 2. 

MEASURING TECHNIQUE 

The decibel has been the cause of the introduction of 
special measuring techniques — because applying decibel 
theory to voltage readings for each frequency can be 
time consuming and tedious. 

The substitution method is far quicker and has 
two variations — both being shown in Fig. 3. The 
first (Fig. 3a) is used for assessing amplifier gain or 
response, using a calibrated decibel attenuator con- 
nected between a test oscillator and the amplifier 
under test. 

A decibel attenuator is constructed of resistors, 
has a constant impedance and is normally calibrated 
to vary the attenuation in ^dB steps from zero to 55, 
60 or 70dB. The meter M is connected to a change- 
over switch S which selects either the attenuator or 
the amplifier output, the latter being terminated with a 
resistance equal to the attenuator impedance. 

Initially, the attenuator is set to zero attenuation and 
the meter switched to it, virtually connecting it to the 



+2 


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28 
26 
24 

22 
20 
18 

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12 
10 
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20,000 



Fig. 2. Frequency response curve for amplifier voltage gain with the equivalent decibel response curve for the 
same amplifier. The decibels curve shows a characteristically smoother response over the audio frequency range 



734 




Fig. 3a. Substitution method of 
measuring the frequency response 
of an amplifier 



AUDIO 
OSCILLATOR 



DECIBEL 
ATTENUATOR 



oscillator output, the signal from which must be 
adjusted to give a convenient meter deflection. 

The attenuator is then set to maximum attenuation, 
and the meter is switched to the output of the amplifier 
under test. The amount of attenuation is gradually 
reduced until the amplifier gives the same output 
reading as that obtained in the initial measurement. 
The amplifier gain then equals the amount of attenua- 
tion in use. This is so because the sum of amplifier 
gain and attenuation must equal unity (the attenuator 
neutralising the amplifier gain) if the meter deflection is 
the same for both positions of the switch. 

The second application checks the loss in a filter 
or attenuator which may be just as important as the 
response of an amplifier. This uses the circuit of 
Fig. 3b — the decibel attenuator now being connected 
across the apparatus under test but isolated from it 
by ganged changeover switches SI and S2. 

The meter is first switched across the filter under 



Fig. 3b. Substitution method of 
measuring frequency response of 
a filter 



test and the oscillator output adjusted for a convenient 
meter deflection. Changing over SI and S2, so that 
the oscillator output passes to the meter through the 
decibel attenuator, attenuation is then inserted until 
an identical meter deflection is obtained. The attenua- 
tion inserted equals the filter loss at the particular 
frequency being used. 

The input and output impedances of the apparatus 
under test should be the same as that of the decibel 
attenuator. 

LOUDNESS 

Loudness is purely subjective and can be defined as 
the sound heard by the human ear when the aural 
senses are stimulated by a given sound intensity, 
i.e. the amount of sound in terms of power and sound 
wave pressure. 

To produce equal changes in loudness the intensity 
must increase (or decrease) in proportional steps. 



130 
120 
110 

100 
90 
80 

70 

I 60 

50 

AO 

30 

20 

10 



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100 



c/s 



1,000 



10,000 



F/g. 4. The upper and lower limit curves of the Fletcher- 
Munson loudness level responses of the average human ear 



Z0,000 



735 



Loudness is approximately proportional to the 
logarithm of the sound intensity. 

Because of this relationship, loudness can be mea- 
sured in decibels related to an acoustic "zero" level. 
A change in sound intensity of one decibel is the 
smallest change that can be perceived by the most 
sensitive human ears, and, in practice, the average 
person can only detect a change greater than two 
decibels. 

Thus, "electrical" and "acoustical" decibels are 
linked. For example, an audio system whose response 
is said to be 3dB down at 5,000c/s will lack treble or 
"brilliance" to most listeners; if 2dB down this lack of 
treble might be detected by listeners of average hearing 
but only the sensitive ear of a musician could detect a 
change of ldB. 

The decibel therefore offers a useful yardstick for 
measuring audio "fidelity". The output of an ampli- 
fier, record player or other audio system having an 
overall response within less than 2dB of that of a given 
reference frequency is considered to be in the range 
of high fidelity. 

ACOUSTIC DECIBEL 

Fletcher and Munson published a set of curves of 
equal loudness and these are outlined in Fig. 4, the 
intermediate curves falling broadly between the two 
limits shown. The upper limit was found to be the 
tolerable Unfits above which any further increase 
causes pain. This limit is known as the "threshold 
of pain". The lower limit indicates what is generally 
considered to be where the sound is barely perceptible 
to the human ear. Any further reduction in level is 
completely inaudible. This limit is known as the 
"threshold of hearing". The curves reveal that absolute 
levels for both thresholds vary with frequency. 

The curves also reveal that the human ear is most 
sensitive in the middle frequency range between about 
800c/s and 6,000 cycles, becoming relatively insensitive 
towards 28c/s and 16,000 cycles— with the lower 
frequencies being "felt" rather than "heard". 

The curves are statistically based and so must be 
accepted with certain reservations; they vary con- 
siderably between different individuals, according to 
health and age. ■£ 



In the August 
Practical Television 
A TRANSISTORISED 
E.H.T. VOLTMETER 

On sole JULY 22 



In the August 
Practical Wireless 
A SOLAR-POWERED 
POCKET RECEIVER 

On sale NOW 

Both only 2/- 



NEWS BRIEFS 



Brighter Sharper Pictures 



Crom January next year, all Mullard monochrome 
1 tubes in the 19in, 23in and 25in sizes will be designed 
to operate at 20kV instead of the present maximum of 
18kV. The increased capability will mean brighter 
pictures, sharper focusing and a reduction in deflection 
de-focusing. 

If all of the extra brightness of the 20kV tube is not 
required the tube may run at a reduced beam current 
to obtain a further reduction in spot size and in deflec- 
tion de-focusing. 

A new e.h.t. rectifier has been designed for use with 
the 20kV tubes. It incorporates special components 
to guard against flashover and a 3-rod method of anode 
construction to improve reliability and life expectancy. 
Numbered DY802, the new rectifier has identical 
pinning and dimensions to the widely-used DY87. 

The extra scanning power required may be obtained 
with existing Mullard deflection valves, but to provide 
a reserve of line-output power a new higher dissi- 
pation version of the PL500 will be introduced shortly. 

To reduce the size of field-output transformers for 
the 20kV tubes, the field-output valve PCL85 has been 
re-designed to give an increased dissipation of 8W. 



Young "Hams" Course 



A longside a week-end course for youth leaders and 
** teachers in Nottinghamshire on "The Hobby of 
Amateur Radio", at the Residential Youth Centre, 
Ollerton, Nottinghamshire on 11 and 12 September, 
there will run a course of lectures for invited estab- 
lished Amateur Radio enthusiasts from the East 
Midlands and beyond. 

The symposium, organised by the Newark and 
District Amateur Radio Society, is being sponsored 
by the Radio Society of Great Britain, who are sending 
speakers of international repute to cover all aspects of 
amateur radio. 

Full details of the course may be obtained from 
Mr. D. A. Graham, Lower House, South Muskham, 
Newark, Nottmgharnshire. 



I.E.EIE. Making Rapid Strides 



The Institution of Electrical and Electronics Tech- 
1 nician Engineers is making excellent headway and 
since April 1st, when membership recruitment began, 
5,000 have been admitted to the Institution. Large 
numbers of membership proposals and enquiries 
are being received daily. 

A specialist committee is now working on a pro- 
gramme of technical lectures and meetings to commence 
in the Autumn and is selecting technical material for 
the broadsheet which will be going out to members at 
regular intervals; this is to be the "pilot" for the 
I.E.E.T.E. Journal now being designed. Another 
committee is working on plans for the setting up of 
Regional Centres, from which a nation-wide chain of 
Centres will radiate. Inquiries regarding membership 
should be addressed to The Secretary, LE.E.T.E. Ltd., 
26 Bloomsbury Square, London, W.C.L 



736 



LEARN 

ELECTRONICS 

-AS YOU BUILD 



over 




CIRCUITS 
EXPERIMENTS 
TEST GEAR 




including . . . 

• CATHODE RAY 

Valve Experiments 

Transistor Experiments 

Electro-magnetic Experiments 

Basic Amplifier 

Basic Oscillator 

Basic Rectifier 

Signal Tracer 

£ Simple Counter 

Time Delay Circuits 



OSCILLOSCOPE 

Square Wave generator 
Morse Code Oscillator 
% Simple Transmitter 
Electronic Switch 
Photo-electric circuit 
Basic Computer Circuit 
Basic radio receiver 
£ A.C. Experiments 
D.C. Experiments 



The full equipment supplied comprises: valves, transistors, photo-tube, modern type chassis board; printed circuit board; full 
range resistors, capacitors and inductors; transformers; potentiometers; switches; transistors; valves; all hardware, wiring and 
every detail required for all practical work plus CATHODE RAY OSCILLOSCOPE for demonstrating results of all experiments 
carried out. AH practical work fully described in comprehensive PRACTICAL MANUALS. Tutor service and advice if needed. 



This complete practical course will teach you all the basic principles of electronics by carrying 
out experiments and building operational apparatus. You will learn how to recognise and handle 
all types of modern components; their symbols and how to read a completed circuit or 
schematic diagram. The course then shows how all the basic electronic circuits are constructed 
and used, and HOW THEY ACTUALLY WORK BY USING THE OSCILLOSCOPE 
PROVIDED. An application is given in all the main fields of electronics, i.e. Radio; control 
circuits; computers and automation; photaelectrics; counters, etc., and rules and procedure 
for fault finding and servicing of all types of electronic equipment. 



NO PREVIOUS KNOWLEDGE NEEDED 
SENT IN ATTRACTIVE BOX 



NO MATHS USED OR NEEDED 
COMPLETE ADVICE SERVICE 



REASONABLE FEE— NO EXTRAS REQUIRED 
EVERYTHING REMAINS YOUR OWN PROPERTY 



A completely NEW up-to-date 
home study experimental course by 

BRITISH NATIONAL 
RADIO SCHOOL - 

Britain's Leading Electronic 
Training Organisation. 



POST NOW FOR FREE BROCHURE 

To: BRITISH NATIONAL RADIO SCHOOL, READING, BERKSHIRE. Please 
send free Brochure, without obligation, to: 



NAME..., 
ADDRESS 



I 



Slock Capitals Please 
OR WRITE IF YOU PREFER NOT TO CUT COUPON 



I 

737 




GUITAR AMPLIFIERS 
WITH TREMOLO 

Five jack socket 
inputs, four with 
separate mixing 
volume controls, and 
one input "straight 
tlirongh". All inputs 
are of Terv high 
sensitivity only 10 
millivolts input is 
required for full out- 
put, ' making them 
I suitable for all types 
I of guitars and micro- 
phones. Separate 
Jiass and Treble con- 
trols, giving a wide 
range of lift and cut. 
Separate master gain 
control. Tremolo 
speed and depth 
controls. Jack 

socket for remote 
tremolo switching. 
.... .nieakcrs. \alves used in the 30 watt and 
50 watl, amplifier Truss. ECCS'S, UL31, HL34. G'lU Tn the l". wirl 
amplifier BCC83, ECCS3, ELS4. KLM, i' ■ /SI An^travalve VfY^'v 

SKSRTf g te|^ fimshed eil ™ «"* "ammer. 1 
PRICES— 

50 watt with tremolo son in n 

50 watt less tremolo ' £19*100 

30 watt with tremolo . : ' " fls'if) n 

30 watt less tremolo , " £14 "inn 

15 watt with tremolo '" *i g"i q"a 

15 watt less tremolo " ' *t1 iftft 

Add carriage 10/- any amplifier. Bend fl. A.E. for iree descriptive leaflet, 

CREDII TERMS ARRANGED 

EXPORT ENQUIRIES INVITED 

STROUD AUDIO 

CASHES GREEN ROAD, STROTJD, GLOS. 



Outputs for 3 and 15 ohms' 



VALVES 

ALL BRAND NEW AND HAVE full written 



GP1 

RF13 

6F'J3 

6F24 

0:301.2 10/- 

20P4 15/- 



GUARANTEE 



9/S 



7/- 
8/B 



30C1 

30C17 

30 F 5 

30FL1 

3QLI5 

301,17 

30 Pi 

3 01' 12 

30P1H 

30PL1 

30PL13 . 

S0PL14 12/- 

DAF91 8/- 

11AF3S. 8/- 

UF98 8/- 



10/- 

10/- 

8/- 
10/- 

9*9 
10/- 

12; 6 
7/6 

la/e 
8/e 

9/6 



DK01 
DKB2 
DKSfi 
DL91 
1)1,93 
DL94 
1)1,98 
LIYNIi 
T)YS7 



ECH31 6 '6 
ECHB3 7''6 
ECHSi 10- : - 
ECLS0 8^6 
ECL«2 
RCI.S3 
EFS0 



EAHC80 8/6 

KliilL 4/ 

EBC41 

K.BCSI 

J-:il FN 

BBP88 

ECC8L 

Bcosa 

BCC83 
EOCS4 

ECC85 
BC9EC49 



7/6 
7/- 
6/- 
6/8 
4/6 
5/6 
5/6 

ih 

em 

6/6 



EF8S 
EFW 

y,is<> 

EFSl 

EFA2 

EF183 

RF181 

EI.34 

EL41 

EL42 

RI.S1 

EVol 

EYSti 

EZ10 



7:6 
9,8 
8/- 

8/- 
7/6 
•/- 
4/6 
47« 
11- 
II- 
9/- 
!,•- 
7 6 
6/- 
6 6 



T.ZU 
EZS0 

EZ8t 
GZ34 
PC86 

PC88 
PC95 
PC07 

f.'Cl'M 

vcam 

PCC8U 

PCC189 10/6 

PCF8K 7,1- 

PCF84 6/3 

PCP8S 8/- 

PCFStll 10/- 

PC-F805 10/6 

PCL82 7/- 

FCL83 S/S 

PCMi 7/6 

PCL85 7/6 



7/- 
5 - 

5 8 
10 6 
10.8 

9/6 

7/8 

7/6 

II- 

10/8 

9/- 



PCL86 


9/- 


PL38 


9f- 


RH5 


Br- 


PL82 


5/- 


PL83 


fi'fi 


l'E84 


7/- 


Pl-aOO 


1.V- 


PY32 


8/6 


PY3S 


10/- 


PVflfl 


,V- 


PYS1 


S'fi 


PYS2 


5/- 


PY83 


Sf- 


PY8S 


716 


I'VBIII) 


6f- 


PY8UI 


8/8 


1'23 


lOf- 


Ffl6 


8/- 


TOM 


M 


1301 


11/6 



BYIOO Silicon Rectifiers 7/6 each 
Power Transistors equivalent to OC2S 6/6 each 



FREE^-FREE— FREE — FREE — FREE — FREE 



POWER TRANSISTORISED 

Complete instructions to build a 50 watt D,C. Converter. 
12-t8 volt input, 250 volt output. This is perfect to run H.T. 
supplies for a T/V in car or caravan. This unit will use 
transistors as above. We can supply transformer for this at 
£2. 15 . 0. Power consumption 2 amps. 



ALL ITEMS DESPATCHED SAME DAY. 



MAIL ONLY. 



NO CALLERS 



TERMS - CASH WITH ORDER. ALL ORDERS OVER El POST FREE 
POSTAGE ON VALVES — 6d. EACH 



STAMPED ADDRESSED ENVELOPE ALL ENQUIRIES TO 

BARKERS, 23 HURSTFIELD ROAD 
WEST MOLESEY, SURREY 




ifopt need! 



HOLE PUNCHES 
Instant Type 

%" diameter 

Screw-up Type 

iV diameter Toggle switch 

I" '.'. B7G ':.'. ;;■ 

i" ,. B8A, B9A 

#* 

** ,. ... 

\" „ 

1i" diameter Int. Octal ,,, ,** 



IS" 
r a 
If 
If* 

2-.V 



B9G 



6/10 

8 6 

8 6 

91- 

9/* 

10/2 

10/8 

11/8 

13/4 

16/2 

18/10 

21/8 

24/4 

33/2 



Meter 

Complete Set £9.3.6. 

No extra charge for postage and packing in (he U.I 

Now supplied by; 

TOMPKINS fi LONGMAN LTD. 

237 GIPSY ROAD 
WEST NORWOOD, S.E.27 

Tel.: Gipsy Hilt S00Q 

73S 



MULTI-TAPPED TRANSFORMERS 
ALL PRIMARIES 200, 230, 250 v. 

Type . Sec. Taps Amps 

A 3. 4, 5, 6, 8. 9, 10. 12, 

15, IB, 20, 24, 30 v. 2 25/- 4/- 

B Ditto 4 39/6 4/6 

C Ditto 5 45/- 5/6 

D Ditto g 59/6 7/. 

E 6, 7. 8, 10, 14. 15. 17, 

1 9, 25, 3 1 , 33, 40. SO v. 3 45/- 5/6 
P Ditto 6 87/6 7'6 

G 12, 18, 20, 24, 30 v. 10 69/6 7/6 

HEAYBERD TRANSFORMERS 
Pri. T 200-240 v. See. 12 v. 4 a. Brand new. 
Fraction of maker's price. 15/-. P.P. 2/6. 
IBM DOUBLE WOUND 
TRANSFORMERS 
Pn. Tapped 220, 220, 240 v. Sec. Tapped, 1 10- 
100 v., 200 v. A. 47/6. Carr. 5/-. Tropically- 
raced. 
BRAND NEWVENNER ELECTRIC TIME 

SWITCHES 
200-250 v. 30 amp switch contacts. 24 hour 
dial. One off, one on. Beautifully finished in 
bakelitecase, Siia 5J x 8 x 4i ins. Supplied in 
original cartons at a fraction of maker's price. 
£1.19.6. P.P. 5/-. 



We have London'* largest selection of 
Low Tension Transformers, Variable 
Voltage Transformers, Smoothing 
Chokes, Capacitors, Sliding Resistors, 
Low Tension D.C. Supply Units. Send 
S.A.E. for lists now, or visit our walk 
round dept,, where we have thousands 
of genuine electronic bargains. 



SAMSON'S ELECTRONICS LTD, 

9-10 CHAPEL STREET, LONDON, N.W.I 
Tel.PAD7B5l Tel. AMBSI25 



RECORDING TAPE. All Brand New 
and Boxed. Excellent quality. 

1" Double Play , 
7" Long Play 
5}" Double Play . 
Si" Long Play 
5" Standard Play , 



plus many others 



2400 ft. 34/6 
I BOO ft. 2 1 :& 
1800 ft. 24/- 
1200 ft. 16/6 
600 ft. 11/3 



A must for the beginner's bookshelf , , . 

BEGINNER'S GUIDE 
TO ELECTRONICS 

by Terence L. Squires, A.M.BriU.R.E. 
191 pages, 128 diagrams, I St. 

From all booksellers or in case of difficulty 16s, id. 
by post from George Newnes Ltd., Tower House 
Southampton Street, London, W.C.2, 

■ - .NEWNES 



LOUDSPEAKERS. New-Top quality 
2 x 8 ohms 9/9 1 2±"x Bohms 9/9 
2Tx 3 „ 15/6 3* x 3 „ 15 9 
3Tx35 „ 19/3 5' x35 „ 22/9 
8' x 3 „ 26/3 j 10* x 3 ,. 32/6 
FANE 12" x IS ohms (20 watt) S GNS. 
CHASSIS made to your specification. 
Standard stock sizes available. 
EAR PIECES. Vast range from 4/1 1 to 
10/6 to suit all transistors. 
TEST METERS. Panel to multimeters 
at very keen prices. An excellent " all- 
rounder is the Multimeter— 20 Kohm7 
volt, £4.19.6. 

AND HERE'S A SNIP! 300 x 100 x 100 
* Xi M £2- 3S0 v OLT WKG. CAPACI- 
TORS AT ONLY 5/3! 

Giye yourself the treat you deserve — 
call at our shop, see our qualified staff 
and discuss your electronic problems, 
"°.,7'? trer how sim Pie or complex— 
we IE do our best to help. 



REMEMBER— 




BOTHWELL ELECTRIC 
SUPPLIES (Glasgow) LTD. 
54 EGLINTON STREET 

GLASGOW, C. 5 

Member of the Lander Group 



has all you need from ferrite rods to 

electronic security devices. See for 

yourself! 

P,S. Have you seen our cable prices? 

Ridiculous, aren't they J 



E\A/ 



S 



r 




K 



New Model 8 Wire Stripper and Gutter 

Multicore Solders Ltd., Multicore Works, Maylands 
Avenue, Hemel Hempstead, Herts, 

The new Bib Model 8 wire stripper is an 
improved version of the standard stripper 
marketed by Multicore Solders Ltd. This new 
stripper is fitted with a pre-set selector gauge 
(this can be seen in our photograph) for strip- 
ping any standard wire between 12 and 26 
s.w.g. It not only strips wire or flex but also 
cuts when required. The model 8 has plastics 
handles and retails at 7s 6d. 



Sub-miniature Indicator Lamps 

Osram (G.E.C.) Ltd., East Lane, Wembley, Middx. 
Our photograph shows one of a range of five 
new sub-miniature indicator lamps now being 
manufactured by Osram (G.E.C.) Ltd. The 
big advantage of these lamps is the ease of 
fitting, by means of flange clips, and high 
operating efficiency under conditions of severe 
vibration and shock. These lamps are obtain- 
able in the following specifications: 28V 0-04A, 
12V 0-1 A, 6V 01 A, 6/8V 004/006A and 
12/24V 04/0-06A. 




New Coded Label Wiremarkers 

Hird-Brown Ltd., Flash Street, Bolton, Lanes, 



Probably the most frustrating tasks the 
service technician and amateur construc- 
tor is confronted with is that of sorting 
out a multitude of wires in a piece of 
apparatus. To help improve this tedious 
problem Hird-Brown Ltd. announce two 
new types of wiremarkers. The first are 
sets of colour coded, through to 9, 
markers in the standard international 
colour code. The second are sets of 
alphabet letters A to Z printed black on 
white. 




Qy^ 



The markers are self-sticking and com- 
prise twenty markers per card. The 
number or letter is printed six times on 
each marker, and is therefore visible at 
all times irrespective of the diameter of 
the wire to which it is fixed. Each marker 
measures 1-J-in by ^in wide and is impreg- 
nated with plastic to be oil, water and 
wear resistant. 

The markers may be removed at any 
time without damaging the insulation and 
a full set of cards with numbers plus 
letters enables wires to be coded with 
any combination. 



k. 



A— 29 



739 




r 



Radio Engineer's Kit 



v* 



740 



Philips Electrical Ltd., Century House, Shaftesbury 
Avenue, London, W.C.2. 

The demand and response achieved by Philips 
Electrical Ltd. to their electronic toy kits has 
prompted them to produce similar kits for the 
young radio constructor. 

Designed specially for the young wouldbe 
future electronics expert these kits offer a good 
practical exercise in constructing equipment 
as well as providing a brief theory of radio, 
which is contained in an instruction book 
supplied with every kit. 

The basic kit RE1 which costs £5 9s 6d is for 
earphone listening. Kit RE2 which costs 
£6 19s 6d is a three transistor radio with loud- 
speaker output. An add-on kit RE1A which 
costs £1 17s 6d is available to bring the RE1 
kit up to the same standard as the RE2 kit. 

The basic kits are constructed by means of 
screw terminals into battery operated medium- 
wave radios with on/off, volume and tuning 
controls. Each kit has an internal ferrite rod 
aerial, but there is provision for attaching an 
external aerial and earth if required. Both 
kits have a two-tone plastics cabinet. 

Additional features incorporated in the RE2 
kit are loudspeaker output and inputs for 
gramophone pick-up and microphone amplifica- 
tion, The more adventurous teenager can 
experiment with a tone control and morse code 
practice. 



Bubble Pack Semi conductors 

International Rectifier Co. Ltd., Hurst Green, Oxted, 

Surrey. 

For the first time in this country individual 
components and semiconductor kits are now 
being marketed on a self-service bubble pack 
display board, This form of service, which has 
been introduced by the International Rectifier 
Co., is aimed at providing the amateur con- 
structor with a wide range of semiconductor 
devices, including solar cells, transistors, diodes, 
Zener diodes, silicon controlled rectifiers and 
selenium photocells which are easily obtainable. 
In many cases instruction books giving experi- 
ments and practical circuits are attached to the 
components to encourage the novice, or ex- 
perienced engineer, to learn to use semiconduc- 
tors for a variety of functions. 

This system of sales promotion, although 
American in origin, should be of wide appeal 
especially to the casual purchaser and school 
science master. 

Space is limited in this feature to enable the 
complete range to be listed, but we recommend 
anybody interested to call at any of the following 
retailers where either the full range or a large 
proportion of it is on display: 

D.T.V. Group, 126, Hamilton Road, West 
Norwood, S.E.27. 

Stern-Clyde Ltd., 162, Holloway Road, N.7. 

Home Radio (Mitcham) Ltd., 187, London 
Road, Mitcham, Surrey. 

G. W. Smith & Co. Ltd., 3-34, Lisle Street, 
W.C.2. 

A. C. Farnell Ltd., Hereford House, North 
Court, Vicar Lane, Leeds, 2. 

R.S.C (Manchester) Ltd., 54, Wellington 
Street, Leeds, 1, and at 326, Argyle Street, 
Glasgow. 

Harmsworth, Townley & Co., 2, Harehill, 
Todmorden, Lanes. 




JUST ARRIVED 



NEW EDITION of the famous 

Home Radio Catalogue 



Yes . . . just off the press— Reprint No. 1 1 of our popular Components Catalogue. 
It's the biggest edition yet . . . an extra 17 pages, listing literally hundreds of new 
items, plus a supplement! It's better than ever too— as you will certainly agree 
when you examine it. The prices are listed in the separate supplement. Your 
catalogue will automatically be kept up to date and will thereby have a much longer 
life than previous editions. 




Due to the greatly increased size of this new 
edition, plus increased costs of printing and 
paper, we have regretfully had to raise the 
price a little. It now costs 7/6, plus I/- for 
postage and packing . . . but we are retaining 
the popular feature of including 5 Coupons in the 
catalogue, each worth If- when used as directed. 
Send off the attached coupon today, enclosing 
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• A Al 1*1.11 II It KITS 

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SUPER 6 

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performance and superb finish of the completed receiver give you 
value equivalent to a £12. 12. commercial model, 
•jt All new parts. •£ & transistors and diode, -fa 3S0mW output. 
•jc Superhct circuit, Fcrrite rod aerial. ^ Weymouth Radio printed 
circuit board, -ylf Component positions and references printed on 
back of board. -7V Nicely styled wooden cabinet, II x 7i X 3i in. 
•fc Vinyl covered in various colours. ~ff 6 X 4 in. speaker giving 
good bass and treble response, if Full instruction booklet 2/-. Free 
with kit. -jc I.F. frequency 470 kc s. jc Lining up service it 
required. 7V All parts supplied separately. Write for list. S.A.E. 
please. * 9v, battery required. VT9 or P.P.9, (3,9 with kit). 



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V.H.F. Pre-amplifier with high signal-noise ratio and gain 
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container 3i ■■■ 3i Urn. high, with strap for eaves, loft or 
skirting fixing. 9 volt battery operated, using transistor 
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741 



0-260* at i amp 
*0-260> at I amp 
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2.5 amps Portable 
*0-260v at 4 amps 
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Buy direct from the importer, I ^^ tdawccaducd 

keenest prices in the country. I £33*^5 InANbhURMfcR 

All Types (and Spares) from ' Input 230v. a.c. Output 

i to SO amp. available from I I Sain continuously variable 

stock. %j£«jjJ from to 260v. at j amp. 

01 ^^F^^ Size: dia. 3in., depth 

■ 3^in. including shaft, single hole fixing. 
Easily built into equipment. Ideal for 
manufacturers or Lab. use. £3/3/0. 

$\TmF, "opIfPTypi "lyTTiAT 

1 Designed for building into equipment 
0, Complete with voltage panel and knob. 
I Output variable O-260v, 
0| Price £4/17/6 post paid. 

^^™ ^^" ^■^^ ^^^ ^^™ ^^mmm ih^hm 

I CRATOR 4 Way 16 Amp 250V A.C. 
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shrouded. ■ with knob. 7/6 p. & p. 1/6. 




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ioo watt 

POWER 
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AVAILABLE IN THE 
FOLLOWING 9 VALUES 

10 ohm, 3 a.; 25 ohm, 2 a,; 50 ohm, 
1.4 a.; 100 ohm, I a.: 250 ohm, ,7 a.; 
500 ohm, .45 a.; 1 ,000 ohm, 280 mA; ) 
1.500 ohm, 230 mA; 2,500 ohm, .2 a. I 
Diameter 3jin. Shaft length I'm., ' 
dia. Aim. All at 27.6 e ach. P. & P. 1/6. | 

INSULATION TESTERS "(NEW)*! 

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ohm,, 12 amp., 17,6; 1,2 1 
ohm, 1 4 am p. 27/6; 75 ohm, 2 

""ohm, 1.25 amp. I available m black, red, 
6.5 to2.Bamp., | white ' yellow, blue and 
tapered winding, geared drive . sreen. New, 15/- per doi, 
(less knob), 37/6. P. & P, 3/6. |r. « P. I/-. 



construction, 500 vo!t, SOti megohms. I 
Price £22. 1,000 volts, 1.000 meg- 1 
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TYPE 34R SILICON SOLAR CELL 





VER0BOARD 



.5 volt units series connected in 



VAN DE GRAAFF ■ 

ELECTROSTATIC GENERATOR | The perforated 

Fitted with motor -Copper Board for 
drive for230v. A.C. I Modern Circuitry, 
giving a potential of | 
approx. 50,000 , <I5 ;-:.l5 pitch, 

volts. Supplied ab- 1 2.5;: 3.75 3/. 

solutely complete, | 2.5 x5 3/8 

including access- . 3 75 ;•: 3 75 3/8 

ories for carrying I 3.75 x 5 5/- 

out a number of in- I Spot face cutter, 9/- 
teresting experi-| Special Veropins, 

ments, and full I Pkts. 200 14/- 

instructions. This instrument is ' p .& p . on all items I U 

(completely safe, and ideally suited f 
for School demonstrations. Price 
£6/6/- pk 



I M/«,- pius 4/- P. & P. Leofleton request. ■ 

ITjuTTdTn effi ~n7stro be I 

•UNIT FOR ONLY 37/6. We 



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METERS 



mpact polystyrene case, flying I S M ppl ? ^^rnple circuit d.agram and I 
*l,all electrical parts including the | 
NSP2 Strobe tube which will enable 



Four 
high 

lead connections. Specially designed 
diffusing lens system to ensure maxi- 
mum light pickup. Output up to 2v. 
at 10 to 16 mA in bright sunlight. 

Wider spectral response, and thirty I "Z"' ,' t ^"Z ^"^ ■" C ,° n0 « l -« I 
times the efficiency of selenium cells 2Sw. jj"™"'"* per m " 1Ute ' 27 > 6 \ 
As used to power earth satellites!' 



you to easily and quickly construct a I /, 
unit for infinite variety of speeds, I q 
. from 1 flash in several seconds to 



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6/6 


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30,'- 


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M'6 


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OC200 ,., 10/6 


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in,'- 


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10'- 


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Get 104... */- 


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in Matched Pairs. BCZII ... 


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NSP2 TUBE brand new, I.O. base. 
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2V' Flush Round 

A.C, AMMETERS 
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each, p. & p. extra. 

A.C. VOLTMETERS 
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All 21/- each, p. & 
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Rectifier £1.9.0. 



m/c 



ied Pairs BCZII ... 10/- I $ oz. tins. Ideal for use with the above 
| Ultra Violet Bulbs. 9,6, plus 1/6 P. & P. 



SOLENOID. Overall length 3£in,, stroke iin 
to £in. Maximum push 8 oi, 12-24 v. DO 
operation. D.C. resistance 35 ohm. Price 8/6. 
P. & P. 1/6. ' 

SOLENOID. Heavy Duty 230 v, A.C. Approx. 
31b. pull. IS/-, P. & p, |/6. 
SOLENOID OPERATED MAGNETIC 
RELAY. Type Sc/3944, 4 Pole c/o., 10 amp. 
Contacts, 24 volt D.C. operation, 12/6 each. 
P. & P. \:6. 



230 v. A.C. RELAY, Type I, 2 c/o, 2 amp 
contacts, 9/6. Type 2, 2x15 amp, break, 2x2 ■ 
amp. make, I ;<2 amp. break, 1 1/6. Both types I 
ex new equip. P. & P. 1/6 each, ' 



ULTRA VIOLET BULBS 

Easy to use source of U.V. for dozens of 
practical and experimental uses. 
12 volt 36 watt A.C.;'D.C. SBC 6/6. P. & P. 1/-. 
12 volt 60 watt A.C.'/D.C, SBC 8/6. P. & P. I/-. 
Transformer to suit the above. Input 200- 
240 v. A.C, 12 volt 36 watts, 16/6; P. & P. 2/6. 
Input 200-240 v. A,C. 12 volt 60 watt, 22/6, 
P. & P. 3/6. 

Set of 4 Colours FLUORESCENT 
PAINT. Red, yellow, green and cerise. In 
oz. tins. Ideal for use with the above 
Ultra V iolet Bu lbs. 9,6, pl u s 1/6 P. & P. 

GM~mTnU fE~MECHAN ICAL~ 
TIME SWITCH 

16 Amp D.P. Switch complete with knob. 
Will switch off any setting between 0-4 
minutes. As New, fraction of makers' price, 
10/- p l us 2/6 p. & p. 

LIGHT SENSITIVE SVV*ITCH. Kit of 

parts, including ORPI2 Cadmium Sulphide 
Photocell, Relay, Transistor and Circuit, etc., 
price 25/- plus 2;6 P. & P. ORP 12 including 
circu it, 1 0.6 ea ch, pl us I / - P. & P. 
A.C. MAINS MODEL 

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Price inc. circuit 47 6 plus 2 6 p. & p. 



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Compares favourably with rants coawea costing tea 
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equipment- yuu du mil need. 

This it a real home-study courie that has been bound 
into one giant 8 ;< 11 in. 210 page manual. Each page 
19 divided into two columns. A wide column features 
the text, while » narrow t'jliiiiui ;U th« ride has the 
instructor"? comments, helpful siiRKestions and additional 
pictures t» simplify the dilfleult parts. 

Everyone ean benefit Irom this practical course. >" j 
old fashioned (or pseudu modern) methods used here, 
just straight forward, easy In understand explanations tu 
help yriu make more Inutiey in electronics. 

Tht price, 1 Ontg 3fl/6 plus pastage J;'5, 

Tennt, 1 Why of course! See Coupon. 

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tit y County, 



LOUSY BUSINESS 

Whenever I browse through the 
small ads in some of our Ameri- 
can contemporaries I am struck by 
the number of different firms selling 
electronic surveillance devices. True 
these announcements are always 
addressed to professional investiga- 
tors and detectives, but I don't know 
whether the firms marketing these 
ultra miniature devices investigate 
the bona fides of intending pur- 
chasers. They certainly ought to ! 

The thought of these obnoxious 
snooping aids becoming readily 
available to all and sundry frightens 
me, for one at any rate. This growth 
industry in snooping devices provides 
an example of how mixed are the 
blessings of technical progress. There 
is something revolting and distasteful 
about eavesdropping in any shape or 
form. When this is carried out by 
reputable authorities for law enforce- 
ment purposes, it is a practice we can 
accept — although with some reluc- 
tance; but the opportunities these 
devices present to unscrupulous 
characters must cause grave concern 
to anyone who gives the matter some 
thought. 

It is only just and fair to explain that 
the electronic industry has also come 
up with the antidote to this menace. 
One often finds other firms urging the 
reader to safeguard privacy by buying 
an instrument that detects electronic 
bugs, wire tapping and snooping 
devices. I suppose it would be quite 
funny if it were not for the sinister 
complications. 

It will indeed be a fine state of 
affairs should it ever become normal 
routine to check over a room for 
electronic "bugs" before it is deemed 
safe for occupancy. 



A SHOCKING TALE 

VA/hen is a dog a model? This 
* ' is not a riddle but a legal point 
the G.P.O. may have to clarify, for I 
understand that the 27 Mc/s model 
control band is being used for dog 
training purposes. Seems a likely 
story, you say? But perhaps you 



haven't heard of the electronic dog 
collar which made its first public 
appearance at the recent components 
exhibition ? 

By operating the remote control 
transmitter, the trainer can give the 
dog a mild electric shock whenever he 
wishes to correct its behaviour, 
Apparently this gadget has been used 
with great success in the training of 
police and sheep dogs. It is to be 
hoped that the general dog-owning 
public do not try to jump on the 
bandwagon, because the electronic 
collar is not intended as a substitute 
for the old fashioned local control as 
administered through the leash, I 
know the model control fraternity will 
echo these sentiments for they have 




Switch that confounded thing off 
and let poor Booboo down at once I 



enough trouble as it is from 
unauthorised (two-legged) users of 
walkie talkie apparatus operating on 
the model control frequency. 

Tail piece. I am unable to confirm 
or deny the rumour that the canine 
world is not over enthusiastic about 
this gadget, but considers it just a pain 
in the neck! 



REAL TIME 

Around about the same time that 
the World's Fair computer was 
forging "hands across the sea", as 
referred to last month, another of its 
brethren was engaged on rather more 
sombre business in New York City. 

Through evidence compiled by a 
computer based on betting trans- 
actions, eighty-six men were indicted 
on gambling charges. The sig- 
nificant point of this case is that 
without the computer the prosecution 
could not have been made. If left 
to mere man, the information could 
not have been compiled within the 
period of the three year Statute of 
Limitations. No doubt, as a result 
of this demonstration of computer 
against crime, many anti-social types 
will feel that time is certainly against 
them now. It only makes the other 
"time" more certain. 



NO JAM TOMORROW? 

^any brains are busily working 
* 'on schemes to prevent our town 
and city centres becoming completely 
stagnant with hordes of motor 
vehicles. By far the most sophis- 
ticated approach suggested so far is 
the idea of a sort of "electronic 
licence". 

This would be a small article, about 
the size of a packet of cigarettes, 
which the motorist would purchase 
from a tax office and insert into a 
special receptacle in the car. Pulses 
radiated from cables buried just 
below the road surface would be 
recorded by this electronic box of 
tricks. When some predetermined 
"count" had been reached the 
electronic unit would indicate 
"licence expired" by switching on a 
lamp mounted in a conspicuous 
position on the vehicle. 

With an arrangement of special 
codes, the count rate could be made 
to vary for given areas. Thus it 
would be possible to price motorists 
out of the more central districts ; on 
the other hand the sparsely populated 
districts would probably be entirely 
outside the scheme and motoring in 
such places would be for free ! Well 
that's the theory at any ntfe^ 

743 




n 



nA 



A SELECTION FROM OUR POSTBAG 



Who's old hot ! 

Sir — When I was reading Readout 
(Practical Electronics, June edi- 
tion) I felt compelled to comment 
on D. R. Bowman's letter "Tran- 
sistors cap valves". 

I agree with him when he says 
that printed circuits are better, in 
many respects, than chassis con- 
struction, but I fail to agree with 
his statement that valves are 
"old hat". 

I have recently constructed a 
20 watt amplifier with total dis- 
tortion only 0-05 % at full output. 
The frequency response at 1 watt is 
2c/s to 150kc/s and the power 
response (20 watt) lOc/s to 
30kc/s, each ±0-5dB. Not even 
P.W.M. type transistor amplifiers, 
can equal this. Surely the EL34, 
as I use, cannot be called a special 
purpose valve ? 

A. J. Gay, 
Bexhill, 
Sussex. 



All aglow 



Sir — When I was sorting out some 
bits and pieces I found an old 
night-light bulb. I tried it out 
and found that it worked, but 
when I switched it off, I found that 
if I touched the glass bulb that 
the filament glowed and as soon 
as I took my hand off the bulb 
it stopped glowing. 

The slightest touch will make it 
glow. Could you please tell me 
the reason for this. 

C. D. Cole, 

Kingsbridge, 

S. Devon. 

This is a neon bulb and it seems that 
when your light is switched off the "live' ' 
mains is still present on one contact of 
the bulb holder (this means that the 
neutral side of the mains supply is 
switched, which is incorrect and can be 
dangerous), by touching the side of the 

744 



bulb you completed a very high imped- 
ance circuit back to earth through your 
body, This is often sufficient to produce 
a siight glow in a neon bulb due to gas 
ionisation. 



Slave clock 



Sir — I was very interested in the 
article on the Electronic Timer 
for Sports Events, in the May issue 
of P.E. 

What f would like to do, is to 
adapt the circuit to operate a 
slave clock that gives the time of 
day. To do this an impulse at 
intervals of 30 seconds is required. 
Can this be achieved by increasing 
the size of the capacitors used in 
the circuit of the timer? 

P. E. Huggett, 

Shirley, 

Croydon, Surrey. 

It will require a little experimenting 
to get the time exactly right, but I would 
suggest changing the 2fiF capacitors to 
50fj,F (ensure polarity is right when 
connecting) and increase the multi- 
vibrator charging resistors to about 
470kCl. This should give about 30 
seconds for each impulse.- — J. Hillier. 



Can you help? 

Sir— As your magazine is now 
obviously widely read, might I 
suggest that a column could, with 
advantage to many subscribers, be 
devoted to a "Can You Help?" 
service. To start the ball rolling 
I would like to insert the following: 
"Can anybody help to locate a 
replacement motor for a 
'Nivico' Radio Phono- 
graph model TRE-2, made by 
Victor Co. of Japan Ltd.?" 

R. M. F. Clarke, 

Porthcurno, 

Penzance, 

Cornwall. 



Powerless experience 

Sir — 1 had a strange experience 
recently which you may think 
worth recording in your columns. 

Wishing to match a low imped- 
ance microphone into the input 
of a tape pre-amplifier, I made up 
a small transistor pre-amplifier 
as shown in the circuit below. 

This did not work very well, 
and I left it until the next day. To 
my surprise, it now works per- 
fectly, giving a large increase in 
volume. On investigating, I found 
that the 4^V battery had become 
disconnected! On checking, I find 
that with no battery, or 10kO 
collector load, 1 am obtaining at 
least 100 times amplification! 

I have decided in my own mind 
why this is, and wondered if your 
readers would care to theorise ? 

I am incorporating this "power- 
less" pre-amp as a permanent 
feature in my recording set up. 

S. C. Hooson, 
Liverpool, 16. 




Lasses 

RADIO 



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THE ELECTRONICS ENTHUSIAST 

1 We consider our construction parcels to tie the finest valne on the home constructor market. II on receipt you feel not com- 
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TRANSISTOR PORTABLES 



THE SKYROVER RANGE 

. transistor and 2 diode iuperhet 

portables- — covering full med. plus 6 
SW Bands. 

The SKYROVER Mk III. 

1 1 11 us t ra t e i ■ . Now suppliedwithredesigned 
plastic cabinet in hlack, grey and chrome with 
edgwise controls. 

Cotilruls^Viivelj.'iN'l^clcrtor.VolilniL'Cnntnpl 
with on/off Switch, Tuninc Control. In l>!a»- 
Hc cabinet, size to X MS X y J in. with metal 
trim and carrying han'lte. 
Can now X? ft 1 Q fi rnsl 
be buffi lot **** ' I » ■ » 5/- extra 
H.P. Tcrmi: SI deposit and ll monthly 
payment! o< 16/6. Total K.P.P. SlO.li.td. 

The SKYROVER De Luxe 

Tone Circuit is incorporated, -with separate 
Tone Control in addition lo V 
Control. Tiiuiiil! Control and Waveband 
Selector, In ■ wood cabinet, size 11! x 6} x 
'.iiu. coi-ereU wiih i\ vaebdiMe mat en id, with 
plastic trim ami carrying handle. Also car 
aerial socket fitted, 

Can now -Pi 1*1 1Q fi ^»* 

be built lor <SO I U ■ I » . O .-,/. rx [r.i . 

H.P. Thith: 25/- deposit and II monthly 

payments ol 20/-. Total H.P.P. £!2.5i. 

Data tor each receiver: 2/6 extra, ltcfunded it you purchase llie parcel. Four 02 

batteries 3/4 estra. All components available separately. 

THE "HARROW" POWER PACK 

Eatterv eliminator tor portable radios, etc. Converts jour batten' radio to A.C. mains. 
KcplacVs 4-1 v,,t; v. unit Si v. batts. Hizc .1111-1- Kin, >■ ajiji. -Jjiti. State voltage 
required when ordering". LASKY'S PRICE 29/6 Fust 2/- 



i LONG WAVEBAND 
COVERAGE IS NOW AVAIL- 
ABLE FOR THE SKYROVER 

A simple additional circuit provides 
coverage, of the IHJO/lUjOM. band ( in- 
cluding ISM M. Light programme). This 

is in addition to all existing Medium 
and Short waveband*, All necessary 
components nltli const ruction data. 
Only 10/- extra Post Free. 
This conversion is suitable lor both recei- 
vers that hare already been constructed. 



SPECIAL INTEREST ITEMS! > 



TEST METER ADAPTOR 

Type P.E. 220 — this is a fnllv transistorised device 
which e.nablcs any SO inkroamp P.O. Multimeter lo 
br nsed in place of a valve volt meter. On the IV. 
ranire an impedance of 1 megohm is offered which 
tocrcasr.a on the 1060 V*. range to IflfJ megohms. 
7 ranges: I to 1 Ot'U volts. Designed f"r immediate 
connection to Avn 7, 8 and similar size meters but 
unite suitable for wu? with any other .10 jnkro.imp 
meter. SizeGx IX •"• in. >cw and boxed, lilt 
Price 7Gnj. 



LASKY'S PRICE 39.6 



I'ostilO. Set of ball 1; 




VEROBOARD - NOW IN STOCK 

A really remarkable time saver in Betting out complicated experimental circuits. 
Veruboard is a high grade laminated hoard with copper strips bonded to it and pierced 
■with a regular matrix of holea. Ideal fur producing single items. 
As featured in " Practical Electronics " April 'K5 issue. 



tl 1603 -: ' 5 in 3/6 

4:«,'1&i»4 2i x SI to 3- 

45/1807 Hi X iiln 5/2 

46/IB08 Sf X 31 in 3,'B 

44/15115 8j X 17 in 13/B 



Accessories 

Termmal pin« — pk(, of LIU 

Spot face cutter tool 

!'i;. hi 1 rling tool 



3 3 
91- 
9/8 



Posted, per item extra. 



TRANSISTORS all brand sew akd guaranteed 

GKT SI, GET S3, GBT 8G 2/6; 873A, S74F 3/6: OC45, OC71, OCBID 4/6; OC 44, 
OC 70. OG 70, OC VI 5/8; (match pair 10/8): AF 117, OC 75. OC 200 8/6; 
OC 42. OC 4a, OC 7;i 0( : *-JI> 7/8: OC 201, OC SW 15/-; OC 205, OC '200 IB/6: OC 28 
84/8. , 

TR ANSFI LTERS By BRUSH CRYSTAL CO. Available from stock. 

TO — OIB 4o5kc/u. ;- 2 kc,'s. I TO— 02D 470 kc,'s. ± 1 kc/s. $'6 EACH 

TO— OlD 470 kc/a. ± 2 kc/s. 

TO— 02B 405 kc/s. ; r ] kc/s. 



P. & P. 6d 



H 



207 EDGWARE ROAD, LONDON, W.2. I 33 & 42 TOTTENHAM COURT ROAD, W.I. 

Near Praed St. PADdington 3271/2 _J Nearest Stn., Goodge St. MUSeum 2605 

Open Alt Day Sat. E'rl. Closing Thurs. \Vi Toll. CI. Ed. Erl. Clair Sat.} Mail Ordertta Dept. #".£., 'X>~. Edgirare Rd„ H',2 



SEMICONDUCTOR BARGAINS 

Silicon Rectifiers 

100 P.I.V. 750 i«A 1/6 

liOO P.I.V. 750mA lh 

400 P.I.V. 750iiiA 2/9 

600 P.I.V. 750mA 4/6 

BOO P.I.V. 750mA 5/9 

1 ,000 P.I.V. 750mA 7/6 

3/3 watt Zener Diode- 12v 4/6 

1 watt Zener diodes 

fiv.. 9v., 10v., lev., fix,, 28v., dOv., 

GOV., 95V 6/- 

10 watt Zener diodes 

4v.. 6v., Sv., 10v„ 16v., 19v., lt\\, 

JS6v., :ii\- 8/6 

10 watt Double Anode Zeners 

32v. Regulates! poe. or nog. nr butli .... 15/- 

Silieon Controlled Rectifiers 

7 amp. 200 P.I.V 18/6 

7 amp. 300 P.I.V 21/6 

18 amp. 300 i\ I. V 25/- 

18 amp. 400 P.I.V. 28/- 

Transistors 

^N1046 p.it.p. 12 amp. 50 watt 10 m/cs. 45/- 

2X1907 p.it.p. 20 ainp. 60 watt -10 iti/cs. 60/- 

SYX 3073 p.u.p. 380m/cs. 150 mw 16/- 

NPN Silicon for Hi-Fi etc. 

2X657 10O\". at) Kain 4 watts 2 m/ca 35/- 

2N1050 ] 20v. HO gain 40 watts 2 m/es . . 40/- 

Speciat Mullard OCP71 15/6 

Postitig ami packing Is. up to any items 
Full Data on nil Hems available 

J. and J. ELECTRONICS 

{CANADA] 

ALL ORDERS TO: 

174 Maybank ltoatl, South Woodford, 

London, E.1S 

Phono: P.UC 9;u5 

ALL 600DS NEW AND GUARANTEED 
RETURN OF POST SERVICE 



TRANSISTOR 
ELECTRONIC 0R6ANS 
FOR THE AMATEUR 

This book presents not only a 
detailed design for a full scale 
organ, but a complete explanation 
of everything to do with transis- 
torised organs. Profusely illustrated 
with clear diagrams. 

By A, Douglas & S. Astley 
18/-. Postage I/-. 

TRANSISTOR TRANSMITTERS FOR 

THE AMATEUR, by D. L. Stoner. 

21/-. Postage I/-. 
INTRODUCTION 

TO ELECTRONICS, by Bureau of 

US Naval Personnel, id/-. Postage I/-. 
ABC'S OF HI-FI & STEREO, by H. 

Fan eel. 14/-. Postage I/-. 
TROUBLESHOOTING WITH THE 

OSCILLOSCOPE, by R. G. Middleton. 

20/-. Postage I/-. 
COLOR TV REPAIR, by M. Clifford. 

21/- Postage I/-. 
WORLD RADIO TV HANDBOOK. 

1965 ed. 26/-. Postage 1/3. 

COMPLETE CATALOGUE I/-. 

BRITAIN'S LARGEST STOCKISTS 
of British and American Technical Books 

THE MODERN BOOK CO. 

19-21 PRAED STREET 
LONDON, W.2 

Phone: PADdi'ngton 4I8S 
Open 6 days 9-6 p.m. 



152 3 FLEET STREET, LONDON, E.C.4. 

Telephone: FLEet Street 2833 

OPES ALL UA r 1H CBSDA i'. Early elating Sal. 



COMMUNICATIONS 
RECEIVERS 




NATIONAL NC190X 

INTERNATIONALLY FAMOUS 
NATIONAL RECEIVERS 

NC190X — 10 valves, 5 10 kc/s to 30 Mc.'s, 
5-meter, noise limicers, product detector, 
bandspread . double conversion. £.99 .0.0. 

NCIII— 6 valves, 540 kc/s to 30 Mc.s, S- 
meter, noise limiter, bandspread .built-in 
speaker. £60 .8.3. 

NC77X — beginner's receiver, S valves, 540 
kc/s, to 30 Mc.s, built-in speaker. £32.8.9. 

Write far illustrated leaflets 

WE HAVE A LARGE STOCK OF 
NEW AND SECONDHAND RECEIVERS 

- MANY SECONDHAND BAR- 
GAINS IN MINT CONDITION 
Just write or phone for full details 

BRIAN J. AYRES & CO. 

Dept. DW, 21 Victoria Road 
Surbiton, Surrey 

Telephone: Elmbridge 2833 



745 



Practical Electronics Classified Advertisements 



The pre-paid rate for classified advertisements is 1/- per word (minimum 
order 12/-), box number 1/6 extra. Semi-displayed setting £3.5.0 per 
single column inch. All cheques, postal orders, etc., to be made payable 
to PRACTICAL ELECTRONICS and crossed "Lloyds Bank Ltd." 
Treasury notes should always be sent registered post. Advertisements, 
together with remittance, should be sent to the Advertisement Manager, 
PRACTICAL ELECTRONICS, George Newnes Ltd., Tower House, 
Southampton Street, London, WC2, for insertion in the next available 
issue. 



EDUCATIONAL 



HOME STUDY COURSES in Practical Elec- 
tronics. Tree Brochure without obligation 
from: BRITISH NATIONAL RADIO 
SCHOOL, Heading, Berks. 



STUDY RADIO, TELEVISION AND ELEC- 
TRONICS with the world's largest home 
study organisation. I.E.R.E., City & Guilds, 
K.T.E.B., etc. Also Practical Courses with 
equipment. All hooks supplied. Write for 
PREE Prospectus stating subject to I.C.S, 
(Dept. 577), Intertext House, Parkgate Road, 
London, S.W.I 1. 



Full-time courses in RADAR and RADIO- 
TELEGRAPHY for prospective marine Radio 
Officers. Govt, approved exam, centre. 

Also courses in basic ELECTRONICS, RADIO, 
TELEVISION and PRACTICAL SERVICING. 

Apply;— Director, British School of Telegraphy, 
2a Penywem Road, Earls Court, London, S.W.5 

A.M.l.Mwh.E., A.M.I.E.R.E. City & Guilds, 
G.E.C., etc. Become a Technician or Techno- 
olgist for high pay and security. Thousands 
of passes. For details of Exams, and Courses 
in all branches of Engineering, Building, 
Electronics, etc., write for ISti-page handbook 
— PEEK 1U.E.T. (Dcpt. 152), London, W.8. 



INNER LONDON EDUCATIONAL AUTHORITY 
LONDON COLLEGE OF FURNITURE 

Applications are invited for the following 

part-time posts. ELECTRONIC MUSICAL 

INSTRUMENTS, 2 days- per week, SU5-12.30; 

1.30-4.30. 

Must he fully conversant with the construction 
and servicing of electronic organs and ampli- 
fiers. PIANO CONSTRUCTION AND MAIN- 
TENANCE, 1 day, 1 evening (0.30-9.0) per 
week, 

Must be capable of teaching modern construc- 
tion techniques and repairs to upright and 
grand pianos of all types. 

Remuneration each whole day: 151/3; 1 
evening: 62/6. 

Pull particulars and form of application from 
the PRINCIPAL OF THE COLLEGE, 
Bitfield Street, Shore-ditch, N.i; 

746 



EDUCATIONAL 

(continued) 



B.8c.(ENG.), A.M.I.Meeh.E., A.M.I.E.R.E. City 
& Guilds, etc., on "Satisfaction or Bei'und of 
Fee" terms. Wide range of expert Home 
Study Courses in Electronics, Computers, 
Radio, T.V., etc. l">tl-page Guide — PUKE. 
Please state subject of interest. BRITISH 
INSTITUTE OP ENGINEERING TECH- 
NOLOGY, 151a College House, Wright's Lane, 
London, W.8. 

THE INCORPORATED PRACTITIONERS in 

Radio & Electronics (I.P.R.E.) Ltd., Member- 
ship Conditions booklet 1/-. Sample copy of 
I.P.R.E. Official Journal 2/-, post free. 
Secretary, Dept P, '.i'i Kidmore Road, Caver- 
sham, Heading, Berks. 



SITUATIONS VACANT 



EXPERIENCED TEST ENGINEERS 

Vacancies exist for experienced test engineers 
in the Pinal Inspection Department of Londex 
Ltd. Applicants should possess a minimum of 
Q.N.C. or equivalent and have current prac- 
tical experience of testing and adjusting auto- 
matic electrical control equipment. 

JUNIOR TEST ENGINEERS 

We also require several junior testers. Suitable 
applicants will be encouraged to study for 
technical qualifications and a day release 
scheme is in operation. The work is interest- 
ing and demands a methodical and enquiring 
mind. Reliability, accuracy and integrity 
are more important than speed. These are 
important vacancies which have a direct 
bearing on the Company's reputation and a. 
high sense of responsibility is vita). There are 
ample opportunities for promotion: many of 
our senior executives entered the Company 
through the Test Department. 

FEMALE TESTERS 

Vacancies exist for women who have had some 

test experience. Working conditions are 

attractive and salaries will be in accordance 

with experience. 

In all eases, write in first Instance to: Mr. If. G. 
STERN, Londex Ltd., 207 Anerley Road, 
London, S.E.20, SYDenham 3111. 



METAL WORK 



CABINETS • CASES 
CHASSIS 

Anything in metal, "One-offs" a pleasure 

Send your drawing for quote 
Stove enamelled in any professional finish 

MOSS, WATSON p.e. 

40 Mount Pleasant Street, Oldham 
Lanes. MAIN 9400 



RECEIVERS AND COMPONENTS 



A.1 POST FREE BARGAINS. Guaranteed 
reclaimed valves. Send for full list to 
Dept. MO/E, A.l RADIO COMPONENTS, 
14 The Borough, Canterbury, Kent; 



TRANSISTORS, POT from It., NPN high 
gain from 5/-, power types, 20 wat t from 7/6, 
diodes 6d. Ail guaranteed. SAE list, 
LONGLAND'S, o Mauslleld Place, Ascot. 
Berks. 



OVER 300 ELECTRONIC COMPONENTS in one 
great parcel including printed circuit panel 
with condensers, resistors, coils, diodes, tran- 
sistors, silicon rectifiers, potentiometers IP's, 
valve base's, tuning condensers, transformers, 
etc. \ ou can't afford to miss this great bargain 
offer. Send 10;- plus P. <fc P. 2. '6 to D. i- W. 
LTD., 224 West Road, Westclifl-on-Sea, Essex, 



R. &R. RADIO & TV SERVICE 

Dept. P.E. 
44 Market -.Sfreef, BACUP. Tel. 465 

Salvage Valves 



6FI3 


4 6 


6FI5 


tth 


6LI8 


4/6 


6K25 


10/- 


6U4GT 


5/- 


6BW6 


5,'- 


6/30L2 


5/- 


EB9I 


1/- 


6FI 


2/6 


EBF80 


5/- 


EBF89 


5/- 


EF80 


1/6 


EF91 


2/6 


EF8S 


5/- 


ECC8I 


4(- 


ECC82 


*h 


EY86 


*h 


ECL80 


4/- 


20P3 


s/- 


20P4 


7/6 


30F5 


*/- 


30PLI 


31- 


PL38 


6/- 


PL36 


7/6 


PY33 


7/6 


PCC84 


4/- 



PCF80 


4/- 


PCL82 


«/- 


PCLB3 


5/_ 


PL8I 


5/- 


PL82 


4/- 


PLB3 


4/- 


PY8I 


3 6 


PZ3Q 


5/- 


U80I 


7/6 


U301 


6/- 


U329 


31- 


I0F1 


H- 


1 OLD II 


Sh 


I0PI3 


5/6 


I0PI4 


31- 


20LI 


31- 


20F2 


5/6 


20OI 


2/- 


20PI 


6/6 


20P5 


6/6 


30FL1 


6/6 


30PI2 


5/- 


30P4 


7/6 


PY32 


61- 


PYB2 


31- 



Postage on valves fid. — 3 or more post free. 
Cfosed for local holidays, July 23rd — August 5th, 1965 

1 Pole 8-way switch, complete with 8 resistors 2 

@ IK, 2 @ 15K, one each of 22K, 15K, 18K, 

6.8K. 3 6 incl. post. 

Panel mounting 8 inch flexible extension shafts 

for stnd I inch controls, will operate over 180 

degrees. 3/6 incl. post. 

Speakers ex T, V. 6 X 4 inch 3,'6. 8 inch rnd 6/-. 

Resistors New ; | watt 3Jd., 1 watt 3d., 2 watt 

9d. ail 10%. 

S.A.E. with all enquiries. All goods subject to 

satisfaction or money refunded. 



RECEIVERS AND COMPONENTS 

(continued) 

LIGHT SENSITIVE TRANSISTORS, hundreds 
of interesting applications. Unrepeatable at 
5/-, P. & P. fid. wliilc stocks last. MEADOWS, 
10 HeolyllHii, Barmouth, Merioneth, 



"P.E." R/C BRIDGE, VA.fi Broadcast 

^Receiver, Integrated Transistor t Amplifier, 
Two Band Bartio Tuner, Inexpensive Oscillo- 
scope,. Milliard Miniature Kleetrolyties and 
Hi-stab Eesistors. R.a.e. for itemised price 
lists. A.TAX ELECTSONICS, 18a Kumbold 
Itoa<1, Fulham, London, S.'W.fi. 



GUARANTEED BRAND NEW IN 
ORIGINAL WOOD PACKING 
CASE. CANADIAN MARCONI 
52 RECEIVERS-FEW ONLY AT 
£10 . 10s . Od. 

Mains Power Unit £2 . Os . Od., 
supplied with outer esse and 
Handbook, circuit set has crystal 
calibrator, speaker, etc. Range 
1.75-16 Mcls. 

J. T. SUPPLY CO. 

38 Meadow Lane, Leeds II, Yorkshire 



TESTED TRANSISTORS 

I/- each, Red or White Spots. 

27- each, XA101, XAI02, XBI03, 
OA90, XA III. XAII2, OC430, 

VIO/IS. 

3'- each, OC44, OC45, OC70, 
OC7I, OC8I, OC8ID, XAI5I, 
XBI04, XCIOI, XC10IA, OCI69, 
OC200. 

4/- each, AF1I4, AF1I5, AFI16, 
A F I 17, OCI70, OCI7I, XAI03, 
XAII6, XB102, XBI05, XCI2I, 
XU6II. 

5/- each, OCI39, OCI40, OC204, 
ORP60, XA701, XA703, GET7, 
GETS, GET9, XCI4I, BY 1 00. 
OA2IL 

10.'- each, OCI9, OC22, OC25, 
OC26, OC28, OC35, 2SOI3. 

ZENER DIODES 4.7 v. to 30 v. 
| watt, 3/6, 1.5 watt, 5/-, 7 watt, 
6/- each. 

Plus many more, send 6d. in stamps 
for Full List and Equivalent Chart: 

B. W. CURSONS 

78 BROAD STREET 
CANTERBURY, KENT 



TRANSISTORS AT GIVE-AWAY PRICE! 

KKT 124/5 switching transistors. Also capable 
of being used in all stages of a superhet. 
fi for 1 0/-. Ncwiriii rkct 405 10/- each. Miniature 
earphones with phig and lead 5/-. Transistor 
rleeirolylies 1/64. each. Brand-new tin 
speakers 10'-. fimids under 10/- add Cd. post- 
age please. ' fi. F. MrTAVARD. 17 Peel Close, 
Drayton Bassett, Stalls. 



RECEIVERS AND COMPONENTS 

( continued ) 

TELEVISION TUBE SHOP 

FOR 

Unused, Guaranteed. Tubes 

OVER 2,000 IN STOCK 



At prices from 50% to 75% of 
normal List Price 

All tubes tested before despatch 
and Guaranteed for 12 months 

CARRIAGE 10 -via B.R.S. or 
15/- via passenger train 

TERMS £2 down (plus 

carriage) and balance at £1 

per month 

See our advertisement in 

PRACTICAL TELEVISION for exact 

prices, or write for details 



TELEVISION TUBE SHOP 

48 BATTERSEA BRIDGE ROAD 
LONDON, S.W.I I. BAT 6859 

OPEN ALL WEEK AND SATS. UNTIL 4 p.m. 

NOW 

RFADY' 

l»WrAL# I ■ A modern way of 
instrument case 
assembly using our "Die Strip". The strip 
has been specially made for us at Birmingham 
on qty. production, for low price to the public. 
It is made of high strength alloy and wilt enable 
anyone to assemble an instrument case or 
cabinet in minutes. Full details of these pro 
ducts will be sent free. Please send largi 
envelope self addressed. 



RECEIVERS AND COMPONENTS 

(continued) 



rge 



88 set transmitter receiver. Chassis less valves 
20/- each. Post paid. 



Copper Laminate Board, single or double sided, 
5 - per square foot panels, either type 3ft. by 
4ft, 33/-. 



High Stab Resistors, 5% «d.; 2% M.j 1% I .'-, 
Every six packed in 7-compartmenc linen finish 
component box. 



Speakers, 3 ohm P.M. 5in., 5'-, 6in.. 6'-, 
7 X 4in., 7>, 8in., 8,'-, I0in„ 12.6. 



Please send SAE. for full Lists of other goods 
on offer, 



U.K. ONLY 



E. R. NICHOLLS 

Mail Order and Retail Shop 

46 LOWFIELD ROAD 

off SHAW HEATH, STOCKPORT 

CHESHIRE 



L.S.T. COMPONENTS 

IB2B HIGH ROAD, BENFLEET, ESSEX 

More bargains from our new list: 
Silicon Power 2S0I2 10.'-. HF Power Mesa 
2S025 100 watt 10 mt/s 307-. Red spot NPN 
transistor! I,'-, OC71 equivalents 9d- 
Still available: Our famous 25 for 10;'- offer, 
state 2G37I.8I series (AF) or 2G4I4/7 series 

(Rf), 

100 Diodes for 12/-, Post paid over 5,'- order- 
Send 6d. stamp for our latest list. 



SO TRANSISTORS all tested, marked and guar- 
anteed. AF.RF. Silicon and P.N.P. Vnob- 
tainable elsewhere at this low price of 35/- phis 
P. <fe P. 1/-. D & W LTD., 221 W08t Boad, 
WeBtcHIT-oa-Sea, Bssex. 



TRANSISTORS AND DIODES 
ALL POST FREE 
MULLARD OC4S. OC7I, OC76. OC8I, 
OC8ID, OCB4— 3/-; OC75— 3/6; OC8I, 
OCB4 pairs-6.'-; OC35— 7/6; OA70, OA79, 
OA81, OA96— 1/6; AF I IS— 5/6. 
TEXAS 2G344a, 2G345b, 2G37U 2G37lb, 
2G374a, 2G374b, 2G378b— 3/-; IS 100— 2/3. 
FERRANTI ZR3IC, ZR3ICR— IS. BTH 
GJ5.D— 2 3. STC Silicon 800 PIV, 500mA 
—4,6. MA393— 3/6. 

All amateur requirements supplied. Trade 
enquiries invited. 

THE RADIO CONSTRUCTORS CENTRE 

363 Westborough Road, Westcliff-on-Sea, 
Essex Phone Southend 49686 



TRANSISTORISED SIGNAL INJECTOR. Com- 
plete kit of components and circuit of injector 
for testing amplifier or radio, 10/- only. 
Tost free. G-. F. MITAVABD, 17 Peel Close, 
Drayton Passett, Staffs. 



TRANSISTORS AND COMPONENTS 

OC7I— 2f9d. each. OC44, OC4S, OC72, 
OCai, OC81D— 3/Od. each. OC42— 2/6d. 
each. OC26. ORP12, GETS7— 7/9d. each. 
AFH6, AFJI7. OCI70, OCI71— 3/6d. each. 
OC82, GETB, BY 1 00— 5/0d. each. 
Latest Mullard types AC 1 26— 8,'Od, each. 
ACYIB— 7/6d. each. ASY28— 6/6d, each. 
AFI86 cut of FREQ 800 Mc/s- 26,'-. Silicon 
Rectifiers 200 volt P.I.V. at 6 amps — 5/- each. 
Branded Maida ECCBS valves — 4/6d, each. 
10 watt Transistor driver and output trans- 
formers — 22/6d. each. 

Aeos Record Player cartridge, suits Collaro, 
Garrard, B.S.R., etc. — I2/6d. each. 
Latest Mini 2 Motor Transistor Tape Recorder 
£6. 15, Od, post paid, 
tvelek Signal Iniecror— 22/6d. 
Transistor Walkie Talkies — 9 GnsVpr. 
Caby A 10 Multi Meter 2000 O.P.V.— £4.l7.6d. 
Baby B40 Mutti Meter 4000 O.P.V.— £5. 1 S.Od. 
5.E.— 200 Min Lab Incorporating A/C D/C 
Volt Meter, Resistance Measurement, RF 
-Sig, Gen AF Sig. Gen. R.F, Field Strength, 
Condenser Check — £8.5. Od. complete, 

ZENER DIODES 

OA8I, OA9I Diodes— I /6d. each, 

OAI0 Gold Bonded Diode— 5/0d, each. 

Crystal Set Diode — I /3d. each. 

Matched Pair OC82 + I OC82D— l2/6d 

37V 4 1V 50mA 

4-1 V 45V 50mA 

86V 9-SV 45mA 

4-8V 6'4V 45mA 

4-5V 4-9V 250mA 

4-8V 5 4V 250mA 

5-8V 66V 225mA 
10-4V 1I-6V 125mA 
22 7V 25 -5V 55mA 
2B-4V 3I-6V 45mA 
34 -2V 37-BV 30mA 
40 BV 45 -2V 30mA 



10011 300mW 

I20U 300mW 

SOU 300mW 

BOO 300mW 

toil isw 

1-SW 

1-SW 
■5W 
■5W 
ISW 
1-SW 
ISW 



ISIi 

un 

2S£i 

i2oa 
i6oa 

I 251 J 
90Q 



3/4d. 



3.6d. 



All types Valves in Stock. 

5.A.E. all enquiries. 

Closed for Holidays 30 luly 1965 to 9 August 

1965 

Mail Order Only; 

All Above Post Paid 

J. ROBINSON 

(Radio & T.V.) 
4 Highcliffe Road, Blackley, Manchester 9 



CONTINUED OVERLEAF 



747 



RECEIVERS AND COMPONENTS 

(continued) 

RESISTORS! You can't resist these! 1,000 
assorted war tape anr1 value. Cannot be 
repeated ar £2/10/- per 1,000. G. V. MIL- 
"WARD, 17 Peel Close, Drayton Basseit, Staffs, 



WITWORTH TRANSFORMERS LTD. 

26 ALL SAINTS ROAD, LONDON, W.I I 

Tel.: BAY 9071 
26Q-0-260V. 80mA. 6.3v.2a, 0-5-6. 3v.2a 18/- 
2S0-0-2SOV. 160mA, 6,3v.4a, 0-5-6. 3v 2a 17/- 
260-0- 260V. 180mA, 6.3v,4a, 0-5-6. 3v.2a 281- 
■400-0-400V. 200mA, 6.3v.4a, C.T.OS-6. 

3v.3a SO/. 
ISOLATING TRANSFORMER, ISO Watt, 

1:1 Ratio. 200-250v. Range 50/. 

All Transformers have Standard Primaries, 

Screened and are Fully Varnish Impregnated 

We Manufacture all types of Transformers small or 

large . . . quantities ot competitive prices 

12 Months' Guarantee. S.A.E. All Enquiries 

Postage and Packing 3/. C.O.D, 5/. 



FOR SALE 



CRACKLE PAINT, Blade or Grey, J pint tins 
4/-, post fid. from the component specialists, 
BBJRVIO JIA1HO. 156-3 MerLon Koad, 
Wimbledon, London, S.V.19. 

CONDENSER BARGAIN! Miniature paper 
condensers, tin •: Jin, Ideal for transistor sets. 
.0001. .001. .ok-2, .005, .""J. AUfiY; also small. 
SOO/yi'Fnnrt H.-lnnV condensers. A117/6d. per 100. 
£3 per 1.000. U. F. Ml 1. WARD, 17 Peel Close, 
Drayton Jiassel I, Staffs. 



CONSTRUCTORS parcel containing useful 
assortment of radio and electronic spares. 
Relays, .switches, Resistors, Condensers. 30/-. 
'Jen times value fruaranteed. AV'DHH'KAFT, 
20 Kettering Road, Northampton. 302*1, 



A.C. STANDARD. Mains Motors Fractional 
"11. V. :Hin diax-tin long with ]in spindle. 
Many uses. Brand new, 25/- each. 1*. & V. 2/6d. 
Small Battery Motors Ijin diax-Jin lOBg— 
4£ to 9 volts. Heavy const ruction: onlv 7,6d. 
each. P. &. p. ]/-. WAj.TO.NS WlRELKSM 
STORES, 15 Church Street, Wolverhampton. 

TRANSISTORS UNMARKED UNTESTED. 
40 for 10/-, P. tfe P. 1/-, i packets post free. 
Belays, thousands of types, special catalogue 
free. General Catalogue of Mechanical " A 
Electrical (iear, Tools, etc., u.000 items, free. 
K. R. WHISTOX (Dept. PET), New Mills, 
Stockport. 

DID YOU KNOW that Suffolk Tubes, still the 
largest independent fiihe rebuilders. Rf'va a 
tree ilelivrv service Itv van or passenger 
train to all parts of (he U.K. Each tube' is 
guaranteed 12 months and all types are alwavs 
available off the shelf at. keenest prices, 
1-3 Upper Richmond I {cad, Putney, London, 
8.W.15. Telephone Vandyke 4304/5267. 

NEW £18 DYNAM0T0RS. Input 12/18 volts. 
Output 240 V, 12ii 200 watts, AC.'DC, bargain 
£4. J. U'BKIEX, 1, Hijjbtown, Waterfoot, 
Jtossendaie, Lancashire, 

VENNER TIME SWITCHES. R.-cnndi tinned, 
14 day clock, once on once off every 24 hrs. 
Jewelled movement, fully guaranteed, t amp 
25/-, ."> amp 32 6d., 15 amp 39,'6d. Post etc. 
2/tid. Cast Aluminium Cases 7 6d". A. it. 
HATCH E J. O It, ;t',i;, .Dcpt. 4 Park Road, 
Bromley, Kent. 



MISCELLANEOUS 

CONVERT ANY TV SET into an Oscilloscope. 
Diagrams and Instructions, 12/6. REDMOND, 

42 Dean Close, Portslade, Sussex. 

GOVERNMENT SURPLUS Electrical and Radio 
Equipment. Our new catalogue No. lii now 
readv, 2/6 Post Free, cost refunded on purchase 
of goods over 82. ARTHUR, SALL1S RADIO 
CONTROL LTD., 93 North Road, Brighton. 

748 



MISCELLANEOUS 

(continued) 



HAMMER FINISH PAINT. The modern 
finish for electronics. Can be BRUSHED or 
sprayed. Blue or silver. 2ioz tins 3/8, 
post 8rf., 1 pint 7/6, post 1/0, 1 pint 15/-, prist 
2/9. Retailers supplied, write for details. 
Amazing results: Return of post service. 
Orders over 30,'- post free. FIN NIG AN 
SPECIALITY PAT NTS, (PE). Miekley Square, 
Stocksfleld, Northumberland. 

MAINS TRANSFORMERS rewound. Specials, 
and Output Transformers to vonr own specifi- 
cations. RATCLTFFE, 27 ' Station Road, 
Holmflrth, Yorks. 



SERVICE SHEETS 



SERVICE SHEET5 for all makes of Radio and 
TV 1985-1966, Prices from 1/- with free 
fault-finding guide. S.A.E. inquiries. Cata- 
logue of 6,000 models, 16, Valves, modern and 
obsolete. Radio/TV Rooks. S.A.E. lists, 
HAMILTON RADIO, Western Road, St. 
Leonards, Sussex. 



TRADE SERVICE SHEETS. Radio. TV, etc. 
Mixed dozen .« */-, 100 22/6d. p.p. TEI.I1 A V, 
Maudland Bank, Preston. 



STATE MODEL NO. Radio 2/-. TV 2/6. 
S.A.E. DARWIN, 10 George' Street, St. 
Helens, Lanes. 



SERVICE SHEETS 

4/- each, plus postage. 
We have the largest supply of Ser- 
vice Sheets for all makes and types 
of Radios, Televisions, Tape Recor- 
ders, etc. in the country. Speedy 
Service. 

To obtain the Service Sheet you 
require, please complete the at- 
tached coupon: 
From : 
Name: 

Address: ... 

To: S.P. DISTRIBUTORS 

44 Old Bond St., London, W.I 

Please supply Service Sheets for the 

following : 

Make: 

Model No.: Radio/TV 

Make: 

Model No.: Radio/TV 

Make: ... 

Model No.: ., 

New 1965 List now available. 
I also require list of Service Sheets 
at 1/6. 

(please delete items not applicable) 
I enclose remittance of .... 

MAIL ORDERS ONLY Au8 pe 

"PRACTICAL ELECTRONICS" 

CONSTRUCTIONAL DESIGNS 

All specified 1st grade Components, complete 
Metalwork, Full range of Materials, engraved 
Panel Places, Ancillary Equipment and Assem- 
bled Units. Comprehensive lists available for each 
*'P,£. lh Constructional Anisic, 

Please send 6d, in stamps for each design 

MALVYN ENGINEERING WORKS 

Engineers {& the JUtiii" and £9tectTO»£ff Industries 

7CURRIE STREET, HERTFORD, HERTS 
^_^ TKtKPSOHS ; HERTFORD 22114 _ 



RADIO AND 
ELECTRONICS BOOKS 

ON FREE TRIAL 

Then only 5/- weekly for those you keep 1 



Ke. 9C. P IN-POINT TRAHSISTOE TROUBLES IB 
12 MUTUTES. By Louis K. liorner, Jnr. 485 pages. 
Companion manual in the veil •known 'Pin- Point T.V. 
Troubles in 10 Minutes* using the famous Ciimc Check 
C'hart Trouble Shooting Method. Covers alt kinds at 
equipment including radios. T. Vs., audio amplifiers, pre- 
amplifiers and just about everything. There are hundreds 
of photos, illustration*, diagrams ami nheek charts: 
valuable reference itectinriH, Supplies are limited SO 
order your copy now ami avoid disappointment. Price, 
49/6 including postage. 

Mo. 1BH. RADIO SERVICING. Sol pages (hurt! 
rovers), with hundreds of illustrations, circuits and 
diagrams. By (J. B. Patched and B. Fozard. Price 
28,'fM. including postage. A wry thorough approach to 
learning radio servicing, starts with simple explanations 
and goes on to mure advanced radio theory. Doesn't 
miss .-i single point. One of the must complete radio 
manuals ever published. A l«iok you will use for years 
to come. This is the Hrst time this hook has ever been 
ottered on a free trial basis. Order your coos' now, see 
coupon below. 

No. 13N. TELEVISION SERVICING. 320 pages, hard 
covers, S9fi diagrams. Price, 26/- including postage. As 
1 1 escribed above, lout leaches television repair. 

No. 39. RADIO St ELECTRONICS COURSE, 21': 

pages, quarto size, :)5 i- pktr Lessons. You will rind 

this course easy to understand. The lessons are CRY- 
STAL CLEAR, PRACTICAL. EASY TO MASTER AND 
USE. Early lessons make fundamentals clear even to 
the beginner while other lessons will give you the practical 
knowledge of an espcrl! This is a modern course, that 
teaches without resorti mr la domic strip methods , . . 
Thousands of KUOWM Ki.KOTiiosn.-s and Practicai, 
WrBEi.Kss readers have taken fhis cuurse and enioved 
every minute of It . . . Why not you'/ Price for "the 
complete course, 41/- including postage. 

No, 22, PIN-POINT COLOUR T.V. TROUBLES IN 
IS MINUTES. Jiy Robert (I. Midi! let-on. D4ft pages. 
;lfl2 check charts. Just about the biggest ami most 
useful manual on (.'oliiur T.V. available anvn here. Nun 
is the time to gel the complete information on this 
important new subject. Price. 49/8 including postage. 

No. 8. PIN-POINT T.V. TROUBLES IN 10 MINUTES. 
Over 340 cross indexed pages, covers 7d svmptouis, 
700 trouble spots, ha* 30 time saving cheek charts, 
2D0 diagrams. Over 30,1100 copies now used in the CK, 
alouei 

NOW REPRINTING. Orders accepted for delivery ir 
Jour weeks' time. One of the best manuals we have 
ever handled, well worth waiting for: Price, 41/- 
including postage. Bend coupon today for earliest 
delivery. 

IRONCLAD GUARANTEE 
Any book not satisfactory may lie returned within 
10 days post-paid for full refund of the purchase price. 

FREE BOOK OFFER: 

Send cash with order and qualify for any free book listed 

on the coupon as follows. Minimum 40/- One book. 

80:- or more Two hooks. 120,- Three books. 

NOTE. These books are authoritative and loaded with 
useful information, cost from 4/6 to 5/- each in book stores, 

FREE TRIAL OFFER! 

To Sim-Tech Technical Books, Dept. EI, 
Gater's Mill, West End, Southampton, Hants] 

~\ Please send (lie following books, I have, 
circled. 

90 12\' l;SX 39 



"if not deligh ted I may return any bonk post- 
paid without further obligation on my part, 
otherwise 1 will pay cash price or 5/- weekly 
(10/- fur! nightly) oommenolng not later thaii 
K» days after delivery, l am over 21 years of 
age. (If under ^l parents should place order). 

"] T enclose cash to the sum nT£ 

I understand you will refund this nionev 
if I am not 100% satisfied (provided I return 
the book in good condition within 10 days). 

Please send me the free bt>uk{s) I have ticked. 

^] Oscilloscope Dunk. 
Q Electronics Gadgets Book. 
Q Transistor Book, 

3] Badio Instrument Bonk. 

Xanie 

Address , 



ASTONISHING LOW PRICED RADIO KITS (all Guaranteed) FROM CONCORD 




MAKE 

5 

DIFFERENT 

TRANSISTOR 






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Amaxing Rmlln ('i-iirtrnt-tioti Set! Become a 
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tHferactfnnti f-tr euch design, Step-by-Step 
}>(mi, nil Triiluristttr*, kuulspenkfr, ii<?i>iiuiil 
pbonc. kiinhs, scrcurjf, etc.. rtf! you fteetL Box 
riw I4"x l(l*X2* (jmrta available Beparate), 
Originally Cft. HOW 85/- plus 3/6 P.& p. 



New RADIO Anyone CAN BUILD in E-3 

honrs: Only 19 6: 

EVEN THE: : 

O L D E R\ 

CHILDREN- 

BUILD THEM: I 

. . -. mi &Q I ■ [-: in _ I 

— only 16 o>">nuee- 1 

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after stiitJuQ.-i 

Al'X 21* X IT- 1 : 

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sets stteeessfutly, it in the Jir*t tint* / ^'■' , «wf 

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hare ohrioitsly been rertf carr/filljttt/oH'jttt uttt to 

that even the matt dim emt f&ttw them ■ » ." 

19/6 plna 2/6 post, etc. 




Bradford, 



TRANSISTOR RADIO 

Sold in Dpjsartment Stores at £5.8.0 

OUR 
PRICE 

37/6 

p.&p, 

3/6 

extra 

Well-known brand Transistor Radio Kits 
- YOU SAVE £3.15.6. Covering all medium 
flaag wave with pans including Mullitrdricmi 
Gondlsstonl 48 imgi- instruction manual. 
Knteniilning & educational. No soldering, 
|est PiVg in, making many different Badlos 
ina lew miiis. Money back it not delighted. 




CONCORD ELECTRONICS LTD (Dept. PESO) 9 Western Road, Hove, Sussex 



ASTONISHING CIGARETTE 
RADIO! 

ONLY 1 8.-6 

Yes a perfectly 
ordinary packet ; 
of nigarettes!- 
but it" f etches in i 
station after j 

station, loud and i 
clear! Molds 10 I 
Cigarettes — 
cleverly concf 
highly sensitive, fully transistorised circuit 
[ML tiny battery). Even a young buy c*o 
assemble it in under 2 hours, Mn soldering. 
No eitperien<'e necessary. Only If* i'nnnflc- 
tinns. From our bulging testimonial die, 
Mr. D. B. of liuddcrsHcl.l ivritcs: '■.../ 
hare fitted [he parts in and it is irorkina wonder* 
fulls ..." ALL FAET8 including Semi- 
conductors, A.B.C. Plans, elv. ONLY 18/S 
plus 2/6 post, etc. 




QUALITY RECORD PLAYER AMPLIFIER 

A top-quality record player amplifier. This amplifier 
(which is used in a 29 gn, record player) employs 
heavy duty double wound mains transformer, 
ECC83. EL84, E2B0 valves. Separate Bass. Treble 
and Volume controls. Complete with cutout trans- 
former matched for 3 ohm speaker. Size 7in. w. 
x2*in. d.xS^in.h. Ready built and tebted. PRICE 
69/6. P. & P. 4/9. 

ALSO AVAILABLE mounted on board with out- 
put transformer and 6En. speaker ready to fit 
into cabinet below. PRICE 89,6. P. & P. 5/9. 

OUAL1TY PORTABLE R/P CABINET 

Uncut motor board. Will take above amplifier 
and B.S.R. or GARRARD Auiochangcr or Single 
Record Player Unit. Size IB x Mn3iin, 
PRICE £3/9/6. Carr. 7,6. 

4-SPEED PLAYER UNIT BARGAINS 
All brand new in maker's original packing. 
SINGLE PLAYERS 

B.S.R. TU/12 £3/9/6. , Carr. 56. 

GARRARD SRP10 £5/9/11. Carr.5 6. 

B.S.R. GU7 with unit mounted pickup arm. 

£4/18/8. Carr. S.6. 
AUTO. CHANGERS 

B.S.R, UAI5 £6/19/6. B.S.R. UAI6 £6 19 6 

Latest B.S.R. UA2S Super slim £6 2 6 

Latest GARRARD ATS £8 8 

GARRARD AT6 £10 10 

GARRARD Auto-Slim £6.10.0. Carr. 6 6 on each. 
All the above units are complete with t.'o mono head 
and sapphire styli or can be supplied with compatible 
stereo head for 12 6 extra. 

BRAND NEW CARTRIDGE BARGAINS! 
ACOS7I-5. Single sided Crystal Cartridge for 
Stereo and L.P. records. Complete with diamond 
stylus and universal mounting bracket. List price 
£2.6.4. Our price 18/6. P. & P. I/-. * 
GARRARD GC2 MONO complete. List price 
14/1 I. Our price 12/6. P. & P. 1/-. 
RQNETTE STEREO 10S CARTRIDGE 
Stereo/LP/78 complete with two sapphires. Original 
l ist price 67/9. Our price 24;'.. P. & P. I/-. 

MAINS TRANSFORMERS 

Fully shrouded, can be mounted upright or drop 
through, Tapped pri. I 10, 200, 220. 240v. See. 250v. 
* wave at B5mA and 6-v. 2 amps. c.t. Stack size 
3" X 2i" >. U". PRICE 12/6. P. & P. 3/6. ALSO Semi 
shrouded drop thro' type. Pri. 200, 220. 240v. Sec. 
2S0v. J wave at 70mA and 6 3v, at 2 amp. c;t. Stack 
size 3" ■; 7[" .< U". PRICE 11/ ■ P. & P. 3/-. 

BRAND NEW 3 OHM LOUDSPEAKERS 

Sin,, l2 6;6Ain.. IS'.; 8 in.. 21 '-; 10 in., 25/-; 12 in.. 

27,6; (12 in. "15 ohm, 30/-). 10 in. x 6 in., 26/-. 

E.M.I. 13J x 8 in. with high flux ceramic magnet. 

42;-. {IS ohm, 45/-). 

P. & P. 5 , '2/-.6! , '&8 , '2/6, 10"& 12" 3'6 per speaker. 

41 n HIGH FLUX TWEETER. 

3 ohm and IS ohm imp. Famous British make. Few 

only 12.6. 

ROLA CELESTION. Approx.9 in. x 6 in. 3 ohm. 

Middle register speaker, 10 6. P. & P. 3.-. 

ACOS CRYSTAL MIKES. High imp. For desk 

or hand use. High sensitivity. I8'6. P. & P. 1/6. 

TSL CRYSTAL STICK MIKE. Listed at 45 - 

Ourpr.ce. 186, P. & P. I 6. 

BRAND NEW. 12" ISw. HD Speakers. Current 

production by well-known British maker. Offered 

below list price at 89/6. P.&P. 5,- (25w.guitarmodel 

£5.5.0). 

MATCHED PAIR OF 2'. WATT TRANSISTOR 

DRIVER AND OUTPUT TRANSFORMERS. 

Stack size I '. x I £ x 2 in. Output trans, tapped for 3 

ohm and IS ohm output. 10,- pair plus 2,- P. & P. 

BRAND NEW PLESSEY 12 v. 4 pin non-sync. 

vibrators. Type 12 I.4SD. ONLY 8.6. P. & P. 1/6 

4-WAY NON-TANGLE TELEPHONE CABLE 

Latest spring. back coil type, extends 12 In. to 5 ft. 

Complete with rubber bushes, 4/6 each. P. & P. 1/6, 

VYNAIR AND REX1NE SPEAKER AND 

CABINET FABRICS app. 54 in. wide. Usually 35,- 

yd., our price 13.6 per yd. length {min. I yd.) P. & P. 2/6. 

S.A.E. for samples. 




STEREO AMPLIFIER 

Incorporating 2 ECL82s and I E2B0. heavy duty, 
double wound mains transformer. Output 4 watts 
per channel. Full tone and volume controls. Abso- 
lutely complete. 

ONLY 

£4.19.6 

P, & P. 6/6 

Super De- 
luxe version 
withECLBs 
valves, sep. 
bass & treble controls, full 
Feed back. S gns. P. & P. 6/ 6 

HIGH GAIN 4 TRANSISTOR 
PRINTED CIRCUIT 
AMPLIFIER KIT 
Type TAI 

• Peak 
output in 
excess of 
1 1 watts. 

• All stan- 
dard British 
components. 

• Built on 
printed circuit panel, size 6 X 3in, 

• Generous size Driver and Output Transformers. 
f) Output transformer tapped for 3 ohm and IS 
ohm speakers. • Transistors (GET 1I4 or SI 
Hullard OC8ID and matched pair of OC8I o/p). 

• 9 volt operation. • Everything supplied, 
wire, battery clips, solder, etc. # Comprehen- 
sive easy to follow instructions and circuit diagram 
I/6 (Free with Kit). AH parts sold separately. 
SPECIAL PRICE 45,'-. P. & P. 3 -. Also ready 
built and tested, 52/6. P. & P. 3,'-. A pair of 
TAls are ideal for stereo. 

TAPE DECKS 
B.S.R. MONARDECK (Single speed) 3£in, 
per sec, simple control, uses Si-in, spools, £6/15/- 
plus 7/6 carr. and ins. 

COLLARO STUDIO DECK 3 motors, 3 speeds 
push button control. Up to 7in, spools £10/10/- 
P. & P. 7/6. (Tapes extra on both.) 




10/14 WATT HI-FI AMPLIFIER KIT 

A stylishly fin- 
ished monaural 
amplifier with an 
outputof I4watts 
from 2 ELB4s in 
push-pull. Super 
reproduction of 
both music and 
speech, with neg- 
ligible hum. Sep- 
arate inputs for 
mike and gram 
allow records and 
announcements to follow each other. Fully shrouded 
section wound output transformer to match 
3-tSiJ speaker and 2 independent volume controls, 
and separate bass and treble controls are provided 
giving good lift and cut. Valve line-up 2 ELB4s, 
ECC83, EF86, and EZ80 rectifier. Simple 
instruction booklet 1/6. (Free with parts.) All 
parts sold separately. ONLY £6/l9'6. P. & P. 8/6. 
Also available ready built and tested complete 
with std. input sockets, £8/15/-. P. & P. 8/6. 




3-VALVE AUDIO AMPLIFIER 

MODEL HA34 

Designed for Hi-Fi rcpro* 
duction of records. A.C. 
Mains operation. Ready 
built on plated heavy gauge 
metal chassis, size 7-^in. w* 
x 4in. d. x 4iin, h. Incor- 
porates ECCB3. EL84, EZ80 
valves. Heavy duty, double 
wound mains transformer 
and output transformer matched for 3 ohm speaker, 
separate 'Bass, Treble and volume controls. 
Negative feedback line. Output 4+ watts. Front 
panel can be detached and leads extended for 
remote mounting of controls. 

The HA34 has been specially designed for us and 
our quantity order enables us to offer £A R fl 
them complete with knobs, valves, ***f.J«w 
etc, wired and tested for only P. & P. 6/-. 





HSL'FOUR' AMPLIFIER KIT. 

A.C, Mains 20O.'250v., 4 watt, using ECC83, 

EL84, EZ80 valves, 

•^ Heavy duty double- 
wound mains transformer 
with electrostatic screen. 
-ir Separate Bass, Treble 
and Volume controls, giving 
fully variable boost and cue 
with minimum insertion 
loss. -^t Heavy negative 
feedback loop over 2 stages 
ensures high output at 
excellent quality with very low distortion factor. 
~tc Suitable for use with guitar, microphone or 
record player ^T Provision for remote mounting 
of controls or direct on chassis. "^ Chassis 
size only 7£in, wide x 4in. deep. Overall height 
4J-in. ^c All components and valves are brand 
new, St Very clear and concise instructions enable 
even the inexperienced amateur to construct 
with 100% success. ■+( Supplied complete with 
valves, output transformer (3 ohms only), screened 
lead, wire, nuts, bolts, solder, etc, (No extras Co 
buy.) PRICE 79/6, P. & P. 6/-. 

Comprehensive circuit diagram, practical layout 
and parts list 2/6 (free with kit). 




HARVERSON'S F.M. TUNER Mk. I 



• F.M. tuning 
head by fam- 
ous maker. 

• Guaranteed 
non-drift. • 
Pe rm ea bill ty 
tuning # Fre- 
quency cover- 
age,8B-IOOMc/sl 

• OA8I □-.. 
anced diode output 

• Two I.E. stages and 
discriminator. 9 Attractive maroon and gold dial 
{7 x 3in. glass). #5elf powered, using a good 
quality mains transformer and valve rectifier, 

• Valves used ECC85. two EFSOs, and EZ80 (rec- 
tifier) Fully drilled chassis, • Size of completed 
tuner 8 x 6 x 5-jir., f) All parts sold separately. 
Set of parts if purchased at one time £5/19/6, plus 
8/6 P.P and ins. Circuit diagram and instructions 
1/6 post free. Mark £1 Version as above but 
complete with magic eye, front panel and brackets, 
£6/12/6. P. & P. 8/6. 

Mark 111 Version as Mark I but with output stage 
<ECLB2)»and tone control, £7/7/-. P. & P. 8/6. 
Handsome Metal Cabinets. Choice of Black, or 
Green. To fit Mark 1, 25/-. P. & P, 3 -. To fit Mark 
II, 17/6. P. & P. 3;-. 



HARVERS0N SURPLUS CO. LTD. 

170 HIGH ST., MERT0N, S.W.I 9. CHErrywood 3985 



Open all day Saturday 



Early closing Wed., I p.m. 



A few minutes from South Wimbledon Tube Station. (Please write clearly) 

OVERSEAS P. & P. CHARGED EXTRA, S.A.E. with all enquiries. 



SPECIAL PURCHASE 

TURRET TUNERS 
By famous maker. Brand 
new and unused. Complete 
with PCCB4 and PCF80 
valves. 34-38 Mc/s t.F. Bis- 
cuits for Channels I to S and 
8 and 9. Circuit diagram 
supplied. ONLY 25/- each. 
P. & P. 3/9. 



749 




Essential books for the 
serious enthusiast 

RADIO ENGINEERING 
FORMULAE AND 
CALCULATIONS 

by W. £. Pannett 

Problems in radio, radar and television engineering are usually presented 
either in the form of examination questions and answers, omitting many 
intermediate steps, or are framed solely for the instruction of the 
student. In this book, examples have been selected from everyday 
practice in design, installation and operation and are shown fully worked 
and generously illustrated. Although it is intended primarily for the 
practising engineer, it will be found equally valuable to the technical 
assistant and the student about to embark on an engineering career. 

Covers I. Aids to Engineering Ca k u fa tions— 2. Formulae and Examples: Resistors and Voltage 
Dividers — Inductors— Capacitors — A.C. Applications of Ohm's Low— Circuit Theorems- 
Gains and losses Electrical Tofe ranees — Frequency and Wavelength — Resonant Circuits — 
Coupled Circuits Attenuators and Filters — Thermionic Amplifiers — Amplifier Noise — Receivers 
- ■Oscillators — Transmitters— Sig nail ing and Modulation- Valve Cooling- and Ventilation- 
Aerials and Propagation— Radio-frequency, Transmission Lines — Power Supply — A.C. Rectifiers and 
SmoothingFilters — Transformers and Reactors — Cables, and Lines — Tests and Measurements — 
Transistors— Principles f Television — Radar Fundamentals — Great Circle Searings— 3. Unit and 
Symbols — 4. Mathematical Formulae, Data and Tables Index, 

208 pages 163 figures 17s. 6d. (19s. by post) 
« PRACTICAL WIRELESS" 

RADIO AND TELEVISION 
REFERENCE DATA 

compiled by J. P. Hawker 

This handy book provides the practical reference data that radio and 
television servicemen, radio constructors, enthusiasts arid amateurs 
always need. It has been compiled with the day-to-day requirements of 
servicemen particularly in mind. 

Contents include: full details of colour codes; a comprehensive collection ofpracticol, everyday 
formulae for calculating the values of biasing components, potential dividers, etc.; aerial 
dimensions; a quick frequency-wnve/engtb conversion toble; fall lists of radio and television 
broadcasting stations and frequencies; common symbols and abbreviations; notes on Amateur 
radio and a list of catl-sign prefixes; communication receiver I.F.s; mathematical data including 
logarithm tables; wire and cable data; battery cquiVa/ents; and a full and up-to-date listing of 
valve, transistor and cathode-ray tube pin connections, bases, ratings and equivalents, including 
selected CV types. .6 



36 pages 62 pages of tables 



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POCKET BOOK 



750 



edited by J. P. Hawker and J. A, Redd though 

Fully covers. ., FUNDAMENTALS: Behaviour of Electrons in Electric and Magnetic Fields— 
M^ki 5 ™" Electrons— Conduction and Current— Voltage Relationships. CIRCUIT ELE- 
MENTS: Diodes— Thermionic Triodes- Tetrodes and Pentodes— Thyratrons— The Transistor - 
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l^VJ^l'xiV.U ^,. r ^S"' U 1 eor £ ' ements - Photo-Electric Cells— Transducers. ELECTRO- 
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pmbtucb ?i crTDnMir^nl ^'1^ Generators-Wide-Range Pulse Generators. 
FURTHER ELECTRONIC CIRCUITS: Electronic Switching- Diode Clomps -Phase-Sensitive 
Detectors— Pulse Modulation. COUNTING DEVICES AND CIRCUITS: Counting Circuits— 
Radiation Detectors POWER SUPPLIES: A.C. Rectification- Rectifier .Circuits— Ripple 
Reduction— Voltage Regulation— D.C. Converters. THE MAGNETIC AMPLIFIER ELEC- 
TRONIC MEASUREMENT AND TEST GEAR. INDUSTWAL ELECTRONIC CONTROL 
ELECTRONIC COMPUTERS. INSTALLATION AND MAINTENANCEUNITS 

294 pages 205 diagrams 21s. (22s. 6d. by post) 

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BEGINNER'S GUIDE TO 
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by Terence L. Squires 

This book provides a "short-cut" for those wishing to obtain a quick acqaint 
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theory and calculations: what it does is to describe as simply as 
possible the basic concepts of importance in electronic engineering, 
and the various components used in electronic equipment, so that the 
reader gains an understanding of the terms used and the practical side 
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The book will enable the reader to go on to more specialised 
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Contents: Electric Currents — Direct and Alternating Currents — Electronic Components .- 

■ — Basic Electronic Circuits — Test Instruments — Radar — Medico/ Eiectronics — 
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192 pages 128 diagrams 15s. (17s. by post) 

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ENGINEERING MATERIALS AND DESIGN ^ - 1 

HIGH FIDELITY SOUND 
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edited by £. Molioy 

The high quality reproduction of disc and magnetic tape recordings and 

of radio programmes has made remarkable strides in the past decade. 

The introduction of long-playing gramophone records, V.H.F./'F.M. broadcasts 

and the availability of first-rate amplifiers, loudspeakers and pickups have 

all created a growing interest in the faithful reproduction of music in the 

home. The aim of this book is to bring together authoritative and 

balanced information on the technique of Hi-Fi in terms that will be 

readily understood. 

Contents; Introduction — Subjective and Objective judgement of Performance — The 
Acoustics of Sound Reproduction— Multiple Channel Systems Amplifiers and Pre-Amplifiers — 
Dynamic Loudspeakers — Loudspeaker Enclosures — Electrostatic Loudspeakers — Record Repro- 
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751 



BSfMaraiiEaa 




E^ntvc vmir communiration nrobteisiB ivilh this latest 
4- STATION TRANSISTOR INTERCOM Byetein (1 
MASTER and IS HUBS), in de-luxe silastic: cabinets fur 
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operates to call when switched oil, thus saves battery. 
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Ou/off switch. Volume uonlrol, 2]ln, dynamic 
e u takers. Full y t r 1 1 1 ufa to r i i e il to 1 ast tor yea ra. ideally 
suitable to modernize; Ollioe, Factory, Workshop, Ware- 
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Unless you put your X between the two O r s the 
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April !2th H ** I'm glad I wasn't playing it for 
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at 3d a go, refunded lor a drawn game, raised £3 
*n three hours for charity. Full circuit, wiring 
diagram, instructions for this fabulous unbeat- 
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PLANET INSTRUMENT CO. 

25 DOMINION AVE., LEEDS 7 



BBC2 (625 LINE) TV AERIALS 




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BATTERY ELIMINATOR & CHARGER Price 27/6 

r*e your TRANSISTOR RADIO or INTERCOM from 
domestic A.C. mains. Mid charge dry battery PP3 
or 006P 9 volts thus boost battery's life many time,=. 
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P. & P. 2/6. Complete with Plug, Lead and Snap cord. 
Full price refunded if not saiislied in seven days, 
WEST LONDON DIRECT SUPPLIES (PE/11) 
6 Chignel! Place, West Ealing, London, W.13 



BATTERY ELIMINATORS 

The idea) way of running your TRANSISTOR 
RADIO, RECORD PLAYER, TAPE RECORDER, 
AMPLIFIER, etc. Types available: 9v; 6v: 4jv 
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9v + 9v; 6v + 6v: or 4Jv + 4iv (two separate 
outputs) 42/6 each. P. & P. 2/9. Please state 
output required. All the above units are 
completely isolated from mains by double 
wound transformer ensuring 100% safety. 

R.C.S. PRODUCTS (RADIO) LTD. 
(Dept, P.E.), II Oliver Road, London, E. 17 



DUKE & CO 


. (LONDON] LTD 


# 


621/3 


Romford 


Rd., Manor Park, £.12 


ILFord 


oQOt-2-3 


Stamp for lis! 




T,V. 


TUBES 




I7in.- 


35/- 


I4in.- 


15/- 


Most makes and types available. Set 
Guaranteed good picture. Ex Rental 
Depts. Stock. Carriage 5 
RESISTANCES 10/- per 100. Brand new 
High Stabs. Assorted parcels. P. & P. 2;-. 


Tested. 
Service 
'- extra 
mostly 



■\ 



MAST MOUNTING ARRAYS, 9 clement 
45/-; wide spaced high gain, 1 1 element 55/-; 
14 element 62/6. WALL MOUNTING 
WITH CRANKED ARM, 9 element 60/-; 
wide spaced high gain, II element 67/6; 14 
element 75/-. CHIMNEY ARRAYS COM- 
PLETE, 9 element 72/-; wide spaced high 
gain, I I element (JO/-; 14 element 87/6. LOFT 
ARRAYS, 7 element 32/6; wide spaced high 
gain, II element, WITH TILTING ARM 
62/6; 14 element 70/-. ALL HIGH GAIN 
UNITS HAVE SPECIAL MULTI-ROD 
REFLECTOR. LOW LOSS CO-AXIAL 
CABLE 1/6 yd. VHF transistor pre-amps 
from 75/-. 

BBC * ITV * F.M. AERIALS 

B.B.C, (BAND ». Tele- 
scopic loft 21/-. External 
S/D 30/-. 

I.T.V, (BAND 3). 3 Ele- 
ment loft array 25/-. 5 
element 35/-, Wall mount- 
ing. 3 element 35/-. S 

element 45/-. 

COMBINED B.B.C. I.T.V. 
Loft 1+3, 4li3; I +5. 48/9. 
Wall mounting 1+3, 56/3; 
I +5, 63/9. Chimney 1 +3, 
63/9: 1+5,71/3. 

VHF transistor pre-amps from 75/-. 
F.M. (BAND 2>. Loft S/D, 12/6. "H". 
30/-. 3 element, 52/6, External units 
available. Co-ax. cable 8d. yd, Co-ax. 
plugs, 1/3, Outlet boxes, 4/6. Diplexer 
Crossover Boxes 12/6. C.W.O. or C.O.D. 
P. & P. 3/6. Send 6d. stamps for illustrated 
lists. 

K.V.A. ELECTRONICS (Dept. 2) 

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CRO 2527 




Advertisers' Announcement 

Readers will be glad to know that catalogue 

transistors suitable for use in the circuits 

discussed in this issue are: 



ARTICLE 
Low Voltage 

Battery Pack 
Simple Analogue 

Computer 


POSITION 
TR1&TR2 


NKT TYPE NO. LIST PRICE 

NKTZ72 8- 

NKT 272 67- 

Postage Extra 



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EASTERN AERO ELECTRICAL SERVICES LTD 

BUILDING 424, EASTERN PERIMETER ROAD 

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LTD, 10 KING STREET MEWS, BELFAST 1, 

JAMES SCOTT (Electronic Agencies) LTD 
90 WEST CAMPBELL STREET, GLASGOW C2. 

S.D.S. (Portsmouth) LTD, 67/60 COMMERCIAL 
ROAD, PORTSMOUTH, HANTS. 



752 



Now in its I ith Revised edition . . . 

ELECTRICAL 
ENGINEER'S 
REFERENCE BOOK 

A revised edition of this comprehensive thirty-three 
section standard reference work covering all branches 
of electrical engineering. New and thoroughly re- 
vised sections include materials ; cables and wires ; 
wiring and installation ; applied electronics ; instru- 
ments and measurements, etc References are also 
made to many new aspects including germanium and 
silicon ; printed circuits ; transformer windings and 
design ; electronic motor control ; cold-cathode 
lighting, etc. The "Progress" section is again 
entirely new and includes an authoritative survey of 
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2,212 pages, 2,096 diagrams, over 300 photographs, 
76 specialist contributors, 33 sections, I Ith Edition. 120s. 

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FULLY DETAILED AND ILLUSTRATED 

CATALOGU E 

Over 90 big pages. The largest PRICE 
range available in the country. 2/6 

All types of components and (post paid) 
equipment at competitive prices. 



PROVED and TESTED DESIGNS 

FULL AFTER SALES SERVICE AND GUARANTEE 

• CALL IN FOR DEMONSTRATIONS * 

DETAILED LEAFLETS FREE ON REQUEST 






MW/LW POCKET SUPERHET RADIO 

TOTAL COST 

TO BUILD 

85/- p £ 

(Battery 2/6 
Phone 5/-) 

•if All parts sold 
separately, 
if 6-Transistor design. Push-pull output 
if 2|in. Cleartone speaker. Printed circuit, 
■jf Attractive moulded cabinet, 
if Slow motion tuning. 
T#T Full med. and long waves. 
•k Size: 5 X 3 x liin. 
•AMAZING SENSITIVITY & SELECTIVITY* 



Prebuilt and 
tested units. 
Low distor- 
tion, low 
noise 



if 6-Transistor push-pull design. 
if Uses factory built panels, 
if Permeability geared tuning, 
-jfc- Full med. /long wave tuning with push- 
button wave change. 
if Double tuned IFT's. 
■if Chromed front panel plate. 
if Size: 7 x 4 x 2in. Fits any car. 
if Pre-built units sold separately. 

TOTAL 
COST TO 

BUILD 



£8.l9.fi« 




(7in. x 4in. speaker with car fixing kit and 
baffle board 20/- extra). 

TWO WAVEBAND ALL TRANSISTOR 

CAR RADIO TO ASSEMBLE 
• HIGH PERFORMANCE SUPERHET* 



RECORDERS 



2- AND 4-TRAGK TAPE 
TO ASSEMBLE 
Pre-built 

Equipment — 6 

Valves — Collaro 

Studio Decks — 
Portable Cabinets 

with Speakers. 
Complete record 

and playback. 

* 2-track deck 10 gns. P.P. 5/-. Amplifier 

1 1 gns. Cabinet with speaker S gns. 
OR SPECIAL PRICE P.P. TWO 

tfiO 8/6 TRACK 
ir 4-track deck £13. 19.6, P.P. 5/-. Amplifier 

12 ens. Cabinet with speaker 5 gns, 
OR SPECIAL PRICE fqn PP. FOUR 

Ml 8 ' 6 TRACK 




10 Watt & 20 Watt HI-FI AMPLIFIERS 




UNITS 




• POWER AMPLIFIERS. 10 

watts R.M.S. music power, 20 
watts peak. 6-Transistor design. 
Panel size 4 X 2j X Jin. Response 
40 c/s to 20 kefs, lOOmV into 
33 Kohm input, 

UNIT I. For 12/15 ohm 
speakers. PRlrp . p p 

«X !Klt£5.I9.6 p jS 

UNIT 2. For 3 to 5 ohm 

speakers, poire bp 

SB** EnS£5.io/i5 

it MAINS UNITS. 59/6. To 
power one amplifier or 69/6 to power 
two amplifiers (State 24 or 40 volt 
version). 

PREAMPLIFIERS. Mono and stereo 
versions, 8 inputs, 1$ to 300mV at Ik 
to 500k. Response 30 c/s to 20 kc/s. 
Complete range of controls. Mains 
unit or battery operated. For pickups, 
tuners, tape, microphones, etc. 
UNIT 3. Mono full-function pre- 
amplifier. Size: 9$ x 2| x 2in. 
PRtCEfr , n n P.P. (Brown/Gold front 
BUILTt3. 1 U.U 21- panel plate 8/6) 
UNIT 4. Simplified version of Unit 3. 
Price 45/.. P.P. 1/6. Panel plate 6/6. 
UNIT S. Stereo preamplifier for 
usi with two units I or 2. Size 
9 a 3i X l{in. 



THE FINEST QUALITY HI-FI 
AT UNBEATABLE PRICES 

TRANSISTOR 

PORTABLE 

TEST 

EQUIPMENT 

All units size 
H X 4f X 2*in. 
if RF generator, 
150 kc's to 350 
mc/s in 8 ranres. 
RF, Mod. RF, 
AF outputs, 
PRICE £9.10.0 P.P. 2/6 
-if Kesistar.ee/capacitance bridge. £8.5.0. 

P.P. 2/6 
if Audio generator 10 c/s — 100 kc/s. 4 
ranges. £16.15.0. P.P. 2/6 



PRICE 
BUILT 
(Front panel plate 



1 1 0.19.6 P.p. 3/6 
12/6) 




We stock: 

TRANSISTORS 

RECTIFIERS 

VALVES 

CRYSTALS 

MICROPHONES 

TEST GEAR 

TAPE DECKS 

SPEAKERS 

MULTI-METERS 

RADIO 

CONTROL 

AMPLIFIERS 

RECORDERS 

TUNERS 

RECORD DECKS 

TWEETERS 

RECEIVER5 

GENERATORS 

COMPONENTS 

AND 
ACCESSORIES 



SINCLAIR 
DESIGNS 

if Micro-6MW/ 

radio 59/6 
*TR750 "Addon" 

power amp. 39/6 
+ Micro injector 

27/6 
•if Micro amp, 28/6 
■A-XIOAmp. kit 

£5.19.6 
BUILT £6.19.6 




4 WATT AND 1^ WATT 
PACKAGED AMPLIFIERS 
•ff 6-Transistor push- 
pull printed cir 

cuit designs 
if Size only 2± X 

2 X liin. 
* 4 watt 12/18 

volt, 4 watt 

9 12 volt 
if For 3 to 5 ohm 

speakers 
•^ 7mV into I 

Kohm. 40 c/s 

to 15 kc/s 
PRICES, i n - , P.p., „„ ,„ p p 
BUILT IjjW. 65/- 1/6%. 79/6 1/6 




4-CHANNEL MICROPHONE 
MIXER 

Transistorised, 4! 
inputs up to 1 00 1 
Kohm. Full mixing. 
PRICE . n/c P.P. 
49/6 1/6 




VALUE FOR MONEY DESIGNS 



'■'{ ->,-v-; 




''m| 



VHF FM 

TUNER 

TO 

ASSEMBLE 

if Two pre- 
built units 
plus metal 
work and front panel 
if Siie: 9i x 3± x 4in Total Cost 

if 88 to 108 mc/s tuning £12.17.6 

if 1 00m V to lOOKohm cutout P.P. 2 6 

■jfc 6-Transistor printed cct. superhet design 
(All units available separately) 



TWO WAVE BAND PUSH-BUTTON 

TRANSISTOR PORTABLE TO BUILD 

TCTAL 

COST 

£7.19.6 "« 

(Batteries 

6/- 

*5in. 
speaker 

if 6-Transis- 
tor push- 
pull design 

if Easy to follow printed circuit 

if 8in, ferrite aerial. D/T IFT's 

if Push button wave change 

if Geared tuning. Full Med./LW 

if Attractive sturdy cabinet with 
Size: 10 x 7 x 3iin. 




handle. 



SENSITIVE SUPERHET RADIO 



Let us quote for parts for your circuit. 

Send a list for quick reply. Quality 

components at realistic prices 



VHF.FM TRANSISTOR TUNER TO BUILD 
TOTAL 
COST 

£6.19,6 

P.P. 2/6 (com- 
plete with 

frontplate 
(Gold sprayed 
cabinet 20/- 
extra). 

if 5-Transistor 4 diodes 

■jfc- Printed circuit superhet 

T*r Geared tuning 87 to 105 mc/s FM 

if RF stage and double tuned IFT's 

■*■ Output up to 1 volt peak up to 100 Kohm 

if 9 volt 9mA supply^ 

if Size in cabinet 4 X 3£ X 2$in. 

if All parts sold separately 




HENRY'S RADIO LTD. 

303 EDG WARE RD., LONDON W2 

PADdington 1008/9 

Open Mon. to Sat. 9-6. Thurs. I p.m. ' 

Open all day Saturday