THERadio ConstructorAUDIO ELECTRONICS

VOLUME 15 NUMBER 2 A DATA PUBLICATION PRICE TWO SHILLINGS

September1961

The JR1 Stereo Tape Recorder U n it - design details Pocket Audio Injection Probe Unusual 2 -Valve Superhet Pre- , Attenuators and Mixers Shorted Turns Tester Magnetic Guitar Pick-up and Transistorised Tone Control Pre -amplifiers The "Finger -Tip Five" Receiver Understanding Radio, Pt. 2 Resistance Measurement HARVERSON SURPLUS CO. LTD

2 -BAND SUPERHET CHASSIS 4 -STATION PRESET CHASSIS WITH SPEAKER ONLY £5.17.6 ONLY £4.17.6 WITH SPEAKER Plus 6/6 post and packing PI us 6/6 post and packing

A compact, 4 station preset mains transport- able receiver, for operationfrom AC/DC mains. Two simple con- trols, volume on/off and 4 posi- tion stationse- lector. The latter issettoLight programme (Long wave), Third programme, Home service and Light programme (Medium wave), but may of course be A quality 4 valve AC/DC superhet chassis made by a world adjusted to alternative selections if required. A frame aerial famous manufacturer. Long and Medium wave coverage. with throw -out extension is supplied, making this receiver Fitted with a cord and drum reduction tuning drive and ideal as a general purpose transportable set for the home. A attractive illuminated glass dial (size 6+" x 24").Controls: fully smoothed power supply is provided from AC/DC mains volume on/off, tuning and wave change. The receiver is self - input by a mains dropper and a valve . The good tonal powered, employing a mains dropper and a valve rectifier. qualities are assisted by the provision of a quality 5" speaker, Chassis dimensions 64" x 9" x 54" high.Supplied complete which is ready -mounted on the chassis (this is easily detachable with a good quality 5" loudspeaker, valves (UCH42, UAF42, if alternative positioning is required). Valve line-up: UCH42, UL41, UY41), AC/DC mains input lead,ivory knobs, etc. UAF42, UL41, UV41. This chassis (size 9" x 64" x 54" high) Don't hesitate, Order Now 1This unbeatable bargain is supplied complete with valves, knobs, mains lead, aerial, is bound to sell out quickly at on y ES.17.6, plus 6/6 etc.It is beautifully made by a famous maker, and is a first- post and packing. class buy at the rock bottom price of E4.17.6. RAM CHASSIS OUTPUT STAGE AND SPEAKER HARVERSON'S FOR FM TUNER UNIT Allparts including speaker, ECL82 valve and FM TUNER KIT simple instructions to make two -stage output unit, for converting f.m. tuner into f.m. receiver. ONLY 45/. plus 4/6 P. & P.

E.M.I. 4 -SPEED RECORD A chassisof distinctionbya famous TURNTABLE AND PICK-UP maker. Covering Long, Med. and Short Heavy 84" metal turntable. waves, plus gram position, thischassis Lowflutter performance, (size 154" x 7" x 64" high) incorporates 200/250V shaded motor the latest circuitry, using fully delayed with tapat80Vfor a.v.c. and negative feedback.Controls: valve filament At last a quality FM Tuner Kit at a price tone, volume on/off, wave -change (L.M.S. ifrequired. Turnover you can afford.Just look at these fine and gram), tuning.Tapped input 200- LP/78 head. features,whichareusuallyassociated 250V a.c. only. An attractive brown and with equipment at twice the price! gold illuminated dial with matching knobs 89/6 COMPLETE * FM tuning head by famous maker. make this one of the most handsome, in P us 4/6 P. & P. * Guaranteed non -drift. * Permeability addition to being one of the best per- tuning. * Frequency coverage 88-100 forming, chassis yet offered.Complete Mc/s. * OAB1 balanced output. with valves (ECH81, EF89, EBC81, EL84, * Twoi.f.stages anddiscriminator. EZ81), knobs, output transformer, leads, SUPER STEREO KIT MARK II * Attractive maroon and gold glass dial etc. OUR PRICE ONLY A A kit of ready -built units only requiring inter- (7" x 3"). * Self powered, using a good plus 4/6 post & packing £9. 19.67.0 connection.Comprising two midget 3W ampli- qualitymainstransformerandvalve fiers,push-button switch, transformer, control rectifier. * Valves used ECC85, two THE WORLD FAMOUS E.M.I. ANGEL unit (bass,treble andvol.), power pack, two EF8Os andEZ80(rectifier).* Fully speakers,indicator light,valves (ECL82, EZ80 drilled chassis. * Everything supplied, TRANSCRIPTION P.U. (Model I7A) range), and comprehensive instructions. down to the last nut and bolt. * Size of completed tuner 8" x 6" x 54". * All P& p/6 parts sold separately. Plus86 f4. I 9.6 P.P.&Ins. FM TUNER HEAD Circuitdiagramandillustrations,1/6 A permeability tuned tuner post free. head by a famous maker, supplied without valve WESTERN ELECTRIC (ECC85). A Pick-up for the connoisseur originally TRANSISTOR SPEAKER plus 1/9 Size 24" x 14" deep.3 ohm impedance. priced at C17.10.0. The last remaining few 18/6 P.& P. offered at 11/9 P. & P. 1/6 £4.10.0 Plus P. & Valve 8/6 extra Please turn page for valve 83 High St. Merton SWI9 cH3r9757:0d1 Bargains .411,411P-OKINO,15.11,11,.. AT z PRICE WHILE THEY LAST! Introducing HARVERSON'S 39/6 GOLDRING MU -METAL CASED CARTRIDGES Monaural Amplifier Kit Sapphire styli. Brand new and boxed In response to numerous requests from delighted purchasersofour "SUPER OUR PRICE L2.15.0 Plus P.P. 1/6 inc. ins. STEREO KIT"we have produced a "MONAURAL AMPLIFIER" onsimilar lines. * A UCL82 valveprovidesa amplifying stage, and a pentode output BARGAIN MONTH FOR stage (: watts), enabling good amplifica- tion and sparkling reproduction to be POWER GET102 7/6 combined withphysical compactness 0C36 10/- XA103 8/6 0C44 9/- PXA101 (amplifier size 7" x 3+" x 64" high). 9/6 * Modern circuitry design, good quality 0C45 8/- PXA102 9/6 o.p.transformer (tomatch 3Q) keep 0071 5/- 0075 6/6 AMERICAN hum and to a low level. 2N388 6/6 * The controls, volume on/off and tone, 0076 6/6 0078 6/6 2N1485 6/6 are complete with attractive cream and 25712 7/6 gold knobs. OC78D 6/6 GET15 * The amplifierhas a built-infully 9/- smoothed power supply, using a good GET15 (matched pair) 16/6 0A81 3/- qualitymainstransformer(a.c.mains Postage 6d. each only) and metal rectifier. * All you needissuppliedincluding easy to follow instructions which guar- antee good results for the beginner and expert.All components, leads,chassis, THE HARVERSON COMPLETE valve, knobs, etc., are first grade items by prominent manufacturers. FM/VHF RECEIVER KIT .19.6 OUR PRICE Plus 4/6 Post and Packing39/6 At last! A complete FM Receiver inkit form. 5" LOUDSPEAKER TO SUIT, 14/6 EXTRA Specially designed with the home constructor in mind, this kit CHILD'S NURSERY LAMP enables the construction of a com- A child's night light of unusual design. Contemporary styled lampholder of pletely self-contained VHF receiver robust construction finished in either red at a fraction of the normal cost of or yellow. Entirelysafe(bulb socket comparableequipment. Thisis shielded from "prying fingers",) complete withflexand a push-buttonswitch. basically a quality self -powered FM 200/250 voltsa.c.only.The low -con- tuner plus 2 audio amplifier stages sumption bulb elementis made in the and output transformer & speaker. shape of either flowers or angel fish, and when switched on, glows in fluorescent * FM tuning head by famous maker colours(the flowerspink with green leaves,or thefishgreen with purple * Guaranteed non -drift weed). Made by a famous manufacturer * Permeability tuning and originally priced at 29/6. Please state lampholder colour preference * Frequency coverage 88-100 Mr/s and whetherfishorflowerelementis required. * 0A81 balanced diode output OUR BARGAIN PRICE ONLY 10/9 plus 9d. post and packing * Two i.f. stages and discriminator * Self -powered, using a good quality mains transformer and SUPERHET CHASSIS - LESS VALVES & CABINET valve rectifier Modern AC/DC chassis with printed circuit and ferrite rod aerial. * Valves used: ECC85, two EF8Os Although not completely built, the main components are mounted. and EZ80 (rectifier) L. & M. wave coverage, 4 valves (UBF89, UCL83, UCH81, UY85). Everything supplied except valves andcabinet. With simple * Fully drilled chassis instructions. L3.6.6 fp'l.131/.6 * A good quality speaker * Welldesignedoutputtrans- TRANSISTOR AMPLIFIER KIT former A complete kit of parts to build a compact 4 -transistor amplifier, * Attractivemaroonand gold with tone and volume controls.Two GT3 driver transistors, glass dial transformer coupled. Output 1 watt from matched pair GT15. * Two output stages (using ECL82 Complete with output transformer to matched 3 ohm speaker, valve) transistors and attractive dial plate. OUR PRICE 59/6 P. & P.4/6 * Everything supplied, down to the last nut and bolt CONDENSER/RESISTOR PARCEL * Compact size 50 mixed pF Condensers and 50 mixed Resistors. An assortment * All parts sold separately of usefulvalues. Allpopular sizes-all new-a must for the serviceman and constructor. 4/6 P. & P. 1/- ONLYI °h OUR PRICE 16.19.6P.& usP..

SEPTEMBER1961 81 HARVERSON SURPLUS CO. LTD * HARVERSONS UNEQUALLED VALVE SERVICE *

0A2 17/66F6G 7/-10F1 26/635Z4GT 6/-DH76 5/- EF40 15/-H N309 24/7 P L84 12/8UABC80 9/-XFY34 17/6 OB2 17/6 6F11 17/310F9 11/635Z5GT 9/-DH77 7/- EF41 9/-HVR2 20/- PL820 18/8UAF42 9/6X H(1.5)6/6 OZ4 5/-6F12 4/61OLD1115/11 43 10/-DK32 12/-EF42 10/6HVR2A 6/- PM84 17/7UB41 12/-X5G(1.5) 6/6 1A5 6/-6F13 11/610P13 15/-5005 10/-DK91 6/6 EF50(A) 7/-KF35 8/6 PX4 10/6UBC41 8/6Y63 7/6 1A7GT 12/-6F15 15/310P14 19/350CD6G DK92 9/- EF50(E)5/-KL35 8/6 PY31 16/7UBC81 11/4 Z63 7/6 1 C5 12/6 6F23 10/612A6 5/- 36/6DK96 8/6 EF54 5/-KLL32 24/7 PY32 12/6UBF80 9/-Z66 17/6 1D6 10/66F24 12/612AC6 15/350L6GT 9/6DL33 9/6 EF73 10/6KT2 PY80 7/6 U BF89 9/6Z77 4/6 1G6 17/66F32 10/612AD6 17/353KU 19/11 DL66 17/6 EF80 6/-KT33C 10/- PY81 8/6U BL2123/3Z719 6/- 1 H5GT 10/66F33 7/612AE6 13/1177 8/-DL68 15/- EF85 6/-KT3629/10PY82 7/-UCC84 14/7 1 L4 3/66G6 6/612AH7 8/-78 6/6DL72 15/- EF86 10/6KT41 23/3 PY83 8/6UCC85 9/-Transistors 1 LD5 5/-6H6 3/-12AHB 12/6 80 9/-DL92 7/- EF89 9/-KT44 12/6PY88 13/3UCF80 16/7and 1 LN5 5/-6J5 5/-12AT6 7/6 83 15/-DL94 7/6 EF91 4/6KT61 12/6PZ30 19/11 UCH21 23/3CG1C 7/6 1 N5GT 10/6 616 5/612AT7 6/-85A2 16/-DL96 8/6 EF92 4/6KT63 7/- Q P21 7/-UCH42 9/6 CG4E 7/6 1 R5 6/6617G 6/-12AU6 23/390AG 67/6DM70 7/6 EF97 13/3KT66 15/-QP25 14/6UCH81 9/6CG6E 7/6 154 9/-617GT 10/612AU7 6/690AV 67/6 E8OF 30/- EF98 13/3KT88 24/-QS150/15 UCL82 11/6 CG7E 7/6 155 6/-6K7G 5/-12AV612/890C1 16/- E83F 30/- EF183 18/7KTW61 6/6 10/6UCL83 19/3 CG10E 7/6 1T4 3/66K7GT6/-12AX7 7/690CG 37/6EA50 2/- EF184 12/6KTW62 7/6 R12 9/- U F41 9/-GD3, 4, 5, 1 U5 6/-6K8GT 10/612BA6 8/- 101 13/6EA76 9/6 E K32 8/6KTW63 6/6 R18 14/-UF42 12/6 6, 8 4/- 2021 15/-6K8G 6/6128E6 9/-15082 18/-EABC80 9/- EL32 5/-KTZ41 8/-..R19 19/11 U F80 10/60A70 3/- 2P 26/66K25 19/11 128H7 21/3 161 10/6EAC91 4/6 EL33 12/6KTZ63 7/6 RG1 /240A U F85 9/-0A73 3/- 2X2 4/6 6L1 23/3 12E1 30/-185BT33/2EAF42 9/- EL34 15/-L63 6- 54 -UF86 17/11 0A79 3/- 3A4 6/-6L6G 8/-1215GT4/6 304 10/6EB34 2/6 EL38 26/6M HL4 7//6 RK34 7//6 U F89 9/-0A81 3/- 3A5 10/66L6M 9/61217GT9/6 305 10/6 EB41 8/6 EL41 9/-MHLD6 12/6 5130 22/6 U L41 9/-0A86 4/- 3B7 12/66L7GT 7/612K5 17/11 807 7/6 E891 4/- EL42 10/6 M L4 8/6 SP4(7) 14/6U L44 26/6 0A91 3/6 306 5/-6L18 13/-12K7GT 5/6 956 3/-EBC3 23/3 EL81 16/7MS4B 23/3 SP41 3/6 U L46 14/60A95 3/6 3Q4 7/66L19 23/312K8GT14/- 1821 16/7 EBC33 5/-EL83 19/11 MU12/14 8/- SP42 12/6UL84 8/60A210 11/- 3Q5GT9/66LD20 15/1112Q7GT 5/- 4033L 12/6 EBC41 8/6 E L84 7/6N37 23/3 SP61 3/6UM4 17/30A211 20/- 3S4 7/-6N7 8/-125A7 8/65763 12/6 E BC81 EL85 13/11 N78 19/11 SU25 26/6UM34 17/30C1648/- 3V4 7/66P26 19/11 12SC7 8/67193 5/- E BF80 9/- E L86 17/3 N108 23/3T41 9/- UM80 15/30C19 48/- 5R4GY 17/66P28 26/6125G7 7/-7475 7/6 EBF83 13/11 EL91 5/- N308 20/7TDD412/6 URIC 18/70C23 87/- 5U4G 6/66Q7G 6/612SH7 8/69002 5/6 EBF89 9/6 E L95 10/6 N339 15/-TH41 26/6UU6 19/11 0C26 25/- 5V4G 10/-6Q7GT 11 /-12517 8/6AC/PEN EBL1 29/6 EL820 18/7 P61 3/6TH23333/2 UU7 16/7 0C28 25/- 5Y3 6/66R7G 10/-125K7 6/- 5 -pin 23/3 EBL21 23/3 EL822 19/-PA BC80 TP22 15/-UU8 26/60C35 25/6 5Z3 19/11 6SA7GT 8/612SQ711/6 7 -pin 15/- EBL31 23/3EM34 9/6 13/11 TP25 15/-UU9 7/60C44 5Z4G 9/-6SC7 7/6125R7 8/6AC2PEN EC52 5/6 EM71 23/3 PCC84 8/-TP2620 33/2 U Y1 N 18/70C45 10/- 6A7 10/66SG7GT 8/-12Y4 10/6 DD 12/6EC54 6/-EM80 9/- PCC85 9/6TY86F13/3 UY21 16/70065 22/6 6A8 9/-6SH7GT 8/- 1457 27/10AC6PEN 7/6 EC70 12/6 E M81 9/-PCC88 18/-U12/148/6 UY41 7/6006625/- 6AC7 4/-6517GT8/-19AQ5 10/6AC/TP 33/2 EC92 13/3 EM84 10/6PCC89 11/6U16 10/6 UY85 7/-0070 6/6 6AG5 5/665K7GT 6/- 19H1 10/-AT P4 5/-ECC32 5/6EM85 17/3PCF80 8/-U18/20 8/6VMP4G 15/-0071 6/6 6AG7 7/66SL7GT 6/6 20D1 15/3AZ1 18/7ECC33 8/6EN31 53/- PCF8210/6U19 36/-VMS4B 15/-0072 8/- 6AK5 8/-6SN7GT 5/6 20F2 26/6AZ31 10/-ECC34 24/7EY51 9/-PCF8416/7U22 8/-VP2 12/6007316/- 6AL5 41- 6SQ7GT 9/- 20 L1 26/6AZ4113/11 ECC35 8/6EY83 16/7PCF8615/-U24 29/10VP4 15/-0075 8/- 6AM5 4/6 6SS7GT 8/-20P1 26/6 B36 15/-ECC40 23/3EY84 14/-PCL8210/-U25 17/11 VP2B 14/6007715/- 6AQ5 7/6 6U4GT 12/620P3 23/3 BL63 7/6ECC81 6/-EY86 9/-PCL8310/-U26 10/-VP4B 23/30078 8/- 6AT6 7/-6U5G 7/620P4 26/6 C1 12/6ECC82 6/6 EZ35 6/-PCL8412/6 U31 9/6VP13C 7/-0081 8/- 6AU6 10/-6U7G 8/6 20 P5 23/3C1C 12/6ECC83 7/6 EZ40 7/-PCL8516/7U33 26/6 VP23 6/60C170 13/6 6AV6 12/86V6G 7/-25A6G 10/6CBL1 26/6ECC84 9/- E Z41 7/-PCL8616/7U35 26/6 V P41 6/-0C171 14/6 6B8 5/-6V6GTG 8/-25L6GT 10/-CBL3123/3ECC85 8/6 EZ80 7/-PENA4 23/3U37 26/6 VR105 8/-0C200 16/6 6BA6 7/66X4 5/-25Y5G10/-CCH35 23/3ECC88 18/- EZ81 7/-PENB4 26/6U43 9/-VR150 7/60C203 24/- 6BE6 /-6X5GT6/-25 Z4G 9/6CK506 6/6 ECC91 5/6FC4 15/-PEN4DD U45 9/-VT61A OCP71 29/6 6BG6G 23/36/30L210/-25 Z5 9/6CL33 19/3ECF80 10/6FW4/500 8/6 26/6U50 6/6VT501 5/-T11 40/- 6BH6 8/-7A7 12/625Z6G 10/-CV63 10/6ECF82 10/6FW4/800 8/6PE N25 4/6 U52 6/6W76 5/6T12 45/- 6616 6/-7B6 21/327SU 19/11 CY1 18/7ECF86 19/11 GU50 27/6PEN40DD U54 19/11 W81 M 6/-T13 50/- 6BQ7A 15/-787 8/62807 7/-CY31 11/- ECH326/6GZ30 9/- 25/-U76 6/-W107 18/7 TP1 40/- 6BR7 12/67C5 8/- 30C1 8/- D1 3/-ECH21 23/3GZ32 10/-PEN44 26/6 U78 5/-W729 19/11TP2 40/- 6857 25/-7C6 8/- 30F5 6/-015 10/6 ECH35 6/6GZ33 19/11 PEN4519/6U107 16/7X24M 24/7 TS1 10/- 6BW6 8/67H7 8/- 30FL1 10/-D77 4/-ECH429/-G Z34 14/-PEN46 7/6U191 16/7X41 15/-TS2 12/6 6BW7 6/-7R7 12/6 30L1 8/-DAC32 10/6 ECH81 9/-G Z37 19/11PEN383 23/3 U201 16/7X61(C) 12/6TS3 15/- 6C4 5/-757 9/6 30L15 11/6 DAF91 6/-ECH83 13/11 H63 12/6PEN453DD U251 14/-X63 9/-TS4 24/- 6C5 6/67V7 8/630P4 12/-DAF96 8/6ECL80 9/-HABC80 33/2 U281 19/11 X65 12/6V30/10P28/6 6C6 6/67Y4 7/630P12 7/6 DD41 13/11 ECL8210/6 13/6PEN/DD U282 22/7X66 12/6XA10123/- 6C9 13/68D2 3/630P19 12/- DET25 7/6ECL8319/3 H L2 7/6 4020 33/2 U301 23/3X76M 14/-XA102 26/- 6C10 9/-803 4/6 30PL1 10/6 DF33 10/6ECL8616/7HL23 15/3 PL33 19/3U329 14/-X78 23/3XA103 15/- 6CD6G 36/69BW6 15/330PL13 16/6DF66 15/- EF9 23/3H L23 DD 7/6PL36 12/-U339 16/7X79 23/3XA104 18/- 6CH6 9/-9D2 4/-35A5 21/3 DF91 3/6 EF22 14/-HL41 DD PL38 26/6 U403 16/7X109 17/3X8102 10/- 606 6/6 10C1 13/-35L6GT 9/6 DF96 8/6 EF36 4/- 19/3 PL81 10/6U404 8/6X0(1.5) 6/6X810314/- 6E5 12/610C2 26/635W4 7/6 DF97 9/-EF37A 8/-HL42DD PL82 7/6U801 29/10XFG1 18/- X1310410/- 6F1 26/610D2 12/-35Z3 10/6DH63 6/6 EF39 5/6 19/3 PL83 9/-U402016/7 X FY12 9/6XC10116/- SPECIAL OFFER !ONE DOZEN 6K7G£1 Plus 2/6 p. & p. The above list supercedes all previous issues WE SPECIALIZE IN OBSOLETE VALVES - IF YOU DON'T SEE IT ABOVE, WRITE AND ASK BRAND NEW COSSOR 10" TUBES 108K OR 75K 18/6plus p. & p. 6/6. REGUNNED TUBES - ANY TYPE ! - ANY SIZE SUPPLIED ! WRITE FOR LIST ! OSCILLATOR COIL FOR ANY TAPE DECK5/6. p. & p. 9d.

82 THE RADIO CONSTRUCTOR elesigned tot

clefmniclabi

The new "AVO" Mk. IV Valve Characteristic Meter is typical of the ingenuity of design and high standard of workmanship that exemplify all of the multi -rangy instruments in the wide "Avo" range. It is a compact and comprehensive meter that will test quickly any standard receiving valve or small transmitting valve on any ofits normalcharacteristics under conditions corresponding to a wide range of DC voltages. The method of measuringmutualconductanceensures that the meter can deal adequately with modern TV receiver valves.It does many usefuljobstoonumeroustomention here,but a comprehensive pamphletis available on application.

ListPrice£92 completewithInstruction Book and Valve Data Manual

IZT AVOCET HOUSE 92-96VAUXHALL BRIDGE ROAD LONDON S.W.I. VICroria 3404 (12 lines) P-1 A MEMBER OF THE METAL INDUSTRIES GROUP OF COMPANIES

SEPTEMBER 1961 83 The decision is YOURS. To be a success in your chosen career; to qualify for the highest paid job ...to control a profitable businessof your own.I c s home -study courses put your plans on a practical basis; teach you theory and practice; give you the knowledge and experi- TECHNICAL ence to take you, at your own pace, to the top. LEARN AS YOU BUILD TRAINING Choose the RIGHT course. RADIO & TELEVISIONPractical Radio Course ENGINEERING . INDUSTRIALGain a sound up -to -professional - standards knowledge of Radio TELEVISION . RADIO AND TV and Television as you build YOUR in radio SERVICING . RADIO SERVICEown 4 valve T R F and 5 valve AND SALES . ELECTRONICS . superhet radio receivers, COMPUTORS AND PROGRAMMINGgenerator and high -quality multi - meter. At the end of the course television c s provides thorough coachingyou have three pieces of perma- for professional examinations:nent and practical equipment A M BRIT. I R E, City and Guildsand a fund of personal know- Telecommunications. ledge and skill ... I c s Practical and C. & G. Radio and TV Servicing,Radio courses open a new world C. & G. Radio Amateurs. to the keen radio amateur. electronic engineering with THERE ARE ICS COURSES TOOther I c s courses include: MEET YOUR NEEDS AT EVERY FIRE, STAGE OF YOUR CAREER. MECHANICAL, MOTOR, CHEMICAL, ELECTRICAL AND Postthis coupon today:InCIVIL ENGINEERING, ETC. return you will receive the FREESELLING AND MANAGEMENT, 60 -page t c s Prospectus listingARCHITECTURE, WOOD- technical examinations and theirWORKING, FARMING, GARDEN- appropriateI C Scourses PLUSING, ART, PHOTOGRAPHY. details of over 150 specialisedPlease state subject in which you ICS subjects. are interested on coupon.

I INTERNATIONAL CORRESPONDENCE SCHOOL (Dept. 248)Intertext HouseParkgate Road London SW11

NAME

ADDRESS

OCCUPATION AGE

SUBJECT 9.61 TRIPLE CRYSTAL UNITS STC for Frequency Control of F.M. Tuners

The STC quartz crystal assembly Type 4434 comprises a trio of quartz elements mounted in a single B7G based glass envelope. The three elements each work on their 5th overtone at 107 Mc/s below the radiated frequencies of the three F.M. transmissions in each area of the United Kingdom. Improved manufacturing techniques and quantity production of crystal units designed specifically for F.M. application enables STC to offer the units at less than a quarter of the normal cost. F.M. radio is by nature a "local station" service and variable tuning is unnecessary. Switched tuning, instead of variable tuning by dials, is a saving and an attraction to the user.

Hermetically sealed B7G STC 4434

STC TRIPLE CRYSTAL FREQUENCIES M/CS STC CRYSTAL BBC LIGHT THIRD HOME

4434/A Wrotham 78.4 8o6 82.8 4434/B Peterborough 79'4 81.6 83.8 4434/C Rosemarkie 78.9 81I 83.3 4434/D N.H. Tor 77'4 79.6 8I.8 4434/E Sutton Coldfield 77.6 79'8 82.0 4434/F Pontop Pike 77'8 80.0 82.2 4434/G Meldrum 78.0 8o2 82.4 4434/G Blaen Plwyf 78.0 8o2 82.4 4434/H Holme Moss 78.6 8o8 83.o 4434/F Rowridge 77.8 80.0 82.2 4434/B Divis 79'4 81.6 83.8 4434/7 Douglas 77'7 89.9 82.1 4434/K Kirk O'Shots 79.2 81.4 83.6 4434/C Llanddona 78.9 8II 83.3 4434/L Llangollen 78.2 8o4 82.6 The List Price of all the above items is k3..r5.od each For circuit diagrams and further information ask for leaflet MQIIo4.

COMPONENTS Standard Telephones and Cables Limited GROUP

QUARTZ CRYSTAL DIVISION: HARLOW ESSEX 61/8MQ

SEPTEMBER 1961 85 THE WORLD-FAMOUS RANGE OF EQUIPMENT For the Discerning who require THE BEST PERFORMANCE AT MINIMUMPRICE

HI -Fl FM TUNER This model is available as two units which, 4 -WAVEBAND TRANSISTORISED PORTABLE for your convenience, are sold separately. They comprise an R.F. Tuning Unit, Model RECEIVER, ModelRSW-1 FMT-4U (13.5.0 including purchase tax) with I.F. output This of 10.7 Mc/s, and an Amplifier Unit complete with attractively possesses Medium, Trawler and two Short-wave bands andis mid -way styledcabinet,also power supply and valves. Model between the domestic broadcasting and FMA-4U (111.11.0) making a total cost for the equipment of professional general communications re- 114.16.0 ceiver.Ideal and inexpensive for those AMATEUR Model DX -100U who wish to listen to world broadcasts, Thisis the most popular Amateur trans- shipping and aviation communications, etc. mitter intheworld andrequiresno It is not the set to buy if you wish introduction to "Hams" the world over. only to enjoy domestic broadcasting.In a handsome solid Coversallbandsfrom160-10metres. leather case, it has retractable whip aerial and socket for Self-contained, includingpowersupply, car radio use. Modulator and V.F.O. 150 W. D.C. input. 181.10,0 122.10.6 0 Csi isi:PsZi GP i°0 THE "MOHICAN'' GENERAL COVERAGE RECEIVER Model GC -1U In the forefront of design with 4 piezo-electric transfilters, variable tuned B.F.O.and Zener diode stabiliser, this is an excellent fully transistorised portableor fixed station receiver for both "Ham" and Short wave listeners. Other features include printed circuit boards,telescopic whip antenna, tuning meter and large slide -rule dial of approximately 70". Uses10 transistors. 138.15.0 MONEY -SAVING "PACKAGED DEALS" THE "COTSWOLD". This isan acoustically designed enclosure 26" x 23" For the benefit of customers wishing to purchase several x 158" housing a 12" bass speaker with 2" units of their Hi-Fi equipment at the same time, useful speech coil,ellipticalmiddle speaker price together with a pressure unit to cover the reductions are offered.Such "Packaged Deals" fullfrequency rangeof 32-20,000 c/s. may include RECORD PLAYERS and TAPE DECKS of Capable of doing justiceto the finest yourpersonalpreference,notnecessarily featuredin programme source, its polar distribution our catalogue. makesitideal forreallyHi-Fi Stereo. Two money -saving examples are given Delivered complete with speakers, cross- below and quotations for your own special requirements overunit,levelcontrol, Tygangrille will gladly be sent on request. cloth, etc.All parts pre-cut and drilled for ease of assembly andleft"in the white" for finish to personal taste. £21.19.0 GL -58 Transcription Unit £20.12.2 TA -IM £18. 2.6 THE "COTSWOLD" S-33 Stereo Amp. £12. 8.6Collaro "STUDIO" E17.10.0 Twin SSU-1 Speakers USC-1 £18.18.6 HI -Fl EQUIPMENT CABINETS (Bookcase Type) £21.15.0MA -12 £10.19.6 £54.15.8 £65.10.6 You have four different Packaged 151.10.0 equipment cabinets de- Packaged 159.10.0 signed to meet the wide varietyof tastes and PRICE OF TAPE DECK PURCHASES WITH AMPLIFIERS requirements.Thereis Separate Together the 'CHEPSTOW', for TA -IM with Collaro "STUDIO" £35.12.6 E30.10.0 those who have minimum TA -IS with Collaro "STUDIO" £40.16.0 £35.14.0 floor space; the 'MAL- TA -IM with TRUVOX Mk.6 £54.17.6 £48. 5.0 VERN' in contemporary TA -IS with TRUVOX Mk. 6 £60. 1.0 £53. 7.0 design for the Tape and Gram.enthusiast,and ,,,C,C7, 0 .0.00,000,0,, 0 ,,,,C,,, ...4,,,G,C, ,C,,,,, 0 4,0 0 . 0 G. AZ the 'GLOUCESTER' Mk. I andII for those with All prices include free delivery U.K. The "GLOUCESTER" traditional tastes. All (open) parts pre-cut and drilled Deferred terms available over 110. for ease of assembly and left "in the white" for finish to personal taste.Send for details of whole range.Prices from £11.5.6 to £17.18.6. Available direct from DAYST ROM LTD DEPT. RC9 GLOUCESTER

86 THE RADIO CONSTRUCTOR Easily- built Equipment /-Itea-po of excellent qualify AT MUCH LOWER COST

TAPE RECORDING/REPLAY AMPLIFIERS, Models TA -1M and TA -15. Available both monophonic (TA -1M) and stereophonic (TA -1S) and the former can be modified later to stereo with modification kit TA -1C.Special features include bias level control, thermometer type recording level indicators, press -button control. Housedinattractivemetalcase. TA -1M E18.2.6 TA -1S E23.6.0 GRID DIP METER, Model GD-1 U. A very handy instrument for the lab., the "Ham" of Service Engineers.Complete set of plug-in coils provided covering 1.8 Mc/6 to 250 Mc/s. Additional plug-in coils at 15/-.500 micro -amp panel meter used. E10.9.6 GD-1 U TRANSISTORISED version of above, model XGD-1, 1.75 Mc/s to 45 Mc/s £10.8.6 and 5" : 0-12U. "Y" sensitivity 10mV/cm, 3 c/s to over 5 Mc/s.Rise time, 9.08 gsecs XGD-1 or less.Sweep, 10 c/s to 500 kc/s.Electronically stabilised. E36.10.0 21" PORTABLE SERVICE OSCILLOSCOPE: OS -1.Ideal instrument for service and portable use.Size 5" x 8" x 14". Wt. 101lb. £19.10.0 DECADE CAPACITANCE BOX: DC 1U.Provides capacity values from 100 mmf to 0.111 mfd O -12U S in 100 mmf steps.Ideal for experimental development and design work. E6.5.6 VALVE VOLTMETER: V -7A. The world's largest -selling VVM.Measures volts to 1,500 (DC & RMS) and 4,000 pk. to pk.; resistance 0.10 to 1,000M0 DC. D.C. input inpedance 11 Megohms. £13.0.0 HI -Fl STEREO 6 WATT AMPLIFIER: S-33.Low-priced but high quality; less than 0.3% distn. at 21 watts per channel. £12.8.6 OS -1 HI-FI STEREO 16 WATT AMPLIFIER: S-88.Superb reproduction for the man who wants the best in Hi-Fi. Only 0.1% distortion at 6 W/chnl. Many special features. £26.12.6 AMATEUR TRANSMITTER: DX -40U. 75W CW; 60W pk. c/c phone; 40W into Aerial. £32.10.0 HI -Fl SPEAKER SYSTEM: SSU-1.Ideal twin speaker/ducted-reflex cabinet for stereo/mono in average room (left "in the white"). Legs E1.1.0 extra. £10.17.6 AUDIO GENERATOR: AG -9U.10 volts, 10 c/s to 100 kc/s pure sine -wave. Switch -selected frequency and attenuator. £19.19.6 JUNIOR TRANSISTOR RADIO: UJR-1. Youngsters are not excluded from our kit programme. This special single transistor set is an excellent introduction to radio and an instructive present. E2.16.6 V -7A TRANSISTOR PORTABLE RADIO UXR-1In elegant solid hide case, with golden relief. Six S-33 S transistors, dual -wave, fine reproduction, very easy to build. £14.18.6 SINGLE CHANNEL 12 WATT HI -Fl AMPLIFIER: MA -12.Ideal for stereo conversions, etc. Generous auxiliary power provided. E10.19.6 COLLARO "STUDIO" TAPE DECK. This extremely attractive and compact 3 -speed monaural tape deck features digital counter, pause control and piano -key switches. 417.10.0 (Following models not illustrated) DX -40U MULTIMETER, Model MM -1U. Sensitivity 20,000 ohms per volt D.C..5000 ohms A.C. Ranges 0-1.5, 5, 15, 50, 150, 500 and 1500V. AC and DC. Current 0-150 micro -amps to 0-15 amps in 5 ranges. Resistance ranges RX1(15 ohm centre scale) RX100 and RX10,000.4+" 50 micro -amp meter. £11.18.6 CAPACITANCE/RESISTANCE BRIDGE: C -3U. Measures capacity 10pF to 1,000p.F.Resistance 1000 to 5M0; Pwr. factor. £8.6.6 VARIABLE FREQUENCY OSCILLATOR: VF -1 U. 10V output; covers 10 to 160 metres. £11.2.0 AUDIO WATTMETER: AW-1 U. Up to 25W continuous, 50W intermittent. E14.14.0 SSU-1 AG -9U AUDIO VALVE-MILLIVOLTMETER: AV -3U. 1mV to 300V AC. 10 c/s to 400 kc/s. £13.18.6 ELECTRONIC SWITCH: S -3U. This extremely useful device extends your single -beam "scope" for double -beam uses. £10.15.6 ca-s1® ° DIRECT READING CAPACITANCE METER: CM -1U.Full-scale ranges of 0-100 mmf, 1,000 mmf, 0.01mfd and 0.1mfd. E14.15.0 AUDIO SINE -SQUARE WAVE GENERATOR. Model A0 -1U.Inexpensive generator covering 20 c/s to 150 kc/s and square waves to 50 kc/s in four ranges. Maximum output 10V., distortion less U JR-1 than 1 per cent. E12.18.6 UXR-1 R.F. SIGNAL GENERATOR, Model RF-IU. Up to 100 Mc/s fundamental and 200 Mc/s on harmonics and up to 100mV output on all bands. 411.18.0 GOLDRING-LENCO TRANSCRIPTION RECORD PLAYER, Model GL -58.This four -Speed Unit is offered for those who want a domestic unit which is of transcription quality.Fitted with G60 pick-up arm it has infinitely variable speed adjustment between 33; and 80 r.p.m. as well as fixed speed of 16 r.p.m.Balanced turntable (3+ Ib).Unique p/u lowering device. 420.12.2 All prices include free delivery in U.K. Deferred terms available on orders above E10 MA -12 "STUDIO" *SEND THIS COUPON NOW Without obligation please send me (Tick here) FOR FURTHER INFORMATION BRITISH HEATHKIT CATALOGUE (Please write in BLOCK CAPITALS) FULL DETAILS OF MODEL(S) NAME. DAYSTROM LTD DEPT. RC9 I GLOUCESTER ENGLAND ADDRESS A member of the Daystrom Group, manufacturers of the I WORLD'S LARGEST -SELLING ELECTRONIC KITS

SEPTEMBER 1961 87 ARMSTRONG AF 208 AM/FM C.R.T. BOOSTER TRANSFORMERS For Ray Tubes having heater cathode BAKER SELHURST RADIOGRAM CHASSIS short circuit and for C.R. Tubes with falling emission, fullinstructions supplied. LOUDSPEAKERS TYPE A. LOW LEAKAGE WINDINGS. 12in. Baker 15w. Stalwart, 3 OPTIONAL 25% and 50% BOOST ON or 15 ohms ...... SECONDARY: 2 V. OR 4 V. OR 6.3 V. OR 90/- 10.3V. OR 13.3 V. WITH MAINS PRI- 12in. Baker ditto, foam sus- MARIES. 12/6. pension, 15 ohms ... E6 OUR LATEST SUPERIOR PRODUCT. 12in. Baker Ultra Twelve, 20 MAINS INPUT TYPE A2. HIGH c.p.s. to 25 kc/s E17.10.0 QUALITY LOW CAPACITY 10-15pF. OPTIONAL BOOST 25%.50%,75%. 15in. Auditorium, 35 w., E15 16/6 each. TYPE B.MAINS INPUT. LOW CAP- ACITY.MULTI OUTPUT 2,4,6.3, 10 and 13 V. BOOST 25% AND 50%. THIS LOUDSPEAKERS P.M. 3 OHM. Sin. Rola,17/6; TRANSFORMER IS SUITABLE FOR 7in. x 4in., 18/6; 4in. Hi-Fi Tweeter, 25/-; 8in. Plessey, ALL TV TUBES.21/- each. 19/6; 61in. Goodmans, 18/6;10in.R.A., 30/-;12in. * Full VHF Band (87-108 Mc/s,) and Medium Band, Plessey, 30/-; 10in. x 6in. R.A., 27/6; 12in. Baker 15 w. 187-570M. * 7 Valves * 5 Watts Output * 15dB 3 ohm or Negative Feedback * Separate wide range Bass and 15 ohm models, 90/-; Stentorian HF1012 Treble Controls * 2 Compensated Pick-up Inputs 10in., 95/-; HF1016, £8. * Frequency Response 30-22,000 c.p.s. *2dB * Tape MAINS TRANSFORMERS CRYSTAL DIODES. G.E.C.,2/-; Record and Playback Facilities * Continental Recep- GEX34, 4/-; 200/250 AC 0A8 I, 3/-. tion of Good Programme Value * For 3, 7( and 15 STANDARD 250-0-250,80 mA.,6.3 ohm speakers. Send S.A.E. for leaflet. v. 40 CIRCUITS FOR GERMANIUM DIODES, 3/L. 5tapped v. 24 v. a. 4 a., andRectifier 4 v.6.3 v.2 a.22/6I a. tapped Price 22 Guineas Carr. Free H.R. , 4,000 ohms, brand new, 22/6 15/- pair. MINIATURE, 200 v. 20 mA., 6.3 v. I a. 10/6 Low resistance phones, BAS, 7/6 pair. MIDGET, 220 v. 45 ()IA., 6.3 v. 2 a. ... 15/6 SMALL, 220-0-220 v. 50 mA., 6.3 v. 2 a. 17/6 SWITCH CLEANERFLUID,squirt spout, STANDARD, 250-0-250 65 mA., 4/3 tin. LATEST "E.M.I." 4 SPEED SINGLE 17/6 HEATER TRANS., 6.3 v.11 a. ... 7/6 TWIN GANG CONDENSERS.Miniature tran- RECORD PLAYER 10/6 sistor gang 208 and 176pF,10/6each( 365pF, miniature, I fin. xI (in. x I1in., 10/-; 500 pF standard Ditto 1.4. 2, 3, 4, 5, 6.3 v. I1 a.... 8/6 Acos 73 Hi-Fi Pick-up for LP, and/or 78, 7",10" and M ULLARD "510" OSRAM "912", with trimmers, 9/-; midget, 7/6; midget with trim- 12" records.Silent motor, heavy turntable, auto stop. 300-0-300, 120 mA, 6.3 v. 4 a. c.t., 6.3 v. mers, 9/-. 38/6 Special offer f6. 5. 0 post free GENERAL PURPOSE LOW VOLT- SHORT WAVE.Single 50 pF, 75pF, 100pF, Stereo/Monaural £6.19.6 AGE.Outputs 3,4, 5, 6, 8, 9,10,12, 160 pF, 5/6 each. 15, 18, 24 and 30 v. at 2 a. .. 22/6 AUTO. TRANS.150 w., 0,10, 120, TUNING AND REACTION CONDENSERS. 22/6 100 Pr, 300 pF, 500 pF, 3/6 each, solid dielectric. AUTO. TRANS. 500 w., 0,.11.5, 200, BUILD THIS REPRODUCER BARGAIN 230, 250 v...... 82/6 CONDENSERS. 0.001 mfd.7kV T.C.C.,5/6; ditto 20 kV., 9/6; 0.1 mfd. 7 kV., 9/6; 100 pF to 500 pF SPECIAL SINGLE PLAYER KIT Micas, 6d.; Tubular 500 v. 0.001 to 0.05, 9d.; 0.1, 1/-; 0.25, 1/6; 0.1/350 v., 9d.; 0.5/500 v., 1/9; 0.01/2,000 v., B.S.R. TU9 4 -speed Gram Pick-up Unit L4.5.0O.P. TRANSFORMERS. Heavy duty 50 mA, 4/6. 1/9; 0.1/2,000 v., 3/6. Handsome portable case 13" xI I" x'61" £2.5.0Miniature 3V4, etc., 4/6.Small, pentode, 4/6.Multi - Ready -built 3 -watt, printed circuit, amplifier ratiopush-pull,7/6. Multi -ratiopush-pull 10 w., CERAMIC CONDENSERS. 500v.0.3pF to 15/6. Goodmans heavy duty10/20 w. 6K push-0.01 mfd., 9d. with two valves and speaker £3.12.6pull, 30/-. or £9. 9. 0 complete kit, post free L.F. CHOKES 15/10H. 60/65 mA, 5/-;10 H. SILVER MICA. 10% 5 pF to 500 pF, 1/-; 600 pF to 3,000 pF,1/3; close tolerance (plus or minus I pF), 85 mA, 10/6; 10 H. 120 mA, 12/6; 10 H. 150 mA, 14/-.1.5 pF to 47 pF, 1/6; ditto I% 50 pF to 815 pF, 1/9; I.F. TRANSFORMERS 716 pair 1,000 pF to 5,000 pF, 2/-. 465 kc/s Slug Tuning Miniature Can.II" TELEVISION REPLACEMENTS r x 1-.High Q and good band width.By Pye Line Output Transformers 465 K//s. SIGNAL GENERATOR.Total Radio.Data sheet supplied. from 45/- each, NEW Stock cost 15/-.Uses B.F.O. Unit ZA 30058 ready and other timebase components made. POCKET SIZE 21in. x 41in. xlin. Most makes available.S.A.E. with all enquiries Slight modifications required, fullinstructions New boxed VALVES 90 -day Guarantee supplied.Battery 7/6extra 69v. -I- IS v. Details S.A.E. IRS 7/66K8G 7/6EA50 1/6EZ80 7/6 155 7/66L6G 10/6EABC80 8/6E148 1/6 FULL WAVE BRIDGE SELENIUM RECTI- IT4 6/-6N7M 6/6EB9I 6/-H1ABC80 12/6 FIERS.2, 6 or 12 v.IIa., 8/9; 2 a., 11/3; 4 a., 17/6.WAVECHANGE SWITCHES 2X2 3/66Q7G 8/6EBC33 8/6HVR2A 6/6 Free charger circuit. 2 p. 2 -way, 3 p. 2 -way, short spindle . ... 2/6 3S4 7/66SA7 6/-EBC4 I 8/6MU14 9/- 6 p. 4 -way 2 wafer, long spindle ... 6/6 3V4 7/66517M 6/6EBF80 10/-P61 3/6 CHARGER TRANSFORMERS. Tapped input2 p. 6 -way, 4 p. 2 -way, 4 p. 3 -way, long spindle 3/6 5U4 7/66SN7 6/6ECC84 9/6PCCB4 9/6200/250 v. for charging at 2, 6 or 12 v.11 a.,15/6; 3 p. 4 -way, I p. 2 -way, long spindle ...... 3/6 5Y3 7/66V6G 6/6ECF80 9/6PCF80 9/62 a., 17/6; 4 a., 22/6. Wavechange "MAKITS". Wafers available: I p. 5Z4 9/66X4 7/6ECH42 10/6PCL82 11/6 12 wafer, 2 p. 6 wafer, 3 p. 4 wafer, 4 p.3 wafer, 6AM6 5/-6X5 6/6ECL80 10/6PEN25 6/64 AMP. CAR BATTERY CHARGER with amp.6 p. 2 wafer. I wafer, 8/6; 2 wafer, 12/6; 3 wafer, 6B8 5/-12A6 7/6ECL82 10/6PL81 12/6 meter Leads, Fuse Case, etc., for 6 v. or 12 v., 69/6 16/-.Additional wafers up to14, 3/6 each extra. 6BE6 7/612AT7 EF39 5/6PL82 10/6 8/- 6BH6 9/612AU7 8/-EF4I 9/6PY80 7/6 TOGGLE SWITCHES, s.p., 2/-; d.p., 3/6; d.p.d.t.' 6BW6 9/612AX7 8/-EF50 5/6PY8I 9/6 BOOKS 4/-. 6D6 6/-128E6 8/6EF80 8/-PY82 7/6 6F6 7/6I 2K7 6/6EF86 12/6SP61 3/6 6H6 3/6I 2Q7 6/6EF92 5/6UBC4I 9/6Valve and TV Tube Equivalents ... 9/6 JASON F.M. TUNER COIL SET, 29/-. 6.15 5/635L6 9/6EL32 5/6UCH42 9/6TV Fault Finding H.F. coil, aerial coil, oscillator coil, two i.f. trans- 616 5/635Z4 7/6EL41 9/6UF4I 9/6 formers10.7Mc/s., detector transformer and 6.17G 6/680 9/6EL84 8/6UL4I 9/6 Quality Amplifiers ...... 4/6 heater choke. Circuit and component book 6K6GT6/6807 5/6EY51 9/6UY4I 8/-Radio Valve Guide. Books I, 2, 3 or 4 each 5/- using four 6AM6, 2/6. Complete Jason FMTI 6K7G 5/-954 1/6EZ40 7/6U22 8/- kit,Jasonchassis withcalibrateddial, com- Transistor Superhet Receivers ... 7/6 ponents and 4 valves, £6.5.0. DK96, DF96, DAF96, DL96, 8/6 each or 30/- set VALVEHOLDERS.Pax. int. oct., 4d.EA50, 6d. CRYSTAL MIKE INSERTbyAcos8/6 BI 2A, CRT, 1/3.Eng. and Amer. 4, 5, 6, and 7 pin, NEW ELECTROLYTICS FAMOUS MAKES Precision engineered. Size only 1r dia. x 1" 1/-. MOULDED MAZDA andint.Oct.,6d.; B7G, B8A, B8G, B9A, 9d.B7G with can, I/O. B9A TUBULAR TUBULAR CAN TYPES ACOS CRYSTAL MIKE 40... 25/ - with can,1/9. Ceramic, EF50, B7G, B9A, Int. Oct., 1/-.B7G, B9A cans, 1/- each. I /350v. 2/-50/350v. 5/616/450v. 5/- 2/350v. 2/3I 00/25v. 3/-32/350v. 4/- 4/450v. 2/3250/25v. 3/-100/270v. 5/6 8/450v. 2/3500/ I 2v. 3/-2,500/3v. 4/- 8/500v. 2/98 + 8/450v. 3/65,000/6v. 5/- 16/450v. 3/-8 +8/500v. 5/-32+32/350v. 5/- 16/500v. 4/-8 +16/450v. 3/932 +32/450v. 6/- 32/450v. 3/98+16/500v.5/632 +32 + 32/350v.7/- RADIO COMPONEN1 25/25v. 1/916 +16/450v.4/350 +50/350v. 7/- 511/25v. 2/-16 +16/500v.6/-64 +120/350v. 11/6 50/50v. 2/ -32 +32/350v.4/6100 +200/275v. 12/6 Our written guarantee with every purchase. Buses 133 or 68 pass door. S.R. Stn. Selhul

88 THE RADIO CONSTRUCTOR VOLUME CONTROLS 80 CABLE Coax ALADDIN FORMERS and cores.fin. 8d., fin 10d. Long spindles.Midget Semi -air spaced fin. 5Kohms to 2 Meg. 0.3in. FORMERS 5937 or 8 and cans TVI or 2, Stranded core, 6d.yd. fin. sq. x 25in. or fin. sq. x 40 yds. 17/6; 60 yds. 25/ - I fin., 2/- with cores. No. sw. D.P. Sw SLOW MOTION DRIVES. Epicyclic ratio 6-I, 2/3. 3/- 4/6 FringeQuality,Air LinearorLogTracks. Spaced 1/- Yd. SOLON IRON, 25 w., 200 v. or 230 v. 24/-. MAINS DROPPERS. Sin. x If in. With adj. sliders, RESISTORS. Preferred values. 10 ohms to 10 meg.0.3A, 1,000 ohms, 4/3; 0.2A 1,000 ohms, 4/3. w., 4d.; 5 w., 4d.; I w. 6d.; 14 w. 8d.; 2 w. 1/-LINE CORD. 0.3 A 60 ohms per foot, 0.2 A 100 HIGH STABILITY. 5 w. 1%, 2/, Preferred values. ohms per foot, 2 -way, 1/- per foot; 3 -way 1/- per foot. The Milliantly Swownfog 10 ohms to 10 meg. Ditto 5%, 100 ohms to 5 meg. 9d. WIRE -WOUND RESISTORS 1/3 MIKE TRANS. 50:1, 3/9;100:1potted,10/6. 10 watt 25 ohms- 10,000 ohms(1/6P.V.C. CONN. WIRE, 8 colours,singleor Wed. Autetheng.. 15 watt 21- stranded, 2d. yd. Sleeving, 1.2 mm, 2d.; 4 mm, 3d.; I2.5K to 50K 10 w 6 mm, 5d. yd. WIRE -WOUND WIRE -WOUND SPEAKER FRET. Gold cloth,I7in.x 25in., 5/-;BRAND NEW & BOXED POTS. 3 WATT. Pre- 25in.x35in.,I0/-. TYGAN, 52in.wide,10/-: set Min. TV Type. All 4 WATT POTS. Long26in. wide 5/-ft. Samples S.A.E.Expanded Metal, values 10 ohms to 25K, Gold, 12in. x I2in., 6/-. with Cabinet, Amplifier & Speaker 3/- ea.; 30K, 50K, 4/-. Spindle, Values, 50 ohms (Carbon 30K to 2 meg., AMERICAN BRAND "FIVE" FERRO - 31-) to 50K, 6/6; 100K, 7/6. DYNAMICS RECORDING TAPE £12.10.0 CARR. 5/- Long Play 7in. reel, 1,800 ft. 35/- COAXIAL PLUGS, PANEL SOCKETS, I/ - 5fin. reel, 1,200 ft. 23/6 LEAD SOCKET, 2/-. OUTLET BOXES, 4/6 5in. reel, 900 ft. 18/6 BALANCED TWIN FEEDER, per yd. 6d., 80 ohms Standard Play 7in. reel, 1,200 ft. 25/ - RECORD PLAYER BARGAINS or 300 ohms. Sin. reel, 600 ft. I6/ - 4 Speed Autochangers: Double play 7in. 2,400 ft., 60/-; 5in.1,200 ft., BSR, U.A.14 E7.10.0 TWIN SCREENED BALANCED FEEDER, 1/6 37/6; Spare Reels, Sin. 1/6; 4in., Sin., Skin. 2/-0 Collaro Autochanger (7.19.6 yd. 80 ohms. 7in. 2/6."Instant" Bulk Tape Eraser and Head Garrard RC209 (9.9.0 TRIMMERS. Ceramic 30,50, 70 pF. 9d.;100 pF. Defluxer, 200/250 v.a.c.,27/6. Leaflet S.A.E. Garrard RC 210 E10.10.0 150 pF. 1/3; 250 pF. 1/6; 600 pF. 750 pF. I/O; Philips, 4 Speed Single Players: 30 pF. 1/- each. Garrard TA Mk.II E8.0.0 Garrard 4 HF Transcription E17.19.6 BLACK CRACKLE PAINT. Air drying, 3/- tin. QmAx CHASSIS Garrard Stereo Heads E2 extra. NEON MAINS TESTER SCREWDRIVER, 5/ - C UTTE R All Sapphire Stylii available from 6/-. SOLDER RADIOGRADE, 4d.yd., 6 lb.5/-, I lb. 9/-. The cutter consists of three parts: a die, a punch and an Allen screw. ARDENTE TRANSISTOR TRANSFORMERS HIGH TV PRE -AMPLIFIERS Sizes Price KeyType D3035, 7.3 CT:I Push Pull to 3 ohms for 0072, BAND 1B.B.C. fin. 12/9 etc., lin. x lin. x lin., 9/6. Type 3034,1.75:1CT. Push Pull Driver for 0072, Tuneable channels I to 5. Gain 18 dB. ECC84 lin. 12/9 lin. 13/9 etc., lin. x lie. x lin., 9/6. valve. Kit price 29/6 or 49/6 with power pack. Type D3058, 11.5:1 Output to 3 ohms for 0072, etc., Details 6d. (PCC84 valves if preferred.) lin. 13/9 / n. lin. x lin. x lin., 9/6. BAND IIII.T.A.-Sameprices 16/- /6Type DI67, 18.2:1 Output to 3 ohms for OC72 etc., Tuneable channels 8 to13. Gain17 dB. tin. 16/- /6lin. x Sin, x fin., 12/-. ;in. 16/- /6Type D239, 4.5:1 Driver Transformer, fin. x lin. x PAXOLIN PANELS, 10in. x 8in.,1/6. lin. 18/- /6 10/-. lin. 18/- Type D240, 8.5:1 Driver Transformer, lin. x lin. x MINIATURE CONTACT COOLED RECTI- fin. 20/6 //6 FIERS. 250 v. 50 mA, 7/6; 250 v. 60 mA, 8/6; 250 v. 2in. 30/- 2/3 lin., 10/- 85 mA. 9/6. 2ggin. 33/6 2/3 ARDENTE TRANSISTOR VOLUME CON-

SELENIUM RECT. 300v.85 mA.1/6. 2iin. 38/6 2/3TROLS. Type VC 1545, 5K with switch,ldia. .9in., 8/-. Type VC1760, 5K with switch, dia..7in.,10/6. COILS. Wearite "P" type, 3/- each. Osmor Midget in. square hole 29/ - 1/6 "0" type, adj. dust core from 4/- each. All ranges. TELETRON D.W.R. L. & Med.T.R.F.with reaction, 3/6. "REGENT" 4 VALVE WEYRAD FERRITE ROD AERIALS. MM., 8/9; M. & L., 12/6. COILS AND TRANSFORMERS FOR A 2 -WAVE TRANSISTOR SUPERHET FERRITE ROD AERIALS. L & M. for transistor "96" RANGE WITH PRINTED CIRCUIT AND circuits,10/- each. VALVES FERRITE ROD AERIAL FERRITE RODS 8in. xlin., 2/6. Long and Medium Wave Aerial-RA2W. On H.F. CHOKES, 2/6. Kit Price 6in. rod, -7gin. diameter, 208 pF. tuning, 12/6. T.R.F. COILS A/HF, 7/- pair; HAX, 3/-, DRR2, 4/-. OscillatorCoilP50/IAC. Medium wave.For E6.6.0 176 pF. tuning, 5/4. 1st and 2nd I.F. Transformer-P50/2CC. 470 ALUMINIUM CHASSIS. 18 s.w.g.Plain, carr. 4/ - undrilled. 4 sides, rivetedcorners,lattice kc/s,+lin. diameter bylin.high,5/7. fixingholes,21in.sides.7in.Nt x4in.,4/6; 3rdI.F. Transformer-P50/3CC, to feed diode detector,6/-. 9in. x 7in., 5/9; 1 I in. x 7in., 6/9;I 3in. x 9in., 8/6; 14in. x I lin., 10/6; I5in.x I4in., 17/6; DriverTransformer-LFDT2, IT0sin. xSin. I8in. x I6in. x 3in., 16/6. xI/in.,9/6. ALUMINIUM PANELS. 18 s.w.g.,I2in. PrintedCircuit-PCAL Size 2/in. x85in. I2in. 4/6;I4in. x 9in., 4/-;I2in. x 8in., 3/-; Readydrilledandprintedwith component 10in.x 7in., 2/3. positions, 9/6. 7in. x 4in., 35 ohm Speaker, 25/-. These components are approved by transistor AUTOCHANGER ACCESSORIES Makers and performanceisguaranteed. Suitable player cabinets (uncut boards). 49/6. PRINTED CIRCUIT BATTERY Constructor's Booklet withfulldetails,2/-. Amplifier player cabinets with cut boards, 63/-. PORTABLE KIT 2 -valve amplifier and 65 speaker for above, ready mounted on baffle, I2in. x 7in., Sin, deep, Medium and long wave.Powerful 7 x 4 in. 79/6. Wired and tested reody for use. high Flux Speaker. T.C.C. Printed Circuit and NEW MULLARD TRANSISTORS condensers. Components of finest quality Audio 0071... 6/- R.F. 0C44 ... 10/6 QUALITY 2 -STAGE HI-FI AMPPLIFIER. clearly identified with assembly instructions. OC72... 8/6 0C45 ... 9/6 A.C. only, 200-250 v. Valves ECL82 and EZ80. Osmor Ferrite Aerial Coils. Rexine covered Sub -miniature Electrolytics (15 V). I mfd. 3 watt quality output. Mullard tone circuits, attache case cabinet. Size 12 in x 8 in. x 4 in. 2 mfd., 4 mfd., 5 mfd., 8 mfd., 25 mfd., 100 mfd., bass boost, treble and volumecontrols. 2/6. SeparateengravedPerspexfront -panelwith Batteries used 8126 (L5512) and AD35 (L5040), 10/- extra. B.B.C.Pocket 2Transistor. M.W. and de -luxe finish.Heavy duty output transformer Instructions 9d.(free with kit), L.W. Radio Kit, 32/6. Phones 7/6 or deaf aid 3 ohm. Shrouded mains transformer. Stove Mains Unit ready made for above 39/6. Sold earpiece,12/6 enamelledchassissize6in.xSin.xSin. separately. Details free. Bargain price (4.10.0. Circuit supplied. "PW" ROADFARER AM/FM RADIO KIT Transistorised throughout. Advanced design,operated frominternalbatteriesor direct frommains. Four Sectionsallon printed circuit. AM Tuner, FM Tuner, Audio Amplifier,Mains SupplyUnit. AttractivePlasticCabinet. FerriteRod, 337 WHITEHORSE ROAD Aerial for AM, Telescopic Aerial for FM. Order Order now. Lowest price E15. 1PECIALISTS WEST CROYDON ;-tigle,65 "P.W." Pocket 6.Transistor kit.All parts, printed circuit and cabinet. Osmor Designed P. charge 1/-, over E2 post free. C.O.D. 1/6.(Export welcome. Send remittance and extra postage) Kit, (8.15.0.

SEPTEMBER 1961 89 TEST EQUIPMENT OF EXCEPTIONAL QUALITY by Jason in KIT FORM

A number of positive advantages stem out of presenting Jason Electronic Test Equipment in kit form.There is naturally a high degree of satisfactiontobeobtained frombuilding first-class equipment of this kind for yourself. You benefit too from using instruments of a TEST EQUIPMENT Literature onall standard which would otherwise cost very much VALVE VOLTMETER (illus.) Jason items gladly more thanthe equivalent Jason Kit.Jason I senton request. 4 -valve Bridge Circuit.23 ranges inc. D.C. Instruments are in regular use in laboratories Kit inc. valves, 41" sq. meter and case. £23.0.0 and test departments throughout the world. As High voltage probes L3 extra. Kits, they provide excellent opportunities for traininginelectronics.Built,they provide OSCILLOSCOPE OG.10 (illus.) New Argus Tran- accuracy of exceptionally high order together Sensitivityof 10 mV/cm. with bandwidth sistor Radio Tuner with reliability and welcome robustness. 2 c/s. to 2 Mc/s.Push/pull amps. on X and for Recorder and Y plates.With 21" tube, valves and case. C7.10.0 E22.10.0 Amp. AUDIO GENERATOR A.G.10 NEW STEREO/MONO DE Tunes from 10 c/s to 100 Kc/s with output LUXE TAPE UNIT JTL constant within 1dB. Square wave rise time better than 2 microseconds.With valves FOR RELEASE SHORTLY. DETAILS and case. £15.19.0 ON REQUEST. AUDIO ATTENUATOR AA.10. Nine steps by switches from 1dB to 40 dB. AMPLIFIERSTUNERS E7.15.0 (Built). WOBBULATOR W.11 J.2-10. Mk. III Stereo/Mono Amp. £40.19.0 For allIF and RF alignment.Complete kit. J.10 Mono Amp., 10 watt £24.0.0 E14.19.0 FMT.4 FM Fringe Tuner f23.6.9 (inc. L6.15.7 P.T.) CRYSTAL CONTROLLED JTV/2. Switched FM and TV Sound Tuner CALIBRATOR C.C.10. (inc. L6.15.7 P.T.) E25.19.7 For use in 10 Kc/s to 250 Mc/s range with Monitor-as JTV/2 but for cabinet mounting 0.01% basic accuracy. £19.19.0 (inc. L5.4.1. P.T.) f19.19.1

ELECTRONIC TEST EQUIPMENT Jason TEST EQUIPMENT

JASON ELECTRONIC DESIGNS LIMITED, KIMBERLEY GARDENS, LONDON N.4. Telephone STA 5477

90 THE RADIO CONSTRUCTOR JACKSON Sen? SE QS rriVE- - _ the big name inPRECISION components but not temperamentalI Precision built radio components are an important contribution to the radio and communications industry. from Salford -the NEW Be sure of the best and buy Jackson Precision Built Components mmitest POCKET -SIZED MULTIRANGE TEST SET

AM/FM Gang Condenser Type 5320

JACKSON BROS. (LONDON) LTD KINGSWAY, WADDEN, SURREY Telephone Croydon 2754-5 Telegrams Walfico, Souphone, London

SMITH'S of Edgware Road BLANK CHASSIS Precision made in our own works from commercial quality half -hard Aluminium. Two, three or four sided. SAME DAY SERVICE of over 20 different forms made up to YOUR SIZE. Order EXACT size yoU require to nearest -kg" (maximum length 35", depth 4"). SPECIALS DEALT WITH PROMPTLY Onlyrecently introduced, this instrument is proving an outstanding success. Its high sensit- SEND FOR ILLUSTRATED LEAFLET ivity makes it ideal for testing and fault location Or order straight away, working out total area of material required in all types of electrical and electronic circuits. and referring to table below, which isfor four-sided chassis in The instrument is well built and economically 16 s.w.g.: priced. Each instrument supplied with test leads. 48 sq. in. 4/-176 sq. in. 8/-304 sq. in. 12/- (Leather carrying case available as an extra). 80 sq. in. 5/-208 sq. in. 9/-336 sq. in. 13/- 112 sq. in. 6/-240 sq. in. 10/-368 sq. in. 14/- 144 sq. in. 7/-272 sq. in. 11/-and pro rata RANGES: A.C. Volts. 2.5, 10, 25, 100, 250, 1000. Post 1/3 Post 1/6 Post 1/9 D.C. Volts. 2.5, 10, 25, 100, 250, 1000. Discount forquantities.Trade enquiriesinvited. Sprayfinish arranged for quantities of 25 or over. D.C. Amps.50 LiA,ImA, 10mA, 100mA, IA. Ohms. 2000 200,00020 Mn, FLANGES (r, II" or I") 6d. per bend. ACCURACY :D.C. Volts & Amps. ± 2% of full scale deflection STRENGTHENED CORNERS, 6d. eachcorner. A.C. Volts ± 3% of full scale deflection PANELS. The same materialcanbe supplied for ± 5% at centre scale. panels, screens, etc.Any size up to 3ft at 4/6 sq. ft. (sq. in. x Post, up to 72 sq. in. 9d., 108 sq. in. 1/3, Send for leaflet MIN 6009/R.C. 144 sq. in. 1/6, 432 sq. in. 1/9, 576 sq. in. 2/-.

SALFORD ELECTRICAL INSTRUMENTS LIMITED

H. L. SMITH & CO. LTD . PEEL WORKS SILK ST SALFORD 3 LANCS TEL BLACKFRiARS 6688

287/289 EDGWARE ROAD LONDON W2 London Sales Office Magnet House Kingsway, W.C.2. Temple Bar 4668 Telephone PAD 5891/7595 A SUBSIDIARY OFTHE GENERAL ELECTRIC CO.LTD. OF ENGLAND

SEPTEMBER1961 91 ii.,,,t,...:77,surto 6,r83e7s.,,?,,,.....782.d.c,,,,s.

l 1: ..-I MULLARD'S NEW EDDYSTONE840C , "Circuits for Audio ...4:g::- iii .),,,e;-- This smart streamlined ,--'74i:,.....,,,,,_ Amplifiers" communication receiver is ,,,c,."..' a worthy successor to the " - 2nd. edition 136 pages original840A.Advanced design,ruggedconscruc j ' and quality 8/6 plus 1/- post tion, high ,,- CSC*

components used through- 1 ' 1, 1,.7. out. Designedforcon - The second edition ofthis exciting book on Audio design is now tinuousoperationunder available.Prepared byMullard's technical laboratories,itis now -, .. text book on all aspects of High Fidelity all conditions.High-grade, regarded asa standard gear -driven, slow-motion reproduction and Audiodesign.Inaddition to sections dealing covering 480 kc/s to 30Mc/s. with the theory of reproductionand distortion there are practical drive and full width dial.Five ranges designs for twelve differentpopular circuits.Detailed price lists PRICE £58.0.0 (Overseas shipping arranged). are available for the componentsfor these designs which are listed below. The prices shownare average figures for the exact parts as specified by Mallard's. 20 Watt Amplifier £27.10.0 EDDYSTONE 898 10 Watt Amplifier £15. 0.0 SLOW -MOTION 3 Watt Amplifier £ 9. 9.0 -. DIAL 7 Watt DC/AC Amplifier £11.10.0 1 2 Valve Pre -Amplifier £ 6. 9.6 The finest slow-motion dial assembly available. £12. 0.0 i 3 Valve Pre -Amplifier Essentialforreallyhigh- 4 Channel Mixing Pre -Amplifier L 7.15.0 grade receivers, tuners, 3 Watt Tape Amplifier £13.12.6 test gear, transmitters, Tape Pre -Amplifier £14.17.6 etc. Precisioncutgears give smooth110 to 1 7 Watt stereo Amplifier L18. 0.0 reduction and vernier scale 3 Valve Stereo Amplifier £13.10.0 givesexact loggingposi- Stereophonic Pre -Amplifier £13. 0.0 tion.Size 91" x 5,f".PRICE £3.11.4, post 1/6 (Overseas post 7/6).

TRANSISTORS MINIATURE WE ARE ACTUAL STOCKISTS FOR Sensational Price Reduction by Mullard's SPEAKER OFFER THE FAMOUS 0C44 11/-, 0C45 10/-, 0070 6/6, 0071 6/6, 0072 8/-, 0075 8/-, 0076 8/-, 0078 8/-, Brandnewminiature PM HEATH KITS 0081 8/-, 0C170 13/6, 0C171 14/6. Matched speaker 21"diameterand pairs of output transistors available. onlyt" deep, 3 ohms ANTEX "PRECISION" SOLDERING IRON impedance. Idealforport- A wonderful SUB -MINIATURE RESISTORS inter- ironforthe ables, transistor sets, constructor.Five We now stock the range of LAB type LX corns, etc. LIMITED QUAN- different in 10% tolerance. Ratedat,,,watt and TITY ONLY at special price sizes of bits available.All voltages from 6 to 240 size r long andj'" diameter.PRICE 8d. of 12/6, post 6d. volts in stock. Model as illustrated, PRICE 29/6, post each. paid.Leaflet on request.Please state voltage.

CELESTION P4412" LOUD- ARMSTRONG STEREO 12-MK II SPEAKER The most complete radio and Hi-Fi chassis ever produced. Everything you want on one : This popular High Fidelity speaker is available compactstreamlined chassis. AM,VHF/FM .-'..---,...:...;,. ' again in 3 and 15 ohms. 12" unit with heavy- push-pullHi-FiStereo,Pre -amp tonecontrol ''''',:-...... - .' .' .. duty magnet and suitable forhighquality unit, facilities for tape. PRICE 42 gns. All other domestic use or public address and dance Armstrong modelsinstock. AF208 22gns. ' halls, etc.PRICE £3.15.0, post 2/6 JUBILEE 29 gns, STEREO 55 32 gns.

Dark evenings ahead-have fun on Short Waves with the STEREOPHONIC AVO MULTIMINOR "GLOBE -KING" You can explore the world from the PICK-UPS comfort of your own armchair ACOS "Hi -Light" Stereo pick-up andenjoyrelaxationfrom a day's E17.17.0 work.Build this truly amazing little Decca FFSS Stereo Pick-up E21.0.0 one-valver,whichgivesreallylong Garrard TPA.12 Stereo pick-up ..N.r El .0.0 .': distance reception at a minimum 4-7-'4004 cost.Extrastage canbeaddedlater. Learn morse and listen in to shipping HI-FI EQUIPMENT \tA. amateurs,etc.100/Akitwith and We arestockistsforLEAK, k,-.- 3 coilscovering 10 to 100 metres, ',,,... PRICE £3.19.6, plus 1/6 post.Leaflet QUAD, PYE, W.B., GOOD - on request. MANS, WHARFEDALE. A well -designed, simple to use rectifier/moving-coil test meter VALVE DATA ofpocketsizeand sturdy NEW BOOKS HAVE YOU HAD OUR MANUAL construction,completewith STEREO HANDBOOK byBriggs. Seventh edition of this mouldedrubbertest leads 146 pages 10/6 SUPER CATALOGUE book has 156pages and clips.19 different ranges EXTRA EQUIPMENT FOR TAPE andlists 4,800 valves, covering AC and DC voltage, RECORDERS 6/- 2/- transistors, C.R.T.'s DC current and resistance up with base connections to2 megohms. Fulldetails LATEST VALVE DATA MANUAL 6/- plus 9d. post and most equivalents. onrequest. PRICE£9.10.0, Please add 1/- packing and post. PRICE 6/-, post 1/-. post 1/6.

92 THE RADIO CONSTRUCTOR The Radio Constructor Incorporating THE RADIO AMATEUR

SEPTEMBER 1961

Suggested Circuits No. 130: A Pocket Audio Injection Probe, by G. A. French 94 Can Anyone Help? 95 Vol. 15, No. 2 An Unusual 2 -Valve Superhet, by V. C. Jackson and R. A. Ord 96 Published Monthly An Impulse -operated Motor Speed Control Mechanism, by R. J. Hawkins 98 Resistance Measurement, by J. B. Dance, M.Sc. 100 Annual Subscription 29/ - A Crystal -Controlled Oscillator for FM, Part 2, (including postage) by Sir John Holder, Bt. 101 Understanding Radio, Part 2, by W. G. Morley 105 Editorial and In Your Workshop 111 Advertising Offices Microphone Pre -amplifiers, Attenuators and Mixers.. 57 MAIDA VALE LONDON w9 by F. C. Judd, A.Inst.E. 117 The JR1 Stereo Tape Recorder Unit, Part 1, by G. Blundell 121 Telephone Book Review 129 CUNningham 6141 (2 lines) The "Finger-tip Five", by A. S. Carpenter 130 Radio Topics, by Recorder 134 A Constructor's Oscilloscope-A Construction of the Mullard Telegrams Design, Part 3, by D. Noble, G3MAW, and D. M. Pratt, Databux, London G3KEP 138 News and Comment 141 Transistor Shorted Turns Tester, by M. D. Roberts 142 A Magnetic Guitar Pick-up and Transistorised Tone Control Pre -amplifier, by D. E. Maynard 145

© Data Publications Ltd, 1961

CONTENTS may only be reproduced after obtaining prior permission from the Editor.Short abstracts or references are allowable provided acknowledgment of source is given. CONTRIBUTIONS on constructional matters are invited, especially when they describe the construction of particular items of equipment. Articles should be written on one side of the sheet only and should preferably be typewritten, diagrams being on separate sheets.Whether hand-written or typewritten, lines should be double spaced.Diagrams need not be large or perfectly drawn, as our draughtsmen will redraw in most cases, but all relevant information should be included.Photographs should be clear and accompanied by negatives.Details of topical ideas and techniques are also welcomed and, if the contributor so wishes, will be re -written by our staff into article form.All contributions must be accompanied by a stamped addressed envelope for reply or return, and should bear the sender's name and address.Payment is made for all material published. OPINIONS expressed by contributors are not necessarily those of the Editor or the proprietors, TRADE NEWS.Manufacturers, publishers, etc., are invited to submit samples or information of new products for review in this section. TECHNICAL QUERIES must be submitted in writing.We regret that we are unable to answer queries, other than those arising from articles appearing in this magazine; nor can we advise on modifications to the equipment described in these articles. CORRESPONDENCE should be addressed to the Editor, Advertising Manager, Subscription Manager or the Publishers, as appropriate. REMITTANCES should be made payable to "DATA PUBLICATIONS LTD."

SEPTEMBER 1961 93 current flowing in the base -emitter circuit. Condenser C2, connected across winding1-2,modifiesthe The Circuits presented in this frequency of the oscillator note and series have been designed by reduces its tendency to squeg. IS G. A. FRENCH, specially for FrequeleY An outputistakenfromthe Coarse the enthusiast whoneeds only Ca6tre collector of the transistor via the C4 the circuitandessential data 0.01µF condenser C1. When the CI probe is used for fault-finding, the flying chassis lead is clipped to the chassis of the equipment under test, .1C2 whereupon the probe is applied to 34 successivea.f.injectionpointsas required.

Points of Design Most of the work on the prototype suggested circuits was concerned with the selection of oscillatorcomponents capableof R3 giving a reliable a.f. output of good amplitudefortherelativelylow No. 130 A POCKET AUDIO supply voltage of 1.5. The oscillator tends to squeg, and this tendency is INJECTION PROBE of advantage here since it enables the transistor to offer a higher output thanwould begivenifitwere employedasapuresinewave oscillator. In this case a compromise hasbeenreached,condenser C2 ASIMPLE AUDIO OSCILLATOR IS only, and the output is taken from sufficientlyreducingthetendency always a useful item and it may the oscillator in a different manner. to squeg to enable an acceptable be employed for many jobs tonetobegeneratedatgood including, especially, trouble -shoot- The Circuit amplitude. Resistors R1 and R2 also inginthe audio stages of faulty Thecircuitoftheoscillator have an effect on the quality of the equipment. accompanies this article and, as may tone.Apart from providing a bias This month's circuit is for an audio be seen, very few components arecircuit they reduce the a.f. level fed oscillator which employs very few required. The collector of the tran-to the base by winding 3-4 of the components and which is intended sistor feeds into winding 1-2 of the transformer. R1 and R2 may be to operate from a single 1.5 volt cell. transformer, feedback being applied consideredasinserting aseries Due to the small volume taken up to the base via winding 3-4. Winding resistor in the base -emitter circuit, by the components and cell,the 5-6 is not used, and no connection the resistor having the same value as oscillatoris capable of being built is made to its terminals.Resistors RI and R2 in parallel. intoacompletelyself-contained RIand R2 providebiasforthe As may be gathered from the last probe, whereupon it becomes readily transistor and alsolimitthea.f. available for service work in the field paragraph, the quality of the tone as well as in the workshop. The output of the probe is at high impedance, although the oscillator continues to function (with reduced output) if the probe is applied to impedances as low as 100C1. When r applied to the primary of a standard on/off valve speaker transformer, the result- 2 6 ant tone in the speaker is at adequate EN 2082 RI Lead -outs level for fault-finding purposes. Thus, C2 22013M the probe may be used for trouble- 5000 shooting a.f.amplifier stages from pF thespeakertransformerprimary 1.5volt back. 1 I - cell Output probe The oscillator transformer speci- B2 fied in the circuit has been used in an 2ono a.f. oscillator previously described in The RadioConstructor', and the present circuitissimilar in many respects to that given in the earlier issue.In this instance, however, the supply potential required is 1.5 volts I D. J. French,GRAD.I.E.E.:"A Transistor Chassis Transformer: Audio Transformer EN 2082 (Henry's Radio Ltd) Audio Signal Generator", The Radio Con- clip Resistors145 watt 20% structor, August 1959. EII2

94 THE RADIO CONSTRUCTOR generated by the oscillator is not a switched off.If desired, an electro- amplifier or to the primary of a pure sine wave. Itis,however, lytic condenser of some101,.For speakertransformer. Ifdesired, sufficiently acceptable in quality to more could be connected across the variationstothefrequencyand be satisfactory for fault-finding and supply rails after the on -off switch: quality of the note obtained can be servicing work. such a condenser would ensure that obtained by adjusting the value of The frequency of the tone varies winding 1-2 was effectively shunted RI, or C2. However, experience with slightly with load, but this effect is across the transistor atalltimes, the prototype did not indicate that not great. The supply potential has regardless of whether the oscillator any of the component values were so a considerable bearing on frequency, were switched on or not.Similarly critical as to necessitate adjustment. and the component values given here to protect the transistor, C1 should are applicable to supply potentials be a good quality component having around 1.5 volts only. a high leakage resistance, and care Results with the Prototype A possible risk with the circuit is should be taken to prevent the probe It was found, with the prototype, that if the probe is applied to an being accidentally applied to points that an audible note at adequate injection point carrying a high d.c. carrying high a.c. potentials. level was obtained when the output potential, ahighvoltagemay The transformer specified for the was applied to the primary of a valve momentarily appear across the tran- oscillatorisasmallcomponent speakertransformer. Obviously, sistor whilst C1 charges.The tran- whose windings offer a convenient louder tones were given when it was sistor is, however, effectively shunted ratio for the present application.It applied to the output and preceding (via the 1.5 volts cell) by winding 1-2 is readily available through normal gridsof theassociatedamplifier. of the transformer, the low resistance home -constructor channels. The oscillator continued to work ofwhich(approximatelyIson) reliably (at a reduced output level) prevents damage tothe transistor when a 10011 resistor was connected fromthiscause. Nevertheless, Construction across its output. winding1-2 is onlyconnected The construction of the probe The peak value of the output effectively across the transistor when should raise few difficulties, layout voltage,whenconnected to a the oscillator is switched on, with the not being important.When com- 250k (2 load, was approximately 0.4 result that the probe should not be pleted, the probe should be checked volts.Current consumption, for a applied to a circuit under test when by connecting its output to an a.f. supply voltage of 1.5, was 0.4mA.

CAN ANYONE HELP? Requests for information are inserted in this feature freeof charge,subjectto space being available.Users of this service undertake to acknowledge all letters,etc., received and to reimburse all reasonable expenses incurred by correspondents. Circuits, manuals, service sheets, etc.,lent by readers must be returned in good condition within a reasonableperiod of time litrificrafters SX24 Receiver.-L. Orbach, 131 Clarence Valve Types.-A. Lee, 77 Yew Tree Lane, Manchester Gate Gardens, London, N.W.1, urgently requires the 23, has obtained a civilian wartime receiver and requires manual or circuit diagram for this receiver-will purchase to know the base connections of the following valves: if necessary. BVA types 273/4/5/6/7, 243 or 246, 264/5/6, 211 and * * 214/5/6. BC348, Model 3N8Q.-J. Robertson, Aukengill, Wick, Caithness, Scotland, wishes to borrow or purchase the Channel RC Bridge and Signal Generator.-P. D. Webb, manual. 139 Bromyard Road, Sparkhill, Birmingham 11, would * * * like to obtain the service manuals of these and other Ex -Government Receiver Type ZC8931.-R. W. Hilton, Channel products. 8 Hogshill Lane, Cobham, Surrey, is in urgent need of * * * information and circuit details for this 1.5 metre receiver Admiralty Type Receiver R/T Pattern 4660.-J.C. and also, if possible, modifications for 2 metre working. Henson, North Dhuloch, By Dunfermline, Fife, wishes * * * to acquire the service manual of this receiver (marked T1131 or 75C Transmitter.-P. M. Beecham, 2 Fyfield Model No. 850). Road, Enfield, Middlesex, requires to borrow or pur- * * * chase the manual or circuit diagram. G.E.C. Super10 AutogramCat.No. BC3918H.- * * * R. Turner, "Bowmore", Dedworth Road, Windsor, RF27 Unit.-P. M. Griffiths, 5 Hulbert Street, Bury, Berks, is in urgent need of the circuit, willing to purchase Lancs, would like to receive details on converting this if necessary-this appeal is his last hope! unit for use on 2 metres. * * * * * * Marconiphone Radio, Model T32A.-A. G. Ariyoh, 19 Timebase Unit No. 4 ZC24694.-D. Howdle, 52 Braith- Dempster Road, London, S.W.18, requires the service well Road, Revenfield, Rotherham, wishes to know the manual or circuit-or any other information available actual timebase and whether suitable for an oscilloscope. -on this receiver.

SEPTEMBER1961 95 Circuit Design The circuit is shown in Fig. 1.L1 is a ferrite rod aerial and the rest of the circuit around V1 is of a An Unusual fairly conventional mixer/oscillator stage.The i.f. output from V1 is coupled, via L4 and L5, to the grid of V2. V2 performs a dual function, namely if. amplifier 2 -Valve Superhet and audio output stage; and its action is as follows: !.f. are amplified by V2 and fed via L6 and L7 to the D1. L6 and L7 constitute a modified i.f.transformer.About two-thirds of by V. C. Jackson and R. A. Ord the windings of L7 are removed together with the associated tuning condenser, the remaining one- third being pushed close to the L6 winding. The i.f. component is filtered from the audio signals by C11 and R6, the detected audio signal appearing across the diode load R7, the filteredsignal appearing across the volume control R3. From the volume control, audio signals are fed via L5 back to the grid THE REQUIREMENT WHICH LED TO THE DESIGN OF of V2, which now acts as a conventional output the receiver described here was for a small stage. radio to be used in a kitchen. Consequently, As was to be expected in a circuit of this descrip- provision was only made for reception of the tion, one of the most important problems to be Medium waveband, and switched tuning provided overcome was preventing V2 from breaking into for quick (and accurate) station selection of the oscillation. Due to the very high gain obtained at Home and Light programmes.Additionally, only 465 kc/s with a high slope valve, the anode grid a very small shelf area was available, so the receiver capacity becomes troublesome. had to fit into a fairly small cabinet.The actual In Fig. 1 the circuit is stabilised by balancing the cabinet dimensions were 64 x 54 x 4in. valve inter -electrode capacities in a bridge circuit. This bridge is shown in Fig. 2. Balanceis achieved by feeding h.t. to the screen -grid T2 of V2 via the 33012 resistor R4, and decoupling this elec-

c10 2C0 - trode with the 0.001µF con- 2.50V denser C14.ItisC14which I neutralisesthecircuitby II 7 balancing the bridge. V2 We were unable to find the S2 6-3Vf I anode load impedance of an EF9I on -off 0.6A I EF91 when used as an audio 7 output stage, and a suitable AC. Mains ratio had to be found by 2 experiment. In the prototype, Ti matches I51(12 to 311, and therefore has a ratio of ap- mocksEN proximately 70:1. The loud- speakeremployedhasa C diameter of 4in.

C7

2a"= c T

Fig.1. Circuit diagram of the Unusual2 -ValveSuperhet. S101, (tois the station selector

switch, position 1 being that of Slb the Light programme andposi- MI27 tion 2 that of the London Home service

96 THE RADIO CONSTRUCTOR In the interests of safety, a transformer is fitted to Lit&L5 L6&L7 provide h.t. and 1.t. supplies, the type used in Band I converters being ideal for the purpose, together with 0 0 a contact -cooled rectifier. The current consumption T2 of the receiver (h.t.) is 20mA at 250V.

TI &Cc) Grid LI C.0 Cgs

Screen Fig. 2. Equivalent Grid bridge circuit of V2 SI interelectrode capaci- CAnode- C14 ties -Chassis L.S. sla ab R3 8S2 M128 TC, 0L28,L3 The chassis employed with the prototype measured 5 x 3 x lin deep.Fig. 3 illustrates the layout of the 33/4 major components both above and belowthe ICI chassis.

Alignment Provided that pre -alignedi.f.transformers are used, alignment will be found to be a very simple matter. Switch to the Light programme; that is, with 51/4' trimmers TC1 and TC2 out of circuit. Now adjust M129 the core of L2L3 and the position of L1 on the ferrite rod for maximum signal.Following this, Fig.3. Top: above -chassis main component layout; adjustthe coreof L6L7for optimumresults. below: under -chassis main component layout

Components List

Resistors Condensers 22kS2 # watt +20% C1 0.05i.t.F mica R2 22kS2 watt +20% C2 120pF mica (see text) R3 500kSI pot, log, SPST switch C3 120pF mica (see text) R4 3300 watt +20% C4 100pF mica or ceramic R5 22052 watt +20% C5 0.0511F paper R6 47kS1 # watt +20% C6 560pF mica or ceramic R7 220ki2 watt 120% C7 0.0511F paper R8 IMS2 watt +20% C8 100pF mica or ceramic R9 IkS2 I watt +20% C9 25iJ.F, 12V, electrolytic CI() 0.00511F paper C11 100pF mica or ceramic Valves C12}16-1-16µF, 350V, electrolytic V1 6BE6 (X77, EK90, X727) C13 V2 EF9I (Z77, 6F12, 6AM6, 8D3) C,4 0.001µF paper TC1 100pF max TC2 100pF max. Coils Ferrite rod aerial (MW) Switches L2L3Oscillator (MW) S1 d.p.s.t. toggle or rotary L4 L5465 kc/s i.f. S2 s.p.s.t. ganged with R3 L6L7465 kc/s i.f. modified (see text) Rectifier Transformers Contact -cooled 250V, 25mA Ti Output 70:1 Miscellaneous T2 Mains: Primary 200-250V, Sec' D, GEX34 or similar 250V, 25mA; 6.3V, 0.6A Speaker, cabinet, B7G valveholder, chassis etc.

SEPTEMBER 1961 97 Incidentally, note that the "inner" position of this The values of TC1, TC2, C2 and C3 apply to latter is needed to ensure maximum coupling. reception of the Medium wave Light programme Next switch to the Home service and adjust and London Home service. When other stations are trimmers TC1 and TC2 for maximum signal from required these components may need to be altered the local Home service transmitter. accordingly.

An Impulse -operated Motor Speed Control Mechanism

By R. J. HAWKINS

THIS UNIT IS A MODIFICATION OF A SURPLUS that it was rather inflexible in its original condition, electromagneticallyoperatedswitch, Ref. and therefore set about modifying it.The require- 5D/609. As purchased it consists of five sets ment was that the resulting unit should produce the of contacts which are sequentially operated by f011owing speed -sequence: full ahead, half ahead, rotating cams, these being turned by a magnetically- stop, half astern, stop, half ahead.Half speed is driven 12 tooth ratchet. A pair of contacts situated obtained by connecting the motor field and armature above the electromagnet allows the mechanism to in series (these being in parallel for full speed), motor, while the magnet winding is in two sections, while reversing is brought about by changing the one part being switched to operate the unit and the polarity of the field supply. other being permanently energised. All connections When itis modified the unit is approximately are brought to a 10 -way terminal block. 3i x 3 x21in high. The two electromagnet coils The suppliers of the unit recommended it for are connected inparallel, whereupon energising radio control as it stood, but the author decided current is 0.7A for a 12V supply. A boat containing the equipment should be at least 2.5ft long, although Cams this would also depend to a great extent on the size and weight of motor and power supply, as well as an on the ratio of width to length. The unit could also 5EItn be used in a wheeled vehicle with a length of about 1.5 to 2ft. 4E The unitis designed to operate with a shunt- 3E0:0 23/I; wound motor which will consume at least IA at 2E0:0 full speed.In consequence the power supply would I Eern be some sort of accumulator, such as a battery of miniature lead -acid, NiFe alkaline, or silver -zinc A cells.The unit itself, however, takes little power, the action of the electromagnet being practically instantaneous. Two relays, each consuming some 0.02A, are fitted to the modified unit, but these are only operational for part of the time.

M124 The Modification Fig. 1.Plan view of unit and details of tagstrip.The The items required for the modification are as tags should be re -arranged if necessary by unclinching follows: fixing lugs with pliers. Holes A and B countersunk *in (B is already drilled) 5 *in Paxolin washers, dia. with &in hole;

98 THE RADIO CONSTRUCTOR 2 miniature 12-24 volt relays with double -pole Cam A controls the top pair of contacts, cam B the changeover contacts; second, and so on.The functions of the various 2 spacing pillars1 I' in long, tapped 6BA both cams are as follows: ends; A..lights (on when motor is off) Tagstrip, wire, sleeving, 6BA bolts. B ..motor on/off. 30o C ..reversing relay (Ry I). D half -speed relay (Ry 2). E ..unused in the author's model, but may be cut to suit various requirements. The original cams have hexagonal centre holes, 0 but it is sufficient to make the new ones a tight fit on the spindle; they must be fixed so that they take up the orientation shown in Fig. 2.This completes C D A B the mechanical part of the modification. M125 Wiring -up Fig. 2.Patterns of cams A, B, C, and D. Spaces must The theoretical circuit for the complete unit is be cut to a diameter of -in.(Diagram not to scale) given in Fig. 3, this showing the connections to the battery, light and motor.This diagram also indi- All wiring is removed from the magnet, motoring cates the tags, numbered in Fig. 1 to which external contacts, and terminal block, the latter two com- connections are made. The services offered by the ponents then being removed. (A little methylated tags are as follows: spirits may be necessary to loosen the varnish here.) Pair 1 ..motor field. To detach the motoring contacts striker arm it will Pair 2 motor armature. be necessary to remove the magnet armature, taking Pair 3 lights. care to replace the small spacing strips and to re- Pair 4 to receiver or inter -gear relay. align the pivot correctly. Pair 5 12-24V d.c. input. The relays are fixed to the baseplate at the point previously occupied by the terminal block, as shown in Fig. 1.Those used Lights) by the author had two 6BA YJJJ 3rd tog -pair holes in the base. The tagstrip A Motor Field is used to provide easy connec- 1st tag -pair tion to the unit, the old terminal - block being somewhat too bulky. Intergear Relay The tagstrip employed by the Contacts 4th tag -pair writer had every third tag sup- 00001.. RY1 porting brackets. I2 -24V 5th tog-pai

Electromagnet Fig.3. Circuit diagram of the Coils 60/1 motor speed controlunit.All relaysare showninthede - 0000." RY2 energised position

:3 Motor Armature 2nd tog -pair This tagstrip was cut and the tags rearranged (by removing with pliers and re -clinching in alternativepositions)togive two strips of seven, the two end tagsbeinginvertedbrackets M126 having the parts to which the wire is soldered removed. The strips are mounted by means of the spacing pillars, Motoring Contacts as shown in Fig.1. The author considered that difficulties in operation The bracket which supports the cam -spindle is might arise if the motoring contacts were left in unscrewed and the cams removed. New cams are circuit, since it is almost impossible to judge exactly then made from the Paxolin washers as in Fig. 2. when to cut off the supply to the electromagnet.

SEPTEMBER1961 99 This is particularly true when the unit is incorporated and, generally, the accuracy of the instrument will in a boat, where a change in motor revolutions is not be as great as that which might be expected not immediately obvious from the speed of the from methods inwhich alinearscale can be model.Nevertheless, the circuit may be altered, if employed. desired, to give provision for motoring.If it is found The circuit described (shown in the accompanying that sparking between the relay contacts gives rise diagram) enables resistors to be quickly measured to instability in the receiver it may be suppressed by on a linear scale.The main disadvantage is that connecting a 220 resistor in series with a 0.011J.F two meters are required. condenser across them. The battery voltage (about 15 volts) is applied across the 11a2 potentiometer and the portion of Weight and Mounting this voltage which is tapped off by the potentio- When purchased, some units are contained in a meter is measured by the voltmeter, V, which should die-cast case; removing this reduces the weight considerably. The weight of the author's unit after modification was about 20 oz.As the original TABLE fixing holes in the corners of the baseplate are no longer usable, one being used to hold the tagstrip pillar and the other being covered by a relay, it will Current Factor be necessary to drill new ones. They should be about * to in diameter, and spaced to suit the support 1001.A 10,000 available. 1mA 1,000

10mA 100

100mA 10

have a full scale deflection of between 10 and 15 volts.The milliammeter (or microammeter) mea- sures the current passing through the resistor under RESISTANCE test; it should have a number of ranges. The 4751 resistor protects the battery if the test prods should measurement be short-circuited with the full voltage across them. Operation The unknown resistor is connected across the test By J. B. Dance, M.Sc. prods with the milliammeter settoitshighest current range. The range is then altered until the milliammeter gives a reasonable deflection with the potentiometer set at about the centre of its range. The setting of the potentiometer is then altered until the readingisexactly100µ.A,1 mA, 10mA, or AN EXPENSIVE BRIDGE CIRCUIT IS PERHAPS THE 100mA. The current should be chosen from one of best method of measuring resistance, but the these four values so that it passes when there is a use of a multi -range meter is undoubtedly one reasonable deflection of the voltmeter, e.g. if 1001/A of the most rapid methods available. Apart from passes at less than 1volt, the current should be increased toI mA. Each measurement should be commenced with a large current range so that the milliammeter is not damaged. The resistance is found from the reading of the voltmeter.Ifthecurrentpassing throughthe unknown resistor is 10mA, the voltage indicated by the meter should be multiplied by 100 in order to obtain the resistance value in ohms. The factors by which the voltmeter reading must be multiplied for

E113 various other currents are shown in the table. Ifitis desired to make a permanent piece of the necessity of adjusting the zero reading fairly equipment employing this method for measurement frequently (in order to correct for any changes in of resistance, it would be convenient to employ a the voltage or resistance of the internal battery), pointer knob to operate the milliammeter range the multi -range meter method suffers from the switch so that it points directly to the range factor disadvantage thatthescaleisnon-linear.The (as shown in the table), the factors being marked on resistance scale must therefore be specially calibrated the panel around the knob.

100 THE RADIO CONSTRUCTOR A Crystal -controlled Oscillator for F.M.

by Sir John Holder,Bt. Part 2

ADESIGN FOR A CRYSTAL CONTROLLED FRONT-END 5.The crystal must be closely adjacent to the which can be adapted to any f.m. receiver switch tags and Vosc must be closely adjacent to

appears, at first sight, to be rather a tall order. the crystal. Any undue lengthening of the wiring However, alittleexperiment indicates that the associated with the crystal will almost certainly second of the two circuit applications described in cause the crystal to lose control.Further wires Part Iof this series was so "docile" and "pliable" associated with the "switch side" of the crystals that,providedtheconstructorfulfilledcertain should, if possible, not be parallel to the common requirements, he could twist it round in any reason- wire joining the crystals to the cathode of Vosc. able way and still retain an adequate chance of success.These requirements are: Requirements 1.The circuit given in this article must be used in its entirety, together with the specified oscillator valve and coils. 2. No connecting wire carrying high frequency current must be more than lin long.Preferably a wire should be of the order of a *in long. 3.The layout may be twisted and turned around in any way provided that the sequence of circuits shown in the block diagram of Fig. 1is maintained, except that there must be no crossing over of the "flow" arrows shown in Fig. 1.

4.The relative positions of the coilsisalso M118 important. L1 must be Ilin or more away from L2 or L3, whilst L2 and L3 must be separated by Fig. 2.The Jason "Jupiter" conversion.The existing exactly tin, this spacing giving the required mutual coils, valves and switch are retained, the latter having therear wafer removed. The trimmer side -tags coupling. should be soldered direct to the switch tags Cutting Large Holes Existing components on the chassis may preclude the use of a Q -Max cutter.In this case, large holes may be cut quite easily with the aid of an Arborfile (a kind of fretsaw for cutting metal). Left to Right and Backward Arrangement The first application tried was an adaptation of the Jason "Jupiter" tuner.For this purpose, the back wafer of the switch was removed, an oscillator valve and crystal added and the wiring altered as necessary. The original coils were retained but the top end of the ribbon coils was used as the "hot" M117 end instead of the bottom end. The layout is shown in Fig.2.The pentode portion of the original oscillator was retained as a mixer.All that was Fig. 1.Front-end block diagram necessary was to ground pins 1, 9 and 8 to the

SEPTEMBER 1961 101 chassis, the triode portion being no longer required, projecting.Squeeze the end turns inwards slightly and connect a 220pF condenser across the primary so that they grip the former.Slip the coil off and of the mixer anode transformer, to make up for the slideit on to the L3 former.Now construct a removal of the feedback condenser. similar coil for the tuned winding of L2. Both coils should look like RH-thread screws. A Complete Front End Next construct the primary of L2.For this, take The arrangement proved so satisfactory that it a shortlengthof RadioSparesstrandedp.v.c. was decided to use it as the basis of a complete front covered connecting wire (2mm overall diameter). end.Fig. 3 shows the circuit details, while Fig. 4 Slip the turned winding on to the former and twist shows the dimensions. two turns of the p.v.c. covered wire round its lower

o HT+ 200V Components List Resistors (all 4 watt) R1 16052 R2 221a2 R3 27kC1 R4 3.3kO R5 2200 R6 2200 R7 470k0 R8 100kn eting connection (if necessary) Valves V EF80 (Mullard) 0 HT- V2 EF80 (Mullard) VoscECC85 (Mullard) Aerial Heaters pins 455 Crystals S.T.C. 4434/to suit locality

12 Condensers Fig.3.Circuit diagram of the 6.3V C1 1,000pF ceramic AC complete front-end.Note that c13711371 C2 5,000pF ceramic if the existing heater supply is C3 33pF silver mica "floating",twoheaterchokes C4 15pF silver mica should be fitted C5 1,000pF ceramic C6 1,000pF ceramic MI19 C7 47pF silver mica C8 5,000pF ceramic C9 8.2pF silver mica The "Jupiter- coils are no longer obtainable. CIO 15pF (max) tubular trimmer (RadioSpares) Satisfactory substitutes are as follows: L1, use a CI 15pF (max) tubular trimmer (RadioSpares) standard f.m. aerial transformer wound on a portion C12 5,000pF silver mica of a slug. L2 and L3 are wound on 7mm polystyrene C13 5,000pF silver mica coil formers approximately kin long and have v.h.f. slugs.Although there are several windings, con- struction is not difficult if carried out according to Coils the following description: L1 Standard aerial coil wound on slug L2 styreneformerswithv.h.f.slugs. Constructing the Coils L3Woundon 7mm diam. (see text) Proceed as follows: mount L3 former inthe chassis. Hold L2 former by the base in the left hand. Straighten a 6in length of 20 s.w.g. tinned copper Miscellaneous wire and hold in the right hand. Lay the end across Si Midget 4 -pole, 3 -way the former and place the left thumb on it.Now 2 B9A valveholders (nylon loaded, skirted) with the left hand, turn former and wire -end anti- 1 B7G valveholder (nylon loaded, skirted) clockwiseuntilfour complete turns have been Coaxial socket, 2 -way and earth tagstrip wound on. Extend the coil until it is +in long. Bend IF transformer ends out at right angles and cut off so that kin is Chassis

102 THE RADIO CONSTRUCTOR half.Tie the first half of a reef -knot in the ends. The purpose of the primary winding of L2 is Offer up the former inthe chassis and adjust merely to avoid having to construct a tapped coil windings so that all four ends point in the right and the 4 -turn winding of L2 can, for theoretical direction.Pull the half knot tight and fix with purposes, be regarded as the primary.With this adhesive. The tops of both the four turn coils should assumption, we have L2 primary feeding r.f. signal be nearly at the top of the formers.Mount the into the secondary and L3 primary feeding oscillator partially completed L2 in the chassis. The construc- tion of the secondaries is best left until the wiring of the unitisnearly complete.To make the secondaries, take a 6in length of the same p.v.c. covered wire and solder one end to the grid of V2.

v1 vos, M121

Fig. 5.The inter -valve coupling arrangement, solid arrows indicate "sense" of couplings signal into the secondary, both of which will be applied to the grid of V2, but the direct coupling between the two primaries is in opposition to the coupling between the two primaries via the second- aries. The net result is that there will be little if any coupling between the two primaries and we shall achieve the desirable object mentioned in Part1, namely minimum loading of the oscillator.

Method of mounting Trimmers M120

Fig. 4.Front-end chassis dimensions.Holes marked A are those to which earth tags should be fitted

Twist it anti -clockwise .round L3 once. Form a half knot and pull tight.Twist it clockwise round L2 M122 once.Twist the end once round the part which bridges L2 and L3.Pull tight round L2 and tighteh Fig.6. Conversion of variable condenser operated tuner unit.V,sc and crystals added to existing valves. up the twist using a pair of pliers. Cut the end off Note that a better arrangement would be to move the short and solder to junction of R2 and C3. switch and trimmers fin to the left (existing holes in Fix all windings in place, using adhesive. the chassis precluded this) Coupling Coils Check that the windings are in the correct direc- Construction tion.L2 and L3 are inductively coupled.In fact, It is best to carry out construction of the unit in if L3 were placed upside down on top of L2, it would the following- sequence: constitute one continuous coil with the "hot" ends (i) With switchandcoilformersomitted, in the centre as shown in Fig. 5. The two windings connect up heaters (pins 4 and 5, in the case of the secondaries, however, would oppose one of the ECC85) also h.t. positive wiring to another. pin 6 of the ECC85. Use insulated wire.

SEPTEMBER 1961 103 (ii) Add C1, C2, C5, C6, C8, also RI, R3, R4, feed, the anode load resistance was "lifted" from R5, R6 and R7, all lying flat close to the the anode pin of Vi and the primary of L2 inter- chassis. posed,theoriginalcouplingcondenserbeing (iii) Add R2 and R8. :eplaced by a 1,000pF condenser connected to (iv) Connect common side of crystals to pin 8 chassis. Similarly, as V2 formerly oscillated between of the ECC85. screen -grid and control -grid,the back coupling (v) Add coils and connect up. Add C7 and C3. condenser originally connected to thescreen -grid (vi) Add the switch and connect to crystals and was replaced by a 1,000pF bypass condenser to coil former.These connections should be chassis.Fig.7 shows these details "before and very short. after". (vii) Fix the trimmers and remaining condensers in place and connect up. Adjustment The centre spindle of the trimmers should be Part 1 of this article gave details for recognising rigidly connected to chassis via earth tags or thick the correct adjustment. A few further remarksmay bare wire. be helpful. First set L2 slug about three-quarters of theway in and the programme switch to "Home".(In Fig. 3 this switches in C9.) Screw in L3 slug until the position is found where the Homeprogramme can be heard over a few degrees of slug rotation and avoltmeterconnectedbetweentheautomatic volume control line and chassis shows no variation. Carefully find the mean slug setting for this. Now change the switch to "Light" and repeat the process using the appropriate trimmer instead of the slug. Next find the position for L2 slug which gives the same a.g.c. voltage for Light and Home programmes. Alteration of L2 may necessitate a slight alteration of the setting of L3 slug and "Light" trimmer. MI23 Finally, change to "Third" and adjust the remaining Fig.7. Showing alterationsto existing tuner unit trimmer.If L3 slug is altered for any reason, a enabling original VI andV2to be utilised.Left, before corresponding alteration of both trimmers will be conversion; right, after conversion (inter -valve coupling necessary. as in Fig. 3) If desired, a more "open" trimmer adjustment can be obtainedby using 8pF max. trimmers Right to Left Arrangement shunted by 4.7pF fixed condensers. As was stated earlier, provided certain require- Having adjusted the front-end, the i.f. part of the ments are fulfilled, the whole arrangement may be receiver can be checked in the usual way, using the changed around in order to conform to adaptation 10.7 Mc/s signal furnished by the front-endin requirements and the next example illustrates the conjunction with one of the B.B.C. programmes. conversion to crystal control of what was formerly Conclusion a vintage variable condenser type tuner. These three examples should be sufficient to show Fig 6 shows the layout. The variable condenser the reader how to adapt the scheme to his particular and original coils were removed and a switch fitted needs, but for success, he must comply with the rules together with the same type of coils as in the previous given, especially must he keep the wiring associated example and the same type of switch. Note that with the crystals and very short. the new components have been interchangedas Indication that some part of the wiring is too long compared with the previous example. Also,as the will be the hearing of one of theprogrammes when chassis was rather shallow, the trimmer had to be the switch is in the "off" position.If the fault is mounted alongside the switch instead of above it. not too serious it may still be possible to achieve The original V1 and V2 (both Z77's)were retained. crystal control inthe proper manner, and the A slight alteration to the connections of VIwas offending programme in the "off" position,can be necessary in this case.Formerly, the output from silenced by connecting the open contact of Si(a) V1 was shunt fed to V2. In order to alter it to series to pin 6 of Vosc.

CHANGEOF ADDRESS Jason Electronic Designs Limited, manufacturersofhigh fidelity audio equipment and electronic announce their removal from Gt. Chapel Street, Oxford test equipment, STAmford Hill 5477). Street, W.1, to Kimberley Gardens, Harringay,N.4 (Telephone The move has been necessitated byincreasing home space. and export trade and the consequent needfor larger factory

104 THE RADIO CONSTRUCTOR The second in a series of articles which, starting from first principles, describes the basic theory and practice of radio

part 2 understanding radio By W. G. MORLEY

IN LAST MONTH'S ISSUE WE DISCUSSED THE MOLECULE this diagram the brass cap (positive terminal) of the and the atom, pointing out that the latter lower cell connectsrothe zinc container (negative consists of a nucleus around which one or more terminal) of the upper cell, the e.m.f. required by electrons may orbit. By applying an electromotive the torch bulb being taken from the upper brass force, or e.m.f., to an electric conductor there is a cap and the lower zinc container.if two 1.5 volt general movement of electrons in one direction, and cells are connected together in series in this manner, this constitutes an electric current. The basic unit the total e.m.f. at the outer terminals is 3 volts. for e.m.f. is the volt, and the basic unit of current Fig. 3 (c) shows three cells connected together in is the ampere. series.In this case the cells are mounted side by side, and the connections from one cell to the next Cells and Batteries are made by wires soldered to the zinc containers It will be helpful at this stage to introduce some and brass caps. Once more the total e.m.f., appear- practical sources of electromotive force with which ing this time across two pieces of springy brass we areallfamiliar.A commonly encountered strip,is taken from the zinc container (negative source of electromotive force is the cell.Cells are terminal) at one end of the series arrangement, and employed (usually in twos or threes) in electric the brass cap (positive terminal) at the other end. torches, and may have the appearance shown in When three 1.5 volt cells are connected together in Fig. 3 (a).The cell shown here (known as a dry series the e.m.f. available at the outer terminals is Leclanche cell) has a zinc outer container and a 4.5 volts. central carbon rod fitted with a brass cap.Both A series combination of two or more cells is known zinc and brass are conductors, and the e.m.f. given as a battery. As has already been inferred, the total by the cell is taken from the zinc container and the e.m.f. produced by a number of cells connected brass cap, the former providing the negative terminal together in series is equal to the sum of the individual and the latter the positive terminal.The e.m.f. is e.m.f.'s.If we wished to construct a battery offering produced by the action of the chemicals enclosed an e.m.f. of 90 volts (as would be used in a portable in the zinc container and, in thir instance, is of the valve receiver) we could connect together, in series, order of 1.5volts.Often, a sleeve of specially 60 cells offering 1.5 volts each. treated cardboard or paper is passed over the zinc If we wish to do so, we may also connect two or container to provide insulation, whereupon connec- more 1.5 volt cells together in parallel, as in Fig. tion to the cell terminals may be made at the top 3 (d).In this case all the positive terminals are and bottom. connected together, as are all the negative terminals. It is usual to use two or more cells in an electric The e.m.f. available from this parallel combination torch, and these are connected together in series, is,however, only1.5volts;thatis,the e.m.f. as shown in the typical example of Fig. 3 (b).In offered by any of the cells so connected. Whilst the

SEPTEMBER1961 105 parallel combination of cells does not causean Dry Leclanche cells of the type used in electric increase in e.m.f., it can cause an increase in the torches are not capable of being re -charged, andare current which may be drawn. Let us assume that a discarded when they are exhausted.Cells of the single 1.5 volt cell is capable, under certain con- type employed in car batteries may, on the other ditions, of causing a current of, say, 0.1 amp to hand, be re -charged by passing an electric current flow when itis connected to an external circuit. through them.Cells which cannot be re -charged Two such cells, connected in parallel, could then be are known as primary cells, and those which can capable of causing 0.2 amps to flow; three could be be re -charged as secondary cells. A number of other capable of causing 0.3 amps to flow; and so on. cellsfallintothese two categories.A typical Thus, it may be said that connecting cells in parallel example is the mercury cell.This is a primary cell causes the total current capability to be the sum of offering an e.m.f. of some 1.3 volts which, because the individual current capabilities. it has a relatively long life and can be given small physical dimensions, is especially useful for hearing However, this point, which is intended to demon- aids,transistor receivers and other miniaturised strate the result of connecting cells in parallel, must equipment.Alternative secondarycellsare the not be considered as necessarily representing a nickel -iron NiFe cell (1.3 volts nominal anda very sound practical technique. For reasons which will robust type with applications in electrically powered become apparentlater,cellsarenot normally vehicles), the nickel -cadmium alkaline cell (1.2 volts connected in parallel to increase current capability nominal), and the Venner silver -zinc cell (1.5 volts unless they are identical, or nearly identical,in nominal). The latter two cells may be given small

Positive(F)terminalof cell Positive terminal of series combination

Positive terminal E.M.F=3volts of lower cell Fig. 3 (a). A dry Leclanche cell.Nominal connects to e.m.f. is 1.5volts, connectionbeing made negative terminal tothe central brass cap and the zinc of upper cell container NegatIve(-)terminal of cell (b).Two dry cells in series, giving a total Negative terminal of series e.m.f of 3 volts. An insulating cardboard combination sleeve may be fitted over the two cells shown here

E.M.E.4.5volts (c). A familiar type of series cell arrange- ment employed in electric torches.In this Positive(+) Negative() Positive (+) terminal instance the connections between cells are made with wire /Soldered (d).If two, or more, cells are connected in connections parallel, the total e.m.f. is still the same as for a single cell

I.5 volts

Inter -connecting wires Negative (-) 0 MI47 electrical performance. dimensions and can be employed insmall -size Another type of cell with which we are familiar equipment and powered models or vehicles, etc. is the lead -acid cell employed in car batteries. The Two points of terminology need to be mentioned nominal e.m.f. provided by a lead -acid cell is 2 volts, before proceeding further. A term fairly commonly and three such cells may be connected together in series to form a 6 volt car battery, or six cells used in place of "in parallel" is "in shunt". Thus, the cells of Fig. 3 (d) are in shunt.If a cellis connected together in series to form a 12 voltcar concted in parallel with a second cell, itmay be battery. In a car battery the series connections from desc ibed as being shunted across the second cell. one cell to the next are normally made by heavy The term accumulator is frequently used to describe copper straps covered with lead to provide protec- seco dary cells, or to describe batteries made up tion against corrosion. (See Fig. 4.) frosecondary cells.

106 THE RADIO CONSTRUCTOR Inter -cell connectors illustrates a battery having an e.m.f. of 6 volts.It may then be said that there is a potential difference of 6 volts between the two terminals of the battery. Itis usual to consider the earth as having zero potential and, if we connect the negative terminal 2volt cells of our battery to earth, as in Fig. 6 (b), we may then say that its positive terminal has a "positive potential of 6 volts with respect to earth".Reversing the Positive (+)terminal Negat ve () terminal battery, as in Fig. 6 (c), causes its negative terminal to have a "negative potential of 6 volts with respect E.ME =12 volts to earth".The terms "above" and "below" are MI48 sometimes employed to qualify potential, and they correspond to "positive" and "negative" respectively. Fig. 4. A 12 volt car battery, consisting of six 2 volt Thus, the positive terminal of Fig. 6 (b) may be cells connected in series described as being "6 volts above earth potential", and the negative terminal of Fig 6 (c) as being Circuit Symbols "6 volts below earth potential".Most electronic It would, of course, be wasteful of time to repro- equipment is built on a metal chassis, and itis duce actual cells when drawing up a circuit diagram, common to assume thatthechassishas zero and so a readily recognisable symbol is employed potential in just the same way as the earth (even instead. The circuit symbol for a cell is given in though the chassis may not be connected to the Fig. 5 (a), this consisting of a short thick line drawn earth). We may then encounter such expressions parallel to a long thin line. The long line represents as "6 volts above chassis potential", and so on. the positive terminal of the cell, and the short line representsthenegativeterminal.' Twocells connected in series may be represented as shown in Fig. 5(b)and three cells in series as shown in Fig. 5 (c); but it is more usual to depict a battery Potential 4 cell Battery (of any number of cells) in the manner shown in Difference each cell E.M.E= Fig.5 (d),the total e.m.f. normally being indicated = 6 volts 1.5volts at an adjacent part of the diagram. T Potential A very useful concept in radio and electrical Potential: 6volts engineering is that of potential difference.2 Fig. 6 (a) positive with respect to earth 1 A useful mnemonic here is to remember that a sign (positive) has a longer "length of line" than a - sign (negative). Judging from the correspondence received when the "tinder - Fig.6. Threesimple standing Television" series was published in The Radio Constructor, illustrations of potential _LEarth some readers have difficulty in visualising the conceptofpotential. and potential difference In consequence, potential and potential difference are dealt with here at some length. Potential: 6volts negative with respect Negative (-)terminal mlmiNegative (-) terminal to earth

Positive(+) terminal"7" Positive (+) terminal 1 -Earth

Negative (-) terminal jam 1.1.1Negative (-) terminal

It is useful to make an analogy between potential =IN WEI and height.If we have a cliff 60 feet high with a Positive (+) terminal Posive (+) terminal ledge 30 feet below (Fig. 7 (a)), and there are stones on the cliff top and on the ledge, these stones MI49 possess potential energy. A stone capable of falling from the 30 feet ledge to earth level would have a potential energy which corresponded to a height of Fig. 5.Circuit symbols. That at (a) isor a single cell, and those at (b) and (c) for two and three cell batteries 30 feet.Similarly, a stone capable of falling from respectively.The symbol at (d) is foa battery with the cliff top to earth level would have a potential any number of cells, the total e.m.f. usually being energy corresponding to a height of 60 feet. How- indicated in the circuit diagram at an adjacent point ever, a stone on the cliff top capable of falling to the

SEPTEMBER 1961 107 ledge would have a potential energy corresponding terminal, with respect to the centre terminal, is only to a height of 30 feet only.Fig. 7 (b) shows a 3 volts positive. 6 volt battery having its negative terminal connected Fig. 7 (c) shows the 60 feet cliff without the ledge. to earth and a connection made into it at the 3 volt There is, instead, a hill 30 feet high alongside the

Cliff top 6volts positive with respect to earth

Ledge

3volts positive 60ft with respect to0 earth ow

Earth Level

Cliff top

ss C:M.F.6V

60ft ENT= 6volts T

MISI r 30ft Hm. EME= 3 wits

A o

E.M.F 6voits Fig.7. Examples, discussed in the text,illustratingthe analogy between potential and height

cliff edge. A stone capable of falling from the cliff edge on to this hill would, as in the case with the ledge, still only have a potential energy correspond- Bo ing to a height of 30 feet. A similar set of circum- stances is shown in Fig. 7 (d), in which we have taken away the 3 volt connection into the 6 volt battery and have added, instead, a separate 3 volt battery connected as shown. As with the cliff and MI51 the hill, the potential of the upper 6 volt terminal is 3 volts positive with respect to the upper terminal of the 3 volt battery. point.Just like the stones at the 30 and 60eet Let us next add a pit 30 feet deep at the bottom levels, the potentials at the middle and top termi als of our 60 feet cliff.(Fig. 7 (e).) A stone capable of are 3 and 6 volts positive respectively with res ect falling from the top of the cliff to the bottom of this to earth. And just like the stone which could only pit now has a potential energy corresponding to a fall half way down the cliff, the potential of the top height of 90 feet.In Fig. 7 (f) we add a 3 volt

108 THE RADIO CONSTRUCTOR battery in a similar manner. The potential of the conductance.Resistance isthe opposition of a upper 6 volt battery terminal is now 9 volts positive material to the flow of electric current. with respect to the lower terminal of the 3 volt The resistance of a conductor varies according to battery. its dimensions.Let us assume that we have two The exercises of Figs. 7 (a) to (f) should help to equal -length wires having a square cross-section of show the concept of potential and potential differ- the same area, as shown in Fig. 8 (a). Both wires ence.Practical examples similar in basic principle are made of the same material and we can make to those described will be frequently encountered connection to their ends.If we were to measure in radio work. The beginner should pay especial their resistance individually we would find them to attention to the manner in which the 3 volt battery be identical.In Fig. 8 (b) we connect the two wires of Figs. 7 (d) and (f) is connected to the 6 volt in parallel.6If we were to measure the resistance battery.InFig.7(d)itsnegative terminalis connected to the negative terminal of the 6 volt 6 In just the same way as we connected the cells of Fig. 3 (d) in battery whilst, in Fig. 7 (f), it is its positive terminal parallel, except that there is no necessity here to consider polarity. which is so connected. As a final example, let us examine the two batteries of Fig.7(g).What is the potential difference between terminals A and B? The answer is that no potentialdifferenceexistsbetweenthesetwo Wires/ terminals.This is because the batteries are not connected together at any point, and they become, in consequence, completely separate. Wires havesquare sections of The term potential difference may be abbreviated equal area to p.d., and it is expressed in volts in just the same manner as e.m.f.Frequently, the term is omitted altogether, whereupon the upper 6 volt battery terminal in Fig. 7 (b), (d) and (f) would be described -0 as being "6 volts positive of earth". Again, the term voltage may be used, whereupon this terminal could be described as having "a positive voltage, above earth, of 6".3 We have introduced the term "earth" when discussing potential and potential difference. The fact that the earth may be considered as being at zero potential will be explained in a later article. Wire hqs rectangular section We have also, in Figs. 6 and 7, introduced the Area of rectangular sectiontg circuit symbol for "earth".4 equals sum of two square section areas Resistance If an e.m.f. is applied across a conductor, the current which flows will depend, amongst other things, on the material with which the conductor is 0 made. We have seen5 that the flow of electric current through a material is given by the flow of free Wires of equal section,. area electrons ithe direction dictated by thepolarity 0 of the appliee.m.f. (Polarity refers, here, to the

distinction betty positive and negative terminals OO of the source of.m.f.)Obviously, an infinite MI52 number of electronsannot flow in the conductor. There must be a limiti factor, and this will in fact be given by the numbe of free electrons available and the ease with which hey can pass through the Fig. 8 (a). Two wires made of the same material, and material. Some materials allow the flow of electric having the same length and area of cross section. Both current more readily than others, and they can be wires have the same resistance said to have a greater conductance. In radio work (b).If the two wires are connected together in parallel, it is generally much easier to work with a reciprocal the total resistance is half that of either wire quality(i.e.one which decreases as the other increases, and vice versa) and so we refer to the (c).Another wire, having the same length but twice resistanceoffered by conductors rather than to their the cross-section area of the wires of (a) and (b), also has half the resistance 3 The term voltage may also be encountered in place of e.m.f. Thus: "a battery has a voltage of 3". (d).The two wires shown here are made of the same material and have the same cross-section area.The 4 American terminology uses the word "ground" instead of "earth". lower wire is twice as long as .the upper wire, and has 5 In last month's article. twice the resistance

SEPTEMBER 1961 109 of this parallel combination we would find it to be cross-sectional area will obviously also hold true exactly half that of either wire on its own. The forwireswithroundcross -sections,orcross - reason for this is obvious enough: we now have, in sections of any other shape as well. the same length as before, twice as many free Fig. 8 (d) illustrates two wires of the same material electrons to provide the current.Fig. 8 (c) shows and cross-sectional area.One wire, however,is a single wire having a rectangular cross section twice as long as the other. Opposition to the flow whose area is equal to the sum of the two square of current in the longer wire will be two times section areas of Fig. 8 (a) and (b).The resistance greater because an e.m.f. applied to its ends will of this wire is the same as the parallel combination have to modify the movement of twice as many free of Fig. 8 (b) because, once again, we have twice as electrons alongitslength.In consequence, the many free electrons for the same length of wire. resistance of the longer wire will be twice that of Comparing Fig. 8 (c) with Fig. 8 (a) we can see that the shorter wire.The same reasoning may be by doubling the cross-sectional area of the wire we applied for other length ratios, and we can sum up have halved its resistance.It could be shown by by saying that, assuming constant cross-sectional similar means that if we trebled the cross-sectional area, the resistance of a conductor varies directly area we would reduce the resistance to a third of as its length. its original value, and so on. Summing up, it may be said that the resistance of a wire varies inversely Next Month as its cross-sectional area. For reasons of simplicity, In next month's issue we shall carry on with we used wires with square cross -sections in Figs. 8 resistance,introducingpracticalexamples and (a) to (c) but the relationship between resistance and covering Ohm's Law and power dissipation.

Radio Amateurs' Examinationand Morse Classes Grafton Radio Society announce that they haveagain made arrangements with Holloway L.C.C. Evening Institutes for official courses in the Radio Amateurs' Examinationand Morse (both for beginners) to be held this Montem School, Hornsey Road, Holloway, London, N.7. winter at The classes will meet on Mondays, withrepeat lectures on Tuesdays and Wednesdays, commencing Monday 25thSeptember-R.A.E. at 7-9 p.m. (instructors S. and P. Bernal (G3KQZ), followed by Morse 9-10 Iles (G3BWQ) p.m. (instructors L. Barber and A. Ralph). The fee for eithercourse will be 20s., or 22s. 6d. for the two. Enrolment will beat the school any evening (7-9 p.m.) Monday to Friday during the week 18th -22nd September, but application in the firstinstance should be made to the Grafton Radio Society Hon. Secretary, A. W. H. Wennell (G2CJN), 145 Uxendon Hill, Of the 30 who sat the May City & Guilds examination, Wembley Park, Middlesex, so that a placemay be assured. 23 passed making a grand total of 157 in eightyears.In addition to the above, the club meet in the same room on Fridayevenings for the usual club activity, including two transmitters and a monthly SWL meeting, commencing Friday 8th September, new members and visitors being especiallywelcome.

"THE DEPARTMENT IS VERY INTERESTED IN CIRCUITS, JONES, BUT NOT THE ONE AT GOODWOOD!"

110 THE RADIO CONSTRUCTOR This month Smithy the Serviceman, and his able assistant Dick, discuss a subject which has been requested by a number of readers, that of bringing old sound receivers back into service

ISN'T IT FUNNY,'. REMARKED DICK, "I see you've got tinned salmon people look upon them as being as he reached for his packet of sandwichestoday,"he continued `worn out' and just sling them away. lunch-time sandwiches, "the way casually."I'll swap this for one of "So our old set at home," pursued the t.v. sets drop off at the end of the yours !" Dick, hisinterest aroused, "could Summer ?" Very unwillingly, Dick took quite possibly have little more wrong Smithy looked round the Work- Smithy's sandwich and handed one with it than, say, a broken down con- shop.The racks, which normally of his own back in return.Smithy denser or something like that ?" carried a full complement of tele- attacked it with great gusto. "That's right." vision sets in for repair now held a "Why do we fix these old sets, Dick digested this information. few only, these being interspersed anyway," queried Dick, as he bit "There must be quite a number of with record players and transistor listlessly into Smithy's corned beef people," he commented, "with old .Several venerable broadcast sandwich."There are quite a few radios of this type which could pos- receivers stood sedately on one of the service establishments which won't sibly be fixed up quite easily.How shelves, their sober wooden cabinets even look at them, you know." would you set about the job ?" contrasting strongly against the gay "That'strueenough,"replied "Well," replied Smithy."Before and brightly coloured plastic cases of Smithy, his mouth full."But don't you started you would need to be t 'r successors. forget that we don't always repair quite clear in your own mind exactly 've got some reallyantedilu- them ourselves, either.If we think what it is you want to do.A com- vianj bsinaswell," continued the set is beyond economic repair we mon-sense approach would be to say Smithy's assistant."Just look at tell the customer accordingly." that if the old radio can be made good that old-timer over there !" Silence descended on the pair for a enough to bring in the Home and Dick pointed with scorn at a bat- moment as they sprawled comfort- Light programmes reliably thenit tered receiver which must have seen ably in the battered Workshop chairs would make a useful standby set for at least two decades of service. and enjoyed the lunch-time lullin the sickroom or, perhaps, the kitchen. "I suppose," said Smithy, referring their labours. Incidentally I would, personally, only to Dick's first point, "that t.v.re- "We've got an old Medium and tackle mains superhets and I would, pairs have eased off because the Long wave set at home," volunteered even then, make certain reservations. Summer weather has kept the insides Dick ruminatively, after a moment's Given an acceptable mains superhet, of the sets nice and dry.Anyway, deep thought."It packed in about itshouldn't infact be asking too it'stimewe startedourlunch. five years ago and we just stowed it much to expect fairlyreasonable Have a sandwich !" away in the attic. Iwonder ifit reception of, say, Radio Luxembourg would be worthwhile getting it out as well as the Home and the Light. Old A.M. Receivers again and see if it can be repaired. And I would suggest that some three Dick looked suspiciously at the After all, we could always use it as a to four hours for repairs would repre- sandwich offered by Smithy. standby set, or hitch it up in some- sent a sensible maximum time. How- "What sort is it ?" body's bedroom if they became ill." ever, that last point depends on the "Cornedbeef," saidSmithy "It mightn't be a bad idea," re- views of the individual carrying out heartily, "and full of vitamins." plied Smithy."Very often all that the repair." The Serviceman glanced at Dick's goes wrong with these older sets is a "It seems fair enough to me," said lunch package, and a momentary singlesimple fault.But,because Dick,hisenthusiasmmounting, gleam of cupidity shone in his eyes. they've attained the dignity of years, "considering that you are getting a

SEPTEMBER 1961 111 reasonable standby radio as a result gether can't share their lunch in an "There's nothing much else to do of the work.What's the next step?" egalitarian, comradely and unselfish inthepreliminary examination," "The next step," replied Smithy, spirit !" said Smithy, "except to have a look "is the very important one of ex- at the cabinet and, also, to make aminingtheoldsetand seeing Reluctantly, Dick handed over certain that the set hasn't been stored whetherit's worth the trouble of another of his salmon sandwiches in too damp a place, with the result getting it to work again.The first and regarded that given him by the that the chassis is a fruitful source of thing is that, in my opinion, it'sgot Serviceman with marked distaste. verdigris and plant life." to be a superhet or you're just wast- "Why," he asked,attackingit ing your time.Also, the i.f. should gingerly, "don't you think it's worth- be in the range 455 to 475 kc/s. I while bothering with parallel -wired Checking Out must admit that some old supers setswhichdon'thave6.3volt "I'm with this so far," said Dick. with 126.5 kc/s are still, believe it or heaters ?" "We've dug out the old set and not, giving good service.If you feel "Because there are no modern re- given it a preliminary butcher's which like having a bash at any of these I placement types,"repliedSmithy, shows that it might be worth the wish you luck, but don't ask me munching cheerfully."If the set has trouble of putting itinto working where you're going to get replace- a series heater string rather the same order.What's the next job ?" ment i.f. transformers ! applies.An 0.3 amp string is the "I would next get the works out," "After ensuring that it's a super - mostattractive,followedby anreplied Smithy, "and give them a het, check the valve line-up.Apart 0.15 amp string." good old blow-out to clear the fluff from the rectifier, you should have a "What about 0.2 amp strings ? and grime away.After which you frequency -changer, i.f. pentode, Plenty of English sets had these." can get down to real business.First double -diode -triode, and output pen- "Yes, they're O.K. too," agreedof all,look over the chassis for tode or tetrode.Sometimes, you Smithy, "and there are still plenty of obvious burn -ups.If there are any, may get a single diode instead of the 0.2 amp valves in the surplus market you trace the faults causing them in double diode, and it might just pos- which may help out here as well. the normal manner.After that, you siblybe tucked awayinthei.f. "The next thing to check," con- can quickly check the h.t. positive pentode.You might even have a tinued Smithy, "is the valveholder line to chassis for shorts, apply the Westector diode, this being normally type.If the valveholders are side - mains and switch on.If the set is replaceable, with advantage, by a contact or a similar obsolete type veryold and hasn't been useid for a crystal diode.If you haven't got the you can take a risk that the valves long time I wouldn't stand too close fouramplifyingvalves,plusthe currently fitted are O.K., but you for the first few moments." diode or diodes,I would personally must first ensure that the layout "Hey ?" advise against proceeding further if allows you to swap over to Interna- "I'mquiteserious," grinned you're interested in a quick economic tional Octal whenever you want to Smithy."There's just a faint risk repair.You just won't have the fita replacement valve.That's a of the electrolytics going pop when gain to play with." decision you can make yourself easily they first get h.t. on them !It's ex- "That's narrowing the field a bit, enough, of course." tremely improbable, incidentally, but isn't it ?" queried Dick. the risk exists.After switching on "Notreally,"repliedSmithy. you're on your own, and you follow "Many sets produced in the late 30's normalservicingpractice.Ifthe had this valve line-up and so did Push -Button Tuning valves light up you know that the practically all post-war sets." "Anything elseto keep an eyeheater chain or the primary and "What about an r.f. stage ?" open for ?" heater windings of the mains trans- "Not very common in this coun- Smith thought for a moment. former, as the case may be, are O.K. try." "An important feature," he re-Next, -check to see whether there's "Isthe valveline-up the only marked, "is the tuning arrangement. any h.t., what sort of noise is coming thing you need to check?" If this consists of a nice simple cordout of the speaker, whether the h.t. "Goodheavens,no!"replied reductiondrive,you won't have is getting through to the anodes and Smithy."There are lots of other much trouble here.On the otherscreen -grids, and so on.In other things you have to look out for as hand,ifthetuning arrangementwords you carry out pretty well the Nwell.Valve heater voltages are the employs one of those fantastic com- same tests you make on any Medium next pointIf these are connected in binations of cord, cogwheels and and Long wave receiver which comes rallel they should be 6.3 volts.If Bowden cable which used to be soin for repair." they're not,Ishould think twice popular in the old daysit would "Are there any general points to before tackling the setIncidentally, probably be better to give the set awatch out for when servicing these would you like another sandwich?" miss and return it to the cobwebs. old receivers ?" asked Dick, surrep- Again, the decisionis up to you.titiously reaching for another sand- Dick, suddenly jolted fromhis Rather the same applies if the set wich. thoughts of bringing his old receiver had push-button tuning.Before you "Have another of mine,"said at home back to life again, looked at start, you want to check the button Smithy genially. the Serviceman with suspicion. mechanism to see that it's not worn Dick examined the proffered sand- "What is it this time ?" out, and that the contacts haven't wich with an expression of revulsion. "Cheese," said Smithy brightly. become too heavily oxydised over "There's a big red stain on it." "Justcheese?" the years.It's just a waste of time "That's because it's a jam sand- "Yes," replied Smithy firmly. trying to repair an old set if the push- wich." "Don't say you want another of button tuning mechanism, for which "Jam ?" my tinned salmon ones !" spares will not be available, is past "Raspberry jam," explained "That's a nice friendly spirit,I its useful life." Smithy, coaxingly. mustsay,"complainedSmithy. "All that seems sensible enough," "You certainly go in," commented "The world's come to a pretty bad commented Dick."Where do we Dick, "forgrislylunches." pass if two people who work to- go from there ?" "Nonsense," said the Serviceman,

112 THE RADIO CONSTRUCTOR taking, with a masterful and adroit new condensers should of course smoothed h.t.line.Another point gesture, a further salmon sandwich have approximately the same capa- is that itis inadvisable to replace from his protesting assistant."It's city as is marked on the case of those reservoir condensers with new com- just that I like a little variety in my they replaceYou want to watch ponents having much larger values. food, that's all." out for working voltage, incident- Theincreasedreservoircapacity Dick frowned darkly at the jam ally, especially in the reservoir con- could cause therectifiertopass sandwich which had appeared in his denser.Some of the old sets had higher charging currents than it was hand, but made no comment. energisedspeakers(Fig.1), the designed for. "Paper condensers may also have got leaky in these old sets, and you Speaker Energisi Coil want to keep a special look -out for leaky condensersinanode -to -grid a.f.coupling circuits.There were HT quite a few mica condensers in these Rectifier sets as well, especiallyin. ther.f. Smoothed HT Cathode circuits.Sometimes, these conden- positive rail sers were just varnish impregnated, whereupon they became particularly 'Smoothing + Reservoir susceptible to physical damage. Con- TCondenser TCondenser nection to the plates was made by rivets (Fig. 2), and you might well 47x get an intermittent here." Chassis "What about if. transformers ?" M153 "You want totreat these with Fig.1. In some early sound receivers the speaker care," replied Smithy, "particularly energising coil also served as an h.t. smoothing choke. when you're lining them up.Most Because of itsrelatively high resistance this could of theoldi.f.transformershad necessitate a high working voltage for the reservoir variablecapacitytrimmerswith condenser `live' adjusting screws, some of which might connect to h.t. positive. Since

General Points "You asked me just now," said Metal Screwdriver blade Smithy, chewing happily, "whether there are any general points to look Sleeving Fig.3.I.F. transformers in old out for when servicing these earlier receivers had capacitive trim- receivers.As a matter of fact, there mers whoseadjustingscrews are. IF Transformer might be "live" to one end of "The first thing to look out for is Con ---- the winding they tuned.Apiece electrolytic condensers. I said just of sleeving slipped over a metal now that there's a very slight risk of adjusting screwdriver blade their going pop when they first get Trimmers preventsshort-circuitstothe h.t. on them.At the same time, can

M155

Condenser Body thetrimmerscrewshavetobe reached through holes in the can, they should be adjusted with screw- drivers made of insulating material. NRiyets71- If the screws are so tight you!lure to use a metal screwdriver,I should Metalstrip Lead -outs pop some sleeving over the shaft to MI54 prevent shorts to the can (Fig. 3).If the i.f. transformers had dust cores with an integral screwdriver slot you Fig.2.In early mica condensers lead -out connections should proceed with great caution, were made with the aid of rivets,as shown here. because the cores may have become Such connections occasionally became intermittent, brittle over the years and any core - particularly when thecondensers werevarnish locking compound that was used impregnated and hadlittlephysical protectionin may have hardened up.Use an in- consequence sulated screwdriver that really fits the slots in the cores." it's much more possible for them to energisingcoilactingasanh.t "Isit worth swappihg i.f.trans- lose their capacity with the passage smoothing choke.The resistance offormers on spec," asked Dick, "like of the years.When the set is really such a coil is' usually much greaterthe h.t. electrolytics ?" ancient it's not a bad idea to replace than that of a choke, with the result "Oh no," replied smithy."You the h.t. electrolytics as a matter of that the voltage on the cathode of the only want to change i.f. transformers routine; and you may find that this rectifier and, hence, that applied to if they have a definite snag. Most of automatically clears a lot of other the reservoir condenser, would be the transformers employed in these troubles in the receiver as well.The quite a lot higher than that on the old sets had really high Q's."

SEPTEMBER1961 113 "Are there any other things to them severelyalone,apart from tion away from Smithy's actions. look outfor whilst lining them up ?"trimming, if they appear to be work- "Not normally," replied the Ser- "Not really," replied Smithy. "Justing reasonably well.And don't ex- viceman."But you might get quite line them up like you would a modern pect too much from any Short wave a lot of trouble with if. instability. receiver.There were one or twobands that may be fitted, because You see,it'satthe intermediate smallerreceivers,however, whichthese were a bit of a joke in some frequency that most amplification in needed a little extra treatment. Thesereceivers.In any case the whole an a.m. sound receiver takes place. hadthetuningcondenserfitted point of the repair is to obtain a This holds true for modern sets as directly to the chassis without rubber standby set capable of picking up the well, of course.With the old sets there was a very common cause of i.f. instability which I should tell you about.The i.f. valve was frequently covered with metallising to provide a screen, this metallising being connec- ted to a wire wrapped around the Fig. 4. Early frequency -changers bottom of the glass envelope.If the usuallyhadthesignalgrid glass came unstuck from its base, the brought out to a top cap connec- metallising would break away from tion.This enabled an aerial to the earth wire (Fig. 5 (a)). The cure be readilycoupledintothe for this was to stick the glass back receiver for test purposes into the base again and wrap tinned copper wire several times around the metallisingatthebottom.You M156 then ran a lead down the side of the valve base to the pin the metallising normally connected to, and soldered

mountings.If you got the i.f's.in these sets spot on frequency there was a tendency to go into audio oscillation when you tunedin a Fig. 5 (a). A common station.The reason was that the i.f. fault with metallised Metallising response was too sharp and you were valves. Inthis dia- broken away Earthing wire getting feedback from the speaker gram the metallising from earthing back to the tuning condenser.' has broken away from wire "1 know the effect," chimed in the earthing wire. Dick."The sound from the speaker (b)Themetallising gets back to the tuning condenser, may be re -connected O vibrates the vanes and frequency as shown here. The modulates the signal.The resultant connection to the pin is changed to a.m. on the skirts should be made as of the .. response anti is applied to high up as possible. the speaker." It may be necessary "That'stheidea,"confirmed to file off the plating Ends of Smithy."The whole arrangement onthepinatthe Timed copper wire twisted gives you a positive feedback loop. point of connection to wire wrapped together Anyway, if you get this effect after enable a reliable around glass lining -up it's best to slacken off the solderjointto be alignment a little.You can easily made Wire soldered rock your signal genny when you're to earth pin doing this, to see if you're still getting a decent response." MI57 Smithy took a sandwich from the packet at his side, and looked at it with interest. Home and Light programmes. Don't at this pin (Fig. 5 (b)).This cure "What happens if you haven'tgot forget that, provided the oscillator is earthed the metallising and cleared a signal genny ?" asked Dick, his working, you can always getsome the i.f. instability." eyes glued to Smithy's movements. sort of signal into the i.f. and a.f. Smithy pausedreflectivelyand "Tune in a station and rock the stages merely by applying a short looked down at his hands. receiver tuning condenser across it," aerialtothesignalgridof the "Dear me," he said, in a nostalgic replied Smithy."This'll give you a frequency -changer via a 100 pF con- tone of voice, "1 wish I had as many fair idea of what the response is like." denser (Fig. 4), and this can be jolly pounds as I've cleared i.f. instability useful for test purposes.Since the that way !" The R.F. Stages signal grid often appeared as a top Dick's mind, however, was not on "What about the r.f.circuits in cap in early frequency -changers, the the past but on the immediate pre- these old sets ?" process of applying the aerial can be sent. "Well,"repliedSmithy,"these quite a simple operation." "I do wish you'd do something tended to be pretty complicated in Smithy looked fondly at his sand- with that sandwich you're holding," some cases, with bandpass coupling wich, but made no attempt to eat it. he remarked irritably."It's getting and all manner of things like that. "Could r.f. instability be a prob- on my nerves your looking at it all The best thing to do here is to leave lem ?" asked Dick, tearing his atten- the time."

114 THE RADIO CONSTRUCTOR "Ah," said Smithy, "this one's "There are several ways of doing I must add, though, that this tech- special. I want to savour it." it," replied Smithy, "but what I've niqueisintended for old receiver "Yes, but what's in it ?" always done with cheaper speakers loudspeakers with central'spiders' "I would prefer not to tell you at is to centre them by eye.You first only, and is most definitely not re- this stage," replied Smithy equably. of allplace the speaker, magnet commendedfor expensivehigh Dick sighed. downwards, on the bench and very fidelityunits, or anything of that "Well," he saidresignedly."I lightly hold the cone on either side of order.In the latter case you must shall have to give way in the end, I the centre with your two hands. follow the manufacturer's instruc- suppose, if only to satisfy my curio- (Fig. 6 (a)).You have your thumbs tions.With modern television and sity.Pass it over !" on the top and your fingers, passed radio speakers, of course, no centring Smithy obeyed with alacrity, and through the gaps in the metal frame, adjustment is normally available, as twofurthersandwicheschanged on the back of the cone.Then you they are pre-set at the factory." hands. carefully raise and lower the cone, Smithy paused and lit a cigarette. "This," remarked Dick, after an allowing its own suspension to guide "1 like a smoke after my lunch," incredulous examination of Smithy's it and keeping pressure exactly the he pronounced grandly."By the offering,"is just about the end ! same on both sides, and listen and way, what was that you said just now Untilthis momentInever even feel for any interference between the about poisoning ?" realisedthat you could havea coil and the pole -pieces.If there "Iwasreferringtoptomaine dripping sandwich." is, you loosen the centre -screw of the poisoning," replied Dick carelessly. "I thought you'd likeit," said flexible 'spider' in the middle of the "It's a loose term for the poisoning Smithy. "Dripping is a very rich cone (Fig. 6 (b)) and carefully' re -set you get from food that's gone bad. source of protein and carbohydrates. the cone so thatitlooks central. Like tinned food." And it'sabsolutely crawling with Tighten up the centre -screw again `,`Yes," said Smithy, thoughtfully. calories." and test once more for interference. "I thought you mentioned something Smithy's assistant gave a violent It may be necessary to carry out this like that.But why raise the matter shudder. operation several times, because the now ?" "Well,"heremarked,"you've final turn of the centre -screw some - "Oh, it was a little thing I just wolfed all my tinned salmon sand- wiches, so I suppose I'll just have to eat this horrible thing.What it will do to my stomachIhesitate to think." "It'll do it the world of good," saidSmithy,smackinghislips. "ive the old digestive juices some- thing to really work on." "Perhaps you're right," said Dick. He thought for a moment. "Anyway," he continued darkly, "it's better than ptomaine poision- ing." Smithy looked suspiciously at his assistant. "What did you say ?" Spider'-. securing "Just a thought," said Dick hastily. screw "Anyway, let's get back to these old receivers.What about speakers, for 'Spider at instance ? I should imagine that centre of cone these would be one of thefirst things to replace."

M158

Loudspeakers Fig. 6 (a).Part of the process of centring a loud- "Funnily enough," replied Smithy, speaker, as described by Smithy "that's not entirely true.If the set has been stored reasonably well you (b).The "spider" at the centre of the speaker cone. will often find that the speaker gives The spider -securing screw fits to the centre pole -piece quite adequate reproduction.Not of the magnet assembly hi-fi, of course, but certainly good enough for a Medium and Long wave receiver which is only intended times shifts the 'spider' slightly. The remembered," said Dick, in an off- to be a standby anyway. You would process sounds a bit fiddling but it's hand tone."About tins bulging." be surprised, in fact, to hear how pretty easy in practice once you've "Bulging ?" good some of those old sets sound. gottheknack.The important "Before you openthem.Ap- Shouldthespeaker seemabit thing is to treat the cone as gently as parently, if the ends of a tin of food scratchy it may need re -centring, but possible." bulge outwards it means that the that isn't too hard a task if you're "It sounds a bit hit-and-miss to contents have gone bad and have careful about it." me," remarked Dick. realeased a lot of gas. Gone putrid, "How would you set about it "I don't know," replied Smithy. in fact." yourself ?" "It's worked well for me in the past. Smithy looked uncomfortable and

SEPTEMBER1961 115 stubbed out his cigarette. speaker.The second way out of the ours tonight and see if it's worth "It seems a funny sort of subject troubleconsistsof replacingthe having a go at." to bring up," he remarked eventually. energising coil by an ordinary choke There was silence for a moment. "Perhaps so," said Dick artlessly. in series with a resistor which brings Dick waited expectantly. "Anyway, we're getting off the point. the total resistance up to that of the "I suppose," Smithy started, then I suppose you've got to replace the original coil.The third method if relapsed into silence. speaker in these old sets sometimes." you can get away with it, consists of "Yes ?" said Dick brightly. "Oh, yes," replied Smithy, return- simply replacing the energising coil Smithy swallowed, and tried an- ing thankfully to the subject of old with a resistor of the same resistance. other approach. receivers. "Such replacements If this results in hum you then have "Well," he remarked."You had would be most frequent in sets with to try and remove it by increasing the some of those tinned salmon sand- small cabinets which dissipated a lot value of the smoothing condenser- wiches, didn't you ?" of heat.This heat could, with time, not the reservoir condenser-after "I did not," replied Dick dry out the cone and voice coil the resistor.You should be able to aggrievedly."You scoffed the lot." former, causing them to be distorted get hum -free reproduction in most Smithy looked unhappy, and Dick out of shape and brittle." cases with this technique. decided to relent. "What happens if it was an ener- "You may find, by the way, that "I was just pulling your leg," he gised speaker ?" asked Dick. "You energised speakers had hum -bucking said, "about the salmon being bad." don't get energised speakers nowa- coils connectedinseries with the "Thank goodness for that," said days." voice coil.These coils were moun- Smithy in a relieved tone."It would "You just replace it with an ordin- ted inside the energising coil assem- have been terrible if we'd both been ary permanent magnet speaker." bly, and their purpose was to apply off sick together." "Yes," insisted Dick, "but what a current to the voice coil which "Together ?" about the energising coil itself ? You cancelled out the small variations in "Yes," said the Serviceman in- said just now that this may act as a magnetic field produced by the ener- nocently."Didn't you notice any- smoothing choke.But you can't gising coil acting as a choke.You thing funny about that dripping." replace it with a choke directly be- simplyforget about hum -bucking "Oh, come offit,"said Dick cause the latter would have a much coils when you fita replacement indignantly,"don'ttrythe same lower resistance." permanent magnet speaker and con- trick on me !" "Isee what you mean," said nect the speaker transformer second- "Well," replied Smithy, shrugging Smithy."Well, there are three ways ary direct to the voicecoil." his shoulders."I only thought I'd out of this problem.An easy way An Unanswered Question mention it." consists of unscrewing the energising "And that," concluded Smithy, Dick sighed.He knew it would coil, complete with pole -pieces, from "is pretty well the whole storyon take a good half-hour to get Smithy the s er frame and mounting it in bringing old receivers back to life to admit there was nothing wrong convenient place in the cabinet.It again." with the dripping.But what can will still act as a smoothing choke but "Thanks,Smithy,"saidDick. you do with a guv'nor who insists itwon't now be coupled to the "I'm going to get out that old set of on getting the last word ?

A Divisional Structure for the Institution of ElectricalEngineers Much of the scientific work ofthe Institution has been for manyyears conducted by four Specialised Sections (Electronics andCommunications, Measurement and Control, Supply,and Utilisation). The Council have decided that it will be advantageousfor the four Sections to be replaced by three Divisions, of which will represent "Electronics" and "Power" two interests, while the third, a "General" Division, willcover activities of common interest to all electrical engineers,such as basic measurement and technological education. Each of the Divisions will comprise a number of TechnicalGroups designed to cover the specialisations within its field, and the scheme provides for speedy readjustmentand creation of these Technical Groups which will flexibility which is now more than ever increase the necessary to reflect the rapid developments of electrical science andengineering. In setting up a divisional structure the Council also engineering, and the part being played by electronicsrecognise the increasing importance of electronics in electrical engineers in the work of the Institution which has resultedin its present position as the professional home of electronicsengineers. Minor bye-law changes will be required, mainly ofterminology, and these will be put to the membership Special General Meeting in due course. at a

116 THE RADIO CONSTRUCTOR Microphone Pre -amplifiers Attenuators and Mixers

by F. C. JUDD, A.Inst.E.1

icrophone Pre -amplifiers or from resistive paths likely to be found PRE -AMPLIFIER IS REALLY AvoltageAMPLIFIER in poor quality valveholders and from reversed grid suitable for operation from very low level current. input sources, but with output characteristics s itable for matching to an amplifier having pro - v sion for high level input only. It is commonly used ith most low level and some types of ramophone pick-up in order to build up the signal rom these sources to approximately 1volt r.m.s. cross a high impedance.This allows a volume ontrol or attenuator to be placed between the pre -amplifier and the main amplifier. In some cases, however, the volume control may be included in the pre -amplifier itself and between stages if more than one valve is used.It is not good practice to have a variable attenuator at theinputto a high gain pre- amplifier unless the input signal is very large.If E114 the signal must be limited, it is better to incorporate Fig.1. Circuit of the high gain microphone pre- a fixed attenuator in the grid circuit and use a amplifier variable attenuatorafterthe first amplifier.The pre -amplifier requires the same design consideration as any othervoltageamplifier and particulat: Components List attention must be paid to hum pick-up, noise and (Fig. 1) microphony (ringing effects from the valves), all of which present their special problems. Resistors Random noise includes both thermal agitation R1 5M S2 Hi -Stab and valve noise, much of the energy of this noise R2 2.2kc/ Hi -Stab being distributed uniformly over the whole of the R3 100k0 Hi -Stab frequency spectrum. Noise also comes from circuit R4 390k S2 Hi -Stab components such as resistors, and this will be added R5 47k0 carbon (composition) to that from thermal agitation, etc.Most of the noise in a low level amplifier is due to three principal Condensers causes; noise from the anode load resistor, valve C1 501.LF electrolytic noise, and noise in the grid (input) circuit.Other, C2 0.25p.F paper smaller, contributions may come from the screen and C3 1611F electrolytic cathode circuits. Much of the noise may, however, C4 0.11.1.F paper be reduced by the use of high stability cracked carbon resistors and by limiting the pre -amplifier Valve h.t. supply to between 100 and 200V. V1 EF86 Mullard Valve noise may be reduced somewhat by using triode valves, but at the expense of losing gain and If the output source is of low impedance and the possible introduction of hum. Practice generally coupled to the grid by means of a step-up trans- is to use a low noise pentode valve such as the former, itis not always necessary to design for Mullard. EF86 which has been specially designed as minimum valve noise.In this case the input circuit a high gain, low microphony, low noise amplifier should be arranged so that the microphone im- valve.There' are other sources of noise; namely, pedance reflected into the grid is at least twice, but leakage in the valve itself between the grid and other better, four times that of the valve noise resistance.

SEPTEMBER 1961 117 This may be accomplished by usinga transformer secondaryimpedance of 25 to 40ICSI in which matching transformer witha high ratio and a case valve noise will have a very small effect reflected secondary impedance of251(S) or more on the isused,thesignallevel total noise. This allows amore satisfactory use of will be high and an high mu and pentodes. extremely low hum level is not quiteso necessary. If, however, a low level microphoneor pick-up is directly connected into the grid circuitwithout a transformer, considerablecare will be needed in preventing the circulation of humcurrents and their introduction into the grid itself.The following precautions should be taken whenconsidering design and construction: (1) The amplifier valve, associatedwiring and components must be carefully screened. (2) Matchingtransformersmustbeelectro- magnetically shielded from stray 50c/s fields. This can only be successfullyaccomplished by the use of mu -metalscreens, orientation of the transformer and for exceptionally lowlevel EII5 hum, by the use of hum -buckingcoils. (3)Care must be taken over all "earth"connec- Fig. 2.Circuit of a pre -amplifier for a low impedance tions. microphone Hum loops can be formedeven by external cables. These loops will ofteninduce currents into the grid and cathode circuitsof the valve itself. Components List (4) Heater wiring should be twistedand taken by (Fig. 2) a suitable route, in order to avoid coupling with other leads and components. esistors (5) Valves should be mounted RI 1MS2 Hi -Stab away from mains supplytransformersandelectrostatically R2 2.2k12 Hi -Stab screened. R3 l00kI Hi -Stab (6) If exceptionally high gain is required R4 390k) Hi -Stab it may be necessary to drive the amplifierfrom pure R5 47kS2 carbon (composition) d.c. supplies, e.g. batteries. (7) D.C. h.t. supplies derived from50 c/s mains Condensers must be well smoothed and decoupled. C1 0.054F paper In practice the limit on amplificationis set by the C2 504F electrolytic noise level due to thermal agitationin the grid C3 16t.t.F electrolytic circuit of the first valve, plussome of the noise C4 161.LF electrolytic generated by the valve itself. C5 0.14F paper For a bandwidth of about 15,000 c/s noise due to thermalagitation may be about ' -129dBm.1 Valve If the effective microphone VI level is taken as, say, -60dBm Withan unloaded EF86 Mullard microphone, the maximum possible signal to noise Transformer ratio will be about 72dB.The figure would be reduced to around 68 to 69dB fora loaded micro- T1 Microphone, 100:1 phone.In actual practice, and because of other contributing factors such as hum fields, overall noise may be considered satisfactory if it is within 10dB of the thermal noise.

When crystal microphones are used, almost the whole of the microphone noise emanates from the In - In Out grid resistance, the signalto noise ratio being Out poorest for values around 100KO.Improvement

is gained if the grid resistance is made smallerbut EDO this, however, will affect the frequencyresponse of the microphone. The alternative is to make thegrid Fig. 3 (left).Continuously variable volume control resistor very much larger, a valueas high as 50M Q (attenuator).Fig. 4.Constant impedance attenuator being indicated for very low noise.In practice, a (T type) value around smn is used and this isa good com- promise for a noise voltage of 44Vor so (this equals Hum approximately -108dBv ref: 0dB =1V). The noise In a pre -amplifier the permissible hum voltage resistance of a pentode is negligible by comparison present at the grid of the first valve depends some- what on the maximum available signal input.If a 1 dBm indicates power expressed in decibels with OdB=I mW.

118 THE RADIO CONSTRUCTOR and thus permits a signal to noise ratio of at least 60dB with diaphragm and sound cell types of microphone. Out A Signal Stage Microphone Pre -amplifier The circuit of Fig. 1 shows a simple pre -amplifier, suita le for a crystal microphone of the diaphragm typ with a sound pressure of around 10 dynes/cm2. ElIB Its an amplifier suitable for recording purposes and Fig. 6.Parallel mixing network f r use in a combination mixer circuit where two or more inputs may be fed into an attenuator with the cathode resistors as in the circuit of Fig. 5. network like that of Fig. 6. A recommended valve Any pentode type valve with a sharp cut-off is is the Mullard EF86 for which the anode, grid and suitable although a valve with a high mutual screen resistors should be high stability cracked conductance would limit the maximum attenuation. carbon types. For low impedance ribbon and moving coil Non -Constant Impedance Mixers microphones the circuit of Fig. 2 should be used. This type of mixer employs the simple "volume This employs the same valve but requires a step-up control" type of variable resistor which is commonly transformer to obtain a correct impedance match used for most domestic type amplifying equipment between the microphone and grid circuit. and radio receivers. Various combinations employ- ing these simple controls can be used with or without valves but it must be emphasised that a combination as shown in Fig. 6 for example, is quite unsuitable for high impedance crystal microphones because of attenuation by loading,thepossibilityof hum pick-up, and noisy operation of the sliders.The insertion attenuation is about 10dB. The arrange- ment is suitable for direct mixing of high level signal sources such as the output from a radio receiver or gramophone pick-up. It can be combined with valve amplifiers for mixing microphones and, when used with pre -amplifiers such as those shown in the circuits of Figs. 1 and 2, provides the basis of a multi -channel mixing unit. Another widely used mixing circuit is one employ- ing a valve, or valves, with a common anode load as in Fig. 7. When two valves, such as a double EII7 triode, are used in this type of circuit the anode Fig. 5.Electronic attenuator (basic circuit) resistance of each valve acts as a shunt across the other thereby reducing the gain. With pentodes this loss of gain is negligible, however, and may be Attenuators and Simple Mixers ignored. The continuously variable volume controlis commonly used in tape recorders, simple valve Design for a Mixer microphone mixers, radio receivers, and amplifiers. Combining the parallel network mixer circuit with Its uses as an attenuator are limited because the high gain microphone pre -amplifiers, provides the voltage ratio is proportional to the resistance ratio only when the load at the output terminal is very much greater than the total resistance (R) of the attenuator.(See Fig. 3.)Logarithmic and linear characteristics are used, the former being adopted mainly for volume control purposes. Although this type of control has certain disadvantages as an attenuator, its low cost and otherwise reasonably noiseless operation makes it suitable for even high fidelity amplifying equipment.It would, however, be quite unsuitable for high grade studio recording equipment, which would be more likely to employ a constant impedance device for fading and mixing as shown in Fig. 4. For some purposes an electronic attenuator may be advantageous and a possible arrangement is one EII9 utilising a cathode follower in which the screen Fig.7. Simple mixer using a twin triode with a voltage of the valve may be varied by VR, together common anode load

SEPTEMBER 1961 119 +250V

C7 R20 Ri5 7716µF 2714n 221Rn

R7 Rr3 R2 R3 390Ian 100190 390I9n 10 Okn RIB 5.6Kin

R16 CII 100 -7716pF R14 nen I-5Mn C3 CIO 0.1pF C6 V2 C9 0.01µF EFB6 0.05µF 85 0.1µF R11 R12 V3 RIO 390190470 CI 470kn 470 ECC83 0-05F C4 -I C12 0-05 µF Radio Pickup Output input input. - R21 RV4 RVg RI9 R17 IMn C13 500 I.519n RI R6 500 RV13 CB= 10Mn 19n 2.2Rn 50pf w 02 10 C5 500 50µF 0.25µF Mn 0.25µF Irtn #22 47I9n

sMie.ln ut 2nd Mic. input

EF86 ECC83 93

E120 Fig. 8.Four channel signal and microphone mixer (circuit by permission of Mullard Ltd.) basis for a very efficient multi -channel microphone suitable for connection to a high impedance input and signal mixer as shown in Fig. 8, which was of a tape recorder or high level amplifier and allows " developed by the Mullard Research Staff.2The the use of a fairly long connecting cableif so circuit employs the EF86 low noise amplifier with required. The frequency response of the mixer is high value grid resistors and utilises a four channel flat from 20 to 20,000 c/s and the noise levelis parallel mixing network.This is followed by an -50dB at full gain. intermediate amplifier with negative feedback from which the signals are taken via a cathode follower 2 The circuit given in Fig. 8 is taken from Chapter 10 of Milliard to the output terminal, which has an impedance of Circuits for Audio Amplifiers, and is reproduced by permission of approximately 600 ohms.This makes the mixer Mullard Ltd.

REMOTELY CONTROLLED TELEVISION STATION ON NORWEGIAN ISLAND The Norwegian Telegraph Administration is building a television station on the island of Bokn in Stavanger Fiord and is to operate it by remote control from the mainland by means of a v.h.f. radio link. The transmitters selected for this purpose-two 4kW vision and two 1kW sound-are of Marconi manufacture and are suitable for unattended operation.In addition to the transmitters, Marconi's are to supply and install programme input and ancillary equipment. The equipment will operate in Band III to 625 line C.C.I.R. standards. The two vision transmitters are to be connected for parallel working, as also will the f.m. television sound equipments. Remote control facilities over the v.h.f. link will include the independent on -off switching of all four transmitters; the control of blanking level (including the on -off switching of blanking level feedback), and the control of video and audio gain. An indication of power output at normal, high and low levels will also be provided over the link.It is intended that adjustments to the controls will be made in conjunction with a waveform display derived from a high-grade receiver and oscilloscope sited at the remote control position on the mainland. The order was obtained through the Marconi agents in Norway, Norsk Marconikompani A/S.

120 THE RADIO CONSTRUCTOR Cover Feature The JR1 Streo Tape Recorder Unit PART I.By G. BLUNDELL

This article outlines in detail thetheoreticalfactors which were considered during the development of the Jason JR1 Stereo Tape Recorder Unit.Constructional detailswill commence innext month's issue.-Editor.

IN THIS DESCRIPTION OF A HIGH QUALITY TAPE ments have been made with quarter track heads, recorder the emphasis will be on electronics, a which allow two stereo, or four single tracks on the later section showing how to obtain the optimum standard *in tape. performance with a number of popular tape decks. No wild claims for frequency response will be The various parts of the circuit are described here made-a recent directory showed that some cheaper so that the constructor will have an understanding tape recorders claimed a wider frequency response of the design considerations involved. than the professional and studio types. In practice, A tape recorder requires a tape deck, playback and re- cordingamplifier. Inthe cheaper type of tape recorder, the same amplifier circuitis switched to be used for record or playback, only two heads being required on the tape deck, i.e. a combined record/ playback head and an erase head. In the Jason Stereo Tape Recorder Unit three heads are Pinch Roller used, and a typical arrange- ment of theseis shown in Fig. 1 Fig. 1. The tape is pulled from careful judgment is required in relation tothis one reel to the other by the capstan and pinch roller, question of frequency response, because distortion and is held accurately in line with the heads by the and background noise are also of importance and guides. A recording may be played back a fraction of these three factors are inter -related. The technique a second later as the tape passes from the record to of boosting the playback response with tuned the playback head and the quality of the recorded chokes mayresultinanexcellentfrequency signal may be immediately judged and compared characteristic but it also increases background noise with the original programme. Although this feature and transient distortion. This kind of circuit must slightly increases the cost of the unit, it is invaluable be rejected. The aim is to produce an acceptable when thereis only one opportunity to make a frequency response at 71 -in per second (i.e. reason- particular recording which has to be right first time. ably flat to 15 kc/s), and we can expect the quality The circuits of the Jason tape unit are duplicated and surface noise to be at least equal to the best for stereo, and the switching is so arranged that the gramophone records available. two stereo tracks may be recorded independently; To continue this point a little further, a recent thus the playing time of the tape is doubled when 12in stereo disc is altnost silent between the recorded stereo is not required. In addition, all the measure - items, the "surface noise" which then appears being

SEPTEMBER 1961 121 in fact tape recorder noise recorded on to the disc. the tape running at 15in per second; now we can The gramophone disc is not dead yet and seems achieve this at 3Iin per second with greater output. unlikely to become obsolete while it can be mass- produced so easily.Therefore, in saying that our Range of Frequencies to be Recorded tape recorder is to produce results which are as good The character of a musical instrument is given by the overtones or harmonics Magneti flux induce in tape and these extend in frequency out of the range of human hearing.Some people can hear frequencies up to 20 kc/s, while others, often older people, can only hear up to 10 kc/s. A good compromise Itemanence is that the frequency response should be flat to 15 kc/s and then gentlyfallaway.The H Flux in record pianoandorganprobably head gop cover the widest ranges of Coercivity frequencies, since the funda- mental notes or tones extend from 25 c/s to 4,000 c/s. A violin extends from 200 c/s to Fig. 2a 3,300 c/s, and a man's voice 4 5 from 100 c/s to 200 c/s.To Fig. 2c those fundamental notes must be added the harmonics which provide the character of the sound.

The Recording Process The recording tape is coated Record head input with a material such as ferric Fig.26 oxide,whichiscapable of being magnetised.The be- as the best gramophone disc we are, in fact, setting haviour of thismaterialis a high standard. Our tape recording will not, of shown by the hysteresis loop in Fig. 2 (a). From this course, be liable to mechanical damage and wear, we find that, if the tape is magnetised to point "a" by but it can be damaged by magnetised heads,so that a current in the head which rises and then falls to care must be taken in other directions in order to zero, the magnetic field in the tape will fall only preserve a good recording. History of Tape Recording The first magnetic recordings were made over fifty years ago, and before the war the B.B.C.were using steel tape running at 60in per second. Before the invention could become practical two further ideas were required, these being high frequency biasing(firstusedin1921) and plasticbased magnetic tape, which could be easilyhandled. During the war, the Germans developed magnetic recording to a fine art and, since then, the major advances have been improved magnetic powder on the tape, which allows better frequency response and greater output, and fine gap playback heads, which have improved t',e overall frequency response. At the end of the war a 10 kc/s response required

122 THE RADIO CONSTRUCTOR to "b". This level is known as the remanance of the are given by high frequency biasing. By adding a tape and is a measure of the strength of the signal bias frequency of approximately 70 kc/s to the which may be recorded on the tape.If the current programme signal the distortion shown in Fig. 2 is reversed, a signal amplitude OC will be required can be overcome. The problem in Fig. 2 is that the to bring the tape magnetic field to zero.This tape behaves as though the particles have a magnetic amplitude OC represents the coercivity of the tape, friction which prevents the field in the tape following and offers a measure of how well and how long the the field in the head immediately.The high fre- tape is capable of storing a recording. quency biasing acts as a magnetic lubricant by We can find from the hysteresis loop what will happen to the tape when we feed a signal (Fig. 2 (b)) into the record head. Fig. 2 (c) shows the resulting magnetic field in the tape. The figures on -Fig. 2 (b) represent intervals of time. If we begin at 2 we can read from the hysteresis loop that the field in the tape will be as shown in Fig. 2 (c). At time 3 the record signal has returned to zero, but the field in the tape has not. The curve which we would see on an oscilloscope connected to the playback head would, in fact, show a steeper front and the peak at 2 would be more pronounced. The pronounced peak is due, as is explained later, to the fact that the output from the head depends. on the rate of change of the field, and this has the effect of increas- ing the distortion. As can be seen, Fig. 2 (c) bears little resemblance to our initial sine wave input to the head winding and represents very considerable distortion. D.C. biasing added to the signal input was first attempted to overcome this distortion. Fig. 3 shows that, with d.c. bias, the excursions of the input signal never take the field in the tape away from the top of the hysteresis loop, and that the resulting output, as shown on the right of Fig. 3, is low. Distortion is still present but the sine wave shape is now recognisable in the output. Although subjecting the particles of the tape to very rapid this biasing is an advance, the resulting distortion changes of field.Imagine now that the signal in and low output signal make it a suitable method the head has been increased and then reduced to only for dictation machines. Much better results zero and the tape has been magnetised to the level

Fig.5

SEPTEMBER 1961 123 Ob as shown in Fig. 4.Although the biasing fre- trailing edge of the recording head gap, as is shown quency has been operating all this time let us now in Fig. 6 and the signals to be recorded all undergo consider what is happening at the instant when the this treatment.The magnetic tape is,therefore, record head signal has become zero.As this continuously cycled through the reducing hysteresis particular portion of the tape is leaving the record loops so that, at the moment of leaving the recording head it is subjected to decreasing cycles of the bias head. it is magnetised exactly in proportion to the programme input. The applica- 111311E1=311E1E3 CIEIO Is NIM tion of this idea of high frequen- , A cy biasing represented a con- Playback head gap siderable step forward in the history of magnetic recording. Wire or Tape Recording Coils Fig.7 Wire is never used now for recording except perhapsfor Fig 8 dictation purposes because it is trequency. Shown on Fig. 4 is what then happens not very suitable. Should the wire rotate on play- to the magnetic field in the tape. The first cycle of back, the high frequency response will vary. Also, it the bias frequency takes the magnetic field in the is difficult to join when breakage occurs and, being tape to point e, the next cycle, which has now solid steel, h.f. biasing is not so effective in reducing reduced in amplitude because of the tape movement, distortion and increasing the output.

db

10 Fig.9. Frequency response of single lamination type of play- back head 0 MEI

10 100 11(C 10KC

Frequency('S brings the field to point f, and eventually the field The Recording Head in the tape finishes at the point o. The field in the A typical head, as shown in Fig. 5, has two sets tape has therefore been returned to zero when the of laminations, two coils, gaps at the front and recording current is zero. Because the bias frequency rear, and a screening can. The magnetic field in the is much higher than the signal frequency very little laminations caused by the input signal, bridges the

Milli volts db 4 0

10

OA 20 Fig. 10. Output voltage from the playback head 30

.04 40 10 100 1k( 10KC Frequency CS change in the programme signal has occurred during gap and is largely wasted except for the portionat these cycles of the bias frequency. This cycling of the front, which enters the tape. To the bias frequency is occurring continuously prevent this at the loss the gap is made as shallowas possible (i.e. from

124 THE RADIO CONSTRUCTOR front to rear), allowance being made for head wear although identical heads are often used for record by the tape. A reasonable compromise reduces the and playback. depth from front to rear of this gap to 10 thou- sandths of an inch.It follows that when the head The Erase Head The amplitude of high frequency voltage fed to the erase head is sufficient to magnetically saturate the tape. As the tape leaves the head this voltage decreases gradually as shown in Fig. 6 and the tape isleftin a magnetically neutral state ready for re-recording. A typical gap width is 15 thousandths of an inch. A permanent magnet can be used to erase by saturating the tape in one direction, but this leaves the tape with a high background noise. The concept of magnetic friction in the tape suggests that all the particles cannot be magnetically neutral unless they are magnetised through a number of cycles of the hysteresis loop. Any particle which is out of step produces an unwanted output, and this can be heard as noise added to the output signal. The Playback Head The playback head is very similar to the record head, the main difference being that the front gap is as small as possible to improve the frequency

Fig. 11.The playback amplifier employed in the JR1 Stereo Unit wears its efficiency improves. The pole pieces tips, shown enlarged in Fig. 6, have been drawn slightly rounded because magnetically thisis how they behave. The wave form at the top of Fig. 6 repre- sents the high frequency bias, whichis shown falling gradually to zero because the pole piece is not magnetically sharp, and it is this variation of the magnetic field in the tape at the bias frequency Fig. 13.Multiplication of two frequencies as occurs in the frequency -changer of a normal radio receiver which enables the recording to be made.The width of the gap in the record head is not important because the tape isleft with the magnetic field it response. A typical gap widthis 0.0002in,i.e. receives just as it leaves the gap.However, the 2/10 of a thousandth of an inch.Effectively, the gap trailing edge must be reasonably well defined or the is about 20 % wider due to fringing effects.The high frequency response of the recording will be limit of the frequency response occurs when the gap width is equal to one wavelength of the recorded poor.A typical width forthis gapis0.001in signal as shown in Fig. 7. Two south magnetic poles are shown at the end of the gap so that there is no flux in the head and no output from the coils. The high frequency response will suffer if the heads are not truly vertical.Even of a degree error will halve the output at 15 kc/s.Itis not sufficient that the record and playback heads have parallel gaps, the gaps must be vertical so that tapes recorded on other machines may be played. The playback head will have as many turns as possible to achieve maximum voltage output, but the limit is about 4 millivolts output at 1,000 c/s. More turns increase both the inductance and self - Fig. 12.Addition of the signal and bias frequencies capacity of the head and cause a resonance within in the recording head the audio range, which must be avoided.

SEPTEMBER 1961 125 The screening can around the playback shouldbe tional to the rate of change of flux in the head. This made from mu -metal, a form of magneticsteel having a very low magnetic impedance. is a nuisance because it means that the lower the This frequency the lower the output from the head,as short-circuits any interfering a.c. fields fromthe shown in Fig. 10. The playback amplifier must have motor and nearby transformers.Even steel din the opposite characteristic, and thus the sensitivity thick is useless in comparison with --1-yinmu -metal. of the amplifier at 50 c/s must be about 100 micro- The balanced arrangement of the laminationsand volts.Because of this high sensitivity precautions coils also helps to reduce trouble froma.c. fields. are necessary against hum troubles, and this point The stacked lamination type of playbackhead is dealt with in greater detail later.Fig. 11 shows easily reproduces frequencies downto 20 c/s., the playback amplifier used in the full -stereo unit, whilst an alternative method of headmanufacture, thismeetingthesensitivityrequirementsjust using a single lamination, causesa poor low fre- mentioned. The 9 -way plug and socket shown in quency response below 100 c/s. The wider pole face this diagram is connected to a switch which offers of the laminationeffectivelyshort-circuitsthe differing playback characteristics.. immediately adjacent recording, while thenarrow The first valve is heated from d.c. to avoid heater pole face of the single lamination, shown in Fig.8, to grid hum troubles.

Fig. 14.Resistance R is added to the record head circuit so that the current in this head may be shown on an oscilloscope. At "a" is shown a 1 kc square wave input whilst at "b" the peaks illustratethe treble boostre- quiredtoovercome the head losses. The treble boost often results in ringing ("c") and care Input voltage Current waveforminthe in design of the circuit is neces- record head should he - often is - sary to avoid this effect

allows adjacent signals to increase theoutput at Valve noise may be a problem and therefore a some frequencies and reduce it at others, resulting triode has been chosen for the first stage. A pentode in the response shown in Fig. 9. Thistype of head is normally used because it also embodies extra can be recognised by the thin vertical steel pole in shielding to prevent heater/grid hum, but sincewe the centre of the head. are using d.c. heating, this problem is avoided and Pressure pads may be used to ensure goodtape we take advantage of the lower noise of the triode. contact with the head although this can be achieved The amplifier playback response characteristic by wrapping tape around the head ,for din either which we shalluse conforms tothe standard side of the gap as shown in Fig. 1.If this contact C.C.I.R. characteristic. This states that the field in is not maintained the high frequency outputwill the tape shall produce an output, from an ideal vary. playback head, which is constant when the amplifier has a 100 microsecond time constant correction. The Playback Amplifier Both record and playback heads have losses and The output from the playback head ispropor- therefore some treble boost will be required in both

126 THE RADIO CONSTRUCTOR

the record and playback amplifiers to compensate from the playback head just begins to fall. The bias for these losses. In some designs all the compensa- is then just beginning to erase the signal, and this tion has been made in the recording amplifier. sets an upper limit on bias level. This has the advantage that less treble boost is The treble boost circuit have been carefully required on playback and, therefore, the background chosen to avoid "ringing" troubles.This can be noise is lower. However, the losses in the playback seen graphically by connecting an oscilloscope to a head may not be known if the tape is to be played small resistance, R1, in series with the recording on another machine and therefore the results would head (see Fig. 14) when a 1 kc/s square wave is fed be variable. A further disadvantage is that with all into the input.It is extremely difficult to achieve a the boost on the recording side there is a real danger current in the record head which resembles the input of tape overload. The Americans have a compro- voltage if large amounts of treble boost are used, mise (NARTB response) whereby the top is given and this is a further argument against attempts to a small extra boost on the recording over and above achieve wide frequency responses byexcessive that required to compensate the head losses, and record or playback boost. The same argument also this gains a few dB signal to noise ratio. applies if the playback head gap is too wide. One has to tolerate the resulting poor top response The Record Amplifier because attempts to compensate in the circuit will A constant current is required through the record- result in transient distortion as shown by the "ring" ing head whatever the frequency. The head, through on the square wave. The treble boost offered in the being an inductance, has an impedance which rises Jason unit is shown in Fig. 15. with the frequency. The impedance of a typical head is 10052 at 100 c/s and lokn ar10,000 c/s, and The Oscillator despite this variation, our amplifier has to provide A push-pull oscillator (see Fig. 16) is used in the a constant current. The usual way of achieving this Jason unit so that the output will be balanced and

db +2 0 2 Fig. 15. Treble boost required to overcome record head losses

100 1 KC 10KC Frequency C'S is to insert a high resistance in series with the head free from second harmonic distortion.Any un- so that the total load of the resistance plus head balance of the oscillator causes residual magnetism does not alter so greatly, this combination being fed to be left in the heads, and this, if left in either the from a normal amplifier. An alternative method erase or record heads, will increase the background uses the head as a load for a pentode. The current noise of any tape played. Distortion of the recorded at the anode of a pentode is largely independent of signal is also increased if the bias waveform is not the voltage and the changing voltage across the head pure. To further lower the distortion the oscillator will not, therefore, affect the current through it. coil uses a ferrite core, which increases the "Q" of As explained earlier, high frequency biasing is the circuit.This increase in "Q" can be imagined added at this pcfint and the combined signal and bias as a flywheel, which helps the waveform of the waveform is shown in Fig 12.This addition of the voltage output to be sinusoidal and ignore the effect signals, which occurs in the recording head, should of its own grid current drive, which is one of the not be confused with a radio receiver frequency - main sources of distortion. changer, wherein the signals are multiplied as in Fig.13. Minimum distortion of the recording Demagnetisation of the Heads occurs at a particular bias level.This level should Despite care with the bias waveform itisstill be found with a distortion meter because it depends possible to magnetise the heads and thus affect any on many variables. As the amateur cannot usually tapes played. This can happen in a number of ways: perform this measurement, an alternative method (1) Switching off the mains without the heads is to increase the bias until the output at 10 kc/s shorted.

SEPTEMBER 1961 127 (2) Switching a nearby transformer. signal. A meter should be able to follow a signal (3) Usingamagnetisedscrewdriverwhen with a one millisecond rise time, but, to do this, it making an adjustment. needs to be driven by a 10 watt amplifier.The normal meter circuits fed from a triode are quite inadequate in this respect. A Magic Eye, on the L586.gpop000al other hand, has no moving parts and is capable of

TABLE 1 Playing Time in Minutes Per Track The figures should be doubled if two quarter track stereo recordings are made on one tape, or multiplied by four if four separate quarter tracks are recorded. Tape Length 3iin per second 7+in per second 150 8 4 200 10 5 300 16 8 400 21 10 600 32 16 850 45 22 900 48. 24 1,200 64 32 1,700 90 45 1,800 96 48 2,400 128 64 8 3,400 180 90 Fig.16. The tape oscillator circuit following rapidly rising signals. Therefore, although not so accurate to read, it will nevertheless give a A keen recording enthusiast will, therefore, have reading in some circumstances which the meter a head defluxer.This consists of a coil connected will ignore. On the balance, therefore, the Magic to the a.c. mains placed near the head, and which is Eye was chosen as the best compromise for the then switched on and drawn gradually away. The present application. Since the Jason unit is intended coil subjects the head to a number of cycles of for stereo two Magic Eyes are employed, these being demagnetisation in a similar way to h.f. biasing mounted side by side to enable comparisons to be described earlier and leaves it magnetically neutral. made of the level in either channel. The Record Level Indicator The Recording Tape Thought was given to the record level indicator A recording tape should be strong enough to before deciding between a Magic Eye and a meter. avoid physical damage during normal use, but not A meter has a scale and apparently gives a more so stiff that it will not lie flat against the head. accurate indication. The question is, though-what Unless intimate contact is maintained with the head,

111111.111111111111111111111.11131 .090 70Y5 2RH 4- .031 Fig. 17.Standard track widths 45- .246 .002

are we expecting to read? Obviously, if the signal the output voltage will vary considerably, particu- rising too quickly the meter will be unable to larly at the higher frequencies.The tape which follow and it may in fact ignore a rapidly increasing satisfies these requirements best is known as "long

128 THE RADIO CONSTRUCTOR play tape", which allows a playing time of 96 A good recording tape should have a high minutes, with two separate stereo recordingson a remanence (see Fig. 2 (a)), which means that it can 7in reel carrying 1,800ft of tape.Tests show also retain a stronger magnetic field and thus give a greater output.A high coercivity, whichisa measure of the ability of the tape to resist magnetisa- TABLE 2 tion, is also necessary.At high frequencies, the effective magnets recorded on to the tape become Tape Length in Feet on Various Spool Sizes so short that they are able to demagnetise each other and thus result in a poor high frequency response. Spool SizeStandard TapeLong Play Double Play A further possible trouble, which is worse when the 3 150 200 300 coercivity is low, is "print through". This is caused 4 300 450 600 by the magnetic field of a recording impressing itself 41 600 on an adjacent turn of tape and giving an unwanted 5 600 900 1,200 echo. 5* 900 1,200 1,800 Originally, only one track was recorded on a din 1,200 1,800 2,400 tape, but later it was found that two tracks, and then 8* 1,700 2,400 3,400 four, could be satisfactorily accommodated.To prevent interference between tracks, portions of the tape must be left unused to act as guard tracks.It that this tape suffers less from the phenomena known is advisable also not to record to the edges of the as "drop -out" caused by variations in the magnetic tape, because any mechanical damage is likely to coating, and which is more prominent when the show itself there. track width is narrow. Fig. 17 shows the usual arrangement of recording The standard tape is thicker and only 1,200ft and guard tracks, and the positions of the channels can be accommodated on a 7in reel.The double when recording stereo.The erase head is made a play tape with 2,400ft on a 7in reel gives the advan- little longer, 0.lin for the twin track and 0.04in for tage of extra playing time, but is more difficult to the quarter track, to ensure that any tape deck handle and may bestretched by the braking alignment errors do not leave part of the recording mechanism of some decks. on the tape. (To be continued)

Book Review

FUNDAMENTALS OF RADIO RECEIVER SERVICING. By E. M. Squire. 172pages 152 diagrams. Published by Pitman.Price 15s. net.

This is, on the whole, a well -written and useful little book, but it is firstnecessary to make clear, in view of its title, that it is mainly a description of the way in which a receiver and its componentparts work. Many of the servicing notes are really secondary to this, and are often of a rather general nature. Thus the home constructor, new to the field, but ambitiously building his first 7 valve all-wave receiver, will not find here instructions on how to cure the howls, whistles or plain dead silence thatmay at first greet his efforts. What he will find is a clear description of how the circuits ought to work, written ata fairly elementary level and in a practical way. With the servicing notes, he should then be able to apply intelligently the detailed instructions in servicing manuals. After an introductory survey of the field, in which such basic terms as current, frequency and gainare defined, the author devotes about a third of the book to components. These chapters contain both theory and constructional details, and include an account of printed circuits and their manufacture, and materialon transistors.Surprisingly, there is no discussion of component tolerances-a matter which can be ofsome importance in servicing. The way in which components are used in typical receiver circuits-both valve and transistor operated-is then described, including such refinements as dual-purpose circuits in a.m./Cm. sets. The chapter on power supplies is particularly comprehensive and useful, with that difficult point, the development of grid bias in battery sets, clearly explained. After some notes on the radio -gramophone, the book concludes with two chapters on theuse and care of common servicing equipment, and some advice to the novice on setting about the first servicing job. P.R.S.

SEPTEMBER 1961 129 caused by the aerial and occur more frequently where coupling to the tuned circuit is tight. Loosening the coupling may cure the dead spots The butsignalpick-up may become impaired. In an attempt to obtain optimum by A. S. CARPENTER resultswith such areceiver,the "Mger-tip aerial is some tithes coupled to the tunedcircuitviaasmallvalue variable condenser.Although this works fairly well it means that an Five" extra control is needed on the panel, thereby adding a further complica- tion to the tuning of the receiver. Anotherunpleasantfeatureof such simple receivers is their ability to radiate when reaction is too far HERE IS AN EASILY BUILT LITTLE space, its chassis measuring 8 x 4 x 2in advanced, since there is no buffer, receiver capable of providing and its front panel 8+ x 51in.A between the detector and the aerial. many hoursof enjoyment modern triodezpentode valve is used Even the most careful user is certain despite its simplicity which will tune and this ensures both space economy at some time or other to advance the continuously from 10-2,000 metres. and efficiency. reaction control too far and therefore Although ,the receiver can tune the cause annoyance to others. Medium and Long wavebands it has The Detector The unpleasant features just de- beenespeciallydesignedforthe One of the simplest andleast scribed can be very largely avoided Short wavebands where much of expensive ways of exploringthe by employing an r.f. stage prior to interest is transmitted. Short wavebands is to use a leaky the detector, and such astagemay The receiver is self -powered and is grid detector coupled to an aerial be untuned.It might be argued that intended for use with an a.c. mains via a tuned circuit. Positive feedback, the inclusion of an untuned r.f. stage supply.The chassis is completely orreaction,isalsorequiredto is a waste of a valve but, when it is safe to handle due to the inclusion of increase sensitivity and sharpen the considered that such a stage ensures an isolating mains transformer. tuning.Whilst a great deal of fun that the aerial constants in no way When headphonesareplugged can be obtained from simple appara- affect either the operation or the intotheoutputsocketaself- tus of this nature one or two un- tuning calibration plus the fact that contained receiver results, whilst if pleasant features soon become it forms an effective buffer against a coaxial lead is taken from the same evident,oneof thesebeingthe radiation, most of the argument outputsocket andfedintothe occurrenceof "deadspots",i.e. becomes void-and,afterall,a "gram"socketsofabroadcast sections of the band over which it is certain small amount of gain is likely receiver or to an amplifier it becomes impossible toobtaineffectivere- to result. a tuner.The unit occupies little action.Such dead spots are often Circuit Details Fig. 1 shows the circuit of the receiver, and it will be seen that it includes a mains transformer, and the triode and pentode sections of an ECF80. The pentode is used as theuntunedr.f.stagepreviously referred to, whilst the triode operates as a leaky grid detector -cum -audio - amplifier, with controllable positive feedback (reaction) added for "pep- ping up" purposes. Resistor R4 serves partly to make the grid bias effective for the pentode sectionand partlytoallowthe development of sufficientr.f.for effective operation. Resistors RI and R2 are merely screen -grid and anode feeds respectively for VIA, whilst R5 provides cathode bias.Condensers C1 and C2 aredecoupling com- ponents. R.F., amplifiedto some extent, appears at the pentode anode, and is conveyed to the tuned circuit and the grid of VIB by condenser C5. At this point it should be noted - that the desired wavebandisob- tained not by switching but by the A rear view of the receiver plug-incoilmethod,theDenco

130 THE RADIO CONSTRUCTOR range of miniature inductors being it is felt that this aids simplicity of Table Showing Inductor Ranges chosen since these conveniently fit a operation.The drive mechanism is standard Noval (B9A) valve base. actually a Muirhead type and was A Noval base is in fact used for this taken from one of those excellent purpose and the circled figures shown little RF27 ex-W.D. units.These Range Mc/s Metres onthediagramadjacentto L1 drives are available from advertisers indicate the correct tags; e.g. tag 6 from time to time and, although the 1 0.150-0.400 750-2000 on the valve base used as an inductor precise type is unimportant from the 2 0.515-1.55 195-580 3 holder is wired to the chassis. point of view of appearance,itis 1.670-5.3 57-180 Note that the method of connect- essential that any alternative make 4 5.0-15 20-60 ing the particular inductor in use should be rigidin 'operation and 5 10.5-31.5 9.5-28 permitstheuseofitsprimary permit of no backlash. An excellent winding for reaction purposes. The triode section of the valve functionsinconventionalfashion, demodulating and amplifyingthe signal and passing the resultant audio 0 to the output socket via C4 and the z volume control, C9.The reaction control, C3,is used in conjunction 1=- with the primary winding of LI, R6 ,flrinriraprin1111111.11r (POO `- being included to ensure successful cc ,% operation. Individual Inductor Ranges These are given in the Table and are those published by the manu- facturers, a parallel connected con- denser of 310pF being assumed for tuning.As no trimming condenser is needed and as the inductors are fitted with dust iron cores which give up to 15 % variation in Most cases, the ranges are likely to vary a little as used here. V. ME c., Some intending constructors will already possessavariable tuning condenser of 500pF and this can be 1'11: used for C7 if a 1,000pF fixed value silver -mica condenseriswiredin _1(2)0000 jai series with it to reduce the maximum capacity. If a twin -gang condenser of good quality is to hand already CC this may be utilised for tuning pur- JMI' poses by using one section only. A III twin -gang condenser was in fact used III in the prototype, as can be seen from III the photograph accompanying this ICII I article. MY. Bandspreading Instead of fitting a bandspread condenser across C7 a good quality slow motion driveis employed, as

-to c --- -,F, ..1 0..i O L.. cl 7-. 0a..)a co_se 0 .7. x ...1oc 3 Q CD 's o VI a.: 0ON Li 0 , L> E o x ,-.":3 0 -fp a.) 0 5 0 ,,,5, o 00 -.-. 17 cn 0 93 cu 2 . .... e-, g w-)4. co 2 LU -e k - C a.) Ia-. C X8 o,.. (...) 'C' a a.- gt> O ()93 LLI--r en °'cl > :7 Cd -C t. a 2, 7) al .._,- j7 sa0., csaattacti30..; a) u_ to TS.. a.) ' - e" 3 3 3 3 3 3 .4.. '''' a 1..., = c c',1 sz .....,,, -.._. 21 ,5),:_,5.>-,50 --,sclan z ..-..,,/ -r3 N ,-E as = ...... , no L....u., ELL 4,, ---.- ct, - , ..-+ ..... ,t1,,, c:a a a a aa... a--0 sao .._,-.4- w-, n. x 0 a ,...., ...... X -X -X ..t 0 -Xt..... ,.....0 , a" E, a ct 0 a. cLo 3 g LA .r. '-,n.-- ;-. 0 C ,, 0 C4a) 774 ---fczt .c7d ,.:7-I':

. ,I. , ! 7 r- 0 co <.1--- c, .,..-, ,. _. r- t--- --, l0 as a t < a ou a) ,, ''t H ,.0 ,--, .1- el "I' en t^-1 0, 0 CD0 ,r) 0 cr .1- tn --, = 5 .4 2 0 8 0 e, ,A 2 -r 040,-- -g ... ,., §228',1* -406 °)..73';0M1 0 I 0 t) QZ . `g ,n0 0 C a z cc a cn 2 .-15 -. 2 L- a-a) ....'crs = 7,-,2? 0 a) 05) a) a) a 1..)a.) 0 .5 2 .c...., % `.,..0 . Y. $.4 -.' ..., ,...":..1 ,.., ..., - 0 .,,0 . , .0., C.) at..)=0.)zcla.CCIP. Z3C4C4C4 g g g g g g 106'C O'c'Ycsjc`56° ,....,.t.iH,-, 1-7 U >U A HOH 0 00 cG C.)

SEPTEMBER 1961 131 foACMaIns were used.A mains transformer with to SI toll primary isolated h.t. and heater secondaries must be employed. Usedinconjunctionwiththe mains isolating transformer, Ti, is a midget contact cooled metal rectifier. CMR. This is approximately 1 x 1 x iin only in size, and it utilises the chassis as a heat sink.The a.c. supply, after being converted to d.c. by the rectifier, is smoothed by Rs and Cs and fed to the h.t. rail, some 180-240voltsappearingatthis point. Constructional Notes Due to the use of a "Universal" sectionalchassis,construction is greatly facilitated.The aluminium parts for these chassis are obtainable separately so that one may order a top plate and four sides, all of which bolt together to form a very rigid construction.One great advantage Fig. 2.Above -chassis layout and wirinv alternativechoicewouldbethe Eddystone drive type 843 which has a scale calibrated over 180° in 100 divisions. 4" Power Supply The modest voltage and current requirementsdemanded by the ECF80 mean that a self-contained and simple power supply section is possible, and various small mains transformers designed specifically for -.1--13'4 half -wave working are obtainable very cheaply.It might be tempting to use a filament transformer for the valve heaters in order to save a little Volume/On/Oft Tuning Reaction on the cost but such a method is not recommended as the chassis would necessarily become live to the mains via its h.t. circuit, this being especi- allydangerous when headphones

Fig. 4.Front panel details

is that drilling is considerably eased since each piece can be handled independently of the others. Further- more, should a particular joint be difficult to reach with the soldering iron during wiring up, then a section of the chassis can be removed! To the front flange of the 8 x 4 x 2in chassis specified a panelin thick is bolted, this being made 81in wide to allow a simple case made from tin plywood tofitsnugly. (See Fig. 4.)This case will be described briefly later. For the front panel hardboard may be used as any hand - capacity effects evident during opera- tion may easily be removed by glue- ing metal foil to the inside of the panelandconnectingittothe Fig. 3.Below -chassis layout and wiring chassis. Upon this panel the various

132 THE RADIO CONSTRUCTOR controlsarearrangedina neat symmetrical manner. The rear flange of thechassis carries the aerial and earth sockets and also the coaxial output socket for the headphones. In the prototype the rear flange is also used to mount two of the fixed condensers.Full above- and below -chassislayouts with point-to-point wiring plans are given in Figs. 2 and 3, from which it will be observed that ample space exists and that no cramping occurs. A singletagstripissufficientto anchor the h.t. and It, feed points, themajorityoftheothersmall components being suspended in the wiring. Care should be taken to orient the valve bases as shown, so that short and direct wiring is made possible. A reliable connection must be made between the tuning con- denser frame and chassis. Aperture 2 X I Operating the Receiver On completion of the wiring a thorough check should be made to Top 81/2 X 4I/2 ensure that no short circuit exists between the h.t. rail and the chassis Sides 51/4 X 4I/2 whereupon if all is in order an aerial Back 02 X 3I/4 may be plugged in as well as the Front 02 X 510 headphones, the valve and one of the Base 91/4 X 578 inductors. The receiver should now All dimensions are it inches. be switched on and an attempt made Front panel 1/8thickness - to tune in transmissions with the aid of the main tuning control, at the remainder 1/4 same time adjustingthe reaction control gently to bring the valve to the verge of oscillation.Provided Fig. 5.Detailsand dimensions ofthewoodwork requiredforthe suggested that the volume control is sufficiently cabinet far advanced no difficulty should be experiencedinpicking up signals, and the set should act in a very lively The Case siderably. manner The idea is to secure the chassis indeed. Shoulditbe A suitable housing for the receiver and front panel to a baseboard impossibletostopthereceiver can be made from plywood as stated to from oscillating at any setting of whichisgluedlin moulding or earlier.Band changing necessitates quadrant as shown. Slots cut in the the readion control, switch off and a removable type of cabinet and this either sides of the box assist ventilationand changeR3foraresistor can be achieved by adopting the also permit it to be removed when slightly larger in value or, alterna- principle shown inFig. 5 which tively,connect a it is required to changean inductor. condenserof shows all the woodwork needed for When the case is replaced it fits into approximately 500pF from pin Iof the receiver, with the exception of the well provided by the moulding thevalvetothechassis. But reinforcement strips for holding remember that it or quadrant andisthus kept in the inductor core together without the aid of joints. position.Four rubber feet may be setting may affect the reaction effect Since the author professes no skill fitted to the underside of the base- to a certain extent as it can modify in woodworking the design is very board and the whole either lacquered thecouplingbetweenthetwo elementary and simple, windings. and can or French polished, or treated in doubtless be improved upon con- whatever style is preferred.

Loudspeaker Enclosures In the article entitled "A Small Bass Reflex Enclosure suitable for the `Axiette' Loudspeaker" by M. J. Pitcher, B.Sc., featured on page 40 of the last issue (August), the author wrote a very clear and interesting account of the business of cabinet construction. For the benefit of readers who are interested in speaker enclosure construction and who wish to obtain still further information, we should like to point out that a free book entitled "High Fidelity Loudspeaker Manual" is available from the manufacturers of the "Axiette".In this book, details of an enclosure both for the "Axiette" and other speakers are featured. The publication is available direct from Goodmans Industries Ltd., Axiom Works, Wembley, Middlesex.

SEPTEMBER 1961 133 By RECORDER

for hire in the same manner as a conventional taxi -cab. They must, instead, receive their instruc- tionsviaradio,andthisimposesparticularly stringent requirements on the equipment employed. This fact should be combined with the statement that the current Minicab system, put into service for Welbeck Motors by Pye Telecommunications Ltd., is the largest radiotelephone system in Europe. At THE PHOTOGRAPH ON THIS PAGE SHOWS A the time of writing there are 200 Welbeck Minicabs colourful newcomer to the crowded streets of and it is expected that these will increase to 800 by London.In this picture a driver -operator in the end of the year. one of the fleet of Welbeck Minicabs contacts his headquarters via the radiotelephone installed in his Cab Installation cab. Welbeck Minicabs are Renault Dauphins which As readers will be aware, Minicabs may not ply have been adapted for use as radio -taxis by having

134 THE RADIO CONSTRUCTOR their 6 volt electrical systems (the standard voltage output is 4 to 6 watts according to operating on the Continent) converted to 12 volts. Considered frequency. overall, the cab installationis extremely simple, The receiver employs a single superhet circuit for consisting of a self-contained simplex transmitter- the 25-68 Mc/s band, and a double superhet for the receiver with self-contained speaker, anda quarter 68-174 Mc/s band. On 25-68 Mc/s thereare three wave whip aerial. A microphone with an integral r.f. stages, an overtone oscillator mixer, three i.f. push -to -transmit button is coupled via expanding amplifier stages at 2 Mc/s, a demodulator,a.g.c. cable to the transmitter -receiver and fits ina special rectifier and a.f. amplifier, a noise limiter, and the clip when not required. If desired, this microphone a.f. output stage. On 68-174 Mc/s thereare two troy be replaced by a telephone handset incorporat- r.f. ing a pressel push -to -transmit switch. The second stages followed by a crystaloscillator and photograph shows an engineer fitting multiplier, the first mixer (converting to 10.7 Mc/s), a transmitter - and the second mixer and crystal oscillator.After receiver under the dashboard of a Minicab. this the 2 Mc/s i.f. stages proceedas with the 68- The transmitter -receiver is a Pye equipmenttype 174 Mc/s circuit. Valve line-up is two EC91 (6AQ4) PTC 2007, and is known as the Transistor Ranger. r.f.amplifiers; EC91 (6AQ4) r.f.amplifier (low However, apart from a transistorised h.t.power band) or first mixer (high band); ECF80 (6BL8) unit, all r.f. and a.f. circuits employ valves.The mixer (low band) or second mixer -oscillator (high transmitter section has a 6BH6 crystal oscillator; band); two 6BJ6 2 Mc/s i.f. amplifiers; 6CB6 third 6BH6 multiplier (for 68-174 Mc/s only); QQV03-10 2 Mc/s i.f. amplifier; EBC90 (6AT6) demodulator, (6360) multiplier; and QQV03-10 (6360)power amplifier. a.g.c. rectifier and ,a.f. amplifier; EL90 (6AQ5) a.f. The a.f.sectionof the transmitter, output;6BH6 lowbandovertoneoscillator; following a moving -coil mike, is ECC83 (12AX7) ECF80 (6BL8) high band oscillator/multiplier; and voltage amplifier; ECC83 (12AX7) phase splitter; 0A200 silicon diode noise limiter.After a row of and two EL90 (6AQ5) a.m. modulators.R.F. bottles as impressive as this some sort of noise

SEPTEMBER 1961 135 ought to come out of the speaker. And indeed it Personally,Ipreferred the change from the usual does: typical sensitivity figures for an input of 2v -V geometic Exhibition layout. only are 1 watt a.f. output with 14dB signal to noise Much of the emphasis was, quite frankly, on ratio at 72 Mc/s, and 1watt a.f. output withI ldB Soviet achievements; and the centrepiece of the signal to noise ratio at 160 Mc/s. The a.g.c. control Exhibition was contained in a circular section having range is similarly impressive, there being less than a high blacked -out dome in the shape of a plane- 8dB change in a.f. output for inputs ranging from tarium. A model of the world revolved slowly near 4tiV to 20mV. the apex of this dome, being surrounded by orbits The h.t. power supply unit employs two 0C35's of various shapes traced out in neon tubing. This in a multivibrator circuit running at approximately section also held models of the various Russian 4 kc/s, the output being rectified by a pair of silicon satellitesincludingthatinwhichMajor Yuri junction connected as voltage doublers. Gagarin carried out his epoch-making flight into An interesting feature of the power supply is that space. the decorative front panel also provides a radiating Most of thepurely electronic equipment on heat sink for the power unit transistors. display was of a standard and solidly -made variety, The overall unit is capable of working in the two and my eye was not caught, during my short visit, bands 25-68 Mc/s and 68-174 Mc/s just mentioned by any outstandingly new development. A small (he. overall range is 25-174 Mc/s), and those fitted section was devoted to domestic radio and television in the Welbeck Minicabs have six switch -selected receivers and my immediate reaction to the latter channels.The front panel controls are On -Off, was' that, judging by the depths of the cabinets, the Transmitter Off/Stand-by (which switches the trans- Russians have not yet gone over to 110° picture mitter filaments), and a.f. volume. A squelch level tubes.The television receivers were on a closed- control, which silences background in the absence circuit hook-up, allowing visitors to see themselves of a signal, may also be fitted. Under an inspection via a camera in the centre of the stand. The radio cover on the front panel are controls which include sets were, so far asI could judge, pretty standard transmitteraerialtrimmers and receiver crystal also, with conventional cabinet styling and not too trimmer. There is also a test meter outlet socket. much flashy trim. The power consumption of the unit is 36 watts on The educational section showed some simple Receive, 58 watts on Standby, and 105 watts on electronic demonstration boards employing actual Transmit. components mounted in such a manner that their circuit could be easily followed. These demonstra- The Complete System tion boards included a two -triode a.f. amplifier and The complete Pye installation includestrans- atwo -triodebalancedv.h.f.oscillator working mitting stations based at Hampstead and Forest directly into a dipole of some 3 -metre wavelength. Hill, and these are connected by G.P.O. land lines There was also a do-it-yourself kit for an electric to the Control Room. The given radius of operation motor in a shallow cardboard box complete with from the transmitters is 20 to 25 miles but, with a lovely garish picture on the top of the completed good line of sight conditions, the actual range may job.Just the sort of thing that I used to lap up be considerably inreased.At the Control Room, when I was a kid! A neat gadget in this section initially installed with 20 G.P.O. lines, a conveyer - displayed a sine wave by means of a series of white belt system is fitted which can handle calls at the buttons sliding on vertical black rods against a rate of one every two seconds. bla,ck background. By rotating a wheel at the rear, Quite a set-up,isn'tit?And something to cords pulled the buttons to different positions, ponder over, perhaps, if and when you next ring thereby changing the shape of the "wave". for a Minicab whilst in the Smoke! I was at the Exhibition during the visit of Major Yuri Gagarin, but any hopes I may have had of Russia at Earls Court seeing the astronaut were dashed because of the Iwas able to make a flying visit to the U.S.S.R. fantastic and enthusiastic crowds who waited for Industrial Exhibition held in London on the 7th to him and surrounded him as soon as he appeared. the 29th July.I arrived at Earls Court to find that A fond memory of the Exhibition was occasioned the familiar Exhibition Hall, on whose concrete by a public address call for three missing schoolboys. floors I have travelled many foot -weary miles during The call asked these boys "to report to Section successiveradioshows,hadbeentransformed Four,OuterSpace,immediately". Thiswas completely' bytheRussians. Apart from the perfectly in keeping with the idiom of the Exhibition Fashion Theatre only the ground floor was in use; and capped my visit very nicely. but the individual sections on that floor, which all merged one into the next, had been given very high false roofs that completely obliterated the somewhat Electroluminescent Clock Dial unsightly upper section of the building. The layout Smiths Clocks and Watches Ltd.willshortly seemed at first sight to be a little haphazard, but a be releasing the Callglow electric clock. This clock, glanceat the programme soon showed that a which operates from 200-250 volts a.c. synchronous definite route could be followed which enabled all mains, caused considerable comment when it was the exhibits to be examined without re -crossing exhibited at the Tenth Electrical Engineers' Exhibi- one'ssteps and withoutleaving anythingout. tion at Earls Court last March, and it is of special

136 THE RADIO CONSTRUCTOR interest here in that it will be available with an to be turned fully back. He has also received the electroluminescent dial. The light intensity of the Russian test card on 49.75 Mc/s on five occasions, dial is controllable and, obviously, the latter can be once so strongly that contrast had, again, to be turned read very easily in the dark. fully back. Going back to positive modulation he The phenomenon of electroluminescence has been has received Caen weakly on 52.4 Mc/s and Lille the subject of research work for many years, but it on 185.25 Mc/s, the latter being picked up at such isonly recently that development has enabled strength that a test card was resolved with only a electroluminescent light sources to become available 10in piece of wire in the aerial socket of the receiver! at low manufacturing costs.Basically an electro- Incidentally, I guessed last month that unidentified luminescent lamp consists of a flat panel, which can 185.25 Mc/s transmissions might be from Eiffel be made in sizes up to 12 x 9in, containing a layer Tower, but it looks as though I was wrong. Both of phosphors sandwiched between two conducting Lille and Eiffel Tower share the same channel, and layers. The back conducting layer may be op'aque both have the same power. and the front condUcting layer transparent, where- Mr. I. C. Beckett of Buckingham, whose feats of upon the application of an e.m.f. to the two causes Dx reception formed the basis of the "Long Distance light from the excited phosphors to pass through TV" article in our November 1960 issue, is still the front layer. As may be gathered, the light is pulling them in.As of the beginning of July his radiated from the whole area of the panel, as total of countries received this year is 11, excluding opposed to the "point" light source of filament France and Belgium. The last two must be locals lamps and the "linear" source of fluorescent tubes. to Mr. Beckett! Included in Mr. Beckett's haul is Apart from the unique ability to radiate light theidentificationcardfortheOsterreichischer from an "area" source, electroluminescent lamps Rundfunk service introduced in Austria some years have a very high efficiency.Negligible heat is ago. All Mr. Beckett's Dx is on Band I. dissipated, and practically all the applied electrical The way things are going, I'm expecting a report energy is converted directly to light.A typical any day now on the reception of Transatlantic t.v.! lamp running from a 250 volts supply would A set successfully adapted for 625 line negative consume a current of some 0.2 to 0.3mA per square modulationshouldn'thave muchdifficultyin inch only. resolving a 525 line signal as used in the States. The Smiths Callglow clock will be available in The 525 line signal has a line frequency of 15,750 c/s, illuminatedandnon -illuminatedversions,the whichisonly veryslightly removed from the former having the electroluminescent dial.In this, 15,625 c/s of the 625 line signal. The field frequency the a.c. mains voltage is applied to the conducting is 60 per second, as opposed to 50 per cecond, but layers of the electroluminescent element via a fixed this shouldn't be beyond the capabilities of most limitingresistor and a variableresistor which vertical timebases. controls the brightness.The Callglow clock also Another letter describes the experiences of a contains the normal alarm circuit. reader, Mr. R. Goodsell of Margate, after he had inserted a request for information on an electronic Points from Letters metronome in the "Can Anyone Help ?" column Last month's Radio Topics included a report of in our March issue.Mr. Goodsell writes: "...I t.v. Dx reception by Mr. R. J. Ringrose of Ipswich received replies from Germany, Australia and New Suffolk.Mr. Ringrose has sent me some further Zealand, apart from about two dozen or so from information, this arriving just too late to appear various parts of this country.I really had no idea last month. He has now changed his receiver to that The Radio Constructor got around so much." negative modulation by reversing the video detector The "Can Anyone Help ?" column certainly and he found that he also had to halve the value of seems to be giving considerable assistance to those his video output cathode resistor to obtain sufficient who take advantage of it.And it also proves, of brightness. On his Channel 1 vertical dipole he has course, that the old friendly spirit in the hobby of received Belgian and Spanish transmissions on radio is still with us, and that it remains as strong 48.25 Mc/s, at times so strongly that contrast had as ever.

Lead Consumption Rises

Consumption of lead in batteries in the U.K. has been rising steadily inrecent years and in 1960 the battery industry took some 75,000 tons of lead as metal and oxides-some 20per cent of all lead consumed. Inorder toassistinthe development ofthisimportantmarkettheLead DevelopmentAssociation announces that Mr. P. C. Fryer, B.A. Cantab., has been appointed to the staff. Mr. Fryer isa metallurgist and prior to joining the L.D.A. was on the staff of the Morgan Crucible Company. He will be principally engagedin development work for the lead industry in the battery field.

SEPTEMBER1961 137 A Constructor's Oscilloscope -A Construction of the Mullard Design

Part 3 byD.NOBLE, G3MAW andD.M. PRATT, G3KEP

I.High Impedance Attenuator Probe Brass rod THE VERY SIMPLE CIRCUIT OF THIS, TOGETHER WITH constructional sketches,is shown in Figs. 7 ,==Top plate ana 8.The small trimmer isprovided to hole balance the capacity of the coaxial lead, which should be of the specified length.In the prototype, ci6 BA tag this trimmer was made from a miniature air -spaced type with rotary moving vanes, and consisted of one fixed and one moving vane. Construction The probe is built around standard Neosid coil components. Firstly, the central portion of the coil former is filed away leaving a piece of semi -circular Neosid cross-section supporting the top end, in which a }in 5000 B hole is drilled as shown. A standard brass core is drilled through its axis to take the prod of Bin M99 Fig.8. Construction details of the high r impedance attenuator probe (see text)

10Mn with the end of the former, a 6BA screw may be I le fitted through the former to retain it, a solder tag 0 3 -3LF 21t 75n Coax being provided for the electrical connection. The top plate is fitted in position and three pieces of 18 s.w.g. tinned copper wire are bent and fitted M96 into the spill holes of the top plate and base as shown. Fig. 7.High impedance attenuator probe

Components List (High Impedance Attenuator Probe) 1 10M5I resistor 10% * watt 1 Trimmer 0.3-3pF (see text) 1 Former assembly, Neosid 5000B, complete with insulated top plate I Brass core (to fit former assembly) 1 Crocodile clip (Bulgin) 1 Coaxial plug (Belling -Lee L734/P) 7551 Coaxial cable (2ft) *in brass rod, screws, etc.

brass rod, which may either be sweated in or made a tight fit. A radial hole in the core is drilled and tapped 6BA such that, with the core screwed flush The high impedance attenuator probe

138 THE RADIO CONSTRUCTOR The components may then be soldered in position. An earth lead fitted with a crocodile clip is taken from the earth spill through one of the spare spill holes. The coil can is earthed by means of a piece of copper foil, cut to a suitable shape, which is soldered to the earth spill and bent under the former Components List (High Gain Probe)

Resistors 111 4701a1 IW 10 % R2 47k1) IW 10% R3 4701a2 *W 10% R4 1.5kn iw 10% R5 1201d2 INV 10 R6 4701d2 *W 10%

Pin 5 6 To _ _Oscilloscope External view of the high -gain probe t_ Input _L_ 75nCoax xrcic) base. Upon fitting the can one of the fixing lugs is c 10mv/a41 clamped to the copper foil by means of its 6BA fixing screw. As can be seen the coaxial leadis fed up the centre of the former.It will be found a tight fit, and Pin 2 will necessitate being tapered and screwed in.To Pln 7 enable the trimmer to be adjusted when the probe is assembled, a hole is drilled in the side of the can. Pin! Cconections Checking to Noval Plug As explained earlier, the purpose of the trimmer on Oscilloscope isto make the whole circuit (including all stray MlCO capacity) aperiodic.Alignment of this condenser can be achieved by connecting the input of the high Fig. 9.Circuit diagram of the high -gain impedance attenuator probe from the oscilloscope probe to the cathode of the tube in a television receiver.

Condensers Ci OA ti..F 350V paper C2 100p.F 6V electrolytic C3 0.1µF 350V paper Miscellaneous Si Double -polechangeovertoggleswitch, N.S.F. Type 8373/K7 Vi Mullard EF86 Also required - 1 Noval valve base (McMurdo) Type BM9/U 1 Noval plug (McMurdo Type BLM9/USP1 with No. 22 cover) 2ft of 75U coaxial cable I Coaxial plug (Belling -Lee L.734/P) 2ft 4 way p.v.c. cable

I crococile clip (Bulgin) Prod assembly (see Fig. 11) Chassis and box (see Fig. 10) 1 Tagstrip,Bulgin Type T19 with R.H.tag Rear view of the high -gain probe unit with back platere- removed moved

SEPTEMBER 1961 139 4

3/4° 5k -43/16'-1

15/3idia

Drill No 49 for self tapping screw 3,.6d L

A 1/4" Rubber grommets B 5/16" Rubber grommets C Noval valve base D Toggle switch E Test prod Unless otherwise stated, 3A3 all holes arc 1/8" dia.

Material- 16 SING. Aluminium MIDI Fig. 10.Chassis drilling details for the high -gain probe

If, now, the timebase is adjusted to the line frequency, 11.High Gain Probe the line sync pulse should be obtained, and the The high -gain amplifier probe is of conventional trimmer adjusted untilit appears as a rectangular design giving amplifications of x 10 or x 100-these pulse with no overshoot. being selected by a changeover toggle switch. The circuit is given in Fig. 9. The x 100 position, with a maximum input of 300mV, gives a sensitivity of - I mV/cm., whilst, on the x 10 position, the maximum Q 5/32dia Brass input is 3V and the sensitivity is 10mV/cm. The rod threaded 4BA probe is designed primarily for al. amplifier work 6B4 4BA 6BA 1/2 and has a bandwidth of 5 c/s to 20 kc/s. -0 0 4c-- 3/3"from one end Construction The probe is mounted in a small box 4 x 21 x 4BA Nut made from16s.w.g. aluminium.The valveis 3/8' mounted on a small bracket inside, and the prod is 4BA Solder tag fitted to one end on a piece of -kin Perspex, an earth A43taial: IX Perspex lead being provided through a rubber grommet at 4BA Nut the side. The construction of this should be clear from Figs. 10 and 11. M102 From the opposite end to the prod, two leads leave the uiiit.One is the four-way power supply Fig. 11.Details of the prod for the high - cable terminated by a noval plug which connects gain probe with the socket at the rear of the oscilloscope chassis. The other is the signal lead consisting of a 2ft length It must he remembered that, when checking wave- of ordinary 7552 television type coaxial cable. The Arms of a.c.1d.c. equipment, the oscilloscope chassis positions of the various components can quite must not be earthed, but must be connected to the readily be seen from the photograph. chassis of the a.c./d.c. equipment.This should, if possible, he connected to the neutral side of the mains Checking in order to minimise hum pick-up and also to ensure The high -gain probe unit may be checked by safety to the user. feeding its input to a calibrated audio oscillator.

140 THE RADIO CONSTRUCTOR With maximum Y -gain, a display of 1cm. amplitude should be obtained withan input of lmV on the regulations. A possibly more serious misuse isthe x 100 switch position. monitoring of police messages by criminalsto warn If the specified length of them of the approach of the law. coaxial cable is used, theresponse should be found to be flat to within 3dB up to about 20 kc/s. However, probably every great discovery hasbeen misused by someone, and, when thenovelty has worn off, we do not expect to hear so much about Conclusion this kind of interference. The writers have found this Mullardcircuit to give very pleasing results ina unit which compares -Viewing favourably in size with theaverage commercial kit, and they wish to express their According to figures issued by theB.B.C. in appreciation and respect of the period April to June, 2 million thanks to Mullard Ltd. for their kindco-operation, more without which thisarticle could not have been people watched t.v. compared with thesame period produced. a year before.It is estimated that 32 millionsets are switched on during the average day!The References B.B.C. compute that commercial 1. programmes are Mallard Technical Communications, Vol. 4, No. 32,"Circuit for a Simple Oscilloscope", pages 33-38. (Basedon a report prepared tuned into more frequently than theirown to the by L. S. Brown of the Mullard Applications ResearchLaboratory). extent of 63 % to 37%; the exception beingthe 2.Scope for Service. Mullard Publication No. TP374. Saturday afternoon "Grandstand". ERRATA The number of current t.v.receiving licencEs A Constructor's Oscilloscope-Part issued in England and Wales isnow comfortably in 1 excess of 10 million, and in Scotlandover 1 million. In Part 1 of this series condenserC1 is shown, in the circuit on page 923 of the Taking Great Britain and NorthernIreland together July issue, with the numbers are likelysoon to reach 11 4 million. incorrect polarity. The condenser shouldhave its negativeterminal (Sound only licences are just short of4 million of connectedtorectifierMR1, which nearly million are for car radios.) otherwise damage may result whenthe mains input is applied. The Home Secretary, Mr. R. A. Butler,speaking The table on page 921 did at a British Medical Association conferencedinner, not show clearly that referred to irresponsibilityamong young people and response, with Direct Input or "Probe X 10",is mentioned, among other things, the 2 c/s to 2.5 Mc/s and, with Pre-amplifier, is 5 c/s immaturity and to 20 kc/s. irresponsibility of many televisionprogrammes. One method of achievinga more responsible attitude might be to follow the somewhatfacetious advice given on one of our office calendars "instead of standing them in a corner, childrennowadays are NEWS AND COMMENT best corrected by standing them withtheir backs to the television". Interference A correspondent toThe Timeshas recently sug- Wired Sound and Television gested, presumably not too seriously, that4 -star hotels should lose a star or two if television The chairman's statement issued withthe accounts or radio of Rediffusion Ltd., reveal theconsiderable overseas are installed in the only comfortable lounge. Such use of wired sound and television broadcasts. a comment underlines the difficulty, in In a, heavily references to a subsidiary's activities inWestern populated country, of how to allow freedomto one Nigeria,it was stated that the majority type of person without depriving another. Acurrent of the difficulty is with transistor portables. world's population live in scatteredcommunities, Complaints without power supply or radio andthat anyone of annoyance have been made when thesehave been used on motor bus and beach. finding a successful means of bringingthem infor- This latter can mation and entertainment will havealmost limitless readily be appreciated as these wordsare being opportunities. written at a spot where normallyone can only hear Wired sound and television the sound of waves breakingon the seashore, but was, naturally, dealt today some holiday-makers with in some detail.It was mentioned that regional are listening( ?)to agreements had been made with branchesof the programmes on -their portable and the rest ofus R.T.R.A. for co-operation with the general perforce . .. radio trade.It was interesting to note that Rediffusion This matter has been pinpointed bya statement hope to persuade manufacturers issued by the Town Clerk of Eastbourne, to incorporate attention modifications in television receiversso that viewers being drawn to the fact that there isa bye-law may receive signals from either aerial which makes it an offence to operateradio sets, or land -line. record players or other amplifying equipmentin In Brief streets and public places. Offenderscan be fined up The B.B.C. estimate that an to £5. The statement was put out after complaints average audience of 15 million people had watched"The Valiant Years" 'of annoyance had been received fromholiday-makers on the beaches -and promenades. each week, 10 million in the first and5 million in For the same the second showing. These figureswere issued just reason London Transport has reminded its staff that before the conclusion of the series. the use of portable radioson buses contravenes (continued on page 144)

SEPTEMBER -1 961 141 conventional oscillator with a nom- inal frequency of 1 kc, and the other, TR2, as an amplifier controlled by Transistor Shorted the amplitude of oscillations from TRI. TR' constitutes a Colpitts oscil- lator in conjunction with LI and its Turns Tester associated components. RI R2 set upthebiasconditionsforthe oscillator, whilst R4 allows variation By M. D. ROBERTS of the bias point and thereby serves asasensitivitycontrol. C4 de - couples the emitter to the positive In our August 1960 issue, we published details of "A HighSensitivity supplyline and prevents negative Shorted Turns Tester" designed by M. D. Roberts.This unitemployeda feedbackintheoscillator. The 12AT7 valve and required a mains h.t. and heater supply. Ourcontributor oscillations built up across R3 are has now developeda self-contained transistorised version of theshorted passed to TR2 via the d.c. blocking turns tester, and this is describedherewith condenser C5. The signal passed by C5controlsthecurrentflowing throughTR2,thiscurrentbeing THE TRANSISTORISED SHORTED Fig.2,employs two Newmarket monitored by meter Mi. R6 controls turns tester was designed for audiotransistorstypeV10/30A. the bias point on TR2 and is adjusted compactness and, sinceitis One transistor, TR],isused as a formaximumsensitivityofthis completely self-contained, it can be carried anywhere and used in any situation. The appearance of the unit can be seen from Fig. 1.The meter is a 0-1mA moving coil instrument, the size of this determining the size of the complete unit.The batteries are housed withinthecase and should have a life of many months. The case must be made of wood or other insulating material to prevent damping effects on the test probe. There being no valves to warm up, when the tester is switched on itis ready for use immediately; therefore the unit need not be switched on until the moment itis needed, with

Sensitivity Controls

On -off MITI Fig.2.Circuit diagram of the tester

Components List

Meter setting Resistors Condensers RI 100k0watt CI 0.03!).F paper Test Probe Core R2 8.2k0watt C2 0.010 paper R3 3.3k12 watt C3 0.0011.LF paper MI10 R4 1k12potentiometer C4 81/F, 6 w.v. electrolytic Fig. 1.The external layout ofthe R5 22k0 11,- watt C5 81.(F, 6 w.v. electrolytic shorted turns tester R6 100k12 potentiometer Co 81i.F, 6 w.v. electrolytic R7 8.2k0 3g watt R8 2.2k.0* watt aconsequentsavinginbattery R9 5000 potentiometer consumption.The core of the test 1210 6800 -k watt probe is a piece of Ferroxcube taken Miscellaneous from anoldferriteaerial;itis Transistors On/off switch protected by being mounted in a TRI V10/30A Newmarket 6V battery (two 3V units in series, Paxolin tube. TR2 V10/30A Newmarket or tosuitindividualrequire- ments) The Circuit Meter Ferrite rod (see text) The circuit, whichis shown in 0-1mA f.s.d. Paxolin tubing, etc., etc.

142 THE RADIO CONSTRUCTOR stage.R9 varies the current flowing the presence of the shorted turn is linindiameter together witha through MI, and is set to prevent the indicated by an increased reading in length of Paxolin tubing thatis a meter being overloaded. C6 de - M 1 I.If a coil without a shorted turnreasonable push fit over it.Cut a couplesanyoscillationspresent ispassedover the oscillator core length from the tubing lin longer across the meter. extension there is no increase in the than the Ferroxcube rod.Make up Mi reading. two wooden bungs lin long to fit in at either end of the tubing. Put the Construction of the OsCillator Coil Ferroxcube into the tube and cement The construction of the oscillator the bungs in at each end so as to

Fig.3.The manner in whichthe oscillator coil assembly is con- structed before winding

Testing for Shorted Turns With the aid of this unit, coils without cores can be checked to ascertainif there are any shorted turns within the winding. Referring to Fig. 2, it will be seen that Li has a core which extends beyond the actual oscillator coil.If a winding with a shorted turnis passed over this core extension the oscillator coil becomes damped. The

Checking the transistorised shorted turns tester by passing a closed loop of wire over the oscillator core extension.This causes an increase in meter reading.(Theunit illustrated here is an experimental model built to the circuit of Fig.2but employing a layout differing from that in Figs.1, Hole to take end ofoscillator coil 4and5) assembly tubing MI13 coil is shown in Fig. 3.Obtain a completely enclose the Ferroxcube Fefroxcube rod about 31in long and and hold it rigidly in position. Make Fig.4.The case dimensions em- up two Paxolin discs1 lin in dia- ployed in the prototype I Itshciuld be remembered that, in the meter with a hole in the centre of presence of oscillations from TRI, there will be a rectifying action between the base and each allowing them to slide over the emitter,of TR2.This would cause C5 to Paxolin tube. One of the discs re- result is a considerable reduction or, charge in such a manner that the base of TR2 quirestwo smallholesnearits even, a complete collapse of oscillator will tend to go positive, the positive excursion periphery for lead -out wires from the amplitude. The reducedsignal being limited by R5 and R6.Reduction of oscillationamplituderesultsinreduced coil. Cement the discs into position, passedto TR2 then causesthis charge in C5, and would explain the increase as shown inFig.3, remembering transistor to pass more current and in TR2 current referred to in the text.-Ed. that the disc with the two small holes

SEPTEMBER 1961 143 should be nearer the end of the Special attention is drawn to the ponents has to be decided. The Ferroxcube. relatively large diameter hole at the layout diagram given in Fig. 5 will Next, wind 2,000 turns of 32 s.w.g. end of the case, and the two small serve as a though guide. enamelled copper wireinseveral holes on either side. The large hole The layout of components is not layers between the two discs.Lead takes the end of the oscillator coil critical, but if the size of the unit is the two ends of the coil wire through tubing, and the two smallholes to be kept small, component position- the two small holes in the Paxolin allow the leads from the coil to be ing must be planned carefully.All disc and cement the coil firmly into fed into the case.The rear disc on components used in the prototype place. The coilis now ready for the coil can then be cemented to the were miniature types. assembly to the case. end of the box withthe tubing When the unit has been wired, and Batteries the circuit carefully checked,itis ready for testing.

Testing Procedure Make a lin loop with 20 s.w.g. wire. Switch on the unit, adjust R4,R6 and R9 so that they insert maximum resistance and pass the loop momentarilyoverthecore Core Extension extensionoftheoscillatorcoil. Watch the meter for results. Advance Oscillator Coll R4 a fraction and pass the loop over the core again.Repeat this process Tagboards until a position is found where the MI14 meter indicates the most deflection Fig. 5.Illustrating the layout of the major components when the loop is passed over the core. Then proceed to R6 and adjust Construction of Case protruding through. If desired, a this for maximum sensitivity in the Thesizeof thecase depends Paxolin sleeveI in long and with an same way, adjusting R9 to prevent mainly on meter dimensions.In the internal diameter ofI lincan be the meter being overloaded. writer'sinstance,themeter was glued over the coil on the two discs Continue minor adjustments to all 2 x 2 x 11 in deep, and the dimensions to completely seal the coil and make three controls until the unit is at its of a box to house such a meter are a neater unit. most sensitive setting.The shorted given in Fig. 4. After this, the layout of the com- turns tester is then ready for use.

NEWS AND COMMENT (continued from page 141) V/O Sudoimport of Moscow. Diving equipment, The Amateur Radio Mobile Society at their and underwater cutting and electric arc welding second Annual General Meeting reported an increase devices, are carried by the tugs.The Marconi- in membership and that they now have quite a Siebe, Gorman television cameras will enable salvage number of members abroad. it was announced that experts to see work being carried out by divers a ruling had been obtained from the Post Office using pressure air -driven tools. allowing separate log books to be kept for mobile An order for SARAH (Search, Rescue and contacts. Homing) marine equipment has been placed with According to theLondon Evening Standard,Mr. Ultra Electronics Ltd. by the Swedish Navy. This Charles Orr Stanley's Pye Radio and Television is the first marine equipment of this type to be group is linking up with the Ling-Temco Electronics ordered from Sweden. An initial order for SARAH of Texas to form a new joint company to be called aircraft equipment has also been received from the Pye-Ling. The new firm will market vibration test Swedish Army. equipment which is used for testing missiles and The first turf has been cut on the site of a new space rockets.Initially the new firm will be com- building-to be named "Elettra House"-which paratively small, starting with a capital of £160,000. will house all the Marconi Marine Company's staff In order to survey a busy intersection at Southend in the Chelmsford area and approximately fifty of airport which is not visible from the control tower, the Company's East Ham centralstoresstaff. a Marconi closed circuit television camera channel Clearing of the three -acre site at Westway, on the has been installed. Widford industrialestate,Chelmsford, has now Marconi will also be supplying underwater tele- begun and the building is expected to be ready for vision cameras to be used for salvage operations by occupation by the end of next summer. The name a fleet of seven Russian tugs, following an order for of the new headquarters has a historic significance t.v. equipment placed by the Finnish shipbuilding within the Marconi Group of Companies. Marchese firm Valmet Oy.Seven Marconi-Siebe, Gorman Marconi named his famous experimental yacht cameras and monitors are to be delivered to the Elettra,one of his daughters was also calledElettra, Pansio Shipyard, Turku, for installation on board and the Marconi Company's present experimental the diesel -driven salvage tugs now being built for yacht is namedElettra II.

144 THE RADIO CONSTRUCTOR A Magnetic GuitarPick-up and Transistorised Tone Control 0._,, Pre-amplifer -44 BY D. E. MAYNARD

ONE OFTEN SEES ARTICLES DESCRIBINGGUITAR so that it is a tight fit over the magnet. Then, with pick-ups, but they nearly all seem to use a the magnet inserted, about 180 turns of 32s.w.g. crystal mike insert or similar device.Quite enamelled wire are wound on to the former and good results are obtainable inthis way but such terminated in a two -pin socket which is fixed to the methods are subject to oneor more of the following guitar. disadvantages: It should be pointed out here that ale number of turns and gauge of wire required need ( I) Pick-up of extraneous noises suchasthe not necessarily be the same as those just given. rubbing of clothing on the guitar. (2) Feedback if played too closeto the loud- speaker system. (3) High impedance output necessitating theuse of considerable lengths of screenedcable. Coax The method described here is subjectto none of these disadvantages.However, it can only be used To Amplifier with a steel stringed guitar.

101111.1MIZIlnl 1.1111i 1.1111.1111.111.11=111

1.1.11.1.1:141111111 mI05 I_ _J Fig. 3.Matching the pick-up to the amplifier a Experience with experimental models has shown that, whilst it is preferable to fill the former with a large number of turns of fine wire rather than a small number of turns of thick wire, the difference b in output resulting is not great. A pick-up wound MICO with 40 turns of 24 s.w.g. enamelled wire gave only Fig. 1.Two positions for the guitar pick-up slightly less output than that wound with 180 turns of 32 s.w.g. wire. Pick-up Construction A bar magnet slightly shorter than thespan of the strings and thin enough topass between them and the guitar body is needed.Around this a

M104 M106 Fig. 2.The pick-up former Fig.4. An alternative method of constructing the pick-up using two magnets former of thin Paxolin or ivorineor any other stout The pick-up is positioned insulating material is builtup as shown in Fig. 2 on the guitar body as in Fig. 1, it being mountedas close to the strings as

SEPTEMBER 1961 145 is permissible after allowing for the depression of veniently be a miniature "battery pentode" output the strings on high notes.Fig.I shows two alterna- transformer mounted in a small box as shown in tive positions for the pick-up. The steel strings of Fig. 3. From here, about one yard of coaxial cable -6V 4mA 3.9kno 1.91(n Boss OlpF F 3.9kn 50krt 3.9krt 2°1 -IF 100kn 56

39ka WI TR3 Fig. 5. A transistorisedtone 0071 0071 Volume controlpre -amplifierfor the IQD pick-up,offering a highim- kn pedance output 10kn Okn

1.2kn ICO 501(n Ikn NF pF Treble 33kn 33kn

MI07 the guitar become magnetised and, when plucked, is used to connect to the input of a suitable amplifier. create disturbances in the magnetic field surrounding The reason for not having the matching transformer the magnet.These disturbances produce corre- actually at the amplifier input is that it is sensitive sponding voltages in the coil which are subsequently to magnetic fields and thus must be kept well away amplified. from the mains transformer.It may be found From the socket on the guitar up to about 20 feet helpful, in order to reduce r.f. breakthrough and of twin flex may be used to connect the pick-up to hum, to connect one lead of the twin flex to the the matching transformer.The latter can con - outer conductor of the coaxial cable.

146 fl-IE RADIO CONSTRUCTOR here again, the number of turns and wire gauge was not critical) and was connected directly into the emitter circuit of the first stage.About 10 feet of twin flex can be used between the pick-up and the pre -amplifier without any noticeable hum. The first stage is a low noise amplifier providing a small amount of gain, and this is coupled to a common emitter stage TR2, which provides the main amplification.A variable 1001a2 feedback 'resistor is included so that the gain of these two stages can be limited, if necessary. The tone control circuit utilises negative feedback which is fed in with the incoming signal in varying proportions in order to provide bass and treble left and cut.It may be necessary to alter the com- ponents of the tone control circuit if the pre -amplifier is to be put to other uses, since the characteristics were chosen primarily to be of use in the frequency 3.9kn 1.91(n range of a normal guitar. 391e1 TR2 As shown, the circuit has a reasonably high output F impedance and can be connected directly to a normal 20 F valve amplifier. The output covers the range 0-800mV with a level of about 300mV for normal playing. 101n For use with a low impedance output, either an Volume emitter follower stage is added or the output is taken from the emitter circuit of the present last stage as shown inFig. 6 (a). Inthis case the output is matched atthe main amplifier by means of a M106 transformer with a suitable turns ratio. Fig. 6 (a) (above). Modifying the outputstage of the Upwards pre -amplifier to low impedance of 10 feet of twin flex can be used here without any (b). Thelow impedance outputnecessitatesre- noticeable hum pick-up.In this configuration the positioning the volume control between TRI and TR, volume control of Fig. 5 must be discarded and one and deleting the pre-set gain control of Fig.5 fitted between the first two stages as shown in Fig. With the pick-up shown in Fig. 1, bass and treble 6 (h)(in which the pre-set gain controlis also boost is automatically provided; this is because the deleted).Alternatively, the pre-set gain control can magnetic flux is more concentrated near the poles be used as a volume control. of the magnet, and consequently the outer strings produce a greater effect than the inner ones.If the constructor considers this undesirable, and cannot 3.91(n compensate for it in his amplifier, the effect can be greatly reduced by using two magnets as shown in Fig.4. This arrangement provides a more even distribution of magnetic flux through the strings. The tone of the output can be varied greatly by 15n 1 placing the pick-up indifferent positions on the Input guitar.If placed next to the bridge the pick-up IO0pF reproduces several harmonics giving a "twangy" sound; if placed near to the finger board a more mellow sound is produced.However, the method M109 of attaching the pick-up is best left to the constructor Fig. 7.Converting the first stage of the pre -amplifier since guitar shapes and sizes vary so greatly. to grounded emitter The maximum output of the pick-up is approxi- mately 10mV after the matching transformer. If an emitter follower stage is added, the matching at the main amplifier can be effected by a grounded A Tone Control Pre -amplifier base transistor although this greatly increases the In order to provide greater flexibility, the writer cost. has designed a pre -amplifier for use between the For use in other applications the input stage is pick-up and the main amplifier. easily converted into a grounded emitter configura- The circuit of the pre -amplifier is shown in Fig. 5. tion as shown in Fig. 7. The output for 1 mV in is As can be seen it has one grounded base stage and then 300mV with the tone controls in a neutral two common emitter stages. The pick-up used with position. this pre -amplifier consisted of 180 turns of 32 s.w.g. The consumption of the pre -amplifier is 4mA at enamelled wire on a two magnet core (although, 6 volts.

SEPTEMBER 1961 147 BRITAIN'S MOST COMPREHENSIVE PRACTICAL COURSE IN RADIO LEARN BY BUILDING NOW for your

ELECTRONICS TELEVISION! CAREER HOBBY OWN BUSINESS TA/ESE SPECIAL TRAKIN/Ale YOU RECEIVE Complete kits of equipment KITS - YOURS TO /(EEL as illustrated. Complete set of experimental manuals. Complete setof "picture - Multi - Range way" theory books, TEST METER Modern test -yourself examination sheets. Study programme. CATHODE RAY Unlimited consultation with OSCILLOSCOPE Tutors.

RADIOSTRUCTOR SIGNAL GENERATOR TO RADIOSTRUCTOR (DEPT. M.31) READING, BERKS.

Name Complete set of BLOCK Address CAPS Picture Way books and iiiiHIHOHIHM PLEASE iliffiliilint,rn Experimental Manuals 1111,11111111111117I (We do not employ representatives) 9.61

148 THE RADIO CONSTRUCTOR 1'

SUB -MINIATURE COMPONENTS NOW THE I. Ferrite aerial with Long and Medium Wave Coils 4+' long for pocket superhet, complete MARK IV *". 04110,1141011, with circuit showing component values etc. .000000.0.."'*. mAIWWW 7/6d. Read these Testimonials SPOWNOIONMOro 2. Ferrite aerial as above, but I" diameter, 8' D. A. Hilton, Leigh, Lancs. 0.0.1111r.0.***, long for table model receiver or portable. IVIA111,110,01111113110i * "I received 'Pocket 4' on Christmas ***1011.4110.11111911*, 10 /6d. I * Day.made it up on Boxing Day and I 3. Three I.F. Transformers with oscillator coil* am very pleased with theresults.It and circuit details to work with item I. 19/6d. * bringstat1 Itatitounxs ea,,nn yalo foreign *****0OVI*0*.1 4. Three I.F. Coils and oscillator to work with stationsin includingl item 2. SMOIP.All,0001,11 23/6d. * strength. I am 13 years old." **111/1001.*IPIP 5. Smallest possible electrolytics.I MFD, 2MFD, * Mr. J. Bell, Wolverhampton. 11t101111,01111**,' 4MFD, 5MFD, 6MFD, 8MFD, IOMFD, 20MFD, fr111111110110**1/ 30MFD, 50MFD, 100MFD, 200MFD allI/9d.* "I am writing to express my satisfac- each. * tion at the standard of your kit for your 6. Smallest watt resistors all 10% values 5d.* Pocket 4 Transistor set and also to state Our famous Pocket "5" which is doing yeoman service all * that it has come up to my expectationsover the country has been modified and improved to make it each. in regard to performance." an even better receiver. The new features include:- 7. Miniature condenser . I 110d., .5, .04, 02, 01 all 8d. values below this 7d. Mr. R. Belt, Newcastle -on -Tyne. New elegant dial graduated for Long and Medium Waves. 8. Miniature slide switch double pole change'r "I have built your Pocket 4 Transistor Switched Long and Medium Waves. over 2/6d. * set, I am very pleased with it." Slide switch on/off control. 9. Edgewise volume controls 2K, 5K, 10K and * Mr. F. Jackson, Ickenham, Middx. Printed circuit. 20K 2/6d. each. * "Ihave built the Pocket 4 and am Ferrite Rod Aerial. 10. Small edgewise controls with switch 2K, 5K,* more than pleased with the results." Improved reaction circuit. 10K and 20K 419d. each. * Mr. G. Bamford, Ramsgate. Positive spindle coupling to tuner. II. Red Spot Transistors tested and suitable all* "I find this set even better than you Battery containers. A.F. applications 2/6d. claim it to be and most certainly up to The Pocket "5" of course retains its original r.f. circuit which 12. White Spot Transistors tested and suitable as ,"` your usual standardof quality. I feelmeans still no aerial or earth needed. I.F. or mixer 3/6d. .9'that nobody could fail to build it and get 13. Set of six transistors for superhet Mullards in The Pocket "5" Mark IV uses 4 transistors, crystal diode, * results. Even the first -time -ever novice,miniature loud speaker and hasallthe above refinements, original packets, fully guaranteed, comprising* as your circuit diagrams and instructionscomplete in case as illustrated (less motif) 52/6, battery 10d., 0C44, 0C45, 0C45, OC8ID and matched* are so clear and precise." post and insurance 2/6. Motif 2/... pair 0081. £2 the set. * Mr. A. J. Simmonds, Welling, Kent. Pocket "6" as Pocket "5" but with Moving Coil Speaker "Ipurchased from youa week agoand Q.P.P. output stage, 95/-. ,"the Pocket 4 TransistorKit, I putitSeven days' approval. SPECIAL SNIP FOR THIS MONTH * together last night in I) hours, on switch- Order in confidence. We allow you seven days to decide The Pocket "6" as described alongside * ing on the set I was right on Radiowhether or not to make the set, you may return the parcel *Luxembourg. I must say thank you be-as received within this time and your money will be refunded but fully made up ready to work. cause not only has the set a very attrac-in full. *tive appearance, it also behaves fantasti- Read some of the testimonials, over 1,000 of which have f5.15.0 plus 2/6 post and insurance. *4t***********************************************cally." been received about our Pocket Receivers. ELECTRONIC PRECISION EQUIPMENT LTD * Orders received by post are despatched from our warehouse, Dept 34, 66 Grove Road, Eastbourne, and to save time, please post your order to this address. Please include enough for postage. Callers, however, should use one of the following addresses: 520 High Street North 42-46 Windmill Hill 266 London Road 29 Stroud Green Road 246 High Street Manor Park, E.12 Ruislip, Mddx. Croydon Finsbury Park, N.4 Harlesden, N.W.10

23 Tottenham Court Road London WI Telephone MUSeum 3451/2and 309 Edgware Road London W2Telephone PADdington 6963 THE WALTER Battery/Mains Tran- Summer Bargain Offer Introducing THE TELEFUNKEN STEREO sistorised Portable HI -H TAPE "THE CLARION" AMPLIFIER RECORDER Transistorised Battery Tape Recorder For only Original price 55 gns. 09.19.6 NO V,g P. & P. 5/ - ONLY z"GNS. At last perfection is now within the reach of all. Plus P. & P. 201 - This unique Amplifier has been designed to revolution- ary standards,bothinappearance and technical No longer need you design and backed by the full technical resources be restricted to in- of Telefunken. door recordings for Brief specifications: withthismachine Power Output 5 Watts total (21 watts per you can record and channel). playback where - * Frequency Response 30 c/s to 40 Kc/s 2dB. ever and wheneveryou wish. Recordings 45 c/s to 30 Kc/s made with the machine on battery operation * Total harmonic distortionlessthan 1% at maintains the Hi-Fiquality when played back 1 watt output. on mains. These machines are supplied complete Now only I62 gns * Sensitivity sufficient for all normal inputs from with Microphone, Mains Lead and all necessary Tape Recorders, Pick-ups, Microphones Radios. accessories, they are brand new in manufacturers' Batteries Extra 3/4P. & P. 6/ - * Power Requirements 110, 125, 150, 220, 240 originalcartons. Star Features-* 7 stage volts A.C. built-in Amplifier with separate bias oscillator Original Price 25 gns. * Piano key selecting. andrecordlevelindicator.Push-pulloutput * Preselected tone control. stagewithnegativefeedback. Also separateBrief specifications- Constant governed speed of 3f i.p.s. * Size 12" wide x 9" deep x 2" high. feedbackequalisation. * Fullsize, 3 -watts Completely transistor-* Weighs 9 lbs. undistorted output. *7" x 4" High Flux Ellipticalised circuit. Recordings inter -changeable with other * Finish: Hammered enamel in grey/green with Speaker. * Large 5f" sp 5f" Spools. * 3r Recorders. Remarkable gold trimmings, Controls and press buttons i.p.s. Tape Speed. * Revolution Counter. *reproduction on both speech and music. Complete with Microphone, Tape and in cream with black, blue and red lettering. Mixingfacilities. * Super -imposefacilities. Specially designed output transformers have * Safety device on record (preventing accidentalSpare Spool.Fullrange of accessories available. been used having an extremely high transfer erasure). * Volume on/off and Tone controls. efficiency therefore delivering a far greater * Magic Eye Tuning Indicator. Send for full descriptive literature output to the speakers.

SEPTEMBER 1961 149

I THIS MONTH'S SPECIAL OFFER AERIAL Bumper Bargain Parcels of Resistors, BARGAINS Condensers and Pots. 10/- and 5/- Post Free EQUIPMENT

GELOSO V.F.O. UNITS. 4/ PLUG IN NOISE LIMITERS. 102 with new dial and escutcheon. 3 Position Limiting.No Wiring COPPER WIRE. 14g. h.d.: HEADPHONES. DHR58 (very Outputs on 80, 40, 20, 15 and 10. Required. Idealon HRO or 140' 17/-; 70' 8/6; 7/25 stranded: sensitive), 2,000 ohms 18/6.P. & P. For 2-807 or 6146 tubes.Only H.R. Output for PHONES 8/6. 140' 10/-; 70' 5/-, plus 2/- P. & P. 1/6. DLR1 (low res.) 7/6. P. & P. 1/6. £8.5.0. 3 valvestosuit,24/-. P. & P. 1/6. All post free. RIBBED GLASS INSULA- TORS. 3" 1/6 each.P. & P. 1/6. NATIONAL H.R.O. CRYSTAL FILTER UNITS. 455 kc/s with CERAMIC COIL FORM- TWIN FEEDER. 300 ohm twin crystal.Sel. and phasing controls. ROTARY CONVERTERS ERS. 2,+"x1*". IDEAL ribbonfeeder,similarK25,6d. New boxed. ONLY 19/6.P. & P. 6V input,250mAoutput. FOR VFO or P.A. on per yd.K358 Telcon (round) 1/6 1/6. Only 5i" x 3" x 3". 17/6 Mobiles, 1/9 each or 17/6 doz. peryd. Poston above feeder each.P. & P. 3/-. and cable 1/6 any length. MULTI -WAY CABLE. 3 -core BTX. x 11" with32 screened 1/- yd.; 12 -core screened 1 2V MINIATURE Grooves for P. Tanks 6/- ea. SUPER AERAXIAL CABLE 2/- yd.First grade Mike Cable ROTARIES.Only4a."x 1/8 per yd.P. & P. 1/6. 9d. yd. or 6/- doz. yds.P. & P. 1/6. 2,+"overall.Output 360V, TFX. 2i" Dia. 5" WINDING 30mA or 310V, 70mA. NEW SPACE. Ideal Hi Power CERAMIC FEEDER SPREAD- LOW PRICE 12/6 each or Lin. Amps 8/6. ERS. Type F.S. 6" 10d. each or 10 -WAY CABLE (5 pairs), 22/6 for 2.P. & P. 1/6. 9/- doz.P. & P. 2/-. screened and plastic covered. Any length cut, 1/8 per yd.P. & P. CERAMIC "T" PIECES.Type 1/6 min. MOSLEY TRI-BAND BEAMS AT for centre of dipoles, 1/6 each. SUPER BANDCHECKER P. & P.1/-. TOUGH POLYTHENE LINE. AND MONITOR. This new, T33, JR, 3 EL ... E24.15.0 TA32 JR, 2 EL . E17.10.0 NEW MOSLEY POWER Type ML1 (100 Ib) 2d. per yd. or sensitive, absorption wavemeter V3 JR, Vertical 3 Band E7.10.0 12/6 per 100 yds.Type ML2 (220 is fittedwith 0-500 micro - BEAMS.Write fordetails. 300 Ib) 4d. per yd. or 25/- per 100 yds. ammeter and isalso a most PLACE YOUR ORDER EARLY watt, 50 ohm COAX, dia., Post free. usefulphone monitor.Covers very low loss, 1/6 yd.P. & P. 1/9. 3.5-35 Mc/s in 3 switched bands. ABSORPTION WAVE - only 3 gns. METERS. 3.00 to 35.00 Mc/s in 3 switched bands, 3.5, 7, 14, 21 and RACK MOUNTING LTD (Dept R) 28 Mc/s ham bands marked on PANELS. 9" x 5-k", 7", 8+" or CHAS H. YOUNG scale. Completewithindicator lor blackcracklefinish,5/9, 110 DALE END BIRMINGHAM 4 bulb. A MUST for any hamshack. 6/6,7/6and9/-respectively, (Tel. all departments) CEN 1635 ONLY 22/6.Post free. postage and packing 2/-.

*00000000000ILFord 600113 TAPE AMPLIFIER REPANCO REPLACEMENT REBUILT 47.19.6 TRANSFORMERS FOR 10 WATT TRANSISTOR AMPLIFIERS T.V. TUBES H.P. Terms Available Type TT23InterstageTran-sformer Ratio4:1 +1 Compact well designed Secondary Resistance 2+2 ohms 21"99/6 5 valve amplifier. Out- 17" 90/-put 3.5W.Input for Primary Resistance 3.5 ohms 22/6 15", 14", 12" 70/- microphone, gram and Secondary Bifular Wound Ins. carr. 15/6 radio. Size 8+" x 3" (P.P. 1/6) x 4r.Ins. Carr. 4/6. 12 months guarantee 12 months guarantee. 1f1 extra without old bowl, refundable Dial plate 3/6. Knobs Type TT24 Output TransformerRatio1.3+1.3:1+1 if same received within 14 days 2/6 per set. -..... c..= ..=. =.....--- ..-. - -.- ..... Secondary Resistance 0.2+0.2 ohms 14" TV TUBES SCOTCH BOY Primary Resistance 0.6+0.6 ohms 22/6 14KP4 35/- 36/24 TAPES IDue to purchase of renter's replacement 5,1" 19/9 7" 25/ - (P.P. 1/6) stocks. Carriage 5/- Post Free Primary Bifular Wound. 15 ohm or 3.5 ohm output . 17 inch Ex -RENTAL SETS 14 inch 411.10.0 47.10.0 Stack Size of Both Types 22" x 2k" x :-k" ,Excellent table ITA/BBC. As 17". Boxed Complete with 10 watt Amplifier Circuit i models. ITA/BBC. Idealforcaravans, Famous manufac- chalets, weekend curer. 12 months bungalOws, etc; Per - guarantee. Terms sonalcollectionad - MAIL ORDER and TRADE WHOLESALE and EXPORT available. Personal vised. Specialde - collection advised or I liveryratebyar- RADIO EXPERIMENTAL delivery rate by rangement up to 50 REPANCO LTD arrangement up to 50 miles, or despatched PRODUCTS LIMITED miles, or despatched in 3 parcels for easy O'Brien's Buildings in 3 parcels for easy assembly.Carr. and 33 Much Park Street Coventry203-269 Foleshill Rd. Coventry assembly. Carr. 25/- Ins. 20/- Telephone 27114 Telephone 24224 D RD DUKE & CO. (London) LTDMANORPARK E12 1j 44,..0000000000000000000,0,0,.0.0.000(i/ 00.0.0-.0.0.00-X-

150 THE RADIO CONSTRUCTOR 1 3 -TRANSISTOR POCKET RADIO with miniature SPEAKER, FERRITE ROD, and 2 GERMANIUM DIODES.The only 3 -transistor radio available at the price.Builditin 1 evening! Tu...tble over M/L waves. Complete with easy -to -follow instructions and all components (less batteries obtainable anywhere 1/3).27/6. P. & P. 2/-.(Allparts available separately.) 2 3 -TRANSISTOR SUPER POCKET RADIO with MINIATURE SPEAKER. Plus Germanium Diode and Printed Circuit. Size 34" x 4" a 4".Ferrite Rod Aerial. Two Surface Barrier Transistors and one Audio. Tunable over medium and long waves. To build yourself 39/6, P. & P. 1/6.Circuit diagram 1/6, free with kit.All parts of items 1 and 2 sold separately. 3 OSCILLOSCOPE for D.C. and A.C. APPLICATIONS. A high gain, extremely stable differential Y -amplifier (30 mV/C.M.). Provide ample sensitivity with A.C. or D.C. inputs.Especially suitable for measurements of transistor operating conditions where maintenance of D.C. levelsisof paramount importance.Push-pull X amplifier; Fly -back suppression;Internal Time -base Scan Waveform available for external use; pulse output available for checking TV line 0/P Transformers, etc.Provision for external-I/P and CRT Brightness Modulation. A.C. mains 200/250V 615.15.0, P. & P. 7/6 or 30/- deposit, plus P. & P. 7/6 and 12 monthly payments of 26/6. FULL 12 MONTHS' GUARANTEE INCLUDING VALVES and TUBE. 4 A.C./D.C. POCKET MULTI -METER KIT. 2" moving coil meter, scale calibratedinA.C./D.C. volts, ohms andmilliamps.Voltage range A.C./D.C. 0-50, 0-100, 0-250, 0-500.Milliamps 0-10, 0-100. Ohms range 0-10,000.Front panel, range switch, wirewound pot (for ohms zero setting), toggle switch, resistor and rectifier.19/6. P. & P. 1/6.Wiring diagram 1/- free with kit. 5 CHANNEL TUNER. Will tune co all Band I and Band III stations. Complete with P.C.C.84 and P.C.F.80 valves (in series) I.F. 16-19 or EASY TERMS 33-38. Can be modified as an aerial converter (instructions supplied). 32/6, plus 3/6 P. & P.HEATER TRANSFORMER to suit above, AVAILABLE 200-250V, 6/-, plus 3/6 P. & P. 6 MAINS TRANSFORMERS. All with tapped primaries, 200-250V, 0-160 180, 200V, 60 rnA, 6.3V 2 amps, 10/6.350-0-350V, 70mA, 6.3V. EXCEPTING 1 amp, 6.3V 2 amp, 10/6. 250-250V 70mA, 6.3V 2 amp, 10/6.P. & P. 3/-. 280-0-280 70mA 6.3V, 2 amp 6.3V, 1 amp, 10/6, P. & P. 3/-. 280-0-280 120mA, 6.3V, 2 amp 6.3V, 3 amp, 17/6.P. & P. 3/-. AUTO -CHANGES 7 WOLSEY 3 -ELEMENT FOLDED DIPOLE.I.T.V.Aerialless mounting bracket for external use, complete with 12 yds. of coaxial cable, 15/-.P. & P. 3/6. 7

9 SIGNAL GENERATORS. Cash 66.19.6 or 25/- deposit and 6 monthly payments of 21/6,P. & P. 5/-.Coverage 100 kc/s to 100 Mc/s on fundamentals and 100 Mc/s to 200 Mc/s on harmonics. Case 10" x 64" a 54".Three miniature valves and Metal Rectifier.A.C. mains 200/250V.Internal modulation of 400 c.p.s. to a depth of 30 per cent; Modulated or unmodulated R.F. output continuously variable 100 millivolts. CW. and mod. switch, variable A.F. output.Magic eye as output indicator.Accuracy :4 2 per cent. 10 SIGNAL GENERATORS. Cash 64.19.6 or 25/- deposit and 4 monthly payments of 21/6, P. & P. 5/-. Coverage 120 kc/s to 84 Mc/s. Case 10" x 64" x 44". Size of scale 64" x 34", 2 valves and rectifier. A.C. mains 230-250V. Internal modulation of 400 c.p.s. to a depth of 30 per cent modulated or unmodulated R.F. output continuously variable 100 millivolts.C.W. and mod, switch variable A.F. output and moving coil output meter. Accuracy 2 per cent. 11 BATTERY RECORD PLAYER AND AMPLIFIER.45 r.p.m. "Star" motor "Acos" crystal pick-up, 3 transistor, push-pull amplifier complete with transistors. Output 500 milli watts, 49/6, P. & P. 3/6. 12 8 -watt PUSH -PULLS VALVE AMPLIFIER. A.C. mains 200-250V Size 104" x 64" x 24".5 valves.For use with all makes and type of pick-up and mike.Negative feedback. Two inputs, mike and gram. and controls for same.Separate controls for Bass and Treble lift. Response flat from 40 cycles to 15 kc/s, ± 2 dB; 4db down to 20 kc/s. Output 8 watts at 5 per cent total distortion.Noise level 40 db down all hum. Output transformer tapped for 3 and 15 ohms speech coils.For use with Std. or L.P. records, muscial instruments such as guitars, etc.Suitable for small halls, 13.19.6, P. & P. 6/6.Crystal mike to suit 15/-, P. &P. 1/6. 8" P.M. Speaker to suit, 12/6. P. & P.1/6. 13 B.S.R. MONARCH UA8 WITH FUL-FI HEAD. 0. -speed, plays 10 records, 12", 10" or 7" at 16, 33, 45 or 78 r.p.m.Intermixes 7", 10" and 12" records of the same speed. Has manual play position: colour, brown.Dimensions: 124" x 104". Space required above baseboard 44" below baseboard 24". Fitted with Ful-Fi turnover crystal head, 66.19.6, P. & P. 5/-.With Stereo Head 67.19.6. P. & P. 5/-. 14 TRANSISTOR TESTER. For both P.N.P. and N,P,N, transistors incorporating moving coil meter.In metal case, size 44" x 34" x 14". Scale marked in gain and leakage, 19/6, P. & P. 2/6. 15 PUSH-PULL OUTPUT STAGE inclusiveof transistors with input and output transformers to match 3 ohms speech coil, suitable for use with the POCKET RADIO. Kit of parts, including transistors, 19/6, P & P. 1/6. Wiring diagram 1/6, free with kit. c ice/ 16 PORTABLE AMPLIFIER. On printedcircuitfor A.C.Mains 200/250V.Size 4" x 3" with tone and volume control. Valves: ECL82 and EZ80.39/6, P. & P. 2/6. 14 RADIO & T.V. COMPONENTS 23d HIGH STREET, ACTON, LONDON, W.3. (Acton)LTD. ALL ENQUIRIES S.A.E. GOODS NOT DISPATCHED OUTSIDE U.K. SEPTEMBER 1961 FREE TRIAL OFFER ! COYNE'S NEW JOB TRAINING BOOKS Put Money -Making Time Saving Know-how at your fingertips!

Shows you the way to easier TV-Radio repair-time saving practical working knowledge that helps you to repair sets faster! How to install service and align ALL radio and TV sets even colour -TV UHF FM and transistorized equipment. New photo -instruction shows you what makes equipment "tick." No complicated maths or theory-just practical facts you can put to use immediately right in the shop or for ready reference at home. TRY ANY THREE BOOKS ON NO RISK FREE TRIAL Look over the list of books and select the first three books you would like to examine. Circle the book numbers on the coupon. Additional books you would like to see may be entered on a separate piece of paper and these will be sent to you after completion of the first transaction.

No. 8. SPECIAL OFFER COYNEELEMENTARY PRACTICAL RADIO -TELEVISION SET OF THREE VOLUMES total COYNE'S NEW 1,038 pages, sturdy Vinyl washable covers. 63 12s. 6d. the set! PIN -POINT TV TROUBLES These three volumes present the principles of construction, operation and testing of radio and television equipment in a SIMPLE, EASY TO TAKES HEADACHES OUT OF ALL SER- FOLLOW manner. VICING PROBLEMS By using NEW & DIFFERENT methods of explanation these books Your most useful on-the-job "too"! Quickly clearly explain the direct relation between the various parts of sets. This and easily pin -points the exact trouble in any information is especially helpful in repair work where many times a TV set. Covers 70 symptoms, 700 trouble burned out valve, resistor or transformer is actually caused by some spots.Over 340 cross-indexed pages; 50 TV TROUBLES other defective part of a circuit.Until the cause of the trouble is re- time -saving Check -Charts: 290 diagrams and moved the parts would continue to burn out.For this reason, each photos; explanation of circuits and designs. part of the radio or television unit is explained, thus, making the material SIMPLE CHECK -CHART SYSTEM SAVES especially helpful to the experienced radioman, as well as the amateur. TIME One very important way in which these books differ from many other This amazinglypractical handbook shows you radio and television books is that the publishers did not try to assume how to find the trouble in any TV circuit FAST! the "extent of technical knowledge" of the reader.Every subject is Simple cross-index tells you in what section you'll find cause of trouble. explained COMPLETELY-while at the same time keeping it brief and Handy Check -Charts then help you accurately locate the EXACT to the point. trouble spot. Cut waste time, eliminate hours of aggravation, get right You will find hundreds of photos, charts, diagrams, etc.,in these to the heart of the trouble in minutes. books. These have been provided to make it easier to understand the USE THIS RIGHT ON THE JOB-NO TO explanations. To get this special offer, send no money now, then MEMORIZE! 12/6d. plus postage, after free examination, and 20/- per month. This pin -point book was designed especially for on-the-job trouble- shooting. You simply turn to the indexed section, locate the circuit des- No. 9 cription and Check -Chart, and in minutes you have the trouble spot Pin -point located and ready for repair. No complicated theory or mathematics. Down-to-earth,practicalcircuitdescription,service methods and Transistor troubles trouble -shooting techniques. Published by the famous Coyne Electrical School and approved by leading authorities in the field.Price 31/6. in 12 minutes No. 7. TRANSISTOR CIRCUIT HANDBOOK. Louis E. G In this extremely practical handbook, the Jr. Coyne. famousCoyneCheck -Chart Trouble - A practical Transistor Circuit Reference Handbook by the eminently Shooting Method is applied to Transis- qualified Louis E. Garner, Jr., one of the greatest writers on transistor torizedEquipment andincludes such applications.Covers TransistorCircuitry,Basic Circuits,Circuit subjects as Pre -amplifiers and Hearing Applications and General Reference Material. Dozens of how -to -do -it Aids; Audio Amplifiers, Portable Sets, illustrations with more than 200 circuit diagrams. Over 400 pages. and Special Types of equipment. Hun- Vinyl cloth covers. 39/6. (When ordering this book please be sure to dreds of photos, illustrations, diagrams clip the coupon). and Check -Charts; Valuable reference, No. 19. REFRIGERATION SERVICE MANUAL. H. P. Manly. sections. 525pages. SpiralBinding. This manual is primarily an instruction book on accepted methods of Price 47/6.(Please send coupon with servicing and repairing electric refrigerators and refrigeration systems. order). It covers every operation in field service, performed where the equip- No. 4. LATEST INSTRUMENT FOR SERVICING RADIO AND ment is installed, and also the shop operations which may be per- formed with the simpler kinds of equipment. 157 Illustrations, 343 TELEVISION. Coyne. pages, cloth Price 24/ - This up-to-the-minute book tellsall about modern radio, TV and NOTE electrical testing equipment and how to use it.Money -making short "Any Iliffe or Coyne book is available on time payment pier& Send cuts on trouble -shooting, servicing, construction, and other jobs. name of title required. Over 350 pages, 220 photos and diagrams.Covers Multimeters, Just mail coupon for free trial.After 7 days send only low price or Resistors, Ohmmeters, and many others.All data has return books and pay nothing.If you keep more than one book, send LI been pre -tested in the Coyne radio shops. Vinyl cloth covers. 26/ - after 7 days and El each month until completed (maximum three books). No. 5. PRACTICAL TELEVISION SERVICING AND TROUBLE To buy one book send one-half in 7 days, and one-half in 30 days. SHOOTING MANUAL. Coyne. A book of fast time saving methods for servicing TV receivers.In- cludes dozens of new testing ideas all of which have been proven on LIMITED OFFER !ACT NOW I the job.This book shows how radio knowledge can be applied to To SIM-TECH BOOK COMPANY (U.K.) helpsolvetelevisionproblems.Contentsinclude TV servicing methods, TV Servicing Instruments, Tuners, Video I.F., Amplifiers, Mail Order Division, DEPT. RC5, Gaters Mill, West -End, South- alignment, etc., with 200 crystal clear photos and diagrams. 437 pages. ampton, Hants. Washable vinyl cloth covers. Price 34/, 0 Please send me the special Elementary Radio TV Set as per special offer. No.6. COYNE TELEVISION SERVICING CYCLOPEDIA. Harold P. Manly. Coyne. Rush the books circled below for 7 -day FREE TRIAL as per offer. Quick and concise answers to TV problems in alphabetical order, 9. 4. 5. 6. 13. 8. 7. 19. cross indexed, fullyillustrated, covers hundreds of questionsin- Tick here if enclosed full price. Same 7 -day money back guarantee volving radio, TV, electronics operation and repair. 450 illustrations; photos, diagrams, charts, test patterns, etc., 860 pages.Vinyl cloth covers. Price 47/6. Name No. 13. TELEVISION EXPLAINED. Miller and Spreadbury. Address In simple terms and non -mathematical language gives step-by-step survey of modern television receivers and aerial systems, including City County AGC and Flywheel Synchronising.184 pages.12/6. Postage 1/6, orders under [3. 2/- orders over E3.

152 THE RADIO CONSTRUCTOR Speaker Fret -Expanded bronze TRANSISTOR BARGAINS "6 plusI" TRANSISTOR RADIO KIT anodised metal 8" x 8" 2/3, 12" x 8" Brand New-BVA 1st Grade 3/-, 12" x 12" 4/6, 12" x 16" 6/-, 0C44 10/6 873 9/- UNBEATABLE VALUE! 24"x 12" 9/-, 36" x 12" 13/6, etc. etc. 0C45 9/6 GET114 6/6 0081 7/6 0072 7/6 MANUFACTURERS' CURRENT PRO- 2/0081 15/6 DUCTION OFFER. -A fortunate bulk TYGAN FRET (contemp. pat.) OC70 5/6 12" x 12" 2/-,12" x 18" 3/-, XA102 10/- 0071 6/- purchase enables us to offer one of the 12" x 24" 4/-. XA101 9/6 season'smost outstandingbargains in X B103 7/6 GEX34 2/9 Portable Transistor Radio Kits.This kit 4 -SPEED X C101 8/6 0A70 2/9 is a modernsensitivequalitycircuit BARGAIN PLAYER UNITS 874 9/6 0A81 2/9 Receiver Unit with all the latest features. Single Players carr. 2/6 Surfacebarriertype SB3059/6 Six BVA transistors and 1 diode, printed circuit, Med. and Long waves. Garrard 4 S.P. 16.19.6 each All Post Free Ferrite aerial, car radio input 500mW, push-pull output into 3 ohm Garrard TA Mk. 2 17.19.6 SLEEVI NG-Various Colours speaker, calibrateddial and slow-motion tuning, etc.Size approx. Collaro "Junior" 75/- 1mm, 2mm, 2d. yd.; 3mm, 4mm, 8" x 21". B.S.R. (TU9) 79/6 3d. yd., 6mm, Sd. yd. KIT of Parts including BARGAIN OFFER E.M.I. Junior 89/6 printed circuit, gns. Auto -Changers carr. 4/6 CRT. HTR. ISOLATION Set of 6 Transistors and CompleteKitL6/19/6 Garrard RC210 /10.10.0 TRANSFORMERS 1 Diode 45/-P. & P. 2/6. less Speaker Carr. 2/6 Collaro "Conquest" 17.15.0 New improved types, low capa- B.S.R. (UA8) city small size and tag terminated 3 ohm Speaker 7" x 3r -ONLY 15/6.P. & P. 1/6. Send 3d 16.15.0 a.c. 200/250V. stamp for full details. Circuit and Instructions 1/6. Cabinets 25/- extra. B.S.R. (UA8 Stereo) /6.19.6 Secondariesnil, B.S.R. (UA14) 17.19.6 +25% +50% BOOST for 2V, Electrolytics All Types New Stk. 4V,6.3V,10.5V, 12V or 13V Bo dVALVESGuaranteed SINGLE SCREENED LEAD - tubes. Eachtype12/6each. TUBULAR CAN TYPES size, P. & P. 1/6. 1T4 Standard 8d.yd.;Ditto 6/- ECC83 8/- PCC84 9/625/25V 1/98+8/450V 4/6 LightweightforPick-up,etc., TRIMMERS, Ceramic (Com- 1R5 7/6 ECL82 10/6 PCF80 9/650/12V 1/9164-16/450V 5/6 7d.yd.;dittolightweightfor pression Type)-30pF, 70pF, 9d.; 1S5 7/6 ECL80 10/6 PCL83 12/650/50V 2/-32+32/275V 4/6 PVC sheathed,9d.yd.;Twin 3S4 7/6 EF80 100pF, 150pF,1/3;250pF,1/6; 8/- PCL84 12/6100/25V 2/-50+50/350V 6/6 screened sheathed, 1/- yd. 600pF, 1/9. 3V4 7/6 EF8612/6 PL81 12/68/450V 2/360+250/ DAF96 9/- EL84 8/6 PL82 9/64/350V 2/3 275V 12/6 VALVEHOLDERS-Paxolin: PHILIPS, BeeHive Type DF969/- EY51 9/6 PL83 10/616+16/450V 5/6100+200/ Int. Oct., EF50, VR92, 6d. each; (Conc. Air Spaced)-2-8pF, 1/-; DK96 9/- EY8610/- PY32 12/632+32/450V 6/6 275V 12/6 Eng. and Amer. 4, 5 and 7 pin, 3-30pF, 1/-. DL969/- EZ81 7/6 PY81 9/6 etc.,1/-each; Moulded: Int. TUNING COND.-Twin Gang ECC81 8/- GZ32 12/6 PY82 7/6Ersin Multicore Solder 60/40 3d. Oct. Mazda Octal, 7d. each; B12A by J. B., etc.365pF Midget, 8/6; ECC82 8/- EM81 9/6 U25 12/6 per yard.*lb. 2/6, etc. "(CRT), 1/3; B8G, 9d. each; Nylon .0005 mfd Midget, 7/6. Transistor or Moulded Ceramic: B7G, Type, J. RECORDING TAPE -BARGAIN PRICES B9A unskirted, 9d. each; B7G, Bros. 00. Midget Twin Famous American Columbia (CBS) Premier Quality Tape at B9A skirted, 1/- each; B7G with Gang 208pF+176pF, 9/-. NEW REDUCED PRICES. A genuine recommended Quality Tape Can, 1/6 each; B9A with Can, 1/9 SINGLE TUNING COND.- -TRY IT!Brand new, boxed and fully guaranteed.Fitted with leader each; EF50, B7G, 1/- each; B9A Reaction Type, Mica Dielectric, and stop foils. ditto, 1/3 each. .0001 mfd, .0003 mfd, .0005 mfd, Standard Long Play Double Play ENAMELLED COPPER 3/6 each. 5" 600ft, 15/- 900ft, 19/6 1,200ft, 31/6 WIRE -}lb reels 14g -20g, 2/6; Wavechange SWITCHES, 5i" 900ft, 16/6 1,200ft, 22/6 1,800ft, 39/6 22g -28g, 3/-; 30g -40g, 3/9. Other Midget Type -2 pole 2 way, 1 7" 1,200ft,21/- 1,800ft, 32/6 2,400ft, 47/6 gauges quoted for. pole 6 way, 2/6 each; 1pole 12 Post and Packing, per reel, 1/-, plus 6d. each for additional reels. way, 2 pole 6 way, 3 pole 4 way, SPECIAL OFFER -3" mfrs. surplus tape, 225ft, 5/6.P. & P. per reel 6d. PVC CONNECTING WIRE 4 pole 2 way, 4 pole 3 way, 3/6 Plastic Tape Reels, 3" 2/6, 5" 3/-, 51" 3/3, 7" 3/6. -10 colours (for chassis wiring, each. etc.) -Single or standed conduc- FUSEHOLDERS-Chassis Volume Controls -5K-2 Meg - Condensers -SilverMica. All tor, per yd., 2d. Type: Single, 6d.; Double, 9d.; ohms, 3"Spindles Morganite values, 2pF to 1,000pF, 6d. each. Panel Mounting Bulgin Type, 1/9. Midget Type. 1r diam.Guar. Ditto,Ceramics 9d.Tub. 450V "POCKET 6" TRANSISTOR T.C.C.,etc..001 mfd., .01 and FUSES -Cartridge Type, Stan- 1 year. LOG or LIN ratios less .1/350V, 9d..02-.1/500V4/-. .25 RADIO KIT-Med & 11W sizedard 1r. All standard values Sw.3/-. DP.Sw.4/6. Twin 6mA-10mA, 4d. each. Stereo less Sw. 6/6. D.P. Sw. 8/-. Hunts 1 6..5 T.C.C. 1/9, etc., etc.Osmor Ferrite Ae 10/-.Osc. Coil & Close Tol. S/Micas-10% 5pF-3 IF's 22/6.Driver & 0/P Trans. 22/-.MAINS NEON TESTER - COAX 80 OHM CABLE 500pF 8d.600-5,000pF 1/-.1%Tuning Gang 10/6.2f" PM SpeakerVestPocket Screwdriver with 2pF-100pF 9d.100pF-500pF 11d.17/6.Set 6 Transistors & Diode 45/-.Neon Indicator.For Mains 200/ High grade low loss Cellular air 575pF-5,000pF 1/6. spaced Polythene -7" diameter. Resistors -Printed Circuit 8/6.Vol. Control 8/-.250V and ignition Testing. New Full Range 10 ohms -10 megohmsW/C Sw.3/6.Cabinet & Dial8/-.Reduced Price, 2/9. Stranded cond. Famous mfrs. 20%and PA, 3d., 1W Sd. (Midget Now only6d. peryard. Resistor Set 5/ -.Condenser Set 15/-.KNOBS -ModernContinental type modern rating) 1W 6d, 2WHandbook, fulldetails 1/6. types: Brown or Ivory with Gold BargainPrices -Special 9d. Hi -Stab 10% fW Sd., +W lengths 20 yds. 9/-.P. & P. 1/6. 7d. 5% +W 9d., 1% 1W 1/6.Complete Kit REDUCED Ring, 1" dia, 9d. each; 11", 1/ - 40 yds. 17/6.P. & P. 2/-. PRICE L8/ I0/0each; Brown or Ivory with Gold W/W Resistors 25 ohms to 10K Carr. 2/6 60 yds. 25/-.P. & P. 3/-. SW 1/3, 10W 1/6, 15W 2/-.Pre- Centre, 1" dia., 10d. each; 11", Coax Plugs1/-. Sockets1/-. set T/V Pots. W/W 25 ohms. - 1/3 each. LARGE SELECTION Couplers 1/3.Outlet Boxes 4/6. 50 K 3/-. 50 K-2 Meg. (Carbon) 3/-. TRANSISTOR AVAILABLE. METAL RECTIFIERS, STC JASON FM TUNER UNITS COMPONENTS Types-RM1,4/9; RM2,5/6; Designer -approved kits of parts: Midget I.F.'s-465 Kc/s diam. 5/6 RM3, 7/6; RM4, 16/-; RM5, 21/-; FMT1, 5 gns.4 valves, 20/-. Osc. Coil-M/W. diam. 5/3 RM4B, 17/6. FMT2, £7.5 valves, 37/6. Midget Driver Trans. 4.5:1 8/6STC RECTIFIERS-E.H.T. Type JTV MERCURY 10 gns. Midget 0/Put Trans. 19.5:1 8/6Fly -back Voltages:K3/25, 2kV, JTV2 E13.19.6.4 valves, 32/6. Elect. Condensers -Midget Type 5/-;K3/40,3.2kV,6/9;K3/50, NEW JASON FM HAND- 4kV, 7/9; etc. BOOK, 2/6.48 hr. Alignment 1 mfd-100mfd, ea. 1/9.6V/12V wkg. Service 7/6.P. & P. 2/6. Vol Controls -Midget Type with edgeWESTINGHOUSE -Contact Control Knob. 5K, 47K, 1 M/ohm,Cooled: FC116,250V,60mA, Speakers P.M. -3 ohms 21" Ela ea. 2/6. 11/9; FC101, 250V, 200mA, 21/-; 17/6. Goodmans 18/6. 5"RolaSpeakers P.M. -21" EMI 3 ohms 17/6.FC31, 250V, 300mA, 28/6. Tape Recorder Kit Special Offer17/6.6" Elac 18/6. 7" x 4" Good7" x 4" Plessey 35 ohm 23/6. SIEMENS TYPES -Contact Latest 5 valvecircuitbased onmans18/6. 8"Rola20/-. 10' Ear Plug Phones -Min. ContinentalCooled: 250V, 50mA, 7/6; 250V, Mallard's design. Magic eye andR. x A. 25/-.9" x 6" Goodman type, 3ftlead, jack plug and socket.85mA, 10/-; 250V, 125mA, 15/-; tone controls. Printedcircuit25/-.E.M.I. Tweeter 29/6. High Imp. 8/-. Low Imp. 7/6. 250V, 300mA, 26/6. already wired. A sensitive quality recorder BSR Amp Kit95/-. B.S.R. Tape Deck 03.10.0.Col- Send for detailed bargain lists, 3d. stamp. laro. Amp. Kit £6.5.0.Collaro Tape Deck 112.10.0. Set of S We manufacturealltypesRadio Mains Transf. Chokes, Quality 0/P Trans.,etc. S valves 45/-.Special Unit Kit Enquiries invited for Specials, Prototypes for small production runs. Quotation by return. Prices -Send stamp fordetailed list. Construction andcircuit RADIO COMPONENT SPECIALISTS details 2/6. Bargain Complete Kit Est. 70 Brigstock Rd Thornton Heath Surrey Hours: 9 a.m.-6 p.m., 1 p.m. Wed. THO 2188. 116/10/0 Carriage 4/6. 1946 Terms C.W.O. or C.O.D. Post and Packing up to fib, 7d.; 1Ib, 1/1; 31b, 1/6; 516, 2/-; 10Ib, 2/9.

SEPTEMBER 1961 153 VOLUME CONTROLS. All values, long spindle. L/S 2/9, New Tested & Guaranteed s.p. 3/9, d.p. 4/3; ext. spkr. control 3/-. * VALVES P.M. SPEAKERS. 3 ohms 5" 14/6, 6+" 17/6, 8" 21/-, 10" 25/-, 1R5 6/6 6X4 7/6 DK92 7/6 EL84 8/- 12" 30/-; Bakers 12" 15 ohm 15W, 90/-. 155 6/6 6X5GT 6/6 D K96 8/- EL91 7/6 COAXIAL PLUGS 1/- each; SOCKETS 1/- each. 1T4 4/6 12AH8 10/6 DL92 6/9 EY51 7/6 3S4 6/9 12AT7 6/- DL94 7/6 EZ40 6/6 C.R.T. ISOLATION TRANSFORMERS withnil, 25% 3V4 7/6 12AU7 6/- D L96 8/- EZ80 6/6 and 50% boost, low capacity a.c. mains 200/250V for 2V, 4V, 5U4G 6/- 12A X7 7/6 EB91 4/6 EZ81 7/- 6.3V and 13V tubes.All 10/6 each.P. & P. 1/6. 5Y3GT 7/6 12BH710/6 EBC41 9/6 PL81 13/6 5Z4G 9/- 12K7GT 8/6 EBF80 10/6 PL82 10/6 VALVEHOLDERS. 4, 5, 7 pin English and U.S.A.B7G, 59A, 6AK6 6/6 12K8GT 13/6 ECC81 6/- PY81 8/- 10, MO, 88G, 9d. each; B7G, 89A with screening can, 1/6; 6AL5 4/6 12Q7GT 6/6 ECC82 6/- PY82 7/- B12A, 1/3; Aladdin formers + " with core, 8d. each. 6AM6 4/- 25A6G 10/6 ECC83 7/6 PCC84 9/6 6AT6 7/6 25L6GT 9/- ECC84 7/6 PCF80 9/- JACK PLUGS. Miniature standard 3/-; SOCKETS 3/-. 6BA6 8/6 35Z4GT 8/6 ECF82 7/6 PCF8211/- CAPACITORS. Small mica, 5% 1pF to 100pF, 8d.; 120pF to 6BE6 7/6 35L6GT 9/6 ECH81 10/6 PCL82 7/6 1,000pF, 9d.; 1,000V wkg..01, .0015, .0025, .004, .005p,F, 1/- each. 6BR7 10/6 5763' 10/6 ECH42 8/6 R19 12/6 CRYSTAL DIODES.G.E.C., 1/6 each. 6BW6 8/6 DAF91 6/6 ECL80 9/6 U76 8/6 CERAMIC CAPACITORS. Close tol. 500V for V.H.F., 9d. 617GT 8/6 DAF96 EF41 8/6 8/- UBC41 10/- PAPER TUBULAR. .001-.1 500V, 9d.;.25,1/-;.5,1/6;.01 6K7G 7/6 DF91 4/6 EF80 8/- UCH42 10/6 1,000, 1/-. 6Q7G 7/6 DF96 13/- EF86 9/6 UF41 10/- PAPER BLOCKS. 41a.F, 1,000 wkg., 3/6; 4p.F 250V, 2/6. 6SL7GT 8/- DH76 8/6 EF91 4/- UL41 8/- 6SN7GT 8/6 DH77 7/6 EF92 5/6 UY41 8/- RECTIFIERS. Contact cooled, 250V 50mA, 7/6; 85mA, 9/6. 6V6G 7/6 DK91 6/6 EL41 9/- W76 8/6 REACTION CONDENSERS..0001, .0003, .0005u.F, 4/6 each. HEATER TRANS. 200/240V, 6.3V, 1.5A, 7/6; 3A, 10/6. MATCHED PAIRS.EL84, 17/-; EL85, 25/-; 6V6G, 17/-; RESISTORS. and +W, insulated, 4d. and 6d.; 1W, 8d.; 6W 6BW6, 18/-; KT33C, 19/6; 807 14/6 pair; KT66, 32/6. W.W., 1/-; 10W, 2/-. ELECTROLYTICS.Wire ends. 25/25V,1/6;50/50V,2/-; SETS OF VALVES 12/50V, 9d.; 8/450V, 2/-; 16/450V, 2/9; 16/500V, 3/6; 32/450V, DK96, DF96, DAF96, DL96 "REGENT" 29/6 per set 4/-; 8+8/450V, 4/6; 8+16/450V, 4/6; can types; 16/450V, 3/6; DK91, DF91, DAF91, DL92, or DL94 21/- per set 16+500V, 6/-; 32/500V, 6/6; 32/450V, 6/6; 20+20/450V, 4/6; 1R5, 1T4, 1S5, 3S4, or 3V4 21/- per set 64+120/275V, 7/6. 6K8, 6K7, 6Q7, 6V6, 5Z4, "G" Types 27/6 per set WAVECHANGE SWITCHES.Midget: 1p 12W, 2p 6W, 12K8, 12K7, 12Q7, 351.4 35Z4, "GT" Types 35/- per set 3p 4W, 4p 3W, 4p 2W, long spindles, 4/6. ECH42, EF41, EBC41, EL41, EZ40 37/6 per set 35/- per set TOGGLE SWITCHES. QMB, s.p.s.t., 2/-; s.p.d.t., 3/3; d.p.s.t. UCH42, UF41, UBC41, UL41, UY41 3/6; d.p.d.t., 4/-; rotary s.p., 3/-. P.P. OP. TRANSFORMERS. MR 3-15 ohms for EL84, 6V6 CHOKES. 65mA 10H, 5/6; 80mA 15H, 8/6; 100mA, 101-1, 10/6; 6BW6, etc., 18/6; Op. Pen. 50mA, 5/6; 30mA, 4/6. 150mA, 10H, 14/6. P. & P. 6d., over 61 post paid. C.O.D. 2/6 R. COOPER G8BX32 SOUTH END CROYDON SURREY CROYDON 9186

12th EDITION The "Argonaut" (RR3) The popular AM/FM Tuner Receiver based on one of Illustrated Catalogue the proved attested Jason designs2/- (postage 4d.) 9d. POST FREE The "Eavesdropper" (RR4) (refunded on first order) 3 -Transistor local station pocket receiver U.K. and H.M. Forces anywhere 1/6 (postage 2d.)

56 pages photographicallyillustratedon A Versatile 2 -Valve Audio art paper. Over 2,000 new and guaranteed Pre -Amplifier (RR7) lines by the leading makers.Money back -A Mullard design.Complete with circuit and ifnot absolutelydelighted. No junk or main componentlayout,together withphoto- ex -Government goods. graphic illustrations 1/- (postage 2d.) High -Gain Band -I II Pre-Amplifer (Nils) More and more constructors looking out Improve poor I.T.V. reception with this simple but for a better service are becoming regular effective booster. 1/- (postage 2d.) clients.When you want the best makes, theoddordifficultitemwithprompt The Cooper -Smith "Prodigy" 6 -Watt attention consult our catalogue. High Fidelity Amplifier (NNW) Includes the latest modifications.Much additional All orders dealt with by return material is also included, among this being a circuit for a microphone pre -amplifier, signal sources, and SOUTHERN RADIO & choosing a loudspeaker 2/6 (postage 4d.) ELECTRICAL SUPPLIES Obtainable from So-Rad Works DATA PUBLICATIONS LTD Redlynch Salisbury 57 MAIDA VALE . LONDON W9

154 THE RADIO CONSTRUCTOR 10 AMBITIOUS ENGINEERS FRE - THE LATEST EDITION OF ENGINEERING OPPORTUNITIES Have you sent for your copy? WHICH IS YOUR INCLUDING ENGINEERING OPPORTUNITIES PRACTICAL. TOOLS! is a highly informative 156 -page guide to PET SUBJECT ? the best paid engineering posts.It tells Mechanical Eng.. EQUIPMENT The specialist Elec- you how you can quickly prepare at home Electrical Eng., trancesDivision of Civil Engineering, Basic Practical and Theor.e-B.1.E. T.(incorporat- for a recognised engineering qualification Radio Engineering. tic Courses for beginners in jrygE.M.I. Institutes) and outlines a wonderful range of modern Automobile Eng.. Radio, T.V.. Electronics, Etc.,NOW offers youa Home Study Courses in all branches of Aeronautical Eng., A.M.Brit.I.R.E. City & Guilds train - Production Eng., Radio Amateurs' Exam. ruerill"gabrhomewrY with Engineering. This unique book also gives Building, Plastics, R.T.E.B.Certificate practical equipment. fulldetails of the Practical Radio & Elec- Draughtsmanship, P.M.G. Certificate Ask for details. tronicsCourses, administered by our Television. etc. Practical Radio Radio & Television Servicing B.I Specialist Electronics Training Division- GET SOME Practical Electronics . E .T. the B.I.E. T. School of Electronics, explains Electronics Engineering SCHOOL OF LETTERS AFTER Automation the benefits of our Employment Dept. and ELECTRONICS shows you how to qualify for five years YOUR NAME! promotion in one year. A.M.I.Mech.E. A.M.I.C.E. POST COUPON NOW A.M.I.Prod.E. We definitely Guarantee A.M.I.M.I. Please send me yourFREE 156 -page L.I.O.B. "ENGINEERING OPPORTUNITIES" 44 NO PASS-NO FEE" A.F.R.Ae.S. B.Sc. I (Write if you prefer not tocut pate) Whatever your age or experience, you cannot afford A.M.Brit.I.R.E. to miss reading this famous book.If you are City & Guilds NAME earning less than Lao a week, send for your Gen. Cert. of Education copy of "ENGINEERING OPPORTUNITIES" Etc., etc. U today-FREE. ADDRESS BRITISH INSTITUTE OF ENGINEERING U TECHNOLOGY (IncorporatingE.M.I.Institutes) !, (Dept. SE/23), 29 Wright's Lane, London, W.8 ;SUBJECT OR EXAM THAT INTERESTS ME THE B.I.E.T.IS THE LEADING ORGANISATION OF ITS KIND IN THE WORLD

EDDY'S (NOTTM) LTD. INSTALLING HI-FI? 172 ALFRETON ROAD NOTTINGHAM New or Surplus Valves guaranteed and tested by return post `RECORD HOUSING' cabinets are cheaper AC2/PEN EF86 9/6 PZ30 9/6 6F33 6/6 7C5 7/6 than you can make them yourself. DD 7/6 EF91 3/6 TDD4 7/6 615G 10F1 2/9 6/6 MULTIGRAMJUNIOR (illustrated)-price 18gns. DAF966/11 E L41 7/3 VP23 6/6 6.15GT 3/9 12A6 5/3 DF91 3/11 EL91 4/6 VR150/ 615M 4/3 12AT6 7/6 Holds: amp, pre -amp and tuner and a tapedeck or turn- DF96 6/11 EY86 7/9 30 6/9 6.17G 5/- table, plus 100 records.36" long, 181" deep, 14" high, DK91 5/6EZ80 12K7 5/3 6/- Z77 3/6 6K7G 1/11 DL96 6/11 12Q7 5/3 plus 9" legs.Mounting boards measure 17" x 14" and KT33C 6/6 IDS 7/6 6K8G 5/3 ECC81 5/3 MU14 7/.- 1 RS 20D1 8/6 17" x 20".Mahogany finish. 5/9 ECC825/11 PCC84 7/6 155 20P1 9/6 6SG7M6Q7G 4/9 A larger version-the MULTIGRAM SENIOR is 48" ECC83 6/6PCF80 7/6 1 T4 3711' 20P3 12/6 ECC856/11 PCL82 7/6 1L4 3/6 65N7GT 4/3 long, costs23 gns. 30F5 6/11 ECL82 9/6PEN36C8/- 51.14G 4/9 6AC7 4/3 In EF36 3/-PENA412/6 5Y3GT 5/9 6AL5 3/6 35W4 6/9 the background (see illustration) the matching VIKING EF41 7/6PL33 8/3 5Z4G 7/6 6V6G 4/9 3574 5/3 CORNER ENCLOSURE for8"Hi-Fi loudspeakers. EF42 7/6PY80 7/- 6B8G 2/11 6V6GT 6/- 954 1/6 Floor or wall mounted.Price10 gns. EF50 1/9 PY81 6/6 6C4 3/6 6X5G 5/11 655 3/6 EF80 5/-PY82 6/9 6F15 9/6 6X5GT 6/11 956 2/6 POCKET RADIO. 2 -transistor with miniature speaker. Use Record Housing's Complete with all parts, wiring diagram and full instruc- FREE Hi-FiHousing tions.27/6.Batteries 1/-,P. & P. 2/-. Advisory Service. Send CAR RADIO. 7 transistors, Long and Medium, 2 watts details of the equipment output.R.F. stage and auto gain control.Size 74" x youwish to install. We x 21", 6 or 12V (state which), supplied with full instruc- willadvise you on how tions.101 gns. Speaker extra, 17/11.P. & P. 5/6. besttohouseit - NIFE ACCUMULATORS. 1.25 V.Size 3" x 21" x handsomely. 7 amp. hrs.Weight 13oz.1/11 each.P. & P. 2/- one only. Add 9d. per cell. THROAT MIKES. 2/- each, post 10d.Could be used for electrifying musical instruments, etc. Write stating ALL ABOVE ARE NEW AND GUARANTEED convenient shopping Any parcel insured against damage in transit for only 6d. centres, to:- extra per order.All uninsured parcels at customer's risk. Post and Packing 6d. per valve extra. C.W.O. or C.O.D. Dept. RC. 961, only.C.O.D.charge3/- extra.S.A.E. with enquiries. Brook Road, London, N.22

SEPTEMBER 1961 155 OUR NEW 5 STAGE SUPER SENSITIVE REPAPICO TRANSISTOR PORTABLE HIGH GAIN COILS THE "BOBETTE" Dual Range Crystal Set Coil Type DRX1 ... .. 2/6 * Simple to Build. Dual Range Coil with Reaction, Type DRR2 ...... 4i- * All first grade components. Matched Pair Dual Range T.R.F. Coils Type DRM3, pair .. 8/- A trulyportabletransistorradio Total Building Costs Pair Dual Range Superhet Coils Type SH4, pair... .. 8/- givingfull medium wave reception. Miniature Iron Dust Cored Coils Type "R": Incorporates 5" High Flux Speaker, iS. 2s. 6d. Range Aerial H.F. Osc. pushpulloutput,first grade tran- NO EXTRAS TO BUY 800-2,000m. RA1 RHF1 RO1 sistors, High -Q ferrite aerial, socket Allpartssoldseparately. 190- 550m. RA2 RHF2 RO2 each 3/3 forcaraerial,pre -taggedcircuit Send 1/6 for itemised price 70- 230m. RA3 RHF3 RO3 board for easy construction.Attrac- listandfullassemblyin- 15- 50m. RA4 RHF4 RO4 tive two-tone case. structions (free with order). Ferrite Rod Aerial Dual Range Type FR1 ...... 12/6 Miniature I.F. Transformers Type MSE (465 Kc/s), pair 12/6 EXPLORE THE WORLD Putyour Favourite Pro- Standard I.F. Transformers Type TCG (465 Kc/s), pair 13/6 ON THIS1 -VALVE gramme on tape with the SHORT WAVE RADIO R.C.S. TAPE TUNER COILS AND TRANSFORMERS FOR Total Will operate on Building all types of TRANSISTORISED CAR RADIO Recorder. Size a Costs Medium Wave Aerial Coil Type XMA16 10/- only 3i" x 1r 1". High impedance Medium Wave H.F. Coil Type XMF17 10/- output, variable Long Wave Aerial Coil Type XLA18 6/9 3S/- Long Wave H.F. Coil Type XLF19 6/9 P. & P. 1/6 Med. wave tuning. Triple Oscillator Coil Type K015 . 5/- * Receivesspeechandmusic wound Super - Interstage Transformer Type TT11 10/- from all over the world. Hi -Q coil.Easily Output Transformer (12V Radio), Type TT12 ...... 12/6 * Constructionpriceincludes constructed Output Transformer (6V Radio), Type TT13 valve and one coil covering from full Boxed with circuit and practical diagramof all -Transistor 40-100 metres. instruction data Total Car Radio. * Can be extendedto cover and Layout building costs 10-100 metres. Diagrams. Send S.A.E. forlatest Repanco Components Catalogue. * Can be converted to 2 or 3 (As described in 30/- valve. March issue) P. & P. 1/6 Send 2/- for wiring diagram and Send 2/- for wiring diagram and RADIO EXPERIMENTAL PRODUCTS components price list. components price list. LTD R.C.S. PRODUCTS (Radio) LTD 33 Much Park Street - Coventry Telephone 27114 11 Oliver Road London E17 (Mail Order Only)

Ask "ARTHURS" First Note new address at P.W. POCKET SOPHIE 125 Tottenham Court Road London WC1 TRANSISTORISED PRINTED Close to Warren Street Station BOARD You will have the same service and CONSTRUCTIONAL BOOKLET 1/6 obtainallyour requirementsin A -Zincluding "BLOWN -UP" DIAGRAM Radio Components, Electrical Goods, Accessories and Television SIMPLE MODIFICATIONS TO as previously ABOVE GIVING BOOSTED PERFORMANCE FREE ON Test Instruments in stock include REQUEST WITH S.A.E. AVO ADVANCE COSSOR TAYLOR NEW CONTEMPORARY CASE List on request * * * Est. 1919 Ask your Dealer or write for Illustrated ARTHURS FIRST Price List and Free Imformation Proprietors ARTHUR GRAY LTD GRAY HOUSE 125 TOTTENHAM COURT ROAD OSMOR RADIO PRODUCTS LTD 418 BRIGHTON ROAD SOUTH CROYDON LONDON WC1 SURREY Telephone CRO 5148/9 Telephone EUSton 5802/3/4

156 THE RADIO CONSTRUCTOP Red Spot Transistors2/3;White Spot2/3; Yell./Gr.3/3; Ediswan XA102 (Mixer Stage)9/-;XA104 (I.F.$)8/-;XA103 SMALL ADVERTISEMENTS (I.F.$)8/-;XB104 (A.F.) 6/-; Mullard 0071 6/6; 00728/-; 0C44 11/-; 0C45 10/-. Bargain sets 6 Transistors plus Diode- 42/6, 47/6, 42/6. P.W.Superhet Private: 3d. per word, including address. Ediswan Mullard Newmarket £7.15.(Ediswan or Newmarket transistors); Minimum charge 2/6. complete Kit Use of Box Number, 2/- extra. f8.5.(Mullard transistors).Diodes 1/-,2/-, 3/-. Sub. Min. Electrolytics 1,2,4,8, 10,16, 321.1.F2/-each. Ardente Trans. D2398/6;D2408/6;0131 10/-; D132 10/-.Balanced Inserts Trade:9d. per word. Minimum charge 12/-. (as earpiece or speaker)3/6;Silicon Rectifier 70 p.i.v. IA3/3; Terms: Cash with order. Westalite Contact Rectifier 250V 60mA7/6; Transformer 250-0-250V, 6V and 5V15/-. Garrard Record Player Motor All copy must be received by the 6th of the (45 r.p.m.) and Pick-up for Transistor Amplifier70/-;Meter 200mA M.C. F.M. 2k"12/6;5A R.F. (2mA)8/6;Hearing Aid month forinsertioninthe following month's issue. The Publishers cannot be held liable in any Mike31/6;Super Coax. 75 ohms6d.yd; Valves 6X55/6, 6V6 way for printing errors or omissions, nor can they 5/6, 1L45/6;Speaker18/6;Electrolytics: 81/F 500V2/3;8+ accept responsibility for the bona fides of advertisers. :51.0 3/3; 100+100(375V)3/9; V.Cond. 0.0005 T. Gang, Trimmers and Slow M.9/6;Transistor Holders 1/-; Resistors 10% tol.4d.;5% col.9d. Tannoy Mike5/-. Crystal Inserts (new)7/6.Gorier Units, 1 watt Amplifier92/6; I.F.Amplifier (460 kc/spre -aligned)92/6;3 waveband Converter90/3. PRIVATE Manual No. 167 describing and circuits2/9post free. STUDENTS preparing for the R.T.E.B. intermediate examination given expert private tuition in radio theory. Terms reasonable.- Terms-Cash withorder. Postextra,excess refunded. Our J. Armstrong, 185 North End Road, London, W.14. Reflex Rx, best 2 -transistor Receiver.Send 8d. stamps for notes. FOR SALE. Airmec Televet, type 877.The complete television test instrument, with manual. £30 or nearest.Further details on request-Clark, 106 Albert Avenue, Hull, East Yorks. TO REPLACE missing loaned volumes, wish to purchase Vol. 21 MOORE'S EXPERIMENTAL SUPPLIES Chemistry Engineers from Newnes "Electrical Engineers" series. Also Vol. 11 1957/58 The Radio Constructor.-Croft, Railways 8 & 10 GRANVILLE ST. SHEFFIELD 2 Laboratories, Box 703, Bulawayo, Southern Rhodesia. FOR SALE.-Perdio Mini -six pocket transistor radio. Brand new. Telephone 27461 £9 10s. (list £12 Is. 6d.)-Box No. F.I31.

FOR SALE. CR1013/2. Good condition, N/L, manual, £15.- Hunt, 18 Fir Tree Walk, Market Harborough, Leics. FOR SALE. ECL82 amp inc. L.S. 47s.; record player cabinet 17s.; Collaro T.T. plus pickup 53s.; Oscilloscope; also various com- 3 -TRANSISTOR POCKET RADIO ponents. S.A.E.-5 Old Lane, Knebworth, Herts. WITHMINIATURE LOUDSPEAKER FOR SALE. To clear-Valves, at 7s. 6d. each: 5Y3GT, 5R4GT, ABSOLUTELYNO SOLDERING REQUIRED XFG1, RGI-240-A, 6BW6, 83, T20, VT136, 955 with base.At 4s. 6d.: 6AT6, 6SA7, 6SK7, 6AG7, 6BA6, VR150/30, DL92, IS5, UNIQUE DESIGN EL91, 1S4, 6V6, 5Z4GT, I2AT7, 3M4, ECC82. At 2s. 6d.: 6AG5, 6K7, VR91, 6B8, CV5I. New accumulators: Willard Radio -20-2, 39f4Superb appearance. 2 volt 7s. 6d.; Varley Dry VPT, 2 volt 10s.Bell transformers, %, Simple instructions. 200/250V a.c. in., 4-6-12V out. 7s. 6d.Mic. transformer, Woden MT101, 7s. 6d.Rotary transformers: 12V in. 480V 40mA out. Built in an evening. No drill- 12s. 6d.; 12V in. 285V 60mA out. 17s. 6d. Labgear Tx coils p.p. ing. No soldering. Complete DSL 21 and 14, 5s. each. Headset adaptors MC -385-A, high to in every detail.Full Medium low impedance 5s.10 watt mod. choke 7s. 6d. Ditto, transformer, 7s. 6d.Linear L45 watt qual. audio amplifier, 200/250V a.c.,£5. wave coverage.Pocket size Emco-Unimat universal miniature machine tool, many extras, £25. 4i" x 2i" x 11" Prices shown include postage and packing.-"East Keal", Romany Road, Oulton Broad, Suffolk. Or the more powerful FOR SALE. Mullard/Stern stereo 3/3 dual channel amplifier and SAVOY SUPER 3551'6 stereo dual channel pre -amp. Both tested and modified by Sterns. No Aerial required For quick sale £12 o.n.o.-26 Towers Way, Leeds 6. ALL PARTS SOLD SEPARATELY Battery 1/- extra, P. & P.2/- TRADE SAVOY BARGAINS LEARN RADIO AND ELECTRONICS the NEW Practical way. Very latest system of experimenting with and building radio High gain audio transistors, 4/6; P. & P. 3d. apparatus-"as you learn".-FREE Brochure from: Dept. RCIO Radiostructor, Reading, Berks. Ferrite rod, 4" x irk", 1/9; P. & P. 6d. Solid dielectric tuning condensers: 0.0003 mfd., 4/-; FREE FROM THE I.P.R.E.Syllabus of famous radio and 1.v. courses.Membership conditions booklet, Is.Sample copy The 0.0005 mfd., 4/3; P. & P. 6d. Practical Radio Engineer, 2s. post free.-Secretary, 20 Fairfield Miniature dynamic speakers.Resistance 30 or 70 Road, London, N.8. ohms, 4/6; P. & P. 9d. MORSE CODE TRAINING. Special courses for Beginners.Full details from (Dept. R.C.) Candler System Company, 52 Abingdon 5ft phone cord with No. 9 jack plug, 2/-; P. & P. 6d. Road, London, W.8. PANL, recognised for many years as the unique one -coat black crackle finish.Brush applied, no baking.Available by post in SAVOY ELECTRONICS LTD eighth -pint cans at 3s. 9d. from G. A. Miller, 255 Nether Street, London, N.3. 15 Maiden Lane, Strand, London, W.C.2 (Back of Adelphi Theatre) continued on page 159

SEPTEMBER 1961 157 THE ORIGINAL SUPPLIERS HAC.OF SHORT-WAVE KITS No quantity too small NYLON P.T.F.E. List on application One valve Super Sensitive All -dry Short-wave Receiver, Model "K". ROD BAR SHEET TUBE STRIP WIRE Complete kit including valve and chassis, 77/-.(Other S.W. kits BrassCopperBronze AluminiumLight Alloys from 25/-.)Before orderingcalland inspecta demonstration receiver, or send stamped envelope for full specification, catalogue H. ROLLET & CO LTD and order form. H.A.C. SHORT-WAVE PRODUCTS (DEPT. R) 6 CHESHAM PLACE SW1 BELgravia 4300 44 OLD BOND STREET LONDON WI Also at Liverpool, Birmingham, Manchester, Leeds

BLANK CHASSIS ow0-40LEARNAA0vvo in 18 s.w.g. aluminium, with 4 sides, 2" deep RADIO & TV SERVICING 6" x 4" 4/3 10" x 7" 7/- 12" x 8" 8/- 8" x 6" 5/9 12" x 6" 7/6 14" x 10" 11/6 For your own business / hobby Post and Packing 1/- R/C "HILL" TRANSMITTER CASES, complete with chassis. by a new exciting no maths system, using practical Hammer -grey finish. 39/- P. & P. 3/6 equipment recently introduced to this country PLASTIC KNOB ESCUTCHEONS, engraved Treble, Bass, Volume, Selector or Mains On/Off 10id. each or 4/- set of five FREE BROCHURE FROM also PLASTIC TUNING DIALS, engravedforLong and Medium wave. In red, green, blue, gold or black. 1/- each. P. &P. 6d RADIOSTRUCTOR SHIREHALL ELECTRONICS LTD.,

DEPT. G103 READING BERKS. 9.61 Old School Works, Wrotham, Sevenoaks, Kent.

Transistors,Red, White,Yellow Spot types,2/8. UNREPEATABLE T.V. TUBE OFFER Neon Test Screwdrivers, 3/6.Insulated Screwdrivers, So Screwdrivers with built-in Torch, 5/6. Ferrite GENUINE REBUILT Rods 8", 3/3. Litesold Soldering irons 10w mains, 21/-. Condensers .001-.1 uF 9d.Spring Expanding Aerials, 12" Mullard Tube 3/-. Bib cutters, 3/6. Repanco constructional envelopes, 1/6.Crystal set coils, 2/6. T.R.F. Coils, 8/- pair.F.M. Only £2.10.0 Coil sets, 29/6.Pointer knobs, Black, 9d., White, 1/-. CARRIAGE 10/- Guaranteed 12 months Sample range of other knobs, 6/- Refundable.L.R. Earpieces,6/-.Magnet Torches, 6/11. Unbreakable Other types available torch, 3/9.Fuse kits, 17/- box of 72. Vidicon Camera tubes from E20 S.T.S.LTD.35 Pound Street Terms -Cash with order.Postage 1/-.Over f3 free. CarshaltonSurrey W. MARSHALL (Radio & TV) Telephone Wallington 9665 THOMAS STREET SHEFFIELD

*********************************** TRANSISTORS UNREPEATABLE OFFER 3 per set, 5/9 each, 1-873, 7/9 each, THIS SUPERHET TRAN- diode, SISTOR RECEIVER CAN BE sP Ediswan XC121 and XB113, 8/9 each.Post 7d. on each. BUILT FOR ONLY f6.15.6 plus 3/- p. &p. and 2/- battery. BRAND NEW VALVES 8/9 each EL91, EL42, EZ90, EZ40, EF86, ECC81, EF81, EF91, 6V6, ECC33, Features: H L41. 1. Very easy to assemble. Yg 11/9 each-ECC84, EL34, EL37, EL38. Post 7d. on each. 2. Mallard's six latest transistors and Diode. T.V. TUBES 15/- each. 3. Printed Circuit. * 15" CRM153 and 12" CRM121 B. Ex -rental service stock. P. & P. 5/-. 4. 200 mW Push-pull output. 17" TV CHASSIS L10 .10 .0. 5. 21" High flux speaker. All channels guaranteed. Terms available. Carr. 25/-. (Covers Medium Band) 6. Fine leather hide cover. Circuit diagram and instructions supplied free on order. SURRKITT ELECTRONICS LIMITED * P.P. COMPONENTS LTD 219 Ilford Lane Ilford Essex 16 Chalcot Square London NW1 Telephone Primrose 3962 ***********************************Stamp for Free Catalogue

158 THE RADIO CONSTRUCTOR SMALL ADVERTISEMENTS 2 metre SUPERREGENERATIVE continued from page 157 RECEIVER KIT 39/6.-Writenowfor details and copy latest catalogue-stamp appreciated JOIN THE INTERNATIONAL S.W. LEAGUE. Free Services to to cover postage. members including Q.S.L.Bureau.Amateur andBroadcast Translation.Technical and Identification Dept.-both Broadcast Johnsons (Radio) St. Martin's Gt. Worc. and Fixed Stations, DX Certificates, contests and activities for the SWL andtransmittingmembers. Monthlymagazine, "MONITOR", containing articles of general interest to Broadcast and Amateur SWLs, Transmitter Section and League affairs, etc. League supplies such as badges, headed notepaper and envelopes. QSL cards, etc., are available at reasonable cost. Send for League particulars.Membership including monthly magazine, etc., 21s. per annum.-Secretary ISWL, l2 Gladwell Road, London, N.8. SURPLUS RADIO SUPPLIES CATALOGUE No.14. Government surplus and model radio control, over 500 illustrated items, 2s. 60. (refunded on purchase 2 LAING'S CORNER MITCHAM SURREY of £2) post free.-Arthur Sallis Radio Control Ltd., 93 North Road, Brighton. CV45 Voltage Stabilisers (equivalent to S130P) FIND TV SET TROUBLES IN MINUTES from that great book stabilises at 120V 5/ - The Principles of TV Receiver Servicing,10s. 6d., all book houses and radio wholesalers.If not in stock, from Secretary, 1.P.R.E., Relay (single pole change over) 250 ohms. 4 mA. 20 Fairfield Road, London, N.8. Can be adjusted to work down to 11mA. Size SERVICE SHEETS (1930-1961) from Is.Catalogue 6,000 models, 21" x 21 x 1 i" 5/ - Is.S.A.E.enquiries.-HamiltonRadio, 13 WesternRoad, St. Leonards, Sussex. Small Electric Motor size I" x I", reversible 5/ - "MEDIUM WAVE NEWS". Monthly during DX season.-Details Transistor Transformers.Interstage and output, from B. J. C. Brown, 196 Abbey Street, Derby. per pair 10/- THE INTERNATIONAL HAM HOP CLUB is a non-profit making 1/- p. & p. per parcel Send 1/6 for catalogue organisation open toRADIO AMATEURS AND SHORT WAVE LISTENERS. OBJECT: To improveinternationalrelationshipsthroughan organised system of hospitality.MEMBERS offerovernight hospi- tality to visiting members, subscription 10s. per annum.ASSOCIATE MEMBERSinvite radio amateurs to visit their stations.Associate membership 5s. per annum.FAMILY EXCHANGEholidays arranged, alsoFRIENDSHIP LINKS betweehradio clubs.The Club's official journal is free to both Full and Associate members.-Hon. Gen. Secretary: G. A. Partridge, G3CED, 17 Ethel Road, Broadstairs, Kent. Quality Components FOR CONSTRUCTORS capacitors,resistors,coils,valves,diodes,controls, VHF UNIT-ready built.Front end Em. unit.Coverage 85-100 Mc/s, i.f. 10.7 Mc/s. Single valve (ECC85). Price, including circuit chassis,transformers, speakers,pick-ups,cartridges, and data but without valve, £2 12s. 3d., plus 2s. postage. stylii and all types of components in stock. VHF TUNER UNIT-ready built without dial and valves.Price, CONSTRUCTIONAL PUBLICATIONS including circuit and data, £6 16s., plus 3s. 6d. postage. Delivery ex-stock.-(Dept. Ell) Rotopons Limited, 54 Beddington Lane, Mullard Circuits for Audio Amplifiers ... 8/6 Croydon, Surrey. Mullard Tape Pre -amp "C" 2/6 Quality Amplifie'rs, 7 designs 4/6 Jason F.M. Variable Tuners 2/6 SPECIAL AMATEUR LICENCE MORSE COURSE Price lists available on request COMPLETELY NEW METHOD takes all the drudgery out of learning Morse. Passes secured in all cases even after previous 82DARTFORD ROAD failures. DARTFORD KENT By using SPECIALLY prepared recordings (3 speed L.P. player required)studentslearnautomatically and withouteffort, J. T. FILMER TelephoneDartford24057 perfect Morse in half the time required by any other method. Please S.A.E. For Booklet. Tape/Disc/Tape Service also available. G3HSC,45 GREEN LANE,PURLEY, SURREY

SPARES, VALVES, TUBES,1930-1960 Guaranteed perfect, set tested,ex -working equipment RADIO AMATEURS . 6K25 4/6 20P1 4/6EF80 2/-PL33 4/6 PY81 4/6 12A17 3/-20P3 7/6EF91 2/-PL38 10/-PY82 4/6 Get your Licence in 10C2 4/6275U 10/-EL33 4/6 PL81 4/6PZ30 4/6 10F1 3/-185 BT 12/6 E L38 4/6 P L82 4/6 1.124 7/6 Half the Usual Time! 10P13 4/6B36 4/6 EY51 4/6 PL83 4/6U281 7/6 You must be a good Morse operator! 10P14 4/6EB91 2/-KT36 4/6 PY31 4/6PCC84 4/6 A "slap -dash" 12 w.p.m. neither satisfies the authorities, 20D1 3/-ECL80 4/6N37 4/6 PY80 4/6PCF80 4/6 yourself,nor your operator friends.Morse operating 20F2 4/6Pre-war 4 -5 -7 -pin valves,5/-each. is an exacting art unless your training is made simple Postage & packing 6d. per valve. Also old American, side contact, etc. and is based on sound fundamentals.For this reason SPEAKERS, 6", 5/-; Elliptical 7/6.Postage 1/6. the Candler System was invented to take the "grind" NEW TRANSISTORS. Red spot, 2/6. 0C45, 0072, out of Code tuition,turning a tricky subject intoa 0076, 7/6; 0C44, 8/6; 0C35, 0C201, 20/-. pleasurable pursuit. CONSTRUCTOR'S PARCEL. 2 lb. assorted resist., * Send 3d. stamp forthe "Bookof Facts" cond., pots., etc., from Radio & TV, 7/6.Postage 2/6. Send SAE with enquiries or for full list CANDLER SYSTEM CO ST. JOHN'S RADIO 3 Jews Row SW18 (Dept. 55 RC) 25b Abingdon Road, London, W8 Telephone VAN 8822 CandlerSystemCompany, Denver, Colorado, U.S.A.

SEPTEMBER1961 159 * Crystal Lapel Microphone, * Jackson "00" Tuner, * Submin. Condensers.All * TRANSISTORS, STANDARD AND ideal for portable tape 208+176, 9/6. low voltage: 0.1,0.25,0.5, MINIATURE COMPONENTS recording,17/6.P.P. 1/-. 1, 2, 4, 6, 8, 10, 16, 25, 30, We stock the largest range of components in the * ;in square 365pF Tuner, 50,100mfd. All types, country for the home constructor. * Siemens High Speed U.S.A. Poly type, 8/6. 2/- each. Sealed Miniature Relay, 1700- 1700 ohms, 15/- ea. * Crystal Mic. Inserts, 2in, * Standard Miniature: 1, 2, WE HAVE YOUR 12/6; 1kin, 7/6; ;in, round or 4, 8, 10, 25, 30, 50, 100, 200, ITEM IN STOCK. 250, 500 mfd.All types, 1/6 Just ask and we will * 2/in.10 ohm Speaker, square 3/6. P. P. 6d. quote competitive 17/6. each. * Set of OSC. and 3IFs. prices. Size A x x kin, 21/-. * LargerangeofTrans- * PocketIron,220/250V formersforall purposes. A.C./D.C.30watts,com- * Mercury Batteries: 1.3V, Let us quote for your circuit. plete with mains plug, case, 2200mA/H, x 1in dia, 2/6; etc. Handle unscrewsto 1.3V, 5000 mA/H, 2 xin dia, * 3in speaker, 3 ohm, 15/-; POCKET TESTMETER cover element enabling iron 2/6; 1.3V, 500mA/H, I x tin 3in, 25 ohm,22/6;5in, to be carried in pocket. Only dia.,1/3; 1.3V, 14000mA/H, 3 ohm, 15/-. 20,000 ohms per volt 18/6.P.P. 1/-. 2+ x 1+in dia, 5/-. Over 20 scales AC/DC * Ferrite Rod -1st Grade: * 1000 ohm Personal Phone * Low Impedance Mic. 4 x Ain, 1/6; 5 x ;in, 1/6; resistor etc. A new poc- with Leads and Jack Plug and Inserts, approx. 2000 ohms. 8 x .in, 3/6; 8 x ;in, 3/6; ket meter complete with Socket,suitableformost ;in dia. 15/-: x tin, 12/6 4 x Commercial Transistor 10/- 11 in diam., 15/-. 4 x 14in slab, 2/-. leads,instructionsand Radios, 15/6. Match into Transistor Ampli- * Standard Volume Controls batteries. fiers, and hearing aids. dia, kin spindle: 5k, 10k, * 9.065 Mc/s 3rd Overtone 25k, 50k 100k, 250k, 500k, Crystal for all 27 Mc/s Model * LARGEST RANGE OF £6.19.6 STANDARD AND MINI- 1 meg,2 meg.,3/6,less Control Transmitters,12/6. ATURE COMPONENTS switch; 4/6 with switch. p. p. 1/6 IN THE COUNTRY. * 7 section chromed Tele- * Miniature Light Weight, FULLY GUARANTEED scopicAerials,38in.,with * 7 x 4in, 25 ohm Speaker, 44 to 5V, 8mA Relay, 24/-. fixing bracket, 12/6.P.P. 1/6. 22/6; 7 x 4in, 3 ohm Speaker, CRYSTAL MICROPHONES 64in version, 17/6.P.P. 1/6. 20/-. * Lightweight4000 ohm Headphones, 12/6. P. P. 6d. ACOS 39-1.Stick Microphone * 21in. 80 ohm Speaker, ex- * Miniature ;in diam x Ain with screened cable and stand cellent quality, 17/6. P.P. 9d. edge volume controls with * AllPartsinstockfor (list 5 gns.), 39/6.P.P. 1/6. switch: 5k and 10k, 7/6 each; "Repanco" Mini -4 Superhet. * 600 ohm Personal Ear 5k, 10k, printed circuit, 7/6 Booket, 1/3. Leaflet on ACOS 40 Desk Microphone with Phone with jack and socket, each. 50k, 8/6. request. 10/6.P.P. 9d. screened cable and built-in * Driver and Output Trans- stand (list 50/-), 19/6.P.P. 1/6. * 1Watt Push -Pull Trans- former(matchedto8/10 Please allowPostage ohms), 12/6 pair. ACOS 45 Hand Microphone with formers for 0081 Transis- Packing on all lead, sensitive, tors, 3 ohm, 21/-.P.P. 1/ - and screened very *21in 10 ohm Speaker, 17/6. 29/6. P.P. 1/6. orders. MC 43 Stick Microphone with ALL COMPONENTS IN * 5in 25 ohm Speaker, 25/-. STOCK for "WEYRAD" muting switch and screened cable, 27/6.P.P. 1/6. 6 -Transistor Superhet. Book- * Brand New-Fully Guaranteed * let 1/3 post free. Leaflet on request. * MODEL CONTROL RECEIVERS ** RANGER 2 * * 1Ain Square Poly. 2 -gang Lightweight Transistor Tuner with Trimmers, 17/6. Receiversforeventhe ALL TYPES ARE EASY TO smallest model boat, car, BUILD WITH GUARAN- Personal * Sub -miniature Jack Plug train, aircraft, etc. A really TEED RESULTS UP TO Any and Socket, 3/6 complete. fascinatinghobby. MILE. 44 VOLT OPER- Pocket valvetypetonetrans- * Quartz Crystals Over 600 mitter may be used with ATED AND TRANS- types in stock for all purp- the"Supertone" range FORMER COUPLED FOR Radio oses-fully guaranteed. operating on 27 Mc/s radio HIGH SENSITIVITY. control. * TwoTransistor Two Diodeversionof Free List on Request "Ranger -3". See back page.The ideal pocket * "SUPERTONE-RR4". Relayless Re- receiver. * Sub -miniature27Mc/s ceiver, 4 -transistor0C169/0071/0072/ 3rd Overtone Xtal for model V15/20IP, giving 300mA current rise.No. All Parts 59/6 P.P. 1/6 control, 30/-. relay, couples directly to actuator or servo, * PICTORIAL PLANS AND DETAILS etc. Size 24 x 2 x ;in. All parts 72/6. P.P. 1/6 * Personal Earphones used FREE ON REQUEST withRANGER 2and 3, * "SUPERTONE-IC". SingleChannel Output to ADDON AMPLIFIER British made, 12/6. 0C169/0071 /0072 transistors. 250mW push-pullstagewith3 -inchspeaker. relay, 18mA rise, 2; x 2 x lin. Converts any earphone radio to full loudspeaker. * 24,inround-j-kin deep, All parts 59/6. P.P. 1/6. All parts 59/6.P.P. 1/6 3 ohm speaker, 15/, P.P. 1/- * "SUPERTONE-3C", 3 Channel Output to 3 Reed Unit, Diagrams Free giving 3 Channels. 0C169/0071/0072 transistors.Size as * Diodes: GD3, 2/-; 0A70, above. All Parts 59/6.P.P. 1/6. 2 WATT POWER AMPLIFIER 3/-; 0A81, 3/-; 0A91, 3/6; * Designed to boost up the output of Portable 0A10, 8/-; 0A85, 3/-; 0A79, Transistor Radios when used in a Car. Works 3/-; GJ7M, 4/-; Z2A47F, 15/-. SEND 6d. STAMP FOR DIAGRAMS AND DETAILS from 6 or 12 volt (state which) Car Battery-uses power transistor.All Parts 49/6.P.P. 2/-. * DECCA AMPLIFIER * ALL TRANSISTOR Portable Record Player Am- MEDIUM LONG AND ALL TRANSISTOR FM TUNER Type 38, TRANSMITTER RECEIVER plifier with tone and volume SHORT WAVE PRE- Complete with 5 valves.In new condition. These controls. BUILT UNITS IN PRE -BUILT UNITS. FULLY sets are sold without guarantee but are service- STOCK. FULLY ILLUS- ILLUSTRATED BOOK SHOW- able 59/6 P.P. 2/... TRATED BOOKLET ING USES, 3/6 7 to 9 Mc/s22/6P.P. 2/6 SHOWING USES. 2/6 Headphones, 7/6 pair. Junction Box,2/6. *Fully Guaranteed Throat Mike, 4/6.Aerial Rod, 2/6. Opposite Edgware Road Tube Station VALVES OPEN MON. to SAT. 9-6, THURS. 1 o'clock WE STOCK OVER 800 TYPES OF VALVES AND TUBES AT Henry's Radio Ltd Telephone: PADdington 1008/9 REALLY COMPETITIVE PRICES. FREE LIST ON SEE BACK PAGE 5 HARROW ROAD LONDON W2 I REQUEST.

160 THE RADIO CONSTRUCTOR THE MODERN BOOK CO The Radio Amateur's Handbook. 1961. World Radio TV Handbook, 1961 ed. 32s. 6d.Postage 2s. 16s. 6d. Postage 1s. 20 Suggested Circuits. A Data Publica- Model Radio Control. By E. L. Safford. tion.3s. 6d.Postage 4d. 21s. Postage 1s. Short Wave Receivers for the Begin- TV Fault Finding. A Data Publication. ner. A Data Publication.6s. Postage 5s. Postage 6d. 6d. Introduction to .By W. E. Romping through Mathematics. By Pearce.10s. 6d. Postage 9d. R. W. Anderson.5s.Postage 6d. Reference Manual of Transistor Cir- The Stereo Sound Book.A Focal cuits. By Mullard. 12s. 6d. Postage Is. Publication.12s. 6d.Postage 9d. A Beginner's Guide toRadio. By TelevisionEngineers' Pocket Book. F.J. Camm. 7s. 6d.Postage 6d. By J.P. Hawker.12s. 6d.Postage 6d. Practical TV Trouble -Shooting. A A to Z in Audio.By G. A.Briggs. GernsbackLib.Publication. 18s.6d. 15s. 6d.Postage 9d. Postage 9d. We have the Finest Selection of British and American Radio Books in the Country Complete catalogue 1s. 19-21 PRAED STREET (Dept RC) LONDON W2 Telephone PADdington 4185

THE RADIO CONSTRUCTOR BOUND VOLUMES

Volume 14, August 60 to July 61 £1.5.0. postage 1 /9 Attractively bound in blue cloth, with gold -blocked spine Also available: - Volume 12, August 58 to July 59 £1.5.0. postage 1 /9 Volume 13, August 59 to July 60 1.5.0. postage 1 /9 Where all issues of a volume are returned for exchange 12s. 6d. postage 1 /9 "Easibinders" for temporary or permanent binding... I2s. 6d. postage 9d. Indexes for volume 14 are now available, price 6d. postage 2d. A limited number are also available for volumes 4, 6, 11, 12 and 13 at thesame price. DATA PUBLICATIONS LTD 57 MAIDA VALE LONDON W9

Published in Great Britain by the Proprietors and Publishers Data Publications Ltd. 57 Maida Vale London W9 Printed by A. Quick & Co. (Printers) Ltd Oxford Road Clacton -on -Sea England Obtainable abroad through the following Collets SubscriptionService Continental Publishers & Distributors Ltd William Dawson & Sons Ltd Australia and New Zealand Gordon & Gotch Ltd Electronics Publications (Australia) South Africa Central News Agency Holland "Radio Electronica" Registered for transmission by Magazine Post to Canada (including Newfoundland) £e * NNW * 0, IS, II, I.41,4*.*41,41141,WAIN,INIII..11,11K4 1,1* 4* 411,,41VN fi RANGER -3 COMBINED PORTABLE No External Aerial or Earth CONTESSA AND CAR RADIO 3 -TRANSISTOR and 2 -DIODES 6 TRANSISTOR MEDIUM AND PERSONAL POCKET RADIO with LONG WAVE SUPERHET 5 stages giving clear reception on TERRIFIC SENSITIVITY medium wave, amateur top band SPECIFICATION and shipping.Only first grade 425mW Push -Pull Output components used throughout. 6 "Top -Grade" Ediswan Transistors Size 4r x 3" x 1 f"Amazing results. New Type Printed Circuit withall Easy to follow instructions Components marked ALL COMPONENTS with pictorial layouts Full Medium & Long Wave Tuning High "Q" Internal Ferrite Aerial 79/6 P.P. 1/6 Reception of Radio Car Radio Adaption and AVC Luxembourg guaran- Slow Motion Fingertip Tuning with Everything Supplied teed (most areas). Station Names "Hi-Fi" Quality Speaker Free Instrs.& Price L'st on request. Easy to build Attractive Rexine Covered Cabinet. AfterSales Service, Guaranteed Success RED/WHITE or BLUE/WHITE ALL TRANSISTOR TOTAL COST OF ALL PARTS TIME SAVER L10. 19. 6 P P3/6 Office or Home Telephone LEAFLET ON REQUEST JUST RIGHT FOR A DAY PICK-UP AMPLIFIER OUT-ANYWHERE! No more "Holding Up" * I, 1* . IP * ., I* 4,1, di enneew.eeHw P. * wastingtimewaitingfor AVO-METERS * your call to come through. WATT When it does the amplifier 4 TRANSISTOR can beswitchedoffif 1 BUILT, TESTED, READY required. No connections, AMPLIFIER TO USE just Sellotape the pick-up coilto back of phone as 1 watt peak L5. 10. 0.P'R 2/6 above. output. 5" speaker; 3 months'battery life. Now with ±3dB 70 c/s to 400mW output 12 Icc/s.

Portable4 -transistor Baby -Alarm as previously Output to 3 ohm advertised.But now with 400mW output on 5" Built and Tested speaker. speaker. Can be used up to 200 yards, f5.10.0. P.P. 69/6P. & P. 1/6 2/6.Including battery and microphone.Battery life 9 volt operated. 3 to 4 months used every day. Very. sensitive. AVO MODEL8 Kit of parts 62/6, P.P. 1/6 Multi -Meter. (List price £24.10) 6 - TRANSISTOR RADIO Regd. A printedcircuithighgainamplifier size L17. 10. 0 P.P. 5/-. 4" x 2f" x f" using Mullard 0071/0081D Complete with Avo Test Leads and 2-0081 Transistors. Ideal for Intercomm., Fidelity and Batteries. Fully guaranteed Record Player, Tuner Amplifier or any applica- new condition. tion requiring a quality and reliable amplifier. "CORONET" AVO - MODEL 7 FullDetails and uses on request (List price E19.10.0) Regd. "PW" 6 TRANSISTOR MEDIUM 6 -TRANSISTOR MEDIUM & L12. 10. 0 P.P. 5/-. LONG WAVE POCKET RADIO Tested complete with Test Leads & LONG WAVE POCKET SUPERHET and Batteries. 6 MATCHED Size 21" x 41" x 11" Fully Guaranteed. MULLARD Quality Push -Pull Speaker Output TRANSISTORS FIRST GRADE TRANSISTORS AND DIODE Guaranteed for 12 months 150mW Push - 0071 6/6 0C17114/60C1625/- Pull Output. Phone and Tape Sockets 0072 8/- 0C2625/-XB102 6/- Easy to follow Carrying Case 2-0072 16/-10C2836/-XB103 6/6 Printed Circuit 92 gns. XC101 6/6 11/6 withall Com- 0075 8/- 0C42 XC121 7/9 ALL BRITISH DESIGN AND Reg. Post 2/6 0076 8/- 0C44 ponents CONSTRUCTION XC13116/- Marked Incl. Battery 0081 8/- 0C4510/- XA101 9/- Full Medium and Long Wave Tuning. 0083 8/- 0C22281- XA10210/- High "Q" Internal Ferrite Aerial. 3 -TRANSISTOR AND 008411/-r 0C2438/- XC14125/6 29/- Quality 2f" Speaker. DIODE PERSONAL SUPER -3 0C170 0/6 0C35 25/6 XA131 A simple to buildlocal station I OUTSTANDING APPEARANCE I POCKET RADIO radiowithpersonalearphone AND PERFORMANCE output.Built-inFerrite Aerial and Batterylasting 9 months. All Parts Sold Separately 6 MULLARD TRANSISTORS AND No Technical Knowledge Required ALL PARTS DIODE NO EXTRAS TO BUY 1-0C44 1-0071 AND 1-0A81 37/6 P.P.1/6 2-0C45 2-0072 PER SET ONLYTOTAL COST ALL £8. 19. 6 50/ - NECESSARY ITEMS NO EXTRAS TO BUY No Extras to buy Size 41" x 3" x 11" Other Matched Sets Available DESCRIPTIVE LEAFLET Quality output on IDEAL for BEGINNERS personal earphone PRACTICAL TRANSISTOR FREE ON REQUEST.

PLEASE H Contains easy -to -follow plans of 40 enry's Radio Ltd all -transistorunits,includinglight - WE CAN SUPPLY MOST OF PADdington 1008/9 operated switches, amplifiers, trans- THE COMPONENTS USED ON mitters,receivers,testoscillators, CIRCUITS PUBLISHED IN THIS TURN 5 HARROW ROAD, LONDON W2 tracers,hearingaids,radio signal QUOTATIONS PAGE Open Monday to Sat. 9-6, Thu .s.1 o'clock control, etc.All parts MAGAZINE. availaLle separately. 3/6 BY RETURN. Send 6d. Stamp For New Illustrated Price Lists POST FREE