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Accurate taper curves prove correct resistance ments - and adds manufacturing skill and values. When you install a Mallory carbon repeated quality checks that assure you com- control, you know that your customer will get plete customer satisfaction when Mallory the fine, smooth tone gradations that result products are used. from tapers that are mathematically accurate. Mallory offers the most complete line of Mallory uses an exclusive method of applying volume controls- standardized to make them the talcum -fine carbon so that the fields of easy to stock. resistance are perfectly feathered for core rect attenuation.

Mallory makes the three replacement parts that The Mallory 1485 Control Deal This attractive metal cabinet contains the are used on the majority 15 Controls and 9 Switches that will take of your jobs: volume care of 90% of your service calls. Its arrangement makes inventory control almost auto- controls, capacitors and matic-saves you frequent trips to the distributor's e ter. It contains a rack for your vibrators. Into them, Radio Service Ency- Mallory builds design clopedia. You pay only for the Volume Con- experience that has been trols and Switches; the cabinet is included in acquired by constantly the deal at no extra keeping a step ahead cost to you. Check your Mallory distributor on Mallory controls are carefully tested J taper The esrlutire method of applying of commercial radio - this special offer. carbon Aires a Inure gradual taper curve than is produced by n elertronir develop.

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ALLIED has Everything New in Radio!

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SX-62 RECEIVER

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_, 6 N TEST EQUIPMENT NEW 1948 HEATHKIT 5" OSCILLOSCOPE KIT

A necessitysity for the n servicing technique in FM and television at a price you can afford. The Heathkit is complete, beautiful two color panel, all metal parts punched, formed and plated and every port supplied A pleasant evening's work and you have the most interesting piece of laboratory equipment available. Check the features - large 5" 58P1 tube, compensated vertical and horizontal amplifiers using 6SJ7's, 15 cycle to 30 M cycle sweep generator using 884 gas triode, I10V 60 cycle power transformer gives 1100 volts negative and 350 volts positive.

Convenient size 81/2" x 13" high, 17" deep, weight only 26 pounds. All controls on front panel with test voltage and ext. syn post. Complete with all tubes and detailed instructions. Shipping weight 35 pounds. Order today while surplus tubes make the price possible.

HEATHKIT SINE AND SQUARE WAVE AUDIO GENERATOR KIT The ideal companion instrument to the Heathkit Oscilloscope. An Audio Gener- ator with less than 1% distortion, high calibration accuracy, covering 20 to 20,000 cycles. Circuit is highly stable resistance capacity tuned circuit. Five tubes are used, a 6517 and 6K6 in the oscillator circuit, a 6517 square wave clipper, o 6SN7 as a cathode follower output and 5Y3 as transformer power supply rectifier..ectier. The square wave of excellent shape between 100 and 5,000 cycles giving adequate range for all audio, FM and television amplifier testing. Either sine square w available instantly at a toggle switch. Approxi- mately 25V of sine AC a ailable at 50,000 ohm output impedance. Output -6-1 db. from 20 to 20.000 cycles. Nothing else to buy. All metal ports are punched, formed and cadmium plated. Complete with tubes, all ports, detailed blueprints and instructions. HEATHKIT SIGNAL TRACER KIT

Reduces e time and greatly increasess profits of any service shop. UsesUse crystal diode to follow signal from antenna to speaker. Locates faults immediately. Internal amplifieravailable for speaker testing and internal speaker available for amplifier testing. Connection for VTVM on panel allows ual tracing and gain measurements Also tests phonograph pickups, microphones, PA systems, etc. Frequency range to 200 Mc. Complete ready to assemble. 110V 60 cycle transformer operated. Supplied with 3 tubes, diode probe, 2 color panel, all other parts. Easy to assemble, detailed blueprints and instructions Small portable 9" x 6" x 43a ". Wt. 6 pounds. Ideal for taking on service calls. Complete your service shop with this instrument. HEATHKIT SIGNAL GENERATOR KIT Every shop needs a good signal generator. The Heathkit fulfills every servicing need, fundamentals from 150 Ks. to 30 megacycles with strong harmonics over 100 megacycle covering the new television and FM bonds. 110V 60 cycle transformer operated power supply. 400 cycle audio available for 3000 modulation or audio testing. Uses 6SN7 os RF oscillator and audio amplifier. Complete kit hasevery part necessary and detailed blueprints and instructions enable the builder to a emble it in a few hours. Large easy to read calibration. Convenient size 9" x 6" x 434". Weight 4t 2 pounds.

THE NEW HEATHKIT VACUUM TUBE VOLTMETER KIT HEATHKIT The most ess ential tool o radio man can have, 1 now within the reach of his pocketbook. The Heath - CONDENSER CHECKER KIT 1, kit VTVM is equal in quality to instruments selling for S75. 00 or Features 500 microomp meter, A condenser checker anyone can afford transformer powerde. supply, 10e glass enclosed di- to own. Measures capacity and leakage vider resistors, ceramic selector switches, II meg. from .00001 to 100 MFD on calibrated ohms input resistance, linear AC and DC scale, scales with test voltage up to 500 volts. electronic AC reading RMS. Circuit uses 6SN7 in No need for tables or multipliers Reads balanced bridge circuit, a 6H6 as AC rectifier and resistance 500 ohms to 2 megohms. 110V 6 x 5 as transformer power supply rectifier. In- 60 cycle transformer operated complete cluded is means of calibrating without standards. with rectifier and magic eye indicator tubes. 5B0 Average assembly time less than four pleasant Easy quick assemblysembly with clear de- S 2 hours and you have the most useful test instrument tailed blueprints and instructions. Small 4 you will ever Ranges convenient size x x 43/4 own. 0 -3, 30, 100, 300, 1000 9" 6" ". Weight volts AC and DC. Ohmmeter has ranges of scale S1950 4 pounds. This is one of the handiest times 1, 100, 1000, 10M and I megohm, giving instruments in any service shop. ELSE TO BUY range .1 ohm to 1000 megohms. Weight 8 lbs. HEATH COMIP0 11 DEPT. C- ... BENTON HARBOR, MICHIGAN RADIO -CRAFT for 7

110 V. A.C. TRANSMITTER 110 V. A.C. MILITARY RECEIVER KIT SUPPLY KIT POWER SUPPLY POWER For BC -645, 223, 522, 274N's, etc. Ideal for Ideal way to convert military sets. Sup- powering military transmitters Supplies 500 Volts at 150 to 200 MA plate, 6.3 plies 24 Volts for filament - no wiring to 600 C.T. at 4 Amps, 6.3 of 4 Amps and 12V at changes inside radio. Also supplies 250 V. 4 Amps Can be combined to supply 3 -6 -9- 50 -60 MA. Connec- D.C. plate voltage at 12 or 24 Volts at 4 Amperes. Kit supplied tions direct to dynamotor input. Complete complete with husky 110V 60 cycle power with all parts and detailed transformer, 5U4 rectifier, oil filled con- and instructions. Ship. Wt., 6 lbs. 5.95 densers, cased choke, punched chassis, all other pans, including detailed instructions Complete - nothing else to buy. SPEAKER 5" PM TRANSFORMER ONLY $9.50 With output transformer, matching headphone output $2.80v8 Dual receiver rock FT277A with , POWER TRANSFORMERSfieGCct'd connecting plugs .00 A wonderful buy in a w production heavy transformer. Primary 117 V 60 Single transmitter rack duty power $ supply 746 V.CT at 220 FT234A .00 cych,. Secondaries MA, 6.3 V. at 4.5 A., and 5 V. at 4 A. An MILITARY CONVERSION POWER ideal transformer for high quality amplifier modulator, small transmitter or quality radio. TRANSFORMERS Will handle 13 tube radio receivers. Supply Convert your military receivers without rewiring the is Imited, order early. Shipping Weight, 5V filament. "A" type supplies 500 VCT at 50 MA, 11 las. each. at 2A and 24V at t /sA. "B" type supplies 500 VCT at 50 MA, SV at 2A and 12V at 1 amp. $3.95 . . e 3 for $9.95 State whether A or B type desired $2.95 INPUT AND OUTPUT MIDGET TRANSFORMER OUTPUT 6-8 Two units in one case Push pull coil ent input AMATEUR TRANSMITTER KIT carbonrbon I ohm voice coil excellent d output from 1SS to characteristics Complete kit to assemble a 1 Watt battery operated X1.95 150 ohm loud used in No. 800. 3 for amateur 80 meter transmitter, including tube and Handie Talkie No. 744 crystal. Range up to 500 miles. Only accessories special 4 for $ 1.00 OUTPUT TRANSFORMER needed are sending key and batteries. Complete Couples, 6C4, 6J5, tc. instructions supplied. Add postage for 2 lbs. Filter Choke 15 henries at to 500 or 5,000 ohm line 60 MA cased type her- No. 716. 2 for $ 00 ACCESSORIES metically sealed Key (add postage for 2 lbs ) ...... No. 643, each $1 .00 Kit of batteries (add postage for 4 lbs.) ..... 3.25 Q

HEATHKIT HIGH FIDELITY METER T32 TABLE MICROPHONE A M P L I F I E R K I T One of the Army's Lest. Built by Kel. ideal for foc ory call system, Sfat/ Build this high fidelity logg, public address, amateur use. Brand Brand new Delur Model amplifier and save two - in cations, 0 -800 M A. D C. Square thirds of the cost. Push new original $295 312 add postage for 5 be._...... _ L 3" 0 -10 M A basic meter pull output using 1619 Probo- tubes (military type with built in shunt. 616'e), two amplifier bly the best buy ever offered in a 12.95 1 lb. 4' stages using a dual mavnwvvvww"w.rocoa. surplus meter. Shipping weight triode (6SN7), and phase inverter give this S amplifier a linear repro- DYNAMOTOR LOOK AT THE PARTS duction equal to amplifiers selling for ten times of electric motor operating generator and formed Consists ELECTRIC this price. Every pan supplied; punched s e shaft. Many applications operating IN A GENERAL to on - chassis, transformers (including quality output radios m from storage battery - using as motor. voice coil), tubes, controls, and complete 3 -8 ohm Dynamotor C 28 volts, BC -375 TUNING UNIT Add postage for 20 lbs. -VInput instructions. output 220 volts at 60 MA. Ship. 12" PM speakers for above 36.95 ping Weight

6 pounds...... _.. . $1,50 HEARING AID HEADPHONES Dynamotor A -- Input 12 volts, The Army's best - eliminate flat ears output 1000 volts at 350 MA. and outside noise. Complete with Shipping Weight transformer for conversion from low 72 pounds.._ $5.95 to high impedance. With cord and Dynamotor B - Input 6 or 12 $1.00plug Add post. complete. volts, output 500 volts, 160 MA. w age for 1 Ib. Shipping Weight av,m!nwxaa000eaaa«oonweeWwru+,.. 30 pounds. $5.95 WAVE RADIO HEATHKIT Ail INTERPHONE 110 -volt AC operation An ideal way to learn $8.75 2 -WAY CALL SYSTEM KIT radio. This kit is complete ready to assemble, with !1 s --1 Ideal call and com- tubes and all other parts. munication system for case ideal for building Operates from AC. Simple, homes, offices, factories, A beautiful aluminum instructions a receiver or transmitter. Three variable con- clear detailed stores, etc. Makes ex- make this a good radio \_., densers, transmitting coils, transmitting mica 1L f\ baby training course. Covers reg. cellent electronic condensers, ceramic witches, National Velvet ular broadcasts and short watcher, easy to as- Vernier dial, ceramic insulated couplings, 10 wave bands. Plug -in coils. semble with every parf banana jacks, RF chokes, etc. The pans in this Regenerative circuit. Oper- l- supplied including sim- u nit will be useful for years. in surplus utes loud speaker. Battery ple instructions. Distance This is truly the greatest buy - u se wherew h non AC house current is order one while still available. We in- model for up to 1/5 mile. Oper- better available. Add postage for 3 lbs. 514.50 clude plans for converting to an 80 meter trans- ates from 110 V.A.C. mitter receiver all for $2.49. Specify TU26B ...... HS 30 Headphones per set 51.00 3 tubes, one master and one remote speaker. (200 -500 KC.) or TU108 (10 to 12.5 MC.) Ship- 21/2" permanent magnet Ioudsp oksf $1.95 Shipping Weight 5 pounds. ping weight 20 lbs.

DEPT. C ... BENTON HARBOR, MICHIGAN AUGUST, 1948 12 BOOKS IN IN THE RADIO DATA BOOK

The only Rodio Handbook of its kind! . . , 1148 pages, 12 sections, each o complete coverage of one radio subject.

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AUGUST, 1948 10 AUGUST 1948 Editorial The Future of Radio and Television RADIO by R. C. Cosgrove, Guest Editor 17 Electronics (pages 20 -22) The Crystal Detector -Part II by Jordan McQuay 20 CRAFT Radio- Science (page 23) RADIO- ELECTRONICS Image Magnifier Amplifies Light 23 Incorporatine Television (pages 24 -25) SNORT WAVE CRAFT SION NEWS RADIO SION Television Power Supplies by E. J. Bukstein 24 Traaen,arlt registered U. S patent Office "Flying Spot" C -R Tube (Cover Feature) 25 HUGO GERNSBACK Test Instruments (pages 26 -29) Editor -in-Chief Radio- Frequency V.T.V.M. by A. A. Goldberg 26 FRED SHUNAMAN, Managing Editor Audio Oscillator Has Single Control by Richard D. Henry 28 Impedance Measuring Methods by Rufus P. Turner 29 M. HARVEY GERNSBACK. Audio (pages 30 -38) Consulting Editor Electron Music with the Fototone by Lyman E. Greenlee 30 ROBERT F. SCOTT, W2PWG, Simple Tracer -Amplifier by Homer L Davidson 32 Technical Editor . Checking Performance of Phono Pickups by Richard H. Dorf 33 ANGIE PASCALE, Church Bell Records 35 Production Manager The Hi -Fi Expert Tracks Down Hum by James R. Langham 36 I. QUEEN, W2OUX, Editorial Associate Hearing Aid Has Pickup Coil 38 Amateur (pages 39 -42) ELMER FULLER, Shortwave Editor A Folded Dipole 10 -Meter Antenna by A. B. Kaufman 39 Surplus Conversions by Milton Kalesbian 40 G. ALIOUO, Circulation Manager Handi -Dandy Transceiver by William E. Pike, WLKMW 41 An S -Meter for Your Receiver by H. Hatfield 42 JOHN J. LAMSON, Servicing (page 44) Advertising Director ALFRED STERN, Promotion Manager Converting Farm Sets for A.C. by Alfred Shortcut 44 Construction (pages 49 -56) In on Early Issue Compact Radio from Holland 49 TELEVISION Six RECEIVER ALIGNMENT A -Tube Dry -Cell Superhet by Edwin Bohr 51 ELECTRONIC MEDICAL RESEARCH Neon Lamp Experiments by Harold Pallafz 52 Direction Indicator by W. H. Gibson 56 UNIVERSAL TEST INSTRUMENT Theory and Design (page 57) On the Cover: Regulated Supply 57 Foreign News (pages 67 -69) Report from Britain by Major Ralph W. Hallows 67 Radio in Latin America by E. A. Conklin 69 FM (pages 70 -72) A.F.C. Stops Drift by L S. Wecker 70 Multi- Element FM Tube 71 Departments The Radio Month 18 New Devices 43 Try This One .... 58 Radio -Electronic Circuits 60 Question Box 64 New Patents 73 RCA's "flying- spot" tele- Technotes 76 vision light source. The per- World son in -Wide Station List by Elmer R. Fuller 78 the photograph is Radio Business 79 L. E. Swedlund, who devel- Miscellany 80 oped the new equipment. Communications 82 Book Reviews Chromatone by Alex Schomburg from 84 RCA photo by Gordon IV. Hrmescrly.

ABC PAID CIRCULATION 6 MONTHS TO DEC. 31, 1947-102,688. (Publishers Statement) PRINTED FOR AUGUST ISSUE-149,000 RADCRAFT PUBLICATIONS. INC. Hugo Gernsback, President; M. Harvey Gernsback, Vice President; 6. Aliquo, Secretary Contents Copyright, 1948, by Radcraft Publications, Inc. Text and illustrations must not be reproduced without permission of Copyright owners. RADCRAFT PUBLICATIONS INC. PUBLICATION OFFICE 29 Worthington Street, Springfield 3, Mass. Address all correspondence EDITORI/,L AND ADVERTISING OFFICES 25 West Broadway, to N. Y. office. New York 7 N. Y. Telephone REctor 2 -9690. BRANCH ADVERTISING W. WasA,ngton Street, Chicago 6, III. Tel. Randolph 7363. Frank OFFICES: Chicago: 308 Detroit: Holstein, Manager, Room 402 Lexington Bldg., 2970 West Mich. Telephone Madison 7026 -7. Los Angeles: Ralph W. Harker, Manager, Grand Blvd., Detroit 2, 606 South Hill St., Los Angeles 14, Calif. Tel. Tucker 1793. San Francisco: Harker, Manager, 582 Market St., San Francisco 4, Calif. Tel. Garfield 1.2481. Ralph W. RADIO- CRAFT, August, 1948, Volume XIX, No. II. Published monthly on 25thof month preceding When ordering a change, please furnish date of issue. Allow one month for change of address. an address stencil impression from a recent wrapper. All communications about the Circulation Manager, Radio-Craft, 29 Worthington St., Springfield subscriptions should be addressed to 3, Mass., or 25 West Broadway, New York 7, N. Y. SUBSCRIPTION RATES: United States and possessions, Mexico, Central and South American countries, $3.50 a year; $6.00 for two years; $8.00 Canada, $4.00 a year; $7.00 for two years; $9.50 for three years. All other foreign for three years. countries, $4.25 a year, $7.50 for two years; $10.25 for three years. FOREIGN AGENTS: Great Britain: Atlas Publishing and Distributing Co., Ltd., 18 Bride Lane, Fleet St., London E.C.4. Australia: McGill's Agency, 179 Street. Melbourne. France: Brentanó s, 37 Avenue de l'Opera, Paris 2e. Elizabeth Holland: Trilectron, Heemsteedsche, Dreef 124 Heemstede. Greece: International News Agency, 17 Amerikis Street, Athens. So. Africa: Central News Agency, Ltd., Book 5 Cor. Rissik S Commissioner Sts. Johannesburg; 112 Long Street, Capetown; Smith Street, Durban, Natal. Universal Book Agency 70 Harrison Street, Johannesburg. Middle 369 Susil Gupta East: Steimatzky Middle East Agency, Jaffa Road, Jerusalem. India: (Distributors) Co., Amrita Bazar Patrika Lt., 14 Ananda Chatteriee Lane, Calcutta. RADIO -CRAFT for 11

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.... 14.95 221A ... 2.95 861 49.95 KC4 .... 105.00 IN5GT ... .72 6G6G 88 7N7 .69 KU676 .. 22.00 IP5GT ... 88 6116 .60 7Q7 .72 34 1.06 2J31 .... 24.95 222A ... 120.00 864 .88 35/51 .72 2J32 .... 24.95 227A ... 3.95 865 .98 MLI00 .. 105.00 1Q5GT ... .88 6H6GT .... .60 7R7 .84 MLIOI .. 150.00 1114 .88 635 .54 797 1.06 35A5 .72 2.134 .... 24.95 241B ... 90.00 866A ... 7V7 35135 .72 1.95 ML502 .. 300.00 IRS .72 6J5GT .... .54 1.06 2338 .... 37.50 242C ... 5.95 868 1.06 7W7 35L6GT .60 2J39 .... 34.95 249C ... 3.49 869B ... 75.00 MR4 .... 90.00 194 ...... 88 636 1.06 ... 872A 2.50 QK59 45.00 135 .66 6.17 .72 7X7/XXFM 1.06 35W4 .46 2J40 .... 34.95 250R ... 7.95 ...... 72 7y4 .72 35Y4 .72 2342 .... 3-4.95 250TH .. 19.50 874 ..... 2.49 QK60 ... 45.00 1T4 .72 6J7C .98 QK6I 55.00 1T5Gf .... .88 6J7GT .... .72 7Z4 .72 35Z3 .72 2J49 .... 34.95 250TL .. 19.50 876 ... 10 35Z4GT 2J51 34.95 252A 4.95 878 2.49 QK62 ... 55.00 IU4 .72 6J8G 106 1.56 ... .50 .... .66 6K5GT 12A6 .89 35Z5GT .... .46 231351 . 4.95 259A . 4.95 879 .89 RF.L21 .. 4.25 IUS .... 88 25.00 884 .98 RK12 1.95 1V , .72 6K6GT .... 54 12A6GT ... 1.06 35Z6G .... .88 2J53 .... 274A ... 1.25 ... .60 36 .88 25.00 1.25 889 .98 RK21 3.95 1VS ...... 88 6K7 12A7 1.06 2J54 .... 274B ...... 88 6K7G 60 ,72 37 .60 2K25 ... 24.95 301A 4.95 891 110.00 RK22 ... 4.95 1W5 12A8GT ... 2.95 2A3 1.06 6K7GT .... .60 12AH7GT .88 38 .72 2K28 ... 24.95 304TH 7.95 892R ... 200.00 11R25 ... .68 2.95 7.95 RK33 ... .98 2A4G 1.28 6K8 12AL5 .... .72 39/44 .59 3AP1 ... 304TL .. 1.9A 902P1 .. 1.06 3822 4.95 305.4 12.95 905 11.95 RK34 ... .59 2A5 ...... 72 6K8G ...... 88 6K8GT 88 1.06 42 .60 31123 .... 4.95 307A ... 6.25 920 2.95 RK59 ... 3.95 2A6 ... 12ATT .... 1.95 4.95 923 .98 RK60 ... .79 2A7 2.20 6L5G 88 12A116 .... .72 43 .60 3824 .... 310 .88 61.6 1.28 .88 45 .60 31325 .... .98 311A ... 1.98 931A ... 4.95 RK6S ... 24.95 2B7 12AU7 .... 1.06 49.50 2E5 .88 6L6G 1.06 12AW6 .96 45Z5GT ... .60 31326 . . . . 595 316A ... .89 950 RK69 ...... 1.06 2.95 120.00 953B 4.95 RK72 ... 1.95 2V3C ..... 1.10 6L6GA 128A6 .... .66 46 ...... 88 3BP1 ... 322A ...... 69 ,88 47 .88 3C21 5.95 4.95 954 .75 RK73 ... 3.95 2X2A 6L7 128E6 .... .66 .... 327A ... .72 6L7G 1.06 .89 49 .88 3C22 .... 2.95 331A ... 4.95 955 .75 RK75 ... 6.25 3A4 12C8 3C23 .... 4.95 350/A/B 2.95 956 .75 RX120 ... 10.00 3A5 1.29 6N6G 'to' 12FGT .... .60 50 1.56 957 .75 T20 .... 1.95 3A8GT .... 1.92 6N7 12116 .60 50A5 .88 3C24 .... .69 353A ... 4.95 ..... 1.06 .88 5065 .72 3C30 .... 1.50 368AS .. 9.95 958A ... .75 T7.40 ... 2.95 3B7 6N7GT ... 12JSGT ... .51 ..... 3.00 959 .75 UX6653 3.95 3C6/:(XB . 1.28 6P5GT .... .88 12J7G .... .72 5006C. .... 1.06 3CP1 ... 371 ... 2.95 .89 6Q6G/6T7G 1.06 .72 SOL6GT .60 3BPt ... 3.95 371B ,,. 2.95 991 .69 V700 ... 6.95 3D6 12J7GT .,, ... 24.95 .98 3E6 1A6 6Q7 ...... 72 12K7G .... .72 50X6 .88 3F.Pt ... 1.95 388A ... 7.9.'. 1000 spec. VR75 ... .60 3D21A .. 3.00 393A 7.95 1000T .. 75.00 VR78 ... .75 3LF4 ..... 1.06 6Q7G 12K7GT ... .60 50Y6GT ... .60 .75 3Q4 .72 6Q7GT .... 60 .88 53 .88 3E29 .... 4.95 394A ... 4.50 1611 .... .99 VR90 ... 12K8 ...... 1.49 3Q5GT .... .88 6R7 12K8GT .. .88 55 .72 3GPI ... 4.95 417A ... 24.95 1613 .... .75 VR91 ... .8688 4-65A 14.50 3.95 1614 1.75 VR92 ... .75 3S4 .72 6R7GT .... 12Q7GT ... .60 56 .60 ,.. 434A ...... 6S7 .60 57 .72 4-125A .. 27.50 446A ... 1.95 1616 .... 1.39 VR105 .. .75 3V4 .72 66 12SA7 .... 4-250A .. 37.50 24.95 1619 .... .7,5 VR150 .. .98 5AZ4 .42 6S7G 12SA7GT .. .60 58 72 450TH .. 1.03 6S8GT 96 .72 59 1.06 4A1 .... 1.98 503 195.00 1621 .... 1.98 VTI27A 3.00 5R4GY ... .. 12SC7 ..... 6.95 527 1622 1.75 V11111 .. 1.19 5T4 ...... 1.28 6SA7 60 12SF5 .... .60 70L7GT ... 1.42 4APIO .. 12.95 .... .53 6SA7GT .60 71A .72 4.95 49.50 1624 1.75 WL460 . 14.95 5114G .. 12SF5T ... .60 4B24 ... 531 .... 6SA7Y 88 75 .60 4C35 ... 19.95 575A ... 14.95 1625 .... .49 WIA68 . 14.95 5V4G ...... 88 .... 126F7 ... .72 8.95 9.95 1626 .49 WL532A 4.95 5W4 .88 6SC7 .72 12SF7GT .. .88 76 .60 4E27 632A ...... 60 6SD7CT 77 .60 4328 .... 34.95 701A ... 4.95 1627 .... 7.95 WL562 . 150.00 5W4(:T ... .. 96 12SG7 .... .72 .60 6SF5 . . .60 34.95 1629 .69 W1.616 . 105.00 5X4G ..... 60 12SH7 . . .. .72 78 ...... 4J29 702A ... 3.95 ..... 50 4.95 7.50 WI.619 . 49.50 FYF.G 6S5(:T .... T2 128J7 ...... 60 79 .88 SAPI ... 703A ... 4.95 1630 .... .38 5AP4 5.95 1.98 1636 .... 5.95 Z225 ... 1.95 5Y3(:T .... 6SF7 72 12SJ7GT .. .60 80 .42 ... 704A ... .50 6SG7 81 1.28 1.95 1638 .98 0A2 1.69 5Y4G 7t 12SK7 . ... .60 SAPI 705A ... 2.95 .... 63117 .60 82 .88 5B1'4 ... 4.95 706BY .. 24.95 1641 .... .79 0A3/VR75. .98 57.3 ...... 60 ..... T2 12SK7CT .. 3.95 .98 OA4G .... 1.06 57.4 .88 6SJ7 .60 I2SL7GT .. .88 83 .88 SCPI 706CY .. 24.95 1642 .... ,60 1.06 1.98 OB2 2.05 6A3 1.06 6SJ7GT ... . .80 83V 5CP7 . . . 13.95 707A/B . 24.95 1654 .... 123N7GT 29.95 98 OA3/VR90. .75 6A6 .88 6SK7 60 12SQ7 .... .54 84/624 .,.. .60 51)21 ... 708A ... 7.95 1665 .... .60 .75 6A7 .72 6SK7GT . . .54 85 .72 5FP7 3.95 709A ... 9.95 1851 .... 1.25 0C3/VRI05 ...... ,66 12SQ7GT ... 9.95 1.65 1852 .... 1.06 OD3/VRI50 .75 6A8 .72 631.TC.T ... 128R7 .... .72 89 .72 5GF3 713A ... .72 6SN7GT .. .211, 99V 1.28 5JP1 ... 11.95 714AY .. 14.95 1853 .... 1.06 00 .50 6AAG ..... I2SR7GT .. .72 19.95 1963 95 0Y4 .88 6A8GT .... .72 6SQ7 12X3 .98 99% 1.28 715A/B 88 .88 6SQ7GT ... .54 1YZS .88 II7L7GT .. 1.42 5330 ... 29.50 715C . 29.50 2050 .. .98 0Z4 6AA5/BNS. 11.95 717A 07.4G ,88 1.06 6SR7 .60 14A4 1.06 117M7GT .. 1.42 5LP1 ... ".' 1.65 2051 ,,,, 98 6AB7/1853. 6SR7GT 1.42 5TP4 ... 20.00 34.95 2140 01A .50 6AC5GT .. 1.06 60 14A5 1.56 117N7GT .. .AB 720CY ...... 20.00 6397 .. 1.42 6AF6G . 1A3 .... 72 66 .88 1t7P7GT 721A/B . 4.35 5514 4.95 6AC7/1852. 1.06 6ST7 .88 14A7/1287 11723 .54 6C21 .... 24.95 .... 1A4 1.28 .88 723A6 5.95 5516 .... 5.95 1.28 6AD7G . 1.06 6SV7 .88 14AF7/X%D 1177.4CT 1.06 6D4 .... 1.95 4.95 IA4P 14A6 6J4 3.95 724A/B . 5562 .... 10.00 IASGT .... .88 6AC5 96 6U5/6G5 .. .72 88 117Z6GT .. .88 24.95 6AG7 1.06 6U6GT ,72 1467 .88 FM-1000 1.28 6Q5G .. . . 1.25 725A 7193 .... 39 1A6 1.06 ...... 4.95 726A ... 23.50 8005 4.95 IA7CT .72 6AHE 1.42 6U7G .60 1488 .88 1273 .88 7BP7 ...... 106 .88 7EP4 ... 17.95 800 2.25 8011 .... 2.95 1AB5 .... 1.06 6A35 .99 6V6 14C5 9001 .89 7GP4 ... 19.40 801A ... ,98 8012 .... 4.95 1B3GT ... 1.56 6AK5 .99 6V6GT .... .72 14C7 .88 9002 .69 9GP7 ... 15.00 802 2.95 8013 .... 2.95 1B4 1.28 6AK6 .88 6W7G .... .88 14E6 .71 9003 .49 9JP1 ... 3.95 803 8.95 8016 .... 1.89 1B5/2513 .. 1.06 6AL5 .72 6X4 .54 14E7 .88 9004 .49 9JP2 ... 3.95 804 9.95 8020 .... 3.95 1B7GT .... 1.06 6ALTGT .. 1.06 6X5 .88 14F7 88 9005 .98 91.1'7 ... 4.95 805 4.95 8025 .... 7.95 1C5GT .... .72 6AQ6 .66 6X5GT .... .54 14F8 1.06 9006 .49 Prices Subject to Chonge Without Notice All Types in Stock Now Subject to Prior Sale 20% DEPOSIT ALL PRICES WITH ORDERS NIAGARA RADIO SUPPLY CORP. F.O.B., N. Y. C. UNLESS RATED 160 GREENWICH STREET NEW YORK 6, N. Y.

AUGUST, 1948 11

. ALL afzed/on Vad tie VALUES RADIO EQUIP- AND HERE MENT AND RADIO PARTS IT IS FOR YOU!

The biggest selection of Rodio and Electronic bargains you have ever seen, Every item that. Hershel offers you is a value that you can't duplicate anywhere -every dollar that you invest brings you more returns than you ever dreamed possible, so don't delay -stock up today on all Radio and Electronic equipment and parts that you've been waiting to get! BC -AR230 TRANSMITTER AZIMUTH CONTROL tnduding 4 tubes and RF f,mmeler. MN 52H BC -AL229 RECEIVER Including 6 tubes. Used in aircraft. BOTH UNITS ONLY My 105

T -17 TUBES oai calibrated CARBON MIKE 815. . . .01.95 7897...51.49 360 degree fore, 9004...1 .44 11(60...1 .95 ,deal for antenna LIKE NEW mola;ngndi- 89C 3API... 1.95 9197.... 2.95 9006... .44 1T4.... .44 60 lo I MY 160 ro ho with switch. 3891... 1.95 VR150.. .69 5085... .89

WI... 1.95 33 ,94.. .69 354.... .44 lust the NM le. that 1K Anal-. 5997... .95 872A... 1.95 INS. .69 elcal *potation -4TL 899 2500 volts at 400 5894... 1.95 INS....5 MA. An Ideal .69 VT25 TUBE tuba Iw that Induction McN. M (2101.5 .a4 6fele

My 300 JOHNSON PORCELAIN SOCKET 25W. 4 PRONG PORCELAIN SOCKET RT 39-A RECEIVER 25c (ACORN) AND TRANSMITTER

APG 5 contains: (1)829, (1 )2C43, (1 )2C40, 14c POR- (1)2X2A, (1)Adjustable vacuum shorting pop, MY (1)1N213 Xtal, (1)5Y3, -3, (1)VR105, CELAIN SOCKET (2)9 302 (0)6AK5, (I )6ALS, (1 )Blower, IF strip, can be 829-832 ETC. used on television. This equipment brood new $ MY and in original sealed. cotton. 1 301 3 for ; HERSHEL RADIO CO. 5249 GRAND RIVER DETROIT 8, MICHIGAN

IMPORTANT NOTE All orders F.O.B. Detroit -Minimum order $2.00- Michigan customers odd 3% soles to4-20% payment must accompany all orders.

RADIO -CRAFT for 15

ULTRA HIGH- ,FREQUENCY TRANSMITTER AN /APT 5 Brand New!

1500 Megacycle Transmitter, mode for U. S. Government, complete with the following tubes, 2.6AC7, 1.616, 2 -829, MY 450 1.931 A, 1 .6A07, 1.522 Ultra high free. tube. Complete with OILY 49.95 high freq. cavity, 1 Blower to cool the 522,1 tome delay relay, 2 filament trans. cond. and many other component ports for ultra high frequency wark.lt has a frequency checker, complete Lecher wires, with slider and sensitive bulb for checking the HERSHEL RADIO CO. wove length. The lecher wins are calibrated that the set. sing of the slider may be read directly in Centimeters. Oper- 5249 GR9ND RIVER DETROIT 8, MICHIGAN ates on 115V. AC for filaments only. Dees not include. any plan supply. The tubes alma are worth ma y times more than IMPORTANT NOTE what we r selling Me complete transmitter for. Packed in All orders f.0.8. Detroit- Minimum order $2.00- Michigan customers original case-contains instruction book. Wgt. 118 lbs. add 3% scies tac --20% payment must accompany oll orders.

BC No. MX16 Cross pointer 31/2' Meter. Two 200 microamp movements. FM RADIO AND TRANS- Brand new $2.95 702 -A 500 ohm to grid matching transformer /81749 695 MITTER BC-620-A Ceramic Silver Podders Duo' 3 to 12 MMFD or S to 20 MMFD 19. Ceramic mica Fodder single 5 to 20 MMFD per dos. Soc 20 MC TO MY 400 Choke -300MA 20HY. Insulated for 5000V. Heavy Porcelain Insu. $995 Ia:ors. Very consereatively rated. Idle for KW rig $4.95 27.9 MC .. REMOTE POSITION INDICATOR This Xtal controlled FM set has 13 tubes and has dual Xtal controlled channels. It also contains built -in Fil. and Plots 6.12V. 60 Cy. 5' Indicator with 0.360 Degree Dial. Meter. Tubes used: (4)1 LN5, (1)I LC6, (1)1 LH4, (2)1291, (ry{ $245 (4)1299, (1)1294. Ideal for communication between trucks, MY 405 boats, etc. Used, in good condition. Less power supply. Wt. TRANS- 3 HY -5MA -325 OHMS 38 Ibn. Complete with carrying case and diagrams. MITTER 19/4," d. x 11/4" h. MY 406 MY leo STANDARD BRAND ENCLOSED IN A METAL CASE 19c MY 17 t CONDENSERS (4) 2X2 tubes, (I) Squirrel cage blower, 12 -24V., .02- ,t, .1 MFD 995 8000V., 25 MA 2' meter. 2- Wl 95 PAPER OIL 7000 VOLTS .01 at 5000 VDC. .001 at 9500V. CA PACITATORS

1 MFD MY 407 CONDENSERS 6000 V. $495 1 KW MODULATION Cop MFD VOIT Your o.ost 1000 oil 89: TRANSFORMER 2 MFD 1 1000 oil 44: MY 417 $895 8 600 oil 95. 6000 V. 600 oil 69: 9495 MY 111 2 600 oil 49: COAXIAL FITTINGS LIMITED QUANTITY CHASSIS Sise: 19c EA. RCA Modulation Trans. conservatively rated at 550W. audio to modulate that new KW rig. Audio Watts -550, 934 x 4 x1;4" 6 FOR SIN Sec. 1; 450 mils, Sec. 2; 80 mils turns ratio-Pri: Sec.1; 1:1, Pri. Sec. 2 Top 25:1. Impedance ratio -Pri: 1.1:1 Sec Pri: Sec 2 -25:1 Pri: Sec. Top 625:1. DC Resistance -Pri: 5¢ 25¢ 356 200 INVERTER MY 409 135 ohms, Sec ,y1 -I12 ohms, Sec. .1-99 ohms. Trans- ANGLE. AUTOMATIC CHANGE- formers insulation tested: Pri.-8000V. Sec. b1- 11,000V. HOOD SOCKET PLUG ADAPT) R OVER RELAY Sec. .2- 2000V. to the rest of the coils and core. Primary SO -239 PL -259 M-359 $149 center- topped for Class "8" Modulators. Sec. 82 will carry 83-IR e3 -ISP 83 -IAD 11S V. 400 CY. A.C. BO mils to modulate screens of beam power or screen grid 26 V.D.C. tubes. Primary will match any Class "B" tubes up to 10,000 POTTER S. BRUMFIELE to plate, such os 810's, 751',, 8005's, ZB120's, ohms plate ~ ! -e OVERLOAD $19 203's, HYSIZ's, 813',, 828's, 805's, 203Z's. Sire: 91/4471/24 ! RELAYS ATTENTION 500,000 7t/,'. Heavy channel iron mounting brackets. Wt: opprox. 161 - MY 4) lbs. Potter and Brumfield. Relay /1 -5000 ohms, co: cur. Assorted type plugs and connectors too numerous ent 10 MA. Relay/2-110V. 60 Cy., AC coil. EPDT. to mention!! 'Send in your requirements for our WAFFER SWITCHES SELSYN MOTORS rock prices! MY 154 extra special, -bottom TWO KIT OF FOR MY TEN $185O 402 $395 Q SWITCHES

The ideal way of indicating the DUAL VARIABLE Rotary wind in position of beams, e°'81e é U dkator, c. Line chord and In- COND. MY structions for 110 AC operation 430 lgrnished on request. 89 NEW BC 223 AX MY 109 :CiNITION COILS FOR STANDARD SPERTI R.F. TRANSMITTER VACUUM SWITCH BRAND Photo Flash Tubes 920 Volts 95-, 801 Oscillators and 801 power ampli- Used aeann° satch.switch. fiers, 2.46 modulators and 1.46 speech $2995 MY 401 MY 403 amplifier 4 Xtal frequencies and master oscillator on selector kPrimary: 150V. condenser discharge. Discharge resistor Thyrite type SF 130V, AC on DC 95c Resonance ind. neon bulb and gtl:gatm clip I9c switch. 10 to 30 Watts output. Tone voice or C.W. Mod. Ideal Secondary: I5,000V. can also be ;1z Paper Cond..05., 05., 05, 300VDC -round can for 80 meter bond. Comes with 3 coils TU 17A 2000 -3000 Kc. used on model airplanes. I "Al'. Dozen 51.00 TU 25 3500 -5250 Kc. Black crackle case. Includes two separate 30 MC-1F MY 112 cases to store extra coils. Frequenciés chart and tubes Included, WRITE FOR FREE BULLETIN( SILVER- SLUGGED 29¢: packed in original eases, less crystals at this low price,

AUGUST, 1948 16

RADIO RECEIVER 8C733ß $09$ DYNAMOTOR SIGNAL CORPS KEY A sturdy PYRANOL CAPACITATOR A of aircraft good MY part blind landing equipment 77 UNIT key for those who manufactured by Operates on any $r95 43O MY 132 WE. Duo out still prefer o 39c I of its predetermined MY 170 MFD, 5000 VDC, oe Xtal controlled Dynamotstr "pound bro freq. in the range of 108.120MC. Con. Input volt - Shorting switch, Size: 4x4% x314' $295 fain. 10 tube,, 3 which of on WE 717A', and Xtals. age 12 to 24V, heavy contacts, Ideal receiver for adput conversion to IA/MC-Nam Band voltage 400V. 135 fully adjustable or mobile telephone at band,. for 24VDC operation. MA. 800V. at 20 MA, end 14V, x 7 x 4V,'. Complete with tube,. gapping and 9V. of 1.1 amp. spring pressor. CHASSIS Containing: 6V. AC relay. 3 minia- $195 lyre socket, with tube shield,. 5 INVERTER - MG 149 -F MY 150 condensers and 6 res. Size, 3x5.1'. 24 V.D.C. Dual output 26V, MY 410 60 Cy., 250 volt amperes. BK 22 K RELAY 115V, 400 Cy. 500 volt am- 495 Used in conjunction MY 110 with'CR269F,uhange- peres. Single phase. 28v. WILL OPERATE WITH RADIO sstep relay 5 deck, 6 $295 position switch. I 2v. COMPASS SCR 269 -F BRAND NEW AUTOMATIC DIRECTION FINDER DPST. RADIO COMPASS MY IDO MICA CAPACITATOR MY 166 DETROLA RECORD SCR 269 -F COMPLETE 002. MFD.-3000 W.V.D.C. $7500 13 69c WITH COMPONENT PARTS CHANGER MY 311 Handles FILAMENT TRANSFORMER The Radio Compass SCR269F wos designed to be the 12 -10' - prie records or 10 -12' 110V.,602Cy. Sec. I; 4V. at 16 mary radio navigation compass for the United States Army Automatic $1Z45 recoger. amps, Sec.2; 2.5V. at 1.75 amps, and Navy Air Forces. Constant reception is possible day or insulated for 5000V. Ideal for night so that fixes con always be made to establish the 2X2 and 826 tubes. MY 145 ship's or plane's position. Plotting fixes is omplished by Hermetically sealed. ANTENNA DUPLEXER $195 selecting two or more stations and plotting c these on the equipment Size: 6x31/2 x41/21. Originally used on BNIFF to allow novigaton map. The point of intersection of these lines indi- the use of o common antenna for receiver and transmitter. 156 to 187 MC 55.95 cates the location of the croft. This equipment comes com- A -5 AUTOMATIC MY plete with 17 tubes and superheterodyne receiver which PILOT -$4.95 422 ANTENNA BOTH UNITS is tunable from 200 to 1750 KC in three bonds. A complete ONLY Servel -100 foot instruction book for operation and maintenance accompan- 2 meter pounds max., to use antenna: 157. ies this equipment. 187 MC. as o steering de- Originolly used with $995 e, or compass con- BNIFF equipment - essfully 144 trol on ships. wed on STYPEHEDBRAND MC as o nondirectional PLATE SENS. TELEPHONE TYPE, PLATE I00W. Bleeder consisting of 5 section,, 750 ohm,, 23 49c antenna $5.95 MY 310 RELAY SENSATIVE ohm,, 23 ohms, 7500 ohm,, 3000 ohms, Total -11,296 ohms. MY 147 $149 RELAY MODULATION TRANSFORMER 1195 5000 ohm, MY 421 IF TRANSFORMER AND DRIVER TRANSFORMER Scoil contact 7000 ohm, S.P.D.T.P Mounted in aluminum shield can. 5 MC with air trimmer impedance 95c coil contact, S.P.S.T. coupled BOTH UNITS type. DISCRIMINATOR TRANSFORMER ONLY TO MATCH 95c MY 115 SCOPE TRANSFORMER $495 MY 302 MY 104 Primary 110V. 60 Cy. Sec; THORDARSON $395 4000V. at 10 MA. Size CHOKE RC 1206 modulation transformer. 815 Class ABS, 56W. audio. RC 1205 6x4x3 V1. $245 At 200 MA. Shelled case. driver transformer, 65147 to 815, Clan A82- Companion to RC 1206.

1 0 HY or 1 5 HY at 1.50 MA. MY 152 LIP HIGH -SPEED PHOTO -FLASH TOGGLE SWITCH MIKE TUBE $595 METH MY DPST. 30 HEAD MY 156 CORONA BALLS 116 amps, In 39c BAND 95 Grid and plate connection, for VT 127- 10c EA. Bake.a.Iite 12,000,000 lumens light output. Stops MY 151 AND allaction, Ignition 250 TH etc. Ball Type. Heat coil included on dissipating $100 c use. CORD MY 131 back of bulb. 10,000 Rashes. Dia- silver plated. gram, furnished on request. TRANSFORMER BC -654A PORTABLE ARR7 AIRBORNE VERSION OF Audio oscillating transformer with 95c RECEIVER AND HALII- output and feedback winding. MY 148 TRANSMITTER CRAFTER SX 28A MY VOLTAGE REGULATOR - 95c 112 $12900 Carbon pile, magnetic type, coil current, 105 MA. VIA95 MY 114 Load max. 5 amps at 18.25V The frequency range of both transmitter and re- With 3 RF stages. IOn re.ntodiotion suppressor DON'T MISS THESE SPECIAL SAVINGS! R -E) 12 tubes. Motor end manvol t ing. S.met r. F- selectivity control, Crystal Filter. AVC, phasing c Powdered iron, Ye slug my 118.... 10c ceiver is continuous from 3700 to 5800 kilocycles; trot, ANS. etc. Also furnishes videod output for sun a Jacks for PL55, PL68 and panoramic output for scanning. Complete with or my119.... 10c tubes and Xtal. but without power supply. Pow r Asst mica condensers -per 100 my120....S 1.95 all stages gang tuned by anti -backlash worm gear requirements, 170V. a l l 35 MA. New, in sealed s. cas Pin straightener for miniature tubes my) 22.... 25c SQUIRREL CAGE Eor phones, 2000 ohms, used myl 24.... 95c dial mechanisms. The BC654 -A is 18" wide, l4" BLOWER SCR625 Mine detector, used my127....539.50 $795 75,000 watt Res. MY 169 -ohm 200 Bleeder my413.... 95c high, and 9Y2" deep. Weight -44V2 lbs. Power Y outlet, 110 AC, 60 Cy. Silent Oil lite bearing SILVER CERAMIC CONDENSERS required for receiver-1.5, 45, and 90V. Power motor, with mounting 500 W.V.D.C. 12c ea. 10 for $1,00 bracket. required for transmitter-11/2, 6, 51, 84, Volts DC Available capacity (MFFD's), 2, 3, 4, 5, 7, 8,.8 Y., 10, 1 I, 12, CERAMIC INSULATORS 15, 24, 25, 40, 45, 50, 51, dual 60, 70, 72, 75, 80, 81, 95, and 500. Volts DC at 160 MA. HIGH VOLTAGE $100 100, 120, 470, 500, and 1000. Used. FEED THRU 1 002. MY 103 5 -GANG VARIABLE HERSHEL RADIO CO. CONDENSER COPPERWELD WIRE MY 149 5 Gong approx. 50 5249 GRAND RIVER DETROIT 8, MICHIGAN MY 150 MMFD per section with $295 $195 individual air tuned All orders F.O.B. Detroit -Minimum order $2.00- Michigan customers 3E00 odd soles tax -20% payment must accompany padders. 18 to 1 ver- 3% all orders. nier drive. Shielded.

RADIO -CRAFT for Editorial I 17 The Future of Radio and Television

A Radio Authority Looks Ahead By R. C. COSGROVE, Guest Editor

IT AFFORDS me genuine pleasure to cede this space this made and sold. Attesting to the reliability of the industry, month to Mr. R. C. Cosgrove, Vice- President of the giant even in its earliest public step, is the fact that most of these Avco Manufacturing Corporation and General Manager 4,000 receivers are still giving good service. of its Crosley Division -one of the foremost radio manu- "In 1916, 6,500 television receivers were produced. In facturing corporations in this country. Mr. Cosgrove recently 1947, 175,000 were produced. Now, here is an indication of delivered an address: "The Present and Future of the Radio, the expansion taking place today. In the first four months Television, and Appliance Business," before the National of 1948, more than 160,000 television receivers were built, Electrical Wholesalers Association Convention at Buffalo. or almost as many as for all of 1947. We expect at least From this address I have excerpted the major portion of his 600,000 sets to reach the market this year.

remarks. Coming from an expert, they will be, not only of "By th . end of this month, 29 television stations will be great interest, but highly inspiring as well, to all readers. operating in 19 cities. Seventy more permits to build sta- H. Gernsback tions have been issued by the Federal Communications Com- mission, and 192 applications are pending in 96 cities. By ` =More than 31 million radio sets were produced from the 1949, stations will be operating in 40 cities -supplying pro- end of the war to January 1, 1948. More than half of these grams to areas representing 60% of the nation's population. (about 19 million) were produced in 1947 alone -a record "Great strides have been made in the past 60 days in tele- year for the industry.. Thirty -seven million, or more than vision programming. As a result, you are going to see a 90% of American homes have at least one radio receiver, and sharp upswing in demand for home receivers. Some news- many have three or four. Five million automobile radios and reel companies have arranged to furnish daily newsreels to millions of portables are in use. Altogether Americans cur- television stations. NBC is .photographing its own newsreels rently own more than 65 million receivers. (Latest_ figures of world events. And many local stations will televise local would run to more than 75 million:Editor) news by the same means. "Now, it is misleading to look at these figures and say "For some time,,a network of stations here in the East has that the market for radios is becoming saturated. On the been telecasting historic events from Washington and New contrary, any business that enjoys such universal appeal York. Millions have experienced by television the rare thrill with the buying public should constantly provide a ripe of watching the President of the United States deliver major market if it is a turnover business, and radio definitely is a addresses to the Congress. Already, more Americans have turnover market. There are millions of console radios and seen President Truman by television in one day than saw radio phonographs in use today that are from six to ten Lincoln in public appearances during his entire term. years old. This replacement market is untapped. "Network facilities are moving along briskly, but the job "Hundreds of thousands of new homes are being estab- is tremendous and can't be done overnight. Seven thousand lished this year. Somewhere I have noted that a million and miles of facilities are now installed or under construction. a half marriages will take place. Based upon our 93% figure, Another 7,000 miles will be started as soon as possible. Co- this should mean a market for a lot of new radios. Also, the axial cable will reach as far west as St. Louis by the end radio industry's campaign for a radio in every room is of 1948. Other tie -ups between cities are being made by making definite headway, opening up markets for additional microwave relay. The West Coast should be linked with the millions of sets. We estimate that, with a free flow of ma- East Coast by mid -1949. Meanwhile, the West Coast sta- terials, at least 14 million radios will be produced in 1948. tions are not standing still. They, too, are linking themselves "The broadcasting industry is continuing to serve as a together for improving the shows they put on the air. major stimulus to radio sales. New stations going on the air "Television is not for the few-it is for the many. It is since the end of the war have raised the total to over 1,700 - destined to become as much a part of the American house- almost twice the number in operation before the war. Con- hold as radio has become. Surveys have shown that tele- struction permits and pending applications represent an- vision is by no means a 'rich man's toy.' Three separate, other 300 stations, which will mean more than 2,000 in impartial surveys in the nation's major television area-New operation in the near future. York and its boroughs -have proved that by far the largest "We have developed radio to a fine point. No other in- percentage of television sets are owned by families with mid- dustry has achieved greater scientific success. But by rto dle, and lower middle, incomes. means all the frontiers of radio have been opened. We have "The latest survey showed that 73%% of sets in the New yet to develop, for instance, a truly personal radio. I mean York area were owned by families in the average income one that you can carry on your wrist, in your purse, or in group. 26 were owned by those in the high income group. your vest pocket. When a dependable receiver of this kind is "Sets or the market today range from those with 7 -inch placed on the market -and it will be -you will have an- picture to 3es, which give a picture some 4 x 6 inches, to other new untapped source of sales. projection -type receivers giving a picture as big as a news- "Another development of promise is very small radio paper page. Prices range from less than $150 for small table equipment for two -way conversation between individual sets, to $2,500 or more for large, opulent consoles. users. Almost all technical hurdles in this field have been (As we go to press, Pilot Radio Corporation announces a cleared. 'Transceivers,' as they are called, which weigh $99.50 television set with 3 -inch tube. -Editor) ' only two and one -half pounds and are no bigger than a "What we are now experiencing in television is not a camera, have been approved by the Federal Communications 'boom,' as some have called it, but a logical and stable ex- Commission. With a transceiver of this type you can talk pansion. Barring defense emergencies, television for years back and forth with another party as much as eight miles to come wi!l be a rapidly growing, major business. Most esti- away. It is the 'walkie- talkie' principle made usable for mates on the retail value of annual receiver production by the public. It is a part of your future in radio. 1952 run atouna 45o iu,uvu,uuu. in we nex I. II VC yeura, a Ca "Before the war, about 4,000 television receivers were pect to see television at least a billion -dollar industry." AUGUST, 1948 la I The Radio Month

THE MOON AFFECTS radio trans- With the aircraft at altitudes up to ELECTRONIC PUSH BUTTONS are mission, according to a report last 10,000 feet, the rebroadcast signals used in a new elevator call system an- month by Dr. A. G. McNish of the Na- (sent out on channel 8) were received nounced last month by Otis Elevator tional Bureau of Standards. It is well at surprising distances with excellent Company. The push buttons at each floor known that propagation is affected by picture and sound quality. The en neees resemble the ordinary type, but do not the sun, but recent observations show say that it will be possible to get good move when ,pressed. Instead, the pres- that the moon is also a factor at cer- reception within a radius of 200 miles ence of the passenger's finger causes a tain times in certain parts of the world. from the transmitting craft. current flow in a small electron tube At Huancayo, Peru, where the effect The first stratovision experiments located in the plastic button housing. is very pronounced, maximum usable were made over 21 years ago; the re- The current makes the elevator stop short -wave frequencies averaged 1.7 mc cent tests proving conclusively the capa- when it comes to the floor. The tube lower three or four days after new moon bilities of the system. Westinghouse is lights up to indicate the call. than after the first or last quarter. developing it as a television relay The new control simplifies elevator Dr. McNish explained that just as the method in competition with co -axial system installation by doing away with moon raises tides in the ocean, it pro- cable, unattended relay stations, and about 40 relays in a typical 20 -story duces tides in 'the atmosphere and in other systems. building, as well as reducing the neces- the ionosphere. This explanation, how- sary wiring. Elimination of many me- ever, is not deemed sufficient by itself chanical parts cuts down failures. and more investigations are under way. ULTRASONIC VIBRATIONS force the evolution and growth of new kinds RADIO RECEIVER SALES dropped STRATOVISION tests conducted last of plants and insects, Science Service reported last tnonth. sharply in the New York area during month by Westinghouse engineers from the summer, according to dealer reports. a high -flying B -29 were highly success- The vibrations were produced at 400 Practically the only sets selling well ful. With television transmitting and re- kc by electrically driven crystals. They were the portables. ceiving equipment installed aboard the were used on three different kinds of plane, pictures and sound sent out by plants and on young fruit flies. Subse- TV COMMERCIALS have obstructed ground stations in Baltimore, Washing- quent growth showed genetic changes in any merger between television and the ton, and other cities were picked up and the plants and insects and alterations motion -picture industry, according to a rebroadcast from the bomber. in the heredity -carrying chromosomes. statement made last month by Howard Dietz, vice- president in charge of advertising and publicity of M -G -M. He JOHN F. RIDER, well -known publish- presented at a regular meeting of the predicted that ultimately movies and TV er of radio books, received a silver association attended by 1700 servicemen, would get together, but not as long as plaque last month from New York's was "in grateful appreciation of his programs were sponsored. Mr. Dietz warned that television was about to repeat the errors of radio by presenting only programs which can sell goods. He advocated a system where viewers would pay for programs or some method of keeping the advertising separate from the program material.

J 11111111111111111111111111111111111111111111111111111111111111111111111111111111111111 fl 11111 p- WATCH FOR THE NEW, IMPROVED RADIO -CRAFT COMMENCING with the September issue RADIO -CRAFT will appear in a new dress. It will not only be printed on high - Quality paper assuring good reproduction of illustrations. but it will also have color on a number of editorial pages. A number of other eye- appealing improvements will also be made in the magazine, including better printing. In addition to all this the magazine will be increased in size to 100 pages, thus giving the readers more interesting and valuable editorial material. Don't miss the coming issues of the new improved RADIO -CRAFT for up -to -date E. information in the radio and television field.

HIGH -FREQUENCY TV plans were *rASSOC.üED OAJiJ sER^-EvE com- 0F h.a T7Pn..11Z. announced last month by RCA. The pany will construct an experimental rde l ro.- television transmitter in Washington, D. C., to operate just above 500 mc to chtr' : Rider permit gathering information on u.h.f. ,.,r... s.ntcan...r video transmission. tt,. t.t, ,. ..,. -.?`¡,,,.".,wr Radiating on a channel of 504 -510 mc, -nn..,,.r - aw the station will have an output of 25 kw. It will duplicate programs of WNBW, Washington NBC television outlet, so that picture quality and reception conditions on the 500-mc band can be com- President Max Leibowitz of ARSNY presents a plaque to author and publisher John F. Rider. pared directly with those on the 66-72 - mc channel on which WNBW operates. radio repairmen, acting through their meritorious achievements in behalf of The station will be installed at the prganization, the Associated Radio Serv- the radio service industry during the Wardman Park Hotel where the icemen of New York, Inc. The plaque, years 1921- 1948." WNBW transmitter is located. RADIO -CRAFT for The Radio Monthh 19

45- MINUTE RECORDS containing The set, called the Candid T -V, contains entire symphonies on two sides were a 3 -inch picture tube. The aluminum demonstrated last month by Columbia cabinet measures 14 x 9 ,4 x 13% inches, Records. The new discs are made of and it can be carried from room to room vinylite and are played at 331/3 r.p.m. (a leatherette carrying case may be ob- instead of the usual 78. tained). The small viewing screen makes Known as Columbia LP (Long -Play- it especially suitable for personal use, since the viewer can sit close to the set. Twenty -one tubes are used and all 13 channels are covered. A switch changes tuning from the low to the high television band, and tuning on each band is continuous. Though the manufacturer has furnished no details, the tuner is said to use variable condensers, hereto- fore not used in v.h.f. television tuning circuits. a PHILO T. FARNSWORTH, Utah - born major figure in television development, was honored last month by the University of Utah and Brigham Young University. A medal from the Univer- sity of Utah was accompanied by a cita- McMURDO SILVER died at his home tion "for outstanding achievement in the near Hartford, Connecticut, June 18, field of science." At Brigham Young 1948. Forty -five years old at the time of University he was guest of honor at a his death, Silver was known to all radio- special "Farnsworth Day" celebration. men as a veteran designer, constructor and engineer as well as a manufacturer of high -grade radio components and JOHN MILLS, inventor, author, and more recently of test equipment. He was Dr. Peter C. Goldmark, Engineering Director, retired Bell Laboratories executive died head of McMurdo Silver Co., Inc. CBS, inspects a gold -sputtered master. June 14 at the age of 68. M;. Mills, Always a pioneer and never an imita- originally a teacher at the Massachu- tor of others, many of his original de- ing) Microgrooves, the records are made setts Institute of Technology and Col- with pitches of 224 to 300 grooves per velopments were adopted and became orado College, wrote the pioneering text standard over the whole radio field. inch, in contrast to the maximum of on radio, widely used by the Signal about 100 on present records. The high McMurdo Silver's first contribution to Corps during the first World War. He the radio art was the design of circuits cutting pitch, together with the slower was instrumental in developing the speed, provides the long playing time. which made the superheterodyne prac- magazine Bell Laboratories Record, and tical. Early superhets used a low inter- Although the discs cannot be played was the author of books on atomic with standard pickups, present home mediate frequency (30 kc). Silver con- physics as well as on radio subjects. Two ceived the Idea of using a much higher radio-phonographs can be equipped to of his most recent books were Elec- reproduce them with a small, inexpen- frequency and avoiding the difficulties tronics Today and Tomorrow, and The inherent in what were actually super- sive player. This contains,a slow -speed Engineer in Society. turntable and a pickup. The pickup is a sonic frequency amplifiers. The Haynes- newly -developed type of Rochelle salt Griffin superheterodyne, using coils de- reproducing cartridge with a semi-per- BLIND RADIO TEACHER and ama- signed by Silver, had an i.f. of 100 kc manent stylus of one -third the tip radius teur, Robert Gunderson, W2JIO, was and was the first of the modern supers. of standard needles. The needle pressure honored last month at a luncheon ten- In the mid -twenties, he combined with is only one -fifth ounce -far lower than dered him by the Association for the a distant relative to produce the famous that of any previous pickup. In conjunc- Education of the Blind on completion of Silver-Marshall line of high -grade radio tion with the frequency curve used in his 13th year as a radio teacher. receivers and later manufactured a line making the records, it will produce high - The blind radio teacher has trained under his own name. These Silver Mas- fidelity, wide-range response when con- several hundred sightless radio repair- terpieces were multiband radios which nected to a flat amplifier. The player was men and has helped over seventy to pre- combined the features of high -çlass developed by Columbia and Philco. pare for FCC amateur exams. His ama- broadcast sets with communications re- teur activity is intense-he is operating ceivers. A PERSONAL TV RECEIVER retail- four stations in New York and New More recently he was connected with ing for less than $100 was demonstrated Jersey at the moment -and he is also a Guthman Co. and with Fada Radio, of last month by Pilot Radio Corporation. radio inventor and consultant. which company he was for a time vice - president. At the time of his death he was manufacturing test instruments for the radio repairman. Besides radio, McMurdo Silver's hob- bies included yachting, polo and old guns. His collection of the latter was extensive, and he was an authority on the history of the Colt revolver. He was a member of the IRE and the Radio Club of America.

HAMS of the West Gulf Division, ARRL will hold their 18th annual convention in Houston, Texas, August 20, 21, and 22. ARRL headquarters representatives and members of the FCC, Army, Navy, and research departments The new "personal television receiver" which provides a picture for one or two viewers. of several universities will speak. AUGUST, 1948 Electronics 20 I

The Crystal Detector

Part Il- Crystals developed for radar are the results of experiments over many years

Fig. I- Compare the I N2 I and its early predecessor with adjustable catwhisker. By JORDAN McQUAY MODERN crystal cartridges - tors (Fig. 1) that were once a part of early experimenters were all but for- now widely used for detecting, every radio receiver. Development of the gotten. With vacuum tubes of greater mixing, rectifying, and other vacuum tube ended the crystal era, and efficiency, there was no need for crystal functions -had their inception by 1934 galena and carborundum de- detection in receivers operating at or- in the historic but simple crystal detec- tectors were toy novelties. The efforts of dinary radio frequencies. In 1934, Bell Telephone began experiments at their Holmdel, N. J., Labora- tories to explore the possibilities of using microwaves for communication purposes. Results of these early investigations clearly indicated that it might be possible to raise the upper limit of usable radio frequencies. Evidently, many new operating techniques would be required for microwave reception. In particular, detection posed a problem. Because of limitations imposed by in- terelectrode capacitance and electron transit-time effects, vacuum tubes would 1937 not function adequately at frequencies above 5,000 mc, and thus could not be 1934 1937 used to detect microwave signals. Since transit -time effects as well as capacitance effects are negligible in con- 1935 1937 tact rectifiers, the merits of the almost - forgotten crystal detector were recon- sidered. It proved to be the only satisfactory means of detecting extremely high-frequency radio waves. This 1934 search for suitable materials was somewhat simpler because of the exhaustive investigations conducted by Pickard and other pioneers at the turn of the century'. Engineers of the Bell Laboratories examined and tested over 100 materials and metalloids, 1938 1939 but only silicon and iron pyrites were found suitable for microwave detection. A point contact hard enough to prevent 1939 1939 formation of large contact areas under normal contact pressure was required. The metals finally chosen for the point contact were a platinum- iridium alloy and a fine tungsten wire -sometimes coated with a gold alloy. Subsequent experiments were concerned with improving the rectifying material, the rectifying surface, the i point contact, and the method of mount- 1940 !942 1942 !943 ing or housing the crystal detector. Many kinds of crystal rectifying devices were designed and used successfully at the Bell Laboratories during the following years. An indication of the Fig. 2- Crystal holders are often designed as an integral part of an electronic circuit. wide variety of types and structures is RADIO -CRAFT for Blectromics I21

CO -AXIAL INPUT By about 1939, knowledge o.'_ silicon and size of the first crystal cartridges BRASS BLOCK metallurgy was sufficiently advanced so developed in this country. The trend of that a uniformly active contact surface American design was toward a more INSULATING BEAD could be produced, and patient search- stable and sensitive silicon detector in ing for active spots was no longer nec- cartridge form, with the rectifying con- essary. tact adjusted and fixed during manu- RECTIFIER facture, so that crystal cartridges could INSERT CONTACT ' These crystal mounting blocks were used in many centimeter -wave experi- be interchanged and replaced easily. ments prior to 1940. Somewhat similar Also, simplicity of construction was de- TAPERED BRASS sirable for mass production, PIN apparatus was employed by Southworth and King in their celebrated experi- Following these general specifications, LOCKING work was begun SCREW ments with 25 electromagnetic horns'. by a number of de- The demountable rectifier inserts and velopment organizations, including the POLYST YRENE associated contact points also were used Radiation Laboratory of the Massachu- TAPE as straight detectors, as rectifiers for setts Institute of Technology and the IF AND u.h.f. test and measuring instruments, Bell Laboratories. OUTPUT and for other purposes. But the ability In the work at Bell, the shape and external features of the British DETAIL of crystal rectifiers to function as fre- cartridge OF quency converters in microwave super - were retained, but considerable changes CO-AXIAL CONDENSER process and were ASSEMBLY heterodynes was the chief reason for in design introduced their development during the war years to improve performance and simplify Fig. 3 -Early crystal converter assembly. which followed. manufacture. given in Fig. 2. Designs were generally Important changes included the substitution of fused high -purity silicon for dictated by the requirements of labora- An urgent wor need tory apparatus. Often the crystal hous- the "commercial" silicon of the British ing was an integral part of some elec- The outbreak of war greatly acceler- detector, to obviate any need for search- trical circuit. Other structures took the ated a vast national program of re- ing for active spots on the contact sur- form of replaceable cartridges. search and development of microwave face and to improve general perform- radar equipment. There was an urgent ance; use of diamond saws to cut the need for a standard type of highly sensi- rectifying element from silicon ingots, Mounting blocks tive crystal rectifier, to be used for fre- and subsequent prepar4tion of the con- An outstanding development of the quency conversion in radar super hetero- tact surface by careful polishing and Holmdel Laboratories, prior to 1940, was dynes at wave lengths of only a few etching; and development of a special a crystal detecting arrangement consist- centimeters. impregnating compound to protect the ing of a rectifier insert and a point con- Earlier in 1941, the British had de- cartridge from moisture and mechanical tact, both of which were demountable veloped for their radar receivers a small shock. and standardized. When used with a de- cartridge -type silicon mixer -detector' The result was the ceramic rectifier vice known as a crystal mounting block which pronouncedly influenced th shape cartridge', which was soon standardized (Fig. 3), the arrangement functioned as a mixer (or first detector) in the fre- Fig. 4- (Below) Cut- quency- converting circuits of micro- away a n d exploded wave receivers. In this way, a compara- views of a ceramic tively simple crystal rectifier alone pro- rectifier cartridge. Fig. vided i.f. signals within practical range 5- (Right) Crystal óe- of the u.h.f. superheterodyne receivers. lectors were used as The rectifier inserts consisted of small frequency converters wafers of silicon or iron pyrites, about or frequency changers 1 mm in diameter and 1 mm in depth, for soldered directly to brass studs. Silicon in radar systems gradually replaced pyrites, since silicon bombing and naviga- inserts showed less effects of frequency. tion in B-29 bombers.

911

RCYSTAL ,1 E Y.TENSIDN

CRYSTAL , ARTS RECTIFIER (En4ARGED) A

CAVITY

1 a RETAIN: NG ..UG AUGUST, 1948 Electronics 22 I and is substantially the same today as onto a wooden surface, immersing it in In particular, they are susceptible to when first manufactured nearly seven water, and rapid heating from subzero damage by discharge of static electrici- years ago. to high temperatures. None of these ty through the point contact. Also, dur- tests impairs the quality of the rectifier. ing manufacture, necessary close con -. Ceramic rectifier cartridge trol of mechanical dimensions is ex- Components of the ceramic rectifier Use of the cartridge tremely difficult. To eliminate or mini- cartridge (Fig. 4) include two metallic As a mixer or frequency converter, mize these limitations, the shielded rec- terminals separated by a ceramic in- the crystal rectifier has no competition tifier cartridge' was developed. sulator. The rectifying element is a at frequencies above 3,000 mc. It has a small wafer of silicon soldered to the frequency response hundreds, and some- Shielded rectifier cartridge lower base terminal. The contact spring times thousands, of times wider than Components of this improved crystal is attached to a cylindrical brass pin that of vacuum tube or other dry recti- cartridge are shown in Fig. 6. The rec- which is locked in position by setscrews. fiers, and requires no heater or plate tifier terminates a small co -axial line. This spring is made of gold -plated tung- supply voltages. The rectifying material is soldered to a aten wire formed into an S. The free In application, the rectifier cartridge small brass disc, which is fixed in posi- end of the wire contacts the polished produces a difference (intermediate) tion and connected to the sleeve or outer surface .of the silicon, and the tip is frequency between the r.f. signal and conductor of the co-axial line. The cen- formed electrolytically. The point usual- the local oscillator, which is then ampli- tral conductor -insulated with a Bake- ly is cone -shaped to maintain a contact fied and detected in later stages of the lite cylinder -terminates in a tungsten i of small area. superheterodyne. wire .002 inch in diameter and formed After assembly, the rectifying con- A typical use of the ceramic rectifier into a spring. The cone -shaped free end tacts are adjusted for optimum opera- cartridge as a frequency converter in an of this spring is in contact with the tion. The crystal cartridge is then im- airborne radar system is shown in Fig. polished surface of the rectifying ma- pregnated with a special gel filler, con- 5. This equipment was used in all B -29 terial. sisting of a wax dispersed in a hydro- bombers for navigation and for radar The contact point being inside the carbon oil. This compound prevents me- bombing. outer conductor, it is effectively pro- chanical changes in the contact point Similar types of crystal cartridges tected from accidental static damage as due to temperature contraction. Since it were used as low -power rectifiers in long as the outer conductor is grounded. excludes moisture, the compound also wave meters, probes, and other test The sleeve also shields the rectifying prevents electrical changes and serious equipment. Special types were developed contact from stray radiation. point corrosion due to high humidity. for direct detection of the video envelope Although developed in 1942, the As a final stage in manufacture, the of r.f. signals at low power levels. They shielded rectifier cartridge was not pro- efficiency of a crystal cartridge is im- have a distinct advantage over selenium duced and used on a large scale until proved by striking the side of the car- rectifiers, since they require no appre- much later in the war, when its ad- tridge sharply with a small hammer. ciable time to establish blocking action. vantage over the ceramic type was This simple procedure, known as tap- Some types for use at frequencies up demonstrated conclusively. It is likely ping, also reduces high- frequency con- to 100 mc have a current-carrying ca- that most future crystal rectifier car- version loss and noise. However, the tap- pacity from two to three times greater tridges will be shielded. ping operation is not a haphazard search than the 6H6 vacuum tube. These crys- As the result of research initiated at for a better rectifying contact, for, with tal rectifiers are Used as second detec- Purdue University and continued by a given material, the reaction is regular tors in superheterodynes, clippers, limit- various laboratories, shielded cartridges and reproducible. ers, diode modulators, and for many using germanium as the rectifying ma- Despite their apparently delicate con- functions normally accomplished by terial are available for relatively high - struction, ceramic rectifier cartridges diode tubes. power operation. These rugged types are have high resistance to mechanical and Although used widely and success- used for power rectification, d.c. restora- thermal shock. For example, production fully in many applications, ceramic car- tion, modulation and demodulation, tests include dropping the unit 3 feet tridge rectifiers have certain limitations pulse generation, and other heavy -duty purposes. Further development in this field will eventually produce crystals capable of superseding all diode vacuum tubes and other rectifying devices. References "Crystal Rectifiers and the Rix of Radio," Jordan McQuay, RADIO- CRAFT. Vol. XIX, July. 1949. ' "Metal Horns as Directive Receivers of Ultra - Short Waves," G. C. Southworth and A. P. King. Proc. IRE, Vol. 27, Feb.. 1939. Crystal rectifiers produced by British Thomson- Houston Co., Ltd. ' "Development of Silicon Crystal Rectifiers for Radar Receivers." J. H. Scaff and R. S. Ohl, Bell Sys. Tech. Jour. Vol. 26, Jan., 1947. OTHER BIBLIOGRAPHY: "Ultra-High-Frequency Techniques;" Brainerd, et nI, Van Nostrand, 1942. "Principles of Radar." Staff of MIT Radar School. McGraw -Hill, 1946. "Crystal Rectifiers." Radiation Laboratory Series, Vol. 15. McGraw -Hill. 1948. ASSEMPLY ,!N' 'H. F. Crystal Diodes," H. A. LeDuc, RADIO - IfTAL SILICON INSULATING CENTRAL CRAFT, Vol. XVII, Mar., 1946. WAFER CONTACT tlEAC CONDUCTOR 'Crystal Rectifiers," W. E. Stephens, "Met- tronics ", Vol. 19. July. 1946.

ACKNOWLEDGEMENT Grateful acknowledgement is made to the Bell System Technical Journal and the Bell Telephone Laboratories for permission to use historical information and reproduce certain photograph.. which originally appeared in the Janu- ary, 1947, issue of the Bell System Tech- Fig. 6 -This 1uctifier is protected against static by outer conductor. nical Journal.

RADIO -CRAFT fcr Ierdio-Scicncc r ) I `)) Image Magnifier Amplifies Light

ASTEP TOWARD the long- has been held to a gain of 20 times to dreamed-of electron telescope 'keep the tube's length down. is the image amplifier tube re- The conditions that confror.t the phy- cently developed by the X -ray sician in present day fluorcscopy are Division of Westinghouse at Baltimore. even worse than those enco intered in This tube is intended to brighten the finding a seat in a movie after leaving fluoroscopic images used in X -ray ex- bright sunshine. He has to Clark -adapt aminations. his eyes for twenty minutes to see the Fig. 1 shows how the magnifier tube fluoroscopic image. Even then with the works. X -rays which have passed low brightness available in difficult through the patient's body, just as in a cases, such as a large abdominal thick- Lenses and led in cross -section. standard fluoroscope, ness the strike a fluorescent where brightness may be as exposed to direct and scattered X -rays. screen. Behind this screen, on which is low as .00005 millilamberts, a Separation produced Even televising fluoroscopic images may the image of the patient's or- of 34 inch is necessary before contours well become practical. gans, is a layer of photoelectric ma- can be distinguished. Furthermore this The physician on terial. Each point the photoelectric '4 -inch figure applies only ir measure- TYPICAL ELECTRON PATNS'OLASS yACWM ENVEtIIPI surface emits electrons in direct propor- ments where the contour lines separate *RAYS tion to the brightness of the segment of regions with a contrast of 100 %, as in VIEWING the fluorescent screen facing it. contours between black and white. While SCREEN The electrons emitted by the photo- this is an extreme case it compares with electric surface are accelerated and 30 millilamberts brightness and .001 focused by the electronic lenses, to which inch contour separation as normal con- a high potential is applied. They strike ditions for observing X -ray plates. A ALUMINUM BACKED a second fluorescent screen at the small brightness of .001 millilamberts with a PHOSPHOR end of the tube. Here the image is much required contour separation of 1/32 inch LAYER 'WEAK LENSES brighter than on the original fluorescent is the center of the fluoroscopic range. FLUORESCENT SCREEN MAN LENS screen for two reasons. First, the ac- With the image amplifier tube at- Fig. 1- X-rays strike the fluorescent screen, celeration of the electrons has caused tached to .his equipment the physician releasing electrons which are accelerated by them to strike the small screen with will step into his dark room and see at the lenses. striking the smaller screen with great great force. This gives a brightness gain once an image almost as bright as on velocity and making a brighter image. of 20 times. a movie screen. He may still have to Second, reduction of the image on the dark -adapt his eyes, though ' for only will be able to perceive objects at pres- small screen to one -fifth the size of that three or four minutes, before he can ent indiscernible. on the large screen increases the bright- see all the details. What he sees after The image amplifying system is just ness. Since the same number of elec- that will be a clear, easily discernible emerging from the research stage. West- trons strike the small screen as come feature presentation of his patient's or- inghouse engineers warn that many from the large, their confinement to a gans at work. months of perfection and design en- smaller area increases the brightness of The future possibilities for amplified gineering remain to be done before the any given area. The brightness in- fluoroscopy are impressive. Both patient device is commercially available. The creases inversely as the square of the and doctor will save time and cut down research has, however, irrefutably prov- image size. Since in this tube, the image on the period during which they are en that it is practical and important. size is reduced by a factor of 5, the brightness is increased by the square of 5, or 25. Combining the two increases in brightness -20 due to electron acceleration and 25 due to size reduction -the total brightness gain is 500. By using an ordinary optical magnifying lens system to examine the small screen, the physician sees the image effectively in its original size. The present development is by no means a telescope since it reduces the size of the image to increase brightness. However, television scanning techniques could be used to break the picture down into a series of elements which could be amplified to any extent. Limitations of the optical magnifica- tion that can be obtained without loss of brightness make it unprofitable to reduce the electron image to less than one -fifth the size of the X -ray image in the present design. The electrostatic acceleration Dr. J. W. Coltman of the Wasiinghouse Laboratories adjusts the focus with a magnet. AUGUST, I94II Television TelevIsion Power Supplies Receivers now on the market may haue any one of several high -voltage supplies

By E. J. BUKSTEIN that differ in principle as well as in detail

al'HE availability of cathode -ray Note that the a.c. is fed into the cathode voltage may be obtained from an ordi- tubes on the war surplus market of the rectifier tube, resulting in a nega- nary receiver -type power transformer and the expansion of television tive output from the high -voltage sup- used in a voltage- doubler circuit (Fig. broadcasting have emphasized the ply. This is quite conventional, as cath- 3). Note that the center tap of the high - need for obtaining the high d.c. poten- ode -ray tubes are often operated from voltage secondary winding is not used. tials required for C -R tube operation. negative (grounded positive) power This permits use of the full end -to-end The potential required depends on the supplies. Because the cathode-ray tube voltage, which will be in the order of size of the tube: it may vary from 1,000 will draw only a small amount of cur- 800 volts r.m.s. volts for the small 2 -inch tubes to 30,000 rent, the voltage output is equal to al- As the diagram shows, one end of the volts for the tubes used in projection most the full peak value of the 700 -volt high -voltage winding is connected to the television receivers. There are several input, or approximately 1,000 volts. cathode of one rectifier tube and to the problems which do not exist in low- Also, since the current drain is small, an plate of the other. When this end of the - voltage supplies. Transformer insula- R -C filter employing 0.6 -µf condensers winding is negative, tube Vl conducts, tion and inverse peak voltage ratings of is adequate. charging condenser Cl. When it is posi- the rectifier tubes are the most im- tive, tube V2 conducts, charging con- portant. denser C2. Thus Cl charges on the nega- ooK 1V -1.2KV Since the beam current of a cathode - tive alternations and C2 on the positive alternations. These condensers charge to ray tube normally runs well below a 21V .2 quarter milliampere, the need is for a the peak value of the a.c. input; and 3011 ' since they are connected in series, the high- voltage, low- current supply. This 117VAC reduces the problem of filtering, because total voltage across both of them is over the amount of filtering necessary is a 600V 2,200. function of current drain. Since cur- 16 16 A type of high -voltage supply increas- rent requirements of the cathode -ray ingly popular in television applications is shown in Fig. 4. This is the r.f. power tube are very small, the filter condensers ' 5.3V TO 6x5 d OTHER FILS used in the high -voltage supply are con- supply. It is equally useful for oscillo- siderably smaller in capacitance than Fig. 2 -Dual supply with special transformer. scopes. The only basic difference be- those used in low -voltage supplies. How- tween this circuit and a conventional ever, the voltage ratings of these con- The supply shown in Fig. 2, typical of power supply is that r.f. is being rec- densers are of great importance; they those found in commercial oscilloscopes, tified, rather than the usual 60-cycle line must be adequate to prevent voltage requires a special power transformer. voltage. As shown in Fig. 4, the output breakdown. The high -voltage secondary winding is of the r.f. oscillator is stepped up by an conventional except that it is continued r.f. transformer. This high -voltage r.f. at one end to give an additional 450 is then rectified and filtered in the usual volts. The convenfional portion of this manner. The magnitude of the output secondary winding (400 volts each side voltage is determined primarily by the of center tap) is connected to an ordi- design and turns ratio of the r.f. trans- IRVAC nary full -wave rectifier circuit for the former. These transformers are com- low-voltage supply. Here again the fil- mercially available in ratings as high as tering should be adequate. 50,000 volts. Filtering is comparatively The top of the secondary is connected simple. Since the ease of filtering de- 6.3V TO 6X5 d OTHER FILS to a half-wave rectifier. The cathode is 850 volts (400 plus 450) above ground. .002 RF TRANS Fig. 1 -A supply for a 2- or 3 -inch C -R tube. Because of the small current drain, the 100K RV T he supply shown in Fig. i utilizes output voltage is approximately the full an ordinary receiver -type power trans- peak value of 1,200 volts. fo ner and can develop approximately Five -inch cathode-ray tubes such as 6BP1, 5CP1, 5CP7, 5UP11, etc., re- 1,00 0 volts. It is satisfactory for 2- or 3- the high -voltage supplies deliv- inc h cathode -ray tubes in television require power ceiv ers or oscilloscopes. ering approximately 2,000 volts. This T he transformer used in Fig. 1 de- live rs about 350 volts r.m.s. each side Fig. 4-R. . supply needs little filtering.

of t he center tap. Since the high -voltage sec ondary winding is grounded at one pends on frequency, and since the ripple end, 350 volts is available at the center frequency in this power supply is equal tap. The center tap is connected to a Q to the oscillator frequency, small filter half -wave rectifier for the low-voltage 17VAC components can be used with a saving sup ply. A good filtering system is nec- of money and space. es sary to reduce the ripple voltage suf- Another very common type of power fier ently. supply, the inductive kick -back type, T he total secondary value is 700 volts was very fully described in RAnio -Caarr r.mT.M. which is fed into a half -wave in January, 1948, and will not be further recttifier for the high -voltage supply. Fig. 3 -A voltage -doubler gives 2.000 volts. discussed here. RADIO -CRAFT for Television COVER FEATURE

"HMG SPOT" C-fi TUBE

A new lantern for many television chores

TELEVISION station call letters, picture being scanned. This phototube test patterns, and pictorial pro- output is the video signal which is then gram material may be broadcast, sent to the transmitter for radiation. without using expensive and elab- The flying -spot principle is not new- orate studio cameras, with the help of it was one of the first systems of tele- the recently designed "flying- spot" cath- vision transmission used in experiments. ode -ray tube shown on our cover. Any A rotating disc and light source pro- Fig. transparent or opaque slide can be duced the flying spot. It is, of course, RCA 5WP15 transmitted with the half -tone fidelity much simpler and less expensive than an of photographic film. iconoscope. Until the development of the The new tube is not a camera tube, new 5WPI6, however, an all -electronic would be there in a slide projector. but is a source of light, and is very much flying spot was not used, due to several On the same chassis as the slide hous- like an ordinary cathode -ray picture operating difficulties. ing is a video amplifier into which the tube. The extremely intense spot of light One of these troubles wa:s "trailing." output of the phototube is fed. Above which travels over its face is projected When a cathode -ray tube it, made with that is a chassis containing a 20,000 - through a transparent slide containing most ordinary phosphors, there is an ap- volt power supply for the flying -spot the picture. As the spot scans the slide, preciable time delay in the buildup and tube and a scanning amplifier. Controls the light variations produced by the pic- decay of light. When the electron stream are provided for vertical and horizontal ture are picked up by a multiplier photo- strikes a particular spot on the screen, frequency, size, centering, linearity, and tube and transmitted as video signals. a certain time is required for visible electrical focus of the spot. The tube, designated 5WP15 by its light to appear. If this held true in a At the top is equipment for synchro- makers, the Radio Corporation of Amer- flying -spot scanning system, the photo - nizing signal amplification and a 900 - ica, is shown in Fig. 1. It is about 11% tube would not receive the full amount volt regulated supply for the phototube. inches long, and the flat fluorescent face of light as soon as the spot moved from A 350 -volt supply is in the bottom of the is 5 inches in diameter. a dark to a light area of the slide. The rack. Ordinarily, this 7 -foot rack, which Fig. 2 shows how the tube is operated light would build up only gradually, and contains everything necessary for op- to transmit the picture from a trans- the received picture outlines would be erating the flying-spot transmission sys- parent slide. The spot travels just as in blurred -the black areas would trail tem, is covered with steel panels. the standard television system-525 over into what should be a white area. lines interlaced, 30 frames per second. Decay of the light on a pa ticular spot VERLEHORIZ.SAW1OOTM NORIZ.OUT. AMP. MULTIPLIER spot is focused on the slide, GENERATORS & YERTKAL +- 6 HIGH VOLTAGE PHOTOTUBE The flying of the tube face also took time with the OUTPUT AMPLIFIERS POWER SUPPLY POWER over which it travels, by the objective old -style cathode -ray tubes. If that were SUPPLY lens. As the spot passes through each true in this system, the phototube would t VERT. NORIZ. portion of the slide, the transmitted still be receiving some light after the SCANNING SCANNINO light varies with the density of that por- spot had passed from a white to a black tion of the picture. The light strikes a of the picture. The white in the re- ANODE N'2 area YIDEO AMP.WITN EOItLIZER multiplier phototube type 931 -A, whose ceived image would then tend to trail TO GRID N. I output corresponds at every instant to over into the black. The trailing in pre- is the intensity of the portion of the slide vious systems could be remedied to a - -OBJECT BI DErL.YOAE LENS large extent by high -frequency equaliza- /ULTRAVIOLETULTRAVIOLELSAPS T SAPS SLIDE / FILTER tion in the video amplifiers following the COND. LENSES phototube. However, complex and costly TO LINE AMPS.. equalizers would have to be used. a phos- SYNCHRONIZING MIXED BLANKING_ BLANNINGI The new flying -spot tube uses 514.4EN. SIGNAL AMPLIFIER phor known as P15, which has extremely short persistence, to reduce trailing. In Fig. 2 -Block diagram of flying -spot system. addition, most of the light, emitted is When opaque pictures are to be trans- near the ultra- violet region, in which mitted, operation of the system is very persistence is much shorter than in the similar to that used with transparent visible region. This reduces the trailing slides, except that the phototube picks further. To achieve the maximum bene- up the light reflected from the picture fit, an optical filter is used to screen out instead of that passing through it. With all rays except the ultra -violet. This opaque pictures, the signal is not quite filter is shown between the condenser as strong as with transparencies. lenses and the phototube in Fig. 2. With Interesting effects can be obtained this arrangement only one inexpensive using flying -spot scanning for pictures high -frequency equalizer need be used in or titles used as program material. One the amplifier to give a clear picture and picture, for example, can be superim- an excellent signal -to-noise ratio. posed on another. To do this, the flying - This month's cover shows an actual spot tube, instead of giving a constant - system using the flying -spot tube. The intensity light spot, is modulated by a engineer is adjusting the knob which picture signal. The light caused by this sets the height of the tube for proper first picture, which appears on the tube focusing of the spot on the slide, which face, is then transmitted through the is in the projector -type housing just slide to the phototube. The phototúbe above it. The phototube is mounted be- output contains both signals, one super- RCA's Carolyi Tufts adjusts the tube's height hind the slide, instead of the lamp which imposed on the other. AUGUST, 1948 .b1 Test Instruments Radio- Frequency V. T. V. M. A valuable instrument for aviateurs, radio servicemen, and constructors

By A. A. GOLDBERG

miniature twin diode keeps capacitance Cvi small. Capacitance C. can be kept within tolerable values only if extreme care is used in the construction of the probe. The probe's voltage output can be fed only into an electronic d.c. voltmeter. An excellent circuit for this purpose is the balanced-bridge type, Fig. 2. The cathode -current drop across R3 and R4 Sloping -panel mounting improves appearance. causes the static cathode potential to be +5 with respect to ground. Since the MANY radio measurement prob- grids are at ground potential, the re- lems can be solved efficiently sultant grid bias is 5 volts negative. with an r.f. vacuum -tube volt- Rear view. The probe is connected at left. Under static conditions, the bridge is meter. For those who build balanced and the voltage between points their own receivers, the voltmeter makes available. O r d i n a r y a.c. voltmeters A and B is zero. If the probe output accurate stage -gain measurements pos- (which are most accurate at 60 cycles) voltage is 100, the grid of V3 becomes sible. It will show instantly if the loial may be used as calibration standards. 100 volts negative with respect to and beat oscillators are operating and The R -C time constant is therefore ground. This decreases the V3 cathode with what efficiency. made long enough to prevent excess current until the voltage at A becomes Transmitter power output can be de- charge from leaking off Cl to cause in- -95 with respect to ground. As point B termined by measuring the voltage accuracies at 60 cycles. is still +5 volts, the difference between across a 75-ohm noninductive resistor Certain limitations prevent using a A and B will be 100 volts. If resistor Rm connected to the output terminals. The very large capacitor and resistor to is 600,000 ohms, a 200 pa meter will power is then calculated by the formula: make the R -C time constant extremely read full scale. W = E' /R. long. First, the capacitor must have The bridge circuit has several ad- Adding a pickup stub or tuned circuit very little leakage, which precludes the vantages: It is independent of plate - converts this voltmeter to a very sensi- use of electrolytics and the larger paper supply voltage variation. It is inde- tive field- strength indicator. capacitors. The physical size of the pendent of tube aging, due to circuit large paper capacitors also causes more degeneration. It protects the meter, if r4p: shunt capacitance which reduces the Rm is too small. Full voltage cannot high- frequency limit. build up across points A and B. Capacitance is the most important The actual circuit used is shown in RI Fig. 3. The second section of the 6AL5 EDC high- frequency limitation. Any shunt capacitance appears as a reactive corn - is used to balance out contact potential ponent in parallel with the normal in- on one grid of the 6SN7 by applying an put resistance. Since capacitive resist- equal contact potential to the other grid. ance decreases Although it is not absolutely necessary, Fig. Problems of h.f. voltage measurements. with frequency, a point I- is reached where the total input imped- a contact -potential zero control has been The instrument is an a.c. voltmeter ance becomes low enough to introduce provided. This control has a screw- which reads accurately between two fre- considerable error. It is therefore im- driver adjustment and is mounted below quency limits. The low-frequency limit the chassis. 6.8- megohm is determined by the input resistance - The probe resistors are capacitance time constant, while the isolation resistors. The resistor between high -frequency limit is determined the plates of the 6SN7 prevents any pos- largely by the input shunt capacitance. sible parasitic oscillations. In Fig. 1, alternating voltage Esc The power supply delivers exactly 300 causes diode V1 to conduct' on the posi- volts output. If any other power trans- tive half cycles only. During the nega- former is used, the 6,800 -ohm resistor tive halves, capacitor Cl, charged to ap- should be adjusted until the output is proximately peak voltage of E.c, dis- exactly 300 volts. Two 100,000 -ohm 2- charges through resistor Rl. The time Fig. 2- Fundamental circuit of v.t. voltmeter. watt resistors divide the output into constant of Rl and Cl, however, is so +150 and -150 volts. high that Cl loses very little of its perative to reduce the shunt capacitance There are five voltage ranges: 0-1, 3, charge before the next positive half to a minimum. These capacitances are 10, 30, and 100. These ranges suffice for cycle recharges it. the inherent resistor capacitance Ca. most work in which an instrument of The longest R -C time constant con- and CR., diode plate capacitance Cvs, and this type is used. Multipliers for each sistent with the lowest frequency to be wiring capacitance C.. The first two are range are a combination of approx- used is desirable since variable voltage minimized by using the smallest metal - imately 80% fixed and 20 %variable re- at 60- cycles a.c. is usually the handiest ized resistors available. Using the 6AL5 sistors. The large variation range per- RADIO -CRAFT for Test Instruments 27 mita recalibration in case of tube tulle. A surface -mour t -type power changes and aging of parts. An a.c. out- transformer eliminates the need for cut- let is provided at the rear of the chassis ting a large rectangular hole in the for use by other instruments. chassis. The power transformer is placed as far as possible from the sensi- Constructing probe and chassis tive meter to avoid demagnetizing it. Instrument efficiency depends largely Arranged across the middle of the upon good engineering of the probe. chassis are the five multiplier potentiom- This probe (Fig. 4) requires some lathe eters. The fixed -resistor portions of work, but the appearance and perform- the multipliers are mounted on terminal ance make it well worth while. For strips. those who have no machine tools at The 4 -inch square meter has two their disposal, any local machine shop scales marked 0 -10 and 0-30. These are will turn out for a nominal sum the two for the 10 -, 30 -, and 100 -volt ranges. The simple parts required. 1- and 3 -volt ranges seing nonlinear, The body of the probe is made from corrected scales must be used with these a 3',4 -inch length of 1 -inch outside two ranges for greatest accuracy. Al- diameter, thin -wall, durai pipe. Square though these scales can be drawn on the the ends and remove the burrs. The meter face, the author found it more Bottom view shows how the parts are placed plastic end is machined from a 2 -inch convenient to mount separate correction (6) With the contact -potential zero con- length of 1 -inch round polystyrene rod. curves on the front panel. The dial plate trol beneath chassis, zero the meter Drill a No. 28 hole through the center and correction curves were reproduced once more. This adjustment bal- of the plastic for a 6-32 brass screw. photographically. ances the diode contact potential. Measure the diameter of the .03 -µf, 400 - set 100 volts, way (7) With range switch at volt paper capacitor and bore half Calibration feed approximately 80 volts to the through the polystyrene from the flat Calibrating the r.f. vacuum -tube volt- probe input. Adjust the calibration end to provide a snug fit when the ca- meter is simple. Any step -down trans- control until meter reads correctly. pacitor is inserted. The rear plug is also or resistance voltage di- at the 80% point is the may be ma- former, Variac, Calibration made from polystyrene. It vider connected across the a.c. line can best compromise for any possible chined for a press fit into the durai tube of voltage. One con- Make be used as a source error. to eliminate holding screws. sure venient source of low voltage is a uni- the hole through which the cable passes (8) Calibrate the 30- and 10 -volt scales versal tapped output transformer. Be- in a similar way. is a snug fit. a into fore starting calibration, obtain (9) Because of nonlinearity in the S- Insert the front polystyrene part with close- matched triode ele- No. 42 6SN7 tube and 1 -volt ranges, plot a correction the durai tube and drill three ments, for a better -balanced bridge cir- .holes, 120 degrees apart, through the curve of voltage input versus meter - t oat cathode - the plastic cuit. Also make sure the reading. This curve may later be durai and plastic. Remove heater leakage is low in both elements. for 4 -40 screws. Enlarge the transferred to the meter scale, if.. and tap it One way to determine t ois is to measure holes in the durai to clear the screws. at desired. with shield- the (hot) cathode -heater resistance The cable is triple -conductor the tube socket with an ohmmeter. (10) Place a .dab of coil cement on the ing braid and rubber covering over all. multiplier potentiometer shafts to A polystyrene socket is used with the Actual calibration is done as follows: prevent accidental turning. 6AL5 tube to eliminate the inconven- (1) Set the meter needle to zero with 8. MEG HEAVY WIRE SOLDERED TO ience and danger of cracked glass. Sol- the meter -zero screw. BRAID der the resistors as close to the socket (2) Turn the instrument on and allow as possible, but take care to prevent about 30 minutes for warm -up. melting the plastic. Arrange the resis- (3) Disconnect the probe from the e-727CR WHACK 6.6MEG ' TUBE POE NE the tube co- tors and leads to support chassis, and temporarily connect a Fig. 4- Ground dural tube to shield braid. axially with the metal probe shell. 20- megohm resistor from the pin metal capacitance of the probe The v.t.v.m. is built into a No. 4 grid of the 6SN7 to ground. The input 8 x 8 x 8 -inch, sloping =front cabinet is 8 µµf. This capacitance may be- 2 -inch (4) Set range switch on 1 -volt scale and at very high fre- which accommodates a 7 x 7 x -panel come bothersome chassis. All components are placed for zero the meter with the front quencies. One way to lower it and raise the shortest leads consistent with good zero control. the input impedance is to connect a 390 - wiring practice. The probe receptacle is (5) Reconnect the probe and remove ohm metalized resistor in series with in the rear directly behind the 6SN7 -GT temporary grid resistor. the probe. This impairs accuracy slightly, but where the meter is used solely as a peaking device little is lost. 1

SMEG 02 600V A2 3 óoovt 2:ROCONT 500WW

I 20MEG IN WW 2.2K

35K ww 12 X

o151{ WW' 47K

S L 6SN7 FIES ---r---..6.3m IA -150V

The are screwdriver -adjusted. Fig. 3- Complete schematic of the r.f. instrument. Probe connections are I 2, 3, and ground. Top view. pots AUGUST, 1948 28 Test Instruments;

AUDIO OSCILLATOR

HflS SIflOLE COfiTBOL

By RICHARD D. HENRY

THIS audio test generator is simple this will crowd the high end of the turned to the frequency -determining to operate, easy to build, and inex- scales. The four capacitors used in the network as positive or regenerative pensive. It is tuned with a single frequency network and the two 22,000 - feedback. The resistor value is increased variable resistor, rather than the ohm resistors need not be matched; they until just enough feedback voltage is usual ganged capacitors or potentiom- need be only roughly equal to the values created to cause oscillation. Too much eters. No accurately- matched fixed resis- shown. feedback would spoil the waveform. The tors or capacitors are needed. Only two The coupling method used between amplifier is then kept at the same output tubes are used, in addition to the power- the two sections of the 6SN7 is interest-. by the large grid and cathode resistors. supply rectifier. Output level is constant ing. The right -hand grid is grounded for To help equalize the gain of the two within 2 db from 40 to over 12,000 cycles. audio through a 0.1 -µf capacitor. The triodes, most of the grid resistance is Wave form is as pure as that of the best 5200 -ohm cathode resistor (common to common to both. R -C oscillators, which means that almost both cathodes) is unbypassed. Audio Output is taken from the same plate perfect sine waves are produced. voltage appears across this as the result that supplies the feedback. The two The circuit, adapted from one pub- of audio changes in the plate current of 10,000 -ohm resistors are a voltage divid- lished in Wireless World, a British mag- the left triode. er, and the voltage taken from between azine, uses a modified parallel -T fre- All that is required to modulate a them is R-C- coupled to an ordinary 6J5 quency network. Instead of the special tube is an audio voltage between its amplifier. Although useful output can be 'lamps used as cathode resistors in most grid and cathode. Usually the voltage taken directly from the 6SN7, the 6J5 R.0 oscillators to keep output constant, is placed between the grid and ground, prevents a low- impedance load (or one this model employs an amplifier for the with the cathode grounded for audio. that is not entirely resistive) from hav- purpose. Here the cathode- resistor voltage ap- ing any effect on the oscillator. It also The diagram is given in Fig. 1. The pears between the right grid and gives a larger output voltage. The out- 6SN7 is a 2 -stage feedback amplifier. cathode, but the grid is grounded. Such put side of the 6.15 is conventional, but The frequency- determining components grounded -grid amplifiers are often used it adds the convenience of a low-im- are shown within the dashed box. A 3- today, but usually at v.h.f. and u.h.f. pedance tap. R4 is the output volume circuit 2- position switch selects one of If the 3,000-ohm variable resistor R3 control. two ranges. The lower covers 40 to 850 were reduced to zero, both plates would cycles, and the higher 850 to over 12,000. be at ground potential for audio, due to Construction details R1 is the frequency -control potentiom- the bypass capacitor Cl. Increasing the The 15 x 11 -inch metal cabinet was eter and R2 is a trimmer used to ad- resistance of R3 places the right -hand on hand, so a 3- inch -high chassis to fit just the ranges so that they overlap. Rl plate slightly above ground, allowing a it was procured. This is really much is a standard audio volume control. Do small output voltage to appear between bigger than necessary; a smaller hous- not use a control with a linear taper, as the plate and ground. This voltage is re- ing and chassis would give plenty of

The controls visible in the center ara R2 and R3. Potentiometer in center controls the frequency. RADIO -CRAFT for Test Instruments j29 room for the few components, yet leave JIOK 10N/SOMA more room on the test bench for such /6S147 -GT 7K other essential items as the amplifier or 524 receiver under test. 22K

The chassis -top view shows the tube 111 layout. The 6SN7 is at the front of the chassis on one side and the 6J5 is on the other. At the rear are the rectifier tube, the power transformer, and the filter 2.2MEi choke. If a smaller chassis is used, be .0005 sure to separate the two inductors as 5.21. SW much as possible from the 6SN7, since VIII YAC the oscillator will tend to lock in with the power supply frequency if there .is I LO any hum pickup. resistor, The tunipg .005- -a R1, is mounted on an angle bracket Fig. I -A single potentiometer controls the fre- about two inches behind the panel. R3 is I .1 quency of this oscillator over its two ranges. beside Rl, R2 behind it. Both of these are screwdriver- adjusted. lower frequencies of each band, but will If the calibrating oscillator is not The under-chassis view shows the extend the highest frequencies. In effect, continuously variable, the known and parts layout. There is nothing critical therefore, it extends the coverage of unknown frequencies can be fed into the here although if leads are too scrambled each range. Do not make R2 any smaller scope and the resulting Lissajou's pat- there may be some instability or un- than necessary for adeçuate overlap. It terns used to determine the harmonic desired oscillation. In the model, the may be necessary to readjust R3. relationship existing between the two leads from the range switch (which is oscillators. Adjust the oscillator to be concealed by the resistor -capacitor Calibration calibrated so the oscillographic pattern mounting board in the photo) were Calibration is best dcne with the aid stands still. Count the number of peaks scrambled, but a 100 -µµf capacitor, C2 of a borrowed oscillator with accurate or loops touching the vertical and hori- in Fig. 1, stopped all trouble. This frequency markings, and an oscilloscope. zontal axes. The ratio of the numbers capacitor may not be necessary in other Feed one oscillator to the vertical input is the same as the ratio of the two fre- models. Use no shielded leads. of the scope and the other to the hori- quencies. The dial is a National ACN, again zontal input. Set the borrowed oscillator Calibration by eat is not too accurate, because it happened to be on hand. It to 50 cycles, then slowly adjust the new especially at the higher and lower fre- poses a slight problem, since it provides one until a stationary O appears on the quencies. In a pinch, however, it can for only 180 degrees of rotation, while scope, indicating that the two oscillators be done. If another oscillator is not the tuning potentiometer, of course, has are tuned to exactly the same frequency. available, a piano can be used for a a 270 -degree range. This problem is Mark this frequency on the dial scale, rough calibrator. Middle A is 440 cycles solved as shown in the following para- then go through the res- of the range in and each octave doubles the frequency. graphs. the same way. Dependir g on the precise A scope can be used, of course, with- phase relationship of the two oscilla- out another oscillator, to give multiples Adjustment tors, the O may be slanting. of the line frequency. After the unit is built and voltages are checked, let it warm up for a few minutes, then set the range switch for the low frequencies. Set R1 in the mid- Impedance Measuring Methods dle of its range, then slowly increase the resistance of R3 until a tone is heard. By RUFUS P. TURNER Rotate Rl over its range with the switch in both positions. Advance R3 until os- when they are bypassed internally cillation is smooth at all times and until AWELL -KNOWN arrangement for cially an a.c. voltmeter placed across the high - measuring impedance requires only to the power line), difficulties arise be- impedance output terminals shows that a decade resistance box (or calibrated cause different points in the test circuit the ratio of minimum to maximum variable resistor), high-impedance a.c. are effectively at ground potential. This voltage output at the lowest- and high- vacuum -tube voltmeter, audio oscillator, has the effect of placing a shunt loop est -level points does not exceed about and s.p.d.t. switch. The connections for around either the unknown impedance 1:1.25 (2 db). the test circuit are shown in Fig. 1. or the calibrated variable resistor. R1 should be connected so that fre- The circuit shown in Fig. 2 overcomes difficulty by providing a single quency rises with counter -clockwise ro- S AUDIO OSC. this tation to take advantage of the taper I ground point which is common to both and spread out the high frequencies. If instruments and to the test circuit. The when the ACN or some other 180 -degree dial CONNECT UNKNOWN IMPEDANCE NERE test procedure using this circuit Is is somewhat different. Throw switch S used, set the switch on the low range and turn the pot slowly to the left. No- 4 i back and forth, adjusting the calibrated Rg.I standard impedan..e -measu ing setup. tice that during the last several de- -A resistor R. Stop the adjustment when grees of rotation, there will be very little The test procedure is to throw the the voltage read with the switch at po- change in frequency. Leave the poten- change -over switch S back and forth, at sition A is exactly one -half the voltage tiometer set at the point where the fre- the same time adjusting the calibrated at position B, and read the unknown im- quency change becomes very slow. Set resistor R. When the meter deflection pedance value from the dial of the cali- the dial to the left end of the scale, then shows ne change as the switch is thrown brated resistor. tighten the setscrew. from one position to the other, the un- Now see if the lowest note of the top known impedance is equal to the resist- range is lower than the highest note of ance of R and may be read directly from thg bottom range. If not, hote the low- the resistor dial. est note of the top range, retune to.the This scheme is widely used, and pre- s highest frequency of the low band, A ONO TERMINALS and sents no difficulty when either the volt- CONNECT UNKNOWN IMP. NERE decrease the value of R2 until the fre- meter or the oscillator is battery -oper- quency is high enough to give overlap. ated. However, when both of these in- R2 will not have much effect on the struments are a.c.-operated (and espe- Fig.2- Improved impedance- measuring method. AUGUST, 1948

s:::s-..... Audio

looks F ° #O #One comele #ed I lHow #he

Y' looti°4eoses t Which tob e d toe\ectrtc Aoeonten-keyed hee\ Ph tone MAN E BY Y

THE Fototone is an unusual musi- the note produced is C, the succeeding on the tone disc revolving underneath. cal instrument which -as its name rings will give succeeding notes of the C- At front center the motor is mounted implies - uses the photoelectric major scale. Since there are 10 rings, the upside down so that its shaft goes principle to produce tones. It is highest note will be E of the next octave. through the Masonite base. The tone disc shown in Fig. 1. This case contains the If motor speed is changed so that the is attached to the shaft just under the keys, the mechanism, the photocell, and lowest note is D, for example, the other base with the spots facing up. At the two controls- tuning and volume. notes will form a D -major scale, ending front left is the rheostat which controls Fig. 2 illustrates the principle by at F- sharp. which the instrument operates. A tone In the actual instrument there are 10 disc (shown in the photo, Fig. 3) con- separate lamps,each positioned to beam A tone -wheel cannot be printed without sists of 10 concentric rings of black dia- a small spot of light on one of the con- some distortion due to the curved plates centric rings of bi ck spots. The photo- used in printing any large magazine. There- mond- shaped spots. The spots are equal- fore the authors have arranged to supply ly spaced within each ring, but the num- cell is so placed that all light reflections from the disc will reach it. The tone pro- accurate discs at a cost of $1.00. A complete set of blueprints will be supplied with UY duced then depends on which lamp is. each disc. Address Lyman Greenlee, do lighted. The keyboard holds 10 keys, 25 Broadway; New 930 RADIO- CRAFT, West each of which is a momentary -contact York 7, N. Y., enclosing a $1.00 postal note. PENLIGHT switch connected to one of the lamps. Fig. 4 shows the top of the Fototone with the cover removed. The vertically - motor speed, and at the right the volume mounted chassis at the rear contains the control. preamplifier and wireless oscillator Layout for each of the lamp holders is 'TONE DISC (described later). On its front are the given in Fig. 5. The metal used is thin u oscillator -rectifier-amplifier tube socket sheet brass. After drilling the holes ac- 'TRW IT MOTOR (left) and the phototube socket (right). curately, nick them as shown with a I111v IN/SOW The lamps are mounted, five in each of small file or hacksaw, and then roll the -, two brass holders, so that their light corners of the nicks in opposite direc- T will shine down through the oblong hole tions to form a rudimentary thread, Fig. 2- Reflected light excites phototube. ber of spots -and the spacing between consecutive spots -in each ring is different. To return to Fig. 2, the .disc is rotated by a motor. The spot of light from a small flashlight lamp is centered on one of the concentric rings. A photocell is placed where the reflection of the light will hit it. When the disc revolves, the reflection of the light from the disc will not be steady; each time a black spot comes under the light spot, there is no reflection. The reflected light pulsates, the pulsation frequency depending on the number of black spots passing under the light spot in a given time. The photocell picks up these pulsating reflections. Output of the cell is amplified and fed to a loudspeaker, where the pulsations appear as audio tones. The tone disc is designed so that if the light spot is centered on the inner ring and motor speed is adjusted so that Fig. 3- Bottom view of the Fototone, with the tone disc shown in the left foreground. RADIO -CRAFT for audio I31

the corners engaging in the threads of the flashlight lamps. Bend the strip of brass in the center along the dashed line. The unpunched half will go under the Masonite base, over the edge of the oblong hole to fasten the lamp holder in place. The layout for the Masonite base is given in Fig. 6. Reference to Figs. 3 and 4 will show what each hole is for. No holes are shown for the motor, since this will depend on the particular motor used. Any motor whose speed can be varied by a series rheostat is satisfactory. Mounting holes for the chassis are likewise omitted. The lettered holes at bottom are for the 10 key contacts. These are brass rivets or screws, which should be put in place before the keyboard is attached. Each key is made as in Fig. 7-a. The top is Masonite and the end is wood. Cut, drill, and slot a piece of bronze weatherstripping, as shown in Fig. 8, to make the key contact strip. Mount it to the base with a % x 9 -inch strip of Masonite to hold down its rear edge. Fig. 4 -Top view, showing lamp mountings. Inside of phototube shield should be blackened. N 1/2 FACIE mounted in their two brackets. The Paste the photographic print of the brackets are a common contact for all tone disc on the aluminum, being ex- the base shells, and strips of spring tremely careful to match the center of M/e metal contact the tip of each lamp. the print to the center hole of the alumi- One side of the battery is connected to num. Use Duco cement or something -.I 1.1/2 both brass lamp holders. The other side similar, but don't use too much. The á/s l.- 2 S/S I ' DIMENSIONS IN INCHES is wired to the bronze Contact strip for finislied disc must be absolutely undis- Fig. 5 -Each holder takes 5 screw -base lamps. the keys. Then each key contact (the torted, with no lumps, wrinkles, or other rivet or screw mounted under the key variations. on the Masonite base) is wired to the The motor shaft should project down brass strip which contacts the corre- through the Masonite base in the hole sponding lamp. Note from Fig. 6 that marked X in Fig. 6. Disassemble the mo- the lamps are staggered (C on the right, tor and thread the end of the shaft, D at left, etc.). The letters indicate the either on a lathe or with a die. After re- notes for each key and lamp; corre- assembling the motor and mounting it spondingly lettered studs and lamp con- atop the base, fasten the disc to the tacts should be wired together. When shaft with a pair of nuts. Adjust the en- the lowest key is pre tsed, the front tire motor and disc mounting so that the right-hand lamp should light, and so on. disc will run true without wavering. Now prepare the tone disc. Past ex- Each lamp is coated with black paint perience has shown that this cannot suc- except for a small clear spot at the tip. cessfully be duplicated from a magazine o -.r- 3/8. illustration; the authors will, therefore, D E F G A B C' D' E' supply discs at cost. See box on page 30. ®or- L Be very careful not to crease or bend Fig. 8- Cement key to contact strip. the disc. Get an 8 -inch aluminum - base instantaneous- recording disc ("ace- tate") and remove the black lacquer

coating by immersing the disc in warm Fig. 6 -The motor shaft projects through "X ". water for a while before peeling off the coating. The aluminum disc can be cut

YASoNITE SJAIP from sheet stock; but if this is done, the center hole must be very accurately e placed. Fig. 9 -Input circuit for phototube amplifier.

5/e KEY CONTACT f SPRING METAL KEY CONTACT SUP ANTENNA- WnELESS PHONO OSC s 11717-GT 15/16 .OS 6008 DIMENSIONS IN INCHES Fig. 7-Keys are constructed as in a and OOP! I MEG . -.J' rUTP mounted on contact strips as shown at b. This Masonite strip is shown in a side view in Fig. 7 -b. Now bend up each of CHASSIS GND the 10 projecting strips so they do not touch the key contacts which are on the 6W base. Using Duco or a similar cement, fasten a key to each strip. Refer to NTYAC ®SI .05 /600V Fig. 7 -b for the completed arrangement. Figs. 3 and 4 show how the lamps are Fig. 10-A standard 3- wilding phono oscillator coil is used. Bleeder supplies bias for 930. AUGUST, 1948 32

Simple Tracer - Amplifier

By HOMER L. DAVIDSON

gram), a .03 -µf paper capacitor couples with the simple R -C power supply filter. the incoming signal to the grid of one Hum is negligible even with the larger of the triode units of a 6SN7-GT. Since speaker. Both sections of the filter ca- this amplifier is used as a signal tracer, pacitor and the 6V6 -GT cathode bypass the blocking capacitor is needed when are in the same can, mounted next to the checking the audio signal in a defective power transformer, as the chassis photo receiver where B- voltages are present. shows, to eliminate overcrowding. The amplified signal - Volume control projects through cabinet. is resistance capacitance- coupled to the grid of the EXT SPKR primarily to test de- second triode section of the 6SN7 -GT. 8SN7-GT 8V8-GT CONSTRUCTED A 01 fective record changers and as a half -megohm volume control is used. 27 500K signal tracer, this small utility amplifier The power output stage is a 6V6 -GT Di has greater possibilities. It can be used beam -power amplifier with the screen - Oì as a small PA system, as an amplifier grid operating at a little lower voltage DE- E for small receivers when greater output than the plate. An output transformer is desired, and for call systems. (8,000 ohms primary impedance) is Since the amplifier had to be compact coupled to the 6V6 -GT with a switch- za zsv enough to be carried around as a test ing arrangement on the secondary side. instrument, careful selection of tubes With this the built-in 4 -inch PM speaker and parts was necessary. It was con- can be put in circuit when the unit is S 450w 25K 6X5 -GT structed on 4 x 6 a -inch chassis. The used as a signal tracer or small am- z 1K/2W cabinet is 5% inches in height, 6% plifier. For PA work or for testing rec- inches in width, and 4% inches deep. ord players, the secondary is switched to SW A small 650 -volt, 50 -ma power trans- an external 8 -inch speaker enclosed in a former with only two secondary wind- baffle. There is a phone jack at the rear 1417 VAC .05T ings was used. of the amplifier the for latter. This circuit is Starting with the input (see dia- Surprisingly good results are obtained simple and easy to build. The chassis was made from a 7 x 10- inch sheet of aluminum. After corners were cut out and the necessary holes The author uses the made, the sheet was bent to form a amplifier to check a chassis . top 6 x 4 inches with sides 11/2 small receiver. The inches high. built -in speaker is in the top under the han- The cabinet was made from another dle. Rows of I/8-inch aluminum sheet 16 x 17% inches, bent holes let sound come to form a bottomless cover. through. The switch in The audio- tracing test lead consists of the center selects the a shielded cable with a test prod at the built -in s p e a k e r or end and an alligator clip connected to leads to the external the shield for ground connection. The speaker. It is a 2 -posi- other lead, for signal tracing, is similar tion switch. to that on page 50 of the February, 1948, issue of RAnto- CaArr.

ELECTRON MUSIC (Continued from preceding page)

Adjust the position of each so that it il- with a crystal microphone. Good results necessary, depending on the hum pres- luminates only one circle of black spots may sometimes be obtained with lower - ent. It does no harm in either case be- on the disc. It should throw almost no gain amplifiers, if the lamps are 2.2 -volt cause it also shields the tube from any light on any other ring. types and two flashlight cells are used. unwanted light. Paint the inside of the That about completes the mechanical Fig. 10 is a combination preamplifier shield black, using a fiat paint. construction of the Fototone. It should and wireless oscillator which may be The rheostat used to control motor be mentioned that when the chassis is used. With it, either photocell output can speed in the original model was as made up, its most important mechanical be picked up on a nearby broadcast re- shown in Fig. 2, but, depending on the detail is the placement of the phototube ceiver or the receiver's audio system can motor used, it may be different. In the socket so that it will position the tube be connected directly. The oscillation can model, this rheostat allowed speed vari- directly over the oblong hole through be stopped by opening S2. S1 is mounted ations from about 50 to 1200 r.p.m., which the tone disc is visible. See Fig. 4. on the preamplifier volume control. The which was enough to give a range of The basic circuit for connecting the 6 -watt lamp is a safety device; if the five octaves, more than enough for any 930 phototube to the first tube of an am- preamplifier is connected to an a.c. d.c. purpose. plifier appears in Fig. 9. If a PA ampli- receiver and the lamp lights, reverse The cover and music rack can by de- fier is used, the microphone charmer will the a.c. plug of either the receiver or signed to the builder's taste. It need only be needed, since the phono input will not the Fototone. be a box of Masonite with the right give sufficient gain. For connection to After making up whichever variety of dimensions to allow it to be slipped over the a.f. system of a receiver or to a circuit is desired - oscillator- preampli. the completed instrument. Those who straight phono amplifier, a preamplifier fier or a complete amplifier -mount the wish to duplicate the original model will also be needed. If a special ampli- chassis on its side at the rear of the exactly will be able to use the blueprints fier is built for the Fototone, it should Masonite base. The phototube shield which the authors send with the tone have enough gain to give good results shown in Fig. 4 may or may not be disc. RADIO -CRAFT for audio 133

"--111115111111111111111 1,1161 I1 If 11111111111111111111111111111 1111111111111111111111111111111111111 (1IIInIIONII nll IIHIINII '1111111111111111111111111111111111111111111 illülllll IIIBI!Ri11111 11111111111111111111111111 111111110111111111111111111111111111111111111111111111 Nf epee r-enOacKSarue o

Popta, 7'eciveeftd

Courtesy Cray Research & Development Co.

d ill'I!III!hlll i By RICHARD H. DORF 21E11 IIIIIpIIGIII 11IIIIIIIIIIIIIIIIIIIIII11IIIIIIIIIIIIIINII1IIIIIIIilI1111UI1i1111111111111!IIii1 JI 111111 11111111E1111111

FEW sound men can deny that for During recording, stylus travel is put impedance of the amplifier. Connect many years the reproduction of greatest at the low frequencies. Volume the output meter across the resistor. phonograph records has been a at the low end of the range must, there- High- impedance headsets for listening t very haphazard affair. Following fore, be reduced to prevent the stylus to the test record may be connected the usual procedure, the constructor from cutting over into adjacent grooves. across the resistor also. The setup is walks out of his distributor's store with That makes some bass boost necessary shown in Fig. 1. any one of the crystal pickups available in playback. for under ten dollars, connects its two Most surface noise or scratch is in the The low frequencies leads to the phonograph input of his am- high- frequency range. Record makers In American -made recordings, the plifier or receiver, and starts listening boost the highs during recording to get to records. low- frequency band extends from about a favorable music /noise ratio. To restore 50 cycles up to a turnover frequency of The results are generally far from the proper balance the I.ighs must be re- ideal from about 500 cycles. American records the standpoints of frequency duced during playback. While restoring should be equalized with the response, record wear, and distortion, the musical balance, this reduction of Columbia 10004 -M tone record, which has - among other things. In commercial home highs noise a 500 brings the surface down, too. cycle turnover. In European discs, the radio-phonograph combinations, The the rea- equipment necessary for measur- low range ends at about 300 cycles. They ing and adjusting a phonograph system includes: should be equalized with the 10003 -M, which has a 300 -cycle turnover. Use of 1. Frequency test records. Several are the American characteristic and the available, but of tC1Âo for purposes discussion 10004 -M disc shall is recommended, at least we use the Columbia 10003 -M and at first; the final complete equalizer can 10004 -M discs. be made variable to accommodate 2. An output meter (a.c. voltmeter) both PHONES types of record. of good frequency characteristics, pref- Set the needle on the 500-cycle band. Fig. I -Setup used in checking phono pickups. erably, but not necessarily, calibrated Adjust amplifier gain until the output in decibels. meter gives a reading on some even di- son for this lack of perfection is princi- 3. A supply of semilegarithmic graph pally that each extra penny spent in provision. Make a note of the reading. (We paper, 3 cycles by 10 divisions. assume duction counts. In specially built equip- The that the meter is calibrated only amplifier should be a good one in volts.) This reading is now known as ment it is a lack of knowledge. In this with flat frequency response and low article, we hope to supply much of that the reference voltage. It corresponds to knowledge from a practical standpoint. 0e 50 100 300 1000 zero decibels on the graph to be made. Starting at the 500 -cycle band, play First let us scotch the rumor that o IIIIIA 1111111 "phonograph records don't the remainder of the record, the fre- contain any- s 111111=rE011111 quencies from 500 down to 50 cycles. thing above about four or five thousand 11111111 cycles anyway." The more recent rec- IO 11111=' As the meter comes to rest for each fre- quericy, make ords of the better manufacturers have 1s 111UÌ N11111 a note of the reading. Then convert these voltage readings to a very usable response up to at least -20 MINI 1111111 8,000 cycles, and, in very many cases, decibels in the following manner: i records are good up to a full 10,000 Fig. 3 -Ideal vs curve of magnetic pickup. If, for example, the reading for 250 cycles. The response is smooth within distortion. The pickur arm should be cycles was 3 volts, and that for 500 this range, and, with proper equaliza- adjusted if possible to the recommend- s+ tion of one of the modern pickups, per- ed stylus pressure. No change should be .1 270K formance approximating a live FM made in stylus pressure after measure- 270K broadcast may be expected. Even sur- ments are completed, since any change face noise will be almost unnoticeable. will alter the high -frequency response The frequency response of records is of the system. (Usually, the greater the ,.02 not uniform throughout this range. This pressure, the less the high response.) is not a fault, but, rather, a technical The loudspeaker should be replaced with necessity. a dummy load resistor equal to the out- Fig. 4- Circuit for boosting the bass notes. cycles (the reference voltage) Voltage Voltage Voltage Voltage was 6 Ratio Db Ratio Db Ratio Db Rat-o Db volts, divide the larger number by the .06 0.5 1.58 4.0 3.55 I 7.97 18 smaller. 6/3 equals 2. The 2 is the volt- .12 1.0 1.68 4.5 3.98 2 8.91 19 .19 1.5 2.00 6 4.47 3 10.0 20 age ratio between the refegence reading .26 2.0 2.24 7 5.01 4 12.6 22 (at 500 cycles) and the 250 -cycle read- .34 2.5 2.51 8 5.62 5 15.8 24 .41 3.0 2.82 9 6.31 6 20.0 26 ing. Find the number 2 under "Voltage .50 3.5 3.16 10 7.08 7 25.1 28 Ratio" Fig. 2. Opposite it, in the decibel column, is the number 6. This indi- Fig. 2 -The table of voltage -decibel ratios above is sufficient fo picku 3 measurements, cates that the system output at 250 AUGUST, 1948 audio 34 I cycles differed by 6 db from that at 500 Often when using a crystal pickup Many systems are good up to a cer- cycles. It was, of course, lower, so place nothing need be done about the low tain frequency, but will not go as high a dot at -6 db on the graph paper at frequencies. If adjustment is needed, as 10,000 cycles. With these systems, the 250 -cycle division, as in A of Fig. the load resistance into which the pick- curve ABE should still be obtained as 3. The dot on the zero -db line at 500 up works can be changed. Increasing far as the system will go. Boosting inter- cycles indicates the reference voltage, this gives more bass; decreasing it re- mediate frequencies to compensate for corresponding to zero decibels. duces bass. the lack of highs will result only in poor- After determining the decibel equiv- It is not possible to correct the mid- er sound. alent for each of the frequencies, and dle range, except with very involved High -frequency equalization should placing corresponding dots on the circuits, without also affecting the high be either variable or (preferably) ad- graph, connect the dots with a pencil range. Ideally, output in this range justable in steps by a rotary switch. line.Ain Fig.3 shows the resultant curve should be flat. Magnetic pickups may Different amounts of equalization can from a perfect magnetic pickup through be flat, but crystal pickups will usually then be used for records which do not a perfect amplifier. Notice that the vol- not be. sound right when played with the NAB ume level decreases as the frequency curve. Some foreign -made records do not gets lower. Bass boost will have to be The high frequencies have as much high- frequency pre -em- used to bring up the lows. In making the graph for the range phasis as the American ones; a curve The B curve of Fig. 3 shows output between about 1,000 and 10,000 cycles, like AB in Fig. 7 -not having so much from the same record, using the same the 500 -cycle reference voltage should de- emphasis -is useful for these. Very procedure but with a perfect crystal be retained to represent zero' decibels. noisy records may require a sacrifice of pickup. Because crystals have different A preliminary run of the 10004 -M fidelity for the sake of quietness. Addi- characteristics from magnetics they disc on a perfect magnetic pickup will tional de -emphasis, for instance that of show a practically flat output. However, curve AC, can be used. Another help 50 wo sa e00 to minimize noise, almost all commercial with very bad discs is a cutoff at around records are made with a boost or pre - 5,000 cycles, as shown in ADF. (The. response of most inexpensive crystal pick- iiì110111111111111111=nriii emphasis in the high range. No two manufacturers agree on the ups cuts off between 4,000 and 8,000 Illlw\1FlIII Min1u amount of pre -emphasis, and often two cycles, anyway). IIII111111111/41:!Il0SIill records from the same manufacturer So far we have been using the Colum- III0111!ANNIIIIIM\lulll will be different. A certain curve has bia 10004 -M test record to equalize for American recordings. It is a good idea :íllIMIMI111111111M\S111 been arrived at by engineers of the -.1 National Association of Broadcasters to provide for European records too. for use on broadcast transcriptions. To do this, simply use the Columbia Fig. 5- Recording and compen sting curves. Most good modern American phono- 10003 -M disc and re- equalize the low work exactly opposite), the bass will be graph records adhere more or less close- range for flat output. The equalization reproduced properly, but the highs will ly to this curve. Conformity to the NAB used should be included on a switch need boosting. characteristic is neither universal nor position, so that it can be cut in when necessary. Rather than adding a com- No matter what type of pickup is used D IPERIMEIQ FOR VAWE plete separate equalizer for European or how the original curves turn out, the 2 K object is to get flat output at the low records, it is easier to use the same IITAL PU eOOSTi equalizer used for American records and end of the range. After equalization, a NORMAL curve taken on the system should look r- SOOK simply to vary the single component - a like B (Fig. 3). usually just resistor-which regulates Fig. 6-Typical circuit for crystal pickups. Output from most pickups will be the amount of bass boost, without changing the components which deter- very much like the curves shown, ex- accurate, but as a compromise for ad- cept that arm effects may be present. mine the frequency at which the boost justing a playback system, it is useful. starts. R is used for purpose in Fig. The arm in which the pickup is mount- Curve GBD Fig. this of 5 shows the NAB D0 $0 500 CO 5000 .' ed is very important. Like any solid ob- characteristic used in making record- o ject, it has a mechanical resonant fre- ings. ( Notice that the low -frequency sec- A quency which causes a large "hump" tion corresponds to Ain Fig.3.) The rec- -s in the curve. Unfortunately, nothing ords have a high- frequency pre -em- -10 can be done about it except to buy one phasis reaching +16 db at 10,000 cycles. -IS of the better arms with a resonance fre- The playback system must counter this -20 quency below audibility. If that is not rise with attenuation while boosting the possible, then equalization must be ad- bass at the same time. The entire play- Fig. 7- Special -purpose compensation curves. justed for a compromise. back equalization is shown in curve 4. The result will not be quite as accur- The next step is to insert equalizer HBE. ate as with the more complicated meth- circuits to correct whatever deficiency The test record has the same bass od, but it will relieve the excessive boom - is shown in the graph. For the mag- drop G as standard records, so the iness heard when European records are netic -type pickup of A (Fig 3), for in- actual bass response wanted from the played on an American system. To save stance, bass boost must be used to coun- system when using the test disc is curve the investment in an additional test rec- teract the drop shown. Fig. 4 shows a A. But it should be clearly under- ord, the adjustment can be made by ear typical bass -boost equalizer. Cl and C2 stood that the test record includes no while playing European records. determine the frequency at which the treble boost. Therefore, the output from The equalizer diagrammed in Fig. 4 boost begins (the turnover frequency). it after equalization should look like can be used at almost any point within The 270,000- and 27,000 -ohm resistors curve ABE. an amplifier. However, depending on the control the approximate amount of When using a good magnetic pickup, output of the pickup used, it may be boost. R is used for fine adjustment of equalization must be added to the circuit necessary to add extra amplification to the amount of boost. The circuit values to reduce the high -frequency response to offset the loss (about 40 db) in the shown will be about right to compen- approximately that of curve E. A con- equalizer. If that is the case, Vl and V2 sate for American records played with denser across a grid resistor will reduce may be the two sections of a 6SC7, with a good magnetic -type pickup. In effect highs. Experiment with condenser the tube being used as a preamplifier this is a bass -boost equalizer, but it values. ahead of the main amplifier. really does tjps job by reducing the mid- A crystal pickup initially showing a Other equalizer circuits will be found dle and high frequencies. Inserting it in response like AF must be boosted to in Ranro- Canrr. Any one of these, if it an amplifier will reduce the total gain reach the desired curve E. Fig. 6 shows has the proper frequency characteristic, of the amplifier considerably, and an ex- a suitable high -boost circuit for crystal can be used to correct the pickup re- tra stage will probably be necessary. pickups. sponse. RADIO -CRAFT for

.ar.:.' _ Audio I35 ee eCo4d4 New method of engraving soured tracks in steel makes records of great durability

method of recording and on the other arm. As Fig. 3 shows, the ANEWreproducing the sound of .church head is placed so that the magnetic flux bells has been devised by G.Chancenotte, passing from the magnet to the winding a French inventor. The recordings con- must pass through thé sound track. As sist of engraved sound tracks on tapes the track moves, the varying width of or cylinders of magnetic material; the the raised track varies the permeability sounds are reproduced magnetically. of the steel path at an audio rate. The The special virtue claimed by the inven- flux reaching the coil therefore varies, tor is the durability of the recordings. and the induced coil current is amplified The sound is recorded first on a strip and fed through speakers to produce of motion picture film, using the vari- the sound. able -area method. When the film is de- The playback head does not actually veloped, the sound track looks like Fig. touch the sound track, so there is no 1. Several of the tracks are recorded problem of wear. Demagnetization of the sound track is not a factor, because Fig. 6- Setting the bells for desired time. the track is not magnetized in the first place. ing the speed of each. The cams and one Several sound tracks and playback of the cylinders appear in Fig. 4. Note heads are placed on each of two cylin- the six sound tracks on the cylinder ders in the unit used in churches. Each (bottom of picture). track contains one of the desired bell Fig. 5 is a closeup of the playback sounds and cylinder rotation speed can head used for the topmost track. The be varied to produce still other tones. other photograph shows the control Speeds for the cylinders are normally panel of the electronic bell system. The 30 r.p.m. for the one containing the clock is set to start the bells automati- higher -pitched sounds and 20 r.p.m. for cally at certain times and the other con- the other, which contains the bass bells. trols provide for ringing them "manu- Each cylinder is about 3 feet in diam- ally" or setting up the various possible eter. special effects. Fig. Several typical sound -track specimens. I- A complex system of relays and cams has been devised by the inventor to play side by side on one strip of film. The film certain selections automatically and to LOUDSPEAKER RECEPTION is then used to make a photoengraving produce various effects by mingling It is difficult to attach a loudspeaker on a steel tape or cylinder. sounds from the two cylinders and vary- A section of the track engraved on directly to the outputs of surplus SCR - the steel is shown in Fig. 2. Whether the 274-N command set receivers because tape or the cylinder is used, the ends of the impedance is incorrect and the level the track are joined to create an endless- too low. The circuit shown illustrates belt effect. Therefore the bell sounds a method of obtaining the advantages of may be played for as long a period as- speaker reception and increasing selec- desired. tivity and gain. The reproducing head is made of a TO ANT POST BC RCVR; . piece of mu -metal bent into the shape of a square U. One arm has a beveled end; on this arm a low -impedance winding is placed. A permanent magnet is placed ti LAST IF SCR -274 -N RCYR An insulated wire is wrapped around the lead which connects the plate of the final i.f. stage in the receiver to the i.f. Fig. 4-A complete set of rslays and tracks. transformer. The wire is connected to the antenna terminal of an ordinary ST EL TAPE OR CYLINDER RAISED SOUND TRACK broadcast set. Since the i.f. of the 3 -6 -mc Ag. 2 -How the track is engraved in steel. receiver is 1415 kc, the broadcast set, when tuned to that frequency, will pick up the signal from the surplus receiver, convert, amplify, and detect it, and feed it through the loudspeaker. The two receivers become one double superheterodyne. If the bróadcast set is an all -wave type, the 40 -meter receiver from the SCR -274 -N may be used in the same manner. Its i.f. is 2830 kc. MAGNET FRANK BODINE, W4JVZ, Fig. 3- Detail of the track and pickup system. Fig. 5 -A closeup of sound tracks and pickup Fort Wayne, Ind. AUGUST, 1948 audio

THE HI -fl EXPERT TRACKS DOfflfl HUffi

Hum is one of the trickiest troubles known to the sound engineer. Mr. Langham relates a hum -filled adventure with a tuner -amplifier.

By JAMES R. LANGHAM

I raised my eyebrows. "There's no occasion," I said stiffly, "for you to raise your voice like that to me." Then I dodged and she missed. I turned it all on again and started in earnest. I cranked the gain down, The author communes with his soul, but the hum buzzes merrily on. and the hum went down too. It was about 2 or 3 db less than the program THE worst case of hum I ever saw down the amplifier and started prodding level. I paralleled each condenser with or heard was one of my own. Nat- around among the filter condensers. a known -to -be -good one. No change. I urally. Nobody else I know uses They all seemed to be O.K., so I turned listened with phones at practically every such screwy circuits or makes such off the amplifier and connected the spot on that chassis. The B -plus was dumb mistakes. Whenever I use standard tuner directly to the speaker. clear and free all along the line, and circuits, I get satisfactory -if uninter, The program came through- faint, so was the fixed -bias line. My grounds esting- results; but when I improve on but clear of hum -so I tied the ampli- were all fine and bright. Everywhere circuits -brother, that's a humdinger! fier to the speaker instead and cranked there was, a signal there was also that The time I'm thinking of wasn't that the gain way down to avoid offending the hum. Right back to the input. deal with the preamplifier on one of the XYL's ears. No hum. Upped the gain a Aha! I switched off the tuner-the XYL's ice trays. ( "We Learn the Hard bit, then more, and then all the way. hum and signal died together. "Barking Way," RAro-Ci r'r, Jan., 1944.) This Very, very slight hum at full gain with up the wrong tree, hunh ?" The XYL one involved a simple tuner- and-ampli- a lot of tube hiss mixed in. spoke from behind my shoulder. fier combination. "Hmm. Intermittent ?" I banged in- I nodded and put the amplifier back I had built the amplifier first and it dividual condensers, popped light together and then back on the shelf and sounded pretty good -a pair of 2Á3's in switches, and finally started tapping a pulled the little tuner down in front of class Al with fixed bias -so I threw to- screw driver against the amplifier itself. me. I opened it up, and it was so simple gether this simple little t.r.f. tuner, "Here, try this." But I scorned the that I couldn't see where there could be just one r.f. amplifier feeding an in- hammer the XYL held out to me. any trouble in it. Heck, it didn't even finite- impedance detector. I lined it up "You don't hear any hum now, do have a.v.c. strictly by ear, and it sounded pretty you ?" I demanded, turning the gain I prodded around inside with head- nice over the headphones. So I hitched wide open. phones. No hum there at all. I had the it up to the amplifier. She shook her head. "It was probably XYL listen. Then I tied it into the am- Man! That thing had a terrific hum my imagination before. You know me." plifier and turned it on and, HMMmmm, level. The XYL cocked an eyebrow. I didn't trust it, but I hitched it all there it was again. I tracked it up to "What, again ?" That ice -tray deal still up again the way it had been and then the detector itself, and filters didn't help rankled a little. turned the switch on. at al. I coughed delicately. "Must have That hum was terrific, but instead of I turned off the whole shebang and popped a filter." I disconnected things switching it off right away I went sulked. It didn't make sense to me. and pulled off the bottom plate of the through my routine of tapping and Either one alone was free of hum, but amplifier. Then I realized that rasp was banging at the tubes and filter cans. together they hummed. no filter -I must have mucked up- the "On second thought," the XYL "Maybe it's the broadcasting station," ground circuit; so I put it back and shouted at me, "maybe I do hear a little the XYL suggested. connected it right, ground side to hum at that." I shook my head. "It was KFI. They chassis, hot side to grid, and flipped the I put one hand to my ear. "How's wouldn't have anything like that." I switch on. that ?" I shouted back. pulled down Terman and began study- The hum was still there, so I flipped I flipped the switch as she repeated it ing. Then I pulled down Reich. Then the switch off again without looking in and her last words echoed all around the Henney. Then the Hambook. the XYL'a direction. This time I took whole neighborhood. After awhile I turned it all on again. RADIO -CRAFT for Audio 37

I turned the plugs in the wall socket. 'doing and why it should stop hum but how and why. I snowed. her under with I put little condensers across the line as I wired the condenser in. Then it popped words and until she reads this she filters. Nothing did any good. itself out -began smoking-so I re- hasn't known that I didn't know what I Could it be some appliance in the placed it with a regular buffer con- was doing then. house? I wondered. I began turning denser. Higher voltage. b(See Fig. 1.) Since then I have run into the same lamps and stuff on and off. Then I You see, I still believed in class Al modulated -hum trouble in other outfits. turned the volume up so I could hear then, and I liked the fixed bias so I had On three occasions I cured it the same while I went out to fiddle with the fuses a separate bias supply for the 2A3's. way -right first try out of the box - in the kitchen. Out there I heard bqth Well, not wanting to have that fail and and the owners thought I was a fine en- signal and hum go off and come back and leave B -plus on my plates and so burn gineer to have diagnosed the trouble so go off again. up my tubes and output transformer, easily. On the other occasion an a.c. line I had installed a relay. I used the relay really was causing the hum. We found Hum on carriers only coil as a filter choke for the bias supply that out by unscrewing fuses from the household box. I raced into the room to find the XYL twisting "Look," As for unmodulated hum, the or- the tuning condenser. dinary kind, she said. "I think it is the station at it's usually caused by in- sufficient filtering. Obviously. When it's that." a Tuning off the station killed hum as high gain job, I always suspect the ground circuit. Ground loops can do well as signal and. left silence. strange Then she turned to another station things. I like to run my ground and there was the hum again. All over as a lead and tie it to chassis at just one spot. I generally pick that spot experi- As, that dial there was hum wherever there mentally, was a signal, but no hum in between. sometimes near the power "Are they all humming ?" tube and sometimes near the lowest "No, we're modulating the carrier level. Theoretically it should be either ourselves some way." I knew that much. at the point of highest current or low- I went back to the books again and est level. I am never sure which, and studied. After a while I ripped out the I'm not sure there is an arbitrary standard. I've seen amplifiers built with filament wiring in the little tuner and RELAY =- 5Y3-GT over 100 -db rewired it with 2-conductor shielded gain and with all grounds made to chassis at the handiest points. cable. No change. Then I got drastic and Fig. I -The buffer condenser cured the hum. Some of them have been quiet lot heated the tubes in the tuner with 6 and a volts of flashlight battery. and had some whacking big condensers have been terrible. Still that hum. So I got discouraged (low- voltage ones) as filters along with and we listened to Jack Benny on the it. That must have been the trouble. I Sound engineer's credo other little radio and then went to -bed. had some very funny reactances there, I blliéve all shielding should be I don't know now how long I played and it was putting out a peculiar field grounded at one end-not both-and around with that outfit before I got that would modulate any neighboring grounded to chassis. I believe the No. 1 on to the deal, but I do remember lis- r.f. Putting that buffer condenser across pins on tubes should be tied to chassis. tening to a musical program on the lit- it upset those reactances and resonances. I believe signal grounds should be kept tle radio and turning on the big ampli- and killed the deal. separate from chassis grounds and fier to play some of our records after- The XYL heard the outfit playing B -minus except at one point. That point ward. As the amplifier warmed up, here and came in to see how I'd fixed it. I should be either at the output tube or came that same hum out of the little couldn't tell her how or why it worked, the input tube. radio. Terrific hum. but I showed her that it did. She asked I also like to parallel electrolytics I turned off the amplifier and the hum so many questions, though, that I with small paper condensers, but that's died. Turned it on again and there it blamed it all on the guard -relay circuit more to prevent oscillatory trouble than was. Well, instead of playing records and redesigned it, as shcwn in Fig. 2. hum. that night, I fooled around the inside I used a different switching circuit One case I remember was a PA sys- of that amplifier with every trick I knew and arranged to flip the tubes over to tem where the preamplifier tube or ever heard of. I hooked in potentiom- self -bias when the fixed bias failed. I hummed terribly. The trouble was eters to the transformer windings that told tier that was better and showed her ground loops. We didn't have time to were supposed to be center -tapped to ground and grounded the pots so I could move my ground from side to side to compensate for any unbalance in ti the transformers. I raised the level of my filament string from zero to as high as 20 volts. I paralleled all the electrolytics with paper condensers. I did everything I could think of, humming all the while. After I had tried all the things I could possibly imagine any reason for, I began doing things without knowing why I was doing them or how they could possibly help. The same idea as beating a tin pan to chase the devils away, I guess: I was fooling around with a small paper condenser when the hum sudden- ly stopped. I stopped daydreaming and looked. What I had done was tie this small condenser from plate to filament of the 5Y3 -GT rectifier of the bias supply. It killed it. No hum. I took it off, and there was hum. I couldn't figure out just what I was A smart hammer blow is one vay to stop hum but the author does not recommend it-very often. AUGUST. 1948

38 I rewire the whole outfit, it was one of it's not critical-will give at least a 5- portant. It's amazing how many other- those deals where the wiring is laced to 7-db hum reduction on the average wise smart radio men will keep their and then varnished. Lovely to look at, outfit and considerably more on some. irons too cool. Cold joints are nasty but oh, that hum! It had to be used I've often heard of curing hum things. that afternoon. It had a 6SJ7 input, and troubles by raising the whole filament Also important is to tighten poten- the final was a pair of 6L6's. I pulled supply several volts above ground, but tiometer nuts and use star washers un- I've never succeeded with one of those der them. I lost a star washer when I cases myself. I've tried it-oh a dozen was putting together our present unit 2A3(2) times-on hummy amplifiers, and not so I left it out. Presently the set once have I seen it work. It might help hummed from time to time. The XYL on the millions I never tried, but I can't humbled me by stopping it-she put a confirm that. book on top of the knob. The pressure The best solutions are (1) watch your made the contact good enough to cure layout; (2) watch the grounds -sepa- the hum. It was one of those silly things rate grounds for chassis, signal, and I should have known better about. B- minus; (3) use metal tubes or tube Finally, of course, I got a star washer

TI shields in low -level stages; (4) use a and put it in, but the XYL still brings 2.5VFIL 100 -ohm potentiometer across the fila- it up in conversation with other radio 50 /I50V -. ments and ground the center tap; (5) men; and I daresay she'll remember and =-. 5Y3-GT use a hot iron. This last is most im- tell about it when I'm 83.

1 DPOT RT ; HEARING AID HAS PICKUP COIL 4 NN SON ANEWLY developed hearing aid T2 523 150;150V "2"-Y \v uses a magnetic microphone, which ss= is unaffected by temperature and hu- 000 1501U 1O0K midity, in place of the more common 1I SW crystal type. Another important feature 6 of the unit is an inductive pickup coil (Fig. 1) for use when telephoning which TI -T2 - SEC SHOWN. PRI TO LI}IE TIED OGETHER is built into the front of the plastic case. 6.3V FILS THROUGH 5W 6 FUSE In use, the telephone receiver is held Fig. 2 -This is the redesigned guard circuit. near the front of the case, and the amplifier input is switched from the micro- out the 6SJ7 and substituted a 12SJ7 phone to the pickup coil. Court,'sy E. a. Mt r, & Sun and then ran a d.c. filament by wiring Inductive coupling through the mag- Fig. I- Inductive pickup coil is in case front. it in series with the B- minus. The cir- netic field of the telephone induces a cuit appears in Fig. 3. The total drain voltage in the pickup coil. tube with a small screw results in a was close to 150 ma, which just lit the While the crystal microphones in reduction in low -frequency amplification. 12SJ7 nicely. The 6L6's didn't seem to hearing aids do give good results, their The hearing aid amplifier has three miss the lost 12 volts from their plate efficiency is reduced at the operating stages, with an over -all voltage gain voltage, and the hum was way, way temperatures normally encountered (90 from the first grid to the last plate of down. Later the owner rewired the am- degrees F), and they may be ruined in about 20,000. Tubes are of the submini- plifier with more attention to ground time by either humidity or dryness. ature type: two CK512AX voltage am- loops and cleared up the situation. You The magnetic microphone used in this plifiers and either a CK522AX or a could argue that the trouble there was hearing aid is made almost entirely of CK507AX as output tube. The micro- filament induction rather than ground metal. It consist of a thin aluminum phone and pickup coil are transformer - loops, and you might be right. I do know, diaphragm cemented to the edge of an coupled to the input, and the output is however, that it was cured by (1) d.c. aluminum case (Fig. 2). An aluminum - transformer -coupled to the air- or bone - filaments, (2) rewiring the ground. alloy driving pin soldered to the center conduction receiver. Self -bias on the All the high -gain amplifiers I have of the diaphragm transmits vibrations output tube results in stable perform- fooled with since 1939 have had poten- to a smaller diaphragm and armature ance. tiometers across their filament supplies made of nickel -iron. As the armature The frequency range of the hearing with the center arm grounded. If they vibrates, it induces a voltage in the bi- aid is deliberately limited to approxi- didn't have them when I got them, they polar magnet coils spaced beneath it. mately 300 to 3,500 cycles to minimize had them when they left me, because A resonance tube connects the air be- the effects of noise and nonlinear distor- I've run into a lot of transformers whose hind the aluminum diaphragm with the tion. A noise control reduces amplifica- centertaps haven't been in the center, outside to give a considerable increase tion on frequencies below 1,000 cycles electrically speaking. That little trick in low frequency response. Closing the and above 2,000 cycles. with a potentiometer -100 ohms or so, THIN RUBBER ALUMINUM ALLOY M ¡DRIVE PIN 12SJ7 INDUCTIVE LOW FREQUENCY SEAL SUBSTITUTED PICKUP TUBE ARMATURES COIL FOR ALUMINUM FOIL 6SJ7 / ,...// / /Z. r \ MIAOW // % iAlr DIAPHRAGM SOUND ENTRANCE SOUND ENTRANCE SHOCK MOUNTING ( rI\ -PLASTIC Ì -- CASE `i FRONT \ _p.ut_r_ ALUMINUM CASE ENTRANCE TÓ L.F. TUBE \%//~ \ ., aNN, :OM, MAY BEGLOSED WITH e-ec . , n A SCREW FROM BACK ALNICO V'MAGN ET POLE PIECES L_ ALUMINUM BACK CÁSE B- BROKEN TO INSERT I2V FIL and the resonance chambers. Fig. 3 -A change of tubes stopped hum here. Pg. 2- Cross-section of microphone, showing inductive pickup RADIO -CRAFT for Amateur :i9

A Folded Dipole 10 -Meter Antenna

By A. B. KAUFMAN

Directional dipole in i its place on the roof.

THE folded dipole has become very The element support is made of knot- the flange must be welded to the bear- popular for FM and television an- free wood which is not likely to split. ing pipe at the proper angle to make the tennas and, recently, for use on As Fig. 2 indicates, the majn support pipe exactly vertical. To determine this even the lower -frequency bands by is a piece of. %- inch -Thick wood 4 x 10 angle, use a protractor and a liquid amateurs. Usually, the antenna is made inches. Attached crosswise to each end level, the kind employed by carpenters. of 300 -ohm ribbon line. is a 4 -foot length of 1 x 1. It is to these Fig. 3 shows how the protractor is held This 10 -meter beam uses the folded crosspieces that the elements will be on the roof. The level is adjusted to cen- dipole, but adds a reflector to it. The mounted. ter the air bubble, and the roof-slope front- to-back signal ratio is 10 to 15 db, angle is read from the protractor scale. and the gain is about 5 db over a single Be sure the flange is welded to the bear- half -wave antenna. The beam is rotated ing pipe at exactly this angle. by a surplus gun mount. Construction is IG' 0- The flange itself need not be round, less difficult than for the usual rotatable --y r f~3 6.-1 .1-3/4`..1. but it should be large enough so that it beam. can be screwed to two of the shingle A two- element beam was chosin for B B A support FIBER TUBING boards. To make the assembly several reasons. First, it will work effi- rigid put long machine screws right ciently over a much broader band of 300. LINE through the shingle support ATTACH TO INSULATOR boards and frequencies than will an antenna of the flange and tighten nuts on the ends, three or more elements. It is certainly I/2- DURAL OR BRASS TUBING TUBING CLIPS using big washers under the nuts. easier to build, and the supports and To Fig. I- Dimensions of the radiating element. prevent water from dripping down rotating motor have less of a load to the antenna pole and through the hole carry. Five stand -off insulators are used for in the roof, cut one end off a large tin A reflector was used as the parasitic mounting the folded dipole: one at each can, and then in the other end. cut a element rather than a director because of the fastenings A (Fig 1), one at each hole equal in diameter to the antenna its spacing is much less critical. A re- point B, and one at the center of the pole. Slip the can over the pole with the flector can be spaced farther from the unbroken dipole rod. The insulators are open end down, so that the open end is radiating element than a director, and attached to the A points as shown in the over the upper end of the bearing pipe. yet give the same gain without cutting detail drawing of Fig. 1, and the others Calk and tar the hole in the other end down radiation resistance so much. are fastened to the rods directly with so that the can will stay ini position on A folded dipole was used as the driven tube clips. The insulators are then the pole and no water will get through element because of its high radiation re- screwed to one of the wooden cross- the hole. To keep the can in place it may sistance and its broad tuning. The re- pieces. be necessary to use setscrews as indi- flector brings this resistance (normally The reflector rod is fastened to the cated in Fig. 3. r 300 ohms) down to between 60 and 150 other crosspiece with tubing clips and The distance between the attic floor - ohms. A 70-ohm line can be used to feed insulators in the same manner. Three the lower support for the pole -and the the antenna, though even 300 -ohm twin insulators are sufficient. bearing pipe determines how high the lead will work satisfactorily. The vertical pole supporting the beam antenna pole can be. The leverage The folded dipole and the reflector are is made of durai, brass, or thin -wall should be not greater than 4 to 1. That made of durai or brass tubing to the steel tubing about 2 inches in diameter. means that with a floor- to-roof height dimensions given in Fig. 1. The driven Do not use water pipe, it being too of 5 feet, for example, the pole should element is made in three pieces, one 16 heavy and not sufficiently rigid. A flange be not more than 20 feet above the roof, feet long and the other two about 7 feet welded to the top of the pole holds the giving a maximum total pole length of 11 inches each. Tubing clips are used at wooden beam support. 25 feet. This is a rather dangerous the ends of the assembly to hold the rods Fig. 3 shows how the beam is mount- maximum, however, and preferably the together and to short them electrically. ed. The rotating mechanism (details pole should be much shorter. At W6YOV It is not a good idea to drill the tubing, later) is on the floor of the attic. The since this weakens it. The reflector is pole goes through a hole in the side of 16% feet long. the sloping roof. At this point, a short Additional tubing clips are used to length of pipe is used as a bearing. Its hold the folded dipole rods together near inside diameter should be enough larger the center. At this point, however, the than the outside diameter pf the pole to rods must not be shorted to each other, allow the pole to turn freely, but not so so a tight- fitting piece of fiber tube is much larger that there is excessive play. placed over each rod and .the clip The bearing pipe is attached to the clamped over fiber. the roof by a flange. Since the roof slopes, This closeup shows rotating element clearly. AUGUST, 1948 40 Amateur the pole extends 8 feet above the roof. the motor has two leads for the arma. critical. Minimum spacing will give the A surplus K7 gun mount, sold by ture and two for the field. A 6 -wire best match for a 70-ohm transmission many radio stores for just this purpose, cable is run from the attic to the oper- line; maximum will be best if 300 -ohm supports the bottom of the pole and at ating desk. A d.p.d.t. switch controls the ribbon is to be used. direction of rotation, and a push- button 14 -4.0 -s' operates the motor. The microswitches are normally closed units. If the motor SURPLUS CONVERSIONS off when a microswitch does not go By MILTON KALASHIAN 3/4-TNICII opens, reverse the field connections. -r If the motor has a center -tapped field, Many articles have been published in o- only three wires and a s.p.d.t. switch the past couple of years on conversion will be necessary, as shown in Fig. 4 -b. of surplus equipment for ham use. This If the microswitches do not operate index of these articles enables the own- PIPE MOUNTING FLANGE properly, reverse field connections. er of a piece of surplus gear to find all If the motor used is a 24 -volt d.c. unit, the available information quickly. r.r a line- dropping resistor or a tungsten Symbols used are RC (Radio -Craft), TOP VIEW lamp will have to be placed in series RN (Radio News) and RH (Radio Fig. 2 -Some details of the rotating member. with the 117 -volt a.c. line. These motors Handbook, 11th edition, Editors and the same time provides a means of ro- will overheat on continuous duty. Prob- Engineers, Santa Barbara, Calif.) tating it. Remove all excess parts and ably a 117 -volt a.c. motor would be best, 150.8 Transmitter QST Sep 47 p. 22 gearing, and bolt the gun mount secure- though perhaps a little more expensive. Improving c.w. operation of ST May 48 p. 69 APS -13, 420 -mc operation of ST May 4$ P. 51 ly, base down, to the attic floor. To its -274) REFLECTOR ELEMENT FOLDED DIPOLE ARC- (see SCR top secure a piece of tubing just large ART -13 Transmitter RN Dec 46 p. 50 co Feb 47 p. 33 Nov. 46 p. 13 M enough to receive the base of the an- Speech amplifier....RH p. 437, CO Dec 47 p. 19 RH p. 436 tenna pole. A single 8-32 bolt passed DURAL OR STEEL POLE BC-191 as modulator PC-221 Frequency Meter through this tubing and the pole base as c.w. monitor RN Apr 48 p. 160 will hold them together. WATER -PROOFING SHIELD (CANT Modulation of QST May 48 p. 68 Power supplies for 1;15T May 47 p. 72 Mount a small motor (some 24 -volt Co Apr 47 p. 30, Jan 48 p. 28 d.c. surplus motors can be operated in- BEARINGP ROOF as v.f.o RH p. 445, QST Mar 47 p. 43 INGLE SUPPORT BC-3I2 Receiver termittently from the 117 -volt a.c. line) PURGE A.c. power supply for RC Jan 48 p. 74 on the rotating framework and attach BOLT L WUT Conversion RH p. 431 BC-342 Receiver, conversion OST Sep 46 p. 42 the flexible drive cable from the gun BC-348 Receiver mount to the motor shaft. Conversion QST Jan 47 p. 19, Nov 47 p. 66, 48 25, RH p. 435 PROTRACTOR ANO CQ Apr p. If the antenna is allowed to rotate OST Feb 48 p. 59 LIQUID LEVEL Dial backlash elimination continuously more than 360 degrees, the ROTATING MECHANISM S -meter for RN Apr 48 p. 68 BC-375 Transmitter leads to the motor (which rotates with ATTIC FLOOR Conversion QST Dec 46 p. 38 the gun mount) and to the antenna will as Modulator ...... RH p. 436 BC-406 Receiver CO Feb 46 p. 18 3 the mast goes through the roof. eventually be pulled out by the roots. Fig. -How BC-412 Oscilloscope RC July 46 p. 70 Slip -ring arrangements are possible, but Oct. 46 p. 18 The motor should be geared down so as Television receiver RN Aug 47 p. 45 a good deal of trouble. It is better to that the antenna does not rotate faster BC -453, 454, 455, 457, 458, 459 limit total rotation to about 330 degrees (see SCR-274) than about 1-4 r.p.m. This holds true, BC-610 Transmitter (see SCR -299) whether the K7 gun mount or any other BC -624, 625 (see SCR-522) BC-645 Transmitter- Receiver, 420 - worm -gear- and -pinion arrangement is mc operation OST Feb. 47 p. IS may be necessary to bypass the BC- 652, 653 (see SCR -506) used. It BC-654 (see SCR -284) motor with a 0.1- to 1 -µf capacitor to BC-696 (see SCR -274) eliminate noise pickup in the receiver. BC -746 Tuning Unit as pocket c.w. transmitter OST Jan 48 p. 62 There is no reason why this antenna BC -779-A Receiver, improving sta- be on higher -frequency bility CQ May 48 p. 32 could not used BC -946 Receiver, conversion . RC Feb 48 p.,26 bands. BC- 1068 -A Receiver 2 -meter operation ...CO Jun 47 p. 25. RH p. 442 The dimensions given for the lengths as Television receiver RC Jan 48 p. 57 of the elements were figured roughly BC -1284 Preselector CQ Mar 47 p. 32 CAY 47150 Tuning Unit as carrier - for the high end of the 10 -meter band. current RC Oct. 47 p. 24 For any other frequency on any other CW -3, F-3 Receivers, !vl and NFM conversion QST Apr 48 p. 48 band, use the following formulas: For LM Frequency Meter the folded dipole, the length in feet from Modulation of QST May 48 p. 68 in mc. Power supply for .RH P. 445 end to end equals 955 /frequency es V .o QST Aug 46 p. 34 Length in feet of the reflector equals PE-110 Power Supply, conversion . . RH p. 441 Propellor pitch changer as beam 492 /frequency in mc. Spacing between rotator CQ Apr 48 p. 38 elements should be between one and two SCR -211 (see BC-22I) is too SCR 274 tenths wave length, but this not Receivers CQ Nov 47 p. 24, RC Feb 48 p. 26 The K7 gun mount which rotates the antenna. BC-453 as Q -Ser OST Jan 48 p. 40 C T FIELD MOTOR 3 -SWIRE -3 WIRE CABLE Connections RC Mar 48 p. 44 SA FUSE CABLE Transmitters 4e and make the motor reversible. Orient 8C-459, 40 -, 20 -meter opera. 50 PB SW IRIGHY LIMIT SW ti A tion CO Mar 48 p. 31 antenna so the dead spot is in the R the -60-RO 50 . S I `ow Mobile use CQ Jan. 48 p. 22 least useful direction. as V.f.o. ....CQ May 46 p. 18, RN Mar 48 p. 57 91 LEFT LIMITS W FIELD is done with micro - SCR -214 The limiting Mobile installation CQ Mar 47 p. 26 mounted in a small box or at- use CQ Oct 46 p. 28 switches 14 WIRE MOTOR- 6WIRE CABLE Portable SA .R SCR-522 tached to some part of the gun mount LFT LIN SW I r -.. -CABLE Receiver (BC -624) support. A small piece of metal or wood II7VAC 5060. 2 -meter operation CQ Jul 47 p. 27 to the rotating mechanism RC 9ep 47 p. 24. RN Oct 46 P. 35 attached Bandpass converter QST Mar 48 p. 34 38 should be adjusted to ride over one of as FM receiver - RC Jun 48 p. the switches at each end of the rotation Output increase CQ May 48 p. 22 RT LIM SW Transmitter (BC -625) swing. Be sure to arrange matters so 2 -meter operation CQ Jul 47 p. 27 RC Apr 47 p. 35, RN Nov 47 p. 35 if the antenna coasts after the FIELD that, PR SW I 1 6 -, 10 -meter operation RN Apr 48 P. 50 power is off, the microswitches will not -o QST May 48 p. 58 SCR -536 Handie- Talkie RC Jul 46 p. 684 be ruined! SNACRI ATTIC TBY-7 Transmitter -Receiver, 6 -, Two wiring diagrams for the rotating Fig. 4-a, below -Motor connections; b, above 10 -meter operation RN Oct 47 p. 39 motor are shown in Fig. 4. In Fig. 4-a -connections for a center -tapped motor field. TS-47 /APR Test Oscillator RN May 46 p. 32 RADIO -CRAFT for Amateur 41 Handí,-Dandy Transceiver

.1 l 1l -l11l -nue portable-mobile phone that uses only four dry -cell tubes

By WILLIAM E. PIKE, W 1 KMW

audio circuit which is employed as a tubes to support RFC1 and RFC2 and modulator when transmitting and as also to serve as a connection to the un- an audio amplifier drivirg the 5 -inch derside of the ehassis. The tube sockets, PM speaker when receiving. The chassis raised from the chassis, are supported is made from a piece of 6 x 6% -inch by s4 -inch bushings. The 1C5-GT is lo- aluminum 1/16 inch thick. Dimensions cated at the left front of the chassis, for bending and for lwating socket while the 1G4 -GT is at the right. holes may be seen in Fig. 3. The front Fig. I -The A bottom view the author transmits from his bicycle. panel of chassis is shown is also made from a piece of 1/16 - in Fig. 5. A 4- terminal strip is mounted inch thick aluminum 7 x 10 inches. 7"HE "Handi- Dandy" is a compact Placement of parts isn't too critical, REAR APRON battery - operated transmitter - re- although the oscillator and detector cir- ceiver for the 144 -148 -mc ham cuits are located at the rear of the -1r band. This versatile little rig, en- chassis to reduce hand capacity. tirely self- contained, is just about the The oscillator circuit .s located on same size and weight as a portable the left rear of the chassis. The detector 7/3 radio. It may be carried and operated components are on the right rear. The practically anywhere. It may be used as detector and oscillator coils L2 and L4 2 1/e a monitor in the station or as an emer- are each 4% turns, 3 inch in diameter, gency transmitter, and is fine for hunt- of No. 14 wire. They are about % inches ing hidden transmitters on ham field long. With these coils there should be days or other mobile work. In this latter about 40 to 50 degrees of band spread case it was used on a bicycle (see Fig. on the dial. The coils are soldered di- 11VeOIAE21` 1). rectly to the tuning condensers with all The entire unit, including batteries leads kept as short as possible. and a 5 -inch PM speaker, is housed in a The tuning condensers are mounted ve 411 metal cabinet only 7 x 10 x 6 inches. on small angle brackets made of poly- _ The circuit (Fig. 2) is conventional. styrene and are connected to the Na- Operating efficiency and economy were tional Velvet Vernier dial; with flexible

AM on the rear apron of the chassis for battery connections. S2 is also mounted R, S here. 957 5 1G4-GT IC5-GT 957 /SDYY/YICA is located DEI AUDIO Ti at the left in Fig. 5; the Soyyf MICA 4 Ll LI L2 .-4 send -receive switch S1 is located in the 5 center and mounted on the front panel. T2 is mounted on this switch. The audio choke CH is at right. Regeneration control is mounted on the front panel. Two small jacks are mounted on the front panel underneath the chassis. One is

REGEN used for the microphone, and the other may be hooked up for a pair of head-

R S phones if desired. Note that the filaments of the 957's

CONDS 400V UNLESS NOTED are wired to the send -receive switch S1 so that only one is on at a time. This A +I.5. S e+90V di A- )ye- conserves the batteries. Fig. 2 -The 957 at left is the superregenerator. The transmitting oscillator is at right. The antenna coupling coils Ll and AUGUST, 1948 42I Aaateler

L3 are each 2 turns, 34 -inch diameter, This is secured to the side of the cab- Little or no difficulty should be en- No. 14 wire. The oscillator coupling is inet. The front end of the shaft pro- countered in getting the equipment into fixed, and the coil is supported by a trudes through a bushing on the panel. operation. An absorption -type wave - small stand -off insulator mounted on the The antenna coils aren't secured in meter, or a couple of stations of .known aide of the cabinet. It is spaced about place until the set is in the cabinet. frequency, can be used for "spotting" 1 inch from the plate end of the oscil- The cabinet is 7 x 10 x 6 inches. It the band. lator coil. Experiment to determine the is made of 1/16 -inch aluminum, held to- Reliable contacts over several miles exact spacing between the two coils L3 gether with small angle irons and 6 -32 can be expected under normal condi- and L4. If the coupling is too tight, the screws. A handle is fastened to the top. tions, but of course location and height 957 will pop out of oscillation. The 5 -inch PM speaker is mounted on play a major part in the performance of The variable coupling for the detec- the inside top of the cabinet. Several v.h.f. equipment. tor is made by drilling two holes the holes were drilled in the top of the While there are no restrictions on cabinet to make a grill. The antenna is a piece of 1 -inch brass rod 38 inches long. This is one- half wave for the 2 -meter band. A quarter-wave antenna 19 inches long will work just as well. The rod is soldered into a small banana plug; which is plugged into a jack on the rear right of the cabinet top. Two 45 -volt portable batteries in series are used for the B- supply, and a 1.5-volt hearing -aid battery is used for filament supply. A 4.5 -volt battery furnishes microphone voltage. The B -bat- Fig. 4 -Top view of the Handi -Dandy chassis. teries are located one on either side of Fig. 5- Transformers are under the chassis. the chassis, between the chassis and side size of the No. 14 wire into a s/4 -inch of the cabinet. The filament and micro- building and experimenting with radio polystyrene shaft about 6 inches long. phone batteries are underneath the equipment, a federal license is required The wire leads of Ll are passed through chassis, secured to the bottom of the to put a transmitter on the air, regard- the holes and secured in place with a cabinet. Standard battery plugs and less of its size or power. couple of drops of sealing wax. A short cables are used to connect the bat. Amateur licenses are issued free of bracket for supporting the shaft on the teries to the terminal strip. charge to any United States citizen and coil end is made by drilling a h -inch With these batteries, several months' are obtained upon taking an examina- hole through the center of a piece of service may be expected, using the unit tion at any of the radio inspectors' of-

T -inch-thick polystyrene 1 inch square. a couple of hours a day. fices throughout the country. An S -Meter for Your Receiver By H. HATFIELD hams have been searching for netting to the screen supply of the set lightweight plastic (Plexiglas was MANYa simple and accurate S -meter to or by any other convenient means. The handy) and drilled small holes in them measure the strength of incoming sig- resistance of R2 may have to be reduced. as shown. nals and to provide visual tuning. The socket for the 6C4 and a 4-lug After connecting the transmission line This S -meter will operate with any to the center of the antenna, I clamped the ribbon between the two pieces of S/I 6C4 Plexiglas, passed screws through the o-1 w holes, and tightened nuts on them. The plastic apron protects the connections from the weather. The system .g2 u: weathered a windy winter and is still in good condition. 6+ 6.3V FIL CIRCUIT ONO MIC RICHARD HENRY, RI IOOR - TO RECEIVER New York, N. Y. Fig. I -This is the I -tube S -meter amplifier. broadcast or short-wave receiver having 0 APRON FOR WEATHERPROOFING a.v.c and a 6.3 -volt or a 0.3 -amp. series filament supply. In sets having a 12.6 - volt filament supply, a 12AT6 may be substituted for the 6C4. The B- supply LgrA /j i may be either 100 -165 or 225-350 volts. I The circuit, Fig. 1, shows that this ACTUAL SIZE FOR AVERAGE METER i+.+ ANTENNA S -meter works on the principle of a Fig. 2 -Make a new meter scale as shown here. E l' PLASTIC / vacuum -tube voltmeter. A change in sig- 11$ á't nal strength causes a change in the terminal strip are fastened to a small ! a.v.c. voltage, which is used to bias the metal chassis used to mount all com- iá ponents, including the meter. The a.v.c. / /i /' 6C4. The resulting variations in plate / '',,..-$."14, current actuate the 0 -1 -ma meter, which wire must be shielded, and the shield is as in Fig. 2. used for ground return to receiver. is calibrated 6.32 MACHINE SCREWS r NUTS AND (SI Use R1 to set the meter to zero sig- FORMED PLASTIC 4 ARDUND nal (full scale) on any quiet spot on the ANTENNA DOWNLEADS I 1 300. LINE band. I use a 40 -meter folded dipole made I /4' ROO ¿I wind APRON END VIEW the meter does not read 30 db on of 300 -ohm ribbon line. After the DOWN If t' LEAD a powerful local station, reduce the B- had torn the down lead from the an- < voltage supply to the S -meter by con- tenna several times, I cut two pieces of DOES OF APRON BROUGHT CLOSE TOGETHER FOR PRESSURE FIT RADIO -CRAFT for C' IIC'1CCS, 1 43

recordings 12 hoots MICROPHONE - at any time al) to STAND in advance. COIN RADIO Dazor Manufacturing Corp., Three tape speeds are possible: the Tradio, Inc., ANTENNA MOUNT St. Louis, Mo. slowest affords an hour s recording Asbury Park, N. J. South River Metal Products Co., time, and the 15 The Floating Arm is an adaptation fastest minutes with Described by the manufacturer frequency range to 12,500 cycles. Five as the South River, N. J. from the desk lamp brackets made by smallest coin -operated radio in The input channels accommodate micro - the Chimney Mount antenna base is the same manufacturer, the lamp be- world, the 6 -tube Tradio phones, tuners, phonographs, and lines. -ette is 71/z used fo fasten FM and television an- ing emoved from the end and a stan- tenna The playback amplifier gives IS watts masts to chimneys. Two galva- dardr microphone holder sub- nized steel bands are stituted. output with less than 1% distortion. passed around Variable equalizers are included. the chimney to hold the mount in RADIO-CRAFT - position. The mast is inserted into the two vertical rings and held with set - Screws. TV SIG GENERATOR Installation is said to take only e Hickok Electrical Instrument Co., few minutes. Marring the brickwork by Cleveland, Ohio drilling holes in it is unnecessary. The hardware furnished is rust- resist- Model 610 Television Generator re- ant, and the steel bands have a com- places the usual sweep generator, used bined tensile strength of 3,000 pounds, with marker generator, trap alignment -RADIO -CRAFT generator, and crystal calibrator. It permits the technician to align any of inches square and 5 inches deep. De- the 13 channels, i.f. stages, and traps, signed to be placed in booths in res- and to insert an accurate marker at taurants and bars, the receiver has an any point on the i.f. response curve. r.f. stage, and a squelch circuit to Self- contained marker frequencies are silence interstation noise. directly calibrated on the instrument's Installation requires only plugging in dial. to the power line; a built -in antenna An advantage of the arm is that is provided. The the microphone aluminum cabinet con- can be placed in any tains the coin box. Playing position raised, lowered, time can - or moved be adjusted by the owner from T/2 min- sideways- without the necessity of ad- utes to ,¡usting one hour. Maximum volume is setscrews. The microphone will preset to avoid annoyance stay in any to other position in which it is set, patrons. -RADIO -CRAFT according to the maker, because of a patented enclosed spring. Much less bulky than the usual boom TELEVISION BOOSTER POWER INVERTER stand used for the same purpose, the Jerrold Electronics Electronic Specialty Co., Floating Arm Corp., may be obtained with Los Angeles, Calif. a floor pedestal or with a universal Philadelphia, Pa. mounting bracket permitting it to be The Jerrold Booster is a preamplifier The Ranger Inverter converts 117 -volt clamped or screwed to any surface: The generator also provides crystal which incorporates a selector switch to a.c. line voltage to d.c. Originally de- RADIO -CRAFT controlled signals from I me to the provide amplification on any of the 13 signed for use with vibrator -type elec- top TV band. -RADIO -CRAFT TV channels. With a minimum gain of tric shavers, which operate best on d.c. the inverter BATTERY VTVM 25 db on each channel and a full 6 -mc may be used in any band width, the unit makes good re- application requiring 15 watts or less. Hewlett Packard Co., FUSE -RESISTOR -RADIO -CRAFT Palo Alto, Calif. International Resistance Co., The 404A vacuum -tube voltmeter is Philadelphia, Pa. housed in a metal carrying case and Type OWA resistors consist of small - uses standard flashlight cells and 45- diameter resistance wire well -spaced volt B- batteries as a power source. A.c. on an insulating core. The wire is bare measurements from 2 to 20000 cycles and the winding is not coated. are accurate to ± 3%, with frequencies to 50 kc measurable to within ± 7 %. ception possible in areas of low signal strength. Multiple receiver installe Under normal conditions in the cir- tions, such as those in dealers' show- \\ cuit, the resistor functions as usual, but rooms, apartment houses, and hotels, if an overload occurs, the wire opens. are also improved by the extra gain. TELEVISION PROJECTOR The heat creates no smoke or fire In cities the booster often eliminates hazard, since there is no inflammable the need for an outside antenna. Cortley Television Corp., The material in contact with the wire. unit is contained in a furniture - New York, N. Y. These fuse resistors are useful in com- style walnut plastic cabinet whose di- This projection televiser can furnish mensions plying with underwriters' requirements are 7x4x4 inches. Built -in pow- a picture as large as 12x16 feet. Oper- er supply operates 1n a.c.-d.c. receivers, as well as in pro- from the 117 -volt ation is seid to be as simple as that tection of other types of equipment. line.- RADIO -CRAFT Resistance values from 15 to 150 ohms are available.- RADIO -CRAFT PA AMPLIFIER SELENIUM STRIPS Altec Lansing Corp., New The ro. qe which may be measured York, N. Y. Standard Arcturus Corp., The Model with the 404A extends from .001 to 300 A -324 portable amplifier Newark, N. J. is rated at 15 watts volts. Input impedance consists 10 output with flat of Kotron rectifiers are thin half -wave frequency response megohms shunted by 20 ppf. from 20 to 20,000 Audio measurements are facilitated selenium units. The entire rectifier is cycles. Two low -impedance microphone by the constructed flat, rather than in usual inputs are provided, each with 95 -db decibel scale. Continuous read - gain ings from -62 to +52 db may be taken. and a separate volume control. The instrument may Two low -gain inputs permit phonograph also be used as a SEIMED tuner high -gain a.f.amplifier.- RADIO -CRAFT and connection. pile -up fashion. Cooler operation re- Variable bass and treble equalizers sults, since heat can be dissipated di- are included. -RADIO -CRAFT TAPE RECORDER rectly, instead of being passed from Amplifier Corp. of America, one plate to the next. New York, N. Y. The Kotron rectifiers employ no more than four rectifying The Model SP850 Magnetape Recorder elements, giving of a home movie projector; minimum voltage drop. They are avail- only four is a high -fidelity unit, designed for pro - operating controls are furnished. A in 75 -, 100 -, fessional and semi - professional able and 200 -ma. ratings. use. -RADIO -CRAFT special plastic screen eliminates glare. Recording, monitoring, and playback Front or rear projection is controlled amplifiers are contained within the by a switch. rack -type cabinet, as well as the erase PROTECTIVE TUBING The metal cabinet, 35 inches high and and bias ollllators 221/2 s and the mechanical Walter L. Schott Co., inches long mounted on rubber - components. tired wheels. -RADIO -CRAFT Beverly Hills, Calif. Walsco Protecto-Tube is a flexible synthetic tubing designed for insulating AUTOMATIC KEY the handles of pliers, screwdrivers, test Electric Eye Equipment Co., prods, and similar tools. Danville, Ill. The Mon -Key is an electronically timed automatic key that makes dots and dashes spaced in relation to their length. Also, it is a monitor, produc- V -O -M METER ing a tone that can be regulated as Triplett Electrical Instrument Co. to volume or cut out entirely as may be desired. Bluffton, Ohio Regardless of the speed to which The Model 2405 -A is a volt- ohm -milli- the key is set (B to 45 words per min- ammeter with a sensitivity of 20,000 ute), dashes are always The kit contains several three times as sizes of tub- ohms per volt on the d.c. ranges and long as dots. The spaces between suc- ing and a bottle of "expanding solu- 1,000 ohms per volt on a.c. cessive dots or dashes are always equal tion." To insulate a tool, the user Voltages up to 1000 on a.c. and d.c., to the dot length. selects tubing of a slightly smaller 50 pa to 10 amps on d.c., and 500 ma The Mon -Key is activated by a light- diameter than the tool. Dipping the to 10 amps on a.c. are included The VU meter, provided principally in its weight aluminum paddle -type key. It tubing into the expanding solution 35 ranges. The ohms range is from 0 for visual monitoring, is also -40 is not affected by vibration. The unit used to swells it. so that it can be slipped megohms in 4 steps. measure bias and erase voltages. A condenser is is basically a multivibrator, and does An over the tool. After drying, he tube in series with the output voltage jack, automatic timer permits the user to shrinks not operate on the adjustel;le- weight making o tight fi.-RADIO. and the ranges are the same as preset the unit to begin and and for principle but is completely electronic. CRAFT' 0.c. volts, RADIO -CRAFT -

AUGUST, I 9 4 8

4t Servicing, 44

2ND IF TRANS r I 6Q7 SPKR 3 i ;i3,;

ANT 5 IF 47014C

-'rB L- -1 , 5.1000 ALL CONOS VC TONE CONTROL GANGED TO ON-OFF SW

LINE D N° PL 6Q7 657 6AB 25L6 257660n 6814 9í B 2 2 o/ CP 25Z6 1 2 7 2 7 51EG 27 21 AVC .01 /600V.. SEE

from a transformer -less power supply. The battery tubes of the Philco Model 38 -38 were replaced with those more suitable for operation Co0werting 7arm Sets forA. C. An opportunity for rural servicemen supply fixed bias for the 6A8 and 6K7 ALFRED SHORTCUT control grids. This permits operating By their cathodes at ground potential. A.v.c. is taken from the high side of SLOWLY but surely the Rural Elec- numbers. Tie the screen grids of the the volume control and filtered through trification Administration is 6A8 and 6K7 together and connect them a 1- megohm resistor and a .05-µf con- bringing power to localities where to B -plus through a 27,000 -ohm drop- denser. A 5- megohm resistor supplies it was totally unavailable a few ping resistor. The original .05 -µf screen contact bias for the 6Q7. years ago. Most of the radios in these bypass stays in use. (Better make sure The power amplifier is the only stage areas were operated from storage bat- it's good.) The 1C7-G oscillator anode with cathode bias. This is developed by a teries or combinations of storage and voltage was supplied through a filter 150 -ohm, 1 -watt resistor. Connect the dry batteries. Many of these sets are network consisting of a 4 -µf condenser blue terminal of the original electrolytic still in use in recently -electrified areas. and 5,000- and 2,000-ohm resistors in condenser to the cathode of the 25L6. The cost and inconvenience of battery series. Remove the 2,000 -ohm resistor Replace the output transformer with one charging and replacement can be over- and the condenser, and connect the having a 3,000-ohm primary. come by converting them to a.c. opera- 5,000 -ohm resister to B -plus. Replace Disconnect the bottom end of the an- tion. The Philco Model 38 -38 is a typical the 120,000 -ohm oscillator grid resistor tenna primary from the chassis and 2 -volt farm radio. The diagram shows with a 68,000 -ohm unit. The high side connect it to the ground terminal so a how it was converted to a.c. operation of this resistor is connected to the a.v.c. doublet antenna or outside ground can using parts costing less than $8. The line through a 15- megohm resistor to be used. Realign the set. heavy lines show circuit changes or new wiring. The portions of the circuit shown in light lines are not changed. A WELL -DESIGNED RADIO SERVICING WORKBENCH Values of parts already in the set are underlined. An a.c. -d.c. circuit was selected for economy and easy installation. The 1C7- G, 1D5 -GT, and 1H4-G (second detector) sockets were rewired for the 6A8, 6K7, and 6Q7, respectively. The 1H4 -G driver was replaced by a 25L6, and the 1J6 -G by a 25Z6. The 1E5-GP socket was not used. s The first step is to rewire the filament pins in series with the 160 -ohm line - cord resistor in the order shown in the diagram. Wire up the power supply, using the 25Z6 in a voltage -doubler circuit. B -drain is low so you can use the old driver transformer as a filter choke. If the primary is open -it usually is if the set has been out of service for a while - use the secondary. It will filter well and still carry the load. Take care when wiring the switch into the power line. One set of its contacts shorts to ground. If you use this section, you will short one half of the rectifier to ground. Use an two ohmmeter and be sure. The service bench of Hambrick & Crecente, radio technicians of Moultrie, Georgia, has 6 -volt The oscillator circuit requires little complete sets of equipment that can be used simultaneously. Eight a.c. outlets and one rewiring because the elements of the d.c. outlet provide operating voltages for a.c. and auto radios. Drawers and compartments pro - 1C7 -G and 6A8 have corresponding pin vide ample storage space for spare parts, tools, wire, and public address equipment. RADIO -CRAFT for

.4, s-:_ _ _t_ , ä , .. _:.., - á- - - ..:: tiew 1948 and F.M. ífitanuah BIGGEST BARGAIN IN RADIO DIAGRAMS Make these two new mammoth volumes your money- saving source for data on all recently released receivers. Learn about modern circuit developments, be ready to repair any new radio no matter how complex. You pay only $2 for each of these large manuals. With these two volumes on your workbench there is nothing else to buy, nothing else to pay -a whole year of radio diagrams and service data yours for a couple of dollars total. Again Supreme Publications beats all competition and gives radio servicemen greatest bargains in service information. Other volumes for previous years described F.M. and Television New 1948 Manual below. No -risk examination granted to servicemen. Use this new giant manual of Be prepared to repair quickly factory instructions for trouble- all new 1948 receivers. In this big shooting, repairing, and align- single volume you have clearly - FIND ALL RADIO FAULTS DOUBLE -QUICK ment of any 1947 -1948 F.M. and printed, large schematics, needed Television set. Every popular alignment data, replacement parta You can speed -up and simplify radio make, including new F.M. tuners, lists, voltage values, and informa- repairs with AM -FM combinations, and all tion on stage gain, location of SUPREME PUBLICATIONS Manuals. Service all radios types of television receivers. De- trimmers, and dial stringing, for tail circuit diagrams, theory of almost all recently released sets. faster, better, easier, save time and money, use these operation, test hints, alignment Makes toughest jobs amazingly most- often -needed diagram manuals to get ahead, earn data, including both meter and easy. Find faults in a jiffy. oscilloscope methods. This is the Speed -up all repairs. The time more per hour. For the remarkable bargain price (only material you need to fix any saved on your next job will pay modern F.M. or Television set. the $2 bargain price for the $2 for most volumes) you are assured of having in your Don't turn this profitable work complete manual -after that you shop and on the job, needed diagrams and away for lack of knowledge and use it FREE. A worthy com- other essen- information. Use this newest panion to the 7 previous volumes tial repair data on 4 out of 5 sets you will ever service. Supreme manual to save time used by over 120,000 shrewd radio and money on your very next servicemen. New manual coven Every popular radio of all makes from old- timers to new F.M. job. Data presented on 192 models of 42 different manufac- including F.M. and large pages,855x11 in. turers. Giant size: 1948 sets, Television, is covered. Sturdy, manual -style ,$ 81/4x1lw, 192 pages + Clearly printed circuits, parts lists, alignment data, and binding. Just pub- index. Manual - style lished. Special price.. binding. Price only 00 helpful service hints are the facts you need to improve your servicing ability. Save hours each day, Models Mate by: R.C.A., Zenith, every day, begin to earn more by making re- Philco, Sears, Fada, pairs in minutes instead of hours. Let these Emerson, Belmont, manuals furnish you with diagrams for 80% Detrola, Crosley, of all sets. There is no need to spend large G.E., Westinghouse, Arvin, Majestie, sums for bulky, space- wasting manuals, or to Stewar t- Warner, buy additional drawings every few weeks ; be Admiral, Delco, wise, use SUPREME Manuals to get the most Stromberg. Carlson, in diagrams and service data for the smallest Wards, West'n Auto, Sparton, Motorola, cost. Act today and be money ahead with and many others. Supreme Publications.

.41

Use coupon Select Supeme Diagram Manuals and Record Clanger Books you want to examine. to order manuals for examination Send the no -rink trial coupon. Use the manual In your am hone or shop for 10 Fnpulur sets of all makes from 1926 to 1948 are included. days at our risk. See for yourself how coy It is to flu all sets with the right data. You will agree that 8u1weme Publications are the greatest values In senlrc manuals. You must be completely satlafed, or relum manuals and gel your money back. Record Changers Manuals 4- ti Post -War Models Pre -War Models : NO RISK TRIAL ORDER COUPON Service :pertly Il modern 11945 -19481 Just what you need to repair putdly record Hungers. All popular makes. Just thousands of prewar (before 1942) auto- SUPREME PUBLICATIONS, 9 S. Kedzie Ave., Chicago 12, ILL. follow slmrslified factory instructions to matic record changan, manual units. make needed pick- adjustments and repairs. ups, wireless oscillator., recorder, and Hundreds of photographs and exploded combinations. Hundreds Ship the following manuals on trial under your 1948 views. of mechanical and Large sire: 8% r 11 inches. 144 electrical diagrams. 128 large pages; guarantee of satisfaction or money-back. PRICED facdlled pages. ]'rice slam 1947 only 61.50 postpaid size: 8% a 11 inches. (Rice. anti 61.50. New F.M. and Television Manual.. $2.00 1946 AT ONLY See Your Radio Jobber or Send Coupon Post -War Record Changer@ 1.50 1942 17 1941 - Pre -War Record Players & Recorders 1.50 S2 1940 I am enclosing . EACH 6 send postpaid. 1939 trreit hu iccztis EJ Send C.O.D. I am enclosing 6 deposit. 1926-1938- $2.50 PUBLISHERS OF RAI)10 BOORS. MANUALS, AND DIAGRAMS Name:

9 South Kedzie Ave. Chicago 12, Illinois Address: AUGUST, 1948 11:

Gr Vt eCmOn, 7eMFAtESr NEINS of 7ifE yEAFt-

/dro%'c#ig- THE FIRST ALL SERVICE COURSE J IN CREI HISTORY

U V likvásáon adl VIONat Practical On- the -Job Training Program for the Receivers will be marketed in 1948. In years to come millions more will flow into American homes. With Better Serviceman Who Wants Greater Earn- Television comes FM receivers and circuits. This new ings and Security In This Expanding Field field demands a tremendous increase in the number of properly trained television and FM technicians to install THIS basic CREI Servicing Course paves the way to and service this equipment. greater earnings for you. Since 1927 thousands of professional radiomen have enrolled for our home study CREI EQUIPS YOU TO INSTALL AND SERVICE in Practical Radio Engineering. Now, for the courses ALL TYPES OF TELEVISION AND FM RECEIVERS first time, we introduce a Practical Servicing Course. You do not have to be, or want to be, an engineer to Now ... with the help of of the "top third" now en- the this new CREI streamlined gaged in service work to benefit from this course. It is written for you - Service course you can move enter the ultimate profitable average good serviceman! It's not too elementary for ahead to unlimited oppor. field of television and EM the experienced. It's not "over the head" of those who tunities in your chosen field. installation and service. year! and CREI has again taken the This can be your big have limited experience -if they have real ambition lead by offering a course so Don't waste another day. natural ability. entirely new that for the first CREI has the answer to your time in our twenty-one year future security in this new CREI developed this course at the request of several history we can offer a down - servicing course. Write today large industrial organizations. The urgent need of to -earth course of training for complete information. for servicemen. In offering The cost is popular. The capable, trained servicemen is one of the big problems this course at a popular price, terms are easy. The info', of the industry. Hundreds of thousands of Television CREI is enabling thousands mation is free. Write today...... « ...... e...... , Radio Service Division of CAPITOL RADIO ENGINEERING INSTITUTE 2 16th A Park Read, N. W., Dept. see, Washington 10, D. C. RADIO Gentlemen: CAPITOL Please send me complete details of your new home study course in Television and FM Servicing. I am attaching a brief resume of my experience, education and present position. ENGINEERING INSTITUTE NAME An Accredited Technical Institute STREET Dept. 588, 16th & Park Rd., N. W., Wash. 10, D. C. CITY ZONE ... STATE LJ I AN ENTITLED TO TRAINING UNDER 6. I. ILL. Branch Offices: New York (7) 170 Broadway San Francisco (2) 760 Market St. RADIO -CRAFT for

presents the amazing RADIO INDUSTRY RED BOOK

GUIDE RED BOOK BUYERS REPLACEMENT PARTS Approximately Receiver BUYER'S GUIDE 11,000 Models Covered

Covers ives you instant Ten Nears: voluma o{ 1948 authoritative thousands 1938 to MA -a SINGLE parts {or replacementlacement all other on All than in to Use reliable data useful data Easy receivers.. . All Data popular radio COMBINED and manuals Quick to Find arts guides replacement p 440 Pages FOR THE FIRST TIME IN RADIO HISTOR. Smythe -bound COMPLETE! All 9 Major Replacement Components listed Industry Opens flat The First Cooperative Behalf of the Effort in 17 leading arts Manufacturers Represented Technician Radio Service

COMPLETE DATA ON ALL RECEIVER REPLACEMENT PARTS - ALL IN THIS ONE GREAT BOOK!

Save time! Stop wasteful hunting! Only the RED BOOK gives you ALL 18 months in preparation -over $90,000 to pro - Get ALL the parts data you need - this invaluable data. Herds everything duee.The RED BOOK is the product of thousands of man - you need to know about the replacement hours spent in laboratory research and in cooperation quickly -from this single book. parts for the receivers you service daily. with 17 participating manufacturers to produce the most NOW -for the first time -have all the re- The RED BOOK gives you original manu- complete, accurate, authoritative parts replacement guide placement parts data you need -ALL in one facturers' parts numbers, proper replace- ever published. Every bit of information in this amazing single, authoritative volume. No more waste ment parts numbers and valuable installation book has been painstakingly checked to insure maximum of valuable time searching through dozens notes on Capacitors, Trans formers, Controls, accuracy and usefulness. Over $90,000 was spent to of incomplete manuals and catalogs. The IF Coils (including Peak Frequencies), RED book that brings you RED BOOK, first and complete parts Vibrators and Phono Cartridges. prepare the BOOK -the only only Speakers, need know bit of replacement guide ever produced, covers approximately Tebe and Dial Light data includes number everything you to -every 17,000 radio models made from 1938 of tubes in each chassis, with type number parts data you want to make your work easier and more through 1947 -l0 full years. Lists parts for each tube, plus dial light numbers. profitable. You can't afford to be without the RED a made by 17 leading manufacturers -not just Battery data includes replacement numbers BOOK. It's the indispensable guide you'll use profitably one! Gives you complete. accurate data on on A, B, and AB packs. The following every single day. Stop hunting for the right answers all 9 major replacement components -not leading replacement parts manufacturers are now-order your copy today. just one or two. Clear, concise. easy- to-use- represented in the RED BOOK: over 440 pages (81/2' x I1') bound in a sturdy sewed cover, arranged alphabetically AEROVOX ASTATIC THE INDISPENSABLE by manufacturer and model number for BURGESS CLAROSTAT $395 quick reference. Does away with confused CORNELL -DUBILIER IRC RED BOOK ... ONLY... collections of separate books and manuals - EVEREADY JENSEN gives you complete information -PLUS data MEISSNER MERIT that cannot be found in any other source QUAM -NICHOLS RADIART -at a fraction of the price you'd pay for SOLAR SPRAGUE the books it replaces. There's never been Mail This Order Form to Your Parts Jobber Today anything like it- absolutely indispensable STANCOR SYLVANIA or send directly to HOWARD W. SAMS & CO., INC., for every service shop! THORDARSON 2924 E. Washington St., Indianapolis 7, lad. My (check) (money order) for S enclosed. BE SURE TO ORDER YOUR RED BOOK TODAY O Send RED BOOK(S) at í3.95 per copy. (I understand that delivery will be made to me to September.)

Name J HOWARD W. SAMS & CO., INC. Address INDIANAPOLIS 7, INDIANA City State

AUGUST, 1948 New York Telephone Company men watch as a crossbar dial system reports to its test frames at exchange "Watkins 9," New York,

A Dial System Speaks for Itself

As dial systems have been improved, so also at once so that your call can go through with- have the means of keeping them at top effi- out delay. Then on the test frames lights flash ciency. Even before trouble appears, test up telling which highway was defective and on frames, developed in Bell Telephone Labora- what section of that highway the trouble tories, are constantly at work sending trial occurred. calls along the telephone highways. Flashing Whenever Bell Laboratories designs a new lamps report anything that has gone wrong, telephone system, plans are made for its main- and the fault is quickly located and cleared. tenance, test equipment is designed, and key If trouble prevents one of the highways personnel trained. Thus foresight keeps your from completing your call, another is selected Bell telephone system in apple -pie order.

BELL TELEPHONE LABORATORIES EXPLORING AND INVENTING, DEVISING AND PERFECTING FOR CONTINUED IMPROVEMENTS AND ECONOMIES IN TELEPHONE SERVICE RADIO -CRAFT for :Illlstrllctivn (l9

Compact Radio From Holland

THIS little receiver is of Dutch or- The little radio is built igin and in its original form was around and behind its Etbout five inches in diameter by less own speaker. than two inches deep. As described in Radio Bulletin (Bussum, Holland) it was constructed around the smallest of the Philips loud speakers, with all controls at the back. This could be omitted and the regenera- The ticklers of the 10-20- and 20-40 - Available American tubes and parts tion control used to control volume as meter coils are woven between the turns may make such extreme miniaturization well. In that case, the antenna could be of the primary. The others are close - impossible here, but the circuit is adapt- attached directly to the 20014f con- wound about % inch from the ground able to standard U. S. equipment and denser connected to the antenna coil end of the secondary. Primaries may be might repay an experimenter for the primary. 34 to% inch away on the same form or time spent on it. The original constructor used an in- wound inside as described for the broad- The set is a 1 -tube, 2 -stage receiver genious switching arrangement which cast coil. All primaries and ticklers may with a regenerative detector and re- permitted tuning to three important be wound with No. 32 or 34. All forms sistance- coupled audio amplifier, includ- stations on different wave bands with are 1% inches in diameter. Although ing degenerative feedback. The 6AD7 is two coils and three sets of trimmers. there are three windings, one terminal the only U. S. tube adapted to this cir- The American constructor will proba- of each is common, so four -prong coils cuit. (Original was a UCH21 or ECH- bly prefer continuous tuning, either one may be used. The usual reversing of the 21.) An interesting feature is -the an- band with a single coil, or with plug -in tickler is indicated whenever the set tenna resistor used as a volume control. coils if the set is to be a short -waver. fails to oscillate. In the upper position, the tone con- Variations on the power supply are trol switches in a feedback network to possible. Where miniaturization is not reduce highs. The small series capacitor desirable, a full -wave rectifier with a limits feedback to the higher frequen- tube might be used. AR: d.c. operation is cies, so that the gain of the pentode is not recommended, because of the high reduced more at the high end of the filament current of the 6AD7. However, range than at the low end. In the lower the whole circuit could be adapted to switch position (as shown in the dia- dry -cell use with a 1D8 -GT. gram) highs are attenuated slightly by the 200µµf capacitor from grid to ground. This is done to prevent oscillation in the pentode. AM TUNER Standard 3- winding broadcast or Here is a small AM tuner using a short -wave coils may be used. For broad- permeability tuning unit. The tubes are cast use only, the antenna coil may be made by Sylvania, and are the type used Modified schematic of the original receiver. wound on a 1% -inch form with approx- during the war in proximity fuses. Ex- imately 100 turns of No. 28 enamelled cept for size, the 1W5 is like the 1T4 , wire; the tickler coil may consist of 30 and the 1Q6 is similar to the 1S5. turns of No. 32 to 34 enamelled wire This particular tuner was made very wound next to the ground end of the small so that it could be hooked to a secondary; the primary can be 20 to 30 hearing aid. A small switch is installed turns of the same wire wound in a close in the aid to cut out the microphone doughnut just small enough to slip in- and cut in the tuner. side the form, where it may be moved to CURTIS HILL, provide best coupling. Jackson, Mich. For broadcast use, Cl may be 365µµf and C2 160µµf. For short -wave reception these may both be 140 to 1604 Short -wave coils may be wound or standard coils obtained. Either commercial or homewound coils will require some experimental adding or subtracting of turns to fit each individual receiver. Suitable coil constants are: Band Psi Secondary Tickler Meters Turns Turns Spacing Wire Turns 10-20 2 6 1 in. No. 18 4 20 -40 4 12 1 in. No. 18 6 40-80 8 20 own width No.23 10 A- A +I.SV at45V 8- This back view shows the switch and trimmers. 80 -160 16 40 close No. 23 18 J-TD NEARING AID INPUT AUGUST, 1948 50

REMOTE CONTROLLED COIN INSERT AND SPEAKER BOX A Made by Solotone Corp., Los Angeles 24 Volt operated, fused Size of base 51/2" x S" x 10" high Weight 11 lbs. Front grill is sloping, illuminated by two pilot lights PM speaker 6" size with matching transformer, screen and felt protective grills Will accept 5c or 10e coins Each 5c coin gives equivalent of two phonograph records Has Haydon Mfg. Co. timer Has lock installed in top. (with key.) Coin box readily removable, size 11/2" x 7%" x 1%" deep Finished in attractive blue crackle metal, red plastic with chrome plated grill Easily mounted on a wall or a flat base This unit could be used to house coin operated radio Original cost and selling price of this unit was several times our price. BRAND NEW $4.75

REMOTE CONTROLLED COIN INSERT AND SPEAKER BOX CLOSED VIEW B A OPEN VIEW Made by Personal Music Corp., Newark. N. J. Model F 24 Volt operated, fused Weight 61/2 lbs. Size 43/4 x 71/2 x 51/2" high Sloping front P M Speaker 5" size Has 2 Pilot Lights for illumination Finished in chrome metal and grill with red plastic Accepts 1 to 6 nickels Each 5c coin gives about two phono records of music Should be moùnted on a flat base Has Haydon Mfg. Co. timer Lock installed in top. (with key.) Easily removable coin box, size 6" x 3172" x 1/" Requires 4 wires from power unit A beautiful piece of equipment that could be built to house coin operates! radio Worth several times our asking $4.95 It CLOSED VIEW price. Price brand new OPEN VIEW

$2475

MASTER POWER SUPPLY UNIT ADAPTER- AMPLIFIER for Measured Music System Made by Personal Music Corp., Newark. N. J. Made by Solotone Corp., Los Angeles Model F 110 V 60 cycle, input 300 Watts, fused 115 Volta. 60 Cycles. fused 15 Watt output 125 Watts Input 15 Watts output Has high -low AC input line switch Tube line up 815. 6SLT, -6111G'11. 5 l'4G Tube lineup: 2D21, 6AL5, 6SJ7, 6SN7, Crystal. Magnetic or 600 ohm line Inputs 2- 6L6G's, 5U4G Individual v;tiHme, treble and bass co,urols TERMS: CASH WITH ORDER Size 11%" x 17V," x 10" 15 ohm output L Chassis size 11%* x 17.k" x 21/2" Size 105¢' X Mlle x 6h high lvelght 30 lbs. Has Vernier volume, master volume, treble and lasses size 101M' x 151' x 354' high base controls Ilan meter to iletemnine number M plays AMERICAN SURPLUS Gray crackle finish IIas 24 V AC output for the remote speaker boxes. fused Well ventilated Toggle switeh turns remote speaker hoses off and on External handles for carrying it Black Crackle finish Lock installed in top. key.) Well vent l laud PRODUCTS CO. (with Built tnuoun night and day senior Built for continuous night and day service for our Originally sold for several times our asking $24.75 53i N. CAPITOL AVE Originally sold for several times $24.75 prim. Prim Brand New asking price. Price brand new.... INDIANAPOLIS IND. RADIO -CRAFT for LIIIISiPuCilem 51 A Six-Tube Dry -Cell Superhet

A 1.5 -Volt Radio For Use in Rural Areas

By EDWIN BOHR

AN r.f. stage and two stages of 1T4 i.f. stages, a 1S5 second detector i.f. are found in this receiver, and first audio amplifier, and a 1S4 in its size has been kept down by the output is employed. the use of miniature button - The chassis should be cut and punched base tubes which also increase efficiency. before mounting the parts: a slip of a Most battery -operated portables are drill may ruin a speaker or tuning con- designed for local reception only and are denser. unable to pull in the weak stations. A Grid leads should be pressed close to the chassis to reduce stray fields and troublesome oscillation. Use light, flexible hookup wire because the socket lugs are delicate and can be damaged easily. The difficulty of grouping parts around these tiny sockets makes terminal strips necessary. The holes in the centers of the sockets were made to be used in case future tubes had exhaust tips on the bottom. They serve admirably as ground The six -tube superheterodyne is well laid out. lugs. The antenna coil should be mounted above the chassis, and the r.f. coil 6 -VOLT RECEIVER below. By using the center section of the tuning condenser for oscillator tuning, Only a single 6 -volt battery is used in receiver for both filament and plate Though nota portable, set is very compact. a source of feedback trouble is avoided. this supplies. The tuning capacitor is a 365- A 4,700 -ohm resistor and a .01 -µf con- logical step for increasing sensitivity is and r.f. denser decouple the i.f. stage 2 214E0 .00025 to add an r.f. stage. The use of two i.f. B- supplies. This is necessary to prevent 6SA7 stages on the broadcast band is not gen- IRON CORE OR PLUG IN i.f. voltages from feeding back to the MIXER erally necessary, but, by using two r.f. stage when the set is tuned to the stages and applying a.v.c. to only the low end of the band. The 1S5 plate is first, the second can be made to func- bypassed with a 100-µµf capacitor to tion as an a.v.c. amplifier. This gives reduce high notes and noise as well as F ED6ACx COR more satisfactory a.v.c. action. S 6G6 -G to add to the r.f. filtering. O AN7 An orthodox circuit consisting of a RFC 1T4 r.f. amplifier, a 1R5 converter, two The speaker is mounted on the chassis AFT by the bracket intended for an output 3:I transformer, instead of by the flange. This mounting method helps assure a microphonic -free radio. The speaker is FILS a heavy -duty unit with a heavy magnet .0001 which contributes to the set's efficiency. 6V PHONES The tuning condenser used will tune to 1600 kc with a set of standard broadcast coils. The receiver is aligned in the µµf- per -section unit and standard broad- usual way. Use the size padder the cast coils may be used. The i.f. trans- manufacturer specifies for the coils. former may be a standard unit with a The 67% -volt B- battery was chosen regeneration winding or the extra wind- because it could be placed in the bottom ing may be added to an ordinary trans- of the cabinet built for the set. former. With suitable coils the receiver per- JAMES C. SOUKUP, Underchessis photo shows placement of parts. forms well on the short -wave bands. Randolph Field, Tex.

S Ic

d 11 \SPxR IF 4S6RC o6+67Sv 06

o A+ 1.50 oA C(7x 2.2YEG 5W ON VC. >1N

Schematic of the super. Two stages of r.f. and two of i.f. give the sensitivity needed by many dry -cell sets, which are often used in rural areas far from broadcast stations. AUGUST, 1948 Construction 52 I

`The New Model 247 1 GREEN says . . . TUBE TESTER; Checks octal.' LOOK! COMPARE! lectals, bantam jr. peanuts, tele -' FIRST TIME AT THIS PRICE vision miniatures. magic eye,' A REAL HOT SPECIAL . . . . hearing aids, thyratrons, the 1 DETROLA RECORD CHANGER new type H. F.. miniatures, etc. FEATURES: * New element' -a p Plays 10 & The neon lamp used as a photoelectric eye. selector switch 12" reconis

- reduces possibili- 1 sutomati- --_ calls \` -- ty of obsolescence. * When O pact too fit checking Diode, Triode and Pentode section:- most i n- NEON LAMP EXPERIMENTS of multi -purpose tubes, sections can be teet,'d _ atallations. individually. A special isolating circuit allots- - By each section to be tested as if it were in a I HAROLD PALLATZ separate envelope. * Checks for shorts and $11.95 leakages up to 5 Megohms between any and SPECIAL all of the terminals. * The 4 position fast - MANY interesting and useful devices action snap switches are all numbered in UNHEARD OF VALUE!... may be built from the ordinary exact accordance with the standard R.M.A. numbering system. MAGNAVOX P.M. SPEAKERS fluorescent light starter, the type of Model 247 cornea complete with new speed - containing a neon lamp. (Any t/4- You know of starter read chart. Comes housed in handsome, hand - all the quality J watt neon bulb will work.) Remove rubbed oak cabinet sloped for bench use. A these well known speakers. also slip -on portable hinged cover in Need we say more? the metal can and the capacitor from the included for outside use. Size $90 5" $1.39 1 ' starter. Is" x 8Y" x 5%". 6" 2.05 ONLY NET 8" 2.95 Also needed are a 47,000 -ohm, 1 -watt 12" 5.95 s resistor, a .003 -pf capacitor, and a 500,- The Model 650 -An AC Operated a TERRIFIC BUY 000 -ohm linear potentiometer. A source SIGNAL POWER TRANSFORMERS of 90 volts d.c. will be required for the AZThese fatly cased Paver Transformers oscillator experiment. This may be ob- GENERATOR are of exceptional quality at less than tained from two 45 -volt portable radio RANGE: iL price. 100 KILOCYCLES TYPE A-90 Mills -700V c.L 5V at 3 batteries or by tapping the voltage from amps 6.3V $2.29 TO 105 MEGA- 6.3V an a.c: d.c. receiver. If voltage from a CYCLES TYPE B -140 Mille -720V et. at 5 amps & 5V at amps 3.69 used, be *RI, obtainable V TYPE C-160 Mills -700V c.t. 6.3V receiver is careful to avoid separately or mod- at 5!y amps. 5V at 3 amps 3.69 shock. It is a good idea to make sure ulated by the Audio TYPE D -200 M111s -800V at. 5V at 3 amps 6.3V Frequency. at 5% amps 4.29 the receiver chassis is connected to the * Audio Modulat- grounded side of the power line. If a ing Frequency - PORTABLE 400 cycles pure sine wave -less than 2% dis- 117 -volt lamp wired between chassis and tortion. RECORD PLAYER --- -- '.'==_'f ground lights, reverse the power plug. * Attenuation -3 -step ladder type of attenua- 3 tube amplifier, vol- tor IT pad). ume and tone control. * Uses a Hartley Excited Oscillator with a 1 & 12" rec- . Buffer Amplifier. ords.orda. Heavy Alnico '' -Y Audio oscillator * Tubes: 6J5 as R.F. Oscillator: 6SA7 as 5" PM Speaker. In Connect the components as indicated modulated buffer and Mixer ; 6SL7 as audio handsome simulated oscillator and rectifier. leather cane, 121' x .'i ' l ii'=;j:?1$- ' in Fig. 1. A tone should be heard in the Mojiel 650 comes complete with coaxial cable, 10t,í1" x 4t/4 . Just headphones, and of con- test leads and instructions. Housed in heavy plug in A.C. or D.C. adjustment the gauge grey crystalline cabinet A $24.95 Value trol will change its pitch. If the neon is with two tone etched front panel.panel $3995. but no tone is heard, interrupt the Size 91/_" x 10" x ONLY $15.79 lit NET PRICE supply voltage momentarily. Special! TELEVISION PARTS Special! This is a relaxation oscillator, a type The New Model CA -11 Blab Voltage tubular Television Capacitors. Pyre- teen Impregnated -Wax filled used in early oscilloscopes. The capaci- .005 ó000V 38c .001 6000V 380 tor takes a certain length of time to SIGNAL TRACER .0005 6000V 38e charge. When it has charged to about Simple to operate .05 6000V 58e . because signal 60 volts, the neon in the lamp ionizes Dipole I &aReflec or Antenna lms $5.40 intensity readings 300 Ohm Line $1.30 per 100 ft. or "breaks down," discharging the ca- are indicated di- 72 Ohm Coaxial Cable 4e per ft. redly on t h e All Rave Television holsters $20.50 pacitor. Again the capacitor starts THOUSANDS OF TELEVISION PARTS IN STOCK. meter! WRITE US YOUR REQUIREMENTS. charging and again it is discharged by * Simple to OP, ionization of the neon. As a result, cur- ate - only 1 Con- necting cable-no SPECIALS rent through the headphones varies at tuning controls. REPEATED BY POPULAR DEMAND *Highly sensi- a rate determined by the capacitance I prong Universal Vibrator 96e tive uses an im- type - ' et of 2 1F Transformers 456ko 78e proved V ac u u '0/20 450V FT Condenser 39e Tube Voltmeter .loor & Pick -w. special Standard Brand, circuit. *Tutu Both for S4.29 and resistor- capnc- hurter Condensers, .01: ,005: .0075; .02; ity network are 2000V 18e a. built into the Dr- Probe THIS MONTH ONLY tector * 1LED STANDARD BRAND TUBES Completely port- SEALED MANUFACTURERS CARTONS at t he able- weighs 6 lbs. and measures 5" x 6" x 7 ". LOWEST PRICES * Comparative signal intensity readings are Write for Spxial Price List RC-2 indicated directly on the meter as the Detector probe is moved to follow the Signal from An- tenna made for in- ALL MERCHANDISE BRAND NEW to Speaker. Provision is AND 100% GUARANTEED sertion of phones. NO SECONDS! NO REJECTS! NO OFF-BRANDS! The Model CA -11 comes housed STANDARD BRAND MERCHANDISE ONLY in a beautifel hand -rubbed wood- $ en cabinet. Complete with probe, test leads and instructions. 875NET :or -) Deposit required with C.O.D. Orders. All ord. rx F'l7B New York. Minimum orders $2.00. Availaole for Immediate shipment from stock -20% All orders must include shipping chargea. deposit required on all C.O.D. orders. THE HOUSE OF BARGAINS MOSS ELECTRONIC GREEN RADIO DISTRIBUTORS DISTRIBUTING CO. Supplies & Equipment Electronic Figs. I, 2, Schematics for three of the ex- !Le pt. RC -8, 229 Fulton St., New York 7, N.Y, BROOKLYN. N.Y. 3- 482 SUTTER AVE Di. 2 -4444 periments with fluorescent lamp starters. RADIO -CRAFT for 53

MONEY BACK GUARANTEE- We believe units offered for sale by mail order should be sold only on o "Money- Back -If- Not -Satisfied" basis. We carefully check the design, calibration and value of all items advertised by us and unhesitatingly offer all merchandise subject to a return for credit or refund. You, the customer, are the sole judge as to value of the item or items you have purchased. THE NEW MODEL 670 The New Model 770 - An Accurate Pocket -Size SUPER METER VOLT -OHM MILLIAMMETER (Sensitivity: 1000 ohms per volt)

SUPER METER. A Combination Features: - VOLT - OHM - MILLIAMMETER Compact- measures 314," x 5T/s" x 2% ". plis CAPACITY REACTANCE, Uses latest design 2 accurate 1 Mil. INDUCTANCE a n d DECIBEL D'Arsonval type meter. Same zero ad- MEASUREMENTS. justment holds for both resistance ranges. is when D.C. VOLTS: 0 to 7.5/15/75/150/750 / It not necessary to 'readjust i"01//7500. A.C. VOLTS: 0 to 15/30/ switching from one resistance range to 15n/300.'1300/3000 Volta. OUTPUT another. This is an important time -sav- VOLTS: 0 to 15/30/150/300/1500 /3000. ing feature never before included in a D.C. CURRENT: o to 1.5/15 /150 me.: V.O.M. range. Housed in in this price o to 1.5 Amps. RESISTANCE: 0 to 500/ round -cornered, molded case. Beautiful 100.000 dune. 0 to 10 Megohms. CA- Depressed PACITY: .001 to .2 SIM.. .1 to 4 MM. black etched panel. letters (Quality test for elect rolytlea.) REACT- felled with permanent white, insures long - ANCE: 700 to 27,000 Ohms; 13,000 Ohms life even with constant use. to 3 Megohms. SpeslfiestteSs: 6 A.C. VOLTAGE RANGES: INDUCTANCE: 1.75 (o-70 Henries; 35 0.15/30/150/300,1100/3000 voit.. te 8.000 henries. 6 D.C. VOLTAGE RANGES: 0- 754/15/75/ sans. to 150/750/1:00 DECIBELS: -10 to +19. +10 +38. 4 D.C. CURRENT RANGES: 0- 154/15 /150 30 to - +54. Ma. 0 -IX Amps. The model 670 comes housed In a rugged, 2 RESISTANCE RANGES: 0 -500 obm3. 0 -1 crackle -finished steel cab- Megohm. inet card with test The Model 770 cones complete `eats and eerwithg est $2840 with self- contained batteries, striations. Sloe 5/1' X test leads and all operating $1390 NET NET 7' ," s 3 ". instructions. The New Model 450 THE NEW MODEL 777 TUBE TESTER 20,000 OHMS PER VOLT!! Speedy operation -assured by the newly designed rotary selector switch which replaces the TUBE & SET TESTER usual snap, toggle, or lever Tube Tester Specifications: action switches. *'Teets all tub. including New 'Miniatures, etc. Also Pilot Lights. * Tests by the well -established emission method for tube quality, SPECIFICATIONS directly read on the scale of the meter. * New type line voltage. Tests all tubes up to 117 volts. V.O.M. SpetiRcatlons: Tests shorts and leakages up to D.C. VOLTS: et tubes. 20.000 Ohms 3 Megohms In all Tots l'er VoltI. 0 to 7.5/15/T5/130,1730 / both plates In rectifiers. *Ness 1.500 Volts. type line voltage adjuster. Tests Individual sections such as diodes. A.C. VOLTS: (At 10.000 Ohms triades, pentodes. etc.'. in multi- Per \'oit). 0 to 15/30/150/300/ purpose tubes. 1solse Test defects 1.51W'ä,000 Volts. mlaophade tubes or noise due to faulty elements and lave internal D.C. CURRENT: 0 ta 1.5/15/ connections °Uses a 45i' square 150 Sla. 0 to 1.5 Amperes. rugged Meter. \Yorks on 90 to RESISTANCE: 0 to 5.000.!50.- 125 volts 60 cycles A.C. 000 /500.000 Ohms. 0 to 50 Meg - °hins. EXTRA SERVICE-May be used as an extremely sensitive condenser Model 777 operates on 90.120 Leakage type volts SO cycles A.C. e.Oused in Checker. ¿relaxation beautiful handrubbed cabinet. ed in this model Complete with tot da. tube, chcharts and detailed $5995 es dol,cent 50 arts tileR lt fper tons. Sire í13s glene, $39NET 12tí a NET The Model S -35 -- a POWERFUL The Model 88 -A COMBINATION SIGNAL GENERATOR REFLEX PROJECTOR AND COMPLETE WITH BUILT -IN DRIVER UNIT SIGNAL TRACER Signal Generator Specifications: CONSERVATIVELY RATED AT 35 WATTS -WILL EASILY HANDLE UP TO 55 WATTS WITHOUT BLASTING Frequency Range: 150 Kilo- cycles to 50 Megacycles. The Heavy gauge aluminum in the main trumpet section rompleteiv eliminetea lila.d R.F. Signal Frequency is kept log and blaring. New idiotle alt tphracm the wt peaks of II, completely constant at all out- ,dal U'w : also It is absdmvly Import ous toy al mapher it ill ii O't whide.is th, old type was subject to atmospheric cor- put levels. 'Modulation is ac- N'eenabled to guarantee complished by Grid -blocking ac- the unit for one year. tion which is equally effective for alignment of amplitude and Specifications frequency modulation as well as POWER (CONSERVATIVE) -35 for television receivers. R.F. ob- WATTS: AIR COLUMN -31/2 FT.: tainable separately or modu. DISPERSION-80 °; POWER (PEAK) lobed by the Audio Frequency. '-55 WATTS: BELL DIAMETER - Signal Tracer Speelgntlens: IMPEDANCE-6 ohms: FRE- -Is': 1'00, the new Hyivanla 1N34 Ger- QUENCY RANGE -130 to 5000 manium crystal Dude which com- C.P.S. PROJECTION -Ve mile: bined with resistance- capacity network provides a fre- FINISH - Attractive quenp ge of 300 owe tone erystalline. cycles to r50 Megacycles. The Model Comes $2885 Complete with Built-in The Model 88 s complete with all test leads and speratlnp Driver Unit, ONLY $2850NET instructions. ONLY 20!'0 DEPOSIT REQUIRED ON ALL C.O.D. ORDERS

PARK PLACE, GENERAL ELECTRONIC DISTRIBUTING CO. NEW VOR.

AUGUST, 1948 54 Construction bring a strong light close to it. This will make the bulb light. The light obtained NOW! is the result of the proximity of another and stronger light. I5R0Ss14 The operation of neon bulbs as light COMPLETE ONLY.. detectors is somewhat critical and care is necessary in finding the right adjustment. The action is due to ionization of y' ABSOLUTELY NO KNOWLEDGE RADIO the gas in the tube by the light, possibly O OF NECESSARY ` YOU NEED NO ADDITIONAL PARTS! coupled with photoelectric action by the THE PROGRESSIVE RADIO KIT is the ONLY COMPLETE KIT plates. The experiment is somewhat sim- -\ (fit. 110 -120 volts regemployed nce Circuits re fifteen n Contains everything you ci provide excellent performance.including Altogether. fifteen ilar to the famous one of Hertz on the need. end `ll ]lita- circuits are constructed. has the receivers. 1 iodle a=si.., Tubes. Condenser, Rests lors and saty all oilierask( n circuits ti transmitters. The e is start with simple breakdown of a spark gap by light. In radio parts. The Instruction Bask writ- circuits of 1 tube en^ ilexpert radio instructors plus severer, !,-`male- imita lm In surf es a` d Banner. teaches you complex. ana finishp Iar several exam+ice ó[ radin igue his experiment a spark gap was used to os a professional manner. The first using three tithes plus recliner. tic built Is a simple porat detector receiver. FarbEach new tige teints nt PROGRESSIVE RADIO 'tKIT .. ONLY S14.75 and just slightly less than breakdown tectors11RF rand tAFnamplifpllflf ki[ is neat forfnr the and SPECIAL FREE OFFER voltage applied. Application of light amplifier desitrit. Ito sused in ennnr' radioatom. Electrical and Radio Tester sent absolutely FREE with colleges. All of the r m only -used detectors are used. each Progressive Radio Kit. PLUS FREE mernberstun in ionized the air and permitted the spark including diode. grid leak. plate and infinite- Impedanee. Progressive Radio Club. Entitles you to free expert ad- The transmitters are designed with Hanley and Ann- vice andconultation s with licensed radio techni- to jump. n - id acillators. using A and control-grid . Write for further information or ORDER your KIT nadul lotion. Both vacuum tube and selenium rectification NOW! If desired, headphones may be inserted in series with the neon bulb; a click will be heard each time the light is The Hottest Combination in Years! interruRted. 4 TOM THUMB CAMERA -RADIO Combination! . It's here ... the Cann l-mib,. und.: pensable for trips. hikes, ball games, CONVERSADAPTOR every outdoor and v cabra fir tic ity. Combines a fine Reflex Camera and This Conversada ptor is a cheap and a powerful Radio into one easy -to -carry unit. Order now ... you'll double compact method of adding a transmitter the enjoyment of every weekend 1 Precision Built - Excellent Tone Quality ONLY AWT Full Vision Slide -Rule Dial $28.75 - SOaaf MICA The Ideal Vacation Companion 6F6 -GT Portable Radio Battery Operated Less Batteries Reflex Camera, Standard #127 Films RFC

T %HITTER) 470/2W 8 Automatic AUTO RADIO _ °'. _ .. ( R (RECEIVER) OUTPUT S2 Tope in car radios, now at a new low price! Six -tube superheterodyne, IST VAIO with steady, full -toned reception. Mounting brackets included for easy in- ,- -^_- -- stallation in your car. Don't miss this big bargain! Six Tube Superheterodyne Three Gang Condenser A tt Powerful Long Distance Reception Fits All Cars, /44 , Easy Installation Mounting Brackets Included OMM 111V 97

RICO MODEL. 315 VACUUM t.. +) SIGNAL GENERATOR TUBE with micro-cycle band VOLTMETER OUTPUT TRANS/ I spread vernier tuning

}}( ` Vitally Important tuning and

- FM and ces.- a %*id aligning Television MODEL 221 to a standard receiver so as to make - era where tuning to very awp it I and critical. The wide extreme A cg pletel 4 4 a - root". and accuracy a by the and transceiver. etcle band ÁiRe Vol : l _I /.. ` vernier spread linen tuba vol ureter dial as.sures accurate frequency >R- ' The section labelled T in the diagram Ceivemnt for test alignment of broadcast FM or Television at sualmazing eeivere. Vernier dial divided into 100 divisions. Any frequency Price. t4 amazing C% is an ultraudion oscillator built on a within .02cí, accuracy. Spring rfurmance can be tuned and repeated loaded acy, [ °:,..,..: split gears eliminate back lash and play providing smooth - i 4% x 3 x 1 -inch chassis. The section late tuning. Window casing encloses and protects the lighted t'Y linearity. d dial and its fine pointer from accidenta and Jarring out of call- etabl en t trolly found In file type [ beled R is the audio portion of the re- bratirr, and Electronic AC In more in or Range 75 RC to 150 MC Complete broadcast band from 550 rad accurateae te Nan was ever possible with a ceiver to be used. KC to 1700 RC covered onene range without switching Un- not cube urrCompletelyeedpl et ly electronic n coils are automatically out to eliminate dead sirota mate. can and ranges: 0-3.- IO. 100. 500 and 1000 volts' andd absorption ,Near dial calibration. DOES NOT CROWD-UP mmeter treasures t bina fremiency end of dial Accuracy better han 5có from .Z ohm to 1.00(1 meeohma in 5 rite bmtdcur on Each 1nLnelrllffrequencies retlt Just as ac n feltrhleaa enNA rage. Instrument is Nd1- 549.95 of dial as at low end $64.50 vldually ca1NraMd.

WRITE FOR PROGRESSIVE ELECTRONICS CO.WPréná,P alér,n DEALERS Al c.o.D. orders CATALOGUE Dept. RC -16 197 UNION AVE- BROOKLYN 11, NEW YORK shipped collect. and resistance in the circuit and the d.c. voltages with fair accuracy. From breakdown voltage of the lamp. 60 to 650 volts can be measured. A scale s may be made of cardboard and' pasted Voltage regulator on the panel to indicate the voltage. A neon bulb tends to maintain a con- Start at the 650 -volt side and advance stant voltage across its terminals, the control until the bulb just lights. changing Its resistance to compensate Do not advance the control past the for any voltage changes. The voltage point where the bulb just glows as the regulator in Fig. 2 will maintain a con- bulb may burn out. Calibrate with an stant 60 volts regardless of line volt- ordinary voltmeter, a.c. or d.c. (or both) age fluctuations. Similar regulators as desired. were used in army radar equipment and are often employed in test equipment Photoelectric eye and in television. For the electric -eye experiment, simply connect the voltmeter just described Voltmeter to the 117 -volt a.c. power line. Shade the A neon -bulb voltmeter, wired as bulb. Carefully adjust the control until shown in Fig. 3, will measure a.c. and the bulb is just about to glow. Then Subchassis holds the transmitting oscillator. RADIO -CRAFT for Construction 55 The PM speaker is used also as a microphone. With the 4 -gang switch Sl in the receiving position as shown in the diagram, the audio input tube is connected to the receiver's detector and the speaker is connected to the audio output. Plate voltage is removed from the 6F6 -GT oscillator tube. With Si in the transmitting position, the first audio grid is fed by the speaker as a microphone, and the oscillator is plate- modulated by the audio output tube. The values of the oscillator coil and condenser will depend on the band used. THEODORE S. GEORGILADAKIS, Crete, Greece AUTO RADIO CONVERSION The advantage of this converter circuit for an auto radio is that very few MP -103 changes are necessary in the receiver, List Price and the receiver can still be used on 512.00 d.c. All new can be 11, at any time. parts mounted on the cover of the metal receiver cabinet. To use the radio on a.c., disconnect the battery and plug the receiver into the line. Close Si, and throw S2 to the a.c. position. It may be necessary to replace the speaker with a permanent- magnet type HIGH FIDELITY VARIABLE RELUCTANCE if a.c. hum occurs. - E. L. RAYNAUD, Mexico, D.F. MAGNETIC PHONO-PICKUP 117VAC 51 5.01 411 ® FUSE yeec YeÌ Ia_ DC S2 AC Mye oiaritu get. #t "

CONVE TING SECTION AUTO RADIO SECTION the V 18 SERVICEMEN ... Satisfied customers are your best salesmen, and CHASSIS amazingly improved record reproduction with the LEAR magnetic

6VOF. phonograph pick -up is a sure winner of these customers. o-et + F 53 In this variable reluctance pick -up LEAR engineering has developed T a "knee action" permanent sapphire stylus that steps over surface noise CUT HERE and actually transforms old style record reproduction into full, rich, %RFC TUBE FILS mellow tones. It minimizes surface noise and assures full tonal beauty of sound on all installations. Fits practically any pick -up arm without alteration. SMALL SHIELD CANS is the reason more are turning daily to the LEAR Shield cans for small coils and minia- This servicemen ture tubes can be made from the casings magnetic phonograph pick -up as a means of extra profit with assurance of old flashlight batteries. of customer satisfaction. Don't wait! Write today for complete discount Some of these have metal jackets in price list. place of the cardboard ones. Straighten the flanges at top or bottom with long - LEAR PRE -AMPLIFIER nosed pliers, and slip the casings off the batteries. To Complete Your The zinc outside of an ordinary cell Sound Installation can be removed by sawing off the top The new improved LEAR pre -amplifier pro. and bottom with a hacksaw, then remov- vide. additional amplification when used with 15IP -103 LEAR magnetic pick -up. Connect. ing the insides of the battery with a directly to old crystal cartridge input. Leads hammer and a large nail. Clean the in- of convenient length are provided for con. side of the zinc thoroughly with soap, Election into existing equipment. Two position switch permits high fidelity re.pon a to re- water, and a small bottle brush. Try A-172 cording.. Can be furnished with an adapter not to get the sticky material from in- to permit fast installation. List Prisa side the battery on your hands. $9.90 Solder small right angles to opposite FACTORY REPRESENTATIVES DISTRIBUTORS: sides of one end. Slide the shield over - the coil or tube, then screw or solder A few choice territories are still available for the angles to the chassis. these and other fine LEAR electronic products. When shielding coils, the zinc will Write today, giving full details. often be better than the steel casings; they will lower the Q less. A. E. FORSBERG, Sauk Centre, Minn. 110 Ionia Ave. N. W. Grand Rapids 2, Mich. AUGUST, 1948 56 Construction Calling all DIRECTION INDICATOR Aside from the antenna assembly and Police cars motor, this direction indicator for a rotatable antenna requires only a pair of square fiber boards, a couple of old volume controls, a 6 -volt relay, and a 24 HOURS few copper rivets. The volume controls, mounted in the center of the fiber squares, are used only Coaliaaaas Ope4440a as bearings, so their "innards" should be removed. Around each control, in a CALLS FOR circle, drill 15 accurately spaced holes. Mount a round -headed copper rivet in all taxis, trucks, each hole. Attach a piece of spring brass to each of a pair old public utility and PUSH -PULL VIBRATOR of knobs and bend other mobile JAMES it so that when the knob is placed on the communication shaft, the brass each rivet in The Vibrator Which contacts systems. Definitely Outperforms turn. Now mount the fiber squares on OUTSTANDING FEATURES: boxes so that they form the tops. ROOF I SHACK 1. Frame cooled reeds (no stack to compress). TOW

-cABIE 2. Push pull driving system (driving power squared) : ®4- r7; ,v e

3. Angular positioned reed arms. MOTOR GEARS ¡ 4. Thick reed (.010 inch) and power to drive it. 5. Fully adjustable ... every vibrator identical. 6. Proper reed stress distribution. 1 I lo N eé ow Ey I 7. Large stationary arm heat dissipation area. --.-o o a= °_T I a-J` q- Complete Information and Replace Guide Available... R IVET S F18ER BOARDJ -\RIVETS 6.3V °oIl RELAY See Your Parts Distributor... Or Write JAMES VIBRAPOR"R Co. Wilma 3224 'X'. Armitage Ave. Chicago 47, Illinois III V AC Mount one box in a convenient position under the antenna, and couple the the antenna pole to the rotating contact, so Better Products for Radio Industry that when the antenna rotates the contact will revolve in step with it. Place the second box on the operating NEW G -C NEW G -C STATIC CHASER desk, and connect thé studs of the two INJECTOR and POWER TUBE PULLER boxes with a cable. Be sure that each Tire static Makes it easy to remove or insert rivet of one box is connected to the cor- powder kits miniature tubes -simple to oper- Inserts or responding of other. - improve ate. extracts tubes rivet the auto radio where fingers will not reach In series with the power line to the reception. -into hard -to -reach places. Eliminates Saves time and money. Ends antenna motor, place the contacts of a wheel static inter- tube breakage, prevents normally closed 6 -volt relay. Connect ference. New pow- burnt fingen. No. one of the relay 6 der is blown into 5093- Miniature Puller List $1.65 end coil to a -volt sup- all the inner tubes-easy to use. For No. 5093 -D Display of 12 List $19.80 ply (a filament transformer will do) every car owner. G -C and the other to the rotating contact of No. 5604 -Injector for G -C Static Pow- "Speedex" der List $1.50 WIRESTRIPPER the box in the shack. The other end of No. 5605 -G -C Static Powder Packet Strips insulation from wire sixes the 6 -volt supply goes to the rotating for 5 tires List $1.00 r8 to a 30; Including the 300 No. 5606 -Kit -On Powder packet and ohm twin F.M. and television contact of the box at the antenna. injector List $2.50 lines. Ideal tool for manufacturers. electricians, mainte- To make the antenna point south, for NEW G -C FIELD nance men, etc. Strips 750 to example, place the rotating contact in CHASS EZ 1000 wires per hour. the shack on the rivet contact which Holds almost any radio chassis in represents south (marked S in the position! Has spe- drawing). Since the antenna motor's cial ible No. 733.12 to 20 UPI wire List $6.00 hooks for flanged 4D PAT. PEND. power circuit is complete (through the No. 733 -K- Standard type chassis or, to tilt chassis back if relay contacts), the antenna will rotate Made with adjust- Speedex Stripper necessary. slide Kit, complete with ment -takes only 5 seconds to install. and the contact on the antenna box will never wear out. seven different size No parts to lose -will blades. List go around with it. When this contact A real convenience for the radio serv- $15.00 iceman! hits the "south" rivet, the 6 -volt circuit No. 5207 Chats Es List $3.65 ore will be complete and the relay will open. G -C Products This will interrupt the supply of cur- at leading Have you seen the new GC available W rite for rent to the motor; the antenna will stop. ¡ "Speeder" Wire Strippers ... writ. distributors. If the antenna turns too freely, some 0 for illustrated literature. copy of our new may be necessary `'rte/ ;our catalog_ kind of clutch to pre- RADIO DIVISION DEPT. D Illustrated vent its coasting past the contact. If finer positioning is necessary, a greater number of rivets may be used in each GENERAL CEMENT Mfg. Co., Rockford, III., L. S. A. box. GIBSON, /s,anufacturers of over 3,000 products Soles othces to principal en es W. H. St. Catherines, Ontario RADIO -CRAFT for Theory and Ilcsi91n 57 REGULATED SUPPLY This regulated power supply uses the PAN1 new RCA 5651 miniature voltage- refer- Shuri1 METERS ence tube. The circuit of the power supply is described in the tube's data sheet. Ammeters -AC, DC The grid of the right -hand section of Milliammeters -AC, DC the 6SL7-GT is furnished by the 5651 Voltmeters -AC, DC with a constant reference voltage. Resistance Meters BIG VALUE BECAUSE...

They're RUGGED . Sturdy construction throughout. Molded inner unit with coil frames and insulators integral for maximum rigidity. Exceptionally high ratio, torque -to- weight. They're . Dials are metal so they stay good looking in spite of age NEAT and moisture. Rich telephone black finish on brass cases. Concealed coils and good readable scales. They're SENSITIVE . Accuracy well within 5 °ó. AC meters are double -vane repulsion type; DC meters are polarized -vane solenoid type. High internal resistance models available in popular ranges. For one year from date of purchase against defective work- They're GUARANTEED manship and material, and will be repaired or replaced if sent to the factory postpaid with 25c handling charge. When the load on the supply decreases, the output voltage increases. They're INEXPENSIVE . For instance, Model 950, 0 -100 D.C.M.A. sells for $1.45; Model 550, 0 -15 D.C.A. for $1.30. Other meters are This increases the plate voltage on the correspondingly reasonable in price. right triode. The left grid, being tied to the right plate, becomes They're AVAILABLE . Stocked by leading electronic distributors in a wide variety also more posi- of types ranges. tive, and the left triode plate current in- and SHURITE METERS 77 HAMILTON STREET NEW HAVEN 8, CONN. SATE CURRENT BALANCING POT 4708 '

68k 4 TECHNICAL KOs REGULATED EXCITING SUPPLY OIL -FILLED TRANSMITTING var. To LOAD 25 to 40 WATTS 250V/ CONDENSERS MICAS 6AS7-G 02254A 10 to 80 METERS FOUNDATION KIT .05 MFD 1000V $0.35 000025 2500V 50.15 .05 500V .14 09005 2500V .15 UNREG.FILTERED .1 2500V .75 00005 3000V .35 I/5 00001 5000v .85 ri0K .1 7500V 1.65 OC VOLTAGE 27.1 7000V 4.10 000067 2500V .20 .12 15000V 7.95 00007 2590V .20 .25 1000V .35 00025 2500V .25 .25 4000V 2.15 00025 5000V .85 .25 0005 2500V .25 OUTPUT VOLTAGE CONTROL 'OT 2 102..26 66Ó00V 1.05 00072 5000V .65 Engineered around the BC -610 series of plug -in .5 600V .28 0008 5000V .85 6SL7 -GT 5651 .5 .40 0001 2500V .25 tuning units. Described in the I 1 ih edition Radio 1000V Handbook. Completed exciter uses 6AG7 crystal .5 2000V .75 0011 5000v .85 .75 400V .30 002 12110V .20 creases. This makes the left plate or electron coupled oscillator, 6L6 buffer -doubler 002 3000V .65 -and and 807 amplifier. Kit includes four tuning units 85 600V .35 the 6AS7 -G grids tied 1.0 1000V .45 00275 2000v .25 to it -more nega- (illustrated at right above with cover removed', 2.0 200V .20 003 2500V .30 tive. Plate resistance of the 6AS7 -G special 514" aluminum relay rock panel, socket 2.0 600V .40 003 30005' .65 for plug -In units and special hardware, together 2.0 1000V .60 004 25110V .35 rises; and since the cathode -plate circuit with full instructions and diagrams for assem- 4.0 600V .60 005 1000T.V .I5 of 6AS7 in bling complete exciter. 4.0 1000V 1.00 005 30005' .65 the -G is series with the posi- No. 31A28, FU -40 Foundation; Spec, 9.95 5.0 220VAO .55 006 20(105' .35 7 6.0 008 1200V .I5 tive side of the supply line, the supply's .V .15 PARTS KIT. Everything needed to complete ex- 8.0 1000V 1.45 01 1200T output voltage decreases. except tubes and supply. Includes 8.0 600V .85 TUBES- CHOKE POTS citer power 8.0 1000v 1.75 V6 Slelal all mica condensors, resistors, RF sockets, Tubes -6 $0.89 At an output of 250 volts, variation is chokes, 10.0 600V 1.00 Tubes -12118 Metal .29 meter switch, 0 -200 ma meter, key jack, and 30.0 90VAC 1.40 Choke- I11OMA -IOU. less than 0.2 volt for load currents of miscellaneous ports. Q7f1. 30.0 330VAC 3.75 250 Ohm 1.59 0-225 ma. No. 31A26A, Special Per Kit, Each `P7 1 Pas: 20K- 50K -100K .19 25 0 25V .40 Dual. i Meg DID YOU GET IT? 100.0 25V .50 '250K -50K' .30 THE BIG B -A 1946 Catalog No. 48 r - *22 Everything in Radio and Electronics. Write SHTELDED WIRE 50 Ft. for .65 RESISTOR KIT Assorted ih&1W 100 for 1.49 if you have not receicved it. FREE on request. BATHTUB KIT 3x.1, .5, .05, ETC. 10 for .58 CONDENSER KIT .01- .00001...100 for 2.99 MICAS .01, .002, .005, ETC. All Values .08 BUIRSTEIN -APPL EE .01 160V PAPER (MIDGET) ...60 for 1.00 1012.14 M4017 S7RECI. °M r 0.1 600V PAPER 8 for 1.00 KANSAS CITY 6. MISSOURI

$2.00 min. order F.O.B.. N.Y.C. Add postage - 50 °6 deposit. balance C.O.D. with all orders. Manufacturers inquiries invited. Send for Flyer. SPECIA L Prices are subject to change without notice. Kay Television Antenna- TECHNICAL RADIO PARTS CO. dipole reflector ft. mast 3 -5 -takes 265 Greenwich St. Dept. RC -3 N.Y. 7. N.Y. minutes to assemble. Price $8.00 including postage. 300 ohm line, 2c ft. extra. INSIDE DOPE Send cheek or money order to ON Kay Distributing Co., Inc. IDEAL AMPLIFICATION : Grego /io,whuck, New York City 446 West 50th Street, New York 19, N. Y. SEND 3c STAMP FOR POSTAGE Phone Plaza 7 -3816 AMPLIFIER CORP. of AMERICA "This is the split personality type!" 398 -10 Broadway New York 13, N. Y. AUGUST, 1948 sa I Try This One.

PHONO ADAPTER quickly with a piece of heavy cloth, and TIGHTENING GRILL CLOTH The photograph shows a good method note the brightly tinned surface. A number of receivers that come into for making an extension for a phono- Tinning the iron this way is not only the shop for repair have sagging grill graph pickup cable or an adapter. cheaper but also more efficient than us- cloths. The receptacle housing is made from ing new solder from a spool. A simple way to tighten them is to the shell of an old fluorescent lamp RICHARD HENRY, sprinkle or spray them lightly with starter. The ears on the starter shell New York, N. Y. water, and then let them dry overnight. were lengthened by filing down the wall The cloth shrinks and becomes taut. between them, then bent over the edge RESISTANCE WIRE Since water is distinctly unhealthy of the receptacle and soldered tC the While constructing a multimeter I for speaker cones, it is a good idea to grounding connections. Shielded wire needed some resistance wire to make remove the speaker before sprinkling. runs through a hole in the top of the shunts for the current ranges. I broke G. J. MACHEAK, shell. open an old tube and carefully un- San Pedro, Calif. ravelled the grid and screen wires. One four-foot piece of this wire had a PRESET VOLUME resistance of 200 ohms. Another was 2% A preset volume control can be a feet long and measured 6 ohms. Dividing blessing where loud radios are annoying. 200 ohms by 4 feet told me that the first Children can be prevented from upset- piece had a resistance of 50 ohms per ting mother's nerves by running the foot; the other, 2 ohms per foot. volume up on the more blood- curdling Knowing the resistance per unit programs. length, it was an easy matter to cut exactly the length needed. S. P. BRUNTON, Kingston, Ontario

TV GLARE FILTER Eye fatigue resulting from watching This solves the problem of making a television programs is often due to the neat connection to a standard phono jack glare. To eliminate this, I fastened a while preserving the shielding through- piece of blue- tinted plate glass behind The auxiliary control, wired as shown, out. the front panel of the set, between the is placed in any convenient position JACK D. SELLERS, kinescope tube and the cabinet aperture. away from prying fingers. It may be Detroit, Mich. The glass is fastened to the rear of the screwdriver -set. Sets using variable bias panel -by straps at the corners. as a volume control may be preset with INTERSTAGE TRANSFORMER As well as eliminating glare, the glass a variable 3,000-ohm resistor placed in series with the regular control. The driver transformer may burn out improves contrast, permits viewing in a well -lighted room, and gives added pro- FRED G. WILLMAR, in old sets in which they were used. If Maywood, Ill. no audio unit with a push -pull secondary tection to the tube. Blue- tinted plastic, is available, two single -ended transform- available at art 6N6 SUBSTITUTE ers can be used. stores, will work as well as glass, but if there is no protective glass in the cab- The 6N6 tubes I needed for replace- inet, the plastic may be scratched. ment in an old receiver are no longer ANTHONY DUTKOWSKI, available. 6K6's placed in the 6N6 Bayonne, N. J. sockets worked fine without any rewiring. ERIC LESLIE, New York, N. Y. Connect the primaries and secondaries in series. Hook the primaries to MODULATOR the driver output as shown in the dia- Here is a method of modulating a flea - gram. power rig when a modulator is not Connect the secondary to the push, available. pulI'grids, using the junction between A carbon mike is switched to the the two transformers as the center tap. grid of the first audio tube of a small If operation is not ideal, reverse the con- receiver. The low- impedance secondary nections of one of the secondaries. MOUNTING STRAPS AT FOUR CORNERS of a plate-to- voice -coil transformer is ORREN REYNOLDS, AIR -CONDITIONED RECEPTION placed across the receiver output, and Dupont, Ohio the primary of the transformer is used When I was younger, my friend and I -modulate IRONS to plate the transmitter. TINNING used to have fun talking from room to S /SGT. BENEROGE, W1QYU, During almost every soldering job room through the furnace pipes. Recent- Grenier Field, N. H. little drops of solder melt from the iron ly, I made practical use of this idea and fall on the bench, the chassis or even when people in several rooms wanted to (the XYL doesn't like this) on the sol- hear the same radio program. CARBON MIKE derer's pants. When brushing off the I turned up the volume of my receiver 1 . I.SV VI EL BOX bench, don't throw away these little and put it, speaker face down, on the solder chips. Collect them in an alumi- cool -air intake in the living room. The ---- T1 num shield can. program was heard clearly all over the After the collection has attained some house, and the cold -air intake does the il bulk, put the can on the stove and let radio no harm. solder When In the summer, when the furnace is 10 the melt. it hardens, it will °XB+ form one solid piece. To tin an iron, first turned off, the radio could be fed file away the corrosion and then clean through any outlet in the house. L- the tip with steel wool. Then dip the tip Although the fidelity probably suf- HEAVY -- DUTY UNIVERS OUTPUT TRANS into the shield can, twisting the point fers, the volume is entirely sufficient. MA- O END OE RECEIVE ARTHUR TRAUFFER, B+ around so that all parts are immersed in D, ROM 2ND DET NB -TAP FOR GREATEST OUTPUT the solder. Take it out of the can, wipe Çouncil Bluffs, Iowa IN-INSERT IN B+ LINE TO BE MODULATED RADIO -CRAFT for Try This One a9 SCREW SIZES If you own a small set of taps and dies, you can make a handy device for measuring screws. It will tell you what size tap to use to accommodate a certain MISTAKEN IDENTITY? screw or, if you keep your screws separated according to size, it will tell you which box a particular screw belongs in. not a chance with Drill and tap several threaded holes in a small oblong block of metal. There should be one hole for each size tap in the set, and the holes should be made f om left to right in order of size. Use a1 lock at least 14,-inch thick. The handle of an old ten-cent -store dinner knife was handy in my case. To determine the size of a screw, try fitting it into the holes. Screw it all the way in to make sure the pitch is correct. The block can be marked with sizes, but, since it is hard to mark metal, simply counting the holes from smallest up will tell you the size. Each Resistor is CLEARLY MARKED to show HENRY HOENIGSBERGER, New York, N. Y. Resistance, Wattage and OMMDTG Trade Mark

MOUNTING SHUNTS r When shunts are needed, to convert Guesswork's gone ... when you use a meter for a greater current range, genuine Ohmite Little Devil insulated com- resistance wire is often used. position resistors. Each unit, in all three An easy way to make such shunts is sizes-%, 1, and 2 watts -is color-coded to wind the wire on the outside of an and individually marked for quick, sure insulated resistor. Use one with a re- identification. sistance high enough not to interfere with the shunting. Wind the wire tight- Millions of these superior quality re ly about the resistor, then solder it to sistors are being used today by manufactur- the pigtail leads. ers, servicemen, and amateurs. They meet Duco or similar cement may be used joint Army -Navy Specification JAN-R -11, to hold the turns in place. The completed including salt -water immersion cycling and be shunt may mounted wherever it is high humidity tests. They can be used at needed, using the resistor leads for connection. their full wattage ratings at 70 C (158 F): A. D. DENTON, ambient temperature. Little Devil resistors Herts, England dissipate heat rapidly :.. have low noise level and low voltage coefficient. USEFUL OLD FILE Ratings for maximum continuous R111S An old three -cornered file with the voltage drop are high: 350 volts for the %- sides ground down to sharp edges makes watt unit, 500 volts for the 1 -watt unit, a good tool for stripping wire, scraping, 1000 volts for the 2 -watt unit. All units and other operations. have high insulation breakdown voltage. The end of the file can be ground to a Little Devils are completely sealed and chisel shape. The end of the handle can be ground to a rounded point and will be insulated by their molded plastic construc- useful for prying up wires which are be- tion. Leads are soft copper wire, hardened Little Devils are available in Stand. immediately adjacent to resistor body, ard RMA values ... 10 ohms to 22 ing unsoldered. Tol. ± 10% and EMIL EPP, strongly anchored, and hot solder coated. megohms. ±5 %. Values to 2.7 ohms available jig 1 -watt Carrot River, Saskatchewan They're light, compact, easy to install. size, ± 10% tolerance. e ISOLATION TRANSFORMER OTHER OHMITE PRODUCTS When servicing a.c: d.c. receivers, iso- wire -wound, vitre. late the set from the power line to pre- BROWN DEVIL RESISTORS -Rugged, dependable, ± vent shocks. An inexpensive isolation ous- enameled. Easily mounted by tinned -wire leads. Tol. 10 %. 5 -, 10 -, transformer can be made by hooking 20 -Watt sizes. DIVIDOHM ADJUSTABLE RESISTORS -Used as multi -tap two identical filament or toy transform- resistors or voltage dividers. Provide odd resistance values quickly. Vitreous. ers back to back. The primary of one enameled. See your distributor for these and other Ohmite products. goes to the a.c. line, the two secondaries are connected together, and the remain- OHMITE MANUFACTURING CO. ing primary feeds the receiver. 4894 FI y Street Chicago 44, III. Be sure to use transformers with high enough wattage ratings. To determine this, multiply the rated secondary volt- NOW age by the rated secondary current. A 6.3 -volt, 3 -amp. transformer, for example, would be rated at roughly 18 for BULLETIN watts. /35 CHARLES E. COHN, KMHTh Chicago, Ill. RHEOSTATS RESISTORS TAP SWITCHES AUGUST, 1948 60 Radio-Electronic Circuits

LIGHTNING ARRESTER CRYSTAL RECEIVER equal. This adjustment should be repeat- Surplus T -R radar tubes, such as the Here is a crystal set which gives good ed periodically, since aging of the 6N7 721, 1B25, 1B24, 1B27, or 702B, are used results with a loudspeaker on strong may cause unbalance. in this lightning arrester. If lightning local stations. Despite the 6SJ7 voltage amplifier, strikes the antenna, it causes the tubes The two identical coils for the tuned the 'unit will not have enough gain for to break down and lead the charge to circuits are 90 turns of No. 20 enameled most microphones. The 6SJ7 merely re- ground. wire on forms 1% inches in diameter stores gain lost in the equalizer network. ANT and 3% inches long. After each coil is The amplifier will, however, work well wound, cover it with a piece of wrap- with a good phonograph pickup. ping paper and wind 30 turns of the WILLIAM D. JOHNSON, wire over the center. Oakland, Calif. TO RCVR OR EMITTER The set .was constructed breadboard - e style. The coil forms are mounted ver- CONTACT MICROPHONE tically 1/32 -inch apart to give proper A surplus T-30 throat microphone coupling. The 2 -gang, 500- µµf-per -sec- makes an excellent contact microphone tion broadcast tuning capacitor is at- for amplifying tached to the base with wood screws. musical instruments. 7 -R TUBES These small carbon units, which can be For maximum safety, the ground wire Fahnestock clips serve for antenna and fastened ground connections. to the instrument with Scotch should be run in the same direction as tape, work best when the back of the i the feeders from the antenna and should To line up the receiver, tune in a microphone, strong remove the speaker from rather than the rounded have no sharp bends. The lead -in from signal, front, is against the wood. the circuit, and connect a 1 -ma meter the tubes to the receiver should come The connection to the amplifier is from the arrester circuit at right angles in its place. Tune the trimmers for highest meter reading. shown in the diagram. If no carbon to the antenna and ground leads. microphone transformer is G. J. MACHEAK, on hand, a This arrester may be used with trans- 3 -to -1 audio interstage San Pedro, Calif. unit can be used. mitting antennas if it is inserted at a Adjust the 200 -ohm variable resistor so low -voltage point in the feeders. that satisfactory operation is obtained CHARLES KNOOP, with the greatest possible amount of Saginaw, Mich. resistance in the circuit. Don't forget to open the switch when the assembly is BATTERY CHARGER not being used. After building some portable equip- KENNETH S. FERRIN, ment, I discovered I had no way to Fort Wayne, Ind. charge the 12 -volt storage batteries. PHONO AMPLIFIER Here is my inexpensive charger. This amplifier uses a cathode -follower IKE OR 3:1 AUDIO TR Two selenium war surplus rectifiers output stage. The triode -connected 6L6's PRI THROAT MIKE rated at 120 volts, 5 amperes, were pur- give about 8 watts without any measur- chased. As the diagram shows, they able distortion. They can be driven to 1111 were arranged into a bridge circuit. about 11 watts, but distortion will ap- 200 4.5V FULL WAVE SELENIUM BRIDGE pear. The output transformer need not - be a high -fidelity unit, but it should be BALANCING POWER TRIODES STORAGE BATTS IN SERIES 117VAC 117V of reasonably good quality with a A.f. power triodes, such as the 2A3, + - ^ SA rat- 0 -10 AMP ing of about 16 watts. 6A3, and 6B4 -G, are very susceptible The normal frequency response is to unbalance when used in push -pull. uniform from 40 to 15,000 cycles. The The circuit shown corrects this. equalizer circuit allows highs to be 2A3, 6A3, 6B4-G boosted about 6 db at 8,000 cycles, and BULBS TO CONTROL RATE OF CHARGE the lows to be boosted about 7 db at 50 Up to three 12 -volt batteries may be cycles. connected in series for charging. When It is very important that the 470,000 - using the charger, first connect the bat- ohm plate resistors of the 6N7 phase teries, then insert a 25 -watt lamp Into inverter be well -matched. The power one of the sockets, leaving the other two supply output voltages must be within empty. After plugging into the 117 -volt 5 volts of those shown. Some adjustment a.c. line, read charging current on the of the voltage can be made by trying meter. If it is too low, change to a different values for the filter input con- higher- wattage lamp, or add other denser. Adjust the 6L6 cathode resistor lamps in the parallel sockets. The lamps until the tubes draw 110 ma. act as line- dropping resistors; the high- Adjust the phase inverter by feeding Bí300 -325V er their wattages and the more of them a constant tone into the amplifier and Rl is adjusted until the plate currents connected in parallel, the higher will be (with a vacuum -tube voltmeter) meas- of the two tubes -measured by a milli - the charging current. uring the audio voltage at each 6L6 ammeter inserted at the points marked DAVID SIMON, grid. Adjust the 50,000 -ohm potentiom- R-are equal. Then' R2 is varied until Montreal, Quebec eter until these voltages are exactly the total plate current for the stage is of the proper value. 6SJ7 .015 270K 6N7 In this arrangement, each triode grid is above ground for d.c. The phase inverter which drives the power stage must be so connected that this d.c. does not appear on its grid. There will be no trouble if the split-load type is used; but if a voltage is tapped off the grid resistor of one of the power tubes to obtain the out-of-phase signal, a capacitor should be inserted to block the d.c. from the inverter grid. M. HARVEY, Westfield, N. J. RADIO -CRAFT for Radio-Electronic Circuits 61 A.C. -D.C. PHONO AMPLIFIER When a 6 -inch PM speaker is used ONLY $09'50 IS THE COST OVER 100 BARGAINS on this a.c: d.c. amplifier, it has enough output for comfortable room volume. EVERYTHING BRAND NEW Since it reproduces frequencies only up Money Back Guarantee to about 5,000 cycles, it is not a high - fidelity unit, but it will please juke -box ONE POUND FINEST ROSIN SOLDER $ .49 enthusiasts with its good bass repro- t1LN5 TUBE, Sylvania, list price $2.65 .39 CATHODE RAY TUBE, #7BV7 .98 duction. Of course, the speaker must be LINE CORD, 6 feet complete with plug .14 properly baffled. It should be a good - TOGGLE SWITCH, SPST .15 ANTENNA HANK, 15 ft. on handy spool .15 quality speaker with a large magnet. TWIN LEAD -IN WIRE, 300 ohms, 100 ft 1.95 Notice in the diagram that the ground TWIN LEAD IN WIRE, 300 ohms, 500 ft 7.50 TWIN LEAD-IN WIRE, 300 ohms, 1000 tt 13.75 wire is for the circuit ground only. Be- CO -AX CABLE, RGS9U, 72 ohms, 100 ft 5.25 tween this wire and chassis are a 0.1 -pf CO -AX CABLE, RG59U, 72 ohms, 500 ft 24.75 ZIP CORD, 20 gauge, 1000 ft. 13.50 capacitor and a 500,000 -ohm resistor. PHONO AMPLIFIER, incl. 3 tubes 3.95 The arm of the pickup should be con- PHONO MOTOR, including turntable 2.95 CRYSTAL PICK -UP, incl. hardware 1.95 nected to chassis -not to the circuit " CARTRIDGE, fits most pick -ups 1.45 ground -to avoid shocks. for the SENSATIONAL-NEW -IMPROVED 671/2 V. BATTERY, personal portable type 1.71 45 VOLT BATTERY, 51/2" x 31/2" x 13/y " 1.50 YTAL PU 10 INCH 41 VOLT BATTERY, 43/4 "x3 !s" x I 1/4e" .52 2.5K.. PM loos ASSORTED CONDENSERS, .001 to .02 3.95 12BA6 SOBS ' 100 ASST. PILOT LIGHTS, #44, #47, etc. 4.95 210K S S 100 ASST. SOCKETS, loctol, octal, min 4.95 TELEVISION KIT 4.95 00025 .00025 I 100 ASST. KNOBS, screw and push on 1 100 ASSORTED RESISTORS, V2 watt 1.50 .OI l less tubes I 4.- r:_ VOL. CONTROLS, w /s, 50K, /2 or I meg .39 with 13 channel tuner. all parts and Complete 4" PM SPEAKER, alni. #5, I -oz. mag 1.19 step-by -step following instructions and easy 5" PM SPEAKER, alni. #5, I -oz. mag 1.39 schematics. 6" PM SPEAKER, alni. #5, I -oz. mag 1.15 3.3 $89.50 less tubes 8" PM SPEAKER, alni. #5 heavy mag 3.95 10" PM SPEAKER, Omni. #5, heavy mog 4.95 Kit complete with all tubes 8149.50 12" PM SPEAKER, alni. #5, heovy mag 7.50 f. Cost of cabinet 825.00 OUTPUT TRANSFORMER, to match 50L6 .39 Using the new 13 CHANNEL TUNER which la pre- OUTPUT TRANSF., push pull 12 -251_61 .59 wired and factory aligned for the entire telerlslon spectrum. The kit builder merely Installs this unit OUTPUT TRANSFORMER, match 6V6 .65 Into his chassis and makes three connections. Contains OUTPUT TRANSF., push pull (2 -6V6) .79 470K an R.F. stage. oscillator and mixer. It Is extremely OUTPUT TRANSFORMER, universal .95 35W4 small and compact. Using new I.F. coils which pro- A.C.-D.C. CHOKE .39 vide maximum gain and definition. Sound .1 TO PHONO MOTOR picture I.F. TRANSFORMER, 456Kc .39 reception U high quality F.M. for complete listen- 456Kc CHASSIS ing OSCILLATOR COIL, .19 pleasure FM, TRANSFORMER, 10.7mc .83 SAME TELEVISION KIT -7 INCH. complete less -I.F. tubes 559.50; complete with all tubes $99.50 FM, LIMITER TRANSFORMER, 10.7¡nc .83 II7v C/DC 7 FM, DISCRIMINATOR TRANSFORMER .83 IMMEDIATE DELIVERY FROM STOCK FM, OSCILLATOR COIL .19 R.TAPPED AT 125( FM, AERIAL COIL .19 4.1NDICATES COMMON NEGATIVE FM, VAR. CONDENSER, 88 to 108 me .95 ELECTRONIC 8 SELENIUM RECTIFIER, 100 ma .59 The parallel .005 -pf capacitor and the fY'iZetiiwpvlilan INSTRUMENT CO. ANTENNA LOOP, for A.C. -D.C. radios .39 250,000 -ohm in with the RESISTANCE CORDS, 150 or 180 ohms .39 resistor series Dept. RC 42 WARREN ST. N. Y. 7, N. Y. - AUTO RADIO ANTENNA, side mount 1.95 pickup raise the high frequencies some AUTO VIBRATOR, standard 4 prong 1.19 what. Different capacitor values can be TELE. FOLDED DIPOLE ANTENNA, 7.25 In- ELECT. SOLDERING IRON, 60 watts 1.77 tried to get varying treble response. ELECT. SOLDERING IRON, 100 watts 2.36 creasing the value of the .01 -µf ca- TOGGLE SWITCH, DPST .25 pacitor output transformer TOGGLE SWITCH, DPDT 37 across the VARIABLE CONDENSER, 420/162 mmfd .68 primary will vary the bass. -W. G. VARIABLE CONDENSER, triple 920 mmfd 1.45 Eslick RADIO CHASSIS, 6 tubes or less .29 100 -TUBE CARTONS, GT type .95. 100-TUBE CARTONS, peanut type 75 SIMPLE TRANSMITTER - RECEIVER RADIO TUBES - KNOWN BRANDS This transmitter and receiver operates Each 80, 5Y3GT, SY4GT, 6C4, 9002.._ - .42 with a plate potential of only 6 volts for 35W4, 25Z5, 2526GT, 3525._..._...» .45 the receiver and 12 volts (often less) for 6F5GT, 6)5, 6SA7, 6SK7, 6SQ7 ...... »._ .47 36, the CHOCK 37, 77, 78, 6H6, 6D6 .49 transmitter. 12AT6, 12BA6, 12BE6, 12SQ7 .. »_.. .49 The receiver has 2 stages, a regenera- 12SA7, 12SK7, 6F6GT, 75 .49 FULL 6J7, 61(7, 6Q7, 6SFS, 6SN7...... 55 tive detector followed by an audio am- 35A5, 35L6, 50L6 OF 5085, .55 plifier. Although the usual filament volt- BUYS! 43, 6A7, 6A8, 25L6, 12SR7 .59 1A5GT, age for these tubes is 6, 3 to 4 volts has IA7GT, 1H5GT, 1N5GT .59 024, 6X5GT, 7F7, 7Y4 .65 A TELEVI IRS, 154, 155, 1T4, 3Q4, 3Q5, 3S4 ...... _ .65 RAOIR 14A7, SION PARIS NITS 1486, 14Q7, 35Y4, 6V6 .69 PUBLIC ADDRESS 6ÁC7, 6L6G, 7017, 11723 .95 I LC6, I LH4, I CA. 1LA6, 11726 .95 I NTER- COMMUN 25Á6G, 117L7GT, TORS RECORDERS 117P7GT 1.15 RECORS CHANGERS A MUST for all TEST INSTRUMENTS Service Deniers I USES AMATIUR Antnrcuta CONDENSERS EQUIP'T CHANCELLOR Experimenters Per Hundred loch RADIOS HARDWARE Industrsela .001 -600V .. 3.95 16 -150V I4 05ions .18 TLCHNICAI ROOKS Ins .002 -600V .. 3.95 20 Gm er smwnt -150V .25 Agruc .003 -600V .. 4.40 20/20 -150V .26 .005 -600V 4.40 30 -150V .28 RADIONIC EQUIPMENT COMPANY .006 -600V .. 4.40 40/40/- 20 -150V .44 The wiring of both units is extremely simple. .01 -600V .... 4.40 50 /30 -150V .44 170 NASSAU ST., NEW YORK 7, N.Y. .02 -600V .... 4.95 8-450V .27 1, hune rhea,. Ent,a,,e .05-600V .... 4.95 16 -450V .36 .1 --600V 1.1. w0,,h 2.0421 (able ' (HANSIOR ' 7.20 16/16 -450V -. .59 .9- .25 -600V 12.50 20 -450V v .39 .5 -600V 17.50 30 -450V .47 RADIONIC EQUIPMENT CO.. Cept 1,8 10-50V 18.00 40 -450V .59 170 Nassau Street. New York 7. N. Y. FM CONDENSER er COIL KIT 4.95 Send at mice your tree catalogs. .unnlemenu and bar- TELEVISION I.F. incl. peak gain lists as published- Ilnine product d leading KIT, coils 13.77 manufacturers d radio. electronic parts and equipment. INTER -COM. SYSTEM, used os baby sitter 12.95 BROOKS INVERTER. 50 watts 8.95 VM RECORD NAME CHANGER 14.50 DETROLA RECORD CHANGER 13.50 P.O. BOX or STRH/r BROOKS 4T. \T'F. RADIO DIST. CORP. The transmitter left and receiver (right). 80 VESEY ST., DEPT. A, NEW YORK 7, N. Y. AUGUST, 1948 621 Radio- Electronic Circuits been found sufficient with this type of circuit. I :4G'OffIL I The transmitter hookup is conven- TERRIFIC BARGAINS tional and several good contacts have RADIO FILTER NEW, FL -8 -A. ea. 75c been made with it. The receiver brings NEW RADIO RECEIVER BC -AC -229, with 5 tithes including 3/VT -49; 1 /VT -37; 1/VT -38, wt. approx. '6SJ7 /6C6 121/2 Ibs. Mfg. by Western Electric Co. .0001 ..... Only $4.75 1 NEW RADIO RECEIVER BC -341 -A U.S A. Signal Corp. type with 3 tubes, Including 1/VT -103: 1!VT 91 -A, I/VT -104, In original packing. Each $3.95 SE LSY N, MODEL .#2.11G1, tan be usec$1 00 on 110 V. 60 rye. Instructlena Ind. New. ea. RADIO CONTROL BOX U.S. Army ' - with 3 positions seiet'. switch. rd. control.. e4. JACK BOX NEW BC -366. U.S.A. Signal Corp. with 5 positions selective switch. volume control. Fach 75c ELECTRIC MOTOR 1/5 H.P. 27 V. D.C R. P. M. 3800. NEW. Each `P$4.50 FI S 3 -4 SV DYNAMOTORS NEW CHECK LIST AND ORDER NOW. ALL BRAND NEW AND PERFECT IN ORIGINAL PACKING. INDIVIDUAL The 2 -stage receiver uses only 6 plate volts. DYN. NEW G. E. 985 NVA. Input 27 $4.50 V.D.C. Output 115 V.A.C. WL 16 lbs DYN. NEW G.E. Type D. Input 28 V, A19, Output 6SJ7/6C6 1000 Volts D.C. A. .35 Wt. 38 Po. Fach $4.95 DYN. NEW Type S. 3416.1 Input 9 V. $2,50 7 Ea output 400 V. amps and .08 amps. L2 1\ 12V DYN. NEW MODEL 323350 Input 27 V D.C., 1.75 Amps, Output 285 V.D.C. .075 Amps. L Each W$1,25 ... 6V = DYN. NEW, Model DY -22 /ARC Input 28 V$1.50 D.C. Output 210 V. D.C. Each RARE GENERATOR BARGAIN Guaranteed Brand New and perfect Navy Type #211220 -A 430 Volta D.C. 86 Watts. length of SHAFT 155 -. 1n original Parking. Wt. 21 lbs. Shipping wt. atipms 23 Dis. Chance of a lifetime to arquire a magnificent $7 52 piece of equipment. Only 50 BRAND NEW SCR -625 Send creek or money order. No. c.o.d.'s. Priem f.o.b. ANA K.C. On orden $1.50 or las please Include 35 Cetus CARBON MIKE . 51 MINE DETECTOR postage. The transmitter can operate on c.w. or phone. GENERAL SALVAGE COMPANY in numerous foreign stations, especially Attention, Prospectors, DEPT. 1, 2920 E. 27th St., Kansas (sty, Mo. on short wave. Any desired band may be suitable -in coils. Miners, Oil Companies, WAR SURPLUS BARGAIN SPECIAL! chosen by plug Plumbers, etc. This little station has been used as Brand New an interhouse communication system BEAM ANTENNA with excellent results. Used by the Army to detect ROTATOR The increased electron emission due buried metallic mines. Its pri- MOTOR to the positive voltage on the control vate use suggests the location and screen grids enables these tubes to of underground or underwater $595 operate efficiently on such low voltages. pipet, cables and ore -bearing P. T. NARASHIMAN, Postpaid in Tarnbaram, South India rock, the location of metallic Continental U.S.A. could be adapted to fragments in scrap materials, OPERATES DIRECTLY ON 110V AC, 60 CYCLES (This equipment logs, etc., and the screening (Requires only 12 MFO Condenser) use dry -cell tubes, which would make it NO STEP -DOWN TRANS. NEEDED much more portable. -Editor) of personnel in plants for car- NO LINE RESISTOR NEEDED HIGH TORQUE - NO FREE SWING rying of metallic objects. New, APPROX. a R.P.M. REMOTE THERMOMETER complete in original over- REVERSIBLE - ONLY THREE WIRES NEEDED The temperature of a remote point ELECTRICALLY 8. MECHANICALLY QUIET seas packing container. Orig- LIGHTWEIGHT, RUGGED, QUIET is indicated by this electrical thermom- inally sold by War Assets for MOTOR 8, GEARS OIL SEALED eter which works on the principle that NO EXPENSIVE CONVERSIONS $166.00. The U. S. Forestry the resistance of copper changes with FLAT MOUNTING SURFACE - Service has recommended pro- FOUR TAPPED HOLES temperature. It can be made entirely 2 20 BEAMS cedure for using the SCR -625 FO. FOR -6 -10 -LITE from old radio parts. The shows a 0-1 milliammeter Mine Detector to find con- ALVARADIO SUPPLY CO. circuit So. Alvarado drawing current from B1 through a in tree logs Dept. RC2, 903 cealed metal and Los Angeles 6, California fixed resistor and a rheostat. If the other timber products. meter is connected as shown, this current will cause it to read in the usual direction. $ The current from B2 is oppositely Price 7 950 polarized, however, causing the meter to read backward. The difference in the Shipping Weight 125 lbs. two currents will be the actual reading Size: 81/4" x 2814" x 16" of the meter. The resistor labeled "coil" is actually 11 an old loudspeaker field coil or any homemade coil of copper wire with a resistance of about 1,150 ohms. It is the Batteries not furnished we can sensit've element. supply for $4.50 extra

. and retinae. especially ere finding out that bell B2 coin radio operation in their locality Is an easy. All Prices F.O.B. Indianapolis 820 400 Profitable adjunct to their own business. Requiring a TERMS: CASH WITH ORDER minimum of investment in both time and money. Tradio is a natural for big earnings and a steady, COIL 0 -IMA IDPSTSW long time Income. You merely place the sets on SEE TEXT percentage basis in hotels. motor courts, taverns, lilt restaurants, etc.. and let them work for you. ev BI Send for complete I Write In winding the coil, a fairly small size informot ion today Dept. U-8 of wire will be best in order to keep the finished product down to reasonable di- 537 N. CAPITOL AVE. mensions. A core should be used for con- INDIANAPOLIS, IND. TRADIO, Inc. NEW RJERSEY venience in winding. Any wood or paper RADIO -CRAFT for Radio- Electronic Circuits s:t tube will do, since the coil is not required e % aa..±.xx..VIsAle.N10 to act as an inductance. Scramble -wind- / / YOUR 3 BEST BUYS ing is easiest and quickest. / If the coil is placed in the location Klt Model B -4, A 4 -Tube Portable Receiver esa' whose temperature is to be measured, / Model B -4 is our new / 4 - tube portable re- its resistance will change as the heat / ceiver which operates present varies. The resulting change in / on self- contained bat- B2 meter will cause / teries. Approximate current through the / size: 8 x 6%/4 x 4. Uses a change in reading corresponding to the following tubes: / IRS. IU4, 155 and 3S4. the change in temperature. ' Power switch is con- fit/ To calibrate the unit, place the coil in / veniently located on / front of set. Alnico 5 a location which is as cold as the lowest / permanent magnat desired scale marking. (The original dynamic speaker. Case covered with fine grain / leatherette. Complete with tubes, ready for unit went down to -10 degrees.) Note / assembly. the reading of a good mercury thermom- / 31101 / Kit Model 210, a 3 Way Portable Receiver eter in the same location, then mark this / Model 210 operates reading on the lowest point of the meter / on either AC or DC / or self -contained bat- scale. Adjust the 400 -ohm rheostat until / teries... power switch the needle points to the marking. / conveniently located / on front of set so Now increase the heat and mark other / that "battery" or points on the scale, leaving the rheostat "AC or DC" may be selected without open- alone. / ing case. Five Inch The sensitive coil may be located at / Alnico 5 permanent / speaker. Case cov- any reasonable distance from the rest of / ered with fine grade , leatherette material. paraffin for weatherproofing, but allow / Complete with tubes. ready for assembly. excess paraffin to drip off. Do not re- / Multitester Kit / Model M-3C move the coil from the circuit until the / A versatile, compact batteries are turned off. To conserve / multitester 4" s 7" s 3" batteries, on the / using a 3y =^ rd. meter turn unit only when / of 1000 ohms per volt taking readings. / sensitivity. Employs the RUSSELL GARRETT, / following ranges: Volts B. AC or DC 0/5/50/150/ Hanover, Pa. / 500/1500. Milliamperes / DC 0/550 /150. Ohms Spark Plugs ore minia- / 0/2000/20,000/200,000. ture broadcasting sta- A.C. WATTMETER / tions send signals that / Man y other kit models available interfere with radio This "wattmeter ", which shows the / Write for Catalog K reception, distort tele- amount of power drawn from the a.c. / vision. The New Auto - / Lite "R sistor" Spark line by any receiver or amplifier, is very / RADIO KITS COMPANY Plug reduces this in- useful for detecting excessive power / 120 Cedar Street New York 6. N. Y. terference.` consumption which might be caused by shorted filter capacitors or by other bad Disconnect all cathode resistors from NfIV parts. ground, but leave the bypass capacitors Current through the transformer grounded. Connect each resistor to one primary is determined by the amount of contact of a meter switch, as shown in current drawn by the set under test, which is plugged into the a.c. outlet. The T0 CATt100E RESISTORS current in the secondary is determined AUTO-LITE by that in the primary. Secondary cur- PLUG IN METER NERZ rent is rectified by the small dry -disc rectifier and read on the 10 -ma meter. SHUNT The transformer has a 6 -volt primary. *rims,MCK It was the power transformer of an old TO SWITCH auto radio. Other meters may be used, the diagram. (This is a Centralab type or higher wattages. may be measured G wafer.) The almost circular rotor SPARK PLUG by shunting the meter. grounds all contacts except one. This one is led to a jack into which milliam- Here's How It 117V AC 6V PRI meter leads are plugged. Cathode cur- Works to End I I rent of the tube associated with that OUTLET contact will be read on the meter. Interference CENTER TAPS NOT USED HALE WAVE METER RECT The "Resistor" acts If all tubes in an amplifier are to be to dampen the spark Open the meter and turn the dial scale checked, determine the reading for the plug radio signal to an acceptable level' over. On the white under surface mark tube with the lowest normal current. while still delivering the wattage calibrations. Plug in a 25- Then insert a shunt, as shown, on each the full high voltage watt lamp, note meter reading, and tube, to bring the meter reading to discharge required to ignite the fuel. M mark the scale "25 ". Other lamps will about the same point. The shunts will give other calibration points. not affect the bias values. Auto-Lite Ignition Engineers, working After its initial calibration on 117 Condition of each tube can be checked with leading automotive manufacturers, volts a.c., the wattmeter will be incor- once a day or as required by plugging have developed the new Auto-Lite "Re- rectly marked for other voltages. How- in the meter and rotating the switch. sistor" Spark Plug with this built -in ever, for the normal variations between Any meter reading that is not normal resistor that reduces spark plug inter- 110 and 120 volts, the error will not be indicates a tube that will probably fail. ference! Remember, the "Resistor" also important. If it is replaced immediately, no more helps deliver smoother idling, improved economy, longer electrode life. Dealers J. T. RODGERS, than a few seconds of operating time, are being supplied as rapidly as pos- Bandera, Tex. if that, will be lost. sible. Write for Booklet M -1186 The jack is a shorting type so that, for full information. PLATE CURRENT CHECKS even if the plug is not in, the tube which THE ELECTRIC AUTO -LITE COMPANY Wherever it is important that equip- is switched to the meter will continue Toronto. Ontario Toledo 1, Ohio ment remain in service at all times, such to operate. as in a recording or broadcasting studio, RICHARD HENRY, .Under 35mv; 'nitwit 540 k.c. to 150 m.c. at 50 ft: this circuit should be valuable. New York, N. Y. Tune In "Suspense," Thursdays, 9:00 P. M., E. T., CBS AUGUST, 1948 s1 - _question Box AMPLIFIER Al!-PURPOIfMIKE PHONO Please design an amplifier suitable used to amplify high, low, and middle WAR SURPLUK for a phonograph or tuner, and having tones, respectively. Rl, R2, -and R3 give , BARGAIN separate channels for bass and treble. separate control of each, as indicated. (r Nof be, -R.R.P., Lakewood, Ohio The right -hand section of the second V or A. In the circuit shown, the first 6SN7 6SN7 is used as a cathode-follower °fie{Y,f °bea P'' uf s °rPlus and the left section of the second are split-load phase inverter for the 6F6's. esVern flecVrife e.rce//e beauli! c ul nt PHONO enit in TUNER ZJAp, Or F/ee/rea/ e 500. s r470K .00005MICA .1 6SN7 includedl°9 andesf. 47o66F63 40/450V ho,ne AW1. é° LS hi^ 6SN7N7 y.l J 41 ad reco, .' /de on9 500 I '? h dress d,n a/ ~ Ba !or 006 1.005 RI GU//LKtROER erY wbo'n' H R3 Y, MICA

e 6JS 1.88 HI-- 50ÒK NICOLE EMS ERANDNfW495 20/25V IK 25V 56N. se.. 10/450V = IOOK JOM ION 820 H 33K .1 Include for Postage 33K 20 -11111r 6 F6 10/450V 4.7N CORDS 1300V UNLESS NOTED +310V fg --_- PL W 6.3V H /120MA OFFENBACH & REIMUS CO. 17VAC s -,BCD` 372 Ellis St. San Francisco 2, Cal. SW 5V/3A 1.5K SW 4 5Z3 350V 3 120MA 30Kí IOW 350V 16/450V PE -109 32 -Volt -il DIRECT CURRENT PORTABLE G- M COUNTER POWER PLANT of a delivers the necessary voltage and cur- This power plant con. t Please print a circuit portable Wets of a gasoline en- Geiger- Muller counter giving visual and rent in the secondary circuit. It has 117 - gine that is direct audible indications. Headphones and a volt a.c. and 4 -volt vibrator primaries, coupled to a 2000 watt 82 volt DC generator. neon lamp are to be used in the indica- and can be used by using a dropping re- This unit is ideal for tor circuit. For more exact measure. sistor and operating the 3A5 filaments use in locations that are not serviced by mente, I want to use a 4 -range meter for in series. commercial power or indicating 1, 10, 100, and 1,000 counts to run many of the surplus items that re- Adjust Cl to obtain the lowest battery quire 24 -32V DC for operation. The price of per second.- K.E.S., Syracuse, N. Y. drain. Its rating is approximately .0005 this power plant is only $58.95. We can also µf 2,500 volts. The G -M is used furnish a converter that will supply 600 Watts A. In the portable counter circuit at tube at 11Óv AC from the above unit or from any shown, dry cells supply operating volt- in a self- quenching circuit. Adjust Rl 16 to 12v at 88 Amperes DC source for 612.95. ages A 2 -volt storage for most stable operation of the tube Due to the fact that the PE-109 comes to us for the 3A5's. sealed in a heavy steel -strapped govt. case, it battery supplies the filaments and the and set the taps on the 25,000 -ohm bias- is impossible to inspect the individual units resistor best operation of the to determine if they are new or used, or what vibrator pack. The vibrator transform- ing for the condition is if used. Consequently we must er used is a special item and may have tubes. (Additional material on G -M sell them "as is." In general they represent be However, it may counters will be found in RADIO- CRAFT', a terrific bargain. to wound to order. be possible to use one of the transform- February, 1944; Electronics, January, BUFFALO RADIO SUPPLY ers designed for portable photoflash 1947; Sylvania. News, May, 1947; Elec- 219.221 GENESEE STREET. BUFFALO 3. N. Y. DEPT. 8C units. The Thordarson type T -22R43 trical Counting, by W. B. Lewis.)

GE GER- MÜLLER TUBE PHONES .3A5 470% GLIB.RESIST08S3KaEA. 1.001/2KV W .25 SK 0-IMADC GREYLOCK 10111.110¡l 11 A Dependable Name 2706 PI in 10MEG 500/25V1 l'o, T boob RADIO TUBES GT, Glass, and Miniature Types Al f WEG ALL TUBES Ls, INDIVIDUAL CHITONS 39e. 39e. 39. 49e. 49e. 49e. S9c. OW I .5 V4W NEON 6A8GT 12AT6 25L8GT 1155 6A K5 6X4 6L6GA 6K7GT 12BA6 25ZOGT IT4 NAGS 25Z5 6U5 +1.4V- 60767 12BE3 35W4 1U4 6A125 6A7 43 6SA7GT I2K7GT 45 165 613E6 6C6 70L7 ADJUST BIAS TO OBTAIN 6SK7GT 120767 46 364 6ßA6 606 84 700 IS OV DC 1.47 TUBE CURRENT CUT-Off 6SO7GT 12SA7 47 3Q4 6A116 75 117L7 2w 5517/CKI013 6V6GT 12SK7 :085 3V4 6816 117Z3 32L7 AND BEST OPERATING 12607 50L6 VIO. TP- SE E TE eT CONDITIONS 12A8GT 2v vis Webster All Nakao. alastie arm 51.49 TERMS: Net C.O.D. No der wasted for less than 3.3NE6 EA Write for Bargain Catalog C-8 .01 2KV 25K Wow400í150V GREYLOCK ELECTRONIC SUPPLY CO. 30 CHURCH STREET NEW YORK 7, N. Y. .5 /SCV 2v WET CELL ON- OFF 5W I.0 1- -II111 -I1 CORDS 450v UNLESS NOTED 83.5V C. 90VB ELEMENTS OF MAGNETIC RECORDING AND TAPE 1 -TUBE RECEIVER 999 APPLICATIONS P] by A. C. SHANEY Please print a diagram adapting A. The complete receiver, revamped Only 25c the receiver described in the August, for use with one tube, is shown. Make ® AMPLIFIER CORP. el AMERICA 1947, RADIO- CRAFT, for use with one the variometer of two concentric card- tube.R.W.H., Atlanta, Ga. board or fiber hoops about 53, inches in RADIO -CRAFT for 1.11.1111111111.11061.11.11.111111WRIMIRIP"

Question box 165 diameter, wound with six turns of No. satisfy these requirements. While.2 -volt creased. Ll and L2 are not critical since 24 or 28 wire each. The 400 -µµf tuning tubes might require a smaller A- battery, only the desired portion of each is condensers add to the frequency range, a larger number of stages would have selected by the tap. L1 might be about which will be almost 10 to 1. to be used. The 6 -volt tubes have the 30 or 40 turns and L2 around 300 turns, advantage that they may be .operated both on a 1- to 2 -inch diameter fqrm. GANGED a MH 108-GT directly from the storage battery used Unless an isolation transformer is NGED to drive the vibrator supply. When us- used between the a.c. line and the power

3 02/400V ing the vibrator, adjust the value of C for lowest battery drain. RFC is 55 30 on IH4-6 2 turns of No. 12 wire close -wound on a .661 'XTAL DET 1 l .00925 3 ,00025' .05 -inch form. 15-400upf MICA 1 ...fi A dynamotor giving 180 to 250 volts MAG SPIU1 TUNING GONDS 4001 400V output at 50 ma or more from a 6 -volt A +1.5-2V 2-10 MEG 11 CM input could also be used. The filtering shown is more than sufficient for a dyna- 1.05í600V 100 MA SEL. RECT DPST Sw motor. 47 III-.' A+ 1.24 0+67.5Vl 67VM W .OS/MXW 9 1 -TUBE CRYSTAL SET PORTABLE AMPLIFIER Please give a diagram for a crystal supply, be very careful about touching , receiver using a type 30 tube for audio components. It is advisable to enclose Please give me a diagram of a a portable amplifier. It should have about amplification and a selenium -rectifier the set in cabinet. 6 watts output, and should operate from power supply.-L.G., Pilot Grove, Mo. dry batteries or from a 6 -volt vibrator REMOTE ANTENNA supply.-E.C.B., Streanlatown, Alberta A. Here is the circuit you requested. ': The rectifier is a 100 -ma selenium unit. I am about 150 miles from the near- A. The amplifier diagrammed will If B- voltage is too high, R may be in- est broadcast station and in a very noisy location. I have set up a 30 -foot pole and placed a 19 -foot whip antenna atop it at a spot about 300 feet from my sit 8C4 1.1.3 379 SPXR 6V INPUT CAN BE STORAGE 8AT1 C- .005:001 /1600Y house where noise is at a minimum. How Sor 1 /600V / VIB POWER SUPPLY . ' 11 can I run a transmission line to my receiver, picking up least possible noise along the way ? -J. H. H., Inyokern, 511 8 Calif. 40MA ri. 40 10 .001 A-e- 450V 400v A. The schematic shows location of the

A+6V l -.o01 ,TosREC coils necessary. Wind L2 with 24 turns MAllOf1Y RF46I,OR EOUIV. of No. 24 d.c.c. in a single layer on a

¿ureaf/f 50500 Sß)95 PHANTOM ANTENNA BC-959 3 CONDUCTOR L RPM used TELEPHONE WIRE Braided gf< s 3 conductor but insulated copper & steel A transmitting is telephone wire. It antenna, for use goon made of copper for con- opprooimately 450 ductivity, and steel for MC. Complete with strength. Worth at least X95 standard coo. con- SHIPPED 3c per ft. Yet due to an EXPRESS exceptional buy, we can nector A weather now offer it nt less than proof unit. I Add CHARGES tc a ft. 25c to cower hand- 3.2 lers.' and postage.. COLLECT Shipped Erpteas Collect

Ideal for o boom rotor, plenty of power. Ori gamily designed for 24 volt IN oprot,on, but easily d, 110 volts AC. Complete instructions included. Ec.11ene for other uses too. Brand new, surplus, guerontd. t Add 40c oat to cover posto9 end handling I

Brand now Bowen D.C. Volt mater 0 to 9 volts in 2" case with 2 3/4" IMPORTANT! Clang. .Bch .99 Brand n w Bowan D.C. Anmter 0 to 100 amp BOO le, '600 TO Brand All merchandise subject to prior now MM. 3 0 3, DC oltmt.r nt with 100 omp shunt,g 2" round sole, minimum order $2 00. No cou. Mt.r hos 450 ohms cam.rco. as volt meter och 99c C.O.D orden accepted Mich, .,stone '150 ohm. per olt. Add 15e ach to Add 20e sock to covet, postage gon resedents must add 3 State co po.tog and hand. Imq and ha.dlenq soles to, I,N. SILVERSTINE 6532 EAST McNICHOLS ROAD DETROIT 12, MICHIGAN

AUGUST,( 1948 Question Box 66 I 114 -inch diameter form. Over it place a wire pie -wound, 143 -inch wide. Vary the NOW -A REALLY HIGH -POWERED- strip of lead foil as a static shield. To turns on L4 to allow good tracking in avoid the effect of a shorted turn, in- the receiver. sulate the ends of the shield from each VERT. ART-45,0' Radio Engineering other and ground the foil. Over this pie - wind Ll with 30 turns of 'No. 30 d.s.c. Make the pie about 1,k -inch wide. Be Library r I is TATK I sure the center tap on L2 accurately I SHIELD STATIC SHIELD placed. 1 lu L3 and L4 are handled in the same L. 12 .ru - I manner. L3 is 44 turns of No. 36 close -

wound, and L3 is 124 turns of the same 1 1RE ONE

NOTE: CRYSTAL PROBE The Library comprises selection of books culled from c- tPlease print a diagram for a probe r, 00025MKA 47K Graw -Hill publications In the ra- rCAeLf dio field. I can use with the signal tracer -injector NorD; ' N yyf M R 4 K j.00025`_s e 2201 especially selected by radio 'specialists of 111e- described on page 31 of the September, MICA Jr Grew -Hill publications IN34 XTAI } Ì 1947, RADIO-CRAFT.--E. F., Tampa, Fla. 111 to give most complete. dependable coverage of 61400-4 j- fasts needed by all whose fields are grounded on - - -- radio fundamentals A. The probe shown is what you want. PROBE available at a special price and terms uses a 1N34 crystal. It will work 20,000 to 100,000 ohms, whichever works THESE books cover circuit phenomena, tube the- It . ory, networks, measurements, and other sub- well with any signal tracer. Loading ef- best for you. The probe is suitable for jects -give specialized treatments of all fields of fect exists, but is slight. almost all i.f. and r.f. frequencies found practical design and application. They are books of recognized position in the literature -books you Resistor R may be any value from in ordinary repair work. will refer to and be referred to often. If you are a practical designer, researcher or engineer in any field based on radio, you want these books for the help they give in hundreds of problems CRYSTAL PIC KUP CABLE throughout the whole field of radio engineering. Will 10 -foot cable between my The capacitance of the cable across 5 V OLUM ES, 3319 PAGES, 2289 ILLUSTRATIONS a A. 1. Eastman's FUNDAMENTALS OF VACUUM TUBES crystal pickup and the amplifier cut high the pickup will not cut highs because the 2. Terman's RADIO ENGINEERING ? R.H.,. New crystal is itself capacitive. may, how -, 3. Everitt's COMMUNICATION ENGINEERING frequencies appreciably - It 4. Hund's HIGH FREQUENCY MEASUREMENTS N. Y. ever, reduce overall level. 5. Henney's RADIO ENGINEERING HANDBOOK York, to days' examination. Easy Y Special price under this offer less than books bought separately. Add these standard works to your library n ; p small monthly installments, while you use the books. COIL DATA 30 DAYS' FREE EXAMINATION -SEND COUPON

McGraw-Hill Book Co., Inc. 888 W. 42nd SL, N.Y. C. 18 I am building Send me Radio Engineering Library. 5 vols., for 10 BAND COILS TURNS TAP FROM PADDER days' examination on approval. In 10 ,Lys I will send a superheterodyne $2.50, plus few cents postage, and $5.00 monthly till (me) GROUND END C5 $27.50 Is paidor ref books postpaid. (We pay post- to cover the broad- (turne) (µf) age on orders accompanied by remittance of the Drat in- stallment.) cast band and 80, 40, 20, and 10 Name meters. I am using Brwdcast LÌ, 3, 5 145 0.55- 1.6 L2, 4, 6 35 Address a 4 -gang, 1.40 -µµf L7 115 34 0- .00018 City and State t u n i n g capacitor with 4- to 30 -µµf Company trimmers. The i.f. 80 meter4 LI, 3, 5 24 3 -5.7 6 Pn. won is 465 kc. L9 21 6 .0011 Please supply me with data for winding the coils, and 40 meters LI, 3, 5 13 5.4-10 4, 6 give values for the L7 12 -4 .0012 AUGUST socIAL necessary padding capacitors. - L.I., 3 TUBE PHONO Compton, Calif. 20 meten L1, 3, S 8 9.5-18 L7. 4s' 6 7.5 - 005 AMPLIFIER A. The coil table 3 shows the data you require. To get all $1.95 10 meten LI, 3, 5 4 the coils to track, it 15-30 12. 4. 6 3 4 2 none COMPLETELY WIRED, may be necessary L7 VOLUME AND TONE CONTROLS to adjust the turns or lengths slightly, All coils wound on 11/2-inch diameter forms. All 1.2, 4. 6 coils spaced Set 01 3 tubes: 50L0. 3525. 12A6 $1.10 .4. inch from ground ends of LI, 3, 5 coils. All wire No. 24 Output trans. 5016 .35 as well as the pad- approx. ,Meg. vol. control with 1w. .35 enamelled except broadcast band coils which use No. 32. All coils close- 4" pm speaker .95 der values. Taps on wound except LI, 3, 5 on A0, 40, 20, and 10 meters. which are spaced to 1.15 5" pm speaker 1 inch. - 6' pm speaker 1.55 8" pm speaker 2.73 12' pm speaker 4.89 4 x 6- pm speaker 1.89 Astatic pickups 1.89 Astatic crystals 1.59 Alliance motor & turntable 2.50 Vie .400 intermix changer 26.95 FAMOUS ,MAKE CONDENSERS 50 30....150v... .45 16 450v 39 20 20.... 150v... .35 400v or 600v ... per 10 20020 (10) 150v (25) .39 .01, .02. .05 .49 8 x 8 450v.... .49 .001..002, .005 .. .49 25 25v 29 25 50v 29 All prices F.O.I. N T.C. -on C.O.D. 25éó Deposit. Write for free catalog. I ROSE COMPANY 1 THE the oscillator coils may be varied as 17 4711 Broadway, Dept. C, New York 7, N.Y. 88 West well to obtain optimum performance 6C5ETC with your particular tubes and circuit. RADIO -CRAFT for Foreign' Sews s7 Report From Britain By Major Ralph W. Hallows

RADIO -CRAFT EUROPEAN CORRESPONDENT

part of Britain can be televised to any High- frequency I undering other part without calling on some view- Sometime ago Sir Edward Appleton, ers to sit up far past their usual bed- Director of the National Physical Lab- time or on others to rise at uncanny oratory, announced, as the result of a hours if they want to see what's going series of experiments, that it would on. shortly be possible to extract the dirt from soiled fabrics by the use of su- HE growth of personic vibrations. Further experi- television in Man -made static ments have been carried out by the Mul- Britain during Whatever kicks in the pants Mother lard Company and a recent demonstra- the past twelve Nature may deal out to radio enthusi- tion was most striking. The instrument months has been asts in the form of static, blackouts and used is called a transducer. It converts remarkable, espe- fading, she confines mainly to fre- the energy from an oscillator into pres- cially when you consider that reception quencies below 30 mc. Above that point sure waves in water. Two very dirty is still confined to the London area, that the human race unhappily devises laboratory overalls, one soaped and the (owing to restricted output from the sources of man -made static which easily other unsoaped, were put into separate factories) televisers haven't always been beat all Dame Nature's efforts on the tanks of water, each provided with a easy to come by, and that many homes lower frequencies. One of man's worst transducer. The unsoaped overall came in some parts of London have unsuit- efforts so far has been automobile and out a little less white than the other, able power supplies. British standard truck ignition systems. This produces though it was perfectly clean. There is current is 230 -volt 50-cycle a.c.; but at the worst kind of radio interference still a good deal of work to be done be- the moment the word "standard" is more above about 40 me and almost the only fore the first radio- electronic laundry is of a pious hope than a reality. Actually sort beyond 90 mc. Research has shown opened. It has been shown that clothes you may come across a.c. with queer fre- that this interference can easily be sup- can be washed without soap, but some quencies like 30, 40, 83 (!) and 100 pressed by a 10,000-ohm resistor in the way of whitening them has to be found. cycles. In the London area you may main distributor lead. All vehicles ought And there's a great deal to be discov- find houses on one side of a street with to be so fitted before they leave the fac- ered about the right frequeneies.for use d.c. at 100, 200, 205, 210, 215, 220, 230, tory, but that hasn't come about yet, in with different fabrics. Too low a fre- or 240 volts and those on the other side Britain at any rate. The General Post quency means that some dirt remains; with 100, 105, 200, 205, 210, 220, 230 or Office, the radio trade associations, and if the frequency is a good deal too high, 240 volts of a.c. All this would have been some other concerns are having all their not only is the dirt shaken out, but the ironed out before now if it hadn't been vehicles fitted with suppressors; but fabric itself may be shaken to pieces. for the war. Thus by no means every there remains one offender who is still home can accommodate a televiser. giving a lot of trouble -the private car Olympic PA In spite of that, the number of sets owner. For his special benefit a 10,000 - An interesting PA system for the in use has risen from just over 18,000 ohm resistor gadget is sold for about Olympic Games is being installed at a year ago to more than 45,000 now, an 30e. A threaded tip for the distributor the Wembley Stadium by the Philips increase of 250 percent. It would have lead screws into a socket in the distribu- Company. One of the difficulties about been much greater than that if radió tor. There's another type available for ensuring that announcements are clear- manufacturers could obtain all the raw the "push -in" lead: Thus for a low price ly heard by members of a big crowd is materials that they need. Meantime, and little effort the private car owner that their clothes and bodies absorb the work on'the second television transmit- can get the greater part of the advan- higher frequencies. Unless something ter at Sutton Coldfield near Birming- tages of complete suppression. is done about it the higher sound of ham is going ahead fast. When it.comes into action in the fall, television will get another big boost. If only our radio factories could get the materials, I believe that there would be half a million or more televisers in use by this time next year. For several reasons England is probably peculiarly well situated as a country for the quick development of television. Geographically the territory is small: you can't find two places. in Britain which are more than 800 miles apart; over 80% of the population can be covered by half a dozen television transmitters, éach having a service area with a radius of about 40 miles; the majority of the great sporting and other events which have the biggest of all ap- peals to televiewers take place within easy co -ax or radio link range of these six centers. Further, there is no handi- cap of large time differences between the Suggested by: eastern and the western parts of the D. F. Donnell, country. An interesting event in any Vancouver, B. C., Canada. AUGUST, 1948 Foreign News 68 I speech may be so completely lost that little but a series of unintelligible "woomphs" is heard from the loud- SUMMER SPECIALS: speakers. Here's' how the problem has Over 1,000,000 Tubes On Hand - been tackled. The 24 main loudspeakers for TERRIFIC TUBE BUYS Largest Stock In Country Other Types Available -We Invite are arranged in pairs on 12 standards. "See AMERICAN First" Inquiries on quantity Prices These are 25 -watt 12 -inch cone speak- SPEC.... 368AS 7.50 826 1.45 8025 2.50 C100E .79 ers. Immediately above each main speak- 10 .4 9 3718 3.50 829A 2.50 9001 .49 FG105 5.00 15 E .95 388A 4.25 833A 29.50 9002 .49 EF50 .50 er is a 12 -watt high -frequency unit with 30 SPEC .75 434A 3.95 637 1.75 9003 .39 RK59 3.50 45 SPEC .49 450TH 12.75 841 .69 9004 .39 RK73 5.75 a triple square- section horn. Between 120 5.95 WL468 5.50 843 .69 9005 .49 RW30 39.95 I23A 7.50 527 1.95 851 60.00 9006 .39 RK2I 1.50 these and the amplifier is a bass -cut cir- VT127A 3.95 530 29.50 CG861 40.00 IA5GT .79 RK25 3.50 cuit. The of both volume 204A 25.50 531 20.00 864 IA7GT .99 control and 2058 3.50 575A 10.00 865 .95 1824 2.19 frequency range is quite independent of 211 .79 815 .95 866 .75 1829 .99 KLYSTRONS AND 215/1 1.95 W L632A . 5.00 876 .69 1832 .96 MAGNETRONS the main loudspeakers. Thus the tonal 221A 1.95 703A 5.95 .75 I P24 .25 222A 75.00 7078 12.50 9538 12.00 11121 1.45 2J21A 2J36 2155 balance can be adjusted as may be 242C 4.95 713* 1.25 954 .39 1R4 .99 2122 2138 4126 249C 1.95 714AY 8.00 955 .39 174 .89 2128 2139 4128 necessary to suit the size of the crowd 250TH 14.00 720CY 12.00 956 .49 IHS .89 2132 2140 4129 at any time. The denser the crowd the 250TL 8.00 721 A 3.25 957 .39 INS .99 2133 2151 256A 12.00 724A 3.95 1616 .85 2C2I .49 Any Tube Above. Ea. $14.95 greater the treble boost needed. 268A , 10.00 728/1 10.00 1619 .49 2C22 .39 1625 .49 2C26 .25 417A 8.95 2748 1.00 800 1.95 6.95 285A 1.95 801 .75 1626 .29 2C26A .39 723AB 286A 1.45 BOIA .95 1629 .29 2034 .35 725A 11.95 Vest -pocket B- supply 304TL 1.25 802 1.25 1638 1.00 2C40 .95 726A 6.25 304TH 8.00 803 6.95 1641 .59 2C44 1.50 A British battery- making company 305A . 805 3.50 1665 .79 3C22 15.00 CATHODE RAY TUBES has 307A 5.95 806 9.95 2050 .75 3C23 4.50 just produced what must be about 31M 4.95 807 .95 2051 .39 3822 3.95 905 ..3 1.75 78P7.. 2.75 the smallest high -voltage dry battery 316A .85 808 2.75 7193 .19 3824 .75 2API.. 1.75 7DP4.. 12.95 313CD 1.95 809 1.50 8001 3.90 3C30 .65 3API. . 1.75 7EP4.. 17.50 going. Weighing 71/2 ounces and meas- 331 A 9.00 810 4.50 8005 2.95 2K25 15.95 3BPI.. 1.75 9LP7.. 4.95 345A 5.95 811 1.75 8011 1.50 2X2 3CPI.. 1.75 100P4 34.50 uring 3 29/32 x 2 19/32 x 2 7/64 inches, 350 2.75 812 2.95 8012 2.95 2304 .69 5AP1.. 1.75 10FP4. 39.39 350A 5.75 813 5.50 8012A 3.50 2807 1.75 58P4.. 3.75 I2GP7 9.95 it has an output of 300 volts. It is -in- 3508 7.75 814 3.95 8013A 2.95 50535 8.00 3DPI. . 2.95 12JP1. 53.00 tended primarily for photographers' 815 1.95 4.50 4APIO 3.50 I5AP4 109.50 re- 353A 1.95 8020 CW93 4.95 peating gas -filled flash tubes, but other ideas for its use concern radioactivity RCA 2 -WAY FARNSWORTH meters, insulation testers and portable INTERCOM SYSTEM RECORD CHANGER television receivers. It certainly packs a A Special Buy Per- Latest Automatic Changer punch! Connect a few of these midgets mits Us to Offer in series and you're up in the thousand Plays full stack of 10" or le records. Stops automati- These at Low Cost - cally after last record. Complete with permanent sapphire volts region. Yet you could carry the lot wile. QUANTITY LIMITED. Each $24.95 For This Month Only! Lots of 10. Euh 21.50 in a pocket. Farnsworth changer above with GE reine- $26.95 Includes: 2 stations, 1 ampli-Spedai Complete tance cartridge fier, 100 feet hookup wire. QAA 50 Ideal for the office, proles- $22 DETROLA RECORD CHANGER German scientists have organized the sional, factory, or home use. Famous Max Planck Society for the Advance- QUANTITY LIMITED Model 650 - Lots of 10 $19.50 ea. ment of Science to replace the war ruined Kaiser Wilhelm Society. The or- SPECIAL .. $1195 SPEAKER SPECIALS ganization, named for Prof. Max Planck, Lots of 10. $10.50 ea. who won the 1918 Nobel prize in physics, Permanux Alnico r)I 9 1.10 J Lots of 10 9.50 for his development of the quantum v' l'erndlux above with output 1.45 10 for 12.50 SPECIAL! G I RECORDER theory, held its first meeting recently in 0' Permdtux Alnico PM 1.5 os. 1.35 Lots of 10 12.00 Single Speed Goettingen. lU' 01 Alnico Beery 1'7s1 4.7 on 3.95 Cutter and Purpose of the Society is to foster Lots of 10 37.50 12' RCA or Magnavox P51 6.8 or. 5.95 Playback free research in Germany. Lots of IO 57.50 12' Electro 1500 ohm í1r61 5.95 18 RPM Lots of 10 57.50 HEAVY -DUTY MOTOR PICKUP 8 CARTRIDGE SPECIALS $15.95 AMERICAN Castel Cartridge re- New Canadian bands and modes of placement for Standard Practically for the Prise of Pickup and motor Alone: All Car- Lots of 10 $12.95 ea. operation are: Eighty-meter band; Al- tridges, such as As- SPECIAL t at 1 o L26- 140 -L70, 3.5 to 4.0 mc, A3 --3.75 to 4.0 mc, FM- Shure P87, etc. $125 TRANSFORMER 3.8 to,4.0 mc. Forty -meter band: Al- 7.0 to 7.3 mc. Twenty -meter band: Lots Of 10 310.25 SPECIALS! Al- 14.0 14.4 mc, A3 14.35 mc, 6.3 Volt 80 MA. Power Transformer. High- to -14.15 to WEBSTER est Quality. ion Priced. Ideal for melvert- FM -14.15 to 14.25 mc. Eleven-meter Ing Surplus Equipment such as BC -348. Flyweight Pickup For 6X5 rest. band; Al -27.16 to 27.43 mc, A3 -27.16 700 VCT /Soma $2.25 Assembly Lob of 10 $17.50 to 27.43 mc, FM-27.16 to 27.43 mc. a SPECIAL Ten -meter band; Al -28.0 to 29.7 mc, Special Webster Flyweight pickup I'niv. Output Xformer 8 watt 01.10 1048.50 with permanent needle. New type re- Univ. Output Xformer 16 watt 81.85 10 14.50 A3 and FM -28.2 to 29.7 mc. Six-meter tractable cartridge. Steg. mer $10.041 $395 50141 Output Transformer 39e Lots of 10 3.35 Iles. OYri Output Transfmner 39e Lots of IO 3.35 band; Al, A2, A3 and FM-50-0 to 54.0 Lots of 10 $32.50 l'lniVit l'l'rin Output Nf'rmer. 69e 10 for 5.50 Inc. Canadians interested in obtaining licenses write to Room 2212, No. 3 Tem- All Merchandise Guar- porary Bldg., Ottawa, Ont, Room 403 anteed. Your Money FM -AM CHASSIS ASS'Y Back If Goods Returned Youville Place, Montreal, P.Q., or the Prepaid To Us in 10 Famed 9 -Tube HOWARD Chassis nearest District Radio Office. Days. Complete with all necessary mounting radio operators hardware, antenna, 6x9" oval speaker Canadian amateur lean take larger SPECIAL are required to operate c.w. exclusively Send 20.3. With Order, -peaker, if desired). Your coat Balance C.O.D. All Complete FM cover- for a period of six months or more prior Prices F.O.B. New age 88 -108 Mc. $4995 to applying for permission to operate York. Minimum Order -telephone stations in the 10- and 55.00. Lots of 10 ....645.00 ea. WITH SPEAKER radio 11 -meter bands. After operating an active station for one year or more, they must pass an examination in advanced radiotelephone theory and operation and TA _ _ . merman a ió upp a 15- word -per- minute code test to qual- 120 CEDAR STREET Phone: BArclay 7- 2685 -6 NEW YORK 6, N. Y. permit on 80- WRITE-CABLE ify for an operating the and 20 -meter bands. RADIO -CRAFT for Foreign News

RADIO IN LATIN AMERICA

By E. A. CONKLIN

SEVERAL noteworthy radio -electronic developments are taking place in Central and South America. In Costa Rica all radio servicemen must appear for a 3 -hour oral technical examination before a Wireless and Elec- tronics Commission, composed of three radio servicemen who have been in the servicing business for five years. Each candidate is asked 15 questions concern- ing circuits and servicing techniques. Passing score to obtain a servicing license is 86%. Licenses remain valid for 3 years, after which a new examination must be taken. The license costs about $100 a year. In. Nicaragua police are using television to conduct criminal line -ups. a Eleven TV transmitters have been erect- ed in communities about 75 to 100 miles ':w!á+54.: tt'a :utd in apart. Pictures of criminals caught Now we can offer you, for the first time, the cream of CONTENTS any of these communities are televised articles on construction and servicing prepared by fRANSITRON OSCILLATOR -ITS USES to other communities in the chain for foreign technicians. MAKE A. V.H.F. SUPERREGENERATOS YOUR FREQUENCY identification. The 1948 RADIO -CRAFT REFERENCE ANNUAL CHECK with some IDENTIFY THAT STATION In Venezuela experimentation is be- brings this world -wide information, along CONSTRUCTING A B. F. O. of the best of our own country, in one volume. Just AMP. ing carried out in the use of radio fac- run your eyes down the contents listed on the right TODAY'S D. -C. AUDIO simile by the public. A number of offices of new and im- METAL LOCATOR and see for yourself what a wealth LOW -LEVEL TONE CONTROL have been set up in key Venezuelan portant material it contains. Each article has been presenting information not PHOTO -PRINT TIMER cities and citizens may transmit mes- selected wit!. a view to SUPERSONIC DOOR OPENER appearing elsewhere in textbooks, manuals, or periodi- sages which include drawings. At pres- has POWER SUPPLY STABILIZER cals printed in. the United States. Each accurate NEW CIRCUITS FOR OLD ent, rates are approximately $5.00 for a schematics and detailed data enabling you to get at features easily, and SIMPLE TUBE VOLTMETER 200 -word message plus 1 drawing 234 x constructional and operational 2 PORTABLE models. - -TUBE 434 inches. if you so desire -to duplicate similar SIGNAL TRACER FROM OLD RECEIVER In Lima, Peru, a complete wing of a Another feature of the Annual is the RADIO -CRAFT HI -FI TRF TUNER Index, covering issues between Oct. 1946 and Sept. 4 -TUBE REFLEX SET recently built hospital is devoted to elec- 1947. This Index enables you to locate the important LOUDSPEAKER FIDELITY tronic and radio surgery. Short -wave articles appearing during the year on such special PHONO AMPLIFIER WITH ADJUST- diathermy equipment, electronic knives subjects as come up in the course of your work or ABLE FEEDBACK studies. Taking all in all - - the worldwide construction MULTI- CIRCUIT CLIP SET for bloodless surgery, and other elec- STAGE DESIGN and servicing articles - - the handy kinks and short A. F. EQUALIZER tronic apparatus is being used. Experi- cuts, and the RADIO -CRAFT Index you have a well FM RECEIVER mentation with ultrasonics in the treat- rounded reference book of inestimable value. Get this NOVEL CLASS A AND B AMPLIFIER valuable 1948 reference book by subscribing to RADIO - V.O.M. -COND. TESTER ment of tumors and cancerous growths RADIO-CRAFT INDEX OCT.46 -SEPT. 47 is being performed. Under a new plan CRAFT at once. doctors in Peru will be given a 90-day MAIL COUPON WITH YOUR REMITTANCE TODAY course in electronics and radio as ap- RADIO -CRAFT 25 West Broadway. Dept. R.C.B New Yerk 7, N. Y. below. and pend me a free plied to surgery. Enter my subscriptlem to RADIO-CRAFT, or the period Indicated Gentlemen: I encase my remittance. In La Paz, Bolivia, radio servicemen copy of the new 1040 RADIO-CRAFT REFERENCE ANNUAL 3 Years B3.00 are being supplied with screens which Q 1 Year $3.50 S Teen $6.00 Extension can be mounted over their service This Is a new order Renewal benches, and slide projectors. Each 6 each a blown - Name month slides are issued, print clearly) up schematic which the repairman can (Plane consult as he goes about his receiver Address analysis. state CRY Zote each year; Foreign. 75cá In Bogota, Colombia, automatic radio I Cana.11a0 add 50e for a. control equipment is being experimented with in helicopters. In the same city table -model television receivers are be- businessmen may ing installed in restaurants, diners, and with recorders so that TO SUCCESS as they travel. Chilean 500 FORMULAS cabarets, where, for the equivalent of dictate letters IVIANY million started are now using elec- with a lame. for h 50 cents in American money, 1 hour of airport restaurants ey pain hl[ price. Here you have 500-no less -tried and tented televised entertainment is offered. Re- tronic grills which can prepare sand - and processes making thing. uler ceivers are installed in booths so only wiches,.steaks, and chops in a few sec- lously low price of 25e. Here 1s your opportunity to start booth occupants can see and hear. onds. Susine.. with but few dnuars. In Buenos Aires, Argentina, a new In Risbanba, Ecuador, trucks are be- capital spectwYo undreamedaÌM of hese formulas in your own home cto t with radar to eliminate household a Dennexnto the bone. Or short -wave transmitter is beaming ing equipped put then, in with each other in the heavy workshop to cut moete as much transmissions one -hour periods to collisions l Ecuadorean radio Quit payln[ t many dollars In each of 16 other Latin -American coun- native rainstorms. Pron. to manufacturers, whoaaten, -boxes and dealers,a s when you a make the tries. Each day's hourly program is de- servicemen are now renting juke same thing yourself for few Cents. TVs so easy when you follow our voted to news of the world, discussions to private families. The radioman in- simple instruction. on Argentinian culture, Argentinian stalls an automatic phonograph in the 60 PAGES. 3200 WORDS IN TEXT AYoND Send .- music and drama. Multilingual an- home and calls once a month with an day. [Ott 'o.e 25e OthÑ' *Lh sl on''t bey for nother cent now or later. Sold on a money - nouncers speak Portuguese, Spanish and assortment of 30 new records. He picks back guarantee. other languages. up the old records and leaves them at NATIONAL PLANS COMPANY In Chile, airlines are being equipped another home. P. O. BOA 26 B. STATION N. New York 23, N. Y, AUGUST, 1948 70 PM SUPER VALUES A. F. C. STOPS DRIFT It can be added to existing radios. from MID -AMERICA! Stromberg -Carlson DYNATENNA By L. S. WECKER

. This=--n` famous-make FM mitting station. Illus- MOST FM and television set owners on a phase -shifter network consisting antenna has been ad- trated instructions soon realize these units are of R1 -CL The resistance is vertised and sold for and all necessary that of Rl much many times the low hardware. A screw- much more difficult to tune than the larger than the reactance of Cl. The price MID- AMERICA driver is only tool broadcast sets to which they have be- reactance of the blocking condenser is asks! Covers both FM needed for assembly. come accustomed. Many of these sets sò low, and the grid -leak resistance so bands. Delivers FM Dynatenna is seam- high, reception et its best. less, hear must be retuned (at least once) during that neither affects the phase -shift Complete with 60 ft. of all aluminum . the warm -up period because of drift in network. The current through this net- 300 -ohm twin lead -in. will withstand the oscillator and other tuned circuits. work is in phase with the r.f. tank volt- Line Is standard p- severest weather.; Some manufacturers have made tun- age. Since voltage lags current 90 de- proved flat -type. solid grees dielectric with weather - ing easier by using slow-motion dial through a capacitor, the grid resisting insulation. 495 drives and tuning indicators. Attempts voltage lags the tank voltage by 90 de- Mounts anywhere each have been made to stabilize receivers grees. In a vacuum tube the plate cur- easily .. vertically or completely by using temperature-com- rent is rising and falling with horizontally to match $4.45 each the grid polarization of trans- In lots of 3 pensating capacitors and regulated volt- voltage, so the plate current is lagging ages in the oscillator circuit. the r.f. tank voltage by 90 degrees. This lagging plate current is drawn through Ose REACTANCE TUBE BLOCKING CORD the tank circuit, giving the effect that RI FILTER an inductive reactance has been con- t DISCRIM nected in parallel with it. This produces an increase in the resonant frequency of / ___B 'OLEAN the oscillator. PERMEABILITY APPARENT INDUCTANCE In a capacitive -reactance circuit (Fig. TUNER 2) the positions of Cl and have been Build a really HOT 5 or 6 -tube AC -DC superhet receiver! Fig. I -This circuit adds apparent inductance. Rl Takes place of old -style gang condenser, of and antenna reversed and the reactance of Cl is coils: regular .155 KC intermediate frequency. MA -2167 Complete with permeability tuned oscillator coil. These measures are, in most instances, much larger than the resistance of Rl. 4' x2'S' x 24'; 24' diameter dial drum. Com- T plete with diagrams for building Sand 6 tube sets. but a partial solution to the problem. In this circuit, the grid voltage leads the Order MA -2169 Loop Antenna IBe Automatic frequency control (a.f.c.) can voltage Order MA -2914 tank by 90 degrees and produces Drilled, punched Chassis 20o be added to the average FM or television a plate current leading the tank voltage set to compensate further for drift and by an equal phase angle. BANTAM 1- WAITER to make tuning simpler. This addition The magnitude of the apparent react- costs little and is easy to make. ance is controlled by the d.c. bias on the BCR -746 -A tuning unit An a,f,c, circuit consists of a con- used as foundation for B+ Bantam I- Natter de- trolled oscillator, a discriminator, and .NEAtt.TUBE -1 AUDIO scribed in Jan. 1948OST. CT'N Sagf a reactance or DISCRIM Makes tiny crytal - modulator reactance tube a controlled CN :miner as they are called in control A Measures only 33. ' long. circuits. 2K' high, l',,' wide. Re- Since almost all FM and television sets ' r+ S , quires only 1!5 volts "A", 30 to 90 470 volts "0 ". Draws 8 to 15 ma have an oscillator and discriminator, IMEG load. Supplied less24astal, EWE crystal, IS4 tube and plug - a.f.c. can be added to them simply by la coil MA-907 installing a reactance tube. I ' 1 OSC.SECTION L_.0001 SPECIAL AUDIO TRANSFORMERS How reactance tubes work Fig. 3- Diagram shows complete a.f.c. circuit. Exceptionally highyuality universal output transformer for up to 12' speakers. Rated at 12 watts. Matches any single, In FM transmitters and signal gener- grid of the reactance modulator. This push -pull or parallel tubes to 6 -8 ohm voice coil. 12' color - coded leads. 2' high with 24' mounting centers for installa- ators, a reactance tube shifts the oscil- control bias is developed by a discrimi- tion on chassis or speaker. Complete willnnstrnc- 1 Lions e .1 a lator frequency in response to modula- for matching tube impedances. MA -1205 t7 1 1 a7 nator in a.f.c. circuits. Hermetically sealed 200 ohm Single 3000 -ohm to 4-ohm tion. In a.f.c. circuits, the oscillator is The discriminator converts frequency CTto50.000 ohm grid. Use as voice coil output for 60I6 to microphone transformer 35f.6. etc. NS' high on 24' shifted its correct operating fre- variations into voltage variations. When line -to -grid, etc. 24' mounting centers. IMO we tune it to the center frequency of a x114214'. MA -1262 68 MA -1255. . . .. 4 ¢ REACTANCE TUBE carrier, no voltage is developed across Heavy Duty Noise its output. However, should we move Filters lower, we Rated onto amps, 115 -volt AC. Measures only l'z1 TS'aquare. the carrier higher or would 6 Install right in amplifiers, receivers and other equipment y get either a negative or a positive volt- where line noises must be kept at a minimum. Na: 760 -known B+ tionally manufacturer. MA -2164 . all age developed across the output of the Filter for mobile power supplies. Rated 10 amps, 6-30 VDC. r APPARENT CAPACITANCE discriminator. By the same token should Has additional 2 mfd. 100 VDC condenser. 2' high, 2' square. MA -2165...... s7 the local oscillator, i.f. amplifiers, or the Fig. 2-Here the reactance tube is capacitive. transmitter deviate from mean center SPEAKER SPECIALS quency whenever the receiver or trans- frequency, the discriminator develops a All with Heavy ALNICO 5 Slugs mitter drifts. negative or positive voltage that can be filtered and used to bias the reactance 31/2' PM MA- 2062.. $1.39 4x6 Oval PM MA -2167 $1.39 When a reactance tube is connected 5' PM MA -2071 . . $1.39 6' PM MA- 2189... $1.95 across a tuned oscillator circuit, it can tube grid. be made to appear as added inductance ORDER FROM THIS AD! or A.F.C. for FM or TV receivers Quantities are limited, so get your order in now! Minimum capacitance by causing its grid volt- order shipped, $2.50. Send 25% deposit, balance C.O. D. age to lag or lead the oscillator tank Fig. 3 is the circuit of an a.f.c. circuit Get on MID -AMERICAS mailing list to receive BIG BAR- GAIN BULLETINS that list latest, greatest boys in radio voltage by 90 degrees. that can be added to many existing FM parts, electronic equipment. Send orders to Desk RC -88. Fig. 1 is the circuit of an inductive - and television sets. A 6J6 is shown as reactance circuit. The reactance tube is a combination oscillator and reactance connected to the oscillator through a tube. In sets using a separate triode coupling condenser with low reactance oscillator, the oscillator socket can be at radio frequencies. Grid voltage for rewired to take a double triode such as the reactance tube is taken from a point a 7F8 or 6.16. One triode is wired into RADIO -CRAFT for RAI the oscillator circuit and the other used as the reactance tube. When a single tube is used as oscillator and mixer, an EVERY SERVICEMAN additional socket can be mounted for the reactance tube. A 6C4 is a good choice since it shouldn't be hard to find space CAN near the oscillator to mount it in almost any receiver. Control voltage is taken from the a.f. output circuit of the discriminator and passed through a filter network consist- SUPERIOR ing of a 1- megohm resistor and .0001 - -TEST EQUIPMENT and 01 -µf condensers. This filter re- moves a.f. and residual ri. voltages. The New Model 670 The r.f. choke in the plate lead prevents r.f. voltages from flowing through the power supply. This may be a standard SUPER METER A Combination VOLT-OH M-MILLIAMMETER plut v.h.f. choke or may be about 28 turns of CAPACITY REACTANCE. INDUCTANCE and No. 24 enameled wire close -wound on a DECIBEL MEASUREMENTS I,4-inch form. D.C. VOLTS: 0 to 7.5/16/75/150/750 /1500/ 7500. A.C. VOLTS: 0 to 15/80/150/800/ 1500/8000 Volta. OUTPUT VOLTS: 0 to MULTI- ELEMENT FM TUBE 16/30/150/800/1500/3000. D.C. CURRENT: O to 1.6/15/150 Ma.; 0 to 1.5 Amps. RE- SISTANCE: 0 to 600/100,000 ohms, 0 to 10 IMITING and detection of FM sig- Tslegohms. CAPACITY: .001 to .2 Mfd., .1 in a single is made pos- to 4 Mfd. (Quality teat for -electrolytical. nals tube REACTANCE: 700 to 27,000 Ohms; 18,000 sible by a recent development by Dr. Ohms to 8 Megohms. INDUCTANCE: 1.75 of Zenith Radio Corpora- to 70 Henries; 85 to 8.000 Henries. DECI- Robert Adler BELS: -10 to +18, +10. to +88, +90 to tion. The new tube, simple, though un- +58. The modal 870 comes housed In conventional in design, does the dual e kle-fnlehed steel carubbed,inet complete with test loads $28.40 job with the aid of only one tuned cir- and operating Sias NIT cuit and without any problems of critical S rtnstruetlond. we manufacturem complete line of radio test eduipment. transformer coupling. r Dept. RC for FREE catalog today! MFD. ET SUPERIOR INSTRUMENT CO. 2 27 Fulton St., New York 7, N. Y.

at your regular jobber . t.

Structure of the new FM limiter- detector tube. says: ACORN SU'IDEtS OF ()UNITY tADIO INDUCTANC1S SihCE 1024 these PRICES! The diagram shows the tube sche- COMPARE NOW AVAILABLE matically. Electrons emitted by the rec- JENSEN IO' PM SPEAKER Alnico V Magnet TO THE SERVICEMAN tangular cathode are focused into a Jensen Stdnd anl l-er lc " l'iut ST 119. An excellent speaker P.r -,u,d t O lit,' radio sets or PA AND EXPERIMENTER narrow beam by the lower focusing elec- systems. Output undistorted 8 watts. Voice coil Impedance 6-9 ohms. trode which is connected to cathode. The A great value at $4.69 THE FAMOUS beam passes through the slit in the UNIVERSAL POWER TRANSFORMER lower accelerator, to which a positive Primary 115V 60 cyder Secondary î20v c.t. at 150 toile potential is applied. 6.3v at 4 . 5.0v t 3 am,, When the limiter grid is at a certain Flait shell mar with mtg centers 21.'S by 31 s Size 3sa' minimum negative potential, it turns Only 83.49 -3 for $10.00 a THE FINEST back few electrons, allowing most of MINIATURE POWER TRANSFORMER them to pass through it, through the PRIMARY I cycles I. F. TRANSFORMER SECONDAI It I t 100 mils EVER slit in the upper accelerator, and on to 0.3 V at 3 a amps half shell mlE Mtg. centers l2 5 /16'ía 121x' MANUFACTURED! the quadrature grid and plate. When the Made by Thordaraun. Shipping wt. 5 Ihs. grid potential is somewhat more nega- Now 62.89-3 for $8.25 ONLY 2Va"HIGH BY Y." SQUARE tive, it turns back a few of the elec- HAMMURLAND MIDGET CAPACITORS "MC" MC 250 260mmrd. $ 69 ea. 10 or 06.50 SHELL CORE PERMEABILITY TUNED. STABLE SILVER trons; in an ordinary tube, this would MC 325 320nunfd. .79 ea. 30 for 7.50 MICA FIXED CONDENSERS - NOT MICA COM- merely result in a proportional reduc- PRESSION TUNED. ELECTROLYTIC OIL CONDENSERS UNIQUE SNAP CLIP MOUNTING FOR ROUND HOLES tion in plate current. However, in this CONDENSERS 2 5 .02 mrd 1500v 5.69 IN CHASSIS. FP TYPE IN CANS .1 mfd 3500v 79 SO. tube, the turned -back electrons upset the 10 350v I ..5.30 .1 nW 7500v .... 1 79 48S KC jput transformer gain Band width at 2 times 30 300V .25 mfd 3000v 1 19 16 KC: at 10 times 40 KC. 20.2 26V i .... .15 mfd 4000V 1 39 4S5 KC outpx1 transformer gain 110. Band width at 2 times A00 OUTPUT 30 450v ... PLATE 10 450v .5 mfd 5000v .. 1 89 18 KZ; at IO times SO KC. 3010 450v H 1.0 mfd 2200v ... 1.29 262 KC ' p2f transformer gain 65. Band width at 2 times QUADRATURE GRID 20 25v 1.0 mfd 1200v .99 9 K2.`; N 10 times 23 KC. 20.20 430V 74 4.0 mfd 1000v ... .89 262 KC output transformer gain 130. Band width at 1 times 20-20-20-20 e 4.0 mfd 600V .45 10 KZ.; at 10 times 27 KC. LIVRER GRID 29 .... 3.3 mfd 600v .... .79 CAT Ne. ITEM NET MICE TUNED TO SIG. 20.20 400v -250v .44 I 8.0 mfd 800v .79 11.81 241 KC Np0F I F Tran,. $1.15 t F REO. 1 10. 321v .. .89 11 Ní 20 EC Ourput I F T'an, 1.23 2Ó 8+1 mfd 1000V .. 1.39 SIG.MPUT 11 I. li.,., 10 mfd 000V .89 -GI 4SS KC Input F. I.20 30 -30 450v .... .79 It -C7 435 KC Outpw I. F. Trans. 1.20 (FROM 1.69 If 100 30v 49 15 mfd 1000V .. . 1.O mfd 33ovAC 1000 25v 89 / 39 Thé K- TRAN -is distributed 10- 10.10.10 400v 59 1.5 mfd 333vAC/ nationally to the jobber only 1000DC .39 BATHTUB by J. W. Miller Company. CONDENSERS FILLED ACCELERATORS B TLA OIL M.n.f ad .ad« It TRANS. Patent 2.0 Mfd 600v with side 4.0 mfd 600v 1.49 (POSITIVE) CATHODE Oarminals 44e es. NuoMn 2421410 40 242946f of Autometh 10 for 53.90 2.0 mfd 1000v ... 1.39 Manufacturing Corp. Terms: 200o Cash with order. Balance C.O.D. FoCUSING ELECTRCOES prices F.O.B. N.V. Minimum order 52.50. ACORN ELECTRONICS CORP. J. W. MILLER COMPANY h0 Vesev St. Dept. C N. Y. 7. N. Y. 5917 S. MAIN ST LOS ANGELES, CALIF. Schematic diagram shows how the tube h mode. AUGUST, 1948 721 FA1

space charges which allow the beam to pass through the lower accelerator slit. Alt. )adio .s'atvicaman The beam is diffused and many electrons $$$$ are absorbed by the accelerator. As a re- ADDITIONAL FOR YOU EVERY WEEK sult, plate current reduction is very great. With a slightly more negative grid, plate current drops abruptly al- REPAIR ELECTRICAL APPLIANCES most to zero. WITH THE AID OF THE NEW MODEL 40 The difference in grid voltage required to produce maximum and minimum UTILITY TESTER plate current is very small, since nega- A NEW KIND OF INSTRUMENT FOR TESTING tive grid signals not only limit plate ALL ELECTRICAL CIRCUITS AND current in the usual manner, but also APPLIANCES SUCH AS- limit it further by diffusing the beam. RANGES "WASHERS 'VACUUM CLEANERS As long as the input signal exceeds 'SHAVERS FANS *AIR CONDITIONERS about 1 volt, a square-wave output is ob- HEATERSMOTORS *REFRIGERATORS tained, making any IRONERS *TOASTERS *SUN LAMPS amplitude variations *WASHING MACHINES ALL TYPE MOTORS in the input signal ineffective. FROM FRACTIONAL H.P. TO 2 H.P. Detection is obtained by means of the THEMODEL 40 UTILITY TESTER quadrature grid. This is connected to Will test Thermostats under ACTUAL WORKING ground 4 CONDITIONS: Will measure the ACTUAL CUR- through a tuned circuit which is RENT CONSUMPTION of any appliance either adjusted to the center frequency of the A.C. or D. C. WHILE THE UNIT IS IN OPERA- input signal. TION- reading will be direct in amperes -the ap- The quadrature grid ob- pliance or utility may be plugged directly into tains its signals from the electron front panel receptacle --a special pair of insulated clip -end leads is provided for motors; In- stream; it then affects the space charge corporates an ultra -sensitive direct -reading re- surrounding it. The effect with no audio sistance range which will accurately measure all modulation appliance and utility resistances down to a frac- is exactly 90 degrees out of tion of an ohm; Will test bulbs, fuses, condensers phase with the input signal. The two field coils, etc.; Is ideal trouble shooter as it will 90- degree -out-of instantly locate opens, shorts and grounds; Will -phase or quadrature locate cause of failure in three way heat control signals both reach the plate, interacting switches; will indicate when one side of an ap- to produce an pliance or motor connected to line under test is output of a certain fixed "grounded "; Will indicate excessive leakage be- amplitude. tween a motor and a line; Will indicate when a The Model 40 Utility Tester come. three motor is running erratically due to When the signal is modulated, the fre- housed in a ragged T`B phase crackle finished a blown" fuse; Will indicate whether the volt- steel cabinet th portable , IaY11 quency swings away from its unmodu- complete with all test leads and oper- $1515 age is 110 Volts or 220 Volta, if the current is ating Instructions -only V A.C. or D.C. and if the frequency is 25 cycles lated value, at an audio rate. Since at or 60 cycles. most instants the modulated signal fre- legt R.C. quency is different from that to which GENERAL ELECTRONIC DISTRIBUTING CO. Ñ WAROR KLA . the quadrature grid circuit is tuned, the phase difference is usually not 90 degrees. Therefore, the plate current, which is dependent on the mixture of the phased signals, varies along with the ELECTRIC phase difference. Since the phase dif- GENERAL ference depends at any instant on the 150 WATT TRANSMITTER a.f. modulation, so does the plate cur- the rent. Capacitor C filters out the r.f. Cost Government $1800.00 from the plate circuit and audio is pro- Cost to you $44.50!!!! duced across the plate resistor. This is the famous transmitter used In U.S. Army bombers The new tube does the work of three and ground stations, during the war. Its design and Irm- struction have been proved in service. under all kinds of or four separate tube sections in the conditions. all cotr the world. The entire frequency range 111 standard FM receiver covered by means M plug -In tuning units which are include. circuit-one or two limiters ' colla and condensers. and antenna tuning circuits-- earhadesignledg to olperato and two discriminator frequency range. Transmitter at top efficiency rwithin oitsr particular and accessories are finished In black crackle, and the mllliammarr. voltmeter. and diodes. The smaller requirements for RF ammeter are mounted on the front panel. Originally designed KC to cover the frequency range from 200 to 500 and 1500 to 12.500 KC. WIII operate on IO and 20 Meter Rands with alight modification. here are the parts and tubes will allow important specifications: OSCILLATOR: Self -excited. thermo compensated, and hand calibrated. POWER AMMPLIFIEIt: Neutralised class "C" stage. using 211 tube, and equipped with antenna coupling circuit which matches practically production economies. any length antenna. MODULATOR: Class ' R" -uses two 211 tubes. POWER SUPPLY: Supplied complete with either 12 or '24V dynamotor (SPECIFY). which furnishes 1000V t 350 MA. Complete conversion Instructions for 10 and 20 Meter as as bands well 110V AC maliucatlons are furnished. SIZE: 2154 a 23 x 944 inches. Total shipping weight 20n lbs., complete with all tubes. dynamotor power supply, live tuning units. antenna tuning unit and the essential plugs. These units have been removed from unused aircraft but aro guaranteed COMMERCIAL FACSIMILE condition. to bo in perfect Facsimile Broadcasting on a commer- BUFFALO GNESEE STREET RADIO SUPPLY BUFFAL09 -221 SC cial basis was authorized by FCC to take effect on July 15th. Operation pre- viously has been experimental. The authorization allows facsimile to LEARN RADIO ELECTRONICS be transmitted over standard FM sta- EASY TO LEARN CODE - tions by either the simplex or the mul- FOR ONLY SS 972..PAGE T AINING tiplex method. With simplex transmis- It Is easy to learn or increase speed with an Instructograph Code 'reacher. Get complete basic Ita llo -roc- sion, the entire channel is devoted to Rords the quickest and most prac- tronlc training -.fast -at hone -for tical method yet developed. For be- only facsimile while pictures are being trans- `Inners 55. l;hirardi's big RADIO or advanced s t u d e n t s PHYSICS COUILSH book starts mitted. With multiplex, the regular Available t a p e s from beginner's you at the very beginning-with alphabet to typical messages on all Basic Electricity takes yon aural programs Speed range -then are transmitted at the lubiects. 5 to 40 WPM. FOR through the entire Radio-Electronic Always ready -no OHM. BEGINNERS: same time as 35 COURSES IN ONE field. Breathing explained as alm- the facsimile. ply as A-11-C. This giant book la ENDORSED BY THOUSANDS! more widely used for home study To avoid interruption of sound -pro- Teacher and was more widely used for signal Carps. etc. wartime gram service, the Commission literally rtakesgth. olee* of .pnr training than any other of its kind, has lim- ltor- Instructor and bles anyone to earn and master code without READ IT 5 DAYS -AT OUR RISK ited simplex operation to 1 hour be- assistance. Thousands of eeseful operators have Send 53 (55.50 oco with st foreign) cash or money order far tween 7 am and midnight. Multiplex RADIO PHYSICS COURSE. or we will send boot C.O.D. tI today forr convenient rental and purchaserchaa plant.lwrie (in U.B.A. only). You can then pay postman this amount is permitted for a maximum of 3 hours plus a few cents postage when bax.k arrives. IF YOU ARE NOT -MOIID THAN SATISFIED. return book to us with- per day between 7 am and midnight. Use INSTRUCTOGRAPH in o stays and be COMPANY your 55 will refunded promptly. of either system between midnight and RC -68. MURRAY HILL BOOKS, 4701 Sheridan Rd., INC.. 232 MadileeM0., Dept. RC. Chicago 40, III. NEW YORK 16. N. Y. 7 am is unlimited. RADIO-CRAFT for New Patents 73 TV ANTENNA Patent No. 2,440,597 Horace Atwood, Jr., Bellville, N. J. (assigned to Du Mont Laboratories, Inc.) HOT SUMMER SPECIALS This antenna is especially suitable for indoor use, as in an attic. It is effective over a wide COMMAND LOOP LP -21 frequency band and can be coupled to a low - impedance line. RADIO COMPASS RECEIVERS INDICATOR ANTENNA A metal foil or plated surface covers the area I'an be used far Small beam rota- of 'the two cones which are of bard insulating BC-948 520- to 7500 KC '' tor. Loop otata) by selsyn motor. material. The conducting surface connects to emetic. $18.95 also has s-lsyn indicator trills. for metal rings near the middle of the antenna. The nmote Indication. Slip ring assi BC.454 3 to 6 \1e. v - (3). Contacts and rings mude o1 transmission line is soldered to the rings as silver. Imp is onrLsed ill teal Shown. $5.95 drop honing. Wiling diagram Pn' A wooden rod through the antenna axis gives AC operation is Inched $3.95 RC Y.1 with Schematic. ed. Used. but Tested.. the unit a firm support. Its ends may be sus- Mc. $7.95 pended or supported in any manner. 4 DUAL RECEIVER RACK -New $1.00 SELSYN INDICATOR AND TUNING CONTROL CRANK .50 , -1 MEAL RINGS MOTOR -r TRANSFORMER FOR RECEIVERS -115 Volt. '250.0 -2:50 Volt '0 MA: CP ,.1. l' -iman: See. 0 -360 cali- with AC Schematic.. 7 Part of LP -21 Loop. Volt mid Volt. bration ou seism. Wiring Si matit included. Comm. WOODEN ROD TO TV RCVR C 456 MODULATOR for $2 U sed (Tested) $2.95 5th Sehomalie -New $2.5050 R -C OSCILLATOR Patent No. 2,439,245 INTERPHONE 1 -82 5" INDICATOR James C. Dunn, Philadelphia, Pa. Radio ('rupees indicator (assigned to Philco Corp.) AMPLIFIER BC -347 f lsyns for remote (n,li, -a- tim (Used and Tested) at x$2.95 p One form of an improved audio oscillator Type: trees eF5 r- which of good wave form and wide Army Aircraft J New $4.95 is capable Tube. Contains two (8) Midget frequency range is shown in the accompanying tilgt Fidelity rTC amcer trans - figure. It uses only one tuning control, a variable i, .,Tars (6': 16'). Input 20, ..l:m to single or push -pull Grid: resistor. Innpur 200 ohm from single or SELSYN 2JIG1 The invention consists of a 2 -tube amplifier co 0i-pull plate, plus resistors. with the second tube coupled to the first through md.. etc. Completely enclosed. Suggested wiring for 110 with Schematic. Size: 2j4' Solt. 60 cycle included. Nor takes - a bridged -T network. Negative feedback ". Less Tube, wally operates from the fixed in this network, once -each -New place through resistor 79e $2.00 cults. 400 eyrie. Used (Test- and regeneration is obtained through the variable Or three 13) for ed) Per Pair- $3.50 resistor. only As the T network is adjusted, there is one 250 014M HEADSET -Can he wed with 97e frequency which is balanced out. This frequency alone as Mie. & Ito. IIS -31 -NEW DYNAMOTORS depends upon the R and C values of the network.; At this frequency there will be almost no nega- SPECIAL OFFER MOBILE USE -4 Volt le tive feedback to the 7W7 cathode, and therefore put; output 405 volts :,:l M. \. from 6 Vol CHART to Commercial Also will operate the circuit oscillates. The 100 -ohm resistor in the TUBE CONVERSION -VT Input: output 280 Volts ti grid circuit of the first tube is the regeneration -furnished at no charge with your Order. MA. Slae: 3' x $3.95 control. It is set at the lowest value which will 7'. DM 635x .. permit oscillation. MINIMUM ORDER -52.00 Prices Lima. Ohio 25°' DEPOSIT On C.O.D. Orders The component values given are for a frequency range of approximately 2 -20 kc. The capacitors 132 SOUTH MAIN ST. may be changed to give other frequencies. RADIO SALES LIMA, OHIO 7W7 8K8 FAIR 2.7MEG II 1.214fG

B+

100 C 880 2208 .002 .002 5.68 MAGNITUDE AND PHASE

CONTROL ..y receive[ Patent No. 2,441,334 by SignO' to icSpeedapproaMly William H. Sayer, Passaic, N. J. Tervicin9 Dynamic fM Modern, fells HOW in (assigned to Du Mont Laboratories, Inc.) Simple' problems, s s s - The Only a positive pulse can trigger a thyratron. and to learn simple, direct language. ur chose This circuit can reverse the polarity of a signal olignment NOthin9 complex so an input pulse of either polarity can be used esita equipment New 9th edition now off the press. No non-obsolescent 100 pages of valuable information. if' its magnitude is great enough. Test Equipment The middle of the plate load resistor is ground- only 5osic ed. Therefore voltage polarity is different on each Employs) Available from all leading radio parts and side. Furthermore the value of this potential in- equipment distributors or directly from factory creases as P is moved away from ground. The at only 40c per copy. contact is set at the point which provides enough positive voltage to operate the thyratron. ^RECISION APPARATUS COMPANY, Inc. 92 -27 Horoce Harding Blvd., Elmhurst 4, N. Y. The figure shows how the circuit may be used ahead of an 884 or similar tube to generate saw - tooth waves. If the input signal is positive P is moved towards the cathode end of the potentiometer. TERRIFIC VALUE - The capacitor-selector switch chooses the capac- PORTABLE ELECTRIC DRILL itor which will give the time -constant desired for (Sold at lass than established factory price so we cannot mention brand the saw -tooth wave generated by the thyratron. name) Only $19.95 equipped with 'h' Jacobs Geared Chuck and Key. Not an Intermittent duty .frill. but a full size rugged Rol. Most convenient type switch, natural grip handle. alai balance like a six - shtoner. Precision cut gears -turbine type tooling blower-extra long trusties. No stalling under heaviest pressure because of powerful 110 Volt AC -DC motor and multiple ball thrust bearing. Other bearings self -aligning lifetime-lubricating Chrysler Oilito type. Made for toughest year -in and year-out genie° In liant or on construction jobs. Amazing perpetual fart°q gu tnnt cw- assures 3,a1 of a lifetime of trouble -free use. 25% depositpo o ('.0.1).'x. Full refund (yo pay transportation) if not pleased with drill after trial. BUFFALO RADIO SUPPLY 219 -221 GENESEE STREET BUFFALO 1 N. Y. DEPT. 9C

AUGUST, 1948 74 New Patents NOISE REJECTOR Patent No. 2,438,501 Donald L. Hings, Ottawa, Ont., Canada. (assigned to Electronic Lab., Inc.) The inventor of this circuit claims that many types of noise are practically eliminated by it. The noise is amplified separately and then mixed with the incoming signal in a pentagrid tube. If the noise level is adjusted correctly, it will oppose the noise in the signal. The result is cancellation of noise without affecting the desired signal.

BIGGEST VALUES in TELEVISION! Large -Image, Direct -View TV Kits at Low Cost! Kits Engineered for EASE of ASSEMBLY and Top Performance. Cabinets designed and built for Beauty, Utility, Durability. NO TECHNICAL KNOWLEDGE REQUIRED FOR ASSEMBLY.

L JFILTER The signal is applied to the control grids of VI and V2. The amplified signal (including the noise) is transmitted through the transformer tò one diode plate of V3. Here it is rectified, and part of it passes through C to the control grid. The remainder of the ri. component is filtered MODEL 10BL out while the a.f. component aplican at R. 115 Sq. In. Picture This is followed by a high -pass filter with cutoff Gives at about 3 kc. These higher frequencies passed by the filter (shown in the dashed box) include most of the noise. The noise is amplified in V3 and then applied to the grid No. 3 of VI. The noise voltage opposes the signal voltage at grid No. 1. The control R is adjusted for the proper level to ae_ produce noise cancellation.

VOLTAGE MULTIPLIER Patent No. 2,439,224 Winfield R. Koch, Haddonfield, N. J. Le (assigned to Radio Corp. of America) for full 180° Visibility A potential of 25 kv or more muet be used for Consolette Model 7CL Roto -Table projecting large- screen television. This voltage line of high quality may be obtained by rectifying the pulses from TRANSVISION manufactures the most extensive the scanning circuit and then doubling or tripling Television Kits, Cabinets, and Components. Models illustrated and listed as required. The ordinary type of voltage -mul- here are only representative of Transvision's leading values. tiplier is not satisfactory because it uses several See your distributor. condensers in series to bring up the total volt- MODEL 10BL, TV /FM Kit, gives 115 sq. in. picture; complete FM aire. Regulation is poor when a series circuit is Radio: receives all channels: streamlined cabinet NET $299.00 used. The circuit shown here is a voltage- tripler ltoto-Table for Model 10BL, gives full 180° visibility NET $ 24.95 in. consolette cabinet with in a parallel arrangement. Each rectifier is sup- MODEL 7CL, TV Kit, gives 60 sq. picture: plied by great- itoto- Table: streamlined design NET $199.00 its own condenser. Regulation is MODEL 7BL, same as 7CL except that it is a table model NET $189.00 ly improved. 110 wire. ell prices Include cabinets, tubes. antenna. Lot ft. of le:si-ln (Models Each rectifier must be connected with polarity F\I for small addle onal met.i rl. and 710L ran be supplied with complete hail' n.s shown. since the input is not symmetrical. ('I becomes charged to the peak voltage E, and "SERVICE NOTES" during the next few pulses the charge leaks off -FREE - voltage and places a E upon C2. During each Fascinating by TRANSVISION pulse, V2 is subjected to a voltage 2E, the sum BOOKLET tho Ncr to Successful of the potential upon C2 and the pulse voltage. Television Servicing . On Television ConfidentialTelevlslmm Notes and Information. Ili ost rated 20 -page 2 -color product of eapc noire b",klet gives you excellent with a 211.111$) 1 tele- basic Information on tele t 1111 /I elo vision. ('all at your dlstrlbu- vision sels. tor's for a FREE COPY' or With photos. diagrams. untie to us for names of dL- \vowtL a small Punos. tributors. font is unit $1.95 NET PULSE INPUT

All prices 5% higher west of Mississippi; all prices fair traded. E( CI 2E( C3 C5 )3E OUT For further information see your distributor, or write to: TRANSVISION, INC. Dept. R.C. Therefore C9 becomes charged to a voltage 2E. NEW ROCHELLE, N. Y. During the next few pulses this voltage appears In Calif.: Transvision of California, 8572 Santa Monica Blvd., Hollywood 46 across C4 because of the leakage current. V3 is now subjected to a potential 3E, made up of BIG TELEVISION SHOW at the WALDORF! the voltage across C4 in series with the input. Therefore a voltage 3E appears across C6. Out- On August 16, 17, and 18. Transvision will hold its 2nd annual ex- put is taken from this point. hibit at the Waldorf- Astoria Hotel in New York ... RE. SURE TO Additional stages may be added for still higher COME and see the many sensational new television developments. voltages. The output remains fairly constant even J when the load changes. RADIO -CRAFT for New Patents 75 SQUARE WAVE GENERATOR Patent No. 2,440,992 Richard C. Webb, LaFayette, Ind. (assigned to Purdue Research Foundation) the radio A good square wave generator needs two main controls: pulse width and frequency. Neither that should have much effect on the other. These requirements are met in this simple generator. It uses a double- triode tube, such as a 6SN7, and a triode cathode follower. AMAZES When power is first turned on, Cl is uncharged so grid G1 is at ground potential. G2 is at high positive potential because it connects to B plus even the through a condenser. The heavy plate current through T2 produces a large negative voltage drop through its load and this voltage appears EXPERTS at 03. The large plate current also flows through the common cathode resistor and a large negative bias is placed on GI to cut off this tube. As the negative voltage leaks off Cl the grid becomes more positive and the other grid (G2) becomes more negative. Now TI conducts and T2 is cut off. Plate voltage on T2 rises to the full power supply value and it appears on G3 as a high positive voltage. After a short interval the high positive voltage on CI discharges. G1 voltage becomes more negative and 02 more positive. As the Ti plate current drops the increasing voltage across its load is transferred to G2 through the condenser C2. Finally G2 reaches a high positive potential and the cycle repeats. The frequency is determined by the rates of charge and discharge and is therefore controlled by B. The pulse width is determined by the ratio of C2 to Cl. These condensers may be controlled simultaneously so that one increases as C2 Cl the square 5BP1 5GP1 the other decreases. When equals There is no other radio like Hallicrafters wave is symmetrical, C -R Tubes 5 Four bands precision -made Model -38. Brand new 511P1 /5GP1 cathode ray tubes, perfect bring you thrilling land, sea, air commu- for oscillograph use. Green fluorescence with medium persistence. Five inch screen. medium nications from all parts of the world shell magnal 11 pin base. 6.3 volt heater, 2500 plus. finer quality on your favorite broad- volts on anode No. 2. Each tube individually boxed. About one-tenth list price. Quantity ex- cast program. Perfect for den, library, tremely limited. office. Extra clear, strong reception any- XPS916 -58P1 Tube $1.39 where. AC DC Write for Catalog P38 While They last. Your Cost and where to buy CINAUDAGRAPH High Fidelity Model S -38. . .$475O CIN -12A 12" Cinaxial Speaker An exceptionally fine buy in high fidelity speakers. Especially designed for FM and television RADIO sound use. Assures efficient operation at all fre- hallicrafters quencies from 55 to 12,000 cps. The low frequencies are propagated in a large 12" unit and ELECTRONIC MOTOR CONTROL the high frequencies are produced in a smaller 3" Get a Halllerofters and listen for the Gaftl- Hallicrnfters unit mounted co-axially within the dimensions of Patent No. 2,440,600 mobile, radio-equipped expedition now operating via the 12" speaker. A bridging network is built into Murray G. Crosby, Riverhead, N. Y. short wave from th Mountains of the Moon, Africa, the speaker to handle both units -no controls are (assigned to Radio Corp. of America) THE HALLICRAFTERS CO. necessary to allocate the crossover frequencies to 4401 W. Fifth Ave., Chicago 24, Illiioit the proper speaker unit. Especially designed for Less than a volt is enough to start or reverse FM, the speaker is equally suited for use with a a motor operated by this circuit. The first tube is 10 -watt output amplifier for television sound, a mixer. About 0.6 volt at 60 cycles is applied to DUE TO POPULAR DEMAND wide range phonograph work, studio monitoring 01 to modulate the electron stream. The tap at or similar installations of this rating. Voice coil impedance, 8 ohms output, 10 watts ; Alnico V P places about half this voltage on G3. WE REPEAT THESE electrons are trapped by the screen which magnet. Shpg. wt. 6 lbs. Some X19118- is not bypassed. This produces an a.c. voltage drop $16.17 across the screen resistor. This voltage is 180 Your Cost degrees out of phase with the potential applied to TERRIFIC BARGAINS G3. P may be adjusted so that the two voltages have equal and opposite effects. Three assorted new MICROPHONES, including push -to -talk type 81.99 TUNING ELEMENT M 3L Ten assorted R. F. Chokes including I high frequency types 8 .35 s Five assorted AUDIO or FILTER CHOKES S .99 B Aó One Hundred assorted RESISTORS $l.95 AIL NOW PHASE SHIFTER Ten assorted JAN CABLE CONNEC- TORS, including SCR274,522 and New York 09+ BC376 types 8 .99 100 SIXTH AVE. CONTROL POTENTIAL M =MOTOR Six assorted OIL FILLED CAN TYPE 110 Federal St., Costal 10' Balance is maintained until amplification due CONDENSERS, all with mounting 24 Central Ave.. Newark 2 to G3 is changed. This may be done by a d.c. brackets $1.49 control potential. If this potential is positive the Ten assorted METAL -& BAKELITE effect of G3 is greater than that of the screen KNOBS -(no wooden knobs) S .39 which negative potential will cause opposes it. A Six assorted VARIABLE CONDENS- the screen voltage to predominate. When the etteRado ERS, including butterfly types 81.49 polarity of the control potential is reversed, so asserted POWER and AUDIO t RADIO WIRE TELEVISION, INC. is the phase of the plate current. Six TRANSFORMERS, all new - 81.98 The motor has two windings. The phase of B Dept. JH -8, 100 Sixth Avenue, N. Y.13 is shifted 90 degrees by a condenser. The current Six assorted isolantite and bakelite R. F Send : XPS916 @ 1.39 ea. quantity and $ through A will then be either in phase or com- COILS, shielded unshielded .99 X19118 @ 816.17 ea. quantity money order pletely out of phase with the input a.c. Therefore The above ten assortments totaling over 512.00 at the Enclosed: cheek unbelievable. bargain prices listed can be purchased Send catalog New Flyer C42 it either leads or lags current through B by 90 together as one lot at a supersteclal total price of degrees current. The motor runs in one direction only 810.00. All merchandise guaranteed to be as or the other depending upon the polhrity of the advertised. Name control potential. This voltage may be taken BUFFALO RADIO SUPPLY from a frequency discriminator. It will be posi- Address BUFFALO t. N. Y. tive or negative depending upon whether an in- 219 -221 GENESEE STREET DEPT. 8D Zone. . State coming signal frequency is too high or too low. City AUGUST, 1948 761 Technotcs

VARIABLE CONDENSER CLEANER OPPORTUNITY AD-LETS When variable condenser plates are CAN'T GET TO GOV'T SALES? Advertisement, in this section cost 25c s word for each insertion. Name, address and Initials must be too close to clean with a pipe cleaner, Included at the above rate. Cash should accompany the in Then the best thing is to get this all elasslOed ubertlsemonts unless placed by an put cleaner a vise and apply pres- accredited advertising agency. No advertisement for sure. The new flattened shape will fit less than ten words accepted. Ten percent discount six issues. twenty percent for twelve Issues. ObJec- easily between most condenser plates. ttnneble or misleading advertleninents tot accepted. SPECIAL GOV'T RADIO Advertisements for September. 1918, Issue must H. R. NEWELL, reach us not later than July 24. 1918. Radio Craft 25 W. Sway New York 7, N. Y. Bradford, N. H. SURPLUS ASSORTMENT RCA MODEL 85T RADIOMEN. SERVICE:KE.N. BEGINNERS - MAKE more money. easily, quickly. $250 weekly possible. Wo The tubular condensers in this set show you how. Information frees Merit Products, 216 -32L usually go bad and cause intermittent We buy large quantilles of 132nd Avenue, Springfield Gardena 13. New York. these items, divide them reception. It is a good idea to check all into choie. assortments BUILD A SUPERONIO OCrO31ETER: AN ULTRA modem Instrument, inowporating a V.T. Voltmeter, which we E00 test these condensers when this set is know you would V.T. Ohmmeter -Signal Tracer -Signal Generator-Am- be pled to have $ for this pll8er- Auxiliary Power Supply -Speaker, Microphone and brought in for repair. price if you could see Pick -up toter. In ono small portable cabinet. For ran - them. u, Chassis BRIAN BAILEY,, plete Diagram.. Schemed®, Panel Template, layout. assembly and operating instructions. send $2 end Brownwood, Cils ad, to: Grand Federal Supply, Box 57. Argentine Texas CHEAPEST WAY TO BUY WAR lirmtch, Kansas City 3, Kansas. 1288 & 25B8 TUBES, BRAND -NFRV, SOLD ON MONET- . . RADAIR MODEL 101 SURPLUS RADIO MATERIAL bark guarantee-$2.49 each, 10 for $22.50. Tubes & parts If interference and oscillation is very 69% to 80% off -write for fier bargain catalog. Commer- cial Radio, 36 Battle St.. Roston 8, Mass. noticeable, the set is probably out of On a deposit of $5.00, we will ship WANTED: SOSIE 35260 RADIO TUBES. IRA L. LES, alignment. The i.f. on this receiver is 2 you C.O.D. (Balance $20.00 Freight llatagar, Ala. mc, someone may have tried to align it SELECTED 0ROUI' OF MEN, GRADUATES OF WELL - Collect) an amazing quantity of sur- known trade Rehout, desire employment in Radio Field. with the signal generator tuned to 456 plus radio items, subject to your in- Will travel anywhere. Qualified In radio srntcing, instal - or 465 kc, since the proper frequency is spection lation. test Instruments. circuit operation, etc. Contact and approval at freight sta- Placement Dept.. Eastern Technical School. 888 Purchase not indicated on the chassis. l tions. Unless Street, New Bedford. Mass. you are more than ARTHUR L. JOHNSON, pleased, have Agent return to us, EMERSON RADIO TUBES 80% OFF UST. ALL TUBES individually bored with 90 -day guarantee. Send for cir- Hutchinson, Kan. freight collect. Your money refunded culer. Max Volpian, l 2239 Third St. East, St. Petersburg immediately. All it will have cost you 6. Florida. will be the freight charges one way! MAGAZINES (BACK DATED)-FOREIGN, DOMESTIC, art.. hooks. booklet., mbecriptlms, pin -ups, etc. Cata- RADIO -CRAFT wants Teehnotes de. log 10c (refunded), Cicerone's. 863 First Are., New In fact, you can probably sell just a 'York 17, N. Y. scribing common troubles of well - few of the items you don't need, to WESTEILN ELECTRIC CARRIER TELEPHONE AND known receivers or telling how rare or more than cover cost of the entire Telegraph Equipment and Components. Filters, rePeating difficult problems were solved. A six - lot. tell, transformera. equalisers. Types CF', CF2, R, C. and Our warehouses are filled with alter cartier equlement. Telephone and telegraph repeat- month subscription will be awarded thousands of choice Gov't. Surplus ers. Box No. ItC -A8, Radlo -Craft. 25 West Broadway, New for each unillustrated and a one -year York 7, New York. Radio items. The cost of inventory- subscription for each illustrated Tech - YOU CAN ACCURATELY ALIGN SUPEIt1IFTE1tODYNH ing, itemizing, grouping, etc., would receiver, without signai generator. Complete Innructlons note published. only multiply their cost to you. $1. Moueybaek guarantee. Chu. Gates, Pocos 2, Tesas. Therefore, we make this offer. LANCASTER. ALLWINE & ROMMEL. 436 ISOWEN Building, Washington 5, D.C. Registered Patent Attorneys. . ZENITH MODELS 5R216 AND 55218 Practice before United State. Patent Office. Validity and However, if you mention a few infr'ntement Investigation. and Opinions. Booklet and Several of these receivers had the items you desire, we will try to form "Evidence of Conception forwarded upon request. same complaint, low volume with a loud include them in the assortment. AMATEUR RADIO LICENSES. COMPLÉTA ThEORY hiss on stations below 650 kc, even with Send for our special Value preparation for passing amateur radio examinations. nome Bul- study and reniaient cames. .4 merlran Reille Ina? llute, a good antenna attached. Low -frequency letins on 191 West 63rd St., New York City. See our ad on Page 89. Radio and Photo- stations came in much stronger when graphic Supplies. Tell us your NEW CARTONED RADIO TUBES 39c. WRITE FOR wants. bargain catalog. Henshaw Radio, 3313 Delavan, Kansas the chassis was turned on its side. City. Kansas. The trouble was traced to a shorted WH REPAIR ALL TYPAS OF ELECTRICAL INSTRU- ent,, tube checken and analysers. /limetton Instrument antenna coil primary. The improvement GAS ENGINE POWER PLANTS Co. (Electric Meier Laboratory), 140 Liberty Street. New BARGAIN PRICES FOR QUICK SALE York, N. Y. Telephone- B.trelay 7-4239. in reception when it was on its side was 2000 WATTS -115 5000 WATTS -115 due to the unshielded antenna coil sec- V. D. C. V. A. C. 34.8 amps 44 90% ondary acting as a directional loop 17.4 Amp,. Wlarionaln PF. 60 cycles, Onan type ierooled 4- rynnner, 4 FM STATION LIST antenna. cycle engine. cycle gas engine. Water Remote start A universal replacement coil . á ell' Next month we are printing a complete FM restored RF Oat .. $199.00 $549.00 the set to normal. Ali unit, ondula de,l a guaranteed. Order n Station List. Managers and Chief Engineers write for further details 90°ßr deposit required with orders. of FM stations which have come into opera- WILLIAM FORD, tion since our June list vies published are Chicago, ill. with us, giving the The invited to communicate REDUCING DRAIN ABELL Distributing Co. call, and frequency of their stations. FM ob- When using an external device, such 7 E. BIDDLE ST. Dept. 11 servers are also requested to help us keep as a phono preamplifier, which draws BALTIMORE 2, MD. our list up -to -date. its power from the receiver or amplifier, current drain on the filament supply can be reduced by replacing the pilot lamp s with one of lower current rating. For 6.3 -volt lamps, use No. 40. or 47 (brown bead) tb replace No. 44 or 46 (blue SCR -274N COMMAND SET bead), saving 100 ma. For 2.5 -volt e1 lamps, use No. 42 (green bead) to re- The greatest radio equipment value in history place No. 41 (white bead), saving 150 ma. A mountain of valuable equipment that includes 3 receivers LEWIS SWANSON, that use plug -in coils, and consequently can be changed Toronto, Ontario to any frequencies desired without conversion. Also included are two Tuning Control Boxes; I Antenna Coupling . . PHILCO 1201 SERIES Box; four 28V. Dynamotors (easily converted to I10V. If a very loud hum appears (it may operation); two 40 -Watt Transmitters including crystals, show up as an intermittent buzz), re- and Preamplifier and Modulator. 29 tubes supplied in all. gardless of the setting of the volume Only a limited quantity available. so get your order in fast. Removed from unused aircraft and in guaranteed control, check for a short where the electrical condition. A super value at $34.95, including wires to the phono motor switch pass crank type tuning knobs for receivers. through a metal sleeve. BUFFALO RADIO SUPPLY 219 -221 GENESEE STREET GORDON S. WEEKS, BUFFALO 3, N. Y. DEPT. SC High Springs, Fla. RADIO -CRAFT for .

Tcchnotcs 77 . . SPEAKER REPAIR a multiple of the . When a speaker voice coil is rubbing 60-cycle line fre- against the pole pieces, find out which quency. A neon side of the voice coil is rubbing by gen- bulb connected to ,e tly prodding the center of the cone with the 60 -cycle line mi, 1' _ 11 the fingers. Then insert a piece of cot- and held hear the ton or a ball of paper between the cone movipg vibrator TAPE RECORDER and the speaker frame in such a posi- contacts will make provides tion that the voice coil no longer rubs. them appear to Dampen the cone lightly with, carbon stand still or slow FULL HOUR of tetrachloride. When it is dry remove the d o w n. Improper paper or cotton. The rubbing will usu- operation can eas- Continuous ally have been eliminated. ily be noticed. B. E. STEWART, High Fidelity Recording For best results, and Play Back Moberly, Mo. the room should be Through evolutionary method of recording on two range 50 to 9000 cycles . CCINTINENTAL MODEL 6C darkened so that Frequency tracks on the tape instead of single tract, your the only light shin- 3 db. playing time is doubled, resulting in greatly in. A particularly irritating grinding Individual bass and treble equal. red convenience. and laps costs c 1 in half! noise in this set sounded like local inter- ing on the vibrator (ration controls. An automatic switch and solenoid instantly reverses Five watts output. the direction of the tape at the and of the eel, ference. Noise- reducing methods had no is that from the Portable and standard models eliminating the necessity for rewinding. No special neon lamp. available. knowledge i required to thin professional e. effect. The defect was finally localized Extremely low hum level. (DC on suits! The ideal recording- playback instrument for in a partially open filter condenser by A. CREMAILH, heaters). the home, industry, eleboretory, and broadcast studio. 16" wide by 14'4" deep by 13" the use of a condenser analyzer. Douala, high. Her. is magneti: tape order that's n w, dif- Provision for playing disc records. ferent, and better! It enables you to record and BRIAN BAILEY, voice per. French Earphone jack provided. play beck music and with a quality of for matched by any other m and offers Brownwood, Texas Cameroon Sockets for VU meter and foot witch. this extra added premium - a full hour's program high fidelity recording 1/p All components easily accessible. of one standout hour reel of magnetic . AUTO SETS duty motor. tape running et the standard 7 %j" Heavy recording per second. To find out if the vibrator power (Vibrators re- (Eliminates possibility of over. paired by filing the heating). But that's not all you get in this ultra -modern TWIN pack in an auto set is defective, discon- negligible. contacts be- Flutter and weer TRAX recorder. Not only ca crophon record. nect the B -plus lead and supply the high often ings be made easily, but simple connection made come to your radio enables you to record any program s you listen to if.s FacliGesn are provided voltage from an external power pack or defective on the recorder for copying your valued duc records. dynamotor. The voltage is again very soon, filament sup- If not available at your dealer, order direct. or end for literature describing and featuring the plied by the battery. If the set now and the technician mewing TWIN.TRAX recorder. should replace worn haae,n,:. operates, the trouble is in the power Booklet vibrators except of A. C. Showey s Famous supply. "ELEMENTS MAGNETIC Price $219 50 course in cases like AND AAPE RECORDING A light current drawn from the bat- 4055 nnn Is Still Available at 25: tery before the B -plus lead was cut in- that above, where dicates a probably defective vibrator. If obtaining a re the current is excessive, either the buffer p lacement might ' OF condenser is shorted or the vibrator take many months.5 AMPLIFIER CORP. AMERICA 1398 points are sticking. ' -Editor) -10 Broadway New York 13, N. Y. FRED P. STEINMETZ, GENERAL ELECTRIC RT -124S 15 -TUBE TRANSMITTER- RECEIVER Chandler, Indiana COMBINATION TERRIFIC POWER-120 two Instantly Model re- adjuatvdcfrequencies from 435 to 500 Mc. Transmitter uses 5 tubes Including a Western . PHILCO 41-605 Electric 316 A final. Receiver uses IO tubes includ- 802 -N ing 955's, as first detector and oscillator, and 3- Heating of the power supply voltage - "DYNOPTIMUM" 7HT'e as IPa, with 4 hie -teased 40 Mc. IF trans. former, plus a 7H7. 7E0' u and 7F7's. In addition divider resistor was caused by a shorted unit contains 8 relays designed to operate any tort of froexternal equipment when actuated by received igrsal filter condenser. m a similar set elsewhere. Originally designed for and 12 volt olc sono, power supply i not included, as H Replacing the XXD tube with a TUBE SET TESTER Is eilleh fur any amateur to arl nect this unit for 11ÓV AC. using any supply asante of 400V nDC at - 135MA. The Ideal unit for use in mobile or stationary 14AF7 caused oscillation at the high the 000'issary no license Instn,Telephonetions nanBand iagrams frequency end of the dial. This was A compact, aupplted for running the RT.1246 transmitter on either code or voice in AM or FM transmission or reception, cured by replacing the 10,000-ohm oscil- for use mobile low - priced public address system, as n 80 to 110 Me. FM Immaterial receiver, as a Facsimile lator plate circuit resistor with a 5,000 - trenamluer or receiver. as amateur television transmitter o elver, for remote nctntoil relay hookups, ohm resistor. instrument fr Gelger'Mueller counter applications. It sells for only 529.95 or two for 353.90. If desired for n urine TEws RAmo SERVICE, eimobile u the dynamotor which will workt on for greater ther 221V 1 DC and supply all power vfor the 14Sc.) Milwaukee, Wis. is no ly 615.00 additional. profits BUFFALO RADIO SUPPLY 219 -221 Genesee Street. Buffalo 3. N. Y. Dept. RC . ADMIRAL CHANGERS ONLY A common trouble is failure of the changer to complete its cycle. This is $59.50 often due to a worn drive wheel (part No. G400 A179). Wear can be detected Multiply your productive service time with this by running the fingers around its rub- completely modern, accurate tube and multitester. It provides maximum test operations with mini- ber tire. Replace it if it is bad. mum switch settings -speeds your service checks Another common difficulty is failure for field and counter work. Order from your local jobber. Write direct for catalog. I of the set-down assembly (part No. Check these features: G400 A152). If the adjusting screws Simple to operate as a tube tester or set test- will not index properly, the set -down er- combining accuracy and speed Usual AC voltage errors due to frequency assembly may be slightly bent and and temperature virtually eliminated with scraping against the frame. Straighten- germanium crystal rectifier Tests paper, mica and electrolytic condensers ing it will complete the repair. for leakage EARL E. WEITZ, Resistance measurements through a 200 million to I range Chicago, Ill. Famous Dynoptimum circuit for tube testing -giving accurate speedy tests for quality- ifASTERPIECES VIBRATOR REPAIR short- leakage and noise CABINETRY Set tester includes AC-DC voltmeter-out- t/1 in When replacement vibrators are hard put meter -decibel meter-ammeter-milli- Television cabinets specially engineered for ammeter-ohmmeter--all multirange 12" and 15" Standard and De Luxe "Trans - to get, the technician may repair the old vision" models. Also available for 12" and 15° R.C.P. . one by filing the contacts. To observe the INSTRUMENTS . . BEST FOR EVERY TEST Standard and Champion "Television Assem- repaired bly" models. Exclusively designed ' tables to unit in operation, use a neon match. Various finishes. Write for particu- lamp as a stroboscope. RADIO CITY PRODUCTS CO..INC. lars, Dept. B. The usual frequency of a vibrator is TEL -CRAFT COMPANY in the neighborhood of 120 cycles. This is 108 Havemeyer St., Brooklyn 11. N. Y. AUGUST, 1948 11'oorIuI -'iuIe i ratio,. List ONLY 50c EACH Edited by ELMER R. FULLER have noted that this de- Cjet ,gfé 70 $5.00 SET OF 10 READERSpartment has skipped a few issues during the past several months. This has been due to the new FM station list. These Books Keep You On Your Toes! In the future, the Short -Wave Station List will appear in two sections in suc- 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 IO is worth many cessive months, and the FM List will times its 50c price if you will just apply a small portion of the information gained to your daily appear the third month. A complete work. You'll be glad you have the complete set handy whenever you are trying to work out a particular problem in construction, testing or servicing. You'll like the easy -to-read type -the clean -, world -wide log will be printed in the cut printing -the smart, modern, flexible covers, and the great number of illustrations. They all October and November issues (half in help to make learning pleasure. Order as many as you need today- better still. make it all 10. each issue) so be on the lookout for it. Below you will find something differ- No. 29-HANDY KINKS AND SHORT ent we in de- CUTS. A carefully tdited compilation oL than usually print this time sayers. Kinks on Antennas - lower partment. Here is a list of the least - Supplies -Test KOUipment- Servicing -In the Shop -Phonographs and Amplifiers- heard and possibly hardest-to -get sta- Coils and Transformers-511scellaneous. tions. We would like to have 'you do a No. 30- UNUSUAL PATENTED CIR- little dial twisting, and give us a re- CUITS, 1944 -1946. A gold mine in new port on any of them that you hear. Most honk -ups! A selection of unusual circuits many a result of wartime research-of great of them have been reported as being re- value to anyone interested In electrode:. Control Circuits- Detector and Amplifiers ceived on the east coast, so they are not -Power Supplies- Miscellaneous Circuits 91111.11111 II Foreign Circuits. impossible to get. A Dx -ers program from Sweden is e'SO colt No. 31 -RADIO QUESTIONS AND ANSWERS. Answers to most fromently transmitted every Saturday on 6.065 me 4 asked questions. Clear schematics. Ampli and on 15.155 me at 0245 EST, with a fiers Receivers- Transmitters - Meters and Test Equipment- Interphones-Power Sup- second transmission on 10.780 me and -Phono Amplifiers-P. A. Systems. plies on 15.155 me at 1000, and a third tuans- No. -32- ADVANCED SERVICE TECH mission on 9.535 me and on 10.780 me NIQUE. An up-to -date collection of Infor- mation for the advanced serviceman: Visual at 2000, EST. Reports may be sent to Alignment -Tracking Problems - Negative Dx Feedback -Tone Control Circuits- Adding Editor, Radiotjanst, Stockholm. Microphones to Sets-Matching Loudepeak- Radio -Hew. juke Boxes- Servicing Record Monte Carlo is now using Changers -Hum Elimination-FM Servicing. 6.035 me and may be heard from 0230 st tuts to 0430, 0700 to 0900 and'1400 to 1815 No. 33- AMPLIFIER BUILDER'S GUIDE. Invaluable for the designer and daily. Reports may be sent to: Radio builder of audio equipment. Tells how to Monte Carlo, 16 Bd build a wide variety of amplifiers. Detailed Princesse Charlotte, design information on: Push -Pull-Phase Monte-Carlo, Monaco. Inversion -Rau d Treble Iìooetera -VOI- radio, ume Expanders -Resistance Coupling-In- test ternal Feedback. - instruments Free. Station Location and Schedule No. 34- RADIO- ELECTRONIC CIR- CUITS. An extensive collection of circuit 3.910 ZQP LUSAKA, SOUTHERN RHODESIA: diagrams. with brief. to- the -point descrip- 1030 to 1200 11110 CCU of each. Intercommunica- 4.780 SINGAPORE. MALAYA; 0345 to 1000; 1 fIllslt tions including: tions Systems-Power Supplies- Balancing 11110 CRAFT 2330 to 0130 rircults -V.T. Voltmeters-Ampliflers-Re- 4.900 ZOH COLOMBO. CEYLON: 0430 to 1145 ceiven - l'hnno Amplifiers -- Short Wave 4.940 HJCW B OGOTA. COLOMBIA; 0645 to 1115: Adaptor- Electronic Relays. 1600 to 2315 5.880 IRK CAPETOWN, SOUTH AFRICA; 2345 to 0130; 1100 to 1600 No. 35- AMATEUR RADIO BUILDER'S 5.980 ANDORRA; 0600 to 0830: 1300 to 1900 GUIDE. For the "ham" who builds his 6.040 RANGOON. BURMA; 0915 to 1015 own. Practical. down -to-earth. Tells you 6.060 TETUAN, SPANISH MOROCCO; 0230 how to Build: A 2 Meter Rand Acorn elementary to 0300: 1330 to 1500 Tube Set -Miniature Canununlrallons Re- radio 6.100 VUD3 DELHI. INDIA; 1200 to 1245 reliera- -Long Lines Transmitter- Begin- 6.100 WARSAW, POLAND: 1100 to 1800 Preselector Rotary ers Transmitter - -- servicing 6.150 EQB TEHERAN. IRAN; 0930 to 1400; 2230 Beam Aerial -Power Supplies. etc. to 2315 6.150 CS2WD LISBON. PORTUGAL: 1330 to 1800 6.200 FK8AA NOUMEA, NEW CALEDONIA; 0200 No. 36. -RADIO TEST INSTRUMENTS. to 0400; 0430 to 0500 A MUST for every radio man. This latest luta -11/11 ulnlr 6.360 HRPI SAN PEDRO BULA. HONDURAS: book on building test oqulpmenL places em- 1100 to 1415: 1800 to 2330 phasis on practical construction of Signal 6.370 CSX LISBON, PORTUGAL: 1230 to 1800 Tracers- Capacity Meters- Portable and 50 nut 6.770 SINGAPORE. MALAYA; 0330 to 1200 Bench Multi- checker -Signal Generators--- ISSAU. Tuhe Checkers-,-Electronic Voltmeters-and 7.100 B PORTUGUESE GUIANA: many others. 1345 to 1730 7.130 VQBNI HARGEISA. BRITISH SOMALI - LAND; 0800 to 1030; 1200 to 1300 Ns. 37- ELEMENTARY RADIO SERV 7.290 VUD3 DELHI. INDIA: 0800 to 1100; 1730 ICING. For the radio man who knows to 1825: 2100 to 2300 little about servicing. How to get started. 7.290 Z0Y ACCRA. GOLD COAST; 1045 to 1300 and even more Onportant, how to keep go- 7.570 EAJ43 SANTA CRUZ. CANARY ISLANDS; ing: Planning the Service Shots-Equipping 0730 to 0900; 1230 to 1700 the Shop-- Syetcn,atic Circuit Checks -Sig- 7.850 ZAA TIRANA. ALBANIA; 1300 to 1630 nal Tracing Methods- Servicing the Midget . 7.950 ALICANTE. SPAIN; 0700 to 1000; -Soldering- Servicing Volume Controls- 1400 to 1800 How to Sen ice Speakers. 8.030 FXE B EIRUT, LEBANON; 0000 to 0115; 0515 to 0800: 1030 to 1800 9.080 CNR3 RABAT. MOROCCO; 0145 to 0300: No. 38-HOW TO BUILD RADIO RE- 1315 to 1900 CEIVERS. This book contains a sufficient 9.370 EAG MADRID. SPAIN: 1330 to 1600; 1830 variety si sets to appeal to even radio fan. to 2200 Includes: Short -Wave.Bro 9.460 TAP ANKARA, TURKEY; 1000 to 1615; t' Operated. (a d ast 4t n dard Sun, Mon' Thun. 1530 to 1545 Itereners. Complete coil-winding data. 9.500 01X2 LAHTI. FINLAND; 0100 to 0130; 0610 to 0740: 1000 to 1600 A.. 9.520 ZRG JOHANNESBURG. SOUTH AFRICA) 091111 to 1045 9.520 02F COPENHAGEN. DENMARK; 111; to 1545 9.520 SEAL COLOMBO. CEYLON: 1933 to 122011 JADIO -CRAFT LIBRARY SERIES 9.700 FORT DE FRANCE. MARTINIQUE; 1730 to 1845: and later 11.040 CSW6 LISBON. PORTUGAL: 1230 to 1530; 1800 1800 RADCRAFT PUBLICATIONS. Dept. 88 See Your Radio Dealer to 11.090 PONTA DEL GARA. AZORES; 1500 25 Wut Broadway, New York 7. N. Y. If He Can't Supply You. Use Coupon to 1600 11.730 SINGAPORE. MALAYA: 0325 to 1200 10 Send me the volumes (50e each. postpaid) checked. My radio dealer ls All 11.830 CONSTANTINE. ALGERIA; 0130 to . unable to supply. Bakt $5.00 0315; 0630 to 0915: 1315 to 1400; 1430 to 1700 I enclose $ 02 3O 15.270 SINGAPORE. MALAYA; 0330 to 1200 15.290 VUDII DELHI, INDIA: 2215 to 0030; 0125 Your Name 30 35 to 0150: 0200 to 0400; 0500 to 0700 (Print Clearly) 15.300 SINGAPORE. MALAYA; 0330 to 1200 Address 03 38 17.770 SEAC COLOMBO, CEYLON; 2300 to 0730; Dealer's Name 32 37 1100 to 1200 18.130 PMC BATAVIA.. NETHERLAND INDIES: Address O 3 3O 1100 to 1130 RADIO -CRAFT for Radio IguISiimess 79 FM PRODUCTION BOOM RADIOMEN! ELECTRICIANS! FM will become a $750 million business by the end of this year, predicted Get this Valuable Book "Bill" Bailey, recently. Bailey, executive director of the FM Association, a group REE Explain for Merely Examining composed of FM station lidensees, said Latest that over $48 million has already been Seta Coynes NEW Pay-Raising invested by FM stations, with an addi- a Your tube worries are over when you tional $54 million investment to be made buy from SENCO. With each and every by the 543 construction and con- purchase, you are assured of beat permit Here's a PRACTICAL set of radio books just off the the - ditional grant holders. Press! Owes you "know Mw" on everything In GUARANTEED - merchandise at phe- Radio today. Buie principle, to newest In Televi- nomenally low prices. Our policy of More than two million receivers have sion and F.M. -how construct. Install. service. Quantity buying, low overhead, cash since end, said Latest trouble -darting methods. 1000 Illustrations, sales, direct merchandising -eliminating been produced the war's over 1500 pages. Ideal for reference or home train- all unnecessary expenses add to ing. To prove how valuable these greet books van be that Bailey, and an estimated five to eight to you, Coyne will give you FREE Spy of our your price -enables us to pase these large million will be turned out during 1948. new, helpful "150 New Radio Diagrams Eplelned" savings along to you. Compare our tube for looking over the 5 Vol. Set. OFFER LIMITED list now and prove to yourself that only Production during the first quarter of -ACT NOWT We will send you 5 vol. set AP- SENCO gives you these values! PLIED PRACTICAL RADIO for 7 days FREE ex- this year was roughly a half million. amination together with Radio Diagrams. Lmk set Retail value of RMA- manufactured over for 7 days. If you like It send 815 cash. or $3 THOUSANDS OF TUBES! after 7 days and 89 monthly until $16.75 L paid. - sets in 1947 was over $311 million for If you don't want the set. ALL BRAND NEW! return It and you owe - the 1,176,000 units made. $500 million NOTHING. Either way you keep Diagrams Book Free. Individually Cartoned! is the figure predicted for this year. SEND NO MONEY! Cou- pon mini to see R.M.A. GUARANTEE According to the FCC, commercial books free and FM stations now on the air total 482, get your gift book F R E E for doing itl send IMMEDIATE DELIVER Y! with 543 construction permits and 47 coo= NOWI Educational Book Publishing Division 1 Lots of Lots of applications pending. w 10 COYNE ELECTRICAL & RADIO Type Each I Each Type SCHOOL. Dept. C8 -TI Each Each 024 69e 59. 6V6GT/G 45e 500 South Pauline St.. Chicago 12. Illinois I 39e IA3 45 39 6X567 49 39 OK. Rend me, Coyne', new 5 volume let. /G postpaid, IA5GT/G 59 49 7A4 53 43 "APPLIED PRACTICAL RADIO" for 7 Days FREE IA7GT/G 45 FM HOMES DOUBLE IN YEAR per send. absolutely FREE. 55 7A7 59 49 TRIA1, yart rifer. Abo IH5GT/0 59 49 786 44 150 New RadioR Diagrams Explained" as a gift. 35 FM receiver ownership is well over I L4 49 45 7F7 49 44 NAME AGE I I LA4 49 39 7N7 40 44 156,000 in the metropolitan New York ILH4 69 59 7X7 ADDRESS I LN5 69 59 (XXFM) 44 35 area, according to a survey made re- 'TOWN ZONE STATE INSGT/G 59 49 44 35 1115 55 49 711446 29 25 cently by The Pulse, Inc., radio research 185 59 55 12Á80T 35 28 ITS 69 55 2ÁT 50 45 organization. This is more than double ITSGT 59 49 12Á7T6 69 59 the number in the area as compared SPERRY TUBES IU5 36 30 ÁE66 5 0 45 IV 45 39 12I2 50 45 with January, 1947. The area covered AMPLIFIER 6A8 64 6C5 59 24i3 45 35 12607 39 34 by the survey has approximately 2'$ Brand new Servo 1215GT 25 19 6D6 59 2X2/875 35 29 121707 45 39 million radio homes. The figures show amplifier contain- 34 1257G1 45 39 that the percentage of homes where 6F6 69 AQ5GT 55 9 ing two beam pow- 6H6 54 55 12Q7GT 4355 3295 there are FM sets is about 5.6. 51.14 Ó 4450 12SA7GT /0 40 32 er output tubes 6K7 .59 T/0 34 12SC7/1634 19 39 607 69 5X40 39 128F7 35 32 (1632) similar to 5Y3G 42 37 12807 43 37 6SA7 59 5Y3GT/G 40 33 12s17GT 55 49 TAX HITS BRITISH RADIO 25L6, two twin 5Y4G 39 32 128K7GT /G 45 35 65H7 54 5Z3 49 39 128C7 49 43 triodes (1633 and 6SN7 69 5Z4 59 49 123Q 40 32 British radio sales have experienced 6A7 50 45 12387 35 32 1634) similar to 6V6 54 64867 49 39 14A7 65 55 a serious slump of late, blamed by the 6A87/1853 53 1486 7C5 69 46 59 49 makers on the high government pur- 65C7 $3.95 so 24A 49 39 7F7 69 6AC7/1852 6s 60 2546 69 59 64G7/64 K7 89 79 L6GT chase tax. The levy has increased to 69 /0 Turbo Amplifiers 7Y4 6AK5 74 69 49 39 662/3% in the last two national bud- I2A6 49 6B7 55 49 25260T/ß 45 39 Aircraft 6BG6 79 69 26 45 32 gets, from its former figure of 33 1/3%. Amp. I2J5 54 6B16 69 59 27 6C4 29 25 32L7GT As a result, over 10,000 of the 55,000 Ideal for parts 12SK7 59 6C5GT 40 35 35/51 42 32 radio factory workers in England have 24a 49 6C5MG 89 79 35L6GT/G 45 39 6C6 45 32 35W4 4.340 lost their jobs, and two manufacturers 25Z5 54 6080 37 29 35Y4 43 40 $1.95 6D6 49 44 35 27 54 have gone out of business. 6F5 45 35Z5GT/0 43 39 The Radio Industry Council, 80 49 6F6GT 45 39 36 35 29 repre- MIN. DEPOSIT OR ORDER $3.00 6H6GT//G 45 39 39/44 35 29 senting British radio makers, has ap- 203/4 ON LARGER ORDERS 615G7/8 45 39 41 49 45 616 59 49 42 47 41 pealed to Sir Stafford Cripps, Chan- KAY ELECTRONICS CO. 6J7GT 42 38 43 54 47 P.O. Sox 25 HOLLIS 7. N. V. 6K6GT/G 45 49 39 cellor of the Exchequer, to reduce the 6K7G 50 419 45Z58T 59 49 6K7GT/Q 49 39 47 49 39 tax to 33 1/3% and to do away with it 6K8G 55 49 50A5 60 55 for receivers and 6L6G 79 69 50135 42 32 television tubes. 6N7 84 73 501661 50 45 6P50T 59 49 50Y681 50 45 PEN -OSCIL -LITE 6Q7GT 47 39 56 55 45 6bnely convenlent set oscillator for all radio 6R7 55 45 57 45 39 HIGHER POWER FOR eareelelnE; Ilgnm ent Small Self 6R7GT 59 49 45 39 WRUL Range from audio 126 v. e0ß tma sellera e OOutputffrpnn ro 49 39 7ÌA 39 29 International shortwave radio WRUL et Coed by Signal Corp. Writs for 6347GT/G 44 37 75 50 39 LLow Inn. 65B7 - 55 45 76 49 45 (Bostop, Mass.) has applied to the FCC 6sD7GT 39 34 77 35 27 GENERAL TEST EQUIPMENT 6SF5 49 39 78 49 39 for permission to increase its power to SS Argyle Ave. Buffalo 9, N. Y. 6SG7 44 39 40 38 6SH7GT 40 32 83V 79 69 250,000 watts. This would make it the 6S17GT 44 37 84/624 49 39 6SK7GT/G 49 39 85 49 45 most powerful broadcaster in the West- 6S L7G T 49 47 99V 35 25 ern Hemisphere. 6SN7GT 49 47 6S076T/G 44 37 99X 35 25 $3.00 FOR CARTOON IDEAS 6SD7 49 39 117Z6GT/G 89 76 SUS 49 39 1825 99 89 RADIO -CRAFT sevoral radio cartoons 61.17111 1231 prints ) 35 25 39 29 GE STARTS TV RESEARCH even, month. Readers are invited to amtrihute 6VSG 59 49 1644 39 29 humorous radio Ideas which can be used In car- MINIMUM ORDER $1.00 A new television division has a been toon form. It is not necessary that you draw WHEN ORDERING-Send 25% deposit set up in the General Electric research sketch, unless you wish. for all C.O.D. Shipments. Include suffi- laboratory, Dr. C. G. Suits, GE vice - IDEAS NOT WANTED cient postage- excess will be refunded. ho electrical or radio definitions wanted. Some Orders without postage will be shipped president and director of research, express collect. All prices F.O.R. New 01 these were published In the past, but the York announced last month. He explained subject is about exhausted. that in view of the company's large ac- All checks are payable on publication. tivity in television, it was appropriate Address RADIO CARTOONS. RADIO -CRAFT that it be in a position to make basic 25 West Broadway, New York 7, N. Y. l' contributions to the art. 73 West Broadway New York 7, N.Y. Telephone BEekman 3 -6498 AUGUST, 1948' 80 Miscellany CHARD -TO -GET PARTS.S Rabio Tfjirtp-jfiUe Dears Ago '%M/!!u/!%Caf%0'it" POWERFUL ALL- PURPOSE INDUCTION 31n éitntsbarlt pubhratlmts BEAM ROTATING MECHANISM MOTOR ID _L FOR EXPERIMENTERS -101 USES HUGO GERNSBACK Sturdily constructed widerd, self-startingtrsI:,t Founder pole A.C. Induction t erful enough for a of lI Some of these are: nAuntomatic T.. - Modern Electrics 190$ ev Current Inter Electric is Fans. Electri Chin,... Electrical Experimenter 1913 Window Duplays. Photocell Conti of Devices. Vibrators. Small Radio News 1919 . i kOdl{.m to - Electric Grinders, Duffers and Polishers. Science & Invention 1920 s MiniatuSirens.umps. Mechanical ' immmling facility. \.,,. e and other at uMon. Radio - Craft 1929 lions. -Wave g.rII,titiI,eil. corJ et; with 110 vac t0 on u about ly watts of Short Craft 1930 12 rat step -doom xitur $16.50 Dower a armed if 3.1704, Wireless Association N America 1908 geared down. this sudhentry unit will constantly o DYNAMOTORS 1R -inch turntable loadeddete with 200 lbs. dead w gill- THATS POWER! Some of the larger libraries in the country still hay Input Output Radio Dimension. deep: copies of ELECTRICAL EXPERIMENTER on file fo Type Volts Amps Volts Amps Set Prise hacon8convenient nt motioningi rits1 studs: °it is I ii Interested readers. BD 77KM 14 40 1000 .350 BC 191 $9.9514 by 3/ß and runs In self-aligning 11 $5l.9 retaining bearings. 10.20 vol.. 50 -00 PE 73 Shp. 9 28 19 1000 .350 BC 375 $4.95N ITEM NO. 147 r FROM THE ELECTRICAL EXPERIMENTER, DM 21 ('9ea5 14 3.3 235 .000 BC 312 $2.791.N YOUR PRICE s$2 77 1914 DM 21CX 28 l. 235 .090 BC 312 22.49N JULY, DM 25 12 2.3 2t0 .0.50 BC 367 $2.4912 DM 28R 28 1.25 275 .670 BC 348 $.3.05N ULTRA MAGNET The Speaking Are Light by H. Winfield DM 33 08 7 540 .110 RC 456 $3.95N 42 LIFTS MORE THAN 20 TIMES Secor DM 14 46 515 .110 SCR 506 $3.95LN ITS OWN WEIGHT 11130 .050 . LITTLE GIANT MAGNET Radio Transmission and Weather by PE 55 12 25 500 .400 SCE 245 $4.95LN Lifts 5 lbs. easily. Weighs 4 oz. A. A. Taylor Made of ALNICO high- magnetic PE 86 N 28 1.25 no .060 11C 36 $1.95N Complete with keener. Wold Progress in Radiotelegraphy PE 101 C 13/28 12.6/ 401 .135 SCtt 515 $3.49N Tmoststeel. powerful meant ever made. 6.3 800 .020 b. experimenter and hobbyist will A Vacation Radio by o M' 1.12 and hundreds of excellent uses for Pocket Set Harry BD AR this high quality permanent meanet. 93 28 3.25 375 .150 $4.95N Measures 13/4- a l ta. Ship. Wt. V. Johnson 23350 27 1.75 285 .075 A1'N -1 $3.50N as Ilia. 35X0458 28 12 236 .000 $2.25N ITEM NO. 15E $1.50 A Novel Detector Switch by Albert St. ZA .0315 12/29 4/2 500 .050 $3.9314 YOUR PRICE ZA .0516 12/24 8/4 275 .111) $4.25N Cyr B -19 peek 12 9.9 275 .110 )lark II $6.95N GENUINE MICROPHONE TRANSMITTERS 500 .050 A Loop Aerial Switching Scheme by N -New. LN-Like New. le,inn0 trans. manortern taken from large Thomas Benson wicphnne supply cot...- TRANSMITTER TUNING UNITS papy r k. ork Experimental Radio Station by C. F. son IVs: From ls, 375: TU -9 (7.7 -10 mc) ; TU 10 (10 -12.5 mc) perfectly on dry TU 22 (350 -650 kc): TU 26 (200 -500 Ise) $2.25 Eaeh Hancock BC tames e ll esystems. lnter- For 610: TU 48 (2.5 -3 mc): TU 52 (6.35-8 me): , Poulsen Receiving Sets TU 53 18 -12 mc) $1.75 Each short-linersltelephone elr. BC fcults. house -in -house 223 Ax: TU 17 (2 -3 mc) : TU 18 arm.to -farm 'phone lines. Microphone Transmitters (3 -4.5 mc) $1.95 Each also to lk throuRli own men, or our INSTRUCTION MANUALS a hone lck tali. Use- FROM THE AUGUST 1914 ISSUE BC 312. BC 342 $1.25 ful placements n bat- SCR 281 $1.25 MARK tery- operated rumí tala. II $75 hone linea. ZA EQP t $75 SCR 508 $1.00 An Efficient Wavemeter by Thomas W. TRANSMITTERS. MADE BY KELLOGG. WESTERN Benson BC 221 FREQ. METER ASSEMBLY ELECTRIC AND STROMBERG- CARLSON. excellent to appearance . a operation. A remarkable and Shelenium Ideal foundation unit for an extremely stable VFO one seldom offered In Mesa times. nip W.tine I M. Cells and How to Use Them or Freq. meter. Consists of temperature compen- ITEM No. 160 Amplifier sated coils and capacitors. Tunes with 220 mmf. YOUR PRICE $1.95 for Wireless Signals condenser. Low range: 125.250 kc: high range: Wireless Receivers (A Symposium) 4500 lic. New. with 220 mmf $7.95 WATTHOUR METER ca and BC 221 schematic Completely overhauled and A Variable Condenser by Irving Byrnes pacitor ready for immediate service. PASS olt Rn for regregular A Peroxide of Lead Detector by James BAND FILTER. ß7O473. Sharp hand pus 00 wirre AM. peaked at 975 CPS (tunable). High -to -high intetlance. circuit. Simple to inetall- L. Green Can he plugged into Morne output of receiver. Cute wires from the une d ut g1151 . wires load. and QSB, Nev, with circuit truced IheIm A High Frequency Sending Buzzer by diagram $2.25 metal tlo CATHODE Ide .5" tie. Weeti Q Thomas W. Benson RAY TUBES house. O. E. Ft. Wee., 3BPI ....$1.25 3FP7 ...81.20 5FP7 ...81.75 SanaaOm other e ilable Automatic Radio Tuning Device 3DPI ... $2.251 3GP1 ...$3.961 51P2 _44.00 make SAD. Mt. 14 lbs. 3EPI ...$2.95 SBPI A New Low Altitude Antenna ...81.20 I2GP7 .$10.95 ITEM NO. 15 YOUR PRI CE $6.50 NEWEST SPEAKER DEMONSTRATOR MAG- AMAZING BLACK LIGHT!! Powerful 250-Watt Ultra -Viole) Source 5130 NETRON INGLASS ENV L- The best end most practical light SPEAKERS OPE. NEW, COMPLETE WITH DATA gnele rae Itimea ftl ad enter- V,`_RIflED tainment use. Makes all nres- $sw r SHEET ;39.50. !nt aubetances brilliantly lumi- nescent. No transformersra N any kind needed. Fite any standard A complete line of microwave egpt. lam socket. Brings ,ut in stock: 10cm, 3cm. 1.25cm. Send tiful opalescent Ines In s s type. KK Swell for for microwave flyer. Parties. pity obtain nique Il kiting effect.. ANTENNA AN /122 -A. Dipole, 12' 16 ideal for ule niy. SID. Wt. g lbs. I. meter br:Un. One .site of dipole for ITEM NO. 87 ad/listable YOUR PRICE $2.50 turning. Get four of them for only $20.00. or S,.,.. each. ANTENNA AN /I04 -A. Tho best deal for two m' WESTERN ELECTRIC BREAST MIKE 21" L. of stream:Mu construction. with 83111 cur This Is a fine lightweight air. tor. a l l set to go. $ 75 ea. or 2 for Sl. emit carbon microphone. IL weighs only 1 lb. ANTENNA AN /128 -A. A complete two -meter b.. Mike with breastplate L igitiaily designed to work with IF'F set RC II. mminar ands has 2-way swivel-I this Unit is extremely compact, rugged. cita . . Mg n llustmeilt no that ca be I Consists of two vertical radlators working aga i. adjusted to n desired position. There are 2 straps; one swi:tro I reflector 3' x 4'. You miff. beat this unit goes aroundand neck. the othct high gain and directivity. NEW $40.00 around n.Straps he Snappednapped on and off nuicklya by an VARIABLE AIR CAPACITORS Larrangement. 2 sect. 363mmf /soc, with cable drive wheel attache). This excellent mike he adapted f, r home tirondew.ting $.O5 systems. lo. 7 sec. 1 -75 mmf, 4 -100 2 -200 private communication mmf. mot. Vernier t di..n euntI tmbreastplate. It Can I.. angle drive, 60:1. Size: 11" a 3" o 3 ". l7aopletely used as desk mike. shielded $3.25 Come. mplele with 6.f....1 AIt1' No. 6558 variable receiving capacitor. 62uunf/ and bard rubber plug. Fini;l...l ,ii.,rdized section. 3 sections. .03" spacing, 8 rotors. Worm drive pnn!late, tinn- rustablc. Shipping weight. 2 lbs. ratio 33:1 $1.75 ITEM 152 $1.49 ARC No. 4990 variable amtg. capacitor. 22.4 -145 YOUR PRICE tutor. .05. spacing, Il rotors. Each $1.00 ARC 51132 Var. Xmtg. capacitor. 29.2 -117 mmf .O6" sat :t:.: Irt ., r.. n.rrin 'trite; 96:1 $1.00 HUDSON SPECIALTIES CO. 40 West Broadway. Dept. RC -8.48. New York 7, N. Y. ---, CROSS POINTER INDICATOR % "l r have circled below me number. of the Items Fm ordering. My full remittance of S In- t rots in lude shipping charges) ta enclosed (NO C.O.D. I hr oft o ORDERS UNLESS ACCOMPANIED WITH A DEPOSIT.) Í OR deposit of S Is enclosed 120Me Ìred). ship order C.O.D. for balance. NO C.O.D. A $2.50 ORDER FOR LESS THAN $5.00. SE SURE TO IN. S1.PAUt CLUDE SHIPPING CHARGES. Cire le Item No. an x160 All merchandise guaranteed. Mail orders prompt- 147 159 87 152 28 ly filled. All prices. F.O.B. New York City. Send Money Order or Cheek. Shipping charges sent C.O.D. Rated concerns send P.O. Name

COMMUNICATIONS EQUIPMENT CO. Addraa Please Print Clearly Output of the receiver at top of this speaker 131 -C Liberty St.. New York City 7, N. Y. demonstrating board can be channelled to any Digby 9 -4124 City "Slate of the speakers. The board is made by Wright. RADIO -CRAFT for Miscellany I 81 TV RECEIVER HAS MIRROR We're GILDING Elr PLEASE TEAR OUT THIS ADV. AS REMINDER the LILY!

This Sightmaster receiver looks like a period girt' furniture piece with a mirror when it is not 'n use. When the false drawer front is folded down, the controls are revealed. The pic- NEW, IMPROVED ture on the face of the cathode -ray tube is een through the mirror which is transparent and acts as a filter to reduce eye fatigue. Model 7 -B -1, RADIO FACTS NEW TUBE TYPES 1001 AND FIGURES Two new miniature electronic tubes, engineered AUDELS RADIOMANS GUIDE -914 Pages, 633 Illus. Potions, Photos, Wiring Diagrams, 08 Bip Chapters, types 6AV6 and 12AV6, have been made covering Radio Theory, Construction, Servicing, Include available by General Electric. Providing Mg Important Data on Developments In Television, to meet YOUR needs! Electronics and Frequency Modulation, Review. an amplification factor of 100, they are Questions and Answers, Calculations & Testing. designed for use as combined diode de- Highly Endorsed -Indispensable for Ready Reference tectors, a.v.c. Carefully engineered, and manu- and Home Study, tubes, and first audio am- S4 COMPLETE PAY ONLY Si A MONTH plifiers. factured of the finest materials, Btepup your own skin with the facts and figures of your trade. Audels Mechanics Guides contain Prac- The tubes are intended to supersede ESPEY Model 7 -B -1 is spe- tical Inside Trade Information In a handy form. the Fully Illustrated and Easy to Understand. Highly the 6AT6 and 12AT6 and may be sub- Endorsed. Check the book you want for 7 days' stituted directly for them in receivers. cifically designed to meet the Free Examination. Both types are duplex -diode triodes, most exacting requirements for Bend No Money. Nothing to pay postman. . CUT HERE - --'#11 having triode sections capable of pro- o replacement chassis, and will --- viding large undistorted output voltages from small lend itself to any type of installa- MAIL ORDER a input signal. Heater AUDEL, Publishers,49 W.23 St.. N hum Ts

voltage , tion. This model is drift- compen- of the 6AV6 is 6.3 volts, while PI.... Send me postpaid for FREE EXAMINATION books that of the 12AV6 is 12.6 volts. marked lci below. If I decido to ken them I naree to sated, AM FM, with 10 tubes mail Sl In 7 Day. on ch book ordered end further mall Si monthly on each book until I have paid price plus rectifier. Supplied complete, -otherwise, I will return them. NEW PARTS GUIDE OUT RADIOMANS GUIDE. 914 Pages . , , $4 ready to operate. ELECTRICIANS EXAMINATIONS, 250 Pages . l A new parts replacement manual, the WIRING DIAGRAMS, 210 Pages ...... 1 Howard W. Sams Radio Industry Red ELECTRIC MOTOR GUIDE 1000 PaePagest I 4 to DEPT. C -8 TODAY ELECTRICAL DICTIONARY]Terms 9000 2 Book, will permit the repair technician Send for ELECTRICAL POWER CALCULATIONS, 425 Pgs. 2 to find instantly not only the manufac- FREE LITERATURE HANDY BOOK OF ELECTRICITY. 1440 Pages 4 ELECTRONIC DEVICES 216 Pages 2 turer's part number for a component, ELECTRIC LIBRARY 12 vol.. 7000 Pgs:, $l.5Ovol. but also a number of alternates. Unlike OIL BURNER GUIDE, 384 Pages 1 REFRIGERATION & Air Conditioning 1280 Pgs 4 earlier encyclopedias which showed only POWER PLANT ENGINEERS Guide, 1500 Pages 4 one correct replacement, this guide gives PUMPS. Hydraulics & Air Compressors, 1658 Pp 4 WELDERS GUIDE, 400 Pages 1 the original part number plus three BLUE PRINT READING, 416 Pages "ESTABLISHED -102, alternates for transformers, four for SHEET METAL WORKERS Handy Book. 388Pgs1 1 T SHEET METAL PATTERN LAYOUTS. 1100 Pgs: 4 capacitors, two Pages . I for controls and speak- need AIRCRAFT WORKER. 240 ers, and one for i.f. coils, vibrators, Do you MATHEMATICS & CALCULATIONS. 700 Pest. 2 bat- MACHINISTS Handy Book. 1600 Pages 4 teries and phono pickup cartridges. BINDING POSTS? MECHANICAL Dictionary, 68 Pages 4 AUTOMOBILE GUIDE, 1700 Pages 4 The XL PUSH POST with Its Spring 400 , Action assuras Constant Contact and DIESEL ENGINE MANUAL, Pages Radar will be installed on all 21 MARINE ENGINEERS Handy Book, 1280 ages 4 Mainufacturedtt Ìn' All Aluminum Type M GUIDE 160 Pages . tankers of the Atlantic Refining Co. at each. MECHANICAL DRAWING I Aluminum Bakelite Top Type SI MECHANICAL DRAWING & DESIGN, 480 Pgs. 2 The operation is expected to take a year 1 tae each. MILLWRIGHTS & Mechanics Guide. 1200 Pgs; 4 Typas CP or NP. ALL BRASS -STAIN. CARPENTERS & Builders Guides (4 vols.). . 6 and to cost $304,000. STEELTE.EL SPRI` O & PIN. PROVEN by 240 1nì. SALT SPRAY TEST as NON- PLUMBERS & Steamñaters Guides (4 vols.) . 6 CORROSIVE at Zee each. MASONS & Builders Guides (4 vols.) . 6 A new optical radar unit is used in ManufacturenD,ieou Ñ lens Liberal MASTER PAINTER & DECORATOR, 320 Pgs: 2 surveying. Pulses of light GARDENERS & GROWERS GUIDES (4 vale.) 6 are reflected X. L. RADIO LABORATORIES ENGINEERS and Mechanics Guidas from the point whose position is be Nos. I, 2, 3. 4, 5, 6, 7 and 8 complete , 12 to 420 West Chine(' . determined. Distance Ave., Chicago 10, III. Answers on Practical ENGINEERING I is measured by the 8 ENGINEERS & FIREMANS EXAMINATIONS 1 time taken for the light to travel. Manse

Interference to aviation radio on the It's nearly reed .the new. !Aimee. bet ter - than -ever WeWelter A. I:e Catalog e Ader,. 6 -mc band which was noted from Oregon Radio and Electronim for 19491 to Puerto Rico and far east into For "priority" delivery, reserve your free OCOMMIMS the Coalof thi`hely ful, f,nnoti'a towing Atlantic been e now.:Simply write: 1949 U.talog' A.C.F. has traced to an electronic Y I ard. Sign your name and áerpt('Y.e W heater in a Johnstown (Penna.) chair adores.. M.ii tw WALTER ASHE RADIO CO. manufacturing plant. 3225 PINE ST. ST. LOUIS 1. MO. AUGUST. 1948 1.IIIIIIIIIIIIirt1111ci11 WELL -BALANCED MAGAZINE REVOLUTIONARY Dear Editor: WANTED I don't think you can ever please everybody with the articles you publish. Your NEW AMPLIFIER But Here is my opinion: Name I agree on our mailing list to receive our NOW AVAILABLE! don't with those readers who Its cleverly designed to defy obsolescence, want RADIO-CRAFT to stick to simple ed- and it's sensational in performance! New cir ucational material. You can buy any, FREE MONTHLY BULLETIN cuits . new materials new processes, number of listing hundreds are combined in this amazing instrument, to books on elementary radio of outstanding produce the MOST SATISFYING sound am. and electronics. I'm completely new in radio bargains. plifier the world has ever known. It you are one of those discriminating persons for whom the field, so I want to know how the To get your name, your address, RSE offers anything less than the best is a disappoint simple devices work. But I also to ment - the ACA -100 was designed for YOU! want know how the more elaborate circuits MIDGET I.F. TRANSFORMERS are made. Print both simple and com- Back again -by popular demand ! plex articles, RSE scores again with a new and better and give newcomers like I, F.! 400 -500 KC range-1W square E me a chance to progress. 3' high --ceramic based mica trimmen- True, I haven't high gain iron cores -pep up old receivers, built the 17 -tube ideal for new construction -and now avail- FM receiver (RADIO- Camr, November, able in either input or output types-for 1947), have peak performance! Individually boxed AMfR but I made a note of it the co in colorful RSE corton. List price 52.10. ,N r u F Its When I get around to fooling with FM, LR1- input; LR2 -output; I will look it over and maybe use all Specify Type. 40 Matched Egg or part of it. Crate let Each Pair Doren of 100 I finished an 18 -tube, 4 -band AM set 36c 69c $3.95 $29.00 ignIPIER -CORP Qp ,ANERIC* about four months ago, and you can bet I got circuits and ideas from RADIO - 398 -10 Broadway New York 13, N. Y. l VOLUME CRAFr, from both the simple and the advanced articles. CONTROLS 1948 MODEL In short, a newcomer always finds Our own private brand-mode by plenty in RADIO-CRAFT that he can un- a nationally known manufacturer. The MUTUAL some kind that net for 51.09. Noise -free carbon con- CONDUCTANCE derstand and plenty of material that struction, standard shaft and bushing. Individually TUBE TESTER RSE will allow him to increase his knowledge. boxed inoorcolorfulcartoncarrying the equality sea I with new 9 pin socket to handledr of approval. e Complete with switch, full range of sixes. all future tube developments ...9a95 I think your magazine is well -balanced 10 M ohms 100 M ohms No possibility of good for the majority of the readers. 15 M ohms 250 M ohms each tubes reading "Bad" SUTTON, 25 M ohms 500 M ohms 59E or bad tubes reading C. O. 50 M ohms 1 Meg ohms per 10 "Good" as on dy- Alameda, Calif. 2 Meg ohms asstd. namic conductance 500 M Knurled Shoff J 50 testers or other ord- 500 M ohms less switch, 39c each, 100 for $35.00 inary emission testers. "Attractive panel EUROPEAN EQUIPMENT and case equal to any PHONO CABINET on the market in ap- Dear Editor: Used in the Zenith "Cobra pearance . Large Orchids to Maj. Hallows! It was a Tone Arm" record demon- 4y," meter.. . Cali - great satisfaction to me to read his re- strators. Solidly built of Vs' brated micromho scale plywood covered with as well as a Bad -Good port that there had been some improve- scale . panel . maroon luggage cloth. 14' s Front fuse.. Individual ment in European receiver design. Dur- 16' square, IV high. Flocked sockets for all tube base typeses -voltages from grill for 8' speaker. Rubber 75 volts to 117 volts and complete switching ing my three war years in the Middle mounting feet, ventilated flexibility allow all present and future tubes East, I worked on practically every rear cover. Brand new in to be tested regardless of location of elements factory cartons. on tube base. . . Indicates gas content and well -known European brand, and I do Every record detects shorts or opens on each individual sec- mean worked. A serviceman must be a and radio shop $299 tion of all loctal, octal and miniature tubes con use these at including cold cathode. magic eye and voltage mechanical engineer and a jigsaw -puz- regulator tubes as well as all ballast resistors. zle Name of the nationally known manufacturer expert to cope with the array of PHONO AMPLIFIER withheld because of special price offer. cams, levers, friction clutches, and push- Model "C "-Sloping front counter case $49.95 buttons on some of these sets. A high quality AC -DC phono Model "P "- Handsome hand -rubbed amplifier featuring the latest portable case 54.95 Please give us more articles by Maj. circuits and tubes. The chassis Built -in -roll chart with either of above Hallows on foreign receivers. Maybe our is only 2' x 23/4' x 5 1/2' and $5.00 extra. includes volume and tone con- own manufacturers can get some ideas. trols, built -in output transformer, BUFFALO RADIO SUPPLY We're far from perfect. and 5' rubber line cord. Com- 219 -221 GENESEE STREET BUFFALO 3. N. Y. plete with 35W4 and 5085 DEPT. BC EUGENE K. GOODWIN, tubes. Operates on 110 to 120 Los Angeles, Calif. volts AC or DC. Supply is limited -first $419 come first served TEST -AID IGNITION RUINS FM? FIRST -AID FOR RADIO -TELE SETS Dear Editor: OZ4'S ONLY I certainly agree that FM is superior at 73% OFF! $159s to AM in some cases but it is not free Until sold out -RSE offers from noise caused by automobile ignition 15000 new guaranteed OZ4 systems. Automobile noise in some loca- tubes. You know ho made tions ruins FM reception. 111 them-You can't COMPLETE go wrong at 59c Is anyone doing anything about this? WRITE FOR I wish RADIO-Caarr would print an ar- CATALOG ticle on how to solve the problem. ORDER INSTRUCTIONS SHEET Louis ZARATTARO, Minimum order -52.00. 25% de- QUICKLY LOCATES FAULTY CONDENSERS AND RESTS. posit with order required for all TORS FOR FAST SERVICING Pittsfield, Mass. C.O.D. shipments. Be sure to include SUBSTITUTES S OF CAP. OR (Are many listeners plagued with this DEMAND THIS sufficient postage- excess will be RES. WITH SET IN OPERATION SOmamf to egmfd ASO- refunded. Orders received without 600 WVDC -27 ohms to 5 meg. problem? Are some locations actually SEAL OF QUALITY postage will be shipped CHECKS CONDENSER LEAKAGE ON DIRECT CURRENT impossible for FM reception or were express collect. All prig SUPPLIED FROM OWN PWR SUP. Mr. Zarattaro's experiences with poor F.O.B. Detroit. OUTPUT INDICATOR FOR ALIGNMENT -CONTINUITY CHECKS a receivers? Reports from other readers PROVIDES 100 VOLTS AT 100 MA FOR EXPERIMENTS. on this subject should be interesting, These are only a few of many uses of the TEST -AID. //thee especially if make of receiver is noted, KHVIV SUPPLY & See the at You' ¡ dealer or wrote CAA., .31arty6,y along with details about the antenna ENGINEERING CO., Inc. direct. location with relation to, automobile 125 SEEDON AVE. DETROIT 1, MICH. 256 E,98th STREET, BKLYN, N.Y. traffic. Editor) RADIO -CRAFT for Communications I 8:3

CONTROLS FOR REPAIRMEN Dear Editor: Radio - Television - Electronic Federal control of radio operators and transmitters has been of great help in Parts & Equipment Specials assuring operation for the benefit of the, 30,000 public. I do not believe, however, that TELEVISION -CATHODE RAY HIGH the government should license radio re- VOLTAGE 2000 volt D.C. Power Supply SUCCESSFUL pairmen. For an unbelievably low price, we can supply It would be more constructive to form a completely filtered television or cathode ray 2000 volt U.C. power supply. Why bother with a union of servicemen. This organiza- bulky and dangerous 60 cycle supplies or ex- RADIO SERVICE - tion would issue its own technical cer- pensive R.F. power supplies when you can purchase a complete 2000 volt D.C. unit (not tificates, based on standardized exam- a kit), ready to plug into the 110 volt A.C. TECHNICIANS READ inations of prospective entrants into the power line. The ridiculously low price has been made possible b1C a fortunate purchase of high profession. The standards might be set quality components. These units are brand up by the IRE, for example, as an out- new, completely tested and guaranteed. standing independent engineering or- Price $7.95 ganization. Several organizations might 4000-6000 VOLT TELEVISION SUPPLY Similar to the unit above, but has a much be set up, if territorial or other reasons higher D.C. output voltage suitable for use should make it desirable, all using the with the new 7" and 10" television tubes. common set of standards. This would PRICE $12.50 MALLORY RADIO NOISE FILTERS certainly help to strengthen radio serv- Eliminates extremely noisy radio reception due to icing as a profession, rather power line disturbances caused by lights. refrigerators, than a hap- washing machines, vacuum deafen, elevators. NI hazard affair. farmers, diathermy machines. etc. Filters out man -made noises in the broadcast. short - SYLVESTER ROBINSON; Wave, and ultra -high frequency bands. Designed for all radios. appliances, and electrical Kansas Mo. equipment consuming up to 1300 watts (12 amperes) City, at 120 volts AC or DC. Housed in a metal case 1,e" x 3" an," complete with malo and female line connecters. SUB -MINIATURE TUBES PRICE ONLY $1.95 Industrial Type Radio Noise Filter -Will handle up Dear Editor: to 50 amperes. Housed in shielded case 3W a3W'x 2'/. ". We were most interested in the elec- PRICE 63.93 tronic stethoscope on page 66 of the June EASILY ASSEMBLED RADIO KITS issue of RADIO -CRAFT. 5 Tube AC-DC superhet kit furnished in a The item stated brown plastic cabinet of artistic design, cab- that a CK510AX inet size (9 "x5 "x6 ") could be substituted for the first Variable condenser tuned: with 2 double tuned CK512AX if added gain were desired. I. F.'s. Tubes used: 1 - 12SAT. I . 12SQ7, 1 - 12SK7, We would like to remind constructors 1 -3525 and 1 - 50L6 nit that a direct substitution is impossible PRICE Si i.95 St'andaarrd baes without certain changes. In the dia- 6 TUBE 3 WAY PORTABLE KIT EVERY MONTH gram the two CK512AX For operation on 110 volt AC or DC and filaments are battery RADIO MAINTENANCE today fills a breach (hat in series; since the CK510AX requires Superheterodyne circuit has existed in the radio field for a long time. Al- 2% times as much filament current as Full vision dial ready 30,000 technicians read RADIO MAINTE- high gain loop NANCE every month because it is devoted en- the CK512AX, this will have to be Cabinet of Blue Aeroplane cloth finish. tirely to the Radio Serviceman. changed. In addition, a different socket size 13x9%x7" The RADIO MAINTENANCE staff specializes in is required if sockets are used. Tubes used 1A7, 105, SQ5, 117Z6 and the preparation of articles on every phase of 2 - 1N5 Radio Maintenance in series form which may be

C. W. MARTEL, PRICE 613.75 Ea r,oirn ;ie T . beau ;3.7a filed and used for reference. The leading articles cover everything the 'radio serviceman on 6 TUBE. 2 BAND SUPERHET for RAYTHEON MFG. CO, KIT Television, FM and AM; Test Equipment; Elec- Bands severed BC 550 -1600 KC and 6 -I8 MC Power supply 105.125V AC. DC tronic Appliances; Tools; Antennas; Alignment; Newton, Mass. Full vision dial Troubleshooting; Repair; Construction; Pickups Variable condenser tuned. with two double tuned and Sound Amplification and Reproduction I. F.'s 455KC Equipment. Also, in RADIO MAINTENANCE LIKES THE NEW LOOK Walnut veneer each month there are departments on hints and PRICE $15.75 kinks, the latest news of the trade, review of Dear Editor: trade literature, radiomen's opinions, new prod- A SCIENTIFICALLY DESIGNED ucts and news from the organizations. All articles Again Germback leads the field in are presented in a step -by -step precision style, foresight and imagination. PHONO SCRATCH FILTER clearly illustrated, with schematics, accurate Your new Resonated at approximately 4500 cycles effectIvely photographs, specially prepared drawings, white format is certainly a boon reducing objectionable needle scratch without alter- to radiomen. ing the brilliancy of reproduction. on black charts, color diagrams, isometric pro- views. Digging for a particular article will no Contains a HI -Q SERIES resonated circuit. Tested jections and exploded by means of an audio oscillator and an oscilloscope longer be a chore but a pleasure. That to give 22 db. attenuation with very low signal loss. Binders in beautiful green simulated leather "continued on page Attenuation may be regulated by means of a SPECIAL are now available for your RADIO MAINTE- ..." will no longer MINIATURE gain control. NANCE magazines - see the current issue for plague busy technicians. EASY TO ATTACH details. Congratula- lust two wires to clip on. Compact. $1.65 tions! Price P I disagree wiih one point in Ar. THREE TUBE PHONO AMPLIFIER RADIO MAINTENANCE MAGAZINE RC8 An assembled unit ready for installation using tone 460 Bloomfield Avenue, Sanabria's letter published on page 82 and volume control and six feet of rubber $2 Montclair 6, N. J. cord T 95 Please send me RADIO MAINTENANCE for of the June RADIO- CRAFT. There is not (Not including Tubes) really a shortage of technicians for FM With Complete Set of Tubes $3.95 2 years, S5 D I year, $3 and TV servicing. The fact is that the PHONO OSCILLATOR Payment enclosed Bill me later Wireless phone oscillator transmits recording for f industry will not hire inexperienced crystal pick -ups or voice from carbon mike through men. radio without wires.t Can also be used as an intercomm Name by using P.M. speaker as mike. Price $2.95 Radio schools (excluding tubes) Address can only train men, With Complete Set of Tubes 53.95 not give them experience. If no one will SPECIAL! SPECIAL! City -State hire them, they will Mammoth assortment and never get experi- of radio electronic Occupation ence. It is the old parts; not less than TEN POUNDS of new vicious circle: inex- transformers, chokes, condensers, resistors. perienced men can't get a job, but if switches, coils, wire, hardware, etc. A super- Title ...... they don't buy for experimenters, service- work they can't get experi- men, and amateurs $1.25 Employed by ence. for only Satisfaction guaranteed on all merchandise. Independent Serviceman - Dealer Serviceman - It is up to the radio industry to give All prices F.O.B. New York City Service Manager -Dealer- Distributor -Jobber. these men a chance. If it does, there will WRITE FOR FREE CATALOGUE not be a shortage of technicians for long. RADIO DEALERS SUPPLY CO. PHILLIP SPAMPINATO, 135 Liberty St. New York, N. Y. New York, N. Y. AUGUST, 1948 a-1 Book Reviews I ADVANCED RADIO SERVICING. Methods and Ideas. A collection of lectures by M. N. Beitman. Supreme Publications. 854 x 1052 inches, 224 BUFRAD CAR RADIO ANTENNAS pages. Price $3.00. The series is divided into three sec- All of our car radio antennas are made of triple plated Admiralty Brass Tubing. complete with low loss shielded antenna leads and tions, dealing with the business side of high quality fittings. radio servicing, equipment used, and SIDE COWL-BR -1, 3 sections extend to 66". Your price -single radio units -$1.50; in lots of 12 -11.35 ea. circuits and troubleshooting. SKYSCRAPER-BR-2 has 4 heavy duty sections that extend 96 ". Some interesting layouts of shops ap- This super- aerial muet be seen to be fully appreciated. Your price - pear in the first section. The descrip- single units -22.45; in lots of 12 -$2.25 ea. TILT ANGLE -BR-3, may be adjusted to all body contours, 3 sections of radio equipment, however, form tions extend to 66 ". Single unit price -2L50; 12 lot price -$1.25 ea. the most interesting part of book. A VERSATILE -BR-4, single hole fender or top cowl mounting may the be adjusted to conform with all body contours, 4 sections extend to large number of modern test instru- 56 ". Single unit price -22.90; 12 lot price -22.75 ea. ments are discussed with complete sche- THE MONARCH-BR -5, single hole top cowl mounting, 3 sections extend to 56 ". Single unit price -21.90; 12 lot price -21.75 ea. matics and technical details. The typog- raphy is largely style, AFTER OUR ANTENNAS typewriter though SEEING AND COMPARING, some in YOU WILL NEVER BUT ANY OTHER MAKE! chapters are printed standard BENDIX SCR 522 -Very high Frequency Voice Transmitter -Re- type. ceiver -100 to 156 MC. This job was good enough for the Joint Command to make it standard equipment in everything that flew. even though each Bet coat the Gov't $2500.00. Crystal Controlled RADIO DATA BOOK. edited by William F. and Amplitude Modulated -HIGH TRANSMITTER OUTPUT and Boyce and Joseph J. Roche. Published by Roland 3 Microvolt Receiver Sensitivity gave good communication up to and Boyce, Inc. S Jr 7 inches, 1148 pages. Price 180 miles at high altitudes. Receiver has ten tubes and transmitter $5.06. has seven tubes, including two 832's. Furnished complete with 17 Subject matter is divided into ten sec- tubes, remote control unit, 4 crystals, and the special wide band VHF antenna that was designed for this set. These seta have been 1sRl BRl BM BR/ IRS tions: basic circuits; test equipment; removed from unused aircraft and are guaranteed to be in perfect condition. We include free tests and measurements; antennas; parts and diagrams for the conversion to "continuously variable frequency coverage" in the receiver. sound systems; sound recording; tube The SCR 522 complete with 24 volt dynamotor sells for only $37.95. The SCR 622 is also avail- data; formulas, graphs and tables; able with a brand new 12 volt dynamotor for only $42.95. symbols, codes and standards; circuit diagrams; radio dictionary; and radio BUFFALO RADIO SUPPLY books (bibliography). 219 -221 GENESEE STREET. BUFFALO 3. N. Y. DEPT. 8C Most interesting section is the basic circuits, which number nearly 150, rang- ing from crystal detectors to Klystron All- Purpose WAR SURPLUS oscillators. Possibly equally valuable is the large section of formulas, graphs AVIATION GENERATOR and tables, which contain much of the reference data every radioman must seek from time to time. Made by Eclipse Pioneer, Div. of The section on tests and measure- Bendix Aviation ments contains basic descriptions of the Type 314 Model 31 Style A methods of measuring most electronic Guaranteed BRAND NEW Perfect quantities. An interesting feature is the fairly large number of oscilloscope pat- 30 Volt 50 Ampere 1500 Watt terns. The tube data section lists impor- Length 14 ", Diameter 6" tant transmitting and receiving types. Ideal for Radio Generator. Battery Charging and many 7/8 O.D. Irr length shaft

other 1 s. ELECTRONIC TRANSFORMERS AND CIR- Packed in original crates Ct'ITS, by Reuben Lee, Advisory Engineer, West- Original Cost 5170.1'0 Each $10.95 inghouse Electric Corp. Published by John Wiley Cash or Check with order prepaid In U.S.A. 9SEACH Min. R.P.M. 2600, Max. R.P.M.4000 & Sons. 652 by 9% inches, 282 pages, cloth covers. Net weight 34 lbs. Shin set. 50 lbs. Price $4.50. 8 SO. DEARBORN The author has covered the many new NORTH SALES, C. Dept CR ST. AMERICAN IN CHICAGO 3, ILL. problems confronting the designer of electronic transformers with formulas and graphs, and where necessary has in- Get .started in Radio cluded the associated circuits. AMSCO'S AUGUST SPECIALS 10 "HOW-TO-00-1T" BOOKS The first sections deal with core mate- net a solid foundation In radio by rials and windings, dielectric strength these timely boos^, BUILD YOUR OWN Ina b eof 10e eÌt of insulating materials, impregnation, 6 -TUBE SUPERHETERODYNE RECEIVER trated, contains over 15,000 word.. You'll be amazed at the wealth of and size vs. etc. Then follow information packed Into these handy rating, AC-DC hooka. Fxrellent for reference -Ideal - 6 tube super -het. for technical Ilhrary. Your money discussions on rectifier transformers and 2 band receiver back If not Satisfied. reactors, voltage doublers, anode and ; . slug tuning. No. all filament transformers. _ - We furnish 5 BOOKS for S0c ` parts less tubes. 10 BOOKS for $1.00 The action of polyphase rectifiers and is ; Sent to You Postpaid multistage filters discussed also :, » $8295 tuned rectifier filters, amplifier trans- `- No. 1-14ow To Make Four tionary (Leading Term./ Doerle Short Wave Sets No. 6-Now To Nave Fu formers, anode characteristics and low - No. 2 -Now TO Make The With Radie Most Popular All-Wave 1 No. 7 -Now To Read Radio response, harmonic distortion, PARABOLIC REFLECTORS and 2 Tube Receiver Diagrams frequency spun aluminum 1200 No. 3- Alternating Current No. a -Radio for Beginners tr Alrak On. for $3.00 for Beginner No. g- Simple Electrical Rai pentode amplifiers, and amplifier trans- Mc. Up PAIR No. 4 -All About Aerials pert ta MICRO WAVE TUBE No. S- aeginners Radie Die- Ne. 10- Television former design. W E713A $3.95 Remit by Check or nay order -resister letter If you Later chapters deal with wave filter send Cash or stamps. S14 G.E. GLOW LAMPS. Can be $2.49 principles, modulation transformers, used for nits -lights. Box of 10 RADIO PUBLICATIONS driver transformers, iron- and air -core MASTER CONTROL FOR RADIO COM $1 PASS -ARN7. Complete with meter.. NEW 39 2M West B'way. New York (7) transformers, grid- controlled rectifiers, saturable reactors, and peaking trans- 300 OHM TWIN LEAD WIRE . . . per 100 ft. $2.75 formers. Other subjects include pulse TRANSFORMERS RADIO -CRAFT needs more photos of and video transformers, design of pulse Tapped Primary 110V- I18V- 12OV- 126V132V -138V- service shops and service benches. We transformers, saw -tooth transformers, cycle. Secondary 22.3 Volt will pay $6.00 for each 608- or 8x10 -inch 1410 Amp. Brand New $2.89 testing technique, etc. A valuable ap- glossy photo accepted. Do not "dress up" Available [LII 70 Write Ted.y pendix containing useful formulas is in- your bench, but take a bona -fide photo, on sub- AMERICAN SALES CO. preferably with men working. cluded, also a bibliography the nit W. 47th st. Chicago It III. ject and a well-arranged index.-H.W.S. RADIO -CRAFT for Rook leviews, Iii:, RADIO ENGINEERING, by Frederick Emmons Terman. Third edition. Published by McGraw -Hill Aluminum sear bas 18:8:7 that contains two power- Book Co. 6lí x 9 inches, 969 pages, plus prefaces ful electric motors and two matched gear (talus, 62 and contents. Price $7.00. gears in all varying In li:e from 1.4 to 4 Inches in The radio engineering text diameter. Tills unit is readily converted to rotate standard beam antenna or any other similar use $3.00 has been revised completely and is in TUBES -All types In stock, 60% Off on all tubos if ordered In lots of 10 or more. all respects a 1948 work. The older TRANSFORMERS -All types in stet. AUTO. TRANSFORMERS: Steps up 110e, Or steps down chapter on resonant circuits has been 220v to 110h -$1.95. expanded into two -one dealing with FIL TRANS.: 6.3v. 20 Amps. -$1.90- Universal Output Trans. S Nast- --19e; 18 Watt-- $l.29: 30 lumped and the other with distributed Watt $1.69. AUDIO TRANSFORMERS: S. Plate to S Grid. 3:1 -79e; S. Plate to l'.P. Grids-79e: constants. Under Electron Tubes are Heavy Duty Class AB or B. P.P. inputs -81.49; Midget Output for AC -DC sets- -69e: MIKE TRANS- found such subjects as electron optics FORMER for T -17 Shure microphone, similar to we use "revolutionary" advisedly. You'll agree and high- frequency and transit -time UTC mincer type -$2.00. Stancor SB or DB mike to when you add new "805" 100 kc. IF. Amplifier line or grid- $1.95. to your present receiver that the phone /broadcast effects. Amplifiers include the travel- POWER TRANSFORMERS -Half -shell type. 110V, 60 ey. Centertapped UV Winding. Specify either 2.5 selectivity and noise reduction it gives are revolu- ling -wave tube. Klystrons and magne- filament when ordering. tionary. Lesa than this improvement has been oor6,3V 4.5 tube sets -650V. 4OMA. SV & 2.5 or described as "like trons are discussed under Oscillators. Fr 51.49 For 5.0 WOO seta -650V, 45A.4551A. 5V 2.5 or nothing you've Frequency modulation, crystal detectors 6.3V 1.75 ever seen or heard For 6.7 tobe seta -075V. 50MA. 5V & 2.5 or and mixers, and u.h.f. antennas are giv- 1.90 before". Fort/ 7.8 tube seta -700V. TOMA. 5V 4. 0.3 or Added two 2.5V 2.35 to any en space commensurate with their pres- For 7 -8 tube sets -700V, 7OMA. 5V & 6.3 (25 superhet having 3.60 i.f. lying between ent-day importance and radio naviga- Forte 8.9 tube seta -700V -SOMA. 5V -3A. 2.5V' 3.5A. 2.5 -10.5A 2.85 450 and 500 k.c., tion aids (chiefly radar) and television For 9 -11 tube sets-700V. 5V & 6.3V -4A 2.85 Model 805 will For 9 -15 tube sets-600V. 150MA. 5V & 6.3V 2.95 receive a chapter each. CONDENSERS -PAPER TUBULAR 600 WV -.001 .002. cut dial- spread on .005--5c; .01, .05 -9e; .1 -10c; .25 -23e; .5 -35e; even the strongest E LECTROLYTICS; 8mfd 200v-20e; 10mfd 35v -20c; 30mfd 150v-23e; 20 /20m1d 150v 35e: 30/20 150v local station down APPLIED ARCHITECTURAL ACOUSTICS, by 46e; SOmfd 150v-43e; 8mfd 475v -34e: lOmfd 350v by 75% . . . wIR Michael Rettinger. Published by Chemical Pub- CONDENSERS: 800v9e¡ 2mfd reduce noise un- lishing 80- 0v-29e; 3X s8 0v -29erd Co. Stiff cloth coyer.. 5% z 8% inches, SPEAKERS -These PM speakers are the B st that are believably. It 189 pages. Price $5.50. available. All Rave heavy ovenlde Arnim V magnets. gives your present ere 51.15 for 99.53 In a practical, concise handbook writ- 51.15 set a selectivity 486 (oval) for 7h.4Ó curve of 2.4 kc. ten for both the architect and sound en- 5' 51.10 1 for 59.50 wide 2X down, gineer Mr. Rettinger presents material 7e (Car Radio Si..) 54.50 for $21.500 falling almost ver- 10 e . $3.95 for 520.50 tically to only 7.2 covering the general design of buildings s. . $4.95 for 526.50 lo. .. 21 es. .. 57.90 for 530.00 kc. wide at 10,000X down -an engineering dream or rooms in which correct acoustical 12. 21 9a. 57.9E for 542.00 come true. 805 gives single -side -band selectivity, MIDGET 1 WATT RIG supplied completo with the ability t,o reject noises, heterodyne squeals conditions are of prime importance. polystyrene coil forms for 3 hate bands. Size overall 3":1':2h' high. Includes practically all necessary and all QRM on one side of the signal or the Theoretical as well as practical aspects Pans. Details on page 62 of January 1948 QST Your other -yet get clear, crisp speech and music with- have been considered, making this book cost $1.50 out deleterious side -band cutting: Battery pack for the 1 watt transmitter supplying 90 Add Model 805 to your present set, and you also suited as a text book. volts "W' and L5 volts "A" $1.50 have next year's new receiver today. Its selec- 110V. AC Fewer SUpPly kit for the 1 watt trans- The first three chapters deal with mitter $3.50 tivity gain -noise reduction is revolutionary. FILTER CHOKES: 200, 300, 400. 500 ohm light duty geometric acoustics, reverberation, and -59e 200 or 300 ohm heavy duty -99c: 256 ma 35 Price, less 1 ea. 6ßE6, 6BA6, 6C4 tubes S111.90 ohm, Made for U.B. Navy. fully hielded- 51.95; 75 Model 805K Kit with pictorial instructions $15.90 sound insulation. ohm "Meissner Chapters bear such tapped c filter chokes -25e; Choke -condenser combination. ideal to replace any size speaker field when In- ACHIEVEMENT headings as "Motion Picture Theaters," stalling PM speaker -79c. OVER 37 YEARS OF RADIO ENGINEERING LINE FILTERS -110V-each unit contains two 2 mad. "Broadcasting Studios," etc. Ml ailed condensen and 15 amp. iron core choke. This oil burner //G 9/1.44xvsaipe/Y Cp., Applied Architectural Acoustics is a filter, etc. An ten dollar value forfr98e. SELENIUM RECTIFIERS -Dry disc U9e err'. le, 1.2 well written volume packed with hard-to- Amp. maximum, itable for convening DC relays to AC, for supplying filament U rvo In portable radios, find information that otherwise could be convening DC meters to AC applIca 0"n s. and also may 1,0 used In low current changers -90c. found only by a frustrating search 30 MC IF TRANSFORMERS. double slug tuned -25e. 30 MC VIDEO AMPLIFIER COILS-Slug through more voluminous works. Even tuned-25c. TUBES TUBES the nontechnical public address service- 1L114 5 .59 G%SGT/G ...... s .45 BUFFALO RADIO SUPPLY 1LN5 .59 5RYGY .89 man should find wealth rule -of- 219.221 GENESEE STREET. BUFFALO 3, N. Y. the of DEPT. BC 357 .89 SU4G .45 thumb information invaluable in install- 306 .69 12A6 .30 3Q4 .59 12SA7GT .35 ing sound systems. E.B., 354 .49 12SK7GT .40 6 A C7 .59 12S67 ...... 62 RADIO TEST INSTRUMENTS (revised edition), 6AB7 .89 1625 .35 by Rufus P. Turner. Published by Ziff-Davis Pub- 6AG7 .... as 2050 .69 Prepare For A Good Job Now /%7 6AG7 .79 30 .60 lishing Co. 63/4 it 9% inches, 221 pages. Price 6D6 $4.50. .40 34 .89 6J5 .39 803 6.00 The author describes the construction 6SK7 .40 807 .95 of more than 75 separate pieces of radio 6SL7 .40 LOWEST PRICES 6SN7 .40 test equipment including volt- ohm -mil- RADIO 6SJ7 .39 NEW - STANDARD liammeters; vacuum -tube voltmeters; 6V6GT /G .45 BRANDS TELEVISION Di Heptol Sockets (less mounting ring) .50 ea. watt, decibel, impedance, capacitance, SOUNDand 2 a 2 Sockets 35 ea. and inductance meters; oscilloscopes and Octol Steatite Socket 15 ea. accessories; special-purpose bridges; a.f, LEARN QUICKLY IN G. E. Switchettes and r.f. signal generators; frequency THE GREAT SHOPS OF # CR-I070C103 -B3 normally open 35 ea. # CR- 1070C123 -C3 normally open 35 ea. meters; and signal tracers. A few of # CR-1070C103-K2 m.rmall closed... 35 ea. these devices have been described in past COYNE Dynamic Microphone Electro -Voice issues of RADIO -CRAFT and RADIO NEws. Model 600 C (press to talk switch) Photographs and drawings show NOT A "HOME STUDY" High Impedance 4 50 ea. parts COURSE Stepdown Xformer UTC Type 63833 layouts and mechanical construction of Get ready for a better job, bigger pay NOW in 220V to 110V -100 Watts -60 cycles-4.00 ea. Radio. Cash in with "All- around" knowledge of the more complex items. Methods of ad- Radio-Sound -Television. Train on actual equip- Specials: justing, calibrating, and operating the ment not by "Home- study". You learn quickest Small 110V 60 cycles AC open frame at COYNE because it's a real SHOP course) motor IA" shaft, 2700 RPM, 1/70 H.P. instruments are described. mfg. by Barber Colman Co. 2.00 ea. Errors were noted in G. I. APPROVED .. also Finance Plan for three of the os- NON -VETERANS. Don't let lack of cash hold Synchronous Motor cilloscope diagrams. Cathode returns you back. Many earn while learning. FREE Em- 14,w shaft 110V -AC cycle, 4/5, 1, ployment Service to graduates. -60 were omitted from the C-R tube cir- Get facts today( 1 1/6 z 1% R.P.M. 2.2 Watts. Mfg. by Hayden Mfg. Co. 2 00 ea. cuits.- R.F.S. SEND COUPON FOR FREE BOOK Specify speed desired. Send at once for Big Free Book on Standard Brands ELECTRONIC CIRCUITS AND TUBES, by the Radio, Sound and Television. and'facts MM. DC about our Finance Plan. Capacitor-500 200V ...... 1.75 ea. Electronic. Training Staff of the Croft Labora- Oil Filled Condensers: tory, Harvard University. Published by - McGraw sssi MAIL THIS COUPON TODAY 4 Mfd. 2000V DC .. 3 75 Hill Book Co. 6% z 9 inches, 948 pages. Price 10 Mfd. 1500V DC 2 95 $7.50. CoyneElectrical and Radio School 10 Mfd. 600V DC 90 500 S. Pauline St., Dept. ca -so, Chicago The material presented was taken 12, Ill. No sale less than $2.00. All prices FOB N.Y.C. Add Please send Big FREE Book and complete details 25c to cover postage. 20°o deposit required with all from notes prepared for lectures given Orden. at the Graduate School of Engineering s NAME i STREET A. M. RADIO SALES CO. at Harvard University during the war. R CITY STATE 345 Canal St. N. Y. C. 13, N.Y. (Continued on page 87) Ewa ,AUGUST, 1948 86

RADIO SC110O01 DIRECTORY

PRACTICAL TECHNICAL TRAINING WANTED: Men and Women to Fill IN RADIO, ELECTRONICS Specicl /i31Q TOP RADIO JOBS ELECTRICAL ENGINEERING in AM- FM- Television I COURSES Prepare for a successful career in in- If Tou are looking for a career with s future. why not SERVICE loin the hundreds of graduaten from the Don Martin dustry or a business of your own in 6 School of Radio arts now successfully employed in the 6 to 12 Months radio Industry. The demand is great for qualified Electricity months to 3 years. More than 35,000 for- B.S. DeEreo radio personnel In AM- FM- Televlelon. Train now to Welding in Electrical be an announcer. salol writer, disk Jockey news- Refrigeration Engineering caster. or radio ebgineer. Complete day and night mer students in industry the world over.. Free placement Heating Willi Major in classes . . the latest equipment. 1,538 students now enrolled from 48 states Electronics service. Approved for veterans. Write fer free booklet. TECHNICIAN In 3 Years. of Radio Arts I to 2 Years and 13 overseas countries. Faculty of 72 Don Martin School Electricity 1855 North Cherokee St. Hollywood 28. Callf. Radio specialists. Write for Catalog and Per- Electronics sonal Guidance Questionnaire. Refrigeration, Heating and Air Conditioning .4f Terms start September, January, April, A CAREER WITH A FUTURE! PROFESSIONAL July. 3 Years Electrical Engineering 4111`--MILWAUKEEir TELEVISIONISIO\ Bachelor of Science

Degree of DMINEERIN Saw was . saw nraalmin TOUT 1N11 MAI O LIEBRATOD0 Major in Machinery or OHiml 5 A technical Institute Founded 1903 e RADIO SERVICE & REPAIR Electronics E. M. & TELEVISION Dept. RC -848 North Broadway, Milwaukee, Wisconsin TRANSMITTER COURSES n.eo.lnq iw F.CC. LICENSES FM- RADIO -TV Ii.%IIIO TECHNOLOCI' Amin - LITIRN0a1 Ivan (LOAM aD00An lam IIGISUStnn PRACTICAL TELEVISION 1948!! AVAILAStI aine! O. I. alit Train at an Institute that pioneered SCHOOL OF TRAINING the IILI,E IIANTY Four fully-equipped laboratories provide In TELEVISION TRAINING since 1938. RADIO ELECTRONICS PRACTICAL training essential for successful TELEVISION (FCC li- Morning Afternoon or Evening Ses- 105 EAST 13th ST*EfT, NEW YORK 3, N. Y. DEPT. R careers in Radio Communications In- censes) and in Radio -Television Servicing sions in laboratory and theoretical LI a-a.rss sss 1040 -C Ne. Kenmore Hollywood 27. Calif. RADIO -CRAFT for MIMIC cricIrsHA I 87 Twenty-four chapters cover practical- covered completely. A series of ques- ly all types of electronic circuits and tions and problems and a bibliography A Complete, Practical tubes used in communications and elec- appended at the end of each chapter are tronic controlTAmong the subjects cov- useful to the student. Handbook of Present - ered are: Basic a.c. theory, circuit con- This reviewer would like to have seen day stants, filters, amplifiers, transients, re- more space devoted to antennas and TELEVISION ceivers, transmitters, vacuum tubes, transmission lines, especially the effect cathode s, and keying standing on FM and TV. Now, the tremendous opportunities -ray tub( timing of waves in the field of television arc brought circuits. The tables include logarithms, sines within your reach -by means of Oscillators and wide -band amplifiers and cosines, copper wire sizes, letter this crystal -clear book. Written in are covered more fully than in many symbols used in electronics, conversion plain English, concise and up to the texts of this type. The well -known but factors, freq.-wavelength and LC prod- minute, it makes television easy seldom- discussed effects of tightly - ucts, receiving tube data and socket to understand. There is no mathe- coupled tuned circuits on oscillator sta- diagrams, resistance - capacity - coupled matics to confuse you and make ex- bility and calibration are described and amplifier chart, and other useful infor- planationsdúficult to follow. Hun- dreds of vivid illustrations bring discussed in Chapter XV. Design data mation.-H.W.S. every fact and point right before on compensated wide -band amplifiers is your eyes. You'll be amazed at how complete with practical examples of TELEVISION TODAY. by Roy C. Norris. Pub. simple television can become with actuítl circuits. Belied by Rocklift (Groat Britain). 53/4 x 8yß Four appendices: Review of Mathe- inches, 249 pages plus index. Price 21 shillings. Written for the reader with a mod- New Second Edition -453 Pages matics, Brief Review of Electricity and erate knowledge of a.c. and d.c. theory, r Magnetism, Description of a Direct -Cur- this book gives a "from the ground up" rent Source in Terms of Electrical Con- description of how a television system stants, and Symbols and Abbreviations operates. TELEVISION are included.-R.F.S. An English publication, it devotes ELEMENTARY MANUAL OF RADIO PROPA- some space to an interesting compari- GATION, by Donald H. Menzel. Published by son of British and American television Prentice -Hall, Inc. Loose-leaf fiat -ring binding with flexible leatherette covers. 8% z 11% inches, systems, and presents complete informa- SIMPLIFIED 222 pages. Price $7.65. tion on all the important details of A complete work describing the meth- transmission. Am:aka* Instrodor in radio. U.S. Army ods of calculating propagation paths be- Receivers are covered thoroughly, as Air Forces. Formerly Ins, rurror in radio, tween radio stations and the theory be- well as antennas and antenna theory, Illinois Institute of Technology. hind such calculations. Absorption and large -screen television, color and stere- This brand -new, authorita lowest usable high frequencies are con- oscopy, and system adjustment and Live handbook not only con. sidered as well as the more commonly troubleshooting. tains all the information yotl considered maximum frequen- need for success in television, usable The many diagrams are clearly drawn but covers the trouble shoot- cies. The book as a whole serves as and are placed so that each drawing is ing and repair of radio sets. an advanced text to the person with ex- on the same page as the explanatory Beginning with a clear, over- perience in making calculations from text. -R.H.D. all picture of the entire field, the CRPL charts, as well as a complete it breaks down the television manual to the newcomer in the art. FINAL ACTS OF THE INTERNATIONAL receiver into its component A number of chapters are devoted to TELECOMMUNICATION AND RADIO CON- parts and circuits. It ana. FERENCES. Published by the International step by step, calculating the coverage of a given Telecommunications Union. distributed by the lyres them, transmitting station. A number of oth- American Radio Relay League. 5% z 8% inches, showing how they are formed, 426 double pages. Price $1.50. the roles they play, and their er interesting -points, incliding varia- This book contains the new Interna- operating characteristics. bility of the sun, problems of broadcast tional Telecommunications Convention, and lower frequencies, and propagation the International Radio Regulations, BRIEF OUTLINE OF CONTENTS effects deduced from weather conditions, and all the Appendices, Annexes, Pro- are covered in separate Two The Television Field; Ultr-higls chapters. tocols, Resolutions, and Recommenda- Frequency Waves and the Televisioii appendices discuss the theory of iono- tions arrived at during the Atlantic City Antenna; Wide -band Tuning Circuits, spheric and tropospheric propagation. Conference last year. Representing the Radio-frequency Amplifiers; The High. frequency Oscillator, Mixer and Inter. ESSENTIALS OF RADIO, by Morris Slurgberg work of 79 nations, these documents are mediate -frequency Amplifiers; Diode and William Osterheld. Cloth covers; 806 pages; detailed and explicit. They provide Detectors and Automatic gain - control Illustrated. Size 6% by 9 inches. Published by source material on which international Circuits; Video Amplifiers; Direct.cur- McGraw -Hill Book Co. Price $5.00. Tuba; radio regulation will be based for some rent Reinsertion; Cathode -ray This book, written for the radioman Synchronizing - Circuit Fundamentals; with a knowledge of simple high-school years to come. Deflecting Systems; Typical Television algebra, is an excellent treatise which Two official texts of the Convention Receiver -Analysis and Alignment; given on opposing pages through- Color Television; Frequency Modulation; covers all branches of the radio trans- are Servicing Television Receivers; Glossary mitting and receiving art, including FM out the book, French on one page and of Television Terms. and AM. English on the facing one. One of the opening sections deals with EXAMINE THIS BOOK FREE circuit analysis, including the calcula- Hollywood Make Good in at Let this great book prepare you to take tion of inductance of coils and the ca- advantage of the brilliant opportunities Home television offer. Send for it NOW II pacity of condensers. The power trans- Help ou RADIO -TELEVISION Direct from Ilol low,..l. n enter of broadcasting. Tels. vision, Radio and Sound activities, comes R -T -A' time- former is described at length. The calcu- preven and tested home training. Here `at last -easy to MAIL THIS COUPON 1 lation of circuit constants is learn. horn, Instruction that quickly qualifies you for carefully steady, goad -pay loba or your own Radio borines.. 10 big D. VAN NOSTRAND COMPANY, INC. kits of dio parts given at no mare charge. Get full de- explained for both a.c. and d.c. systems, tails at once! Send postal for FREE ROOK "How to Make 250 Fourth Avenue, New York 3, New York with the necessary simple mathematics. Good In Radio-Televlelon. RADIO TRAINING ASSN OR AMERICA. Dept. RCO Please send me "Television Simplified." Receiving circuits and vacuum tubes are 5620 Hollywood Blvd. Hollywood 25, Calta. Within 10 days I will either return the book or send you $2.00 after examination and $2.00 a month for two months ($6.00 in all) 1V CORRESPONDENCE COURSES IN plus a few cents postage. Return postage is guaranteed. RADIO and ELECTRICAL ENGINEERING ELECTRICAL ENGINEERING ° d.: ¡edtrii' éaá cor Name tourare ' dr-WÇ S .tmpl11iW> n. tp ickly, Be a "key" man. Learn how to send and messages in code by telegraph RADIO ENGINEERING °;;e Commerce needs thousand. of work. Trains you to be super- ..cric- m ml n `mid .madi . pay. adventure, in- Address be technician. Servicemen needed badly. Diploma m teresting work. Learn at home quickly completion. po y. through famous Candler System. qual. rd for Rn. Cooler. 1 eye for Amateur Commercial LI- c .e. Write for 1TtEt BOOK. City State :='.:;:;g1.,.7,1..,11:11:4 $75 CeWRITEsti. CANDLER SYSTEM CO. Radio Craft Aug. 48 perimental kits. ete. Dept.3J. Box 928. Denver 1. Colo., D.B.A. Lincoln Engineering9ineering School, Rox931 -C-114. Lincoln2, Nebr. L J AUGUST, 1948 88 INDEX TO ADVERTISERS EVERYTHING IN A.M. Radio Salas Co. 85 Opportunity Adlet 76 Abell Distributing Co. 76 John Porter 88 TELEVISION Acorn Electronics Corp. 71 Precision Apparatus Company 73 Allied Radio Corporation 4 Progressive Electronics Company 54 Alvaradio 62 Radio City Products Company, Inc. a 77 American Radio Supply Co. 68 Radcraft Publications, Inc. 69. 78 American Sales Company 84 Radio Dealers Supply Company 83

American Surplus Products 50 , 62 Radio Kits Company 63

Amplifier Corporation of America ' 57, 64, 7 7, 82 Radionic Equipment Company 61 Walter Ashe Radio Company 81 Radio Publications 84 Audel Publishers 81 Radio Supply 6 Engineering Company 82 Bell Telephone Labs. 48 The Rose Company ...... 66 Boland á Boyce Publishers, Inc. 8, 83 Brooks Radio Distributing Company 61 Buffalo Radio Supply 64. 72, 73, 75, 76, 7 7, RADIO SCHOOL DIRECTORY 82, 8 4, 85 (Pages 86 -87) Latest design Features High Defini- Burstein- Applebee Company 57 American Radio Institute tion, Brilliance and Stability New Syn- Capitol Radio Engineering Institute 2, 46 Baltimore Technical Institute chro -Lock and Contrast Emphasis Cir- Certified Television Laboratories 88 Candler System Company cuits 55 sq. in. Screen Beautiful Cleveland Institute of Radio 11 Commercial Radio Institute Cabinets Communications Equipment Co. 80 Delehanty Institute Coyne Electrical School 79, 85 Don Martin School of Radio Arts RECEIVERS, FM STRIPS. Custom -Craft Mfg. Company 82 TEST EQUIPMENT, KITS Hollywood Sound Institute, Inc. FILTERS. LENSES, DeForest's Training Institute 9 Lincoln Engineering School DECALS, TUNERS, The Electric Auto -Lita Company 63 Melville Radio Institute ACCESSORIES. Espey Manufacturing Company, Inc. 81 COMPONENTS, Milwaukee School of Engineering ASSEMBLIES, Fair Radio Sales 73 RCA Institutes ANTENNAS, General Cement Manufacturing Co. 56 CABINETS Radio -Television Institute General Electronic Distributing Co. 53, 72 Radio Training Association of America G I Salvage Company 62 Tri -State College General Test Equipment 79 SURPLUS RADIO, INC. Valparaiso Technical Institute Green Radio Distributor 52 Western Radio Communications Institute 44 -31 Douglaston P'kwy Greylock Electronic Supply Co. 64 YMCA Trade & Technical Schools Douglaston, L. I., N. Y. Hallicrafters Radio 75 The Heath Company 6, 7 !'lease send me your FREE Catalog Hershel Radio Company 14, 15, 16 Howard W. Sams á Company, Inc. 47 Hudson Specialties 80 Santo Radio, Inc. 79 Name Instructograph Company 72 Shunte Meters .. 57 Kay Distributing Company, Inc. 57 N. Silverstine Co. 65 Address Kay Electronics Company 79 Sprayberry Academy of Radio 5 Town State Lafayette Radio 75 Superior Instruments 71 Lear Radio, Inc. 55 Supreme Publications 45 Leotone Radio Corporation 88 Surplus Radio, Inc. 88 McGraw -Hill Book Co., Inc. 66 Sylvania Electric Products Back Cover SUMMER McMurdo Silver Company..... 85, Inside Back Cover Technical Radio Parts Company 57 P. R. Mallory á Co., Inc. Inside Front Cover Tel -Craft Company 77 Metropolitan Electronic á Instrument Co. 61 Tradio, Inc. 62 PECIALS Mid -America Company 70 Transvision, Inc. 74 J. W. Miller Company 71 D. Van Nostrand Company, Inc. B7 12' CINnUDt,Gnt.eN e AKERS (Ny-12121. Thl. 56 oversizee a0 Oa. Mon Electronic Distributing Company 52 James Vibrapowr Alnicc I,kexn vnlrc ,il. Mono Murray Hill Books, Inc. 72 X.L. Radio Laboratories 81 ILhh.l far Radio. 15 watts. r:PARA.\r National Plans Company 69 'ry,l.le soli A Ft I.. .i_ I transformer. Shpg. wt. 10 Ih. . .. 9 95 National Radio Institute 1 National Schools 3 RM.4 RECORDING MOTO R. Heavy duty 110V. 60 cycle Niagara Radio Supply Company 12, 13 shaded pot induction type. Si. lent rating for WIRE, TAPE North American Sales Company 84 DISC RECORDING. fans. ' heaters, etc. 5 16- O.D. shaft; ` -tb Offenbach á Reimus Company 64 31/2- w. x late Less tum- /- reduc mod- Plate Ohmite Manufacturing Company 59 reduction drive I.

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TELEVISION FOCUS COIL. For use with IM. 12^ or SALESMEN 15^ tubes. 275 ohms DC Q 125MA. Fully shielded. Triangular 41/4" mtg. 1 -9/16" hole. Shp;. wt 4 lbs. A Real Value at .25 $240.49 in Cne `.Peek t1.30 THROAT MIKES. 2 rubber -set carbon but. Unusual?... hsot At AIS! on, exclude outside noise. I banes free. Complete with neckband, PL -291 plug a rubber cord. RAND NEW 39. 12 for ].9E lust Leek at One Week's Earnings i of Those Representatives: ANTENNA LOOPS. High gain. spider wound for W W S $290.99. JMH 6229.75. RJR $262.47, VJM $276.95. plcIoup. 5^ round or 4" x 8" al. Eitler.... .29 JEA $240.49, RWF $'Y31.21. Direct mail campaign brings hot leads right into your home. Remarkable "CONGER" OUTPUT TRANSFORMER (T/R^ product does part 10 1.3/16'). 2000 ohm tapped double primary to of men's work; a natural during voice COIL Excellentfor use with Beam Power these labor problem days. Has perfect sales story: type tubes 49. 12 for 5.00 and sells year 'round. As modern as radar! Special demonstrator offer. We extend credit, deliver. collect. 110V. AC RELAY (W.L). SPST. by dut 20A. Sil- No capital required: no experience needed. You make vered contacts. 700 ohm roil. Slid. on .yea^ hakellte big on sale, and on base. Overall: 31,,^ x lab^ x I I _ ^... Now only 1.49 profit first full credit repeat business. Every business, store. factory,etc. are prospects. SPEAKER ACCESSORIES KITS Write JOHN PORTER, 2433 Indiana Ave., SPEAKER CONES-Kit of 12 asstd. 4^ te 12' moulded Dept. 426, Chicago 16, Ill. & lrre -edge (magnetic inch:. Leas voice oils.. 2.00 SPEAKER REPAIR KIT -A real money L. time ...yr. contains 25 td. paper rings. 10 spiders 25 coil forms. 3 s yds. felt strips. 20 chamois leatnrr segments, kit of 16 shims. & tube of speaker cement. All for 3.49 CONE RINGS -50 sta. cardboard ctg, TELEVISION RECEIVER -$1.00 ino in popular s . 3^ to 12' 1.49 building SPEAKER CEMENT SOLVENT -3 Oa. each of all Complete Instructions for your own television purpose cement & thinner.i with brush .69 receiver. 16 pages -11'x17' of pictures, pictorial diagrams, clarified schematics. 17'x2'" complete schematic Minimum Order 52.00. 20% Deposit Required. diagram k chassis layout. Also booklet of alignment Please Add Sufficient Postage. instruction, voltage R resistance tables and troubleshooting hints. -All ter $1.00. ' RADIO COMPANY CERTIFIED TELEVISION LABORATORIES 65 Dey St., N.Y. 7, N.Y. OROÑL Dept. C, 5507 -13th Ave., Brooklyn 19. N. Y. RADIO -CRAFT for AUGUST, 1948 Correspondence from service technicians and distributors suggests that many may be con- MODEL 911 fused by the question. "What instruments do I TV /FM SWEEP GENERATOR. really need to service TV and FM receivers ?" 2 thru 226 mc.; electronic sweep adjustable 0 to 10 mc.; high output adjustable 0 to 'h volt. Separate 1 mc. and THERE IS NO NEED FOR CONFUSION! The 5 mc. precision crystal marker oscillators to insure correct TV video i.f. curve shape and width; phasing control and answers are simple and direct . . . the new 60-- sine -wave 'scope TV sweep voltage; 120- saw -tooth service techniques easy to master when pic- FM 'scope sweep voltage. All this, yet only $78.50 net. torially presented. Only one new instrument must be added - some older instruments be replaced with new models for efficient and designed for efficient TV and FM servicing, the profitable TV and FM servicing. new Silver Model 911 Sweep Generator takes all confusion out of TV and FM alignment. THE ONE NEW INSTRUMENT needed is Model 911, a wide -range sweep generator for visual REPLACEMENT OF OBSOLETE instruments with alignment. If you get the one the set makers the new "VOMAX ", the famous 906 FM -AM themselves seem to favor you are naturally Signal Generator, adding new "SPARX" AM, best equipped. Equally important, 911 comes to FM, TV Signal Tracer, will really pay off in you with new pictorial instructions. Specially TV -FM service profits.

MODEL 90S -A "SPARX ". Combining signal - MODEL 900 -A "YOMAX". The new "VOMAX" MODEL 906 FM -AM SIGNAL GENERATOR. universal test speaker, 905 -A is is the truly universal v.t.v.m. - makes TV, FM Similarly the choice of the big engineering tracer and free tracer and AM measurements accurately - at highest laboratories plus thousands of service tech. amazingly sensitive yet of usual meter resistance. Giant meter, non -breakable nicians, 906 stands out as maximum value. 90 hum. Vacuum -tube prod with r.f.a.f. switching; PM speak- gloss; 45 ranges; new single probe for a.c., kc. thru 210 mc. in 8 ranges, ±1% accuracy; high -gain high -fidelity amplifier; 6" gives wide d.c., a.f., r.f., volts, ohms, db. and current less than 'h microvolt, including strays to over er; 18 -watt output transformer of impedances. Two essential instru- measurements. Advancing for beyond its prede- 1 volt v.t.v.m.-metered output; multiple shield- choice finest years of cessor, the overwhelming choice of experts, ing; adjustable 0 to 100% amplitude modula- ments in one, 905 -A is the 37 "VOMAX" equips you with the world's newest tion; adjustable 0 to 1,000 kc. FM sweep. Net prize- winning radio engineering experience and finest meter for only $68.50 net. price only $116.50. can design - value far exceeding $44.50 net. r 1 %Xad fitadecWZCd for new catalog OVER 37 YEARS OF RADIO ENGINEERING ACHIEVEMENT of LCETI - Laboratory Caliber Electronic Test Instruments . . quality and prices which amaze 7/1 671044%.- Car-. ,9,er. even the experts. EXECUTIVE OFFICES. 1240 MAIN ST., HARTFORD 3 CONN.

R , C N N F R Y F F I C E 1 2 4 9 M A I N ST., H A R T F O D 3 O A C T O O s HUNDREDS OF SERVICEMEN CASHED IN ON SYLVANIA'S SPRING PROMOTION

N pH/... sYLVANI,q OFFERS THE RADIO S RVIC+N .AN OT#f g R FALL! PLAN OR F Shown at the left is one of Sylvania's national ads to appear in Life, The Saturday Evening Post, Collier's, Radio Best...during September, October, November and December. This series of ads is designed to ell you and your dependable radio repair service to your prospects.

HERE'S HOW YOU TIE UP WITH AND CASH IN ON THESE ADS...

TUBES RADIO SlVpHIA

We Repair All Trues and Brands ú:eá nvn el Rmlíss

4 POSTAL CARD 4 WINDOW DISPLAYS 4 WINDOW STREAM- 8 NEWSPAPER AD 0MAILINGS FOR -ONE EACH -ONE FOR EACH 0 0 MONTH FOR EACH ERS-ONE MONTH MATS -TWO SIZES FOR MONTH Sylvania supplies you FREE Sylvania gives you FREE these EACH MONTH Sylvania suppers these cards 4 big, colorful displays. Each four 2 -color streamers. They Sylvania sends you FREE 2 in 3 colors, imprinted with one is tied in with the na- are also tied in with Sylvania's ad mats for each month - your name and address. You tional advertising using the national advertising. You at- one -and two -column by seven pay only the postage on each same illustrations and copy. tach these to your window as inches. Use thorn in your local card. You send them to your You put them in your window another means of attracting or neighborhood papers and customers and prospects! to attract customers! new customers! classified telephone directory.

also ®RADIO SPOT ANNOUNCEMENTS Sylvania provides FREE serviceman who uses radio - several radio SEVERAL FOR EACH MONTH commercials for advertising. Call or see your each month for the radio local radio station for rates.

THIS 4 -MONTH ADVERTISING PROGRAM PACKED IN ONE HANDY KIT Covering the months of September. October, November and December. this hard -hitting sales promotion program is parked in one big kit. You pay only the postage on the government postal cards you mail. Sylvania supplies everything else sc ithnut charge. RADIO

YOU CAN IDENTIFY YOURSELF WITH THIS DECAL Put this decal on your door. windows and truck. SERVICE It is reproduced in Sylvania's national ads and identifies you as the radio serviceman described in Sylvania's national advertising. Learn how you can participate in this Fall advertising program. Write Sylvania Electric Products Inc., Advertising Department, Empor- ium, Pa., or see your Sylvania Distributor. SYLVANIAV ELECT aaDIo CATHODE RAY TUBES: 'UBES ELECTRo',C DEVICES: FLUORESCE', T LAMPS, FIXTURES. WIRING DEVICES. PHOIOLAMPS: ELEC