elerence /jnnti 1948 ED. r PHONE 4 "3 - Ei 0 X 42. 1. RADIO -CRAFT 25 'West Broadway New York 7, N. Y. qet 411to Here are a total of 640 pages of downright practical knowledge to help you keep punching away at the unknown factors of radio until you have mastered them.Every one of the 10 books is worth many times 50e if you will but apply a small portion of the information gained to your daily work.You'll be glad you have the complete set handy whenever you are trying to work out a problem in construction, testing or servicing.You'll like the easy -to -read type-the smart, modern flexible covers, and the generous supply of illustrations. They all help to make learning a pleasure as well as a profit.Order as many as you need today.Better still, order all 10. $5.00 FOR ALL 10-50c EACH No. 29-HANDY KINKS and SHORT CUTS. No. 34-RADIO-ELECTRONIC CIRCUITS. An A carefully edited compilation of time savers. extensivecollectionofcircuitdiagrams,with Kinks on Antennas-Power Supplies-Test Equip- brief, to -the -point descriptions of each, includ- ment-Servicing-In the Shop-Phonographs and ing: Intercommunications Systems - Power Sup- Amplifiers-Coils and Transformers-Miscellane- plies-Balancing Circuits-V. T.Voltmeters- See your ous Subjects. Amplifiers-Receivers - Phono Amplifiers-Short Wave Adaptors-Electronic Relays. No. 30 PATENTED CIRCUITS, 1944-46. A gold mine in new hook-ups! A selec- No. 35-AMATEUR RADIO BUILDER'S GUIDE. tion of unusual circuits, many aresult of war- For the "ham" who builds his own.Practical, radio dealer. time research-of great value to anyone inter- down-to-earth,it tells how to Build: A 2 Meter estedinelectronics. Control Circuits-Detec- Band Acorn Tube Set-Miniature Communica- torsand Amplifiers-PowerSupplies-Miscel- tions Receivers-LongLines Transmitter-Begin- laneous Circuits-Foreign Circuits. ner'sTransmitter - Preselector - Rotary Beam Ifhecan't Aerial-Power Supplies-and other ham gear. No. 31-RADIO QUESTIONS AND ANSWERS. Answerstomostfrequently askedquestions. No. 36-RADIO TEST INSTRUMENTS. A MUST Clear circuit diagrams.Amplifiers-Receivers- for every radio man.This latest book on build- Transmitters-MetersandTestEquipment-In- ingtest equipment places emphasis on practi- supply you terphones-Power Supplies-Phonograph Ampli- calconstructionof:Signal Tracers-Capacity fiers-P. A. Systems. Meters-Portable and Bench Multi-checker-Sig- nal Generators-Tube Checkers-Electronic Volt- No. 32-ADVANCED SERVICE TECHNIQUE. meters-and many others. An up-to-date collection of information for the use the advanced serviceman: Visual Alignment-Track- No.37 - ELEMENTARY RADIO SERVICING. ingProblems-Negative Feedback-Tone Con- For the radio man who knows little about ser- trolCircuits-AddingMicrophones toSets- vicing.How to get started, and even more im- MatchingLoudspeakers-Remote JukeBoxes- portant how to keep going: Planning the Ser- Servicing Record Changers-Hum Elimination- vice Shop-Equipping the Shop-Systematic Cir- coupon FM Servicing. cuit Checks-Signal Tracing Methods-Servicing the Midget-Soldering-Servicing Volume Con- No. 33-AMPLIFIER BUILDER'S GUIDE. In- trols-How to Service Speakers. valuable for the designer and builder of audio equipment.Tells how to builda wide variety No. 38-HOW TO BUILD RADIO RECEIVERS. on page 42 of amplifiers with power outputs ranging from This book contains a sufficient variety of sets to 8 to 30 watts,Detailed design information on: appealtoeveryradiofan. Includes:Short - Push -Pull - PhaseInversion - BassandTreble Wave,Broadcast,Portable,A.C.Operated, Boosters-Volume Expanders - Resistance Coup- Miniatureand StandardReceivers. Complete and mailto ling-Internal Feedback. coil -winding dataisfurnished. IltAl) I 4, RADIO -CRAFT 25 WEST BROADWAYCRAFTNEW YORK 7, N. Y. handy uuusoul radio Mobs uuuuuu ed advanced amplifier radio amateur how tobuild questions radio elementary Cr circuits service builder's el ttttt nic radio builder's test radio radio guide circuits guide receivers short cuts to44rl94b answers technique instruments servicing 11010-C1111 11111 1111 11111 55111 1010.01/11 II01111 tI111 [1111 111 11011[1111 01111 11111 11 11010.t 0100111, 11010 1110 C. 11010.01111 1010 -[1111 50u 50 ,n; 50 <, 50 ARIi to" 50," Ill% 50 «r11 t0". 11033 50 N0.38 z t`: \ \ \N\ , N \\\\ k CONTENTS A Stable V. F. 0. 2 An Electronic Timer 4 - 2 -Tube Portable 5 Important Uses of Transitron Oscillators 6 Construct an FM -AM Superregen'r 8 A 4 -Tube Reflex Superhet 9 New Direct -Coupled Amplifier 10 Direct -Reading V. T. V. M. 11 Class A and B Amplifier 12 Hi-Fi Tuner 13 Tone Control Circuits 14 Good FM Receiver 16 Loudspeaker Fidelity 18 Experimenters' Clip Set 20 Feedback Amplifier 23 New Circuits from Old 24 Supersonic Door Opener 26 Low Level Tone -Control 27 Power Stabilizer 27 Tracer Receiver 28 Check Your Frequency! 28 Identify That Station! 29 Useful Small Circuits 30 V. 0. M. Condenser Checker 33 Frequency Drift 35 Modern Metal Locator 36 FM and Television Antenna Chart 39 "Radio -Craft" Index (Vol. XVIII, Oct. 1946 -Sept. 1947) 46 Copyright 1948 by H. GERNSBACK 1948 A STABLE V. F. O. No Battery is Needed in This Instrument THEbeatfrequencyoscillator, a calibration; strength of the outputcertain frequency, in this case about though not absolutely necessarymust be under control; the note at all200 kc.The signal from oscillator 2, in the radio service shop, is im-times must be fundamentally pure; andcomprising L2, VC2, and the triode sec- Inensely helpful in many tests. Even athe circuit must be designed to preventtion of V2, will combine with the signal battery instrument is helpful, but to"pull -in" of the 2 frequencies whichfrom V1 and any difference between overcomethedrawbacksofbatterycombine to produce the third 'or beattheir frequencies will appear at the power, the instrument described herenote, even when thedifferencefre-mixer plate. If the difference is small, was designed. quency is only a few cycles. say a few hundred cycles, then this If a b.f.o.isto serve its purpose Referring to Fig.1,the oscillatorsignal will come well into the audible properly as a test instrument, it mustcomprising V1, L1, VC1, and its asso-range and can be passed on to an audio deliver output over the entire audiociated components feeds into the signal amplifier in the usual way. range; it must be convenient to selectgrid of the mixer tube V2. The adjustment of the tuning circuit any particular frequency by means of This oscillatorisfixed -tuned to aL2-VC2 is such that when VC2, the main control, isat minimum capaci- tance, the frequency is the same as that to which Li-VC1 is tuned. Under these conditions there is no difference frequency and therefore no signal. But immediately that the capacitance of VC2 is increased, a signal of a few cycles will be produced and further in- crease will cause the signal to rise in pitch until, at the maximum position of VC2, it is at the highest wanted fre- quency, or, if required, just out of the audible range.Although the first os- cillator is fixed -tuned, it is necessary to provide for some limited manual ad- justment of its frequency by making VC1 variable.This control makes it possible for the instrument to be subse- quentlyadjustedtozerofrequency when the pointer of the main control VC2 is in that position. Referring to Fig. 1, tube V2 is utilized Fig. I (below)-Schematic of audio test instrument.Suitable U. S. tubes are indicated. as a mixer (heptode section) electron - Fig. 2 (above)-Front-panel layout.Space around edge of main dial is for calibration. coupled to the variable oscillator (triode SHIELD SHIELD 20 H 200 V 000 41{c,--° 40K OUTPUT +8 'TERMINALS% o 25K 100 .001 CI 100µµf I300µpf 100µpf .3MEG I II 100µof I00µµf LI 100K VI V2 V3 6C5 6K8 6C5 C4 6J 5 37 8 -"' 300µµ f R I I ook 50 K PRE-SET) 250K l --J vol R2 VC2 2000Af 300µµf 15K 300µµf 500ppf 2 50K K OUTPUT CONTROL 2 1948 .RADIO -CRAFT REFERENCE ANNUAL section). The second triode tube V3 VCI -SHIELDED LEAD n OUTPUT operates as a straight audio amplifier. FROM Ct CONTROL The audio output of V2 is fed to V3 through a high -frequency filter made RI up of RFC1, RFC2, a 100-, and a 300-Awf V.C.2 CHASSIS L2 R2 condenser. A 0.3-meg. resistor, in series SINGLE GANG V2 SHIELDED with the output potentiometer, limits CONDENSER MIXER the input to V3 to maintain good wave- 500 µid form by preventing overload of the 0 TOP CA tube. If V3 is to be transformer -coupled VI le el to a piece of following equipment, to FIXED e / SHIELD maintain good output quality it is es- OSC. SHIELD sential that the transformer be of high- FIXED VANES TO PRE-SET, C2 fidelity type. 0 COND. The shields shown in Fig. 3 (chassis, Elp.F top view) were included as a precaution, while those shown in Fig. 6 (chassis, , e underside) are essential. Material may TO 13+ be aluminum, brass, or copper, well bonded tochassis.Chassis material may be 16 or even 14 gauge, for all POWER TRANS. 0 construction must be rigid.Drill the required holes for wire leads before fastening shields in place.Mica coup- ling condensers may be used. The 0.25- megoutputcontrolpotentiometer should have an audio taper. It is ganged Fig. 3-Parts layout of original v. f. o.Layout may be altered to fit parts available. to the on -off switch, $1. VC2 must be of rigid constructionstep is to remove the ground from theamplifier under test) must be constant and securely mounted on the chassis.grid of Vl. at all frequencies. See Fig. 5. A useful The requirements for "set zero" vari- The b.f.o. may be adjusted by earinstrument for this purpose is the vac-.