Radio-Electronics in All Its Phases Ada 30

Editor RA I O

-1Motap,

GI AMATEU RADIO CLU STATIO SEE PAGE 828

Audio Response Correction SEPT Rebuilding a Televiser 1 9 4 6 Design of Audio Mixers

RADIO-ELECTRONICS IN ALL ITS PHASES ADA 30. PANORAMIC RECEPTION attends the opening of the 20 and 40 meter bands

When the 20 and 40 meter bonds reopened for amateur communication with all the excite- ment and ceremony that usually accompanies a " ight," a Panadaptor sat in on the fun. Below is an account, with illustrations, of the act 'ty that took place before, during and after that long- awaited ha occasion.

(As Viewed by W LNP)

12 MIDNIGHT! All aetivlt, 'Ohio the 2:00 -2:30 A.M.! Signals appeared on the 3i0STAGE. the S Broadcasting I l Bri h Corn. band comet]. The stations e le outside band. Patterns of deflections showed that pony and Spanish w station were still to Point remained on. these only carriers. and not actual seens n and heard on the a0 meter band. thmm antrat Ions. Their signals occupied the center of the On the edge of the screen. but eut. side of the band, were few w and phone stations

4 And the official message from the A.M.! 405.4:30 A.M.! Wlthi few minutes .5 A.M.! The number of stations en the of the official station of ARAL. WIAW, announcement.. ent. abc 1lteen stations as growing. And activity on the 40 'taunted to 40 were on . all amateurs that the 20 and air. arl. rns: W2LNP, irtew band appeared to be normal for the meter bands were again their property. the station to which e thi adaptor wax first time In many years. rigged, exchanged greed with W6SET About the same time. large signal sud - in Fontana. California, station whose deny sprang p . which appeared to be signal appeared on the s n. local station. This was found to come Porn NZSAA in Panama. C.L.

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ELECTRONICS AND TELEVISION

Black -Light Telescope by Sanford Essig 826

HUGO GERNSBACK, Editor -in -Chie) Rebuilding a Televiser by Norman Chaffin 832 FRED SHUNAMAN, Managing Editor Television for Today, Part IV, Television M. H. GERNSBACK, Consulting Ed. R.F. and I.F. Stages by Milton S. Kiver 840 R. F. SCOTT, W2PWG, Technical Editor I. QUEEN, W2OUX, Editorial Associate ELMER FULLER, Shortwave Editor AMATEUR RADIO A. PASCALE, Production Manager- G. ALIQUO, Circulation Manager V.H.F. Receiver by R. L. Parmenter 825 JOHN J. LAMSON, Advertising Director Army -Amateur Radio Club (Cover Story) by Capt. L. A. ALFRED STERN, Promotion Manager Olson 828

IN AN EARLY ISSUE SERVICING Instability in Apparatus The Postwar Radios: Arvin Model 444 836 5 -Tube Superheterodyne Radio Test Equipment Electromagnets in Radio by Shepard S. Litt 837 Complete Tracer in Probe Radio Data Sheet No. 339 (Olympic Models 6.501, 502, 503) 839 Aviation Radio Servicing ice SOUND Published by Radcraft Publications, Inc. Publication Office: 29 Worthington Street, Audio Response Correction Springfield 3, Mass. by John W. Streede 827 Editorial and Advertising Offices: 26 West Audio Mixer Design Broadway, Tel. RE 2 -9690, New York 7. N. Y. by John B. Ledbetter 834 Chicago Advertising Office: Radio-Craft, 808 W. Washington Street. Suite 1413, Chicago 6, Ill. Tel. Randolph 7363. Cleveland Advertising Office: 406 Erie Bldg., Cleveland, Ohio. Burdette Phillips, Manager. CONSTRUCTION Tel. Main 9645. Detroit Advertising Office: 307 -8 Boulevard r= Germanium Crystal Probe by R. E. Altomare 830 Bldg., Detroit, Mich. C. Frank Holstein, Man- ager. Link -Coupled Crystal Set by Carroll Ufermehlen 831 Los Angeles Advertising Office: 606 South Hill Street, Loe Angeles 14, Calif. Ralph W. Harker, Manager. Tel. Tucker 1793. San Francisco Advertising Office: 682 Market i St., San Francisco 4, Calif. Ralph W. Harker, DEPARTMENTS Manager. Tel. Garfield 2481. RADIO -CRAFT is published monthly on the World -Wide Station List by Elmer R. Fuller 842 25th of the month preceding that of date. Subscription rates: United States and pos- New Radio- Electronic Devices sessions, Mexico, Central and South American 844 countries, $2.50 a year, $4.00 for years, two Radio -Electronic Circuits 8554 $6.00 for three years. Canada. $3.00 a year, $6.00 for two years, $7.50 for three years. All other foreign countries. $3.25 a year, Try This One B56 $6.50 for two years. $8.25 for three years. Special rates for members of the Armed The Question Box 858 Forces in U. S., or those addressed by A.P.O. or F.P.O. mail, $2.00. Entered at the post New Radio -Electronic Patents office at Springfield as second -clans matter 860 under the Act of March 3. 1879. All communications about subscriptions should be Communications 880 addressed to: Circulation Manager, Radio- Craft, 25 West Broadway, New York 7, N. Y. Book Reviews 883

Notice of CHANGE of ADDRESS should reach us at least one month in advance. When Biographical Portrait drawings by Constance Joan Naar ordering a change, please furnish an address stencil impression from a recent wrapper if you can. Address changes cannot be made without the old address as well as the new. IIIIIIIIIIIIIllll11f1!Ii1!'P"!!1VIIIIIII IIIIIIIW 1111VIIIIII11111IIIIIIi11V1111111111111111HU1111111111111111111H11111111011111111111111111111 111111111111111111111111111111III111110111111101111111111111111111111111111111111119

Foreign Agents London -Atlas Publishing and Distributing ON THE COVER Co., Ltd., 18 Bride Lane, Fleet St., London, E.C. 4. Melbourne -McGill's Agency, 179 Elizabeth The Army- Amateur radio station, W2OEC, at Fort St., Australia. V Monmouth, New Jersey, is depicted on our cover Text and illustrations of this magazine are this month. Home the copyright and must not be reproduced without of Signal Corps, Fort Mon- permission of the copyright owners. Copyright, 1946, Radcraft Publications, Inc. mouth is crowded with hams from all districts of V the United States, who ore able to keep up RADCRAFT PUBLICATIONS. INC.: with Hugo Gernsback, President the postwar hom M. Harvey Gernsback, Vice Pres. world by means of the station. G. Allan, Secretary Chromatome by Alex Schomberg from Signet Corps Photo 814 Big Boom RADIO INDUSTR in FM Broa WE-NE f astin POISED r SON l 1 A Seen HO E. 'S Let IOW k de Y ou to app' Guide , S za. RADIO To MRROW THIS n111ES ELECTRONICS PPR MODERN"A-B-C" WAY , a.t qaoce

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" VOMAX" is more than a multi -meter ... more than volt- ohm -db: milliemmeter ... more than r.f. vacuum -tube voltmeter of laboratory instrument caliber. " VOMAX" is all of these things. Born out of six years of military research and production, it is new as today. Backed radio's only by a name famous for over 35 years . designed by International Grand Prize winner, "VOMAX" is the standard of comparison. RADIO MAtNTENANCE engineers checked and rechecked the market for the -best possible meter ... most -used instrument in all and core of its new "Modern radio service . to serve as heart Test Bench.' They selected "VOMAX ". Your efficiency and profits will be greatest when you. too, use "VOMAX ". Outstanding . . S. Bureau of tested and sworn to by thousands of serious service technicians ordered and reordered by the U. Monsanto Chemical, DuPont. F.C.0 11 Standards, the Naval Research Laboratory, Western Union . used by Sperry, Grand Island monitoring station, C.A.A., Naval Ordnance Depots, Lapp Insulator, Stackpole Carbon, Fairchild Aviation. competition. Follow the rec -- ( etc., etc. This is positive proof that "VOMAX" is the meter you must have to top smart $59.85 ommendation by Bendix to all BENDIX RADIO distributors and dealers ... "Use 'VOMAX'. It's better than we hoped.' TT

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RADIO -CRAFT for SEPTEMBER, 1946 819 Regularly Scheduled Programs are on the Air! Studio Photos Courtesy of Television Station WCBW Two great broadcasting corporations have entered Television and are today producing programs. Other large organizations have applied for licenses to broadcast Television in all parts of the country! The sale of home receivers is now progressing. In other words, we believe it's the beginning of a vast and exciting new business. Regular Television broadcasting is now a reality! TELEVISION AND YOU The opportunity in Television is far greater for the properly trained man. You owe it to yourself to investigate Television and to prepare yourself to become a valued part of a fascinating new profession. TELEVISION STUDIO CONTROL PREPARE THE "AMERICAN" WAY The American Television Institute is the oldest and largest training organization exclusively for Television. "American" students are trained by top Television engineers with the latest commercial equipment. You will train under actual Television studio conditions. You will learn by doing. You can qualify for your chosen field with the necessary fundamental knowledge plus real studio experience and skill.

VETERANS ATTENTION! WHICH PHASE OF TELEVISION? The American Television Institute has been The American Television approved for Veteran Training under the Institute's tre- 0.1. ill f Rights. During the war, thou- mendous facilities offer a complete sands of signal Corp. men re trained selection contract with the Department. of Television study -broadcast studio and underOur training method* have been developed to high degree and our school has up to control, broadcast transmitter, the minute facilities in every respect. If receiver in- you are' veteran, mark the coupon for the stallation and service -in fact, all depart- Cl.. Questionnaire. ments are thoroughly covered in our laboratories. TUBE MAKING AT A.T.L. WHEN DO YOU START? REQUEST The best time is right now! Immediately! New FOR FREE INFORMATION classes are forming every week. Use the coupon to AMERICAN TELEVISION INSTITUTE, DEPT. A get further details. Mail it today! 433 East Erie Street, Chicago Il, Illinois Please send me complete details of your American Television Institute Television training. DIVISION OF I am a veteran. AMERICAN TELEVISION LABORATORIES, INC. NAME

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CITY & STATE ..

820 RADIO -CRAFT for SEPTEMBER, 1946 By,NtlGO GERNSBACK

1 REALLY HERE?

` The Tub(' tri Not the Final Solution to Television

4 WE HEAR continuously from many of our broadcast; the final film would then be run at the tele- readers who are bewildered -as is the general vision transmission studios and broadcast. This would public -as to the true status of television make it as cheap, or cheaper than motion picture prac- today. There is a great deal of confusion re- tice. Sponsored advertising programs could be presented garding television as a whole. Nor is it abated by the in this way whereby the admittedly still high production industry, which itself is at odds on more than one of costs would leave a profit to the television broadcasters. the art's major questions. The entire video picture is That is another angle. highly complex, to say the least, while little is being This suggestion, however, is not at all welcomed by done to clarify the situation. the television industry who wants none of it, but be- Within the industry certain factions are at odds with lieves that television's credo is that events should be each other. Much could be written about such points broadcast when the event actually occurs, instantaneous- as the disagreement between the industry and the Fed- ly, as for instance, the recent Louis -Conn fight. eral Communications Commission as to time schedules This is only one part of the story. So as not to lose our of operation, freezing of standards, etc. Within the in- perspective, let us turn the clock back to 1921 when dustry one faction is for color television, which is de- broadcasting started. At that time anyone with a $10 nounced by the other. Then there is the size of screen bill -or less-could receive radio broadcast programs for best viewing, whether the image should be on the simply by either buying a crystal detector and a pair cathode tube screen or whether it should be projected of headphones, or by making the detector himself and on the wall (or a wall screen) . These are but a few points. buying the phones. From such small beginnings broad- Commander E. F. MacDonald, Jr., President of Zenith casting began. Radio Corporation, has long taken the stand that com- A little later the radio tube came into its own and then mercial television procedure is all wrong in following with one- or two -tube sets which gave better selectivity, the paid -advertising broadcast technique. He maintains stronger and clearer reception, broadcasting marched -not without good reason -that it will never be pos- on its triumphant way. Still later loudspeakers were sible to have nation -wide "free" television reception as added. Millions of enthusiasts in the United States now we have "free" broadcasting. The cost of good television were building their own sets, and the radio age was broadcasts is in the order of making good motion picture here to stay. Soon -with tens of millions of listeners films. And as everybody knows, production of a good getting programs -the advertised products via the radio motion picture film costs anywhere from a quarter of a waves paid handsomely for the broadcast effort. million dollars to two million dollars. Now let us turn to television. The situation here is What makes matters worse in television is that there far from parallel. To begin with, television must in its cannot be any "retakes." Inasmuch as a television pro- very nature be broadcast on higher frequencies (low duction must be carefully rehearsed and must be letter- wave lengths). That means that the reception range perfect at the moment of broadcast, the television direc- cannot be greater than an average of 25 to 30 miles from tor has no way of correcting any mistakes, as is the the transmitter. Now then, if the entire country is to case in motion pictures. be blanketed with television, this requires thousands of Therefore, a good television broadcast program would television transmitters. The capital outlay, therefore, of necessity cost more than a like motion picture pros for the television broadcast industry will be immeas- duction. Commander MacDonald thinks that the exces- urably greater than was the case with the broadcast sively high cost of television broadcasts cannot be met industry. At the present time we only have a handful of by sponsored advertising, as it is in broadcasting today, television transmitters in this country, in actual num- but that television programs should be paid for in some bers only six stations, now operating on a schedule, other way; either over line wires or by radio using plus three experimental stations. special equipment, where only those who pay for the Against this the radio broadcast industry has 1003 service would have sets that could receive such paid transmitters as of December 1945. Even if we soon programs. That is one angle. had a like number of television transmitters in the U.S., Dr. Lee deForest, of radio fame, has pointed out in they would by no means blanket the entire country to an article in RADIO -CRAFT (April and May 1945 issues), support an advertising- sponsored television program the simplest way would be to take a motion picture film that could conceivably pay out. To cover the entire na- of the production. This could then be edited before the tion with television trans- (Continued on page 853) RADIO -CRAFT for SEPTEMBER, 1946 821 TELEVISION PICKUP relay apparatus capable of relaying signals from the pickup point to a television transmitter within a 15 -mile range, was announced -ELECTRONICS last month by the Radio Corporation of America. This new radio relay equipment produces a frequency -modulated signal with approximately 100 milliwatts of power ;,,,,,,,,,,,,,r,,,,,,,r Items Interesting for the picture carrier. The band width permits reproduction of the finest de- The transmitter control unit is also plified is fed onto the coil at the bulb tail in the camera picture. It operates built into a carrying case. It contains end through a wave -guide and then at any selected frequency in the 6500 all the necessary operating and monitor- drawn off at the other end in the same to 7050- megacycle band. ing controls, plus a regulated power way. The use of a highly directional para- supply for transmission. Either of The wave travels along the coil at bolic transmitting antenna provides a these control units can be removed from the speed of light but because it follows signal gain of about 5000 times, with its carrying case and mounted in a rack the winding, it moves along the length a 4 -foot reflector, or 11,600 times with for permanent installations. of the tube at only a thirteenth of this a 6 -foot reflector, thereby providing an speed. Meanwhile, from the equivalent bulb -actu- power of 500 or 1160 watts, ally, an electron gun -a beam of elec- depending on reflector size, in the direc- WIDE -BAND amplification will take trons is shot through the inside of the tion of the receiving antenna. To obtain on a new meaning, as a result of a new coil down the stem in the same direction this high gain, a hook- shaped wave tube announced last month by Bell Tele- the wave is moving guide and at approximate- literally pours power into the focal phone Laboratories. ly the same speed, i.e., one -thirteenth the point of the saucer -like reflector, much Conservative figures for the tube speed of light. as the filament in an automobile head- show a power gain of 10,000 times over The speeds are not exactly matched, light sends its light to a concave re- a band width of 800 megacycles. By flector for intensification. The same however, and on the average the elec- comparison the present pentode tube trons go faster than the wave. They principle is employed at the receiver of 10 can give a power gain only times tend to slow down, though, and in so unit, where the parabolic reflector re- over a band width of 20 megacycles, and ceives the signal and concentrates the doing, they give up some of their energy a velocity- modulation tube, operating to the wave. As a result the wave gains beam into a wave guide to add another in the microwave range, gives the same gain of 5,000 or 11,600 times. The total a tremendous amount of energy and be- amplification over a band width of 10 comes many times amplified. effective signal gain from the trans- megacycles. mitter waveguide to the receiver wave Preliminary - The tube is remarkably simple. It is a tests indicate the tube guide is therefore approximately may amplify dozens of full color or 25,000,000 times with the smaller little more than a foot long and only a black and white re- few inches across. television programs flector or 132,250,000 times with the simultaneously-should anyone want to larger one. It does not even look much like an or- send that many at once. Or it might The control unit of the microwave re- dinary tube for it has a narrow, glass theoretically handle more than 10,000 ceiver, which is usually located at some stem about a foot long, flaring into a simultaneous cross-country telephone distance from the antenna, is mounted bulb on one end. conversations or over a hundred million in a small carrying case containing the Inside the stem, a long coil of thin words a minute by .elegraph! remainder of the receiver stages, the wire, or helix, runs video unit, and automatic frequency- from one end to the control amplifier, and a master meter, other. The wave as well as other adjustment controls. which is to be am-

The new tube which can handle 10,000 phone conversations at once. Left- Television pickup and relay set, with its recurving waveguide. 822 RADIO -CRAFT for SEPTEMBER, 1946 RADIO SURPLUS SALES are being handled in a "scandalous" manner, Sen- inuluulnlmnlmmu;mnnuu;:nln1 ncnlnonnnl'L` ator Wiley of Wisconsin charged last MONTHLY REVIEW month in a letter to Representative Slaughter, head of the House Commit- tee now investigating war surplus dis- posal Senator Wiley pointed particularly Technician 11111111111111111üIii 111111111111111111Cp:1'7Elnil: Illnlll1in111:IIIIIIIIIf11111n11111111111111h3 to sales of $200,000,000 worth of electrical equipment, from $400,000,000 ITEMS OF THE RADIO MONTH POLICING PLANS to minimize inter- worth declared surplus. Radio, radar ference and confusion in the greatly ex- and communications equipment are in- "Television is getting off on the wrong panded postwar radio spectrum went cluded in this surplus material. foot because the screen on receivers is He said ,priority claimants, such as T. into effect July first, states the FCC. wider than it is high," says James Wartime technological developments veterans and schools, had obtained sup- Mangan, industrial designer and public plies to the value of only $2,120,000, (foolishly have increased the usable spectrum relations expert. "This shape space from a prewar limit of 300,000 "while private, commercial sources got copied after the shape of the movie the- $198,000,000 worth." image kilocycles to 30,000,000 kilocycles and ater screen) necessitates a small of thousands of addi- Veterans and schools and colleges, makes impractical the televising beyond. Hundreds ' and tional channels will be licensed in this despite priority rights, said Mr. Wiley, re- of dancing acts and other features added space to augment existing radio "are being intentionally ignored by quiring full -length views. introduce many new WAA (War Assets Administration)," goes services and to "Before the television industry ones. Despite the vast new spectrum although they desperately need equip- much farther," said Mangan, "someone space available, the demand for radio ment. He estimated that "at the most" ought to be brave and different enough the supply, veterans obtained $50,000 worth and a channels still far exceeds to experiment with an image and making efficient policing of paramount schools and colleges another $50,000 screen that is about one -third higher importance. worth out of the total of $200,000,000 than it is wide. Television must be an When government began that has been sold. copy the federal art by itself and shouldn't try to policing the spectrum in 1911, after the or use the movies in any way!" passage of the first radio legislation, it RADIO COMMUNICATION was concerned only with a few ocean- growth has increased, due to war- New trend in servicing may be going steamers. Today, the government, time technological developments, to such marked by the recent establishment by through the FCC, is confronted with the an extent that some believe the art has Hallicraftere of six service centers for problem of preventing traffic snarls or been pushed forward a whole genera- the checking, repairing and servicing law violation on radio highways which tion, the Federal Communications Com- of their amateur, home, aircraft and were not even imagined before the war. mission reported last month. Expected marine radio equipment. increases in radio services are illus- Set up at strategic points with a com- "PIRATE AMERICANS" have drawn trated graphically in the accompanying plete stock of parts for replacement, the up plans for a commercial radio inva- chart. In tabular form, they are: centers will be manned by personnel sion of England, the London Sunday Standard broadcast stations, from selected for their ability and experience People charged last month. 1000 to 1400. in the servicing of Hallicrafters' radios. The paper states that regular broad- Frequency modulation (FM) stations casts are planned by a string of stations from 50 to 3000. stations from six to 200 or Milwaukee reports its first postwar on the Continent and in Iceland. These Television About 325 hams -mem- would be supplemented by powerful 300. ham meeting. on moored Radio -equipped planes from 3000 to bers and friends of the Milwaukee Radio broadcast stations ships just Amateurs' participated. Num- outside British territorial waters. 50,000. Club- is, of Aviation ground stations from 700 to bers of amateurs from Iowa and Min- Purpose of the "invasion" course, to profit from the rich harvest 2500. nesota, as well as Wisconsin hams, were service autos, taxicabs, present, and there were visitors from of advertising expected on these broad- Two -way for hams casts. Advertising is not accepted by the etc., from one city to 200 cities. Illinois, Michigan, and even two Radio -equipped railroads from one from California. The meeting was ad- BBC, but British manufacturers and Read of the Hallicrafters. distributors found such advertising - road to 150. dressed by Cy over Radio Luxembourg -very profit- Fire department radio from no cities able in the period just before the war. to 5000. Tests made by Bendix on the lines of The rumors were important enough Citizens walkie- talkie from none to the B. & O. Railroad prove v.h.f com- to be discussed in Parliament, where a 200,000. munication practical in tunnels. A spe- government hint that outside commer- Amateur operators from 60,000 to cial system which includes antennas at cial broadcasters might be subjected to 100,000. the tunnel mouths and a single wire "jamming" was fiercely attacked by In addition there will be thousands running through it, produces loud sig- Winston Churchill, who charged that of channels for radar, for point -to -point nals. the citizens' "right to listen" was being communication, for diathermy and many threateped. other safety and special services. Largest television audience at the Louis - P R O J E C T E D Conn fight was at Princeton, N. J., -5N- where 3000 saw the fight projected, on RADIO STATION a 16 x 22- foot screen. The exhibition was put on by RCA Laboratories, using EXPANSION -4K a 60,000 -volt kinescope.

Facsimile transmission from ground FIRE DEPARTMENT to plane was demonstrated last month RADIO by Finch Telecommunications of New York City. STIANDARD BROADCASTING A battery for use with lifeboat and life STATIONS raft transmitters, developed during the war, employs ordinary sea -water as the electrolyte. CHART C RADIO -CRAFT for SEPTEMBER, 1946 823 ATOM BOMB OVER BIKINI

.1 Radioman's Eye-Witness Story of the Great Experiment

SEVENTY million dollars worth direct results of the tests. Comic strip burst would blow a hole in the water of time, energy, equipment and writers injected Bikini into their ad- of the lagoon approximately 150 feet incidental expenses literally went venture strips and predicted all sorts deep and 600 to 600 feet across, and that up in a blaze of glory -and light of things. Human guinea pigs volun- the water falling back into this hole and color -when the fourth atomic teered for the privilege of being aboard would force itself into the air in a bomb to be dropped in the history of the the target ship, but were turned down column -a gigantic water spout four world was unloaded on a phantom fleet by the Navy for obvious reasons. Pub- or five miles high. The original estimate of seventy -seven ships at anchor in licity -mad scientists and pseudo- scien- had to be revised when in scale tests Bikini Lagoon. From the standpoint of tists predicted that scientific advance it was money well all the observers of Elliott A. Witten, RAmO- the CaArT'9 special correspondent tests were at the Bikini atom -bomb test, doomed to die at is well known to our readers Bikini. as a former Technical Editor In short, every- of the magazine and author of a number of articles, chief- body and his ly on problems of the ex -CI brother rushed in and serviceman. He was also to predict what not the author of the article even the scientists "Radio and the Atom Tests" which appeared in the July who actually issue. worked on the Like many another radio- bomb were ready man, he came up by the or able to servicing road, having been comment a radio repairman no lees on. than seven of his twenty -five The Navy found years. Joining the Army in it necessary to 1942, he was given special- create the position ized radio training at New .41 York University and the ¡it( of staff phenome- Universities of Iowa and Wyoming, later acting as instructor and nologist. A top sci- radar operator. Invalided out of the Army after combat service entist from the in the Air Forces, he worked as technician in a New York war Army's Manhattan plant, later as radio writer and editor. Is now a free-lance writer. Hobbies: Instructing radio classes in Radar antenna used in gathering atomic test Engineer District the Civil Air Patrol; painting. data, on the island of Aemende, Bikini Atoll. was chosen to fill spent. While $70,000,000 seems like a this job. His duty was to scientifically with small TNT bombs, only a slight lot, actually it comes down to fifty cents venture to predict what has never hap- depression was made in the surface. for every person in the United States - pened before and what was likely to The oceanography section of the tech- surely a small price to pay for a ticket happen during this test, the first of its nical staff started with a wave motion on Peace, the possible winner in the kind over water. In the course of pre- unit, added oceanographic surveys, and World Sweepstakes. paring for the Bikini tests, his estimates later radiological safety reconnaissance, No one -not even the scientists -quite were revised from time to time. For ex- which was discussed in the first article knew what to expect as direct and in- ample, at first it was believed that the in the July issue of RAnio-CaArr. The measurement of wave motion is the first phase of the oceanographic program. In this respect, the atomic bomb is a wonderful oceanographic tool. Knowing the point of release of the bomb, its time and the amount of energy released, the oceanographers were able to make exact measurements of the height of waves, their action in shallow water, their effect on the sea bottom, and their erod- ing effect on the beaches, in terms of both time and distance. Instruments for the measurement of wave motion fall into three general categories as follows: supersonic echo sounders, aerial photography, and surface photography. In addition, there were maximum water height recorders on Bikini Island and water level meters on several of the other islands of the atoll. The supersonic echo sounders or fathometers recorded the larger waves while eleven supersonic sounders on Joint Army -Navy Task Forcc Our l'hotus buoys recorded the passage of the short - Mother plane in background turns after releasing drone, in rehearsal for Bikini bomb tests. (Continued on page 872) 824 RADIO -CRAFT for SEPTEMBER, 1946 By R. E. PARMENTER

V.H.F. RECEIVER This 144 -148 Me Set Hua an Interesting Tuning Unit

INTEREST in very high frequencies A relatively new tuning system -the has resulted in a demand for a good, butterfly tuning capacitor -is used. Richard L. Parmenter was born modern receiver for the very short This provides practically linear tuning in Brockton, Mass.. 37 years ago. waves. Some of this demand has been and completely eliminates the noise from Became interested in electricity at the moving rotor. A manufactured type an early age-even while in grade supplied by modified war surplus gear. school. Took technical course in The v.h.f. war surplus receivers are a would have been used but none were high school and studied Electrical bargain to the experienced radio man available at the time. Cardwell has ad- Engineering at Northeastern Uni- who can alter them to suit his purposes. vertised two units, one having a range versity -specializing in Communi- cations. Became interested in am- For the beginner and probably for the of 11 to 14 µµf and the other of 6 ateur radio and operated a "ham" average experimenter and ham the to 11 µµf. If the reader prefers a station. WIJXF, on 40 and 80- superregenerative receiver would still ready -made part we recommend the seem to be the best bet. smaller size. It will provide better Q This receiver is easily built, the cir- at the frequencies desired. cuit is simple, the total cash outlay A 6SF5 was used in the first audio (even if all new parts are used) is stage. Greater gain is thus realized even nominal and its performance is very if the plate voltage supply is low. A satisfactory. 6K6 was used in the output section. The circuit is the self -quenched Plate and screen connections are

TO ANT. L2 9002 6SF5 01 6K6 oy6UTTERFLY 400V. SEE T 500K i /- K ¡'M" r' ,Dv'

II Fig. I- Except for the MICA TONAL 10 I SEE TEXT butterfly -tuned super - meter c.w. He has been 2K active on 25v. regenerative detector 5, 2'Fl, 2 and 1% meters. is a During the war SOuuf R.F.C. the circuit plain was employed at Beth -Hingham shipyard as key - 1/4W BANANA three-tube s.w. radio. 75K 30K worker on automatic fire -control 400V. wiring. Now employed at Aerovox PILOT Research Laboratory- working on design and construction of teat I equipment. Amateur radio and 3ViP fishing are his hobbies. RESISTORS I W. EXCEPT AS NOTED

9002 SOCKET CONNECTIONS superregenerator. A 9002 tube is used brought out to two banana jacks on the r.f. stage later if desired. This extra for the detector. It mounts in a "button" rear of the chassis for speaker connec- space also permits placing the audio type miniature socket whose contacts tion. The switch (SW) is for standby. section at some distance from the de- are very secure as compared to some tector. No dimensions are given for types of new sockets. A base connec- SIMPLE CONSTRUCTION JOB actual layout of parts since the photos tion plan is shown on the circuit dia- Construction of this receiver is not show approximate locations. gram (Fig. 1). difficult. A 7 x 10 inch chassis was used. The panel is a piece of masonite 6 This allows plenty inches high by 11 inches long. Holes for of room to add an (Continued on page 866) Left-Rear view of the receiver, showing the antenna- coupling link. Below -A front view. Note the boundaries of the 144 -148 me band.

RADIO -CRAFT for SEPTEMBER, 14b 825 By SANFORD ESSIG* BLACK -LIGHT TELESCOPE New Infra -lied Tube Permits Sight in Total Darkness

SEVERAL animals are popularly they were attached to the service helmet power supply, and is readily held in one accredited with the ability of night much as a miner's lamp, giving complete hand. vision. Such sight is dependent hand freedom while observing the ob- Extensive use of these infra -red tele- solely upon a faster eye lens and jective through the eyepiece. This model scopes applies also to signaling, to night they are helpless in the complete ab- was used by pilots of aircraft and made landing of aircraft, to assembly of para- sence of light. Man now truly possesses possible night driving at speeds up to troopers after landing and to all opera- clear vision in total darkness. 40 m.p.h. with infra -red filtered head- tions demanding that black -out condi- Such vision is made possible by an lamps; greater speeds with more power- tions prevail. electron -image tube designated the ful lamps. The image tube -the essential ele- 1P25, which was manufactured in large Properly dubbed the "sniperscope," a ment in infra -red electron telescopes - quantities during the war by the Farns- smaller type was mounted in sighting converts an invisible infra -red image worth Television & Radio Corporation position on rifles. Closely resembling a into a visible image. It consists of a and others. Instruments based upon the telescopic sight in appearance, it formed semi -transparent photo -cathode sensi- tube were extensively employed in war- gunsights, making possible hits on a tive to the infra -red radiation, an elec- time activities, particularly in the Pacif- target the size of a man at seventy -five trostatic electron lens system and a ic Theatre. They assisted all manner of yards in total darkness-a very formid- fluorescent screen. An infra -red image nocturnal activities, such as night driv- able device for night fighting. on the photo- cathode causes electrons ing, shooting, reconnaissance in air- A third model, the " snooperscope," is to be released in conformity with the borne, land and naval operations. an instrument intended for hand opera- image. These electrons are accelerated Operating on the principle of infra- tion in general use and reconnaissance. and focussed by the electron optical red detection, they were used in con- A small battery -powered infra -red system, shown in the figure, onto the junction with infra -red searchlights, searchlight is mounted below the tele- fluorescent screen where a visible repro- large and small -even with flashlights! scope or pickup device, the entire as- duction of the original image is formed. Light of weight and small in size, sembly attached to a pistol -grip handle. Response of the photo -cathode is con- Illustrating ease of operation, one typi- fined to between 8000 and 10,000 ang- cal strom *Research Dept., Farnsworth Television and general purpose instrument weighs units, the limit of human eye re- Radio Corp., Fort Wayne. Indiana. hut seven pounds, including battery and sponse being approximately 6750 ang- strom units. Therefore, the subject under observation is wholly unaware of OBJECTIVE LENS SYSTEM.. .ißí Epr =, CREEN EYE -PIECE LENS SYSTEM his vulnerability. RUBBER EYE -PIECE,' Alkali metals form the basis of all known best emitters, long wavelength response increasing with atomic weight. Therefore, caesium is used for a surface of high infra -red sensitivity. In processing the cathode, a layer of silver so thin as to readily REFLECTION transmit FROM TARGET IMAGE CONVERTER TUBE light is evaporated on the inside glass surface. The amount of silver deposited is, in fact, determined by its light trans- noon vOLTS mission. The silver surface is partially oxidized This captured German night -sight telescope worked with the and exposed to caesium vapor, aid of an infra -red image tube. then subjected to thermal treatment. Caesium reacts with the silver oxide to form caesium oxide and free silver. The final surface then consists of silver, a layer of mixed silver and caesium oxide with metallic silver interspersed in it, and a bound layer of caesium. The 1P25 tube, as shown in the figure, contains a four -element electron lens assembly, the final anode operating at 4100 volts; operation, in principle, is similar to that of the cathode-ray tube, electron microscope and other electro- statically- focused devices. A fairly large class of materials, termed phosphors, become luminous when bombarded with particles or radiation. The materials within this class which can be excited by electron bombardment are useful as fluorescent screens in image tubes. In view of several desirable screen requirements, such as high efficiency at The Farnsworth and RCA I P25 image tube, heart of Sniperscope and Snooperscope equipment. (Continued on. page 884) 826 RADIO -CRAFT for SEPTEMBER, 1946 By JOHN W. STRAEDE

AUDIO RESPONSE CORRECTION Compensation Circuits for Phonograph Retord Amplifiers THE average magnetic pickup acteristics of various records are shown. product of its intensity and its dura- should be followed by some equal- That labelled a corresponds to a large tion, so a partial compensation for ex- izing circuit for two or three of number of English records and that la- cessive duration can be achieved by the following reasons: belled b applies to many American discs. over -reduction in response at the peaks. is notes However, individual discs vary. It will In designing correction filters, it 1 -The lower frequency (bass) know just what is being are attenuated in most recordings, be noticed that the crossover frequency necessary to is generally lower for the English rec- aimed at, otherwise the filter is apt to usually at a rate of from 3 to 6 db per de- called the ords while these also have a more probe a flop. A simple but correctly octave below some frequency signed filter consisting of only two or "change -over frequency." The rate of nounced rise in the "lower highs." Gen. octave erally speaking, American discs have three elements can easily give results attenuation is usually 6 db per from an elaborate but because such a rate corresponda to more upper highs and lees bass than superior to those "constant amplitude" recording. the English records. The different fre- badly designed one. quency characteristics require different compensation circuits. 1M 1 250N 225N IMEG In Fig. 2, the frequency responses of TO Mgt. a typical good- quality magnetic pickup and an average crystal pick -up are shown. It will be noticed that while in both cases there is a peak at about 20K 20K 100K 4600 cycles, because both employ steel v T.01 TO AMPI.. 10 É000 0000 C10 CL needles, the crystal pickup has a rising Fig. 1- American and English record curves. bass characteristic in addition to bass Fig. 4-Circuits used for boosting the bass. resonance. 2-In some recording systems the POSITION OF FILTER higher frequency notes are given a OVERALL RESPONSE The position of a filter affects its ac- slight boost -there may be a gradual Now suppose we combine the four tion If connected directly after the pick- rise of about 1 db per 1000 cycles above graphs so far presented and see what up, reactive elements in the pick -up about 1600 cycles or there may be a we get. must be considered. If connected after broad peak around the 4000 to 8000 the first tube, the type of tube must be mark. w taken into account. In simpler amplifi- 3-Any pickup contains two resonant EX:E' SASS ers, some compensation can be left until frequencies; the lower or bass resonance the output stage. due to the pickup head vibrating to and Three main types of correction cir- fro and the upper or needle resonance IMIPLII cuits will be considered: due to the armature vibrating against ;AM 1-Resistance -capacity circuits (these the needle -tip (needles are not per- most the É 0000 10.000 are probably the interesting to fectly rigid). C100 l amplifier enthusiast and the easiest to The lower resonance is sometimes Fig. 3- Combination of the previou graphs. build). used-especially in cheap pickups -to 2 -Tuned circuits, including acceptor partially compensate for the bass cut in bans (series) and rejector (parallel) cir- is In Fig. 3, the rising of the crys- recording, but the upper resonance tal pickup gives just about the cor- cuits. just plain nuisance as it occurs at a very rect bass response to the American disc 3- Circuits in which compensation is audible frequency and is excited to a resonance of the magnetic made by varying the amount of negative by surface irregularities in while the bass large degree pickup provides almost enough compen- feedback. the record. sation for the lesser bass cut of the Eng- lish records. Possibly this is why cheaper American radio -phonograph combina- 20K .003 tions almost invariably use crystal pickups while most English "radiograms" employ magnetic pickups. (It should be 500 IOK 2MEG noted that the vertical scale of these graphs has been greatly exaggerated.) r The high frequency end of the graph b ,T.Ae 0001

10000 is still to be considered. High frequency 100 EIOOSO C L attenuation is usually obtained in the highs. F 9. 2- Crystal .and magnetic pickup response. amplifier by means of a shunt condens- Fig. 5 -Two circuits for cutting the er. Scratch and surface noise occurs at Overall frequency characteristics do No account is given of low -pass or all frequencies, high and low, but most - not tell the whole story. Although a band -pass circuits because - although ly around the resonant frequencies. resonance peak may be levelled out, restriction of unnecessary frequency A pickup filter is necessary then for there is still no compensation for the response is sometimes helpful in elimi- three reasons: To compensate for lack longer tine a note (recorded or nating background noise and in scratch of bass, to reduce excessive high -fre- "scratch") is played if it occurs at that reduction -the circuits are difficult to quency response and to reduce the re- resonant frequency. When a sound is adjust and not at all suitable for the sponse around the resonant frequen- heard for a fairly short time, its audi- average amplifier enthusiast. cies. In Fig. 1, the frequency char- bility is largely proportional to the (Continued on page 877) RADIO -CRAFT for SEPTEMBER, 1946 827 Baf CAPT. L. A. OLSON ARMY - AMATEUR RADIO CLUB Sirynal Corns llant Organization at Fort Monmouth. N.J.

FORT MONMOUTH, New Jersey, W2OEC (formerly of Moss Radio Com- operating schedules will be maintained world renowned as "the home of pany, Russellville, Arkansas) obtained with amateur stations all over the world the Signal Corps" is making a new FCC approval of the club charter and to relay routine amateur traffic, as well claim to fame. The idea of having the station license. The club charter, as emergency messages. The Field Di- the world's outstanding amateur radio patterned on the American Radio Relay rector of the American Red Cross at station at Fort Monmouth was conceived League model charter, was adopted by Fort Monmouth will keep in close touch in the mind of Colonel Brooke E. the members of the club on April l'0, with the club so that certain emergency Sawyer, W6CV, (now Mr. Brooke E. 1946. messages may be transferred to usual Sawyer of Redlands, California). Al- The club will primarily serve the en- commercial facilities by the Red Cross. ready The Fort Monmouth Radio Club listed, officer and civilian personnel Code and theory classes will be con- has been organized, chartered, and is stationed in the Signal Corps schools ducted by the club to assist members in operating under the call W2OEC in an and laboratories. It is expected that obtaining amateur radio licenses. effort to earn the reputation envisioned many messages to and from military Due to the concentration of Signal by Col. Sawyer. The trustee and secre- and civilian personnel on overseas Corps personnel as well as the presence tary of the club, Major John M. Moss, duty will be handled. Round -the -clock of a number of commercial radio research laboratories, the area has an un- precedented concentration of hams and ex -hams, many of whom are divorced R A D I O T R A N S H I T T E R BC-610 from their own means of communication. The officers of the Club have calls E.C.OR TAL OSC. BUFFER -DOUBLER INTERMEDIATE P. A. POWER AMP. from the First, Second, Third, Fourth and Eighth Districts, and there is an equal spread of calls in the membership. Indeed, there are rumors of a new over - the -air club, composed of amateurs who have worked all United States districts S P E E C H A M P L I F I E R within Monmouth County, New B C- 6 1 4 Jersey. MODULATION LIMITER n A wide assortment of communications gear has been obtained by the club and DRIVER MODULATOR it is planned that a one -kilowatt transmitter will be maintained on each of the amateur bands below 30 megacycles. The equipment now installed includes four radio transmitters BC -610 (major com- P.A.& MOD. ponent of the famed SCR -299 and POWER SUPPLY SCR -399), two radio SPEECH transmitters BC- AMP. AMPL. EXCITER POWER SUPPLY 452 and one radio transmitter BC -339. POWER TO KEYING See Figs. 1 and 2 for block diagrams SUPPLY CV OP CIRCUIT KEYING MONITOR of the BC -610 and BC -339 transmitters. The BC -452 transmitter consists of an 837 crystal oscillator, 807 buffer stage, and a pair of 813's in push -pull as the r V final radio frequency amplifier modu- DYNAMIC MIKE CARBON MIKE lated by a pair of 805's. A ten -meter rotatable horizontal beam

FIG.I antenna built by Cpl. Jack D. Rode -

3 3 baugh, WBLIO R A D I O T R A N S M I T T E R B C- 9 (formerly of Brush De- velopment Company) has been erected on a fifty -foot pole. This beam antenna 05C..E.CJ RTAL IST RJ AMP. 2ND R.F. AMP. 3D R.r. AMR consists of a single fed element, and a two stacked untuned reflectors, as shown in Fig. 3. The excited element is fed by a 72 -ohm coaxial cable. Two eighty -foot poles were obtained for mounting POWER AMPL. the POWER SUPPLY eighty -meter folded dipole antenna of Fig. 4. When the holes for the eighty - foot poles were being dug water was struck at a depth of four feet, consequently six -foot concrete aprons had to be built around the base of each pole. Additional guys were required to give adequate support to the poles, which

OSC.POWER SUPPLY COMB.PLATE & BIAS POWER SUPPLY EIAS POWER SUPPLY Fig. I, above and Fig. 2, below -Block dia- FIG.2 grams of the BC -610 and the BC -339 transmitters, first to be installed in the new club. 828 RADIO -CRAFT for SEPTEMBER, 1946 An interior view of fhe ham shack. Adjustments are being made on Part of the 80 -meter folded dipole antenna, with the transmission the BC -610, which was actually on the air as the photo was taken. line which is b-ought in on telephone poles to the shack at left. now extend approximately 76 feet above used for wiring and testing equipment. Property Officer -1st Lt. E. J. Mazzi. the ground. This 80 -meter antenna is As can be seen in the photos, there is Activities Manager -Cpl. Jack D. Rode - oriented so that its directivity centers already a considerable amount of equip- baugh, on the middle of Missouri. W8LIO. It is expected ment in the transmitting shack, and Chief Operator-Pfc. Peter N. Borsie. that it will give fairly complete coverage though the skids under one of the trans- Already of the United States. excellent contacts have been mitters indicate that some of the ma- made with amateur radio telephone At present the club has only two re- terial is still in the process of installa- stations ceivers, more in California on the 80 -meter but are expected shortly. tion, it is expected that by the time this band and it is A BC -1004 expected that many GI (Hammarlund Super -Pro) appears in print everything will have and ex -Gi amateurs will is used for the lower frequencies maintain con- while been "shaken down" and the Club will tact with the Signal Corps and Fort a Hallicrafters Model SR -24 with a con- be operating on a regular routine. Monmouth verter is used on through W2OEC. Schedules the higher frequencies. The following is a roster of club of- will be increased Building 498 at Fort Monmouth in number and oper- has ficers: ating time expanded to a full been authorized by Colonel twenty- Hugh President -Capt. Edward L. Neilsen, four hours daily, as soon as traffic in- Mitchell (Commandant of the Eastern W4IAI. creases sufficiently Signal Corps Schools) as to make it practical. the club head- Vice President---M/ Sgt. Phillip H. Hus- The Club would like to make contacts quarters. The building has two rooms, ton, W3EHB (who served in China with any similar Army- Amateur clubs one of which will be used as a lounge with the Office of Strategic Service for visitors throughout the United States (and else- and as a classroom; the as a major). where, if such exist). other room will house the equipment Secretary -Major and will be the operations room. Two John M. Moss, small shelters will be used as workshops the trustee of for persons who want to build their own W2O EC. amateur equipment. One shelter will Treasurer - Pfc. contain equipment for drilling and Francis E. La- punching chassis while the other will be joie,ex-W1HXD.

Right, foreground -10- meter, background -80 -mater antenna. Below, Figs. 3 and 4- Details of 10- and 80 -meter antennas, respectively.

DETAIL ROTATING OF MOTOR AND SELSYNS OMITTED ID" UNTUNED REFLECTORS

1/2 WAVE DIPOLE

DETAIL OF COAXIAL CONNECTION

10 METER BEAM ANTEMIA

FIG.3 ------1X2A------I 6'

DOMEIER FOLDED DIPOLE PLANE OF ANTENNAS IS HORIZONTAL FIG.4 600a LINE TO X ITTER

RADIO -CRAFT for SEPTEMBER, 1946 829 .\°N,`" GERMANIUM CRYSTAL PROBE Another Valuable Application of the Germanium Crystal

THE majority of present-day Vac- small size. The circuit is that of Fig. 2. quencies as high as 100 mc. The input uum Tube Voltmeters are essen- The capacitor C is .01 µf and the func- tially d,c. indicating devices. A tion of R is taken over by the divider ó input of the vacu- NOT rectifier unit is employed to permit resistors across the INPUT OUTPUT measurement of a.c.voltages. um tube voltmeter. In operation the GROUND URT Many factors influence the choice of VTVM is set up to measure negative 0 o the rectifier unit and its arrangement d.c. voltage. Full scale meter reading of fig. 2-A diode probe with germanium crystal. with respect to the d.c. indicator. Since 1.5 volts d.c. may be obtained with the operation over a wide frequency range circuit of Fig. 2 when 1.5 volts a.c. is ap- impedance of the unit shown was found is desirable, it is necessary to make all plied to the probe. To increase the d.c. to approximate one megohm at 1000 cy- a.c. leads as short as practicable. More- output voltage, the value of C must be cles per second. The output is non -lin- over, linear rectification is preferable increased. A value of .01 µf or less is to ear on the lowest range and the meter so the d.c. indicator deflection will be be preferred, however, in order to keep must be calibrated accordingly. A linear directly proportional to the magnitude the input impedance at a high value. scale, however, is sufficiently accurate of the a.c. voltage. An exploded view may be seen in the for most purposes. second photo. The front row of this pho- It is to be emphasized that the a.c. UIl to shows (left to right) the capacitor, C, voltage applied to the probe must be lim- NOT -B+ DIOD as it is soldered to a short length of ited to somewhat less than 50 volts. To al double voltage, two crys- INPUT pointed No. 8 wire and the tiny crystal the applicable and its mounting. The bakelite tubing tals may be used in series. fitted into the plastic case cap and the The above material is considered GROUND case proper are shown in the second merely suggestive. It is hoped the ex- row. In the background of the first perimenter will find many new uses for Diagram of standard type diode probe. Fig. I- photo rests the 7 -prong plug which feeds the crystal. Doubtless, variant circuits A vacuum -tube diode rectifier, mount- the d.c. indicator. can be adapted to special requirements ed in a convenient probe and arranged The crystal will operate well at fre- to suit the user. to feed the d.c. section by means.of a shielded cable, is admirably suited to this purpose. A wide variety of small vacuum tubes may be conveniently used. In general, it is necessary to choose tubes having a low input capacity. Thus the input impedance will be sufficiently high to pre- clude loading of the external circuit. With the advent of the new Germa- nium crystal -diode (Sylvania 1N34), the constructor has a useful device which simplifies probe design. Most of the disadvantages of vacuum -tube diodes are eliminated. A comparison of Figs. 1 and 2 will show immediately the simplicity of the crystal version. Fig. i illustrates a The crystal probe in its small penlite case. typical vacuum diode circuit. Fig. 2 shows its crystal counterpart. Note that a small battery and variable resistor are needed to balance out the a contact potential of the diode. The prop- erties of the Germanium crystal have been adequately described in the literature.* Hence no attempt will be made to discuss the theory of operation. An actuàl probe will be described. The probe is simple to fabricate. It was built into a small penlite flashlight case details of which may be seen in the photo, which shows its use in conjunction with radio enthusiast Russell Suthard's version of the "Electronic - Omnichecker".** Note the extremely

* See "Germanium Crystal Diodes"-Cornelius, Eiectronies, February. 1946. Exploded view of probe. Crystal is at center. "H.F. Crystal Diodes"- LeDuc, RADIO- CRAFT. March, 1946 ** RADIO-C81rr. June and July. 1946

830 RADIO -CRAFT for SEPTEMBER, 1946 By CARROLL UTERMANIEN

LINK - COUPLED CRYSTAL SET A Selective Receiver with Surprising Distance ,Mange

THE Two Timer is a new and differ- times exceeded that of local WITH ! Or- and the detector will not be coupled by ent type of crystal set, and should dinary "run -of- the -mill" DX includes stray capacities. This is most important, appeal to those who have been WWVA, WBBM, and WGY. because if the units are jammed together searching for a truly dependable All stations heard were positively in a small space the operating efficiency mineral operated receiver. Unlike the identified; and, for the most part, the will be but mediocre. I average set of its class the Two Timer signals were loud enough so that the The coils L1 and L4 are exactly alike, offers extreme flexibility, a feature that programs heard were perfectly under- and are wound with No. 26 enameled standable. The best wire on forms 1% -inchs in diameter as dx "catch" to date follows: Wind 10 turns and make a tap; was KOY (Phoe- from this point make taps at the follow- nix, 1000 watts on ing numbers of turns: 15, 20, 25, 30, 550''{c) heard while 35, 40, 45, 50, 55, 60; which means a local WCAO (Bal- total of 11 taps and a total of 385 turns timore, 5000 watts of wire. The 11th tap is the end wire on 600 kc) was still on the coil. L2 and L3 are alike in that on the air! There each is wound on 1% -inch diameter seems to be no limit forms. Consisting of 30 turns (each to the dx possibili- coil) of No. 26 enameled wire, tapped ties of the Two at the 10th, 20th and 30th turn, these Timer, and yet the coils fit inside LI and L4 and are joined antenna require- together by a twisted -pair link -line. Any ment of this set is suitable wire may be used, and the such that a 100 ft length is unimportant, though it will inverted "L" with seldom exceed 20 inches in actual prac- a 50 ft lead -in is ANT tice. When the coils are completed a sufficient for most thin coat of Duco household cement will locations. A shorter antenna may be do much to preserve them and will keep employed for purely local reception. the works from falling apart with con- The "Cut -your- antenna -to- the -listen- stant use. ing- frequency" theory was given the well Band switching is accomplished by known "Bronx cheer" when such long one of two methods: battery clips or wave stations as the Altoona (Pa.) and tap switches. UNE The author made his own LINN Washington (D.C.) airport control tap switches from antique rheostats, towers were heard, along with the air- but battery clips were used to advantage craft beam stations BO, KW, WA, and in the original experimental model. If NHK; while on short wave the police you use switches DO NOT attempt to L I L2 L3 L4 stations WCK, WPDP, WPFS, and "lase" or bind the wires to and from WPFH were heard; as were the Inter- the coils and switches. This might make Above -The Two Timer from the front. Link national 'phone stations WNRX and for a neat job but was found to be detri- lead extends from coil. Below -Schematic of WLWK. mental the set. Coils LI 12 to the overall efficiency of the and L4 have taps each. Before starting the actual construc- receiver. tion of the receiver it would be wise to Assuming that the antenna and is wholly responsible for its unusual make a thorough study of the schematic ground and earphones are connected, bandspread and extended frequency diagram. It should be particularly noted and that a "hot spot" has been found range. that the Two Tinter consists of two sep- on the crystal, the first procedure is to Consisting of two separate units (an- arate units. They may be mounted on (Continued on page 875) tenna tuner and detector) and employ- the same baseboard ing link coupling, the receiver is operat- and panel, yet they ed much in the same manner as a one- are, electrically, as tube regenerative set; one dial is used much separated as for tuning while the other is used as a if they were miles sensitivity apart. This means control. that the coils Living just outside Baltimore (Mary- should be mounted land) the author has heard such stations at right as WGN, angles to WOR, WABC and CBL, short- each other; or on ly after sunset of a winter's evening. a different plane to Later in the evening it was not uncom- each other; and mon to log other stations like WSB, that set WWL, WKBW. the should and After our local sta- be wired in such a tions sign off (excepting one, WITH, manner that the an all -night station) the dx really rolls antenna coupler in. . . with XEG, CBM, CMAC and CMAQ, WIBC, and KXEL being heard Right -Rear view of regularly. WLW, WTOP, WCKY and the Two Timer. Twisted WHAS are logged nightly. The signal leed is the link cou- strength of WLW and WHAS has at pling line.

RADIO -CRAFT for SEPTEMBER, 1946 831

_ 4 e ,a41111Nk.lm 'M By NORMAN CHALFIN

REBUILDING A TELEVISER Modernizing the Pre -War Television Receivers

IT will be at least a year before many new television sets can be produced. Those who now have kit -constructed television receivers may be interested in improving their sets with a few simple changes and additions. The circuit diagram of a typical television receiver kit (Andrea KTE5) is shown in Fig. 1. Changes that have been made are shown in the circuit at the points marked with letter designations. Separate drawings show each of these changes in detail. At "A" the original circuit was revised to include a type 6AG7 as the video output amplifier in place of the 6V6 which was used in the original circuit. In addition to base connection changes the dropping resistor in the screen circuit must be reduced to a value of 25,000 ohms, 5 watts. This change will result in an improvement in brightness and overall detail. When 1852 /6AC7 can wired for the 6AG7 an Chassis changes necessary for new FM sound channel are shown In photo above. be used interchangeably if the lower filament drain of the latter is preferred. Its lower transconductance will make no difference. Changes "B" and "C" are substitution of the 6SN7GT tubes the chassis is desirable but impractical a .006 µf capacitor to ground with con- for the 6F8G's used as vertical and in this case unless a separate power sequent increase in signal. horizontal deflection voltage amplifiers. supply is constructed, as described The changes described above are all A number of base connections must be later. designed to improve the overall per- changed. This brings all connections At F, the insertion of additional dif- formance of the receiver in its present below the chassis. The cathode -coupled ferontiator elements as shown will form. The balance of this article is de- circuit shown in "D" applied to the ver- give improved horizontal synchroniza- voted to the discussion of more ambi- tical amplifier improves the vertical tion and prevent "tearing" of the pic- tious changes of an experimental nature uniformity. This can be seen in the ture by random noise, static or ignition designed to make the author's set adapt- equalization of the lengths of the ver- pulses. The values indicated were satis- able to larger tubes without necessitat- tical wedges in the test pattern. factory for the author's equipment. Ex- ing further changes. The change made at "E" reduces hum periment may provide better values for As this is being written the new chan- pickup in the vertical height control the reader's set. A similar addition of nel assignments for the New York area lead in the low- frequency (verti- leads. It consists of shielding the elements SOLDER AT 50a44a MICR SOLDER AT from the plate coupling capacitor of cal) sync separator string will pre- CENTER TAP PLATE END from the 6N7 vertical sweep oscillator to the vent random pulses triggering the SEC. PRI. picture height control, and also shield- vertical sync out of control, resulting in .-:,...... ing the lead from the slider connection the picture rolling vertically. This is t of this control to the grid of the first shown along with circuits for horizontal half of the 6SN7GT (or 6F8G), verti- sync in Fig. F. cal amplifier. Use of the contrast control on the au- lí . Hum picked up in the video circuits is thor's set to lower the picture signal PRI. t--'ScC. evidenced in the appearance of horizon- level or reduce contrast also brought tal dark areas across the picture which the sound level clown. This condition is 3.30auf 3-30r0,f may remain stationary or move slowly eliminated by lifting the 1000 -ohm e ' o in the vertical direction. Another indi- cathode bias resistor in the 1852 mixer Fig. 2-How the discriminator coil is made. cation of hum is in the appearance of off the contrast control and grounding "S" shaped sides in the raster, with con- it. Thus the contrast control operates are announced. They are Nos. 2, 4, 5, sequent picture distortion. This type only on the video If. and cannot affect in the range below 100 megacycles. The of hum is generally the result of either the sound level. This is illustrated at removal of one full turn each on the hum voltage in the horizontal deflection G. If the cathode bias resistor is grid and tickler of the oscillator coil, circuits, or is picked up directly at the changed from 1000 ohms to one of 260 and the grid and antenna secondary deflection plates from electromagnetic ohms, increased signal will result in re- winding of the antenna -input coil will fields surrounding components on the mote locations. The unby -passed 40 -ohm make possible tuning all three chan- chassis. A soft iron or "mu" metal pipe resistor in the modulator cathode above nels. This appears at H in Fig. 1. A of suitable diameter used as a shield the 1000 -ohm resistor improves high new switch will be required to accom- around the neck of the cathode ray tube frequency performance of the modu- plish the change. It will more than like- will reduce the pickup from such fields. lator tube. Some of us have either shortly be necessary to revise some existing Separation of power components from ed out this resistor or by-passed it with (Continued on pago 879)

832 RADIO -CRAFT for SEPTEMBER, 1946 RADIO -CRAFT for SEPTEMBER, 1946 833 By JOHN B. LEDBETTER

,," ,. ,4 \. " o \ a `\\. llow These Important Devices Are Constructed and Used

IMPORTANT factors in the design of characteristic to frequencies beyond 10 Potentiometers, rheostats, ladders, broadcast audio equipment are oper- megacycles when the terminal leads "L" networks and "T" or "H" networks ational and structural problems pre- were properly shielded. A typical fixed are the basic types of attenuation net- sented by the audio control panel or pad is shown in Fig. 1. works, the latter three types being more mixing console. Fixed pads are generally classified as commonly used in mixing circuits. Since various types of fixed and either "T" or "Balanced H ". There are From the above types of networks variable attenuators go to make up the also a number of additional types known have sprung derivatives such as the greater part of audio mixing equipment as "Ladder", "Pi", "U", Balanced "U", balanced and unbalanced forms of it may be well to touch upon some of "0 ", Balanced "0 ", "L ", etc. These are rheostat, potentiometer, "LL ", "LR ", their more important circuit applica- derived from the two general types "T" bridged "T" and bridged "H ". Some of tions before discussing the conventional and Balanced "H ". Pads may be made these are shown schematically in Fig. 2. audio mixer. to match any circuit impedance to an- Because it cannot maintain a constant Attenuators are essentially resistive other at any desired insertion loss. impedance at various settings the type networks, accurately calibrated to give Fixed pads are probably used more a known insertion loss and designed to extensively than any other single piece match the terminal impedances of as- of broadcast equipment. Some of their sociated input and output circuits be- more common uses are: IN IN 1 impedance transformers (for ex- tween which they are used. -As OUT OUT ample, to match a 600-ohm output to UNBAL.RNEO. Co--- a 600 -ohm line). UNBAL. POT. 2 -To isolate each branch of a multiple - feed circuit from the program bus. N 3 -To bridge a program bus and provide a simultaneous feed to a network of monitoring speakers, at different cNBAL.'LR' levels if desired. 4 -To combine multiple -channel circuits. volume in- IN 5-To allow switching of a IN Fi OU dicating meter from one circuit to another of different level or im- t pedance. UNBAL.'LL" BRIDGED-TEE' 6-To balance the output of several IN monitoring speakers connected OUT across amplifiers of different output

Fig. I -Fixed attenuator (balanced -H type). levels. 7 -To provide the proper amount of in- be basically sertion loss in frequency response Attenuators may divided ALANCED UNBAL.LADDER into two classes, fixed, and variable. measuring equipment. B- YR" T The fixed type is more often referred 8-As a standard reference in com- IN to as a pad, while the variable attenu- parison resistance measurements. N ator is commonly known as a fader, pot 9-To provide isolation between pre- OUT program Co or volume control. amplifiers, mixing circuits, OUT A fixed pad usually consists of a amplifier and transmitter, at the IN OU number of card -type resistors non- same time attenuating or reducing IN BA L AN CED 'L L w inductively wound on thin strips of the output of each unit to the proper BALANCED POT. bakelite and designed to give constant level to prevent overloading, dis- impedance over a wide range of fre- tortion and.cross -talk. IN quencies. Well- designed pads have been In a typical application, four pre- OUT found to maintain a constant -impedance amplifiers feed into a high -level mixer. c a OUT Two of them are used for microphones, IN OUT the other two for turntable equipment. IN Output of microphones ranges approxi- BALANCED "N" BALANCED RHEO. mately from -85 db to -75 db; that of db. IN - OUT the turntables is about -50 Since OUT it is desirable to provide an equal level in each leg of the mixer circuit, both to maintain similarity of fader control settings and to prevent cross -talk or overloading of one mixer leg, a pad of loss (about 30 db) OUT the required insertion IN BAL .LADDER IN OUT and proper terminal impedance is placed RALPH " BRIDGED in the output circuit of the turntables. It is usually connected between the pre- Fig. 2- Typical attenuator networks. amplifier output circuit and the input Another balancedH network of lower wattage. of the fader. 834 RADIO -CRAFT for SEPTEMBER, 1946 ...... ,,..,..r+:...... -;iiNi:...Y4;).MF.tí6* . G.

action removes any dirt or other matter from between the rotor blades. A thin film of lubricant is then applied to the IN ^f OUT IN pI; T blades and the cover replaced.

HIGH VS. LOW -LEVEL MIXING IN IN RI_R iN Faders are usually connected in series or series- parallel, depending on the 2- CHANNEL SERIES 2- CHANNEL PARALLEL number of channels used. They are fed to subsequent stages of amplification RI =RIN through a 1 :1 ratio isolating trans- IN IN former which has an electrostatic shield between windings and a grounded center -tap on each coil winding. The trans- IN former eliminates cross -talk and stray noise pickup, in addition to acting Typical variable attenuator (ladder network). RI as an impedance-matching coil where IN IN RI,2R IN 50-ohm or 200-ohm faders are connected mixer point), where local announce- 3 to a 500 -ohm line. 3- CHANN.PARALL SEP. 3- CHANNEL PARALLEL ments are inserted, and the combined Two types of mixing systems, high - programs fed to either the third mixing level and low- level, are in use. Each has point at Master Control or to the speech its own merits. (See Fig. 4). High -level input equipment of the transmitter. N IN mixing is accomplished by feeding each Keynote in studio console design microphone or turntable output through should be simplicity, flexibility, ease of a stage of pre-amplification and thence operation and quick access to all as- IN IN to the mixer, the action taking place at sociated gear, with neatness and corn - mil the comparatively high level of approxi- pactness playing important parts. De- mately -40 db. In low -level mixing, sign simplicity reduces percentage of IN outputs of the various microphones are operating error by eliminating elements fed directly into a mixing circuit and RI thence to a pre -amplifier. IMPEDANCE OHMS IN DB IN RL3R In the field, low-level mixing makes 600 60 4-CHANN. PARALL.SER. 4- CHANNEL PARALLEL compactness possible in remote amplifier design. Only one amplifier need be SO Fig. 4- Typical mixer networks. unit used, instead of one for each microphone . i11Mlii Il dA' circuit. In the studio, the advantages Ei rL of 3 ®J.I/Ií.l.if 30 high -level mixing more than outweigh i-.S` El1rp "L" fader is used only in circuits where the slight disadvantage of increased Io such variance may be tolerated . or de- unit cost. High -level systems have an sirable. In mixer circuits and other con- inherent noise level 10 db lower than o 0 2.4 6 8 10 12 14 6 10202224262830 stant- impedance networks, attenuators the best type of low -level circuits, and -- CLOCKWISE ROTATION such as the "T ", "H ", and Ladder must a corresponding decrease in sensitivity to be employed. The "T" is used in unbal- tube hiss and the "shot" effect of Fig. 3 -Curve of attenuator pictured above. anced circuits, and the type "H" fader amplifier input tubes. where balance must be maintained. of confusion, while flexibility of oper- The ladder -type attenuator is more STUDIO CONTROL CONSOLE ation allows adaption to a wide variety commonly found in mixer circuits. Part Since the mixing panel or console is of programs, and facilitates easy switch- of its popularity is due to its noiseless the central control and distribution ing or circuit patching in case of operation and excellent frequency char- point for all programs originating in equipment failure. Flexibility is greatly acteristics. It represents a distinct ad- or outside the studio, it may well be increased by terminating the input and vancement over the "T" and "H" types, termed the "heart" or "brain" of the output circuits of all pre-amplifiers, am- affording a constant impedance in both entire program facilities. In fact, one plifiers, attenuators, keys and other input and output circuits over an at- can hardly name a type of program in operating facilities in a jack strip or tenuation range from 0 to 45 db, beyond which at least two mixing points are panel, the circuits being nornxalled to which the attenuation gradually in- not employed. A certain type of net- allow transfer of any part of equipment creases to infinity. The dial is calibrated work program includes mixing and pick- to another circuit. in 1.67 db steps (Fig. 3). up points in a number of widely separ- The input and output terminations of The resistance ated cities, with the master control the line or program amplifier are usu- elements of attenuators ally connected are composed of unifilar windings on point being located in still another city. to a "multiple" set of thin In another case, a remote pickup, con- jacks which allow patching into either bakelite strips or non -inductive circuit without wire -wound spools, either type of con- stituting one mixing point, is fed program interruption. struction allowing production of pads through a studio mixer (the second (Continued on page 863) capable of a noise level lower than -150 db. Contact arms are of heavy, multi -leaf construction. One set of leaf fingers makes contact with the outside resistance -contact studs while the inner set makes contact with a rotor slip -ring. The aluminum back cover is removed to allow access to the contact points for cleaning, a process which consists mainly of wiping the contact points and rings with either carbon tetrachloride or a mixture of half alcohol and half ether, and lubricating with a very small amount of Haven or fine clock oil. A small amount should be applied to the wiping arm, the arm rotated several times, and then the oil wiped off. This Appearance of the RCA 76 -B2 Studio Control Console, a typical and commonly -used type. RADIO -CRAFT for SEPTEMBER, 1946 835 THE POSTWAR RADIOSL Arvin Model 444

the THE Arvin Model 444 is one of the The Model 444 uses a 12SA7 mixer - condenser gang is insulated from second detector, a.v.c. chassis and cabinet to prevent the user more unusual post -war radios in its oscillator, 12SQ7 class. four full -size tubes in and a.f. amplifier, 50L6 -GT a.f. output from being shocked by coming in con- It uses of an efficient a.c: d.c. superhetero- and 35Z5 -GT half wave rectifier. tact with a "hot" chassis. The rotors dyne circuit. It is housed in a cabinet of A 25 -foot "hank" antenna replaces the condensers are connected to the modern design 61/2 inches long by 5 the relatively inefficient loop antenna a.v.c. line. inches high by 4 inches deep. From commonly used on sets,of this type. The There is no i.f. stage in this receiver. all outward appearances, the cabinets secondary of the antenna coil is tuned The 455 -kc i.f. signal from the plate seem to be made of thin plastic. Close by one section of the cut -plate ganged of the mixer is transformer coupled examination shows that they have been tuning condenser. direct to one detector diode. The B -plus stamped from heavy sheet metal. Care- The smaller condenser section tunes lead to the mixer plate is connected to ful tests discovered no cabinet reso- the oscillator, which is a modified Hart- a tap on the primary of the i.f. trans- nance or "ringing" even at high volume ley circuit with the tickler coil con- former instead of to the bottom of the levels. nected in the cathode circuit. The tuning coil in the conventional manner. This connection increases the amplification .00z 50L6GT re and selectivity of the set. The second detector uses a standard half -wave circuit. A 2- megohm volume control is connected so that it will serve as a diode load for the detector. The d.c. voltage drop across this resistor is filtered by a 4.7- megohm resistor and 100 -µµf condenser and used as a.v.c voltage for the mixer. The a.f. signal is fed to the grid of the triode section of the 12SQ7. Resistance -capacity coupling is used between the plate of the 12SQ7 and the 50L6 -GT; a pentode connected, beam -power amplifier supplies more than 2 watts of audio power to a 4 -inch PM speaker. The tuning dial, 2 inches long by 11 inch high, is calibrated at 550, 600, 700, 35Z5-GT 'W 900, 1200, 1400 and 1600 kc. In each (Continued on page 873) Diagram of the Model 444. Positive feedback in the i.f. circuit is especially interesting.

view the receiver. Parts are standard midget type. The Arvin out of its cas,. Cut -plate condenser is plainly seen. Under -chassis of SEPTEMBER. 1946 836 RADIO -CRAFT for ., 4.. EQUIPMENT

Realizing the Most from a Meter in Radio Servicing

TEST equipment used by radio - The single -range shunt (Fig. 1) con- total circuit resistance is 1350 ohms for servicemen must cover a large sists of a resistor placed across a me- all the resistances and 150 ohms for the voltage, current, and resistance ter, thus reducing its sensitivity. If we meter or 1500 ohms. range. Voltages may be as low as a assume a meter with a sensitivity of 1 R total few microvolts in radio receivers and ma and a resistance of 100 ohms (100 R needed - as large as 10,000 volts on peaks in tele- millivolts), and desire to measure 10 ma N (multiplication factor) vision receivers. Currents may be as The multiplication factors for the va- high as 10 amperes in automobile re- rious ranges would therefore be ceivers and as low as a few microam- Fig. I -A simple shunt. x7.5, x37.5, x150, x375, x7,500, x37,500 peres in the plate and a.v.c. circuits. designed to step up and x75,000; t h Resistances may be a fraction of an a current -carrying the resistances would be- ohm and may run as high as sev- capacity of the meter by a multiplication 200 ohms, 40 ohms, 10 ohms, 4 ohms, .2 eral million ohms. The extreme ranges, factor of one hundred. ohm, .04 ohm, and .02 ohm. make it imperative that the user know An additional 1150 -ohm resistor com- exactly what is happening in his tester. pletes the circuit. The higher shunt A working knowledge may mean the of current, a shunt is constructed so that resistance is for improved damping. The difference between a quick repair and a 9 ma flows through the shunt. actual resistances used are 160 ohms, 30 burnt -out tester and the loss of the Therefore the shunt must furnish 9 ohms, 6 ohms, 3.8 ohm, .16 ohm, .02 money invested. 1 -ma paths in parallel, while the meter ohm, and .02 ohm, as they are all in The D'arsonval is the foundation is the tenth. This gives us a formula series. movement for most radio test equip- for calculating the shunt resistance, ment in use today. This part is the which is of the tester. heart Resistance of the meter It consists of a wire coil rotating on 41150 pivots, set in jewels and mounted in the 200a-+ No. of times range is multiplied - 1 .F field of a powerful magnet. Springs - -y mounted above and below the coil serve If the shunt is to have 9 times the - as connectors to the coil, allowing the current -carrying capacity of the meter, 4A entry and exodus of current, and also obviously it will have one -ninth the re- I I 2n sistance. This, parallelled with the re- r j°--- - as the restoring torque to return the 160 I I , 30 I 6 3.6 .16 I 147-07-72- coil and attached pointer to its original sistance of the meter, will result in a position. Sensitivity of the meter is 10 -fold increase in the reading. In p o o o o o p governed by the mathematical language this is ex- strength of the mag- 3MA 15MA 60MA 150MA 3A. 15A. 30A. CM net, number of turns on the coil, and pressed: RM /N -1, where RM is the strength of the springs. meter resistance and N is the number of Fig. 2-The Ayrton shunt applied to a meter. times the range is to be multiplied. In The most common sensitivity in use case: today is one milliampere (1,000 mi- this Since the meter "looks into" a re- croamperes) full -scale deflection. (200 - RM 100 100 sistance of 1350 ohms for all rangea, microampere and 60- microampere move- = 11.1 ohms meter damping remains the same ments are also in use, but their high N -1 10-1 9 throughout. price and extreme delicateness limit The single -range shunt has many dis- their popularity.) D'arsonval meters advantages. In a multi -range instru- D'ARSONVAL MOVEMENT AS VOLTMETER are made with current sensitivities of ment, the meter is not protected when A multiplier resistance is used in con- 40 pa to 10 ma (self -contained). Meters changing ranges unless a shorting type junction with the meter to measure with higher ranges than 10 ma usually switch is used. Since a different resist- voltage. If we have a 1 -ma meter, hav- have shunts built into their cases. The ance is across the meter for each range, ing an internal resistance of 100 ohms D'arsonval movement is usually made damping of the meter will vary. This (100 mv.), and desire to extend the with a scale arc of either 90° or 100 °. means that for the higher currents, it range of the meter to 10 volts, a resistor 270° meters are available. A fl- will become more and more sluggish, the is added in series. The resistor is so inch meter having a 270° arc, has the pointer requiring more time till it comes chosen that a 9.9 volt drop appears same scale length as a 7 -inch meter to rest. Any pivot friction or dirt in across the resistance and only .1 volt having a 90° arc. The accuracy of the thejewels or on the springs will show (100 mv) appears across the meter. smaller model is 2 percent of full scale. up, causing the meter to stick. (See Fig. 3). The resistance of the Larger models can be built to an ac- The Ayrton shunt (Fig. 2) consists multiplier would then be: curacy better than 1/10th of one percent. of several resistances, all connected in E 9.9 When it is necessary to measure cur- series, connected across the meter. The R = -= -= 9,900 ohms rents in excess of about 10 milliam- total of all the resistances can be any I .001 peres, most of the current is made to value consistent with good damping A multiplier to extend the range of the flow around the meter. The device upon the meter movement. meter to 100 volts would be: which permits this is a shunt. Shunts Assume a 400 pa (.4 ma) meter hav- 99.9 are made in two movement types, the ing a resistance of 150 ohms. It is de- R = -- 99,900 ohms single -range and the multiple -range or sired to build a multi -range ammeter .001 Ayrton shunt (sometimes called the having full scale ranges of 3, 15, 60 It is customary to disregard meter ring shunt). and 150 ma and 3, 15, and, 30 amps. The drop for ranges above 50 volts on all

RADIO -CRAFT for SEPTEMB ER, 1946 837 except the highly precise laboratory bration of the meter would be different ment, I, = new scale current with volt-meters. for each range in a multirange instru- shunt added and Rm = Resistance of Many teat equipment manufacturers ment. These changes are caused by the meter. use series multipliers in place of indi- varying load presented to the rectifier An unknown resistor causing the me- vidual multipliers. A series multiplier to by the various multipliers and by the ter to read 54 of the scale will there- extend our 1 -ma 100 -ohm meter to 1, ratio of multiplier resistance to in- fore be: 10, and 100 volts would be 900 ohms, verse resistance of the rectifier. .25 ma 9000 ohms, 90,000 ohms. (Fig. 4) The The simple rectifier arrangement can X50= 1/8X50= 900 ohms section is used for the 1 volt be greatly improved by inserting a re- 1 ma - .25 ma range. The 900 ohm and 9,000 ohm resistor in series with the rectifier and 16 2/3 ohms. sistors are used for the 10 -volt range. placing both across the meter, with con- The shunt ohmmeter scale would there- nections as in Fig. 5-a. It is immaterial fore have its zero point to the left as in whether the resistor or the rectifier is Fig. 3 -A milliam- in shunt with the multiplier. meter hooked with up The resistor tends to both equalize Fig. 6-A shunt ohm- a pair of voltage - the load of the rectifier and reduce the meter, used for meas- dropping resistors as inverse current, giving a better scale uring low resistance. a two -range voltmeter. distribution and the same ohms-per-

COM., 10V. volt for each range. The resistor should be preferably less than 1,000 ohms. voltage and current readings. Such a All three are used for the 100-volt Although higher values give a more resistance scale is called a "kick -back" range. linear scale, they also tend to increase scale since the meter kicks backwards When measuring a.c. voltage with a the inverse voltage across the rectifier. when a resistance is measured. The D'arsonval or any other meter that does A better arrangement is to use a second shunt ohmmeter is a milliammeter with not respond to a.c., a means must be rectifier unit in place of the resistor, a variable shunt. employed to convert the a.c. to d.c. Sev- as shown in Fig. 5 -b. The second recti- The series ohmmeter is basically a eral methods are employed. fier acts as a "short" during the con- voltmeter with a variable multiplier. It Thermocouples are used when the ducting cycle and as a very high resist- is more common than the shunt ohm- frequency range varies and precisions is ance during the non -conducting cycle. meter and will read higher resistance of prime importance. Rectifiers Wier - With such an arrangement, the scale is values. It consists of a meter, battery, mionic), copper -oxide, copper- sulfide, almost linear and the ohms -per -volt of and current- limiting resistor such as the meter is increased. used in the shunt ohmmeter, but the The above are half-wave circuits unknown resistance is placed in aeries and are popular in multi -range instru- Fig. 4 voltmeter 900 -A ments. Full wave circuits are also used. with the resistors The full wave version of the first ex- Fig. 7- Simple series 1450 1.5%( 9K WA ohmmeter hooked up in series. ample (Fig. 5 -c) has two rectifiers con- circuit, as commonly employed in nected back -to -back and two resistances. cheap test equipment. COM IV. 10V.100Ú The full wave version of the second example is the bridge rectifier (Fig. 11x t. selenium, germanium ere used where 5 -d). The only real advantage of the with the circuit (Fig. 7). If the same lost is important. full wave circuit over the half-wave is 1 -ma, 50-ohm meter, 1450 -ohm resistor, Copper -oxide rectifiers are the most the ohms-per -volt, which is greater in and 1%-volt battery is used, and the common rectifiers in use today for the full wave circuit. unknown resistor causes the meter to changing a.c. to d.c. in instruments. OHMMETER CIRCUITS read half-scale, the unknown resistance Copper sulfide and selenium are also is equal to the circuit resistance, 1500 used, and all circuits described can use Two general circuits are used for measuring resistances in radio test ohms. The circuit resistance is com- either of these rectifiers in place of the posed of the 1450 -ohm series resistor copper- oxide. equipment. For resistances below 250 ohms, a shunt ohmmeter is usually used. and the 50-ohm meter resistance. This The rectifier can be connected several can also be written as ways. The simplest method is to insert For resistances above 100 ohms, the series ohmmeter is used. Es-E, it in series with one of the leads of the X RT, d.c. meter. There are several disad- In the shunt ohmmeter, a meter, resistor, and battery are connected in E, vantages. The meter scale would be far where E, is the full scale reading in from linear. The ohms- per -volt and cali- series and the resistor is adjusted so that the meter reads full scale. The unknown volts, E, is the new scale reading in resistance is then placed across the me- volts with the unknown resistance ter (acting as the single -range shunt added, and RT is the total circuit re- described previously). The current flow- sistance with the unknown resistance ing through the battery and resistor out of the circuit. If the above meter will then divide and flow through both should read 1/3 scale with the unknown resistance in circuit, the resistance MULTIPLIER the meter and unknown resistor (Fig. 6) thus causing the meter reading to would therefore be WI 1.5 .5 STABILIZER decrease. As an example, assume a me- - X 1500 3000 ohms. TO AC TO AC ter with a full scale sensitivity of 1 - .5 lal Ibl ma and a resistance of 50 ohms. A 1450 ohms resistor used with a 1.5 -volt cell The series ohmmeter has the zero will cause the meter to read full scale. (Continued on page 861) If an unknown resistor is placed across the meter and the reading drops to i4 DECIBELS scale, the unknown will be 50 ohms. This 1i is true since % of the current (.5 ma) would flow through the meter and r dri through the 50 ohms shunt. The meter r would then register only 1 ma. This t can be written as a formula TO AC TO AC I, s ICI Idl X Rm, I, -I, Fig. 5- Rectifier circuits described in text when I, = full scale current of instru- Fig. B- Decibel adaption chart for voltmeter. 838 RADIO -CRAFT for SEPTEMBER, 1946 1ÓÌDATA SHEET 339

OLYMPIC RADIO -Models 6 -501, 6 -502, 6 -503

Frequency Range 535 -1700 K.C.

Power Requirement 105-125 volts Alternating or Direct current

Power Consumption 30 Watts

Models 6-501, 6 -502, 6 -503 are five tube AC or DC operated superhetero- ALIGNMENT PROCEDURE Output meter- Connect across voice a built -in dyne radio receivers employing coil and turn volume control to maximum. WHEN SERVICING THIS RECEIVER loop antenna which will provide satis- Signal generator-Connect the low DO NOT PLACE CHASSIS ON side reception under all normal con- A of the signal generator to the receiver factory GROUNDED METALLIC BENCH. through .1 ditions. This type of antenna is direc- chassis a mfd condenser and Equipment keep the output as low as possible, then tional noise or interference from Required: and proceed in the sequence shown on the other stations can be minimized by Modulated R.F. signal generator: out- alignment chart. put meter; rotating the receiver. If the receiver is insulated screw- driver; two .1 mfd TUBE LAYOUT where signal strength used in locations 400 volt and one 50 mmfd is very low, as in steel buildings, or in 400 volt -condensers. POWER SNITCH e locations remote from broadcast stations, To align the receiver it Turava: VOLUME CorrtROL is necessary an outside antenna may be connected to remove I/14, IF 2iIF the chassis from the cab- 455KC 455 to the screw protruding through the inet, check that the point- osc. back of the cabinet. A GROUND CON- er is horizontal and TRIA co- Ct NECTION IS NOT REQUIRED AND incides with the two horizontal reference ANT MUST NOT BE USED. lines TRIM on the dial. In this posi- 0 tion the REPLACEMENT PARTS condenser should be Part Description completely dosed. No. Connect CO- 107- Cspacitor- Electrolytic 40 +40/ 150 W V the output meter CV -501-Condenser -2 pang variable tuning and signal generator to condenser the receiver as follows: RCM20A101M -Capacitor -100 mmf -- 20% mica RCM20A221M- Capacitor -220 m 20% mica RCM20A331 M- Capacitor -330 mmf 4- 20°.; mica RCP10W2203A- Capacitor -.02 mid.. 200 volts ALIGNMENT PROCEDURE tubular CHART RCP10W4503A- Capacitor -.05 mid.. 400 volts tubular Connect High Adjust the Following for Capacitor -.01 mid.. 600 volts RCP10W6103A- Side of Signal Set Signal Turn Receiver Maximum Output. (Keep tubular Step Generator REB106M- Resistor -10 meg.. 20 °° e watt Generator Dial To- Signal from Signal Generator REB121K- Resistor -120 ohms 10°,, , watt To- To- as Low as Possible.) REB225M- Resistor -2.2 meg.. 20 °ó ' í watt REB474M- Resistor -470.000 ohms -^ 20 %'.a watt Antenna Section Full Clockwise C6, C5, C4, C3 and repeat REB822K- Redetor -8200 ohms :4.7 10°,, ''e watt Tuning Cond. Position. (Cond. in same order REC221 K- Resistor-220 ohms 10% I watt in Series with 455 KC. Plates Fully SK -110-Speaker-5" Dynamic with output trans- (Ist and 2nd I.F. Transformers) former .1 mfd Cond. Open) TR- 186 -Trans /ormer--Iet or 2nd I. F. transformer 1700 KC. 2 Antenna Term. 1700 KC. C2 (Oscillator) NOTES (170 on Dial) of Antenna I. All resistors ± 20% tolerance, 1/2 Loop Maximum Signal watt, unless otherwise specified. 1400 KC. (Approx. 140 CI (Antenna) in Series with 2. All mica condensers -t- 20% tolerance. -- on Dial) 3. All voltages measured to chassis (B -) 4 50 mmfd Cond. Repeat Steps 2 3 with 20,000 ohms -per -volt meter, with and volume control full on.

ANT. 12SA7 12SK7 12SQ7 50L6-GT F 85V. 65v...... _. --, 85v lióov. .011600v ev iC3; g ó 4 85V. 6 B5v.r 5 4 .2K

.01/600V.

330uu1 2.2MEG 12 f PEAKED Al .02 AI 600V. 10 MEG, IOK 455Kc C2 SC. COIL PILOT N247 35Z5GT /G 450n SPEAKER FIELD 85V. .0540V. 5 --'000 i RESISTORS I /2W. II7V.ACDC 35Z5 -GT/D 501.60125K712SA7 UNLESS SPECIFIED. ®SW.ON V.C. 237 27 72 27 78.

RADIO -CRAFT for SEPTEMBER, 1946 839 By MILTON S. KIVER

TELEVISION FOR TODAY Part IV- Television K.F. and I.F. Stages

R.F. STAGE in any super - is greater than half the band allotted signal. But when the signal is quite heterodyne receiver is defor transmission, no trouble will be en- weak, an r.f. stage does not help it signed to: countered from image frequencies. The clear the hurdle. In these instances the AN 1. Increase sensitivity. thirteen television channels are divided antenna should either be improved, or 2. Increase selectivity. into two groups: those from 44-88 mc else the station forgotten. 3. Improve the signal -to -noise ratio. and those from 174 -216 mc. The width The form of the r.f. stages follows 4. Reject image signals. of one band is 44 mc, the other 42. Half conventional lines. In Fig. 2, we have 5. Reject signals at intermediate of the largest is 22 mc, which is less a typical r.f. stage using any of the frequency. than the 2515 mc video i.f. frequency. newer tubes, such as the 6AU6, the At the frequencies allocated to tele- Hence practically no trouble may be vision (44 -216 mc) we find that the expected from image frequencies. TO ÑEXT GRID usefulness of an r.f. amplifier is not as At high frequencies selectivity con- great as it would be at the considerably tributed by an r.f. stage is low. Fig. 1 lower broadcast frequencies (550 to illustrates a comparison between the 1700 kc). The reason: use of a higher selectivity curves of two receivers, one 3 signal frequency coupled with the great- with, one without an r.f. stage. The er separation between the range of fre- only apparent difference occurs at the quencies at which the r.f. amplifier oper- edges of the band. ates as compared to the i.f. frequency. The gain of an r.f. stage, in most Fig. 2- Typical r.f. stage in television set. Consider, for example, item 5. Pres- high -frequency receivers tested, aver- 6BA6, 7AG7, or 6AC7/ 1852. ent RMA standards place the video i.f. aged between 5 and 8. A comparable the at 25.75 mc, while the sound i.f. is 21.25 i.f. stage would be capable of a gain of High G. and low internal capacitances mc. These signals would hardly be ca- 20 to 30. Hence, from the standpoint of are the criteria by which such tubes pable of developing sufficient voltages gain alone, an additional i.f. stage chosen. In fact, these quantities are so at the receiver input to cause interfer- would be preferable to an added r.f. important, they are oftentimes com- ence in the i.f. channel. The lowest tele- stage. It is questionable, too, whether bined into a ratio vision channel is at 44 -50 mc, which is this comparatively small gain would be G. a full 19 mc removed. At the higher fre- sufficient to raise an otherwise weak quencies the conditions are even more signal to the point where it can produce CI. +C... favorable. satisfactory reception. Observers are known as the "Figure of Merit." Rejection of image frequencies is im- very sensitive to even slight distortions Because the internal tube capacitance portant. It is well -known that as long or poor quality in images. It has been is part of the input tuned circuit, spe- as the intermediate frequency chosen the author's experience that an r.f. cial efforts are made to minimize the in- stage seldom evitable changes that occur in these proved decisive in capacitances with tube operation. One 10,000 raising a really 8, 00 6;000 weak signal to the point where enjoy- 4000 able reception be- RECEIVER WITH R.F. STAGE came possible. 2A0 T h e foregoing Ho at: STAGE I does not infer that 000 1 no r.f. stages will r be incorporated in Fig. 3 -A small amount of degeneration cuts television receivers. down the effect of changes in tube capacity. It does mean, how- common arrangement is shown in Fig. ever, that the ques- .- 3 and consists of a small amount of de- tion of whether or generation introduced by the unby- not an r.f. stage is passed portion of the cathode resistor. z to be incorporated 6; In doing this, however, the cathode is ° must be < tempered no longer directly connected to the con- i with the problem denser C. and is not at a.c. ground po- on hand. Television tential. Under these circumstances, the is a special design screen condenser and the suppressor requiring its own grid should be tied directly to ground solution. An r.f. instead of the cathode itself. < I amplifier will def- 6 Jill The resistor loading of the tuned cir- initely prove help- 6 cuit flattens out the response, as shown ful in borderline 4 in Fig. 1. Its greatest disadvantage lies cases, where the in the fact that this likewise decreases additional gain is the gain. This is the main reason for the 1111111 sufficient to bring low gain of television tuned amplifiers. the signal in and A tuning circuit, when connected across produce a clear 140 41 42 43 44 45 46 47 48 49 0 51 52 53 54 the output of tube, is essentially in se- M E G A C Y C L E S Fig. I- Increased series with the plate resistance of that lectivity due to r.f. (Continued on page 864) 840 RADIO -CRAFT for SEPTEMBER, I9.46 TRANSATLANTIC NEWS

From our European Correspondent, Major Ralph Hallows

tortion, high -frequency beaming and the image have to be made. Four of these results of misaligning preset tuned cir- are made through colored screens; red, cuits, are 'much less distressing when blue, green and yellow. The fifth shows the top is cut. This seems to open a the blacks. The sixth is a kind of key promising field for research and inven- diagram, showing the relative intensity tion, for people want the high audio of the tints. From the first five of these frequencies; but not as the radio receiver the block -maker makes the blocks and N my last month's now reproduces them. with them the printer superimposses notes I men- one color upon another. Till now a tioned the freak STILL PICTURES IN COLOR proper balance has been unobtainable, distances some- The great British telecommunications possibly because the yellow tints in the times spanned by corporation, Cable & Wireless, conducts original forced their way, so to speak, v.h.f. transmission world -wide still picture transmission on to other images besides the yellow, just now. A re- services in addition to its activities in with the result that the cumulative ef- markable instance occurred here on the sphere of telegraphy. It has recently fect of the successive printings was to June 8, when our television service re- made an outstanding advance in the give undue emphasis to this color. opened with a broadcast of the victory matter of still pictures in color. Hitherto procession through London. Both sound all such pictures have suffered from one V.H.F. DIVERSITY AM TRANSMISSION and vision on frequencies of the order shortcoming which detracted very much A remarkable system of multi- carrier of 42 me were well received by an ama- from their appeal to the eye. No doubt amplitude- modulated radio on frequen- teur enthusiast on a home -built set at you have seen many in your illustrated cies of the order of 100 me has been de- Minehead, Somersetshire. Minehead is journals and you can hardly have failed veloped for the British police and fire on the Bristol Channel, over 170 miles to be struck by the undue predominance fighting services. The first experiments from the transmitter at the Alexandra of greenish- yellow hues in them. The were made with FM, two stations 28 Palace, near London. Between London blues, reds and browns are there, but miles apart being used. Operating on and Minehead are several ranges of they are to a large extent swamped and 81.7 mc, with temperature -controlled hills and Minehead itself is, one would the whole picture gives an unpleasing transmitter crystals, the stations had have thought, heavily screened from the impression of sallowness. I have just common modulation applied from a cen- direction of London by the heights of lately seen colored stills transmitted tral control point. It was found that between Britain and Australia which there was a large area, the "area of no. are vastly better than anything of the capture," in which neither transmitter kind produced by any other process. took complete charge of a mobile re- The trouble experienced in the past has ceiver and serious distortion of speech Fig. 1-Diversity reception with one receiver. been found to be due to what is called took place. the yellow Exmoor, at whose foot it lies. There is image. Experiments were therefore made When a still picture in color is trans- with AM. It was decided not to attempt a lot that we still don't know about the mitted radio behavior of the meter -waves. Certainly by by the four -color process to synchronize the two carriers, but to no less than six transmissions on. their range may often be a long way be- of the (Continued page 873) yond the visual horizon, which was once thought to be their limit.

IHE TONE -CONTROL PROBLEM WBILEENEA Fig. 2, left- Simple di- Sometime ago I raised over here the versify transmission cir- question why in nine out of ten homes ¡/ cuit as first tried. one finds the radio receiver operating with the tone control knob turned as BBOnsMi F19.9825uC far anti- clockwise as it will go. The effect of this in most cases is to cut com- \ pletely the audio frequencies above looW STATION A or uMI ES surroN a í00W about 8,500 -4,000 cycles. At first sight the thing is most mysterious. i SLAVE Apart from radio the normal man and 96.3 MC 4563 MC STATION A woman obviously likes the high -pitched CONTROL sounds of music. The violinist who does STATION 00.8 MC /30W \ gymnastics in concert hall or music hall on the harmonies of the E string and M0TT.W 9i,p5YC/7W the soprano who hits high -C are 96321.K. /100W certain to receive rapturous applause. MASTER But with his radio set the average STATION listener firmly deprives violinist and \ 9151t77W ---, soprano of the opportunity of properly \,1266 MC/ 7W 91SMC% hitting any high spots. There must be !\ some scientific reason for this, but no one yet seems to have been able to find Fig. 3 - This 3- station it. E network gave good sig- SLAV STATION B The most likely explanation of peo- nals over all the area. ple's dislike of "top" in radio reproduction is that the effects of many kinds of distortion, particularly harmonic dis-

RADIO -CRAFT for SEPTEMBER, I946 841 Edited by ELMER R. FULLER

WORLD -WIDE STATION LIST

FROM Africa the signals of "Radio "French Infantry Hymn," which has a month at 1235 hours GMT and in the Dakar" go booming through the duration of three minutes. Transmis- Oualof native tongue on every second ether to the antennas of radio sions from Radio -Dakar begin each day Tuesday of the month at 1235 hours sets the world over. Reports reach at 0700 hours GMT (2 am EST), 1200 GMT. the studios daily telling how the station hours GMT (7 am EST), and 1800 Transmitter sites for FGY are at is received in Australia, the British hours GMT (1 pm EST). News in Hann, a small village about eight miles Isles, and the Americas, as well as French comes at 0715 to 0730 hours from Dakar. The monitoring receiver is a Hallicrafters SX -28 receiver with France, Sweden and the Near East. GMT; 1230 to 1245 hours GMT; and ra. of 200 kilocycles For the benefit of those listeners this from 1930 to 1945 hours GMT. A final a Panoramascope written William S. bandwidth. story has been by RADIO TERM ILLUSTRATED Here is a feature that may be of in- Duggan, Jr., of Goshen, New York; as Radio -Dakar runs studios and terest to all of you. he saw it in Dakar, at the a musical request program every week of Poste Fédérai Radio - transmitter site whose selections are requested by lis- Dakar. teners to the service. Those wishing to Poste Fédéral Radio -Dakar is super- have their favorite classical or light vised and controlled by the French gov- music played should write to the stu- ernment. Its daily transmissions are dios giving the name of the request, confined to the area of Africa known along with their name and address. technically as Afrique Occidentale Send all requests to: Musical Request Française. All programs are in the Department; Poste Fédéral Radio - French language, although some discs Dakar; Rue Felix Faure; Dakar, Séné- are cut with English music on them. gal; Afrique Occidental Française. The studios of the stations are located All correct reception reports concern- on the Rue Felix Faure, in the military ing the reception of FGY'a signals district of uptown Dakar. abroad by listeners are very cordially Radio Dakar, using the call letters welcomed and will be verified by letter FGY, operates at present time on or postal card. At the present time Ra- two frequencies, namely 25.61 meters dio -Dakar does not have an official (11.715 megacycles) and 43.37 meters printed verification card, but all re- (6.917 megacycles) with transmitter ports will receive a reply. Please inclose powers of 12 kilowatts and 1200 watts an International Reply Coupon. All re- respectively. As a general call to all ception reports should be addressed to African listeners, the station transmits M. LaCroix; Poste Fédéral Radio - a carrier wave upon which is superim- broadcast of World Wide news is at Dakar; Rue Felix Faure; Dakar, Séné- posed a group of modulated tone signals, 2115 hours GMT. A special programme gal; Afrique Occidental Française. which are used to help listeners identify for the Oualof tribe of Senegal is also We wish to thank Mr. Duggan, who the station. The identification broadcast broadcast in the service from Radio - was a reporter for this department consists of high- medium -low tones, Dakar. In tribute to the gallant service prior to his service with the armed which are emitted for fifteen minutes of this tribe in the French forces during forces; and the officials of Radio -Dakar, prior to the general transmission. the 1st World War the program is who cooperated with Mr. Duggan in Every general transmission from broadcast at the following times: In making this information available. FGY begins with the playing of the French on the 1st Monday of each All Schedslee are Eastern Standard Time

Location Station Frequency and Schedule Location Station Fteglteaty wwd Schedule Location Station Frequency and Schedule

NorthwWt Pae18o 12:30 am: Ceylon beam, ant: EL SALVADOR Middle East rain, 7 to 9:30 am San Salvador YPSA 10.400 evenings 9 to ll pm; 11.700 Southwest Pacific beam. beam. 11 pm to 1 am. London GNW ENGLAND beam. midnight 1 to 5 am; Indian beam. London GRC 2.880 Italian 11 pm to 1 am; South London GRB 6.010 to 2:15 African beam. 10:30 Sou4thwmestl acific beam. London OWE 6.035 am to 4 pm; Near East 1 to 4 am London ORR 6.070 Central American beam. beam. 1 to 4 pm 8 to 10:15 pm GILD 11.750 South African beam. London GWa 9.550 London Landon OWN 6.090 American beam. 12:30 to S am: 10:311 London GSL 6.110 Near Eut beam. 11 pm London CSC 9.580 Central am to 4 West Af- 6 to 10:15 pm: Indian pm: to 11:30 am; Italian rican beam. 1 to 3 am: 4 beam, 11 pm to 122:0' beam. 8 to 9:15 pm Routh American beam. am London GRV 9900 South beam. 4:15 to 10:15 pm: Cen- GWA 6.1_5 to f c pm Near e a m, London 4 pm: tral American b London GRW ß.150 Fast beam. 3 to 9 Mediter- Far Fast beam. 11 pm 4:15 to pm; London GWK 6.165 beam, 1 to 4 am: to 2:30 am; Northwest oan GRIM- 7.120 ,eaimtraIIi eem, t+ Ra 10:30 ant London 11 to to 10 am; 0W.46 am; T4fab -1, n.1 Pacific beam. pm to 2:39 pm; North Af- beam. 1 to 3:41. 1:45 am 4 African beam. rican beam. 2 to am; GSW 7.230 Indian beam. 9 11 London GWO 9.625 West G am London 11:30 pm to 1:45 am: to 10 am; 10:30 pm; Sotnhw Pa- to 4 pm beam. 1 Hs am 4:15 to 5:45 pm; Medi- cific beam, 12:30 London GSN 11.820 West Archon beam, 3 London OWI 7.250 terranean 4 New Zealand to 1:45 am to pm; GSU North American beam, 1 5 London 7.260 North beam. beam. to am; Aus 7 to 11 pm Leaden OVZ 9.610 American 1 New Zealand [rattan beam. to 5 am London O101 7.3220 Northwestern Pacific 7 to 11 pm; London Owe 11.840 berm, 11 pm to 12:30 beam. 1 to 5 am 11 London GWP 9.0.10 Far East beam. 8:1.5 am; Italian beam. London G V X 11.930 North American beam. pm to 12:30 am: Far to 10:15 am GRH 9.631 North American beam. 5 to T am; Far Fast Eastern beam. 11 pm to London 11 4 O and beam. m to am: 12:30 m; South Amer- to ll pm; Central Middle Eat beam. ican beam. 6 to 10:15 South African beam. 11 pm to 1:45 am: North 12:15 to 2:30 pm pm; Near East beam. London G RF 12.095 Near East beam, 1 to 11 pm to 12:30 am African beam. 11 pm to 1:45 am 2:15 am: noon to 1:30 London GWF 9.490 pm: Italian beam. 1 to London GSB 9.510 Near East beam, 11 pm London GRU 9.915 North African beam. 12:15 to 4 Routh 5 am: 6 to 10 am: to 12:30 am; 18:15 to pm; 10:30 am to 4:15 pm 4 pm; South American African beam. 12:15 to beam. 4:15 to 10:15 pm: 4 pm (Continued on page 857) Indian beam. 11 pm to London GRG 11.680 Far Eut beam. 7 to 9 842 RADIO -CRAFT for SEPTEMBER, 1946 WE'LL "LEND"ND YOU ANY OF THESE 2 GREAT BOOKS/oz 5 FULL DAYS Every Cent of Your Money Cheerfully Refunded if You're Not More Than Satisfied

ALL THE SCIENCE OF BASIC RADIO - ELECTRONICS in one big 31/2 Ib. Book For Beginners -36 Courses in One Here is the big book that You'll be delighted how soon makes it easy for beginners it will have you doing experi- to start in the fascinating ments, building equipment, field of Radio-Electronics! etc. Step by step it carries Actually, A. A. Ghirardi's you from the very beginning 972 -page RADIO PHYSICS through Basic Electricity to COURSE book gives you just the most modern Radio-Elec- the basic training you need - tronic developments. Hun- ALL YOU NEED - easier. dreds of readers have com- better, faster-for ONLY $5 pleted it in a few weeks. All COMPLETE. Actually, this you need is a little reading giant book is 36 courses in time plus a desire to get one. If sold in monthly les- started now for a better pay- sons, you'd regard it as a ing future in broadcasting, BARGAIN AT $50 OR aviation radio, F -M, Tele- MORE? vision, radio servicing, manu- You'll be surprised how facturing - or other fast- easily RA D I O PHYSICS growing Radio-Electronic COURSE helps you master branches. 6 - D A Y UNRE. subjects that other courses SERVED MONEY -BACK The most and best Train- make seem very complicated. GUARANTEE? ing for your money - Yov be the judge ! Radio's Greatest Training Buy!

Get o better job start e - w 4- business of your own in THIS AUTOMATIC TEACHER SATO AE AIATOff A fascinating Radio -Electronics! 4,800 DIFFERENT MODELS! Chirard)'s big RADIO TROUBLE- Specific instructions cover over 4,800 SHOOTER'S HANDBOOK is the ideal of the manual most popular models of Home to show you exactly how to re- and Auto-radio receiver' and Auto- pair radios quickly, without a lot of matic Radio Changers of 202 manufac- previous experience and without costly turers! equipment. This 744 -page manual -size Also, HANDBOOK RADIO TROUBLESHOOT- LEARN PROFESSIONAL brings you specific re- ER'S HANDBOOK has hundreds of pair data for the common faults that additional pages of repair charts, tube account for almost 90% of ALL troubles charts, data on tuning alignment, in practically every radio in transformer troubles, tube and parta use today! You don't Study it. Simply substitution, SERVICING WORK home look eta, etc., all designed to at up the make, model, and trouble help you repair all makes and models symptom of the Radio you want to of radios, repair. No faster, and more profitably! A. A. Ghirardi's big, 1300 -page MODERN RADIO lost time! Clear instruc- Only $6 ($5.50 foreign). FIVE DAY SERVICING is the finest, most complete Instruction tions tell you exactly what the trouble UNRESERVED MONEY -BACK course on Radio-Electronic service work for either la likely to be. exactly how to fix it. GUARANTEE! the novice or professional serviceman -bar none: Ask anyone in the business! Read from the begin- Make Money in Your Spare Time! ning, it is a COMPLETE COURSE IN SERVICING by the most modern methods. Used for reference, it is an invaluable means of brushing up on any serv- 5 icing problems that puzzle you. -DAY MONEY -BACK GUARANTEE

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RADIO -CRAFT for SEPTEMBER, 1946 843 6 MODELS RADIOELfCTR0111C DEVICES 9 JUST ARRIVED PRECISION SCOPE Band changing is by turning the band Browning Laboratories, Inc. switch to the desired band and changing SUPERIOR Winchester, Mass. the plug -in coil of the PA. The 75 -GA may be used as an ex- The Model OL -15 is a precision, mul- citer for a 500 watt amplifier by link- ti- purpose oscilloscope using a five -inch INSTRUMENTS tube. ing the plate coil of the PA to the grid circuit of the high power amplifier and IMMEDIATE DELIVERY The response curve of the vertical am- replacing the modulation transformer plifier is linear and without positive with a driver transformer for the Class The New Model 705 slope from 10 cycles to well over four B modulators. -RADIO -CRAFT SIGNAL GENERATOR megacycles. The horizontal amplifier response extends linearly from 10 cycles VACUUM TUBE VOLTMETER to over one megacycle to accommodate a. any type of externally generated sweep Radio City Products Co., Inc. voltage. The sawtooth sweep range is New York, N. Y. from five cycles to 500 kilocycles. The new Model 668 Electronic Multi - Triggered sweeps of one, four, 20 and tester is an a.c.-d.c. volt- ohmmeter and 200 microseconds per inch may be in- capacity meter designed for industrial and radio servicing. Front -panel controls are provided for zeroing the meter for both a.c. and d.c. readings and for line voltage adjustments. RANGES: From 95 kc to 100 mc, continuously variable. Calibration accurate to 2% through broadcast bands, within 3% for high frequency bands. Planetary drive condenser, direct reading calibration, output modulated or unmodulated. Self-contained electronic modulation 400e sine wave available for external use. Special feature provided in having two degrees of modulation at both approxim. 30 % and 80 %. YOUR COST $49.50

The New Superior Model CA-II Signal Tracer augurated by the internal trigger generator or by external pulses. Net Price $18.75 FEATURES: The scope is 15 %x12%x19% inches * 9lgnal Intensity read- and weighs less than 85 pounds. - ings are Indicated directly on the meter. RADIO- CRAFT The ranges are as follows: Six d.c. * Only me connecting v.t.v.m. ranges to 6000 volts. Sensitivity cable -No tuning controls. 16 to 160 megohms; seven a.c. v.t.v.m. * Highly sensitive -saes AMATEUR TRANSMITTER an improved vacuum ranges, 16 to 160 megohm sensitivity, tuba voltmeter circuit. Transmitter Engineering Mfg. Co. * Tube and resistor -capacity network are built into 0 to 6000 volts full scale; seven resist- the Detector Probe. New York, N. Y. ance ranges to 1000 megohms; capacity * Completely portable - weighs 5 lbs. Measures 5 rs a 7 Inches. The Temco Model 75 -GA transmitter ranges from .00005 to 2000 µf.- RADIO- * Provision is made for insertion of phones. is designed for 75 watt phone -100 watt CRAFT YOUR COST $18.95 cw operation on the 3.5, 7, 14, 21 and 28 me amateur bands. V.F.O. or crystal control are optional Immediate Delivery from Stock The New Model 680 with front -panel switching. The 80- 5000 Ohms per Volt SUPREME 543 -S Multimeter $24.75 - meter v.f.o. and crystal oscillators are SUPREME 589 Tube & Battery Tester 48.95 VOLT -OHM followed by doublers and tripiers that SUPREME 599 Tube & Set Teeter 62.50 SUPREME 565 Vacuum tube voltmeter 63.50 MILLIAM- are switched into the circuit when the SUPREME 546 Oscilloscope 89.75 METER band switch is turned to the operating WATERMAN S -10-A Pocket Size Oscilloscope 55.00 ar Net Price....$27.65 frequency. The intermediate stages have DUMONT 274 Five -Inch Oscilloscope 99.50 A single scale is usel for pre- tuned, broadly resonant plate cir- McMURDO SILVER "Sparx" Dynamic all voltage (both A.C. and Signal Tracer 39.90 D.CI and current ranges. Thus all readings are MeMURDO SILVER 904 Capacitance plain and obvious. Radio Resistance Bridge 49.90 servicemen will be de- MeMURDO SILVER "Vomis' Vacuum lighted with this time- Tube Voltmeter 59.85 saving innovation. Meas- R.C.P. 448 Pocket Multitexter 24.50 urea: D.C. VOLTAGES to 29.50 1500 volts; A.C. VOLT. R.C.P. 424A Volt- Ohm-Milliammeter AGES to 15no mite: RESISTANCE to 2 memAms: R.C.P. 322 Tube Tester 41.50 OUTPUT VOLTS to 1500 volta: D.C. CURRENT to lt.C.P. 461 AP Sensitive Multitexter 43.50 150 MA: DECIBELS to +58 D.C. Homed in hand - R.C.P. 664 Electronic Multimeter 45.00 rubbed oak, portable cabtneL Complote with self- R.C.P. 922P Tube Tester (Portable) 45.50 and lnstrwtions. nntalned battery. test leads R.C.P. 915 Tube Tester 59.50 R.C.P. 668 Vacuum Tube Volt -Ohm- YOUR COST $27.65 Capacity Meter 74.50 R.C.P. 665 A.V.T. Volt -Ohmegger Dolmen with Order -Bala$. C.O.D. cuits which do not require tuning. Push - Insulation Tester 94.50 ss,w.M.\ n'SM\..,,..r pull- parallel 6L6's are Class AB2 modulators for the TB35 or 3D23 final ampli- Write for Free Catalog fier. The speech amplifier works from a LIBERTY SALES INC. ATLAS ELECTRONICS COMPANY CO, high impedance crystal or dynamic 115 WEST SROA0WAY 11 Edward M. Morgan PL. N. Y. 32, N. Y. NEW YORK 13. N. Y. mike. Dept. C9.

844 RADIO -CRAFT for SEPTEMBER, 1946 MOST- O N EDEFTEN-D RADIO DIAGRA M S

4 Out of 5 Diagrams NEW, POPULAR, LOW -PR ICED MANUALS You Ever Need 1946 Will need these easy-to-apply. inexpen- Find radio faults quickly. Make the needed repairs siveYou manuals to help you repair radio- in any new radio. Save time on every job. This faster. This volume covers 1941 models, Most Popular large, new, and inexpensive diagram manual has 1 94 1 with alignment data. I.F. peaks, and 1946 radio set replacement part- lists. Compiled by M. N. Beit- Models Made by: the circuit for almost every $ man, radio serviceman for many years, author, and made since V -J day. Large manual, 8 1,4 x 00 teacher. Be an expert in radio servicing: simplify $200 R.C.A., Zenith, 11 inches, 192 pages of circuits and repair your work. 192 pages 8% x 11 inches. Only data. Price postpaid, only Philco, Sears, Fada, Let this important manual give you Emerson, Belmont, over 80% of all 1940 circuits you will Radio, Clearly printed circuits, align- ever need, acquaint you with new devel- Detrola ment data, parts lists, service 1940 opments, train you to service quickly United Motors, and efficiently millions of sets. G.E., Westinghouse, 1942 hints are the facts you need to Data on portables, recorders, speed up all radio servicing. Repair radios quickly 1941 FM, etc. 417 models of 43 manu- $200 A r v i n, Majestic, facturers. 208 Net and properly -follow the factory instructions given. RADIO pages. price.. Stewart-Warner, Includes 351 models of 40 largest manu- DIAGRAMS. Another handy manual Admiral, Delco, facturers. 192 fact packed pages. Large of the most popular dia- Stromberg. Carlson, size, 8%x11 in. Manual style binding. Well $2óo grams you need. Circuit 1939 data. hints and infor- Western Auto, printed. Price postpaid, only mation are time -savers and money -makers for you. Let these diagram manuals guide you to Sparton, Motorola, easier service work. Why try to get Ward s, Gamble, along without helpful diagrams? and many others. Other Practical Radio Manuals Use this volume with 192 pages $200 of diagrams of 39 makes. Only ... RADIO SERVICING COURSE The most popular vol- Let this 22- lesson course help you fix and adjust any ume of the series. Will radio set. Ea..y- to-understand explanations: hundreds of 1926 -1938 pay for itself with the simplified diagrams, pictures, practical hints. Quickly learn how to make needed tests, locate faults, complete time saved during the first day of use. Includes all the the repair. Learn new speed -tricks of radio fault find- popular old timers. Save hours on every job. 427 diagrams ing, case histories of common troubles, servicing short of the most serviced radios of this period, with cuts, extra profit ideas. Many active servicemen used this reduced price radio training for brush -up parts lists and alignment information. 240 pages, and study of new service methods. Large 8% x 11 inches. Sold with a money J size: 8,tx11 inches, 22 lessons, 224 pages. $250 back $250 Hundreds of diagrams, illustrations, charts. guarantee. Price, postpaid,

* STEWART- WARNER MANUAL . . . 50c A r SAVE HOURS ON EVERY JOB Be ready to make repairs in minutes in- * ARVIN DIAGRAM MANUAL . . . . 50c stead of hours. You will be called upon to f`' fix hundreds of models listed in these easy - GENERAL -ELECTRIC MANUAL . 50c to -use Compiled by manuals. Tackle each job with the 64 pages of popular circuits. Size: 51/2 x 81/2 inches M. N. Beitman, needed help found on every page in these radio engineer, handy service manuals. Greatest bargain teacher, author in diagram books. PRACTICAL RADIO MATHEMATICS & serviceman. Send your order today. Introduces and explains the use of arithmetic and Use these manuals this week. elementary algebra in connection with units, color I RAOtOMATM1aATltt code, meter scales, Ohm's Law, alternating currents, ohmmeter testing, wattage rating, circuits, NO RISK TRIAL ORDER COUPON series and parallel connections, capacity, SUPREME PUBLICATIONS, 9 S. Redact Ave., CAIeago 12, ILL. inductance, mixed circuits, vacuum tubes, Ship the following manuals: back guaranteed) curves, the decibel, etc., etc., and has (Money AWL, FARM Newt numerous examples. price, only 25 C 1946 Bargain 1942 1941 0 1940 ' 1939 1926-1938 Radio Servicing Course El Stewart-Warner Arvin See Your Radio Jobber or Send Coupon -> G General -Electric Manual Radio Mathematics I am enclosing S send postpaid. Send C.O.D. I am enclosing t deposit. Supreme Publications Name: Address: PUBLIE:iFRS OF RADIO BOOKS, MANUALS, AND DIA,:RAMS (Ute Coupon or Write Order in a Separate Letter) RADIO -CRAFT for SEPTEMBER, 1946 845 SPRAGUE DISTRIBUTORS i0 SERVE YOU

So many users of the SPRAGUE TRADING POST, our free wartime advertising service, have asked for the names of their nearest Sprague distributors that -well, here's the entire list. These firms will supply you with factory -fresh Sprague Capacitors and Koolohm Resistors of the very latest types. They'll be only too glad to serve you. THE SPRAGUE TRADING POST did its part during the war. Now, both Sprague and its distributors will "follow through" by bringing radio servicemen, amateurs and experimenters the finest components backed with the best service obtainable. As always, we'll appreciate it if you continue to: "Ask for Sprague Capacitors and Koolohm Resistors by name!"

SPRAGUE PRODUCTS CO., North Adorns, Mass. jobbing Distributing Organization tot Product, of the Sprague Electric Company

1 ASK YOUR JOBBER for a copy of the big new Sprague Catalog. Gives full details on the most complete Capacitor line on the market -also Koolohm Res;stors and the Tel -Ohmike Analyzer. .,ry famous Sprague SPONSORS - SPRAGUE CAPACITORS are specified by poet numbers rn the popul,v Of THE FAMOUS ne.. HOWARD W SAMS PHOTO FACT FOLIOS WART/ME SERI//CE -"THE SPRAOPEffl SPRAGUE TRADING POST" CAPACITORS ... . t.

846 RADIO -CRAFT for SEPTEMBER, 1946 >4d4 jon $pcayue Pzoductd 4 71,aoce!

ALABAMA IOWA NEBRASKA OREGON Benemrr- Bessemer Radio Supply Cedar Rapids-Gifford-Brown, Inc. Omaha -Omaha Appliance Co. Portland -Bargelt Supply Birmingham -James W. Clary Camnril BWBs-World Radio Labs., Inc. Radio Equipment Co. Harper- Meggee, Inc. Mobile- Nelson Radio & Supply Co. Drs Moines- Gifford -Brown, Inc. .irontblu$-Joachim Radio Supply Portland Radio Supply Co. Radio Labs Radio Trade Supply Corp. PENNSYLVANIA Montgomery- Teague Hardware Co. Fart Dody - Gifford -Brown, Inc. NEW HAMPSHIRE Southeastern Radio Parts Co. Ken.Els Radio Supply Alentown- -Radio Elec. Serv. Co. Mason City-Radio-Electric Supply Co. Dour -- American Radio Corp. Beaver Falls- Reliable Motor Parts Co. ARKANSAS Sioux City -Power City Radio Company Easton -Radio Elec. Serv. Co. Sioux City Radio & Appl. Co. NEW JERSEY Erie V. Duncombe Co. Fort Smith -Wise Radio Supply -John Water /oo- Gifford- Brown, Inc. Camden -Radio Elec. Sert'. Co. Harrisburg -Radio Distributing Co. Little Rork - Southern Radio Supply World Radio Laboratories, Inc. Texarkana-Lavender Radio Supply Co. Newark -Continental Sales Co. Lancaster- Eshelman Supply Co. Krich- Radisco, Inc. George D. Barbey Co. ARIZONA KANSAS T. A. O'Loughlin & Co. Norristown -Kratz Bros. Co. Pittsburg -Pittsburg Radio Supply Radio Wire Tel., Inc. Philadelphia -Almo Radio Company Phoenix-Radio Parts of Arizona Topeka-Acme Radio Supply Perth Amboy- Bennett's Radio Supply Consolidated Radio Corp. Wichita-Radio Supply Co. Red Bank -J. H. Kelly Company Electric Warehouse CALIFORNIA Trenton -United Tire Stores Co. Emerson Radio of Pa. Bakersfield- Bakersfield Radio Supply KENTUCKY Radio Elec. Serv. Co. NEW YORK N. W. Cor. 7th & Arch Su. Fresno -Jack C. Arbuckle Lexington -Radio Equipment Co. Billings Wholesale Radio Albany -Fort Orange Radio Dstg. Co. 3133 Market St. Hollywood Radio Supply. Inc. Losisoi/k- Peerless Electronic Equip. Co. 3145 N. Broad St. Hollywood- Newport Co. Amsterdam- Adirondack Radio Supply Long Beach-Radio & Tel. Equip. Co. -Apex Distributing Eugene G. Wile Auburn -Dards Radio Service Pittsburgh-Hamburg Bros. Lot Angeles- Figart Radio Supply Co. LOUISIANA Binghamton- Broome Dug. Co., Inc. Kierulff & Co. Federal Radio The John Marshall Co. Lake Providence H. Schneider& Sons, Inc Supply Co. Parts Co. Nelson Brothers Co. -F. Brooklyn -Green Radio Distributors Radio Radio Equip. Distributors New Orleans -Radio Parts, Inc. Pottsville -)ones Radio Co. Dunckelman -Pace Stan -Burn Radio & Elec. Co. Reading D. Barbey Co. United Radio Supply Co. Shreveport- Buffalo -Bars Radio & Electronic Parts -George Universal Radio Supply Co. Koelemay Sales Co. St. Marys-B & R Electric Co. Dymac, Inc. Dstg. Co.. Inc. Modesto -Jack Warren Genesee Radio & Parts Co. Scranton- Broome Oakland-W. D. Brill Company MAINE Radio Equipment Corp. Wilkes- Barre -General Radio & Elec. Co. E. C. Wenger Co. Ambers -Radio Service & Supply Store Standard Electronics Co Radio Service Co. Pasadena -Dow Radio Supply Co. Portland -Frank M. Brown Co. Ebnira- LeValey- McLeod- Kinkaid Ca, Inc Williamsport -Williamsport Radio Supply Sacramento -C. C. Brown Co. Fredonia -C. R. Barker RHODE ISLAND Henderson Bros. MARYLAND Glens Falls Distributing Co. -Ray Providence- William Dandreta & Co. Sacramento Elec. Supply Co. Ba /timon -Henry O. Berman Co Inc. Hempstead, L. 1.- Standard Puts Corp. San Diego -Coast Electric Co. Ithaca- Stallman of Ithaca W. H. Edwards Co. Equip. Distr. Cumberland -Cumberland Radio Whol. Electronic Saksbmry -Dealers Radio Service Jamaica, L. 1.- Norman Radio Distas. SOUTH CAROLINA Shanks & Wright Middletown -L & S Radio Sales Co. San Francisco- Associated Radio Disco. New York City- Fischer Distributing Co. Colombia -Dixie Radio Supply Co. MASSACHUSETTS C. C. Brown Radionic Equipment Co. SOUTH DAKOTA San Joe -Frank Quement Borten -De Mambro Dstrs., Inc. Radio Wire Tel., Inc. Santa Ana -Radio & Tel. Equip. Co. Harry & Young of Mass., Inc Aberdeen- Danielson & Brou Co. Niagara Falls- Niagara Radio & Parts Co. Falls City A. W. Mayer Co. Rochester- Beaucaire Inc. Sioux -Power Radio Co. COLORADO Radio Wire Television, Inc. Masline Radio & Electronic Equip. Co. United Radio Supply Sager Elec'I Supply Co. 1 rear- Inter -State Radio & Supply Co. Schenectady-Fort Orange Radio Dstg. Co. TENNESSEE Cambridge -The Eutern Co. M. Schwartz & Son Holyoke -Springfield Radio Co. Rrsoxvilk -Bomar s CONNECTICUT Symms- Broome Dstg. Co., Inc Lawrence-Hairy & Young of Mau., Ina Syracuse Radio Supply Chemcity Radio & Elec. Co. Bridgeport -Harry & Young, Inc. New Bedford-C. E. Beckman Co. Troy -Trojan Radio Co. C. M. McClung & Co. Hartford-Harry & Young, Inc. Pittife /d- Pittsfield Radio Co. Utica -Beacon Electronic Inc. Metavbis- McTyier Radio Supply New Britain -United Radio Supply Roxbn Gerber Radio Supply Co. Watertown-Beacon Electronic Inc. Nasbvilk- Currey's Radio Service Universal Radio Co. Sp* Cushing Co. Radio & Appliance Corp. New Haven -Thomas H. Brown Co. SpringfieldRadi Co. NORTH CAROLINA TEXAS Harry & Young, Inc. Worcester -De Mambro Dstrs., Inc. New London -Harry & Young of New The Eastern Co. Asheville -Fleck Radio & Supply Co. Abilene -R & R Supply Co., Inc. London, Inc. Radio Electronic Sales Co. Charlotte -Dixie Radio Supply Co. Amarile -R & R Supply Co., Inc. Stamford-Harry & Young. Inc. Radio Maintenance Supply Co. Southern Radio Corp. Aeutin -The Hargis Company Waterbury -Harry & Young, Inc. Fayetteville- Eastern Radio Supply Beaumont- Montague Radio Co. MICHIGAN Goldsboro -Signal Radio Supply Corpses Christi- Wicks- DeVdbiss CO. DELAWARE Greensboro -Dixie Radio Supply Co. Electronic Equip. & Engin. Co. Ann Arbor- Wedemeyer Elec. Supply Co. Raleigh- Carolina Radio Equip. Co. -State Dstg. Co. Wilmington -Radio Elec. Serv. Co. Creek edemeyer Elec. Dallas -MI Battle -W Supply Co. Winston - Salem -C. R. Williams Radio CO. Crabtree s Wholesale Radio Detroit- Ferguson Radio Supplies DISTRICT OF COLUMBIA Southwest Radio Supply Radio Specialties Co. NORTH DAKOTA Wanslow & Co. Washington-Kenyon Radio Supply Co. Radio Supply & Eng. Co., Inc. Fargo -Radio Equipment Co. Fort Worth -Electronic Equipment Co. Rucker Radio Wholesalers Flint-Radio Tube Mdsg. Co. Fort Worth Radio Supply Co. Grand Rapids- Wholesale Radio Co. OHIO Houston-A. R. Beyer Company FLORIDA Jackson -Fulton Radio Supply Lubbock -R & R Supply Co.. Inc. Kalamazoo -Ralph M. Ralston Co. Akron -Olson Radio Warehouse San Antonio Radio Supply faeksonvilk- Kinkade Radio Supply Muskegon -Industrial Elec. Supply Co. -Olsen Major Appliances Ashtabula- Morrison Radio Supply Tyler- Lavender Radio Supply Co. Pontiac- Electronic Supply Co. Canton- Armstrong Radio Supply Waco-The Hargis Company Miami -Electronic Supply Co. Saginaw-Radio Parts Company Major Appliances Burroughs Radio Wichita Falls- Wichita Falls Bat. & Ela. Cincinnati- Chambers Radio Supply Co. Orlando -Radio Accessories Co. MINNESOTA VIRGINIA St. Pereubarg -Welch Radio Supply Schuster Elec. Co. Sarasota- Morley Radio Co. Duluth- Northwest Radio United Radio Inc. Norfolk- Ashman Distr. Company Tampa-Kinkade Radio Supply Minneapolis- Bauman Company Cfeve/and- Goldhamer, Inc. Roanoke- Leonard Elec. Sup. Co. Major Appliances Sidney Rosenthal Northern Ohio Laboratories Richmond- Johnston Gasser Co. Winteradio, Inc. St. Pam!- Electronic Distributing Co. WASHINGTON GEORGIA Co/mbar- Hughes -Peters, Inc. MISSISSIPPI Whitehead Radio Co. Bellingham -Wairkus Supply Co. Atlanta -Concord Radio Corp. Daytors-Hughes-Peters, Inc. Seattle- General Radio, Inc. Southeastern Radio Parts Co. Greenrilk -The Goyer Company Standard Radio & Electronic Prod. Co. Harper- Meggee, Inc. Specialty Dstg. Co., Inc. Meridian -Griffin Radio Supply Eut lire poo /- Hausfeld Radio Sunset Electric Co. Macon- Specialty Dstg. Co. Inc. MISSOURI Kent -Kladag Radio Labs. Spokane- Harper- Meggee, Inc. Savannah- Southeastern Radio Puts Co. Lima -The Northwestern Radio Co. Tacoma -Wible Radio Supply Specialty Dug. Co.. Inc. Cape Girardeau- Suedekum Elec. Sup. Co. Afansfie/d- Burroughs Radio Jefferson City -Central Mo. Dug. Co. Marion -Bell Radio Supply WEST VIRGINIA ILLINOIS Joplin -M. Brotherson Springfie/d- Standard Radio & Electronic Bltefie /d- Whitehead Radio Co. Mardick Dstg. Co. Prod. Co. Charleston- Chemcity Radio & Elec. CO. Bloomington -J. W. Arbuckle Kansas City- Burstein- Co. Steubenville-D & R Radio Supply -Allied Radio Corp. APplebee Hicks Radio Supply Chicago Manhattan Corp. Hausfeld Radio Clarksburg- Trenton Radio Co. Concord Radio Corp. St. Joseph -St. Joseph Radio & Supply Toledo -Toledo Radio Specialties Radio Co., Inc. Co. Huntington- Electronic Supply Inc. Grant St. Louis -Walter Ashe Radio Co. Warren -Radio Specialties Morgantown- Trenton Radio to. Nation Wide Radio Interstate Supply Co. Youngstown- Appliance Wholesalers Radio Parts Company Parkersburg- Randle & Hornbrook Radonics Wheeling- Wheeling Radio Supply Kankakee -Radio Doctors Supply House Springfield-Harry Reed Radio & Sup. Co. OKLAHOMA WISCONSIN INDIANA MONTANA Enid - Standard Measuring & Equip. Co. Oklahoma City -Radio Supply, Inc. Green Bay -Neslo Electronic Dstrs. Angola- Lakeland Radio Supply Batte- George Steele & Co. Southern Sales Co. Madison -Radio Dstrs. of Madison. Wis. Richmond -Fox Sound Equipment Co. Kakspell- McIntosh Music House Tulsa- Radio, Inc. Milwae&se -Radio Parts Co.. Inc. .. *KOOLOHM RESISTORS kE(3 ' ... +i. RADIO -CRAFT fcr SEPTEMBER, 1946 ALABAMA IOWA NEW JERSEY Sera ratan ttontgomery Burlington Bridgeton Broome Dist CO. Teague Hardware Co. Union Supply Co. Joe's Radio Shop 26 Lackawanna Ave. 200 Commerce St. 4th & Washington Sts. 67.69 S. Pearl Sharon Council Bluffs Newark Houes Bros.. Ina ARIZONA 73 Central Way Phoenix World Radio Labs. Radio Wire Television. Ina Dubuque 24 Central Ave. York Radio Specialties & ASPI. Co. Bee Distributing Co. J. R. S. Distributors 401 W. lacksoe St. Variety Electric Co. 646 W. Market St. 498 N. Grandview 601 Broad St. ARKANSAS Sioux City Trenton SOUTH DAKOTA Little Rock Dukes Radio Co. Carl B. Williams Sioux Falls Southern Radio Supply 114 West 4th St. 25 S. Warren St. Power City Radio Co. 409 West Third St. Power City Radio Co. NEW YORK 209 So. First Ave. 513 7th St. CALIFORNIA Binghamton United Radio Supply ltakersfield KANSAS Broome Dist. Co. 211 W. 10th St. Bakersfield Radio Supply Pittsburgh 221 Washington St. 2808 TENNESSEE Chester Ave. Pittsburgh Radio Supply CO. Brooklyn Green Nashville Hollywood 103 N. Broadway Radio Distributors Yale Radio Electric Co. 482 Sutter Ave. Frost Electric Ina Topeka 1922 West End Ave. 6616 Sunset Blvd. Acme Radio Supply Hornbeam Distributing Co. Los Angeles 516 Quincy St. 1639 Bedford Ave. TEXAS General News Agency Wichita Buffalo Dallas 326 West 5th St. Interstate Distributers, Inc. Dymae. Inc. Southwest Radio Supply Papel Bros. 1236 E. Douglas 2929 -31 Main St. 1820 N. Harwood 2639 E. 4th St. Radio Supply. Inc. Genesee Radio & Parts Co. Fort Worth 'an Bernardino 1125 -27 E. Douglas 205 E. Genesee St. Ft. Worth Radio Supply Co. George N. Bagley Co. Jamaica 1201 Commerce 1216 D St. KENTUCKY Peerless Radio Dist. Co. The Electronic Equip. Co. son Diego Lexington 9232 Merrick Rd. 301 E. 5th St. Western Radio & Electric Co. Radio Equipment Co. -Middletown Houston 1415 India St. 377 East Main St. Roskin Bros., Inc. R.C. & L.F. Hall 1015 . 1 n Francisco 23 W. Main St. Caroline St. c Associated Radio Diet. LOUISIANA Mount Vernon Laredo 1251 Foison St. Monroe Davis Radio Dist. Co. Radio & Electronics Supply Co. an Jose Sale & McNeil 66 -70 E. 3rd St. 1219 Lincoln St. Frank Quement Wholesale Radio 301 Pine St. New York City Lubbock 156 W. San Fernando St. New Orleans Federated Purchaser. Ina R. & R. Supply Co.. Inc. enta Ana Radio Parts. Inc. 80 Park Place 706 Main St. Radio & Television Equip. Co. 807 Howard Ave. Grand Central Radio. Ina San Antonio 207 Oak St. Walther Bros. Co. 124 E. 44th St. R. L. Ross Co. 118 Seventh St. COLORADO 714 Howard Ave. Harrison Radio Corp. 12 West Broadway Tyler ctrl Norte MAINE Service Supply Co. Harvey Radio Co. Radio Valley Music & Electric Co. University Plue Bangor 105 W. 43rd St Ill h. over Radio Service Laboratory Waco McGee Radio & Elect. Co. 45 Haymarket S0. Niagara Radio Supply Corp. The Hargis Co.. Ina 1330 Broadway 160 Greenwich St. 1305 Austin Ave. Inc. Radio Products Sales Co. MARYLAND Radio Wire Television. 100 Ave. UTAH 1237 16th St. Baltimore Sixth Salt Henry O. Berman Co.. Inc. TAB Lake City Co. CONNECTICUT 12 E. Lombard 8t. 6 Church St. O'Loughlin's Radio Supply 113 East Broadway R ridgy port Wholesale Radio Parts Co.. Inc. Rochester Pauline Radio & Electric Equipment Radio Supply Co. Coastal Radio Service Co. 311 W. Baltimore St. 1559 Stratford Ave. 192 -196 Clinton Ave.. N. 45 East 4 South ,Vew Britain MASSACHUSETTS Syracuse Standard Supply Co. United Radio Supply Boston. Broome Dist. Co. 531 Sa State St. 912 Erle Blvd. E. 53 E. Main St. Sager Electrical Supply Co. VIRGINIA 201 Congress St. Syracuse Radio Supply Norfolk DISTRICT OF COLUMBIA Melrose 238 -40 W. Willow St. I I Radio Parts Dist. Co. ' ashington Melrose Sales Co. NORTH CAROLINA 128 W. Olney Rd. Capitol Radio Wholesalers 407 Franklin St. 2120.14 St.. N.W. Charlotte Radio Supply Co. New Bedford Henry V. Dick & Co.. Inc. Sun 711 Granby St. Radio C. E. Beckman Co. 311 E. 5th St. 938 N.W. F St. Commercial St. Goldsboro WASHINGTON FLORIDA Springfield Signal Radio Supply Bellingham. Springfield Radio Co.. Inc. 124 8. James St. Waitkus Supply Co. Jacksonville 405 Dwight St. 110 Grand Ave. Radio Parts Co. Worcester OHIO Seattle 712 Main St. Radio Electronic Sales Co. Cincinnati Harper-Megfie Thann Distributors. Ina 46 Chandler St. Radio & Refrigeration Supply 960 Republican St. 806 Main St. 1220 -6 Jackson St. Spokane Miami MICHIGAN Cleveland Columbia Electric & Mfg. Co. Thurow Distributors. Ins. Ann. Arbor Northern Ohio Labs. P.O. Box 1441 S. 123 Wall St. 85th St. 420 8. W. 8th Ave. Purchase Radio & Camera Shop 2073 West Inland Radio Co. Orlando 605 Church St. Radio Surplus Co. W. 923 First Ave. Thoras Distributors. Ina Detroit 648 Prospect Ave. Tacoma 131 South Court St. Hershel Radio W I nterrad io. I ne. C. & G. Radio Supply Co. Tallahassee 5249 Grand River Ave. 1468 W. 25th St. 714 St. Helens Ave. Thurow Distributors. Ina Radio Supply & En0'er'ng Co.. Ina Dayton Prods. A. T. Stewart Co. 213 E. Tennessee 129 Seiden Ave. Standard Radio & Elect. 743 Broadway Tampa 135 E. Second St. Flint WEST VIRGINIA Thurow Distributors. Inc. Radio Tube Mdse Co. Steubenville 115 -117 So. Franklin St. 508 Clifford D. & R. Radio Supply Clarksburg West Palm. Reach Jackson 156 S. 3rd St. Trenton Radio Co. Thorns Distributors, Inc. OKLAHOMA 791.93 W. Pike St. Fulton Radio Supply Co. East Charleston 209 No. Olive St. 707 S. Blackstone St. Oklahoma City La nsi rag Hicks Radio Supply ILLINOIS Radio Supply. Ina 10 Virginia St. Electric Products Sales Co. 724 N. Hudson. Box 597 Danville 427 E. Michigan Ave. Parkersburg Allen Electric Co. Radio Supply Saginaw PENNSYLVANIA John A. Cox Radio Supplies 109 N. Hacel St !Altoona 554 7 St. Chicago Orem Distributing Co. Radio Supply 801 E. Genesee Ave. Hollaback's WISCONSIN Allied Radio Corp. 2221 8th Ave. Appleton 833 W. Jackson Blvd. Radio Parts Co. Kennedy Radio Supply 234 S. Second St. Valley Radio Distributor, American Parts, Inc. 1500 Filth Ave. 518 N. Appleton St. 610 W. Randolph St. MINNESOTA Beaver Falls Hudson Concord Radio Corp. Reliable Motor Parts Co. J. M. Larson Co. 901 W. Jackson Blvd. Duluth 7th Ave. Northwest Radio 1700 109 Walnut St. Radio Sales Co. Lake 109 E. First St. Erie .Madison 615 W. Randolph St. Jordan Electronic Co. Satterfield Radio Supply Inc. Radio Shack MISSOURI 201 W. 4th St. 326 W. Gorham St. 630 W. Randolph St. Cape Girardeau Harrisburg Milwaukee Radolek Company Suedakum Electronic Supply Co. D. & H. Distributing Co.. Ina Acme Radio Supply Corp. 601 W. Randolph St. 902 S. Sprigs St. 311 S. Cameron St. 510 N. State St. NEBRASKA Lancaster Central Radio Parts INDIANA Eshelman Supply Co. Co. Omaha 1723 West Fond Du Lac Ave. Evansville 110 N. Water St. Castrup's Radio Supplies Also Radio, Inc. Philadelphia Racine 1014 W. Franklin St. 411 Coming St. Standard Radio Parts Co. Flanagan Radio Corp. St. All -State Distributing Ce. N.E. Cor. 7th & Chestnut Sts. 1244 State Montour Auto & Machine Co. 2857 Farman St. 517 Locust St. M & H Sporting Goods Co. WYOMING Radio Co. Equipment 512 Market St. Hammond 2820 -22 Farnam St. Casper Stanton Radio Supply Radio Electronics Service Co. Golden Power Oli & Supply Co. 521 State St. NEW HAMPSHIRE 7th & Arch Sta. 260 S. Center South Bend Concord R.ading Cheyrn ne Commercial Sound & Radio Co. Evans Radio Geo. D. Barbey Co. House Radio & Supply Co. 528 E. Colla Ave. 18 N. Main 432 Walnut St. 2008 Carey Ave. DBALBRS: It you are not receiving RADIO -CRAFT please ask for nur Special Consignment Proposition.

850 RADIO -CRAFT for SEPTEMBER, 1946 NOW A VAILARLE FOR IMMEDIATE SHIPMENT!

%lse ?leur WlodeC 6 70 SUPER -METER

(SHl4cKAiGOK

VOLT-OHM MILLIAMMETER

plus CAPACITY REACTANCE INDUCTANCE and

DECIBEL MEASUREMENTS

,added lea Bete: The Model 670 includes a special GOOD -BAD scale for checking the quality of electrolytic condensers at a test potential of 15 0 Volts.

D.C. VOLTS: 0 to 7.5/15/75/150/750 /1,500/7,500 Volts RESISTANCE: 0 to 500 /100,000 ohms 0 fo 10 Megohms A.C. VOLTS: 0 to 15/30/150/300/1,500 /3,000 Volts CAPACITY: .001 to .2 Mfd..1 to 4 Mfd. (Quality test for electrolytic) REACTANCE: 700 to 27,000 Ohms 13,000 Ohms to 3 Megohms OUTPUT VOLTS: 0 to 15/30/150/300/1,500 /3,000 Volts INDUCTANCE: 1.75 to 70 Henries 35 to 8,000 Henries D.C. CURRENT: 0 to 1.5/15'150 Ma. 0 to 1.5 Amperes DECIBELS: -10 to +18 +10 to + 38 +30 to + 58

The Model 670 comes housed in a rugged, crackle -finished steel cabinet complete with test leads and operating instructions. Size 5 %" X 7Vi" x 3 ". s28áä

....'"..1 %'ltzdd 1 670P Jrr w\\ \1 J The Model 670P is identical to the oot °tast y \°b ' r p\oc` V °go F°et cot, Model 670 described in detail except Mt¡t. Q\ÒS o\°t t o\\°bb 11 housed in a hand- rubbed, portable oak b'atv\^ 1 cabinet complete with cover. 1 yt tro\y\oo, v°o°t 1 \ +°QP of 1°b tlb°\. The Model 670P Cts\ ët ocd loo t o et comes complete .MF S'^ò C sto te °t with test leads and t^`â`t et\I \O 75 50ù all operating in- r structions. SUPERIOR INSTRUMENTS CO. I Dept. R 227 FULTON ST., NEW YORK 7, N. Y. (RADIO -CRAFT for SEPTEMBER, 1946 e51 See This NEW Book for 7 Days FREE ORSS VALUABLE HELPS FOR RADIO ENGINEERS RADIOMAN'S HANDBOOK ON RADIO DALA A New, Valuable Book for Men Working HELPFUL MMAINTENANCE CONTROL in Radio, Electronics, Electricity No matter what work you do in radio, this handbook will prove mighty valuable since it contains ex- Ce\ actly the information you wish, available in an instant. You can refer to it easily right on the job. I'm so sure that you wouldn't part with this book for many times its cost that I'm willing to send it to you for a 7-day FREE examination. USE IT DAILY ON THE JOB You can't expect to carry all the necessary information you need on a job, in your head. But you CAN have all the information at your side with this handy book. Once you look through the pages of the Radioman's Handbook and see how the tables, charts, diagrams and data can save HERE'S WHAT THIS time and help you get ahead, you will see why this book is as valuable other tools. GREAT BOOK COVERS as your THOUSANDS OF FACTS NOT A TEXTBOOK MATERIALS RADIO RESISTANCE & INSULATION - Every subject is indexed and condensed to fit in readable space without waste. ABBREVIATIONS (WIRE TABLES, etc.) Over 300 pages packed full of valuable information that will help you in your CIRCUITS CAPACITORS & CAPACITANCE daily work. When you are "on a spot" just turn to the quick index, look up the POWER FORMULAS COILS & COIL WINDING subject you want and you'll find that subject thoroughly explained with helpful diagram has been fully tested in the great Coyne RECEIVING TUBES RESONANCE & COUPLING diagrams and tables. Every Electrical Shops. Every table is scientifically correct. TRANSFORMERS OSCILLATORS & ANTENNAS AMPLIFIERS RECEIVERS SOUND SYSTEMS & DEVICES SEND NO MONEY. SEE IT FREE I am not asking you to send any money -not a single penny. I am so sure BOOKS this is the book you want and need that I will send it to you to examine for 7 days FREE. Then you look it over and you decide. If it isn't all I claim, then COYNE send it back and you owe nothing. If you are convinced that this book is worth OTHER many times its cost, then send $3.25 at the end of 7 days and the book is yours. THEM FREE Send the coupon now, while it is before you! e SEE FREE TRIAL COUPON

SCHOOL, Dept. 66.11 Lie B. W. Cooke, Director, COYNE ELECTRICAL lea I SOO S. Paul Ina Street, Chicago 12, Illinois ElectrletelTe 9 T"wt.' Send me the COYNE RADIOMAN'S HANDBOOK for 7 days' FREE examina- elitistanual tion. 7 days either return the book and owe nothing or l'1I send you a check Rad10 methods of After I'll Electrical i and All new Ón or money order for $3.25. Dlctle trouble sbootrá Data Bask eel ctrteal, IIlere other Coyne Books -I'll send any or I eleetri" Ve are Contains S.300 elec- iriaes.utofld, FP- an on same 7 day Free Kremi nation Offer. troniradio, doát and utomo and n enuiDment. -1 e éntc every aerie 612 Coyne Electrical S Radio Trouble Shooting Manual Volume, $9.00 cash - ins d ar frs rgy and onetruc- es. 1 $9.95 on time -$3.00 after 7 days and $3.00 monthly- 1 year Technical Bulletins Free. uD Know the pp ón Serv- S lion newest uBend Techm al Coyne Electronics for Radiomen 8 Electricians -i Volume, $4.96 after 7 days' Hof the foe meen5'q -D ked ns.Onl 9.95' examination-1 year Free Technical Bulletins. terms. Fe ankt Bulletins. 7 datatohelplD ro: Electrical & Radio Dictionary-vest pocket size. $1.50 after 7 days. d ayss,^d ñ3M =9.00. SOO 36'.'1bpe Aye rNme$CAFRE td7 ebarina Name dava today. coupon now. Mail Mail Address Technical Book Division Town lone State COYNE ELECTRICAL SCHOOL Where Employed? Check here if you prefer to pay postman cash price indicated above when books and money -back guarantee of satisfaction. 500 S. Paulina St., Dept. Ell Chicago 12, III. arrive. Same 7 day examination J

852 RADIO -CRAFT for SEPTEMBER, I946 IS TELEVISION REALLY HERE? (Continued from page 821) mi

RADIO -CRAFT for SEPTEMBER, 1946 853 ...... ,...... -.._.._...... __...... _-_...... -.--...... _ ... . DIDELE(TRDDI( (IP(UI

MONO -BATTERY RADIO With the s.p.d.t switch, the unit may test and indicate relative audio output. This simple receiver does not work be used either as a radio or an inter- If a tapped resistor is connected well on distant stations but "locals" are com. To keep the volume full on in case across the positive and negative ter- pulled in with plenty of volume. Sev- we are called by the remote station, I minals, the power supply may be used eral different tubes have been tried but used a separate set switch and volume to substitute for B batteries. the 71 -A seems to give the best results. control instead of a volume control NORMAN BROWN, No B battery is used and the plate is switch attached. Whittier, Calif. operated at ground potential. Although BOB M. MANNING, W8LRA, Cleveland, Ohio KIERSTAD REVISION the 71 -A operates normally with 5 volts I built the reflex on the filament, optimum performance (The wire that carries the line volt- radio, described by Mr. Rierstad, on page 355 of the March, is obtained with only 3 volts. age should be well insulated to prevent short circuits. Editor) 1945 issue and had fairly good results 7I-A 6C8-G RFC .00025 PHONES RADIO -CRAFT welcomes new and orig- 2KnCR inal radio or electronic circuits. Hook- .00025 LESS ups which show no advance on or 2MEG advantages over previously published WIRE WOUND circuits are not interesting to us. Send + Sw. 20 in your latest hook -ups -RADto -CRAFT 1GI-LA will extend a one -year subscription for each one accepted. Pencil diagrams 25Z6 G The tuning condenser and coil may -with short descriptions of the circuit be acceptable, but must be 20K be salvaged from an old broadcast re- -will f clearly drawn on a good -sized sheet. 40 40 ceiver. 200v 200v EUGENE SKINNER, Wilton, N. Dak. TESTER ITV (Note: Operation and performance Here is a simple output indicator, of this unusual circuit will probably be condenser tester and low voltage power with the 6A8G detector. Later, I acci- similar to that of a crystal receiver. We supply that may be constructed very dentally put a 6C8G in the socket in would be interested in receiving com- easily. place of the 6A8G. I got the surprise ments from readers who build this set. of my life when the set played with -Editor) about five times as much volume as when the original tube was used. NOVEL RADIO -INTERCOM HUGO HEMILLA, A small home receiver may be con- Tarzwell, Ont. verted to a handy intercommunicator unit with the addition of a few simple 32- VOLT RADIO parts. Recently I followed the method de- The receiver has a conventional sec- scribed by Mr. Embree, in the June 1945 ond detector and output circuit. The issue, for converting a 2 -volt battery only additional necessary parts are an set to operate from a 32 -volt d.c. line. output transformer, PM speaker, three Condensers are tested by connecting I tried the 25L6 transformer coupled to switches, and a Three-conductor line. them across the high -voltage leads in a pair of push -pull 25L6's. The volume The switch on the remote speaker series with a small neon bulb. A shorted was low and the tone quality was poor. serves to switch on the a.c. to the set. condenser will cause a steady glow. Using the circuit shown, I replaced the Considerable hum is heard due to run- Good condensers will cause regular in- driver and transformer with a 12SC7 ning a.c. in the remote line, but this termittent flashes. The frequency of phase inverter. The performance of the hum serves as an alarm to let us know the flashes is determined by the capacity set showed marked improvement. that we are being called. Before be- of the condenser. An open condenser A 50-ohm resistor was placed in ginning conversation, the set switch will not produce any flashes. series with the filament of the 12SC7 to may be turned on and the remote one Terminals V and C are connected drop the voltage and a 75-ohm resistor turned off, which will eliminate the hum. across the voice coil of a receiver under connected across the filament to carry half of the filament current. 2NDDET.,IST AUDIO POWER OUTPUT OUTPUT TRANS. ON SET Left - Rad io- intercom. ELMER ARMSTRONG, It CABLE 1 Right-Phase inverter. Smeaton, Sask. ,.

II I I 12SC7 0+ 0 ET >II FROM SPKR 6507 PLATE OI REMOTE 1-011S 1-21.

SET SW.

SSSSSS...... 2S0

ENDS TO CHASSIS PILOT SPOT SW. ALL FILS. 6.3V. . SA. V.C. ON SET o- INTERCOM. DPDT SW. LINE CORD RES. o TALK k LISTEN Y AC LINE OUTPUT TRANS.

854 RADIO -CRAFT for SEPTEMBER. IS TELEVISION REALLY HERE? (Continued freni. page R53) Build Your Own The `íneit there is no real television audience in gn Nadia kits existence and there is not much likeli- The design, engineering and materials hood that there will be one for a number simplify construction and insure excel- of years to come. So much for a few of lent reception and tone. the complex problems that confront tele- Cabinet is beautiful example of crafts- vision today. manship, made of choice veneer. Again, this is not the whole story. Tubes Required: Two 12SK7. One 12SA7, There is for instance the high present One 12SQ7, One 35L6. One 85Z5. cost of television receivers. To sell these YOUR COST WITHOUT TUBES, $15.80 by the tens of millions, the price must Turns- 1i',"o Deposit with Order, Below C.O.D. be low enough to appeal to the great JUST WIRE IT general public in this country. Today All Parts Are Mounted Immediate Delivery the lowest price of video receivers is ATOMIC HEATER .& RADIO CORPORATION around $200.00, and for this amount DEPT R.C. 104 PARK ROW NEW YORK 7. N. Y. of money you do not get much. For a really acceptable televisor that throws a fair size clear image, the price is in the neighborhood of $500.* Remember, television receivers are complex. To have both sight and sound you really must have two set, in one; one for video, the other for sound. This alone increases the price a great deal. It seems improbable at the present state of the television art that the American public would soon be able to absorb Capacity range: 350ío 54 million television receivers -even at $200 a set -a quan- 35,000 wolfs;. 115 to FOR RADIO AND tity necessary to support continuous daily, expensive and 660 volts A.C., 50 to ELECTRONIC APPLICATIONS elaborate television programs to parallel the high quality 800 cycles; 6 to broadcast programs current today. volts D. C.; cour ONAN ELECTRIC GENERATING In our estimation, the present fundamental television tech- tier. A.C.-D.C. ty PLANTS supply reliable, econom- nique is not the final word in the art. The popular price tele- ical electrical service for electron. visor will not arrive until our entire conception of television ice and television applications as has been radically changed. The means current today are well as for scores of general uses. not what television will be in years to come. Driven by Onan -built, 4-cycle gaso- We have made this clear editorially for many years past. line engines, these power units are It is certain that the ultimate solution will not be the present of single -unit, compact design and day scanning cathode -ray tube. sturdy construction. Suitable for issue mobile, stationary or emergency We quote from our editorial in the February, 1934, service. of RADto- CRAFT: idea, my mind, is all wrong and totally Model shown is hoes W35 "This scanning to series; 2000 to 3500 wons unnecessary. When the final television invention comes powered by Ones two -cyl- along, one which may be likened to the radio tube of today inder, water -cooled engine. as compared with the radio crystal of yore, it will be found that the scanning idea is conspicuous by its absence. D. W. ONAN "Some thirty million years ago, nature invented the AND SONS first real television machine which, so far, has not been 2432 Royalsten Avenue duplicated by man. I refer, of course, to the animal eye, Minneapolis 5. Minn. which has been in existence on this planet for millions of years, and is open for study by all television aspirants. "The animal eye (which, of course, includes the human eye) is almost a perfect television receiver and transmitter. Not only does it receive an image from the outside world by means of light rays and then transmit it through the optic nerve to the brain, but it goes the television en- e gineer several steps better; because in the first place, the eye gets along marvelously well WITHOUT ANY SCAN- NING MECHANISM, but the image is received and ' transmitted in colors as well." belief in television, and are certain that was said above in 1934 still HOW TO MAKE MONEY What it is here to stay. However, it will slow- The easy way to start new. or holds true now, if the television indus- expand your present occupation. ly evolve as did radio. Nor do we be- BY MAIL Enraordlnary Plain. simple try is to succeed as has the broadcast country- skill, know -how, act story of lieve that there is a short cut to rich experience of author R. Rice day -by -day. no theory. industry. wide, popular television on the horizon. YOU DID NOT NEED MONEY TO START THIS RICE Basically, television as we know it WAY. His method automatically We wish to emphasize the point that Pars all bills at once, no loans. Day today is technically unsound. Shortly a You go, no worry. Quickly s bone what has been said here pertains only nt your own all paid for. Rlee paid after the year 1800 there was an "auto- to broadcasttelevision and programs re- HOW off on $5.000 mortgage one year in streets in Lon- after using this skillful Idea. Read mobile" running the ceived in the home. It does not refer to how buyers of this bads are making made about two or three miles Hli.v litre's plan go big Does this don. It television in the theatre; television in MAIL sand fishy? welt. Rice has been do- an hour and was built by James Watt DRDF R ing it continuously for 96 years. lie department stores; and television for isivess made this plan work when living in of steam- engine fame. It was as big as other commercial purposes, where the rROFILIB[Y one roan In a limu,m IIXlging house. it Make this effective Idea is with a good -sized room, but nevertheless high cost of a receiver does not matter. anything you are selling or doing. im- Turn your city or country hone, your was an "automobile." It was totally Such specialized receivers are not work. your hotly. Into money. fol. practical and nothing came of it until low for YOUR success the easy busi- bought by the millions and therefore are ness pattern disclosed in this book. Gottlieb Daimler perfected the gasoline (Roth- bound, 514 by 8t4 inches 14th in a class by themselves. edition. best seller, enlarged to 5711 internal combustion engine. Then, in manu- pages, 185 business adventures. no !Dumont, one of the foremost television cut -and -dried teachv talk. Hundreds 1887, his automobile became the first facturers. is selling telecelvers for $1600 and of buyers whose letters we show you declare emphatically practical self- propelled road vehicle. $2400, immediate delivery, and "taking orders" its imperiative goodness. PRICE $2.95 postage paid. mailed for their "cheap" 8600 set, according to recent same day check or money-order is received. Address: We have always been strong in our New York City newspaper advertisements. HOWARD HOUSE. Melrose 76.26. Massachusetts RADIO -CRAFT for SEPTEMBER, 1946 955 SUPER BARGAINS TRY THIS 0111, IN INVERTER FOR SHAVER LOUDSPEAKER RADIO ELECTRONIC Here is a simple inverter that may While thumbing through the October AND be used with a 6 -volt storage battery issue of RAnto-CRAFr I saw Mr. Young- to run a 110-volt motor- driven electric man's description of a door buzzer COMMUNICATION SUPPLIES shaver. made from an old loudspeaker. The edi- High voltage is supplied by a 10 -volt, tor's note-suggesting that a radioman 4- ampere filament transformer with its would prefer to reverse the process - 0, del .7o -daly, windings connected in reverse. The sec- reminded me of a small speaker that I ondary is connected across the fixed once constructed from an old door 9.m rn!.ediate D,eeiu.e4ily, contacts of a vibrator. The primary is buzzer. used to supply 117 -volt a.c. to the I removed the core from the coils and shaver. The capacity of the buffer con- replaced it with short lengths of spring PLATE TRANSFORMER denser, C, will differ from the value shown when other vibrators are used. TO OUTPUT TRANS. 6200 Volt CT 700 MAGNETIZED CORE - Various values of capacity are tried 1000n Mils, 110 Volts, 60 Cycles tapped primary TO CONE 2KVA Amertram. quanti- Limited RADIO-CRAFT wants original kinks from ty 339.95 its readers, and will award a one RMATURE CONDENSERS year subscription for each one pub- Variable Condenser, split stator ceramic lished. To be accepted, ideas must be insulation 120MMF per section .003 spacing $ 1.69 new and useful. Send your pet short- Variable Condenser-E.F. Johnson split cut or new idea in today! stator 15OMMF per section .175 spacing -7000 Volts. Your coat 8.95 1000n 003 mica bypass cond.. 2500 Volts TO OUTPUT TRANS. working- Sangamo Type H .45 for minimum sparking at the vibrator Sprague .1 mfd 7500 V.D.C. condenser 2.89 points. A synchronous vibrator with 4 MFD 3000 Volt G.E. Pyranol 5.95 contacts wired in parallel will operate more efficiently and with less sparking steel wire. This wire was then mag- TRANSFORMERS than the non -synchronous type of vi- netized. The coils were rewound with Driver Transformer -- single 6V6 to brator. fine wire to a resistance of about 2000 push -pull 811 grids. Chicago Trans- The voltage output is 125 with no ohms. A small rod was soldered to the former Co. - 1.50 load and 118 volts with full load of 9 armature and old Plate Transformer built by Kenyon. 1460 fastened to an speak- Volts C.T. 3/ 420 mils, 110 Volt, 60 watts. The input draws 2 amperes no- er cone. Obviously, the armature ad- Cycles primary 7.95 load and 2.5 amperes under load (ap- justing screw was not needed so was A hot trandormer - look at this. 10 proximately 10 watts for the average removed. Volts 10 amps -6 Volts 4 amps -660 shaver). Volt C.T., 126 mils, 110 Volt 60 RONALD G. Bmu..YN, Cycle. primary 2.98 It is doubtful if this converter will Ballarat, Australia Thordarson Transformer 389 V. each side of center 44 200 mils, 5V. 3 VIBRATOR f01V. PRI. amps 6.3 V. 5 amps and matching AC OUTPUT choke 15 henries 0l, 150 mils, special 7.25 DIAL CORDS 866 Filament Transformer 2% V. at 1Ov Dial cords are often hard to replace 10 A. Kenyon- insulated for 10,000 4A. .6 /600V. TEXT on receivers that use a number of Volta -Pri 110 Volta, 60 Cycles SEE 4.25 i pulleys placed in almost inaccessible positions. The method described here MISCELLANEOUS 3A 6V.DC may be used, in many of these cases, In stock Westline Xtals -let us know for a quick and accurate replacement your frega. 2.80 work with a vibrator -type shaver as the on problem receivers. I/," flexible coupling low loss bakelite output frequency is in the vicinity of Attach two pieces of cord to the disc .15 115 c.p.s. proper places on the dial drum. Thread Tube socket for 100 TS tubes made of JAMES A. EASTHAM, the free ends around the pulleys and mycalex 1.98 Indianapolis, Ind. bring them out to a point where they Swinging choke -Langevin 9/60 henries may be tied with a square knot. Satu- 400/60 mile. DC Resistance 72 ohms 12.75 EMERGENCY IRON rate the knot with coil dope or Duco "S" meter -0 to 1 mil movement 2 %' cement and clip the ends. bakelite case -reads up to 10 3.95 Soldering by the carbon arc method has been described previously and needs OTro WOOLLEY, Motor type time delay relay -adjustable in- Colo. Springs, Colo. to 1 minute, 110 Volt 60 Cy. Hayden 5.95 no further explanation. In tight and accessible places I find the following '.I11 a few left Hewlett Packard 200 B (Note: The knot should be small audio oscillators 74.95 method useful. Connect two leads, with alligator enough to run freely in the pulleys so Cool that Kilowatt -Dual Blower blows that it will not jam or throw the cord 200 cubic ft. per minute. Delco 110 clips on each end, to 5 volts a.c. Insert Volt, 60 Cy. Completely noise free 15.95 a small hard carbon motor brush in off the track. Editor) All prices FOB our one clip. Connect the other clip to the ..-arehouse New York City, N. Y. Write for solder several inches from the end. our latest bulletin 4ßC. Touch the brush and solder to the joint COOL RESISTORS to be soldered. For best results, the Hollow high -wattage resistors run cooler when mounted a long NPPYorkó brush and solder should not make direct much on RADIOSS 7vv1 contact with each other. brass screw fastened to the chassis. IAGARA Green e 160 Greenwich ep.,T.ne ALBERT SPARKS, PETER S. WALTNEa, Oklahoma City, Okla. Inglewood, Calif. P56 RADIO -CRAFT for SEPTEMBER, 1946 WORLD -WIDE STATION LIST (Coat ,raid front page 842) for every thing. in Radio

Location Station Frequency and Schedule

London GWO 15.110 West African beam. 1 to 4 pm; ear East bam, 1 to 8:30 am; Smith- western Pacific bam, 1 to 5 am; Northwestern Pacific beam. 1 to 10:15 /e/e am London OSF 15.190 West African beam. 2:30 to 4:15 pm; Indian beam. 12:30 to 4 am; 5 to 10:15 am CATALOG L enden 050 15.180 Italian beam, 4 to 10 am; Central American beam. 4 to 5:45 pm: Near East beam. 12:30 to 5 am; 8 to 10 am; 10.30 am to 2:30 pm Lenden GSI 15.260 South African beam. 10:30 am to 2 pm London O W R 15.900 Near East beam, 5 to 6 am; South American beam, 3 to 5:45 pm; Middle East beam, 12:30 to 1:45 am Landon OSP 15.310 North American beam. 4:15 pea to 7:45 pm; 6 to 8:15 am; Australian beam. 1 to 5 am: New Zealand beam. 1 to 5 am London ORE 15.375 L ondon GRD 15.450 African beam. 10:90 am LARGEST STOCKS OF RADIO to 2:30 pm London GYP 17.700 Middle East bam, 1 to 5 am; 6 to 10 am; AND ELECTRONICS EQUIPMENT 10:30 am to 12:15 pm Leaden ORA 17.715 New Zealand and Aua - trallan beam, 2:30 to Get the handiest, most complete Buying Guide in Radio! 5 am London OVO 17.730 Near East beam. 6 am Packed with the latest, finest values in parts, tubes, test instruments, to now; Central Amer- ican beam. noon to 4 tools, books, communication receivers, Ham gear, public pm: 6 to 8:30 am: Far East beam, 2 to 6 am: address equipment ... more than 10,000 items of nationally Indian beam. 2 to5 am: known, guaranteed Southwest Pacific beam. quality ... the world's largest and most 2 to 5 am complete stocks. For earliest delivery, fastest service, lowest prices, London OSO 17.790 New Zealand beam, 2:90 to 5 am depend on ALLIED! Send for this FREE 1946 Catalog now.

Landa 08V 17.810 South African beam, 1 to 4 am; Indian beam, 5 to 10:15 pm: West Atrlcaa. beam, 2 to 4 am MORE THAN 10,000 ITEMS -Largest and most complete se- Leaden OPP 17.870 Northwest Pacific beam. lection of radio and electronic equipment to serve the needs 1 to 5 am; 6 to 8:15 am; South African beam, of engineers, servicemen, dealers, soundmen, amateurs, and 10:30 am to 12:45 pm builders. All the leading makes. Guaranteed quality. Lowest London ORO 18.025 South African beam- 5 prices. Everything you need from one dependable supply to 9 am; 10 am to 12:15 Tim: West African beam, source! 5 to 9 am; 10 am to 2:30 pm London OVO 18.080 North American beam. 8 am to 6:45 pm; South American beam. noon HAM GEAR HOME SETS to 4:15 pm London 6514 21.470 South African beam, 5 Earliest delivery Paradeof1946 to 10:15 am; Near East beam. 5 to 10:15 am; on latest communi radios and phono - West African beam, 5 cation receivers radios. Handsome to 10:15 am and transmitters. styles. Wonderful London GS1 21.530 Indian beam, 5 to 8:15 am Time payment performance. To- London GST 21.550 plan; trade -ins ac day's leading val. London GR2 21.690 Central American beam, 8:30 to 10:15 am cepted. ues. London GVS 21.710 South American beam. 6 to 10:15 am London GVT 21.750 London 680 25.750 London G8K 26.100 South African b e m, 6:15 to 10:15 am; Weat NEW P. A. EQUIPMENT -Complete Sound Systems for African beam, 6:15 to 10:15 am every public address requirement. All the newest develop- London GSR 26.900 ments. Everything in amplifiers, speakers, microphones, ac- L ondon GSS 26.550 ETHIOPIA cessories. New intercom systems. Also the latest develop- Addis Ababa 4.965 10:30 to 11:30 ments in recording and recordplaying mechanisms. FIJI ISLANDS am Sun VPD2 6.130 Sundays, I to 5 am; other FINLAND days. 3 to 4 pm Lahltl 01 %5 17.800 8 am to 12:30 FRANCE pm Pria 9.520 North American beam. HANDY RADIO BOOKS HELPFUL CALCULATORS 12:30 to 12:45 am; 1 Radio Formulas and Data These radio reference aids Provide Yalu to 1:15 am Dltl,onary of Radio Terms able data quickly: (Continued on page 862) Radio Circuit Handbook Radio Builders' Handbook Parallel Resistance and Serles Simplified Radio Servicing Capacitance Calculator. No. 37 -960 25e Radio Data Handbook R -F Resonance and Coil 500 FORMULAS TO SUCCESS ALL SI% BOOKS No. 37- 799...750 Winding Calculator. No: 37.955. 25c MANY million dollar norme started with a they paid it big price. Here from have 500-no les. -tried and tested formula.. apes and proces.s for RADIO things . . all at the ALLIED CORP. Ìmakingouely rldlc. low price of 25e. 2 -6 Here your opportunity to start a 833 W. Jackson Blvd., Depl.' -02 business ith but few dollars' FREE capital and with Undreamed of profits Chicago 7, Illinois You can formales"in home to cucut t Send FREE 1946 RADIO household expenses to the bone. D CATALOG put use workshop Send Six Books No. 37.799 cut costs s muc í2 ss D 10000en. ° Quit Paying out many dollars in D Send Calculator No. 37-960 $ enclosed prong to manufacturers. wholesalers. and nfmake the Send Calculator No. 37.955 thine' yourself for 1rd you follow our instructions. Name 68 PAGE& 3290 WORDS IN TEXT Send for 500 FORMULAS AND RECIPES" today. . 25c.fiow o r won't be asked Address o another or llater. Solona m ney- back guarantee. NATIONAL PLANS COMPANY City Zoore State P. 0. BOX 26. 5 STATION N. New York 23. N. Y.

RADIO -CRAFT for SEPTEMBER, 1946 857 =Izairrez!!mpf9P,414 11f1Ml`4J1

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The Question Box is again undertaking to answer a limited number of questions. Queries will be answered by mail and those of general interest will be printed in the maga-

a. A fee of 50c will be charged for simple questions re- = quiring no schematics. Write for estimate on such ques-

tions as may require diagrams or considerable research. Ii

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should have a lower resistance than be necessary to remove several turns of yours, for best results. wire from each of the coils or reduce METER RECTIFIER This amplifier will work well with a the size of the i.f. tuning condensers to I have purchased a copper -oxide phonograph pickup or r.f. tuner but reach this range with some transform- rectifier to use with my d.c. meter but it is recommended that a preamplifier be ers. When using this tuner to select sta- have received no instructions for con- used when working from a crystal or tions from a remote point, the receiver necting it into the meter circuit. This dynamic microphone. should be tuned to the same frequency rectifier has five terminals and is de- as the i,f, coils. signed to pass 20 nuc at 4 volts a.c. WIRELESS TUNER Please print a diagram showing how I2SK7 MATTING this device is connected to the meter. - I would like to I2SA7 ANI C.C.M., Cleveland, Ohio. of RECEIVING ANT. 100uu1f have a diagram 100025 a wireless push- 72.-. button tuner to use o h with my broadcast °o I!G+ LI .-I receiver. I would 50K like to operate this éb.a,á device from an a.c.- 260 d.c. power supply r A. A meter -rectifier circuit is shown so it can be 1 that I I l 1 I in the accompanying diagram. The a.c. K built as compactly IIIIIIICI iC2 IC 1C4 I e5 IC6 terminals are usually the ones on either b ;a ;a ;d a side of the center terminal. In many as possible. - ;a E.S.C., Collingdale, 1 rectifiers, the end terminals will be con- Penna. nected internally and there will only IC7 CB C9 CIO C` C be four terminals on the unit. The a.c. A. The diagram IK IW PUSH BUTTON 25 25200Y may be identified with an shown should meet AC-DC CH. terminals SWITCHES - CHASSIS ohmmeter. The resistance between these your requirements. 50Y6 It is equipped with o terminals will be very high regardless 15 15 5 +40 - zo of the polarity of test leads. six push buttons ^150V which will allow 600V T250V 290 5076 12SK7 I2SA7 P. A. AMPLIFIER you to tune in any one of six - pre - 10W,OR LINE CORD RKAC Please print a diagram of a medium selected stations. amplifier a T1 and T2 are power public address using --SW pair of push -pull 45's in the output standard i.f. trans- stage. I have two 27's and a 53 that I formers which may be tuned to fre- 32 -VOLT D.C. TRANSFORMER would like to use in other stages. My quencies between 550 and 600 kc. It may 9. Please publish winding data for a 27 53 45 (21 power transformer to supply 90 volts 27 it from a 32 -volt d.c. storage battery. I 500K 05` plan to use a 32 -volt synchronous vi- PHONO P.U., brator.-E.R., Mandan, N. D. P. F, TUNER, OR A. You may wind your own transform- L PRE-AMP. er on a 1 -inch square core as follows: 25K OUTPUT TRANS. á .6K bK 50K PRI.3.2Kn --c Primary, 300 turns, center-tapped, No. I o 28 enamel wire. The secondary is wound with 1020 turns, center -tapped, No. 32 450g. 25K ÓPM 20+ 500K to No. 34 enamel wire. This design will 1--- give 40 to 50 milliamperes at the rated 450V. voltage. If the voltage is too high a re- IC K sistor may be placed in the B -plus lead or a choke -input filter used. 2500 -ohm field. Wil it be Note well that the "window" must be speaker has a 150K possible. to use this with the amp ifier? large enough to hold the windings, something often overlooked by a be- -T.M., Lonaconing, Md. .5.,9A.áILS.I 6 600v. ginner. meet 5V.,3A. A reference article, "Practical Trans- A. Here is a diagram that will a50K your specifications. A 27 speech ampli- former Design," appeared in the Sept- working JKN- Oct. 1942 issue of RADIO -CRAFT. It de- 27 inverter 12 . K fier feeds a phase o350V. S low. scribed how to calculate core sizes for into a 53 connected as a push -pull driv- o-70MA er. The grid bias should be adjusted by 2.5KaPIELD - given wattages, estimating the window 350X how to put varying the position of the slider on the 117K AC space needed, and actually resistor across the speaker field, which the windings on the form. 1946 058 RADIO -CRAFT for SEPTEMBER, Rabic! Zfjírtp-jfíbe Rem; Sago 3n 44ernsbatk Publttati0ns PRICES Go Do HUGO GERNSBACK AS MORE ELECTRONIC Founder PARTS ARE AVAILABLE Modern Electric¢ 1908 Electrical Experimenter 1913 COMPLETE TRANSMITTING & RECEIVING BRAND NEW! Radio News 1919 SETS as used by government components Science & Invention 1920 -no 3 SETS IN ONE - 15 TUBES Radio -Craft 1929 removed. MADE BY ZENITH & EMERSON Short -Wave Craft 1930 SET A. for telephone and tc.,r raph in- Wireless Association of America 1900 cludes: 6 tube superheterodyne receiver and 6 -tube MOPA transmitter with 807 final amplifier. Grid modulated for Some of the le.-per libraries In the country still has telephone. Specialized circuits make copies of MODERN ELECTRICS on file for interested FC'ity ,x¿(tY this set ideal for network operations. readers. The frequency range of 2 to 8 mega- ( 9 cycles includes the 80 meter and 40 From the September. 1911. issue of MODERN meter amateur bands. ELECTRICS. SET B, consists of 236 megacycle transceiver that can be shifted to the Wireless Tam t* 144 or 226 megacycle amateur bands. On the Motor Boat, by Rich- -I SET C. a complete inter -communication ard H. Foster. "-"""510 system using 3 control boxes and 3 combination headphonee- push -to-talk High Powered Condensers, by Frank microphone, providing intercommuni- C. Perkins. cation or remote control operation in an extremely flex ble arrangement in S different locations. Improvement on Loose- Coupled Tun- POWER SUPPLY: This unit, including dynamotor, operates from a 12 -volt 0 ing Coils, by P. Mertz. storage battery. These seta are ideal for mobile or marine installations. 2 An- $ 5 Helix tonnas, 1 Veriometer Resonater, Spare Set Tubes, Generator, Set of Spare Insulation, Water Resistor, and Parts; 5 acts Earphones, 6 sets Microphones Battery Economizing, by E. Jay Quinby. Another System of Wireless Teleg- NEW RECEIVERS B.C. 3ithMwith twolys °ACT's. Less Freq. Meter B.C. 221 with raphy and Telephony, by John B. Brady. 603 semi -completed, made for $10.00 calibrated chart and tubes, A Sending Condenser, by H. V. 603 Tank F.M. 723 A/B Klystron, for con - less var. vouer, new 10.00 1,000 KC. crystal and mi- Rome. cond. and w Large selection of 3CM Plumbing. cro V dial. The Legality of "Wireless Tapping," front panel, Send far our listings of Wareguide, 120 KC. no tubes. Wavemeten, Attenuaton, etc. to $A /50 by McClatchie. 0 m e g. Stanley Cabinet .25 Complete stock of 400 -2400 cycle 2 ]vSL Transformen. Send us your Perfect. Ducretet Rotary Spark Gap. Long T, eh. Book .50 requirements. Range Potentiometer. Transmitting Pic- tures Wirelessly. A Novel (variable) Condenser. High Pitch Spark Producer, U. S. NAVY MODEL by Robert E. Smith. Increasing Sensitiveness of (head- 4, RAK RECEIVER , -. phone) Receivers, by Earl Clifford. -1 SHIP F- 1 NEW -IN CASES illbs -3 CA AMATEURS!! 15 Kc. to 600 Kc. 6 -tube receiver with Leo W9GFQ Offers \VC -Band pass filter -Audio filter - Noise limiter-precision tuning-Volt- ea Immediate Delivery .tge regulated power supply for 60 cycle a's ON NEW, HIS EXCLUSIVE, LOW PRICED I IS V. --Can be battery operated. Coco- rs - _._ _..___ _-_ -_ __..__- n WRL GLOBE TROTTER plate with spare parts, tubes (in metal '

box) and instruction book. - o TRANSMITTER KIT $7350 _ - ONAMATEURS ACCLAIM RADAR, RADIO COMPONENTS ITS CTN. Receiver RC 406. From SCR -268. Freq. Range: SUPERIOR 201 -210 ma. 15 tube surerhet. 20 mc, I.F.. 2 mc. band width. 1155 -60e opar. $21.93 Performance -- Oscilloscope 5'. BC -412. tram SCI[ -288 usus 115v. a.c. Complete with conversion dia. und Inatr. 54.50 =- Modulation XFMR: 807 to pair of 8077 2.85 $59.95 Modulation XFMR: 8117 to 813. 5.90 Driver: OVO to pair 811's 3.00 The 'folks' amateur rig Completely CI11 Trans!. P.P. Mod. & Driver, 8L8 'a -per pair 3.30 1155 60c/330 -0 -330. 85 ma /6.3V 7.5a 3.95 on the n arko4 today. Wired, S75 MR: /5at4/8.3r -.8a I'WIt: 1155 80c/750v -110 ma /et. /6.3v- 5a/6r -3a 5.95 Place your orders now. (Accessories 513.85 extra) I1.V. Plate: 1155 60c /3200v -150 ma 9.95 ' Swinging Choke: 2.5 by @ 375 ma; 10 N @ 75 ma 595 OK Pyranol 23F47 9 mid 4000 VDC (List $301 8.95 ' SANOAMOO -4 Mica .004 mfd 20.000v 25.50 Mira, Random, F31..0005- 8000VDC (Iist $29) 5.25 New Type PHONO Johnson 5001)35 Variable. 501 mmfd. 3500v (List 811.751 4.75 OSCILLATOR WOW, len TUBES CECO KITS 3 Ti.. 11.00 tubo. at. AMERTRAN PLATE °4 i'^rf^'t Ne. 16.191 S4.95 5111'1, Sylvania 8.75 KITKI 1: 1000 pieces hard - No aerial required Utilises high quality loop both TRANSFORMER 5F1,7. Phillips 11.00 ware. asstd. $2.-I as just radiatingn me. .' 71'4 6.95 KIT 2: 100 -ft. spaghetti, diem Trimmer purtdedretot, frequency to 115v- 60c /6200v -ct 700 ma. 9.11'1 9.95 all sizes 1.3., any pprt,on r Uses SS band between be50 KC Tapped at KIT 3: 60 mica con - end uoo K Uses astio and a5zs tubes $3995 IF CRYSTAL FILTER 28605 dentiers, -, For BC -319; BC -342. asstd. 4.6 Special Price Resonant et 470 Ka. .up KIT 4: 200 resistors, X:al Inr1 asstd. 5.95 FREE! Our Latest Flyer Radio Reference Map (31' x 4}') 1St SEND FOR FLYER Tube -Base Calculator 252 All Tube and Circuit Book 10t All merchandise guaranteed. Mail orders promptly filled. prices F.O.B. New York Cily. Send Money Order or Check. Shipping charges sent C. O. D. Send for Flyers. COMMUNICATIONS EQUIPMENT CO. 131 -C LIBERTY ST., NEW YORK CITY 7, N. Y.

Formerly Wholesale Radio Lab. TELEPHONE WH 4 -7658 Address Dept. RC -9, Council Bluth, Iowa.

RADIO -CRAFT for SEPTEMBER, 1946 859 NEW RADIO-ELECTRONIC' PATENTS

Edited by I. QUEEN

UHF MEASUREMENT convenient method, especially with coaxial line. To simplify the a portion of the co- Ralph W. George, Riverhead, N. process, Y. axial line is arranged in circular form. A mov- Patent No. 2,399,481 able arm containing a probe contacts the internal measurement of u.h.f. voltage very THE is a conductor and feeds the voltage to a detector, difficult process. At the microwave frequen- whose output is indicated as a vertical deflection cies, an accurate measurement is not generally on an oscilloscope. The variable arm is operated possible with conventional apparatus. The in- by a motor which also controls a switching cam vention described here requires only a special as shown. wire element and an ordinary bridge circuit and During each revolution of he arm, the cam power supply. It is effective up to several thou- switch is closed once. This provides the horizon- sand megacycles. 9 REGULATED .6 POWER .7 SUPPLY .6 +105 V. DC 23 R.F.IOLTAGE 'ga .3 x .1 One arm of the bridge is a platinum or wollas- ton wire only 'i" long and .1 mil in diameter, 0 30 6090120150180 having an approximate resistance of 73 ohms at DEGREES room temperature. The arms 1 and 2 are fixed tal synchronizing pulse which starts the hori- resistors and 112 is adjustable. The condenser C zontal deflection. As a result, the pattern shows serves to by -pass the r.f. currents so that they the relative voltage at each point of the cir- do not enter other parts of the bridge. A regu- cular coaxial line. A celluloid screen marked off lated power supply is desirable to energize the in angles as shown makes it convenient to inter- bridge. To operate the circuit, the bridge is first balanced with no r.f. through RW. When the current is turned on, it heats the small platinum wire and therefore causes its resistance to increase, unbalancing the bridge. In order to de- termine the exact value of voltage, a known source of d.c. is substituted for the r.f. and its potential is adjusted until the same deflection is obtained on the microammeter. The two voltages are then equal. pret the standing waves. Cain and deflection con- HIGH FIDELITY AMPLIFIER trols are adjusted until a full wave covers ISO degrees. The pattern may be observed while James B. Crawley, Camden, N. J. necessary adjustments are made. Patent No. 2,400,919 Ills is an unusual 2 -tube amplifier which T shows excellent fidelity to almost 16,000 HIGH FIDELITY DISC cycles per second. RECORDING Henry E. Roys, Indianapolis, Ind. Patent No. 2,400,953 0 Heretofore offered only in cardboard - case container, NEGATIVE feedback is widely used in elec- this type is now available trical mechanical re- in an aluminum can -the postwar Aero- and systems for the vox Type PRVC. 0 15, PERMANENT MAGNET DEGENERATIVE FEEDBACK This truly universal replacement elec- FREQUENCY- CYCLES trolytic readily doubles for twist- prong, spade -lug and screw -base types. To in- The first tube is direct coupled to the screen - stall, center screw is removed, metal grid of the second in addition to capacitance cleat slipped off, wire leads passed coupling to the control -grid. Degenerative feed- DISCRIM, through mounting hole, and back is accomplished through the sac to condenser Ne4ATURE RECT. metal cleat by coupling the plate and suppressor of the and first SHAFT screw now replaced from underside tube. Further negative feedback results because of FIXED CAPACITOR PLATE chassis and tightly drawn up. In- the screen of the second tube is not by- passed sulated positive and negative wire leads. to ground. Note that these effects are secured Multiple sections have concentrically - without using additional components beyond those wound sections with common negative. generally required for other amplifiers. duction of distortion. Greatly increased fidelity In all popular voltages and capacitances. A typical response curve is shown above. can be obtained from a disc recording system by the use of negative Ask Our Jobber... feedback. For best results should Order your Aeru.uc Type it include PRVC metal -can cleat - not only the amplifier mounting elect rub ties from him. Have a stock TO SOURCE on hand for OF but the vibrating stylus those rush jobs. Ask for postwar I catalog - or write us. A.i, CURRE as well. One possible connection uses a coil in which 4.1 the stylus induces a voltage to be fed back to the amplifier in +300V proper phase. This has a tendency to cause STANDING WAVE INDICATION undesired coup ins with the recording coil besides Donald W. Peterson, Princeton, N. J. adding mass o the vibrating system, another Patent No. 2,400.597 undesirable feature. F R RADIO- ELECTRONIC ANDY THE most important measurement which con - An effective solution is the use of FM to de- cerns antenna design is that of standing rive the negative feedback voltage. A small wave ratios. An impedance mismatch results in capacitor plate is used in conjunction (but not INDUSTRIAL APPLICATION, the existence of standing waves along the trans- in contact) with the stylus. Vibration of the mission line. Therefore, it is necessary to reduce latter modulates the frequency of a high -fre- AEROVOX CORP.,NEW REDFORD,MASS.,V,S,A. them for maximum power output. One possible quency oscillator (for example 30 mc.). The method modulated output is applied to a discriminator Elgert:13 E.4001 St.,NewYerklB,N.Y. Cable:'ARLAN' consists of using a v.t.v.m. arranged to slide along the line while the ratio of maximum- and this audio voltage can be used as negative lk Cubic AEROVOX CANADA LTD., Hamilton, Oet to-minimum-voltage is noted. This is a very in- feedback. 860 RADIO -CRAFT for SEPTEMBER, 1946 MODEL 2403 Volt Ohm Milliamm eter 25,000 OHMS PER VOLT D.C.

SPECIFICATIONS NEW "SQUARE LINE" metal case, at- tractive tan "hammered" baked -on enamel, brown trim. PLUG -IN RECTIFIER- replacement in case of overloading is as simple as changing radio tube. READABILITY -the most readable of all Volt- Ohm- Milliameter scales NEW ENGINEERING NEW DESIGN NEW RANGES -5.6 inches long at top arc. 50 RANGES REDDOT LIFETIME GUARANTEE Voltage: 5 D.C. 0- 10 -50- 250 -500 -1000 at 25000 ohms on 6" instrument protects against per volt. defects in workmanship and material. 5 A.C. 0 -10 -50- 250 -500 -1000 at 1000 ohms per volt. Current: 4 A.C. 0- .5- 1 -5 -10 amp. 6 D.C. 0 -50 microamperes - 0- 1 -10 -50 -250 milliamperes -0 -10 amperes. 4 Resistance 0- 4000 -40,000 ohms -4 -40 megohms. 6 Decibel -10 to +15, +29, +43, +49, +55 Output Condenser in series with A.C. volt Triplett ranges. Model 2400 is similar but hos D.C. volts ELECTRICAL INSTRUMENT CO. Ranges at 5000 ohms per roll. Write for complete description BLUFFTON.OHIO.

RADIO TEST EQUIPMENT (Continued from page 838) HAMHEADQUARTERS FOR point at the right end of the scale cali- Equipment and Information bration. DECIBEL READINGS Most volt -ohm- milliammeters have decibel scales printed on them. Decibel meters are a.c. voltmeters having cali- SPECIALS brations that are converted from a.c. Aladdin -5.3 MC IF voltage readings developed across a Transformer i n p u t- specified impedance line and having a output Diode 1.15 stated reference level to decibel equiv- Colonial Radio Corp. alents. These readings are usually based TBY Whip Antenna 1.95 on the reference level: Zero Decibels = BC -312 6 Band RF coils .006 watts (6 milliwatts) into a 500 - with switch Pyrexglass ohm impedance line. If the line imped- insulator with four FOR YOUR ance is other than 500 ohms or if the MTG sere ws .. .39 reference level should be other than 6 3 Mfd.- 2000 Volt milliwatts, these readings are valueless. G.E. 3.50 NEW RIG Fig. 8 is a chart for adapting any 3 x 3 Mfd. 600 Volt Oil Filled .99 We Have a Good Stock of a.c. meter having a 15-volt, 150 -volt, or All Standard Lines 1500 -volt a.c. range to a decibel meter: Tubes- 3C24/24G 1.90 For 15 -volt range read db directly. For Aero Running Time 150 -volt range add + 20 db to db scale. Meter 60 Cycle AC_.. 3.50 SUPER DELUXE SPECIAL For 1500 -volt range add 40 db db -- to Mail Orders Promptly Filled 5 Tube 24 Watt Code scale. Amateurs to Serve You Practise Osc. $29.50 The author has endeavored to de- (205, Must Accompany All A few minor changes the scribe the workings of volt-ohm- milli- C.O.D. Orden,) amplifier can be converted Write Dept. RC to speech or P.A. Audio ammeters so that anyone with a knowl- W6SCQ-W6UXN -W6NAT Amplifier, complete with edge of electrical theory and terms may W688U tubes and dust cuver. understand them. The workings of more complex test equipment such as signal generators, signal tracers and vacuum tube voltmeters, have been amply pre- Radio Product Sales Company sented in previous articles in this mag- 238 WEST 15TH STREET azine, and in books published on these subjects. LOS ANGELES 15, CALIFORNIA PRospect 7471

Location Station Frequency and Schedule Location Station Frequency and Schedule stINSULATED Parle 9-540 midnight to 12:15 a Honolulu KRHO 17.800 Philippine boom, 4 12:30 to 12:45 am:lm 11:30 am COMPOSITION to 1:15 am HONDURAS Pris 11.845 8 to 9:45 pm; 10 to La Ceiba HRD2 G.235 7:30 to 10 pm 10:45 pm; 11 to 11:45 San Pedro Sula HRPI 6.357 6 to 7:30 am; G:30 to RESISTORS Pm; mtdnlght to 3 e 10:30 pm noon to 5 pm; 5:30 to Taiucisaloa HRN 5.875 8 to 10 am; 6 to 11 pm 7:30 pm HONG KONG Parla 15.350 6 to 8 an Victoria 28W 9.495 4:30 to 8:30 am Pris 17.765 8 to 8 am HUNGARY FRENCH EQUATORIAL Budapest HAT4 9.125 A FHICA ICELAND Brazzaville F21 6.023 4 to 8 pm; midnight ts. Reykjavik TF1 12.265 8 to 9 am; 3 to 6:30 1:30 am pm Brazzaville FZI 9.440 11 am to 8 pro: mid- INDIA night to 2:30 at Delhi VUD3 3.340 11 to 11:45 ana Brazzaville F21 11.970 11 am to 6:45 pm; mid- Delhi VUD3 7.290 7:30 to 10:30 am; 9 to night to 2:30 am 10 pm Brazzaville F21 15.595 4:45 to 8 am Delhi VUD8 7.275 6 to 7 am; 11:15 am to Brazzaville F21 17.527 midnight to 2:30 am; 1:15 pm; 6:30 to 7:15 4:45 to 7:45 am; 11 am Pm; 9 to 10 pm to 5 pm Delhi VUD4 9.590 8 to 10:50 pm; 1 to 4 FRENCH WEST AFRICA am; 5:30 to 7 em; 7:45 Dakar 8.840 aftemoone tilt 4:30 pm am to 3:45 Pm GERMANY Delhi VUDIO 9.670 7:20 to 11:30 am Munich 8.160 11 pm to 2 am r* Munich 7.285 11 pm to 2 am; noon Delhi VUO3 15.290 6 to 7:15 am Resistance to 4 pm Delhi VUDIO 17.830 5 to 7 am GREECE IRAN Athens SVM 9930 heard 1 to 6 pm Teheran EQB 6.155 9 am to 2.30 pm; 8 to and Wattage GUADELOUPE 8:30 pm Pointe -a -Pitre 7 GRAH 7.215 to 7:30 pé Teheran EQC 9.680 noon to 2:30 pm GUAM KU5Q 9.140 heard at 7 am IRAQ Guam KU5Q 9.330 8 am Bagdad HNF 9.800 8 am to 3 pm marked on Guam KUIG 10.510 heard coltina NBC IRELAND around 5:30 pm Athlone 9.595 9:10 to 4:30 pm Guam KU5Q 12.255 5 am; 7 pm to midnight ITALY EVERY Milan AFRS 6.135 11:30 am to 4:30 pm UNIT 7 Guam NUSQ 15.920 pm to midnight I APAN GUATEMALA Tokyo J21 9.536 6 to 7:15 am 6.220 6 Guatemala City TG2 to 11 pm Tokyo 1VW2 9.675 2 to 5 am; 5:30 to 7:15 Here is a new composition resistor Guatemala City 6.465 8 am to noms; 6:30 Wt am; 7:30 to 9:40 am; TGWB to 1 am 9:55 to 11:40 am; noon -tiny but exceptionally rugged. Not Guatemala City to 1:40 pm; 4:30 to TGWA 9.685 Sunday evenings 6:45 pm Guatemala CItY Tokyo JVW3 11.725 1 only color coded, but individually TGWA heard at pm 15.170 daytime transmissions Tokyo 121 11.800 8 to 9 am HAITI Tokyo 1VU3 11.897 marked for quick identification. Little Prince 5:45 to 11:30 am Port au HHCM 6.165 5 to 8:30 am; 11 am to Tokyo 15.105 heard at 7:30 pm Devils are sealed and insulated by 2 pm' 5 to 9 pm Tokyo 12K 15.160 heard at 7:30 pm Port au Prince HHBM 9.660 5 to :30 am; II am to Tokyo 1TL3 15.225 515 to 7:15 pm 2 pm; 5 to 9 molded plastic. They dissipate heat pm Tokyo 11P2 15.325 10:45 pm to 3 am HAWAII LEBANON KRHO 6.120 4 Honolulu Oriental beam, to Beirut FXE 8.030 11 to 5:30 am rapidly, have a low noise level and 9:45 am pm LUXEMBOURG MCH 6.020 midnight to 3:30 am; 5 low voltage coefficient, are light, com- to 8:30 am; noon to 6 rn pact, and easy to install. Millions of Luxembourg MCH 9.610 Irregular Luxembourg MCH 11.115 these units have proved their value in MARTINQUE Ft. de France 9.705 heard at 5:30 critical war equipment. Available your aerial MALAYA pm Install Singapore 7.220 11:30 pm to 1:30 m: from stock in Standard RMA val- 3:30 to 5 am; 5:30 to THE 10:35 am ues from 10 ohms to 22 megohms. Singapore 9.548 8 to 9 :30 am Singapore 11.855 8 to 9:30 am Tolerance ± 10%. MEXICO VERTROD Guadalajara XEJG 4.820 heats at 8:30 pm ¡trailable only from Ohmite Distributors Mexico City XEBT 6.000 8:4.5 am to midnight Mexico City XEWW 9.500 8 am to 2 am Mexico City XERQ 9.590 evenings OHMITE MANUFACTURING CO. WAY Mexico City XETT 9.555 4895 Flournoy St., Chicago 44, III. Mexico City XEYU 9.600 late afternoon, and eve ninas Mexico City XEQQ 9.680 even Inge Mexico City 11.950 evenings Mexico City XEUW 6.023 7 am to 12:95 am MOROCCO 2 Rabat CN R3 9.082 2 to 5 pm; mtdnlght to As MODERN as the electric 3 am MOZAMBIQUE refrigerator, compared with Marquis CR7BH 11.718 the old ice box. NETHERLANDS VERTROD -vertical models Eindhoven PC1 9.590 2 to 3 pm; 8 to 9 Dm NETHERLAND INDIES eliminato poles - insulators - Bandoeng 5.400 early mornings lightning arresters - filters - NEW CALEDONIA Noumea FK8AA 6.205 2:30 to 4 am; 4:30 to hanging aeriol wires- climb- 5 am ing. NEWFOUNDLAND St. Johns VONH 5.970 10 am to 2 pm: 3 to VERTROD- 20 models cover 10 pm all wave reception- FM -AM NEW ZEALAND Wellington ZLT7 6.715 4:25 to 4:45 am and Television. NICARAGUA Managua YNOS 6.760 8 to 10 am; 5 Dm te VERTROD - the most perfect midnight Send Now for scientific development op- Managua YNQW 6.910 6 to 10 am: 1 toll pm Bulletin No. 127 proaching complete freedom Managua YNBH 7.008 6 to 10 pm NOVA SCOTIA Gives complete data and horn man made static. Sydney CJCX 6.010 5 pm to midnight list of RMA values. Includes Halifax CHNX 6.130 7 am to 11 pm Tho VERTROD way (with pal - PALESTINE dimensional drawings and Jerusalem JCKW 7.220 10:30 pm to 3 pm handy color codes. enled foulures) ie the modern PANAMA way. At most radio shop.. Panama City HP5H 8.122 6 to 10:30 pm WRITE FOR FOI DER dol Panama City HPSA ll.696 7 am to 11 pm . . . Panama City HPSG 11.780 dorlotesee nd vonings Ee Zglst uuit`i PERU Lima OAX42 5.895 4:30 to 11:30 pm Inca OAX5C 9.785 evenings PHILIPPINES VERTROD Mardis PV 9.305 5 to 7 am: 11 to 11:30 pm PY2 11.640 6:30 to 7:15 am; eve- C R P R I Manna bo1MllTIE O O A T O N nings RHEOSTATS 60 EAST 42nd STREET PORTUGAL Lisbon CSX 6.370 3:30 to 7 pm RESISTORS TAP SWITCHES NEW YORK 17, N. Y. Lisbon CSW7 9.735 7 to 8 pm Lisbon Gex 11.995 7 to 9 am Lisbon CSW 12.070 heard 1:30 to 3 pm

862 RADIO -CRAFT for SEPTEMBER, 1946 AUDIO MIXER DESIGN PREPARE FOR THE (Continued from page 835)

It should be noted here that standard "ea/ gragia/tilde141 procedure must be followed in all equipment patching, especially if the circuit into which the patch is being inserted i n RADIO ELECTRONICS is already in use. Correct procedure is to insert the "cold" end of the patch -cord first, that is, to complete all composite patching, and then patch from the composite output to the required input circuit, never Use Cleveland Institute in the reverse manner. The tip of a patch -cord plug is momentarily shorted home study courses for pro- as it passes through the grounded frame fessional self- improvement. of the strip jack, and if the opposite end of the cord is energized, the result is unnecessary interruption of the program. An example of a straightforward control panel is shown on page 835. It is CLEVELAND INSTITUTE OFFERS the conventional type used at most average broadcast stations, in tvhich key 1. Mathematics for Radio and Communication Engineering. switches and variable attenuators are 2. Advanced Course in Radio Communication Engineering. used in each mixing position. Beginning A college -level Radio Engineering Course. at the extreme left of the panel, at least four channels are provided for micro- 3. Master Course in Radio Communication. phones, a minimum of two for tran- Covers fundamentals of Radio and includes complete scription reproducing equipment, one preparation for FCC Commercial License Examinations. for network, one or more for remotes, 4. Specialized Television Engineering. and one position left as a master mixer. Including post -war Television Techniques. A line -reversing switch to reverse the input and output of the network am- All Courses Include plifier when. feeds originate locally may The Remarkable Workbooks of Instructional Aids, prepared or may not be located on the console, by the instructing staff of Cleveland Institute. depending on individual needs. Utility, Choose the course best suited +o your needs-Start with the section you talk -back, line and monitor cue keys are are qualified to enter -Use the economical CIRE "Pay -As- You -Go Plan." provided as desired. indicating lamps provide visual indication of control. ((-rite for descriptive folder. The line key energizes a set or bank of relays which connect the program CLEVELAND INSTITUTE OF RADIO ELECTRONICS amplifier to the broadcast loop, operate Contractors to the Canadian Broadcasting Corporation an "On the Air" studio light, and ener- Successors to NILSON RADIO SCHOOL SMITH PRACTICAL RADIO INSTITUTE gize a "Standby" light at Master Con- Founded 1939 Founded 1931 trol. Operating the proper studio key at RC -9 TERMINAL TOWER, CLEVELAND 13, OHIO Master Control lights an indicator "G -I Bill of Rights" lamp in the control room, completes A mooed for Veteran Training Under the loop circuit and places the studio (MAIL THIS COUPON Cleveland Institute of Radio Electronics. RC 9 Terminal Tower, Cleveland 13. Ohio. "On the Air ". Gentlemen: Plea,e send information about your Verne study courses in HALO Electroldca. With a Talk -Back key, conversations may be carried on between the studio NAME I desire training In and control room. This is done only I have had experience in broadcasting servicing when the studio line key is not energized ADDRESS operating O mtg. iQ CAA Army -Navy amateur 'O oilier I am a (at rehearsal times) to avoid the possi- CITY bility of program cross -talk. In some High School Grad. College '0 Degree ZONE STATE Vateren w cases, where the talk -back unit is in- Cheek here P r Enrollment Information. cluded as a part of the studio control circuit, the entire talk -back unit is ren- dered inactive by operation of the studio line key, and remains so as long as the ROTA -BASE ELECTRONIC VOLT- OHMMETER studio is "On the Air ". In other systems, NEW HANDY LAB. DIAL. Simply tu,i, the movable dial to Ili- ,tit ,e , the ROTA-BASE 110 VOLTS AC 20 RANGES a patch -cord is used to complete the mid complete. correct connectio ' are instantly indicated on the 'prong. diagram. Filament, grid, plate. 0 /ár10 talk -back circuit, and proper usage is etc. to than 300 tube types are give,,. /50 /IOU /100 /1000 /.;000 volts DC and NNoden stainable time lost n lengthy reading or $1185 1C. 0- 1,000.000,000 ohms in ola over- left to the discretion of the operator. thumbing f pages. ROTA -RASE actually gives POSTPAID lapping ranges. Sensitivity: over MILLION picture se NOW OHMS per VOUr on 5 volt range. ONL`Y`gS1.00. ostageprepaid`'cr sent CO[ n The more complex control boards em- postage Money hark t not delightfully pleased. Complete component punched killudildrilled anedbti tbea., ployed in larger stations and in network REED MFG. CO. ió: panel. Easily assembled and wired. Special alblel ack circuit developed during war by studios often make use of automatic Scient i,t at the Ialifont is Institute of Technology gives amazing sensitivitye and flexibility white completely .lim interlock switching circuits, by means noting necessityn of batteries nd expensive meter. Facia nstrument ois individually calibrated. Dial scale over of which any number of separate or nine inches long: In addition to performing the u ual soit -ohm function.. composite programs may be pre -set and this instrument easily measures thee. voltages: SUPER lI:T OSCILLATOR. AVC. AFC. TRUE. GRID DIAS AT TIR automatically switched in at the proper (:RID. BIAS CELLS without affecting the rin-uit. Measures the exact leakage r.,I.tare or INSI'I.ATION. TUBES. time. Individual cue or monitor positions CONDE.NSF.R.S. It ran be used V, i, a .,goal geueratoe are provided whereby program levels, WHOLESALE RRDID., for SIGNAL TRACING quality, and the required amount of line 2608 Ross Ave. STERLING ELECTRONIC COMPANY equalization may be quickly determined 166 N. Sierra Bonita Ave., Dept. 2. Pasadena 4. Cants. prior to air time. DALLAS 1 TEXAS

RADIO -CRAFT for SEPTEMBER, I 9 4 6 TELEVISION FOR TODAY (Continued from page 890)

llave (4ouSeek tube. See Fig. 4. With a low value shunting resistor, Z, of the expression: Gain = G. x Z, becomes low and with it, the gain. In- Ike Sala Systems? cidentally, this equation demonstrates why high G. values are desirable. Sometimes designers use elaborate interstage coupling networks to achieve It's a bi- monthly magazine the desired selectivity without lowering the gain by excessive resistor loading. of authoritative information Two such possible coupling units between the r.f. stage and the mixer are in the on new developments shown in Fig. 5. The variable con- capacitor field. Simply fill densers in these tuning circuits are of the trimmers variety, pre-set by the in the coupon below if you'd like manufacturer. For each station a separate unit is connected into the circuit to receive this easy -to -read by the station selector, which may be of the push- button or rotary type. Tun- technical publication regularly at your ing of the type employed on the majority of 'sound receivers is manifestly home or at your office. impossible for television with its 6 mc 1689 bandwidth. Imagine the confusion of a a layman trying to center the station with RC Manufacturing 6 mc to play around in. Hence the pre- Solar Corporation set push- button or rotary type of tun- 285 Madison Avenue, New York 17, N. Y. ing. Fig. 6, printed by courtesy of the Gentlemen: Please send me the SOLAR SYSTEM regularly, starling with the current issue.

-M(7 OUTPUT TIM CIRCUTth Name Fig. 4- Equivalent of tube output circuit. Address ..... American Television Laboratories, City Zone No Slate._._._..__... shows the switching arrangement of a television receiver.

CONVERTERS AND MIXERS To take advantage of the benefits of A LABORATORY QUALITY the superheterodyne, it is necessary to convert the incoming signal to the lower intermediate frequency. For this we OSCILLOSCOPE have converters, where the mixing and the oscillator voltage generation are confined to one tube, or mixers, with a For the Service Man .. . separate oscillator. If we attempt to use any of the conventional pentagrid converters (6A7, 6A8, 6D8, 6L7, 6SA7) undesirable interaction occurs between Portable, sturdy, compact -the signal and oscillator. This generally be- CRO -5A is an ideal unit for rapid, comes noticeable at about 60 mc, with accurate, high quality service work. the result that not only does the oscilla- Check the utility and features tor output voltage vary, but more im- which you have always wanted in the instrument on your bench. For better laboratory and production testing .. . For routine Service work ... For studying any variable which may be translated into electrical potentials by means of associated apparatus... Designed with tubes for maximum amplification with minimum noise ... Exceptionally stable trace even under adverse power line variations ... Frequency response -essentially flat from 20 cycles to 350 KC ... self-contained Completely ... 4n is Write to General Electric Company, Electronics Department SRC -6407, Fig. 5-Two methods of coupling r.f. stages. Syracuse 1, New York. portant, the oscillator frequency. More desirable, but still not totally satisfactory, is the triode -hexode converter, the GENERAL ELECTRIC 6K8. Here the oscillator voltage is de- '77 -aa veloped in a separate section of the Fc4 RADIO -CRAFT for SEPTEMBER, 1946 Szetadefie at Ze04144! SURPLUS SPECIALS

MOBILE 40 & 80 BRAND NEW DYNAMOTOR METER XMTR- POWER SUPPLY RCVR SET Don't confuse this FAMOUS MARK II fine apparatus with second hand sur ONLY $3450 plus now on the market. It's but true! You voriometer, 1 "B" set antenna. 1 control brand Hams! It's unbelievable Supplies 500 volts at 160 mils now a complete 40 and 80 box, 1 microphone, I Dynamotor power can own new, in original DC from any 6 volt or 12 volt Heré s supply kit, plus oll the plugs, cable meter mobile rig for only $34.50. battery source. A what you get: Two sets in one. Phone connectors, etc , that ore needed for Signal Corps Car- typical Newark and CW 2 to 8 Mc (Right Smack in operation. And this rig can take it. It 51495 on ton. VALUE! the 40 dhd 80 meter bands!) 6 tube was originally designed for tank oper- Super Receiver,6 tube MOPA Xmv. Also, ation. Remember: Nothing else to buy, a complete 235 Mc transceiver. Included You're on the air with a mobile job In this wonderful buy is: 1 pair head you've been longing for AT THIS SEN- phones, 1 key, 1 "A" set antenna with SATIONALLY LOW PRICE EICOR DYNAMOTOR Each new Ideal for your mobile rig. unit brand and fully guaranteed. This dynamotor has two windings which deliver the following voltages: 500 volts at 50 mils Gt 12 f VOLT INPUT DELIVERS mils HAMS! EXPERIMENTERS! l 275 volts at 110 A compact, sturdy motor used by U. S. Army, make a 10 Meter FIELD ORQE`P Weighs approx. 6 lbs Size: 7t /2' l x 4sq"w x pKpß,o° a INTENSITY METER from this $495 Signal Corps Test Set! A TERRIFIC BUY FOR ONLY Unusual instrument, offers won- SVapku pNOLSE derful possibilities for very high MERCH frequency work. Meter alone NEW YORK CHICAGO (0 -250 RF mils) worth more 115 -17 W. 45th St., New York 19, N. Y. 323 W. Madison St., Chicago 6, III. than price of com- Branch: 212 Fulton Street, New York 7, N. Y. plete unit. Only o WRITE FOR few left. BRAND 95 NEW! Sale Price .. FREE FLIERS AND 'CATALOGS .EIfiÇTRIC CQ.If1C.

tube (See Fig. 7). This, to some extent, are the familiar Hartley; ample of how various coils and small shields the oscillator from the direct in- its modification, the electron -coupled trimmer condensers are tapped in with fluence of the signal. Hartley; the tuned -grid tickler oscilla- each change of frequency. These units The best solution is the use of a tor and the Colpitts (or a modification, are all pre -set and tune the oscillator to separate oscillator (generally a triode) the ultraudion). In previous commercial the proper frequency for each band. and a pentode mixer. Not only does this models, the 6J5 has been widely used, Great stress is given to oscillator completely separate the two from each although any tube possessing low instability, because in a television set, other, but it permits the use of a pen- ternal shunting capacities, a high value recommended stability of ± 0.01 percent tode for a mixer, with a subsequent de- of G. and ability to function at the must be maintained. Nothing is more crease in noise level. With conventional higher frequencies is suitable. Triodes annoying than to see the image become design, the amount of noise generated are preferred because they require but distorted due to a shifting oscillator in a pentagrid converter, as compared one regulated voltage; pentodes need during the course of a broadcast. Be- with a pentode, is in the ratio of 4 to 1. two. The switching arrangement in the cause the main tuning control is fixed, Thus, the converter sets a higher mini- oscillator section of Fig. 6 is a good ex- (Continued on page 870) mum level and naturally lowers the sensitivity of a receiver. As far as noise is concerned, triode mixers would represent an even better choice than pentodes, but when we consider the problem of regeneration due to C,,, we find that pentodes are more desirable. When a separate mixer tube is employed, the injection of the oscillator voltage may be made at the control grid, cathode, screen, or suppressor grids of the pentode. The most likely place is the cathode permitting simultaneous control of both the grid and plate circuits. Another good point of injection is at the control grid, although not as favorable as the cathode. The remaining two grids, screen and suppressor, are seldom used because of the increased driving voltage required. Several typical coupling circuits for control grid and cathode injection are shown in Fig. 8.

TYPES OF OSCILLATORS Four common circuits have been used for the oscillator in the majority of Fig. 6- Switching arrangements for tuning a modern four -channel television receiver. RADIO -CRAFT for SEPTEMBER. 1946 865 MONEY- SAVING V.H.F. RECEIVER SPECIALS (Continued from page 825) regeneration control, the standby might be used if polystyrene is not switch, pilot light and the volume con- available. Details of the modification are Just a few items selected at random from our trol, are drilled in a row along the bot- pretty clearly shown in the photograph. tremendous stocks. Order direct from this ad and save time. If you don't see just what you tom of the panel one inch up from the Fig. 2 and Fig. 3 give drilling details avant, write for our latest bulletin of money- lower edge. These should be placed and provides a full size pattern for both saving specials. symmetrically to maintain a good front- panel appearance. The holes for two Meter and Tester Bargains 10 -32 oval -head screws that secure the M l -G. E. 0.10 A.C. Voltmeter 3''x" Rectangular s 3.94 panel to the chassis should be drilled M2- McLintock 0.300 O.C. Milliameter 3'/x' Rect. 3.93 along the same line, one inch in from M3- McLintock 0.500 D.C. Milliameter 3", either side. Rect. 3.93 M4- Melintock 0.15-150-300 D.C. Mil- hamster 3''x" Rest. 6.90 A hole 2 inches in diameter is then M5 -G.E. 0.1 R.F. Meter Via' Diameter 4.92 cut in the panel. This should be centered b M6-- Marion 0 -I Standing Wave Meter 3'.'2' Round 3.93 and 2 7/16 inches from the top edge. PB- I00-Superior Volt. Ohm- Milliametm' 28.40 The mechanism from an old National P13210- Supertor Volt Ohm Milliameter 35.75 M400- Superior Vacuum.Tabe Voltmeter 52.50 Velvet Vernier dial with the dial re- W- 665-Wetton Selective Analyzer 58.50 moved F- TS2- Feller Signal Tracing Analyzer 29.50 is then installed in this 2 -inch CA.II- Superior Signal Tracer 18.75 hole and secured with 6 F.1-Feller four % -inch, -32 Signal Tracer 9.85 flat head machine screws. This allows the movable part of the dial to come out Wire and Coble flush. A lucite pointer may be attached HPI- Hookup and Pushback Wire. 100' hanks each .89 to this part with the three original Hookup and Pushback Wire 10 hanks screws. The panel then may be given This view presents the parts layout clearly. assorted colors 7.80 HP2- Hookup Wire Odd lengths 2 Ib. pkg 1.39 two coats of flat black enamel allowing EN3- Enamelled wire No. 26- 2830Ik. spools .89 ample time for drying between coats. rotor and stator plates. As shown in No. 22 -24 '',, lb. spools .33 CC4-D. Cotton covered enamelled wire No. 16 An escutcheon plate similar to the one Fig. 2, new stator .plates were cut out per lb. .79 of thin sheet aluminum to get the maxi- SCI -Single Shielded for phono pickups. etc. used should now be made of thin sheet 100' 2.49 brass stock and also given a coat or two mum capacity possible, since we were- SC2 -Single Cond. Shielded wire 100' 3.49 MCI -Microphone cable- shielded rubber of flat black. The dial card (of drafts- n't sure how much would be necessary covered, odd lengths 6 to 40', per foot .05 man's Bristol Board or a good quality for the coverage desired. This accounts M C50-Mi rop vine Cable -50' lengths. $2.95- 5.73 index card) should be made of ample for the difference in the shape of the MC2- Microphone Cable -2 Cond. Rubber cov- stator plates as used and the originals. _ ered. odd lengths 6 to 40', per foot... .08 MC250- Mierophone Cable-2 Cond. 50' lengths 4.95 14-- 13/4' -1 Either may be used. 100' lengths 8.75 I 14-11/16.-01 MC4--4 Cond. I Using a set of two stator plates and Shielded Rubber Co'. able. SOLDERING LUG 100 ft. 10.95 one rotor plate with single spacing, MC8 -8 Cond. Shielded Rubber ear. table. per 100 ft. 16.95 2 1/4 satisfactory bandspread was achieved - TV2 Cond. No. 22 -2 twisted Vlnylite wire. éIUTTERFUac`OF 2mETER COIL per 10O ft. 12.50 in our receiver. This combination with CC- Coas-sable 50 Ohm, per loot ...... IO ample CO -Cosa cable 100 Ohm, foot .12 the coils as constructed gave per n/4 spread for the two meter band. If the SOLDERING LUG FOF builder plans to use the 1? , meter band Servicemen's Kits TUBE CONNECTION he may prefer to double-space the ca- 3 /16`PCi. S YR NE-) MOUNTING ANGLE No. IS -12 popular speaker cones --Y to IV with V.C. Kit 4.95 pacitor and make the coil somewhat No. 2K-50 Assorted Bakelite knobs all set Fig. 2- Details of "butterfly" tuning unit. larger to get greater bandspread. screw. kit Kit 4.75 No. 3N -100 Assorted knobs -push on & set The photos and Fig. 2 show how the screw Kit 6.95 size to allow for the swing of the pointer No. 40-100 Assorted By -pass and Buffer coils are mounted across the stator Condensers. Total value over 920.00 and to match the escutcheon plate. The plates for short connections. The tube Our price only 5.82 card we used when trimmed measured No. 5R -50 Assorted 5.10 & 2D Watt Resistors 5.95 socket is directly behind the coil, mount- No. 6C -l00 Carbon Resistors -25 1W 75''2 W 2.94 21x4% inches and the escutcheon was ed on a small aluminum bracket. The No. 70-200 Assortment t. W Carbon Resistors 3.95 made to match size. No. 80-200 Assortment '' W Ins. Resistors 4.95 this Two or three antenna coupling asembly is two Fahne- No. 9P-50 Assorted padders and trimmers 2.95 half -circles may now be drawn on the No. 10E -50 Assorted Electrolytic Condensers 10.95 stock clips mounted on two small stand- card for calibration purposes. If care- off insulators. Flexible leads connect to fully handled this home -made dial will Transformers present an appearance that will match 29P -Power Transformer 6.3V 3 Amp. 5V 2 that of a commercially -made unit and Amp. 120V input. 6511V 90M 2.95 30P- 5V-6.3V-600 V IOOM 2.95 should be presentable in the most fin- 31P- Crosley 1014 -10 -tube Power Transformer 2.95 320-20 Watt Output Trans former 6L6-eta 1.69 ished station. OED PLATES The chassis should now be prepared t1äE Tube Bargains for Hams by making the socket holes for the two 307 91.70 8298.. 58.90 24P1 5 4.90 audio tubes on the top and that for the 807.... 1.90 9001.... 2.45 5BPIA 12.45 five prong socket on the rear. Two 5/16 - 866.... 1.45 9002.... 1.95 5FP7 9.95 954.... 4.90 9003.... 2.45 5R4GT 1.80 inch holes are drilled for two banana 955.... 2.90 9004.... 1.95 OAKS 1.60 on 4.90 .94 7BP7 14.90 jacks the rear of the chassis near 8005.... 9006.... MODIFIED ROTOR °BUTTERFLY' 8025.... 8.90 V R -105 the 6KG socket, for speaker connections. We have one of the largest tube stars In lice country. s5'rite for our list of tubes available for imme- The detector section construction may diate shipment. well be started by the dismantling of a Write for Latest Bargain Bulletin showing hundreds THIS of items for servicemen and amateurs. Our stock 1s Cardwell tuning condenser, type ZR- TEMPLATE IS ACTUAL ME received tmprocing . . . now Items being every day. 15AS. This is a midget, single bearing rotor type and lends itself well to revision since it is assembled with machine screws and nuts. The original Fig. 3- "Butterfly' capacitor plate patterns. steatite base may be used as a template for drilling a piece of polystyrene for a the movable shna which holds the two - SOUI10 EQUIP. CO., Dept.® new base. This material is preferable turn coupling loop. This coupling loop on a small poly- 911 -913 JEFFERSON AVE.,TOLED02.OH10 due to its kw loss characteristics at is mounted piece of very high frequencies but the steatite styrene tubing ",v th two small machine

866 RADIO -CRAFT for SEPTEMBER, 1946 RHS SPECIAL FALL CLEARANCE SALE! PORTABLE TRANCEIVER, NAVY TBY TRANSMITTER SHELF T66CRN -10 28 -80mc (5 and IO meter bands). Com- Complete RF section uses 1-807 Crystal os- plete with phones, mike, 8 tubes, crystal cillator tripler, I- 807 -RF doubler, I- 257fá, and key. Slightly used, fine condition. RF tripler, driving 2 -2578s RF amplifier in Wonderful buy 42.50 push pull, I -6H6 RF output indicator. All Vibrator & storage battery power supply volts and current read on 2 Weston meters switch. Now on I I0mc. for above $19.95 through panel Slight change to I44mc. Capable 500 watts output. Less tubes and crystal. METER WESTON MODULATION Reduced to . 39.95 Mod. #30I -3" AC rectifier type 1000 ohms per volt. OSCILLOSCOPE KIT Super value at 3,95 5CPI Cathode ray tube ea. 6.95 AMERTRAN HEAVY DUTY Socket for 5CPI 1.98 PLATE TRANSFORMER Anode button for 5CPI .35 NATIONAL DRIVE PW -O Shield for 5CPI 1.49 The ideal unit for 1000 watts 2X2A Rectifier tube 1.25 Exceptional buy at 2.95 Prim. 106 -115v 60 cycle Sec. 3100 -0 -3100, full voltage across Plate cap for 2X2A ceramic.... " .25 sec. 6200v at 700 ma. $39.95 Socket for 2X2A ceramic .20 3 mc I. F. COIL KIT Our Price Xformer, 1700v, 6.3v, 2.5v 110v 60 cycle 6.50 contains 1- input. 1- interstage and I -discriminator all shielded. Condenser, oil .5- 2000v...... 2.10 Set of three coils 1.98 Order Separate or Complete Kit, SPECIAL 16.95 100W DUMMY ANTENNA OIL CONDENSERS: GE., AEROVOX, C.D . etc LOAD FOR 80 METERS TUBES: NEW JAN APPROVED 2mfd 600v 60c 'mid 2000v 95e Metal box contains Millen 160 4 " " 75c 4mfd 2000v $3.95 mmf. Var. condenser .077 spa.. 6C4 .75 6AL5 .75 5BP4 ... 8.95 8 10 " " $4.35 ing, Iso /antite base. easily split 6J6 .85 6AG7 1.25 9002 .... .69 " " $1.10 statored. Many uses. 866 1.19 6AK5 1.60 9003 .... .69 4 " 1000v $1.10 1" 3000v $3.95 Special at $2.9870 813 9.95 6AC7 .95 1625 ... .79 8 t' " ... $2.00 .1 " 7500v $3.95 1629 .79 257B 14.95 872A .... 3.50 ALL MATERIAL IS NEW AND GUARANTEED UNLESS OTHERWISE STATED Please Specify Dep.: "R6" 1T7,,n Ordering. 20% Deposit Required With All Orders. RADIO HAM SHACK Inc., 63 Dey St., New York 7, N. Y. EXPORT DIVISION: WESTERN INTERNATIONAL 168 WASHINGTON ST., NEW YORK 6, N. Y. screws, and this in turn is mounted on the end of the movable shaft which is a 5% -inch length of 1/4 -inch bakelite rod. In similar fashion the tuning capacitor is coupled to the dial using a 2% -inch length of the same rod and a Millen flexible coupling made of steatite. By having the tuning assembly at the rear of the chassis body capacity effects the famous EVERSHARP is home- are eliminated. The r.f. choke PENCIL SET made and is shown in the photo, below PEN and the tuning coil. It is made by winding It's guaranteed forever. lei yours without charge, to prow that OLSON RADIO WAREHOUSE gives the radio 16 turns of No. 24 enameled wire on a service -man more for his money and something besides! y4 -inch form and removing the form HOW TO GET YOUR SET: With every purchase made afterward. Tin the ends of the wire and from us, we will send you "Olson Pointers' (profit. soldering lug THE sharing certificates) according to the dollar value of solder it directly to the goods shipped. Thus, an $18.45 purchase brings you on the grid stator plate. 18 "Olson Pointers"; 34.70 worth of parts brings you In wiring it is excellent practice to BEST 4 "Olson Pointers", etc When you have saved 100 "Olson Pointers". send them to us and you connect up all heaters first, then the will receive the Eversharp Pen and Pencil Set cathodes and then the rest of the audio RADIO FREE, packed in a beautiful gift boa! components. When wiring the detector OLSON gives you value: our prices are lower. DEAL IN OLSON gives you service: we ship same day or- section, keep in mind that short leads der is received are imperative in very- high- frequency OLSON gives you quality: we sell nationally circuits, since only a fraction of an inch 3 YEARS! known products. OLSON appreciates your business; we thank you here and there will add up to sizeable with premiums. values of inductance and capacity when Do you get our BUYING GUIDES regularly) Use the the whole circuit is considered. For in- coupon below. stance, the plate of the tube is connected to the stator by a % -inch wire and the MTO USE grid is tied to its stator by direct con- AY 0/50il RAD/0 WARENO nection to the capacitor and its grid 73 E. MILL ST., DEPT. 42, AKRON, OHIO 11111111111111 leak. I went to start saving "OLSON POINTERS." The coil for the two -meter band is Send me your Free BUYING GUIDES regularly. made by winding 6 turns of No. 20 tinned copper wire on a % -inch form and NAME then removing the form. The turns are then spread to occupy about % -inch in ADDRESS length. The 1% -meter coil is made with (Continued on following page) CITY STATE RADIO -CRAFT for SEPTEMBER, 1946 867 V.H.F. RECEIVER (Continued fro, page 867) IN PHILADELPHIA - IT'S SPECIAL three turns and spread to approximate- ALMO RADIO COMPANY ly % -inch. These will undoubtedly need adjustment when the receiver is calibrated. * PHILADELPHIA'S The five -prong socket at the rear of NEW WHOLESALE RADIO the chassis is for the power connections AND COMBINATION and would be wired as marked in Fig. 1. ELECTRONIC PARTS A spare prong will be noted. Its pur- DISTRIBUTOR! OFFER pose is for the use of a power supply with a built -in voltage divider- If one Surplus- New -Guaranteed of these (or batteries) should be used the detector voltage may be adjusted to approximately 50 at the 75,000-ohm TUBE SPECIALS regeneration control, and the 30,000 - ohm dropping resistor is eliminated. The BRAND NEW RCA - KENRAD - GE external power supply should be a low power unit capable of delivering 200 to AT DEALERS' O.P.A. PRICES 40 250 volts at to 50 milliamperes. The speaker used should have an output TYPES PRICE transformer to match the pentode out- 27- 80 -5Y3G 41e put tube. An inexpensive 3% -inch PM unit gave ample volume and the quality 56- 5Y4G-26 46c was sufficiently good for speech, 45 48c TUNE-UP AND OPERATION The power supply may be turned on 75 Sic VARIAC General Radio type 200 CU, 860 volt - with the standby switch (SW) in the ampere rating, 115 volt input, output variable from 0 to 135 volts at a maximum current off position to note if the heaters are 6F6GT-6J 5-6Q7GT-76-77 .... 54e of 7% amperes. Comes complete with knob correctly wired. The speaker must be as pictured above. Shipped in original G.R. carton. plugged into the 'banana jacks before 6A8GT - 6C5GT - 6C6 - 6D6 the high voltage is applied to avoid 6K6GT - 6K7GT - 6SA7 - VOLTMETER, Westinghouse Model BA -33. ruining the screen of the 6K6. When 6SK7 6SQ7 6X5GT 2 round flush, flange mounted, 0 -iris switch SW is snapped ON - - - vo s A.C. to the posi- 12SA7 12SK7 tion the superregenerative hiss. char- - - 36 60e acteristic of this type of receiver should 6C5 6H6 occur at some point as the regeneration - -= 6SA7GT - 6SJ7 control is advanced. If the set will not I2SJ7 68e regenerate smoothly, some experimenta- IN5GT tion will be necessary. The radio fre- - 5Z4 = 6SG7 - I2K8GT quency by -pass capacitor, marked ".001 - 12SR7 - 83 80c to .006" in the diagram, should be changed until 1,ost perfornlanee is noted. OZ4 - IRS - IS4 - ISS - 1T4 3Q5GT - 5V4G - 6C8G - 6F7 - 6N7 - 6R7 - 6SL7GT - I5Q7 - 14R7 $1.00 5T4 - 6B4G - 6L6 - 7H7 PORTABLE A.C. AMMETER - 7L7 - 12A6 $1.22 WESTON MODEL 528, Dual Range 0.3 Amp. ALSO HUNDREDS OF OTHER and 0 -15 Amp, full scale for use on any fre- TYPES quency from 2 to 500 cycles. The ideal instrument for all commercial, industrial, experimental, home, radio, motor and general repair RESISTOR SPECIALS shop testing. Comes complete with genuine leather, plush lined carrying case and a pair 10 WATTS 50 175 300 of test leads. A very convenient pocket - - sized test meter. -IOM - -25M -OHMS 10c "DONUT" TYPE CURRENT TRANSFORM- 20 WATTS - 2700 - 3500 - ER, to be used in conjunction with above I5M OHMS 12c meter. This transformer extends the ranges - Alb of the meter to 0-45 and 0-90 Amperes making There is little apparatus below the chassis. 25 WATTS 1000 it four range A.C. Ammeter Diagram fur- - 15e nished showing simple operation of the above 50 WATTS meter -transformer combination. In our particular case a 0.002 was - IM - 2M - 3 100 18c best but values from 0.001 to 0.006 All four above units should be tried. The by -pass capacitor MAIL ORDERS FILLED PROMPTLY included in our may or may not be necessary. Values from .05 up to 1 or 2 pf might be used to SPECIAL COMBINATION OFFER eliminate the noise from the potentiometer rotor. If audio howl is present the ONLY . . . $24.50 optional resistor will have to be used. Use the largest possible value since ALMO 25% deposit on all C.O.D. orders. smaller values reduce ,the volume ap- All shipments sent Ry. Exp. Coll. preciably. Values from 1 megohm down RADIO COMPANY to 50,000 ohms may be tried. 509 Arch Street MARITIME SWITCHBOARD When the receiver "soups" satisfac-

PHILADELPHIA 6, PA '. C obard 3 -0513 336 Canal St., New York 13, New York torily, the band to be used will have to be located. With the proper coil con- 868 RADIO -CRAFT for SEPTEMBER. 1946 nected across the condenser the frequency may be checked by the use of a honiemade wavemeter which has been That's a Buy previously calibrated by another re- -- Raytheon 866A It la- ceiver already located in the band. - ment transformer I I5V 60e gel, Usually some neighboring barn or ex- 2.5Vct I IA Sec and perimenter will have one RCA 1590 of these which tubes he will lend you. This wavemeter should With Millen caps

. -. & sockets .... 7.00 be coupled to the detector coil by bring- Raytheon Trans-

. ing them former only .. 3.25 close together. Then tune the RADIO Transformer wavemeter. When the receiver blocks LAFAYETTE High Voltage (goes out of oscillation) the receiver --. Like new I15V- frequency __._._ 6 0 C Y. S o e. is that of the wavemeter and 3200V no C. T. For that California the reading on the wavemeter dial may FLYER! Killowatt S 9.00 BARGAIN For single or P. P. 304T1 tubes be marked on the receiver dial. If the Two units 6400V C. T. wt. 80 lbs. 16.00 wavemeter is deemed accurate enough COPY DC- 9A1Crystal Std. 1000Ko G'Inso. S.C. S 5.95 the megacycle and half- megacycle fOR YOUR G.E. Pyranol 2 mid 4000V wkg. (LP 655.00) 4.95 SEND New W.E. Dynamic microphone D- 173340A points can be marked in. Complete with 50' cable, desk stand or chest plate, feedback reduction attachment, freq. If no wavemeter is available, the re- _ NOW MOO 50 to 9000 cycles "TAB" Special 111.95 With W.E. Input mike trans. KS-9450 13.95 ceiver may be roughly calibrated by Dynamic mike cartridge only D173127 4.95 All 3 units Mike, Transf. rep. Cartridge 18.00 using Lecher wires to locate the bands W.E. pp. Inpt. tnsf. 100.10000 fly -K8. 9448 2.50 and then W.E. pp. Input driver 6V6's to pp. 805 more closely lined up by listen- grids freq. 100 -10000 cy Tnsl KS.9449 4.50 ing for marker stations. Data on the Both units KS -9448 and KS -9449 6.50 W.E. Vacuum Time delay Ill Relay 115VAC., 1.49 construction and use of Lecher wires W.E. 011 Cond 4mfd 400V wise. Two for 1.00 Sprague Oil Cond. 4mfd 1500V wkg. Two far 4.50 is outside the scope of this article but CD TJH 011 Cond 6mfd 1500 wkg. Two for 5.95 was given in the article "144 -Mc Trans- mitter" in the February RADio- CaArr. C ant lete Now Cale practice set In trunk We used a matched impedance type an- McElroy AN /USC-T1 operates on 6. 12. 24. tenna erected at a height of 40 feet 115V Ix` & 115. 230 V A(' for classroom, above ground, which has given very camp or club Cale satisfactory results. There are many practice, gives loth visual, blinker and types which may be used and we strong- audio adjustable freq. tone. Loud speaker ly urge the construction of one espe- also earphones con- cially designed for the band you nection. Room for that You can always count on Lafayette's phones and keys out- intend to operate on. An efficient an- put goal for at lead prices to save you real money. That's be. 100 students. Brand tenna is very necessary on very high new Gov't insp. Poin- cause we turn over thousands upon thou- ts supply with tau frequencies. Vibrators worth the sands of radio parts- like that- just as price alone, While this receiver does not repre- GOv't cost 5197. TAB special 122.50. fast as we get them! Famous brand New S.C. 339 Keys 98c. sent the ultimate in its class, perhaps, merchandise priced so low you won't be- Headphones \V. E. 509 III imp. 8' CD & PL(: 13.97 S.C. Headphones with rubber cushions IA90. it should provide good dependable re- lieve your eyes. (When the world's old- ception and its construction will not est and greatest supplier of radio parts WE test 115V60ey pri.5V264 sec 15000V Ins. 4.50 present problems too says these are the most unusual bargains Conde, Sprague Oil IOmfd660VAC2000VDCwkg 2.70 formidable for the Condor G.E. Pyranol 15mfd660VAC2000VDCwkg 3.90 average builder. in our history ... you'd better start clip - Condor F3L -822 Sangamo 002mfd8000V(LP132) 3.99 pin that coupon below.) Conde, C.E. 3 mfd 330V ACI000V DC 2 for 2.50 ... Gander 011 & insulators 2mfd2000VDC..2 for 4,25 AC Voltmtr Watghse 150V 21/4' BC, G'I 1.98 tat any freq. mtd 2.10mcs ea. 11.51..4 for 5.90 W Crystal IN21.22 -23 new lead sealed 3 for 1.50 Here's a buy that's typical Resistor Kit 100 STY &I W, 50 to 2 megohms 2.50 RADIO -ELECTRONIC QUIZ Mica Condor Kit -qty Silvermica 30 for 2.00 Autosyn Bendix Xmitter & Revr. new G'I 2.95 FILTER CONDENSERS, OIL FILLED Autosyn Bendix Hobart I I5V -60 Cy. New 2 for 18.00 How thoroughly have you mastered Allied Relay 81 OPDT ets New 1.49 II5VAC SAMP 2 mfd. 600 v. round. Allied Relay BO 5000 ohm DPDT IOAMP ate 1.92 the contents of this magazine? Try the XPS498 2T/¡' x11/2' .59 Magnetron JAN 2132 new W'stghso Std ($154) 19,95 following quiz as XPS499 4 mod. 600 a round. 41,4"x 1W' 1.11 WE Raw IN26 Crystal "K" radar bd 1CM .75 a test: SCPI IAN insp new with Duo- Diheptal socket 7.50 HR102 6 mid. 600 v. 43.i"x21/2 "xltä" 13S 30P1 JAN insp new with Duo- Diheptal socket 3.95 1. Would it cost more to produce a HR104 4 mod. 1000 e. VA" x2r/í"x11/4" 1.49 GE 3 cond Tinsel 'Si" new rubber cable 100 ft. 3.50 Mica .OIMFD2500V No. 4 13.40) 2 for 1.00 good television program or a good HR103 I mfd. 2000 v. 4y¡ "x ?1/a "x11/," 1.49 ARRL -Radio Amateur Handbook 1946 1.00 moving picture? See page 821. HR105 3 mfd. 2000 v. 4% /4 Navy sea trunk 12' x 22%' a 18' used L.N 3.95 "x3' "xl%" 2.15 Hallle,afters MO &XTL HT -4 units SCR299 2.95 2. Butterfly UHF condsr with WE 703A socket 3.95 What is the maximum bandwidth Kurman adj. 1000CV AC source complete new .97 that can be handled by an amplifier Punched Chassis 163/4"L a 6 "W a 3' .35 Punched Churls 161/4"L x 13'W x 2" .65 circuit? See page 822. Stepping relay 10 pos new B.C.G'I 24 to 48 VDC 7.50 Is LAFAYETTE New Xtd reef test set TS-268U & spare pts . 22.50 3. the present shape of television New AN /APR -5Ax reeve IISV60C Free 1000 to screens theoretically the best one? 6000 mes pckd overn's cases. ant unit & IS the 75.00 Aircraft JAN runt relay & solenoid HV & CUR 3.95 See page 823. 25 assted Allen Bradley 1 Potentiometers 2.50 4. Did our enemies as well as ourselves RADIO possess night -sight telescopes for RADIO WIRE TELEVISION "TAB" military purpoes? See page 826. NEW YORK BOSTON NEWARK Special 5. How do English and American phonograph records differ? See 1 Rory THY portable ultra page Hl -Fret. 28 to 80 me's 827. transceiver Voice & @V LAFAYETTE RADIO Spot calibrated. including 6. Is a crystal set confined to purely DEPT JI.6 100 Sixth Ave. New York 13, N. Y,I crystal calibrator. all i trhei. ad). ant; phones, local reception? See page 831. I mike, carrying case 149.50. 7. Where would you look for a "pad" in Rush my bargain flyer D Additional spars parts, Vibrator supply. Trunk. a broadcast station? See page 834. I Antenna, manual and other Please enter my order for spares 625.00. 8. What is an Ayrton shunt? See page I 837. Check enclosed..D.. Money Order..0

2 M in. orders FOB N.V.C. Add Postage all order's 9. To increase the efficiency of a tele- Send C.O.D..D., E nd 25% deposit. WH itehall 3 -3557. Send for cata- vision log 300. Specialists In International Export. receiver, would an extra r.f. School, I NAME .... __.... I College & Industnal trade. Buy thru "TAB" and or an extra i.f. stage be more desir- ...... save. able? See page 840. I I ADDRESS "TAB," Dept. D9 10. At what price are television sets now 1 I 6A Church Street, New York 6. N. Y. available? See page 855. I CITY... ZONE...... STATE moons aI6 NM RIM MN ramm sain MD a1r AND am RADIO -CRAFT for SEPTEMBER, 1946 869 HAS IT! HARRISON HAS ITv 44 -50 mc, the video carrier would be at HARRISON 45.25 mc. From the video carrier, the picture side bands extend for 4 mc up ALL STANDARD LINES i HARRISON SELECT SURPLUS to 49.25 mc. The audio carrier would surplus are Your assurance d goal usable. guaranteed. be at 49.75 mc. We low wired -TOP YAI.0 then ntatnrial at tmaatimaliy our large FACTORY AUTHORIZED DISTRIBUTORS ALWAYS! Crane in and browse through Now suppose the oscillator frequency for the top quality manufacturers and we now have MSS Deportment. in stock lots more new. latest improved production is 71.00 mc. The mixing of this with stores today. for everything BEAM POWER TUBE VALUES gear. Visit our $2.30 you need. We promise you fresh. clean material- 807 Always popular! New Amateur net the 44 -50 mc would produce the follow- --and goose all, or quicker --at the lowest current prices HSS-41.75 each! Throe $1,47 ing i.f. our sinceree tilt° to be of friendly, helpful seek.. mare at signals: the ale uAa ed plenty are. Nealoel vprlce 914.00. WroducedllD'om1817.5pwalts tmicatl ma Fqulpweullar eaareddnllvormg d: r 1. For the video, the i.f. will range RECEIVERS HSS $7.45 from 21.75 to 25.75 mc. Actually, the i.f. MAKES-practically all models. 251B ight nail ALL pasibla drives you wmt your new cet ln the quickest power p to 150 Moi 1.9 wxtta Ìf (4F24) Full 524.50 GRID time send your order to liAltltlSONI 930 watts output. Amateur net price is For example: Harrison sells them for $6.90 EN NATIONAL HRO.STA -1. New model with noise only limiter, metal tubes. ham bendaproad mils. 00 0.1 DC MILLIAM- peak000lg°°v working O n Complete w ith peck, speaka er, and $303.00 METERS body O O O 1.7 to 30 Mc. FIL.3"Ia./eíta. roils,p List Wee $29.156.75 O O O O HAM MARLU NO new Super -fro. $310.05 Irakelate nee 3ÿy -lñeñ .S1'C -400 -SIL 1.25 to 40 Mc. diem seer. iy'Aewonval HIS O O O O movement OSC. [LATE HALLICRAFTERS -Model S -36 -A. FM -AM -CW gwellle O O 0 6 meters, a swell 1=-'1,11:...2.;° D for 2 METER NF CHOKES PUTE with peak performance on 10 and F ward-Leonard type beautltul hIBh- Rdelity FM receive :ruin - meter. field O O O 0 pollee Ib, a 1.00 nor both Wd and new hands, an etube Rt piare xt00n et`'veme Dosen O O O O fah equipment-MI la one! Acorn tube RF ton Ee t $4.75 (655 Per Thousand) noise limiter,limiter. (5 texas. 27.6 $30750 O O 0 0 to 143 Me. O O O O S -37. 130 to COAXIAL CABLE! ! $591.75 prises' CATHODE ALL new. perfect. and at (west RME 45. New. revised model with calibrated hum Price ÓOS1p L Witt, speaker $186.00 TYPE Impedance O.D. 1 -100' uP ON ANY RECEIVER GLADLY 52 Ohms .405" 9e Se LITERATURE RG- B/U 7c SENT UPON REQUEST FIG-11 /U 75 Ohms .405" IOe 74 Ohms .420' 14e IOe The PANADAPTOR has TEMCO 7S OA RG -13/U Be co Seil lta a 7r1V-Te s -39/U 73 Ohms .312" Ile TRANSMITTER gG Be 5e a deeldedlY rm -While RG -58/U 55 Ohms 195" to any Ham Write for detail. TWINAX :Ìickit .405" 25e 25e l: has 1199,75 RG -22/U 95 Ohms VHF Doubla Shield CARDWELL to MILLEN SO WATT OSCILLATOR KIT Furnished In one Pie. Within -0% TRANSMITTER - length ordered-ordere Null monaural EXCITER Oar of your hands rrys- $10.80 Wn. 0900e Ich 240 TUBES tops anything you lave Inc set of coils gr 1 Made for 37.50 New INC 13(:241 An FU tube for Sigilai Como they moat fully 1H34 CRYSTAL DIODE RESIST -0.0010E . COoutputto at Specified in palpa, (ul d QOndAd Fig. 7, above- Interne construction of 6K8 for limiten. Color rode indice or part al.. Ham not wasÌu crystal less Ulan the me W- ith,,rd;' SU.00, durcd blank alone. converter. Below Typical 6K8 mixer circuit. I.BU ^e n"1^säú ái1.00. dut Harrison in OC -35 - iëg etc.^gth sells them only 40 METERS ern. and SO METERS NARROW FREQUENCY MODULATION DC-3 96c BAND at $1,48 frequencies generated extend to 27 mc. WITH YOUR CW TIàANSMITTE XTALS (Three Exciter feeds into the crystal socket of VALVE In paid) Whenp0Uro frequency However, the vestigial side band rem- The Sonar ols urrr is the ordering. any power rig. Eliminates BC Interference( Liam bend slat. that nants are from 25.75 mc to 27.00 mc results! 45 BC -406 15 TUBE UHF RECEIVERS 9 such F I pnart, from our customers Harrison Has It Been getting llarri well signai Corps Hadar ryreivora mat and are undesirable. The i.f. bandpass Complete with tubes. about 0,050 sax -arum tuba ICE e Just nui to get for you. 205C:a1 four IF stages: Thnrdartun tuning circuits eliminate them. ASK FOR LITERATURE circuit,Ireuit. tuned to delivering 350 volt, duty power iranafgymer filter: 11.. MAIL ORDERS''- Certainly! Just lit at 145 MA: lour choke and oil condenser 2. For the sound, the i.f. is ad. 00 sycle pentlon: dbut llt/a , centered EVERYTHING you want (items in this volt, used but fully guaranteedgus crut. metal . Slightly 2- or ANY ad, magazine or catalog) and in- with tubes: 5 -054. 1- 955. 4 -05X7. at 21.25 mc. Complete InsUUCtionS e d diagrams fur Os1T,ro2-01V7. I.5T4. 21 dude deposit. to a hot 10 (alto 6 and m 73 de cary The tTa Ìol,i The reason for using a higher inter- a fa` worth receiver 421.94 are uc more than our low mediate frequency for video price the voltages Some. but also has an 11 watt 2/3 ItCM Qt!! #attiiony W2AVA 110Votf.NTi4 and 1 -OSP5 $29.15 arises from the wide band requirements tomits l t01í) áwTGT. of these signals. The higher the inter- - - O mediate frequency, the smaller the ratio of .ARRISON RADIO CORPORATION video 4 mc bandwidth frequency 12 WEST BROADWAY NEW YORK CITY 7 intermediate and the easier it becomes to design band BA RCLAY 7 -9854 pass networks possessing sharp end at- JAMAICA BRANCH 172 -31 riillside Ave. REPUBLIC 9 -4102 tenuation and higher resistor loading. - - Consequently the amplifier gain, from the previously noted equation, is higher. It follows, then, that in order to have TELEVISION FOR TODAY the video i.f. above the audio i.f. we (Continued frone page 865) must place the oscillator above the incoming carriers. a special "Fine Tuning" adjustment has been converted into a front panel control. Its purpose is to counteract small shifts in the oscillator. Electrical- ly it consists merely of a variable condenser across the oscillator tank circuit. See Fig. 6. In the commercial receiver, Fig. 6, the "Fine Tuning" control is Cl. It is current standard practice to place the oscillator frequency above the sound and video carriers. By being above both signals, the highest intermediate frequency produced will be that of the video signal. To understand why, remember that the audio carrier is 4.5 4- mc higher in frequency than the video carrier. For a band of frequencies, say Fig. 8-A° number of oscillator -mixer circuits for conversion in v.h.f. superheterodyne sets.

870 RADIO -CRAFT for SEPTEMBER, 1946 SENSATIONAL SURPLUS RADIO BARGAINS!

SCR -284 TRANSMITTER -RECEIVER

Made to Le u cd , army Jeer, and trucks. a well a field or a headquarters err the SCR -284 is particularly adapta- ble for cxpernnentaal, marine, aircraft, police, and e all amateur, stage, featuring an double-tuned[ 4555 KCr Iron-core 1Ff beat and lo dPowerfulS 0 g to operate large sisespeaker. Thie °trans- mitten employs ° calibrated crystal oscillator. a buffer amplifier. and pair of RK-75 tunes in the nal amplifier stage. The amplifier and modulator will operate with any Ordinary speechmike, or °for we n include Signal Cores wmike, com- G'NreAt rLccrRnc 150 WATT TRANSMITTER plete with 'TresslO$2.75, -BRAND NEW! my 3175. Tills Is the truisms rcuuit. an RF ammeter willbumatch the transmitter 1.iaaon transmitter toed lu U.N. Army >constructionn t.hcn to any length of antenna. The transmitter platee supplied during the Its service by a 500 volt, 180 MA dynamotornes which operates from iher and ha been a 8 or 12 volt automobile battery. The transmitter output is 25 ter all kinds of conditions. 11 over the world. watltts, and rates both phone and CW. The frequency The entire frc.iuency range is Covered1 by Means tuning which rane Is KC on other bands may be In- facilitated 1 uya the plug- 1nlucoils. Circuit diagrams and cluded. Each unit ha ItsY°oxnv ssllatair and Instructions are furnished. power amplifier rolls and condensers, and An- tenna coupling ÌKuus -an designed to operate These sets art specially priced at $30.05. complete with set t toptp ladlemcy With!n Its particular gt. of 13 tubes and crystal. The dynamotor, hich must be used. Transmitter and a ries are fin!shed Inblack If it is not edesired to use 11Oí'. AC is $]15 additional. Where cklemeter the mllltam eter and a pact,and dela:ndable indium power unit is desired. this cr the frroontter, Set is Unbeatable[ Here are the specifieatinns: FREQUENCY RANGE: 200-500 withclight operate on 10 and 20w,1 ter bands cation). OSCILLATOR: Self- excited, thermal AMPLIFIER: Neutralizedeclans stage, ursine 14 -TUBE UHF SUPERHETERODYNE coupling cilrcuiu1 which atchesd practicallynna RECEIVER antenna. MODULATOR: Class .33..-uses two - $39.95 Supplied withwith dynamootoor hÌhhiPdeliverss volts at milliamperes Complete instructions are This beautifully , red was designed eet.cr,a:ly furnished to operate set from 110V-AC. SIZE: for Signal corps co nrcateatmn s and is one of the finest 211. 23 a 0t/a Inches. Total hipping eight, a most e itive e liuta e manufactured.u a Operating from 110V má ete with all aises, dynamotor 60 two tuning rot,.aren.IF...adiodeede- power tun- collator.civet IF ratages, ing unit. °and two profusely Illustrated °Inatruín. [e ue, tuningtanin eye. and two stage amplifier that will drive loin hooks, all in the original factory packing speaker rmahoret. The frequency range Is 158-210 Mea. It It simple [ter to operate on other plete makingktub a slight on the tuning coils. 1 complete sebyt of is in- cludedtsd with.N adh Il Gong with circuit dta50diagram a parts list. The high-voltage power eavv- delivers 150 Ille w, filtered atY wMPÌ oil -filled roiid This buySy lifetime ccostttte rovernment about $700. Amateurs and ex e ter$ will never wain able to Ourdisse fine equipment at such a tremendous s

V.M. RECORD CHANGER- Complete with yon, choice of either blue leatherette cabinet. walnut cabinet. This cheutifulanger is the my medium priced -changer on the market that will play both ten and twelve Inch records intermixed. without any finish- chrome plastic trim. Fao ten. guaranteed' and tpricedanat only $24.05.

Please remit at least 1000 deposit with all C.O.D. Orden. Send for our latest radio parta catalog.

B U F F A L O RADIO SUPPLY 219 -221 GENESEE ST., DEPT. C9, BUFFALO 3, N. Y. l NEWSPAPER VS. FACSIMILE Facsimile demonstrations by Finch NEW WESTON Facsimile and J. V. L. Hogan last month called forth sober comment from publications of widely differing points TEST EQUIPMENT of view. More than a suggestion was made that newspapers might find the from Tip -to -Plug in m o stock -immediate delivery new system more than a serious com- Clas, by ltsell petitor. Model 785 - Industrial Circuit Tester - WWI Pint in Only 0 Meters one in -with selected AC and DC vol- The advertising magazine COOL Nsw Mond. age, current, and resistance range.. With Ur Tide re- Will O voltage, sensitivity of 20,000 ohms per volt. ported: SAril N, cowl I FUL Ilan 225 W.nd is ideal for testing photo-cell and sensitive r. -- lay circuits, alarm systems, electronic equip- "Last fortnight sober thoughts SAVIS CIMI -t,s .,Innint ment, etc., as well as small motors and cpb- crossed the mind of many a U. S. pub- AALAA CIO. S.slly M.nl. trot, lighting circuits, etc. lisher as he beheld the commercial OE INOAal1 - ts..r lstln DC Voltage -Six Full Scale Ranges of: 110 LIGHT WEIGHT (Only t2'/ s.) 50/200 /500 /1000 Volta (20,000 Ohms per volt.. launching of a new development in IHWAp1O TIR Ws 5.11 Cn,.,t ECONOMICAL In Opr.,ran AC radio, what looked like added proof of Voltage -Six Full Scale Ranges of: 5:1 THERMOSTAT Is Ballt In 30/150/300/750 Ohms volt), this innovation's a (1000 per potentialities as SIA IM SCTUS Int.nk.ne..ab DC Current-Six Full Scale Ranges of: "o competitor and, eventually, as an ad- Microampa -1 /10 /100 Milliemps -1'10 Amp, junct, to newspapers in the U. S." AC Current-Four Full Scale Ranges of: .5' 1/5/10 Amperes. The Nation took a more - sober and complicated view of the situation. It Resistance -Five Full Scale Rangea of: 3000.' 30,000/300,000 Ohms -3/80 Megohms. reported: ; For Shop Use le.)* carrying case $ 85.37 "The problems are A KWIKHEAT With oak carrying case 101.63 technical far simpler than the social and economic ones, USER WRITES... Model 798 -Just Out-Mutual Conductance for if the development of facsimile l .. .mainly convinced Tube Checker & Set Analyser -Tube Checker tiaikbeats are the Ranges 0-3000. 6000. 12,000 Miéromhos and broadcasting continues ... city folks but noes that can be ob. Good -Bad Scale. as well as those who live on the tamed. They are really a Analyzer Ranges 0 -15. 150, 750 Volta AC & farms can be supplied with pleasure to work with." DC. 7.5 & 150 M.A. DC, 100,000 & 1 000,tnh newspa- H. P. K. long trench, N. J. Ohms $182.61 pers and other reading material by Model 779 - Supersensitive Analyzer - For radio ... at the trivial cost of the rolls 225 -Weit Iron with #I Tip Sii Simplified Radio Sr t Analysis 74.62 of paper and the electric current . Extra Tips -Sit Styles, sock 3.25 Model 697 -Volt -Ohm Milliammeter 25.89 as events take place, as history is made, the facsimile machines will produce di- VA N AT TA MARITIME SWITCHBOARD rectly in the home a contemporaneous printed record. No newspapers will be KWIKHEAT 336 CANAL STREET, NEW YORK 13,N. Y. able to compete." THERMOSTATIC SOLDERING IRON WORTH 4 -8m7 Apparently facsimile is being taken Sound iqulpment Corporation of (alllornio 3003 San Fernando Rd., Glendale 4, very seriously in some quarters. California

RADIO -CRAFT for SEPTEMBER, 1946 871 ATOM BOMB OVER BIKINI (Continued front page 824) HOW TO PASS Radio Operatos ' er waves -(water, that is!) An automatic clock started the recorders connected with the sounders half an hour Pas FCC LICENSE before the bomb was scheduled to go off. Certain other recently -developed and still secret electronic devices were used EXAMINATIONS... to record wave height versus time at remote parts of the lagoon and at other atolls such as Eniwetok, Kwajalein, Wotho, and Rongerlap. Two radio re- FREE BOOKLET peating wave buoys planted two and four miles from the explo- for point of the Tells you the Government requirements sion radioed the wave heights to one of all classes of commercial operator licenses. the photographic planes. Ten simple maximum -water- height Tells where to apply for and take the examina- indicators were mounted near the tions, examining offices, scope of knowledge water's edge. Each unit consists of 4 required, extracts from FCC Rules and Regula- a pipe, a contactor strip, and a dry Don't Delay - tions, extracts from FCC Study Guide and Ref- cell. It is equipped with a set of fuses erence Material, approved way to prepare for which blow as water passes up the pipe Write Today! FCC examinations, positive method of checking and creates a short- circuit. your knowledge before taking the examinations. RADIO CAMERA CONTROL Edition Limited -Mail Coupon Before Supply Is Exhausted The wave measurement group relied heavily on photography for measurable data. It used simultaneous air -ground CLEVELAND INSTITUTE OF RADIO ELECTRONICS photographs, stereo -pairs of ground camera and television photos, and right - Contractors to the Canadian Broadcasting Corporation angle pairs of ground photos. The first to test was expected to provide a full -scale Successors test of such matters as shielding of NILSON RADIO SCHOOL, Founded 1939 cameras and radios. The analysis of SMITH PRACTICAL RADIO INSTITUTE, Founded 1934 photographs for measuring scientific data (called photogrammetry) depends RC-9 TERMINAL TOWER CLEVELAND It OHIO for its success on stop -watch timing APPROVED FOR VETERAN TRAINING UNDER G. I. BILL OF RIGHTS effected by radio controlling links. These radio links consist of transmitters in MAIL THIS COUPON one of the aircraft. As each control CLEVELAND INSTITUTE OF RADIO ELECTRONICS pulse is received, each camera makes RC -9 TERMINAL TOWER, Cleveland 13, Ohio one exposure and cycles forward ready Gentlemen: Please send your FREE Booklet. "How To Pass FCC License Examinations." for the next pulse. (Note: This Booklet does not cover examinations for Amateur License) Two television transmitters were NAME I have had experience in broadcast- located on towers 2000 feet apart on ing :0 servicing operating Bikini and aimed at the target area. ADDRESS Receivers mfg. CAA Army -Navy O set to the transmitter's frequency were aboard the two photo CITY STATE. amateur other planes. Special motion picture cameras Check license desired: were focussed on these receiver screens I am a High School Grad. College Radiotelephone 1st. Clase 2nd Clase to record the television images perma- Grad. with degree nently. Supplementary receivers set Radiotelegraph 1st Class 2nd Class to the same frequency were on the flag- I now hold these licenses If a War Veteran, check here ship Mt. McKinley and also on the Appalachian. The seismology group of the oceano- 100 Watt Vasco Soldering Iron 73.30 111 Freq. hoaxer. 2 to 4 volta DC .79 graphic section was concerned not only Midget 100 MMFD Variable tbndenser .79 with the measurement of the ampli- THORDARSON TRANSFORMERS 5 loch I'M Speaker 1.77 300 Ohm Amphenol twin lead per 100 ft. 2.90 tude and character of the earth's vi- 75 Ohm Amphenol twin lead per 100 ft. 2.00 115 V., 50 -60 Cy. Primary, BC 312 N. or BC 348 Q Army Receivers 59.95 brations resulting from the bomb, but 6 Volts at 10 Amps. Sec. Sales In Calif. add 2V, ô sales tag also hoped to gain some information Leads brought out on an engraved bakelleht DOW RADIO on the sub -surface structure of the atoll panel -Wt. 5 lbs. Sire 353x3 inches. With 1759 E. Colorado Pasadena 4, Calif. amounting brackets. Suitable for filament sup- by refraction and reflection measure- ply. battery charges. "A" supplies. pin -ball machine., juke boxes, bell -ringers, toys. etc. ments similar to those used in electronic PAPERandMICA CONDENSERS geophysical prospecting. According to PRICE Ea. $1'50 the best available data, the seismo- 50 Assorted Paper and Mica Condens- recorded 6 to a carton no less than 6 sold. graphs absolutely nothing. No - ers, popular sizes $1.00 announcement has been made as to the Cash, Cheek, or Money Order AUDIO SALES CO. information gained on sub -surface PETER BAI.IZER, Dept. C structure. 9 WARREN ST. NEW YORK 7, N. Y. 19 Micieli Place Brooklyn 18, N. Y. The oceanographic work was carried on by means of current meters similar to anemometers; by means of current RADIO -CRAFT wants originel cartoon ideas and will pay $3.00 for each one accepted. poles weighted at the bottom and It is not necessary fo send in a sketch unless you so desire. Send in your cartoon ideas today! (Continued on page 874) 072 RADIO -CRAFT for SEPTEMBER. 1946 TRANSATLANTIC NEWS (Continued from page 841) THE SECRET'S OUT! use carriers with frequencies separated /Veto by 35 kc. Both carriers lie within the '74 and SpecIde band width of the r.f. and i.f. stages of the receivers (Fig. 1) without produc- ACA -100DC AMPLIFIER ing audible interaction. The two trans- ¡ mitters, eleven miles apart, used fre- 9s Rea dit cti 20eliovut quencies of 80.0175 and 79.9825 mc- DESIGNED BY A. C. SNANEY see Fig. 2. A central control station supplied modulation to both by radio links. The first difficulty encountered A revolutionary development in amplifiers cleverly was interference from auto ignition sys- designed fo defy obsolescence and amazing in its tems and this led to the development of performance. New circuits, new maaerials and new a noise -limiter so effective freedom processes are actually combined in this one amplifier that to produce the most satisfying musical amplifier the from all types of interference is stated world has ever known. If you are one of those discrimi- to be as complete as with FM. nating persons for whom nothing less than the best is Tests showed excellent results. No a disappointment, you are one for whom the ACA - distortion could be detected in the area IoODC was designed. Send for technical literature. covered and in towns and valleys the flutter associated with single- carrier v.h.f. transmissions was hardly notice- 13, Y. able. Both carriers do actually flutter, 398 Broadway, New York N. but not as a rule at the same time. The A. C. Shaney's FM -AM AMPLIFIER MANUAL is still available at 25c receiver selects the signal that is the better at any instant and the change- over from one carrier to the other is MORE SMASH BUYS at imperceptible. Throughout the area, sig- c"t'QRADIONIC" nal strength was found to be much National Radio Distributors FOR EVERYTHING ELECTRONIC greater than with a one -station system. IMMEDIATE DELIVERY "Diversity tranrmi':3ion" had proved TESTER 5 Tube AC/DC Superhetero - REINER MODEL 333 MASTER itself to be as effective as diversity re- dyne Hullo Kit using 1'18A7. 128E7, 1284.17, 50L5 ami di:1'cr,,,'. ception and the next step was to use it 2525 tubes. Features built -in slogles oinstruments. on a much larger scale. This is illus- loop antenna, automatic vol- To operate, you need ume control, n e w Alnico merely Insert the trated diagrammatically in Fig 3. weaker. Complote with all proper shunt or multiplier for the range Taking the outward paths first, the !ructions for assembling andinincluding highulpolish desired and you're brown streamline cabinet. Approx. size 9 x 5 x ' ready to take read- 7-watt transmissions on 81.30 mc from Your Net less tubes $13.75 each ings. D.C. ranges Your Not less tubes for lots of 3 $12.95 each only. Supplied com- Police hq. are picked up by a of 5 receiver Kit matched tubes for above $4.95 plete with 6 shunte. at the main transmitting station which 6 multipliers. 2 - ter fuses and le.rnu triggers off a 30 -watt transmitter work- Urns. Net... $27.05 New Post -War 2 Pat Rec- ing on 130.80 mc. Its signals go to re- ord Changer with beautiful leatherette covered que . Write For complete REINER catalog ceivers at all three stations where they W111 take 112e o 12- off 100 ltr records. Extra heavy trigger -watt transmitters work- duty construction assures RADIO BOOKS FOR BEGINNERS! ing on 96.32 mc (main station), 96.28 long trouble -free life. Stops Itl honks ,overing radio building. theory. aerials, automatically after last rec dictionary of radio terme. learning to read dia- mc (slave A) and 96.30 mc (slave B). od is played. Approximate grams. electrical experiments. tele- A 130.60 mc receiver is mico of complete unit 16 x vlshM. etc. Kritten ira simple. 7CC used at the $24.95 Prhniral language. / -Y Alonl 10 books Dilly postpaid master station as well as at the slaves SPECIAL BUYS in order to equalize the 'path and to 3 umbe controls.onPAmplifiers Complete, eady tooperrte.aóox Mr l- (Clip coupon on your letterhead or penny postcard) ensure as far as possible that the three sise 5x34 x 11/4. Uses 501.0. 35Z5 and 12SQ7 tube.. 100 -watt transmitters are modulated in Your less FREE CATALOG! Net lessi tubes in lo ts of 3 13.95 each the same phase. Kit of 3 tubes for R.E. Co. Dept. RAB-Please send me copy of Tubular Typekedlly.Pass Condenseers. All 0ÚÚV.6 fresh stock slues your free catalog of paru, accessories, tubes. Receivers in police autos receive all and fully guaranteed. All available. public address, communicating equipment. teat .001 to .005 lard. Per 10 5.70 Per 100 55.50 , amateur radios. three signals and the results are re- .01 '05 Mid. nuipment, equipment. phono Mad Per 10 5.90 Per 100 59.00 players, elf. markable. Signal strength is constant Kit of 100 assorted sixes, all 600V. up to and including .1 Mfd. 55.95 over practically the whole wide area Tubular Type Electrolytic Filter Condensen fully Nane guaranteed 1 year, with mounting bracket. All fresh covered, even in the deep, narrow val- stink. 20x20 Mid. 200V Per 10 53.50 Per 100 532.50 Addotti leys, and there are no areas of distortion Sala Mfd. 50V P r 10 S6.00 Per 100 557.50 25 Mid. 35V Per 10 52.10 Per 100 519.50 corresponding to those of no- capture 10 Mid. 25V per 10 51.95 Per 100 517.50 City state with FM. The frequencies used show Deposit must accompany all O.O.D. orders. surprising penetration of streets, tun- Write NOW for FREE catalog. nels. and even steel -frame buildings. A Radio Distributors RADIONIC Equipment Co. slight heterodyne whistle is at times to National "Chancellor be heard if the 96.28, 96.30 and 96.32 mc 'Products" 170 NASSAU ST. NEW YORK 7, N. Y. carriers are not precisely evenly spaced. 1029R E.163 St., New York 59, N.Y. WOrlh 2-0421 Coble: CHANSLOS This is easily corrected and in any event the whistle is so faint (30-40 db below FM in the matter of auto ignition inter- signal level) that it causes no interference-the only serious type experi- THE POSTWAR RADIOS ference with communication. enced. One great advantage of AM is On these very high frequencies AM, the simpler and cheaper nature of the (Continued from page 836) perhaps rather surprisingly, shows up equipment required. It may be that some well in comparison with FM. Natural means of eliminating the area of no- case, the last zero has been omitted from static is virtually unknown and inter- capture with two -carrier FM will be the dial scale so that 90 on the dial ference from trams, trolley buses and found. Until this is done it seems that indicates the correct dial setting for machinery is very light at 75 -82 mc, less for the coverage of police and similar receiving a 900-kc station. With the still at 95.5 -100 mc and almost entirely areas and the maintenance throughout 1 -inch direct tuning knob, it is some- absent on 128 -131 mc. With the special them of steady signal strength, v.h.f. what difficult to tune in a high frequency noise -limiter devised AM is as good as diversity AM is the better method. broadcast station "on the nose."

RADIO -CRAFT for SEPTEMBER, 1946 873 ATOM BOMB OVER BIKINI (Continued from page 872)

equipped with yellow pennants, radar LEEDS targets and lights; dye bombs which AM PLIFIER for diffuse dye at a constant rate through the water; and various devices to GUITAR measure oxygen, salinity, temperature, or CONDENSER diffusivity, and other variables. A pre -bomb survey of the lagoon was PHONO made by one of the scientists who donned a Navy shallow water diving suit equipped with special underwater writ - VALUES ing materials- (probably the first recorded use of those pens we've heard so GUDEMAN OIL FILLED much about!) 0.5 MFD 1500 y. 4 .50 Operation Crossroads is undoubtedly 0.23 MFD 2000 c. the first military organization ever to e T119E5, 65.15. 6J5, * Solid Wood 2x.23 MFD 1200 y. .35 6L6, 5V4G Cabinet 4 Tubes Gain Aeroplane Cloth 4 MFD 500 v. have a "radiological safety officer." This -Hi * .50 * Two Microphone Covered has a sinister sound and radiological or Instrument In * Tone Control AEROVOX OIL FILLED hazards are sinister. The normal chan- puts * Heavy Duty * Phono Input 8" Speaker 1 MFD 600 v. .25 nels of your five senses give no warn- * 61/2 Watts -Beam Complete with 1 MFD 1000 v. .35 ing of the danger since radioactivity can power Tubes 2 MFD 1000 v. .95 neither be seen, heard, smelled, YOUR COST $37.00 B MFD 1500 v. 3.75 felt, finr.eï,,,ra..so 2 MFD 2300 V. 3.50 nor tasted. When you do become aware VMI BRUSH CONTROL MIKE -Net $10.40 0.1 MFD 7500 v. 1.50 of it, physical degeneration has already MM TURNER CONTACT MIKE -Net 1 9.45 started. You can then do nothing but CORNELL DUBILIER OILS wait for the end. 2,0.25 MFD 6110 v. type DIR Phono 2:0.1 MFD 600 v. type DIR .25 The majority of the dangers caused 2 MFD 600 v. by the bomb itself are of extremely short Amplifier 4 MFD 4000 v. 8.00 duration and occur within a range of 6 MFD 4000 v. 10.50 3 Tube AC -DC 7000 yards. Danger from blast, heat, Uses: SOLE.. 35Z5. 12SR7, and 450 ohm speaker G. E. PYRANOLS and radiation was avoided by requiring both ships and aircraft be Net S5.97 4 MFD 600 v. 45 to at least 7.5 MFD 330 v. AC 1.25 ten miles away at the time of detonation. TOP L.i1T£iT GAT,4LOG WR/7Y rv. ; 10 MFD 600 v. 1.50 Damage to the eyes of observers was IO MFD 1000 v. 2.25 prevented by the use of high- neutral- 10 MFD 1500 v. 3.50 density goggles. _a 8 MFD 2000 v. 5.00 Persons without gog- ---os gles were warned not to look directly SOLAR at the blast, to turn away, or to shield RAele / SUPPLY 1 MFD 5000 g. 5.00 their eyes with their arms. After the first flash,- they were permitted to view CHATZ(ASTON , W METERS the rising incandescent column with the W.E. 3" Bakelite case naked eye. One sailor who ignored these 100 -0 -100 microamps 4.75 50 -0. 50 milli amps 3.50 warnings and attempted to view the ex- plosion without goggles was removed WESTON 506 from the ship, temporarily blinded. He- 0 -1 MA 500 v. scale 3.50 was probably the first American cas- 18 YEARS IN RADIO ualty of atomic bombs. TRIPLETT 221 Of the two remaining primary haz- GET THIS Rectifier type DB meter 3.00 ards, radiation and radioactivity, (:RUEN 0 -3 MA Bakelite case 1.95 the Tea, CATALOG has milliamp volt scale latter presented the more serious prob- 6E 27v. 54 watt heating elements .10 lem. Radiation occurs at the time of By This Old Firm detonation only, and consists primarily Latest developments In A FEW LEFT -WHILE THEY of free neutrons and gamma rays. With- radio and electronic LAST in parts and devices, new- a certain range, human or animal life est ham gear, gadgets BC 412 Scopes, 110s. AC operation is destroyed by radiation through its at- for experimenters, bar. Complete with tuber 35.00 tack on bIoid- forming cells, the initia- pins In war surplus BC 221 Freq METER tion of serious internal hemorrhages, I terni. Complete with crystal, tuber and through burns or the slow oozing and calibration book 54.50 of the blood into the flesh. Since radia- FREE tion is localized, personnel was com- TO YOU FOR YOUR FREQ -METER pletely protected against it by the dis- Mail the coupon be- Blank calibration book, spec. 2.00 tance from the detonation. low and get this new catalog FREE. This is not true of the radiological A deposit of 25áo must accompany all orders. hazard, which All prices F.O.B. our warehouse New is the emanation of alpha York. particles and beta and gamma rays BURSTEIN- APPLEBEE Co., No order under $2.00 from minute fragments of the bomb and 1012 McGee, Kansas City 6, Mo. We ship to any part of the globe surrounding matter. Among the ele- Send me FREE catalog advertised In ments in sea water, sodium, chlorine, Radio Craft iodine, bromine, and potassium all become radioactive with different half -life CONNECTION IN INDUSTRY LEEDS RADIO CO. periods running from a few seconds to NAMe 75 Vesey St., 45 Dept. many hours. ADDRESS COrtlend 7-2612 New York City 7 The degree of radioactive hazard was Imeasured by Geiger -Mueller counters 4l___STATETOWN STATE_ (Continued on page 876) 874 DIO ..GR A.F T for SEPTEMBER, 1946 FOR IMMEDIATE DELIVERY! LINK- COUPLED CRYSTAL SET I (Continued from page 831)

insert L2 inside of Ll, about 'k -inch from the ground end of the coil. Insert L3 inside of L4 in a like man- Outstanding Offerings Of ner. The entire set of windings of L2 and L3 should be used as a starter, and should not be changed unless necessary. NEW KITS! Place SW1 (on L1) on the next to the 6 Tube SUPERHET 'KIT Two last tap away from the ground end. band - complete with tubes and solid color Place SW2 on the next tap nearest SW1 (green, red, ivory, etc.) wood cabinet. In- but toward the ground end. Place SW3, cludes all parts, except wire and on L4, on a tap to include about three solder $18.50 Per Kit quarters of the length of the coil. (NOTE: While Ll ant L4 are exactly PHONO KIT Consists of AC Phono- alike in physical dimensions the corre- Motor, Pick up, all parts necessary for sponding switches will not necessarily 3 tube phono Amplifier, including 6" P.M. read the same, because two units speaker. Excludes wire,. solder the are and tubes $16.25 separate and are performing two different functions). SW1 is changed only with PA-I2 portable leatherette- covered when a shift is made from one extreme the all -wood cabinet $7.95 of the set's tuning range to the other. Above Kit of tubes $1.85 The position of SW2 should normally be between SW1 and ground. 11 a All prices are F.O.B. New York City. Using your right hand for main tuning and your left for antenna Write for our new catalogue showing tuning, new test equipment, tubes and Woe the main tuning dial, C2, is slowly variety of new replacement parts. We ship anywhere In the U.S.A. - swung across its arc. If a station is prom pria. heard, the antenna tuning dial, Cl, Small, compact, lightweight! should be shifted until the signal in- Full vision in any position. creases in strength. Unless this occurs Ws a complete cathode ray le RADIO DEALERS the set is not functioning properly. Try oscilloscope ' of indicating In vertical and hori- SUPPLY COMPANY a different setting of taps, or move the sentol dimensions. Weighs pickup -coils (on link line) to the ex- only 5% lbs. Precision built, treme ends of their big brothers. fully accurate. The best way to search out the elu- sive dx is to get the set fired up as well as possible on a nearby signal; then MANUSCRIPTS move L2 and L3 OUT slightly from their big brothers in order to increase WANTED the selectivity, moving both the tuning dials AWAY from the local. Once you 25,000 - 35,000 hear a dx station you should try every- words thing in the books to bring its signal strength up. Increase the coupling be- In clear, semi -technical lan- tween circuits, try different taps, and guage on various radio sub- rotate the main dials individually until jects. For Radio- Croft's new you have the station centered. The main 50c book series. object is to drag the dx out into the open while shoving the locals into a Payment on acceptance hole. The author can tune across the band and pick plus royalty. out dx at will, as long as it's coming through at all. Have a For details, write little patience, keep a log, and you, too, can pull in the dx like nobody's busi- Box S ness! RADIO -CRAFT Parts list for the Two Timer: Cl and C2: 365, 450 or 500 µf. DO No. 630 - WHEATSTONE BRIDGE 25 West Broadway, N. Y. 7, N. Y. NOT "GANG" . use separately) M stance from 1 Ll, L2, L3, and L4: See text. Phones: to 11.1 megohms. Accuracy Any good high impedance type. Crystal 1%. Built -in galvanometer, * SPECIAL VALUES! detector: popular sensitivity of 1 micro -ampere, Any mineral detector. per millimeter division. -HURRY- QUANTITIES IIItITED- SW1, SW2 and SW3: See text. NOTE: $75 5' 1000 ohm dynamic speakers... 61.90 1'. M. sneakers. alntrn 5 m.unet.. 1.70 No phone condenser is used. Write for detailed bulletins on Water- .74 .34 man Pocketscope and complete Shall - r... 2.75 cross line. Get our bargain flyer with many money IPOCKET-SIZE VOLT -OHM -MILLIAMMETER -saving radio needs listed. 0-1500 volts AC -Pr; 0 -150 M. A_ 0 -3nn,- nnn L.: F!'I:c'i \I.! . ..516.95 An oceanic layer which reflects sonar waves has been discovered in ,\. .... 2.95 the Pacific. IS" \\ .,I,i.., n.:tR, h.. le. 4.90 The layer is between 1,000 and 1,500 Air- ltaider All-N'avo Nolao- Beducing antenna kit, with matched coupler 5.54 feet below the surface, rising at night Alw. TUBES TEST INSTRUMENTS AMPLIFIERS and sinking in the daytime. Scientists SERVICE CO. OF PENNA., INC. 25% deposit with order. balance C.O.D. believe it may contain suspended matter SCENIC RADIO & ELECTRONICS CO. which reflects back the echoes heard by 7TH AND ARCH STREETS, PHILA. 6, PENNA. 53 Park Place Dept R New York 7. N. Y. the sounding apparatus. Stanches in Wilmington, Del.,- Easton, Penna.. Allentown. Penns

RADIO -CRAFT for SEPTEMBER, 1946 875 ATOM BOMB OVER BIKINI Highest Qua /íty (Continued front page 874) and by strips of photographic film placed on board ships and carried by RADIO and ELECTRONIC personnel. These film strips were peri- odically replaced and those that were carried by personnel were checked for Testing Equipment radioactivity, which affects filin the same way as light does. The Geiger counter consists primarily of a special IMMEDIATE DELIVERY FROM STOCK GUARANTEED gas -filled tubewith two electrodes connected to a battery. Any radioactive The New particle entering this tube ionizes the Weston Ohmmeter 1lodel S -10 -A gas and a small electrical impulse is Model 689 -11 thereby permitted to pass throughthe Pocket Size tube. List Price $25.50 This is amplified to a point where Oscilloscope it can be indicated either by a dial or Our Price: $14.85 Net Price: $55.00 by audible "ticks." Counters may be made extremely This Ohmmeter has a double range Complete cathnd.- r:u- sensitive or they may of 0 -10 and 0 -1000 ohms for the oacilloscope incorpora- be made to operate under conditions of actuate measurement of low re. ting sistance value.. This type is wide- the cathode ray intense radioactivity, ly used for production testing tube, vertical and hor- in every case armature and field resistances of izontal amplifiers, linear time base oscillator, serving to measure the intensity. small motors, relay and coil testing. transform. synchronization means and self- contained winding tests and other similar appliance,. Complete power supply. With these safety precautions care- with operating instructions, test lead; and leather Complete with tybe; and carrying ease. operating instructions. fully observed, no one should have received any injuries from radioactivity. The New The New Fifty medical officers underwent an in- Model 543 -S Model 274 tensive three- months training course SUPREME Dumont Five -Inch which included a flight over the original MULTIMETER Oscilloscope atomic bomb test site in New Mexico. Their Geiger Net Price: counters picked up "ticks" Net Price: $24,75 599.50 indicating a entail amount of continued Input Impedance: Y 1% WIRE WOUND Axis: Direct radioactivity front last Julyl PRECISION RESIS- 5 meg., 60 oaf. X Axis: Direct 5 TORS. Ranges 1000 at meg., 80 uu. Z Axis: 10 ROBOT PLANES IN ACTION ohm, per volt standard rms. volts to blank. Y sensitivity. Full size 3" square meter with a Amplifier: 1 meg., 70 apf. X Amplifier: 5 Radio -controlled drones were used to rugged, accurate 200 microampere movement meg., 30 apt. Sine wave and a knife edged response uniform great advantage in pointer. All ohmmeter within 20% from 20 cycles to 50 KC. Con- this test. Four ranges, including the megohm range are tinuously variable frequency "Mother" operated by batteries range from 8 or control planes controlled and contained within c.p -s. to 90 KC. Synchronizing signal sources: its durable black molded bakelite case. internal or external. four "Babes" or drones. A "Super - mother" or master control plane was McMurdo Silver The New rigged so that it could take over the Model 705 Model 901 flight of any drone that failed to re- Signal spond to the signals from its mother. Capacitance Generator These hovered over the observing ships Resistance Net Price $49.50 until the bombing plane made its final RANGES: Bridge From 93 kc to 100 run over the target. The instant that me. continuously va- the bomb dropped, Net Price $49.90 riable. Calibration a lethal cloud of accurate to 2% through broadcast nanas. within 3% extremely dangerous radioactivity rose, cord /olun tiro t,ono nifd. /megoluus; 0-50'5 for high tro-µleury bands. Planetary drive condenser. power factor; U -300 volt adjustable Internal polarizing sliced reading calibration. output iniehduted or un- reaching 60,000 feet in about six to ten voltage; 0 -IO and 0.100 ma. electron-ray leakage modulated. Self contained electronic modulation 400' current meter: measure. resistance, capacitance under sine wave available foe external use. Special feature minutes after the detonation. This was actual operating voltages! Provided in having two degrees of modulation at both approlim. 30% and 80% predicted, expected, and prepared for. From what we on the Appalachian saw, McMurdo Silve- The New Model the cloud appeared to be about sixteen Model 005 802N Corn- miles in diameter. "SPARX" ',Motion The Babes were impelled toward the TUBE & SET cloud by the watchful Mother planes Dynamic TESTER which remained at a safe distance. (In Signal Tracer Net Price $59.50 this case, the Mother planes acted con- Net Price $39.90 D.C. Voltmeter: n trary to the instincts of a true mother, 10/50 / 500 / 1001 Frequency range from 20 cycles to over 205 1000 n; per volt Feur Ranee A.C. Voltmeter: 0' by sending their Babes into danger cycles. Contains isolating capacitor. resistor end ono 10 /50 /3ño,1o110. D.C. M llliaanMeter: 0/1/10 /1000 UC of the new radar h.f. crystal diodes. Iaoad, el, Ammeter 0 /10. DB Meter: -8/15/15 to 29/29/ to while the Mother remained behind to cult hieing tested with only 3 =Ad. and higher than 49/32 to 55 decibels. Four Range Output Meter- 5 tomato. same as AC Volts. watch the results.) Each plane was to McMurdo Silver Model Vonla6" Vacuum Reiner Model 451 Vacuum Tube Volt -Ohm enter the cloud at a different altitude Tube Voltmeter 59.55 150.00 SUPREME Model 589 Tube Es Battery Tester 46.95 Superior Model CA -11 SignedSi and was to maintain -this altitude while SUPREME Model 599 Tube and bet Testet 6 62.50 Superior Model 1553 Volt Ohm Milliammeter 24.75 SUPREME Model 565 Vacuum Tute Voltmeter 63.50 Superior Model 680 5000 Ohm. Per Volt in the cloud and upon emergence. An SUPREME Model 546 Oscilloscope 69.75 V.O. Milliammeter 27.65 R.C.P. Model 4es Pocket Multifester 24.50 Superior Model 670 Super. Meter...... 28.40 amusing sidelight of this phase was the R.C.. Model 424A Vol*-Ohm-Milliammeter 29.50 Superior Model P5.100 Volt Ohm Milliammeter 26.40 R.C.P. Model 322 Tube Teeter 41.90 Superior Model 450 Tube Tester 39.50 R.C.P. 461 AP Sensitive Multiester 43.90 Superior Model action of one particularly stubborn little Model 650 Signal Generator 46.75 684 Electronic Multimeter.. - 45.00 Superior Model 720 Multi Range AC Ammeter 49.50 drone R.C.P. Model 322P Tube Tester (Portable) 45.90 Superior Model 600 Combination Tube and that disobeyed the frantic signals R.C.P. Model 315 Tube Tester 59.50 Set Tester 62.50 R.C.P. Model 488A Ultra. Sensitive Multitaster 71.50 SHALLCROSS Decade Resistance bee 13.90 from both the Mother and the Super - R.C.P. Model 868 Vacuum Tube Volt -Ohm 27.50 Capacity Meter 74.50 75.00 mother. Nothing seemed to have any R.C.P. Model 66S A V. T. Volt Ohmegger SHALLCRO55 Model 037 Kelvins Wheatetoae insulation tester 94.50 Bridge 100.00 effect on this independent drone and a Reiner Model 333 Master Tester - 27.50 RECORD CHANGER Model VM -200 22.50 Realer Model ter, 530 Squarewave Generator.... 95.00 RECORD CHANGER Model Maguire 24.50 hurried conference was held to decide Write for our FREE New POST -WAR CATALOGUE! whether or not to shoot it down. The control crew decided that since the drone had a limited gas supply, it would end ELECTRONIC & INSTRUMENT CO. up in a watery grave anyway, and so it nee/ioAataa,ft was permitted to continue its merry Dept. C, 6 MURRAY STREET Cable Address: METRONICS way on the course it had set for itself NEW YORK 7, N. Y., U. S. A. Phone: BArclay 7 -5556 -in the general direction of China! 876 RADIO -CRAFT for SEPT -EMBER, 1946 AUDIO RESPONSE CORRECTION FOR ALL (Continued from page 827) i i

RESISTANCE -CAPACITY CIRCUITS frequency (usually the top resonant fre- AVDELS Two main types of circuits are em- quency) but such circuits are usually ELECTRICIANS EXAMINATIONS ployed, those that give a bass boost by failures for several reasons. attenuating all the higher frequencies The designer may omit to take into WIRING DIAGRAMS to a reduced but finite value and those account the inductance and capacity of AVDELS pickup; has too low a "Q" ELECTRICAL DICTIONARY that reduce the highs, approaching zero the the filter AVDELS response as the frequency increases. factor (absorbs too little energy at the ELECTRICALPOWER CALCULATIONS undesired frequency and too much at neighboring frequencies) the inductance AVDELS HANDY BOOK OF IOOK C 500K may be large and bulky and may have hum voltages induced in it. Generally PRACTICAL ELECTRICIT? TO A4PL. the inductance should be very large and the capacity small -a filter composed Y!! of a few r.f. chokes and .006 pi condensers is not very helpful and gives AUDE LS 1A.F.PENTOD a more or less general high-frequency ELECTRONIC DEVICES (_ 2 SOH. AVDELS 2ME4r- cut. In an ideal system the frequency L__ IILOOI' RES. TO ELECTRIC WELDING B+ of the acceptor circuit should be vari- because (AUDEL +ELECTRIC LIBRARY Fig. 6 -Tuned acceptor and rejector filters. able the resonant frequencies as VOLUMES ILLUSiaULTED of the pickup vary with type of needle and wear of needle as well as with PRACTICAL E LE CTRICITY of your finger ends. The first type can be designed to hardness and groove contour of the Answering your Questions and giving the give a "boost" of any desired rate over record. facts and figures of your trade. any frequency range, but the amounts Audels Electrical Guides contain Practical of boost cannot approach infinity as the Inside Trade Information in a handy form. fully illustrated and Easy to Understand. loss at high frequencies due to the filter 6SJ7 L.E BoosT 6V6 Highly Endorsed. Check the books you want is at least equal to the bass boost pro- .001. .0005 500K for 7 days' Free Examination. Send No Money. duced at very low frequencies. If the Nothing to pay postman. If satisfied pay pickup has a very low bass resonant only $1 a month until purchase price is paid. 20 ?Ka frequency, say around cycles, full ASK TO SEE THEM. compensation is needed and the filter Get This Information for Yourself. Mail must a of 6 provide boost around db per E coupon today. No obligation unless O.K. octave. On the other hand, if the pick- To -CUT HERE - up head is fairly light and the needle SPAR ------very stiff and difficult to deflect, the bass resonant frequency will be well in- IK MAIL ORDER H.F. BOOST 30011 AUDEL, Publishers, 49 W.23 St., side the audible region and little com- 2 N1Ó N °. YK = Please send me postpaid for FREE EXAMINATION books pensation is required. Circuits for both below. o I decide Fig. 7-This circuit uses negative feedback. mailk Sl In Days each bookkorJred anagree ñ these conditions are shown in Fig. 4. mail S1 monthly on each until I hay. paid price. ELECTRICIANS EXAMINATIONS. 250 , .11. Now what about the high- frequency Rejector or paralle L -C circuits may WIRING DIAGRAMS, 210 Pages . . . 1. ELECTRICAL DICTIONARY, 9000 Terms . 2. end of the spectrum? This end is never be inserted in the load of the first tube ELECTRICAL POWER CALCULATIONS. 425 Pages. 2. attenuated in recording and is usually to provide a boost around some fre- HANDY BOON OF ELECTRICITY, 1340 Pages . . . boosted, so the problem is how to D RADIOMANS GUIDE, 914 Pages ...... at- quency, usually in the bass, to com- ELECTRONIC DEVICES,216 . 2. tenuate the highs to a reasonable value. ELECTRIC WELDING, 400 Pages 1 pensate for attenuation in recording. ELECTRIC LIBRARY. 12 yoI..7000 Pgs., 11.50 Each If the high boost is progressive, (in- Again there is the problem of hum creasing with frequency) a simple one- pickup. Besides, the introduction of a section filter such as is shown in Fig. resonant circuit means that some notes 5 -a may meet the case. The resistance are prolonged. may be the plate resistance of the first tube in the amplifier in which case - 5001( -sus .05 500K only the condenser is used-or the fil- APPROX.A(K ter as shown may be connected directly D5 after a high -impedance magnetic pick- 500K up. Sometimes when the pickup is a real- 1LC. SPECIAL ly good one with a high needle resonance 5001( B+ New Astatic Low Pressure Crystal frequency, a multi -section filter may be AI 2MEG Pickups L72A 3.5V. Output used to give a sharp cut-off just be- - 6SJ7 Special $2.97 ea. low the unwanted resonance. The cir- Fig. B- Negative feedback direct to pickup. New Astatic Low Pressure LP6 cuit of such a filter is shown in Fig. Permanent Sapphire Stylus Pick- 5 -b, the Care must be taken to see that the ups Special $3.99 ea. constants being suitable for a Glider 500 -ohm or medium impedance job. natural frequency of the L -C circuit is New Shure Curved Arm not at or adjacent to the diaphragm Featherweight Pickups It is very rarely that a boost is re- resonance of the loudspeaker or the bass Special $2.88 ea. quired in reproducing the upper highs resonant frequency of the pickup. The around 5,000 cycles, but if required, the American Parts, Inc. frequency may be changed by trial and 510 W. RANDOLPH circuits of Fig. 4 may be used with the STREET error by shunting capacities across the CHICAGO e. IR. series resistor bridged by a small ca- inductance. These bass -boost tuned cir- pacity such as a .002 microfarad con- cuits are usually easier for denser. the amateur to get going than the acceptor "scratch - WIRELESS PHONO OSCILLATOR filter" circuits. To provide a variable NO LICENSE REQUIRED TUNED FILTERS Transmits recordings from phono pickup or control of the bass accentuation a 2- voice from mike to radio without use of wires up An "acceptor" or series L -C circuit megohm potentiometer may be connect- to 500 ft. Complete Kit with tubes $5.75 may be shunted across the output of a ed in parallel with inductance Above Ki[ sembhd :m,1 tested $6.95 the and Immediate Ö five Write for detailed information. pickup or the output of the first tube condenser. CONSTANT ELECTRIC to absorb energy at some undesired If the tube preceding the tuned cir- 112 Cowell. Street Brooklyn 21. N. Y.

RDIO-.GRAFT for SEPTEMBER, 1946 877 AUDIO RESPONSE SPEED UP REPAIRS WITH THESE G -C AIDS CORRECTION (Continued from page 877)

G -C is HEADQUARTERS AIDS cuit is a pentode the impedance at reson- PAR and SERVICE ance of the tuned circuit should be at RADIO least equal to that of the following grid resistor and at least twice, preferably AU Types of the of Radio three or four times, the value Cements, usual plate load resistor. Typical tuned - Chemicals, circuit filters are shown in Fig. 6. Coil Dopes, NEGATIVE FEEDBACK Compounds FREE STEEL A simple way of obtaining a boost or in sap- G -C leads the geld CAPINEY accentuation at low or high frequencies plying Radio - Electronic is to provide a large degree of negative Manufacturers and Serv- ice Men with Parts, Tools, or inverse feedback and to reduce this Cements, Chem- ® feedback at the frequencies to be boost- Radio In- teals andred Compounds. VI ed. Condensers are employed to give sist on Genuine G -C Dial Belts, Wire Strippers Quality. Dial Cables, Alignment Tools this effect. A series condenser restricts packaged Hardware, low feedback, giving Kits Ne-O -Lite Testers the frequency a Cabinet Repair bass boost; a condenser connected be- -SEND FOR G -C CATALOG ORDER FROM YOUR JOBBER tween the inverse feedback line and ground reduces the feedback at the higher frequencies giving a treble boost. GENERAL CEMENT MFG. CO These methods of compensation are largely employed by set designers to ROCKFORD, ILLINOIS make up for deficiencies in loudspeakers and baffles. In set design, the high frequencies are attenuated due to sideband cutting RADOLEK and considerable compensation is necessary, but in the design of audio amplifiers to follow pickups the problems are different. If (mind the IF) any high - ELECTRICAL APPLIANCES frequency boost is needed, it should be Fluorescent Kitchen Unit...... S5.25 M. Fluorescent Dealt Lamp. Beautiful Finish ten bulb 8.29 n. limited in value and should occur only Bulbs for above ...... Single Burner Electric Stove. less Switch. 2.55ee in a frequency band well away from Single Burner Electric Stove. with Switch 2.95 ea. Double Burner Electric Stove. with Switch 8.25 ea the top resonant frequency. If a shunt Non -Automatic Electric Iron .15 e large stocks assn,, the finest and most Non -Automatic Toaster 3.75 es condenser is employed in the negative Radiant Bowl Heater 4.25 ea. complete selet o.ss of oll available Berns Cabinet Type Heater 12.00 ea. Electric Broiler DeLuae Type 13.75 ea. feedback network, such a condenser at lower prevailing prices. Thousands .4 should be active buyers depend on us for their Bathe ELECTRICAL ACCESSORIES very small. Typical values are Bakelite Cape .o5S ea. given in Fig. 7. Radio repair and replacement requirements. Rubber Caps Electric Iron Elements .55 B ecause we understand service problems, Niehrome Electric Stove Element e: More low- frequency compensation is wry order is expedited for delivery in Bakelite Heater Plug .10 ea. 3 Way Cube Tap .11 ea required after a pickup than after a datable quick time. Everything we do is Cord Connector .11 ea Replacement Toaster Element .lS ea. radio so planned for convenience and satisfaction to tuner, the series condenser em- CORD SETS evr customers. You will rend It profitable to ployed to reduce low- frequency feed- 0 ft. Appliance Cord with Plug...... 21 ea make Redolek your buying heodquaden. Electric Iron Heater Cord with Bakelite Plug .45 ea. back will be smaller. The bass boost is Electric Iron Heater Cord with Switch Plug .79 ea. Broiler Cord 3 Contact Plug .85 ea. sometimes greater anticipated ow- 15 ft. Garage Trouble Light 1.95 ea. than FREE BUYING GUIDES RADIOS AND PHONODRAPMS ing to the feedback becoming positive Superheterodyne 5 Tubes mplete with at very low frequencies. Take care that Semuw of existing conditions we keep our Bakelite Cabinet and Tubs 22.5 ea. superheterodyne O Tubes complete with there is not too much phase in customers right up to the minute en avail- Wooden Cabinet nd Tubes 28.95 ea. change Phonograph able merchandw by releasing supplements Portable complete t Ile Tubes amplifier, and ho,, 38.90 tea. the otherwise excessive feed- frequently Instead of sending our regular Automat Phonograph complete withw Tubes and eSpeaker 49.93 e.. back may take place at low or high fre- S ig Profit O5id PREPARED ASSORTMENTS quencies, resulting in motorboating or once a year. Send 100 1/3 Watt Resistors All insulated... 2.98 a high -pitched 114 100 L Watt Resistors All Insulated... 3.95 whistle or hiss. th coupon new loo I Watt ResIston All Insulated... 4.45 to get these Free 50 2 Watt Resistors All Insulated.. 3.98 A 50 200 Volt Paper Condensers 2.45 procedure seldom employed but Buying Guide Sup- 50 Mice Condensena 2.95 20 Dry Electrolytic Pllter Condensers 6.78 none the less effective is to use negative plements as they 10 25 ft. Rolla Hookup Wire- Asst'A feedback direct to the pickup, o re laved Colors 1.95 arrang- 10 Volume and Tone Controls - No Switches ...... 1.95 ing the circuit so that the amount of 100 Co. Spaghetti One... 3.95 feedback is proportional to the pickup's WaferunilRa Cricrat.eamicBa nd Si20 3.98 20 Auto Suppressors 2.98 impedance. This results in automatic 50 Electrical Wiring Devices. Plugs. RADOLEK CO., Dept. C-118 Taps, Bases. Elements. Fusee. etc. 5.00 compensation for the pickup resonances, 601 W. Randolph St.. Chicago 61111. SEND FOR TRUTONE RADIO AND COM LETE for at these frequencies the impedance Plesae sand fali gafisg Orin fvpplasan,s Terms. 25% deposit quired with order. Balance C.O.D. Merchandise sent prepeld If fuss ro. is high. Condensers can be placed in Rug mltance accompanies order. the feedback network to give bass boost aoosfff TRUTONE PRODUCTS CO. and high- frequency compensation. To ORDER FROM RADOLEK 703 West 42nd Street. Dept. C. New York (18). N. Y. keep the amount of feedback independent of the volume, the volume control AMPLIFIER may be placed after the first tube,- the Porcelain Low Loss Octal Sockets HIGH QUALITY CIRCUIT output of the pickup being reduced to For Musical, Mike & Phono prevent overloading. This is shown in with Standard Value Resistors and 2 Watts output at 1000 cycles Fig. 8. Enthusiasts who have tried this Condensers wired on. (All Parts Soar cost $5.10 less tubes Brand New). One dozen $1.00. circuit claim that it makes a cheap Write: magnetic pickup sound like MARSHALL a first class GREENWICH SALES CO. STEWART CO., crystal (which means that it is easy to 59 Cortlandt Street New York 7. N. Y. Terre Haute, Ind. obtain excessive bass)!

878 RAD'IO -CRAFT for SEPTEMBER, 1946 Order from LAKE! REBUILDING A TELEVISER You'll Make No Mistake! (Continued from page 832) RADIO Cabinets & Parts types of switch to provide 3 -pole, 3- from the chassis and their incorpora- operation NOW position where the second and tion in a separate unit made room for Available third positions are additive, each in turn the addition of the components for the s441. to the first position. Capacity is add- FM audio i.f. system. Postwar ed to the initial capacity for each of A Meissner 4.3 mc i.f. transformer for . the lower frequency channels. If the FM receivers was pressed into service 2 Post special switch is unobtainable a 3 -pole, by unwinding turns until the unit RECORD - 3- position switch can be used with indi- tuned to 8.25 mc. The discriminator vidual capacitors provided to tune each transformer was constructed from the CHANGER channel. In the first case the highest existing audio i.f. transformer in the With luxurious brown leatherette portable case 15" L x 15" W x 10" D. Latest electronic de- frequency is adjusted first and each kit. The secondary was tapped at the velopments make this modern record -changer lower one in turn. If the second type of center and coupled from the center-tap the finest on the market today 1 switch is used each channel is adjusted with a 50 -µµf capacitor to the plate side List Price.... $49.95 Dealer. net.... $29.91 individually: of the primary. This has proved more Also blank table cabinets of walnut veneer In the left front The oscillator frequencies to provide than just satisfactory. A photograph Side w(Note:'7" haatcespeakerte peakoirr grill.) the proper intermediate frequencies for of the revised chassis arrangement is 3.1 - 55/ L s 51/9111X 4 D$1.95 St 2 -101/a. L s 6A4' H s s D $2.75 New York's stations will be: Audio shown. The discriminator transformer G3 -131/2. L s aw N x Ws. D $3.25 i.f. -8.25 mc, Video 12.75 mc. is shown separately (Fig. 2). ra_wa, L s 7' N s 5V.' G $2.50 Channel 2 54 -60 mc-Osc. Freq. 68 mc Trap alignment procedure with a a Speaker Orenmg in center of front aide. All types and gc s. Channel 4 66 -72 me -Osc. Freq. 80 mc composite first i.f. for the audio chan- blé at Lake's lower Alarge stock i hated in our Channel 5 76 -82 mc-Osc. Freq. 90 mc nel and for the video channel in order cataree. ..RV le RN -R.TA I L.R. An additional i.f. stage and the re- to reduce the response of the latter to ouru customer list today. Order r Mew .Catalog Today! building of the audio i.f. as a true FM possible audio i.f. interference from the Geton mailing list! receiver for the sound channel is an- adjacent or co- channel is as follows: Dept. e other worthwhile improvement. The composite (first) i.f. trap is ad- The circuit for this is shown in Fig. justed for minimum response to 14.25 LAKE RADIO SALES CO. I -1. Note that the added i.f. precedes me at the video detector load. The 615 W. Randolph Street, Chicago 6, III. the existing first video i.f. and is a com- 2nd i.f. (video) trap is tuned to 8.25 mc posite of audio and video i.f. amplifi- (max. response at FM limiter grid). cation at the intermediate frequencies. The 3rd i.f. trap is tuned for minimum Immediate Delivery! The audio is tapped at the same point response at 14.25 mc, and the 4th i.f. as in is Tour Net the original.circuit. It is now, how- trap tuned for minimum response Headphones, Signal Corps. 8000 ohms and ever, in the plate of the first (com- (at video detector) to 8.25 mc. 200 ohms, etch 5 2.48 Lot. of 10..822.00; write for quantity prices posite) i.f. rather than the mixer plate. Proper alignment of the discriminator Two post V.35. recoed- changer: it provides manual or automatic playing of ten standard There follows (I -2) an i.f. stage at 8.25 in the audio i.f. system can be made 12 or twelve 10" discs with a minimum of waiting time between record. 18.95 mc, a limiter and discriminator, and only with suitable instruments, although Phonograph motor for 110 volt A.C., 60 cycles the audio amplifier with and pickup that lists at 310.00: both for 7.95 comprising a volt- great care in tuning, an amplitude - Telegraph keys with cutout swlteh .95 age amplifier and an output stage. The modulated signal generator may be em- 2500 mfd. 3 volt F.P. condensers .49 Hit of twenty 5. 10 and 25 -watt vitreous FM sound channel is essential for post- ployed. With this the i.f. amplifiers are enameled rosletors 1.89 lilt of ten bathtub condensers up to 1 mfd war television -sound reception. tuned for maximum output at the inter- 400 V. 1.95 8 PM speaker, 3.'Vi The removal of the power components mediate frequency (8.25 mc). The dis- SY3a tubes .39 criminator primary is 51t30T tubes .39 tuned for maxi- 635 tubes .48 0 mum response after first detuning the 12A605' tubes .89 1 10-ÓÓ parer transformer, 6.3 V. winding 2V3 secondary. tube ó 2600v. The secondary is then tuned 3.69 II .5/3000V. for minimum response to the a.f. am- Plus shipping charges IOMEG.EACH 141 plitude modulation. There are two peaks. Writs for our illustrated literature featuring all The proper adjustment is the minimum types of radio parts and tubes response between the two peaks. The separate power supply diagram ARROW SALES, INC.

is shown in Fig. 3. Two high -voltage 59 West 14 ubbard St. Dept. D Chicago 10. III i noir transformers are connected in series to o SA. +2300V.DC give approximately 4500 v.d.c after rec- 250K 2ND ANO DE. tification ' -IO,000V. INSULATION for the third anode (intensi- ETC THE YEAR'S BIGGEST OFFER +4600V.DC FOR ACCEL. ANODE" fier) of the 5CP type tube employed in the author's set. Potentials for second 10 lb. Radio Ports Assortment anode, deflection plates and focusing anode are obtained from dropping re- A "find" for the radio serviceman. N.V. PLUG sistors comprising a bleeder across the Hundreds of valuable radio parts. 200n. high voltage súpply. The low- voltage including coils, resistors, trimmer supply is included on the same chassis condensers, lugs, transformers, 300. with high voltage. This II high -voltage switches, hardware, etc. 3 supply will deliver 5V4 _ sufficient potential Only $2.95 for tubes as large as 9 or 10 inches di- 6.3v. TO AL, Write for radio parts circular OTHER TUBES T\ 16?/T ameter. A 7 -inch electrostatic deflection r' RANDOLPH RADIO STORES 600 v. C -R tube type 7EP is listed, but we have been unable to obtain W. Randolph St. 86.3v. TO Cm NO.3 TO ANODE NO.3 one. The 609 Chicago 6, Ill. p TJBE Or 50P4 larger types require magnetic deflection and will necessitate circuit in NO.1 TO EXISTING changes BLEEDER STRING the sweep amplifier sections. TO POWER SW. ON RECEIVER 7ed ncElloy ON ANDREA SET If higher anode potential is desired Wold's Largest Manufacturer of without removing components from the Wireless Telegraphic Apparatus tI7 V. AC INPUT existing chassis this may be accom- ICE tg111rar EPARATE POWER SUPPLY ,011 ANDREA KIT. FOR USE WITI plished by connecting the high -voltage CCELERATOR TYPE E. S. C. R. TUBES. supply additively to the low - voltage McElroy Manufacturing Corp. Fig. 3-Separate high -voltage power supply. (Continued on page 881) s62 Irookll.e Ave.se Bostsi, Massaekusetts RADIO -CRAFT for SEPTEMBER, I946 879 rfiJ III COMMUNICATION II

IMMEDIATE DELIVERY APPEARS DISSATISFIED WITH EDITORIALS WESTON Model 798 Dear Editor: good items, the little GI gets what little THE COMPLETE MUTUAL CONDUCTANCE This is directed to the attention of is left (and believe me gentlemen -it's TUBECHECKER AND ANALYZER whoever writes the "Communications" true, I know from experience). column -just print it if you dare. And maybe I'm a little dense, but After reading the editorials in the perhaps you will explain why manufac. last three or four copies of your pub- turers won't allow a dealer to handle lication, count me, and at least 40 GI's more than one line. I worked in perhaps i and hams, off your purchasing list. the largest Ham Shack in the country Maybe we have been presented in a and we sold competing sets side -by -side. distorted view but while we are out Could it possibly be that with the re- protecting the necks of your money- suiting competition, the prices would hungry manufacturers, we thought we'd come down to where they should be and be given at least an EQUAL chance the manufacturer would make only his with the already established dealers. normal profit? It seems like a very nice That opportunity seems to be a small inter- political set -up - something recompense for three years of a man's REALLY SMELLS .. . $187z life or the thousands of our buddies Thanks again for getting behind the Features lives -maybe we're asking too much serviceman and cutting his throat -we though. for instance the RFC sure know who is on our side don't Mutual -Take - Conductance or "Good -Bad" readings 9 9 9 on all receiving type tubes. the GI is getting the same old shaft wed 9 Complete volt- ohm- milliammeter rangea in ad- ROBERT C. FOSTER, diUon te tube testing facilities. again. After the government, the state W9JWY, Tubechecker ranges -3000/6000/12,000 mitrem- and the big dealers pick over all the Oak Park, Ill. New patented test circuit using differential frequency system. HAS LITTLE TROUBL E GETTING MATERIAL Tubes tested with high frequency signal (5 ko) Adjustable Plate, Screen, Signal and Grid Bias Dear Editor: up." I was unable to get a franchise voltages. Massey's letter for some of the most of Hot neon leakage test between any two tube I was interested in Mr. popular brands elements in the May issue. Last October, I de- radios but was able to get a new brand Analyzer ranges: cided to obtain a good stock of radio which I believe to be as good as, oI Volts AC volts DC 7.5/150/750 7.5/150/750 parts. I talked to some of the local better than, the well-known brands. Current Resistance servicemen and they led me to believe I found that if the product has a 90- 7.5 Milliamperes DC 100,000 Ohms that the serviceman was only able to day guarantee, the customer regards it 150 Milliamperes DC 1.0001000 Ohms get an occasional condenser or resistor. as trustworthy. To date, I have nearly When I presented my problems to a complete stock of radio parts which 1 the distributors, I found them courte- value at $1000. I think that the other Au. DU MONT ous and willing to cooperate. One dis- servicemen either didn't try hard CATHODE -RAY OSCILLOGRAPH tributor told me, "Your appearance is enough or tried the wrong way. neat and your records seem straight so RAY M. DIRBA, Type 274 SAA-so77f I think that we will be able to fix you Wallis, Texas GETS ONLY TROUB LE -NO MATERIAL function Dear Editor: There are a lot of new sets being The Du Mont Type 274 Cathode-ray Oscillo- I have just finished reading your edi- built by the manufacturers and they graph Is an inexpensive, general purpose in- torial on page 529 of the May issue. I have the condensers. Why should all of strument designed for routine laboratory and it is a regard- them be taken by the manufacturer? It production testing, and for radio servicing. feel that fair statement Featuring 5' cathode -ray tube in a compact, ing the Ex- Serviceman vs. Radio Manu- is very discouraging not to be able tD portable, versatile oeclnograph. the Type 274 facturer and that it considered both get vital parts. It makes a fellow want (Willis a long standing need in the instrument sides of the controversy. to chuck the whole business out of the Meld. Here is another "squawk." How about window and try some other line. Have complete stock ON HAND of Aerovox. the poor experimenter, home set builder The only reason that I am writing Simpson, Hamtnarlund. I.R.C.. B &W. Utah, and student? I have been trying to buy this at all is that I feel that I am only 'Fromm( and other nationally known parts and eau a two-gang variable condenser, 365 µµf one of a vast army of students and ex- pment. "superhet type" with trimmers, for perimenters who suffer from the same If not rated, 20^0 with order, balance C.O.D. more than two years. There just aren't situation. Can something be done to

Do, 1. C. any in this area and I have been unsuc- give us fellows just a trickle of the cessful in getting them in the mail -order necessary parts? houses in-Chicago. Some types of tubes C. G. LYTI.E, are also very scarce. Vancouver, Wash. HAS GOOD LUCK WITH POSTWAR 2 -TUBER Radin and ¿Lectaur tics Co -'zf2 Dear Editor: from the back of the panel. Using this lit- You published in your March 1944 issue tie set on my outside antenna I am able tc 200 Greenwich St., N. Y. 7, N. Y. an article by Homer L. Davidson entitled operate a small speaker. With headphones BEekman 3- 2980 -1 "A Postwar 2- Tuber," which I built re- there are few sizeable stations which can- Export Div. -WESTERN INTERNATIONAL cently. I have so much good luck with it not be received on it. 168 WASHINGTON ST., N. Y. 6, N. Y. that I use it as much as my SX28. The panel size is 454 inches wide by 6 inches KARL HEIN, high and the chassis extends only 4t/a inches Kalamazoo, Michigan. 880 RADIO -CRAFT for SEPTEMBER, 1946

INDEX TO ADVERTISERS Adson Radio Co. 882 National Radio Institute .. -- 809 Mitchell Adv. Agency Van Sent, Dugdale & Co. Aerovox Corp. 860 National Schools 817 Austin C. Lescarboura & Staff The Mayers Co. Allied Radio Corp. 857 National Union Radio Corp. 810 George Brodsky Hutchins Advertising Co., Inc. Almo Radio Co, 868 Newark Electric Co. 865 E. L. Brown Co. Charles Brunnelle Advertising PRECISION American Parts Inc. 877 Niagara Radio Supply 856 American Television Institute 820 Burke and Wayo.,rre WIRE WOUND RESISTORS Turner Adv. Agency Ohmite Mfg. Co. 862 IRC - SNALLCROSS - MADISON Amplifier Co. of America 873 The Fensholt Co. Inc. Olson Radio Warehouse 869 For Meter Multipliers, High Fidelity Amplifiers Sternfield -Godley, 879 Jessop Advert ; si -q Ca. and other applications where 1% tolerance is Arrow Sales, Inc. Sander Rodkin Adv. Agency Onan & Sons, D. W. 855 req sired. ara Assoc. OHMS Atlas Electronics Co. 841 Gaves Mitchell Advertising Agency Opportunity Adlets 881 1,000 Atomic Heater & Radio Corp. 855 Pa -Kette Radio Co. 882 4,000 W. Montague Pears3'I Arrow Advertising Ago- -. 877 Panoramic Radio Corp. .. Inside Front Cover 10,000 Audel Publishers Grant & Wadsworth Shappe Willes, Ice. 20,000 Audio Sales Co. 872 Pyramid Electric Co. Inside Back Cover 25,000 EACH Mitchell Advertising Agency The Arnold Cohan Corp. 35. Baliser, Peter 872 Radio Corporation of America 816 40000 Bell Telephone Labs 840 J. Walter Thompson Co. 50,000 N. W. Ayer & Son Radio Dealers Supply Co. 875 80,000 Sr° Buffalo Radio Supply 871 H. J. Gold Co. 3 FOR Agency Radio Electric Service Co. 875 90,000 International Advertising Burstein- Applebee Co. 874 David Zibman Adv. 100,000 Frank E. Whalen Adv. Co. Radio Ham Shack 867 200,000 California Radio & Electronics Co. 811 Kupsick Adv. Agency Radio Maintenance 8'1 each, for Mitchell Advertising Agency .5 megohm 75c 3 $2.00 Cannon Co., C. F...... 88; Shappe- Wilkes Adv. Ag,- -cy 1.0 megohm 95c each, 3 for $2.50 M. J. Werner Adv. Radio Product Sales Co. 861 Capitol Radio Engineering Institute 818 Barton A. Stebbins Ape. 7a -, Henry J. Kaufman & Associates See Page 884 SPECIALS! Cleveland Institute of Radio Elea. . 863, 872 RADIO SCHOOL DIRECTORY - METER American Radio Institute G.E. 3'2'. Round Kenneth Kolpein Communications Equipment Co. 859 Sternfield -Godley, Inc. 0 -20 Microamperes Baltimore Technical Institute Scale calibrated 0. 100, Net U ef1rJ995 Borough Advertising Co. 9 Concord Radio Corp. 853 Candler System Co. DeJur 3,2" Round Q Rand -Ries Adv., Inc. 0 -200 Microamperes, Net E. H. Brow, Adv. Age ^c, 6.95 Constant Electric 077 Commercial Radio Institute Minimum order $2.00. No C D.'s Coyne Electrical School 852 Electronics Institute, Inc. Agency Lincoln Engineering School We nay costly anyrherr In U.S.A. Phil Gordon Crabtree Wholesale Radio .... 863 Buchanan- Thomas Adv. DeForests Training. Inc. Bis Melville Radio Institute MacDonald Cook Co. Seidel) Adv. Dow Radio 872 RCA Institutes Electro -Voice Corp. Back Cover Tri -Stab College Henry H. Teplitz Clem J. Ste,gooeyer Adv. Free Want Ad Service ... B81 Western Radio Institute General Cement Mfg. Co. ... 878 YMCA Turner Adv. Agency Cecil & Presbrey General Electric Co. Radtonic Equipment Co. .... 873 Maxon, Inc, Hirshon- Garfield Inc. Greenwich Sales Co- . 878 Radio Wire Television 859 Harrison Radio Co. ... 870 Reiss Adv. Agency Altamari Advertising Aq" -- Radolek Company 878 RISCO SPECIALS Hershel Radio Co. . 88I Turner Co. Highbridge Radio -Television & Appl. Co. . 883 Randolph Radio Stores 879

Howard House 855 Reed Mfg. Co. . 863 Immediate Delivery N. W. Ayer & So, Risco Sales Co. . 892 Kelvin Electronics Co. . 853 Diener & Dorskind Sternfield -Godley, Inc. Scenic Radio & Electronics Co. 875 Kwikheat Div. Sound Equip. Corp. 871 Sigmon's Radio Supply 874 PHONO AMPLIFIER West- Marouis, Inc. Advertising, Inc. Lake Radio Sales Co.. 879 Solar Capacitor Sales Corp. 864 3 tube A.C. D.C. Sander Rodkin Adv. Agency O. S. Tyson & Co., Inc. co ulstely 'red 51 Leeds Radio Co, 074 Sprague Products Co. 846, 847 Ich d. and $3v{ Mitchell Adv. Co. Harry P. Bridge Co. tone controls Liberty Sales Co. .. 844 Sprayberry Academy of Radio . 813 Sternfield -God ley. Inc. Harry P. phono lilt with 3 tubes-3" weaker $7.95 Bridge Co. Sound Equipment Co. . 866 Sterling Electronic I/ETROLA RECORD ('HANGER 817.50 Lifetime Co. 863 The Miller Agency Co. Stewart Marshall Co. .. 878 VM MIXER CUANCI:R $17.95 McElroy Manufacturing Co...... 879 Superior Instruments .. BSI ASTATIC Shappe Wilkes Adv. Agency Mitchell Adv.

McMurdo Silver Co- 819 Supreme Publications . . 845 Curved Arm Edward Owen & Co. Henry H. Teplitr, Adv. L -70 Meade! Publishing House 883 Sylvania Electric Products, Inc. 849 Manuscripts Wanted 875 Newell -Emmett Co. Crystal Pickup Marcotte Co., A. J. 883 "Tab" Technical Apparatus Bldrs. 869 Morlock Adv. Agency Mitchell Adv. Agency 871 GTC 5016 Maritime Switchboard 868, Terminal Radio Co. . 882 Metropolitan Electronic 8 Inst. Co...... 876 Regent Adv. Agency Output Trans. Mitchell Advertising Agency Triplett Electrical Instrument Co. . 861 Milo Radio 8 Elec. Corp.. 880 Western Adv. Agency 53c Burke & Waybur^e Trutone Products Co. 078 Inc. 843 Marsh INSULATED RESISTOR KIT Murray Hill Books, Terrill Belknap and Assoc. P. Bridge Vertrod 100 assorted-1/2. 1/2. 1 watt 82.10 Harry Corporation 862 BPass condenser kit N. J. Industrial Company 883 Mitchell Adv. Agency 15 assorted - all 600V 89e National Plans Co. ... 857 World Radio Laboratories .. 859 Emerson 20 -220- 150V. elect rand .44 National Radio Distributors 873 Pfeiffer Adv. Agency Ose. coil center lapped- 456kr. 12SA7 IS Burke & Wayburne X L Radio Laboratories .... 881 25 asstd. mira tond. - color coded .00 Phosphor bronze dial cable, 25 ft 25 Signal Corps Telegraph kegs with cw. switch 75 25% heuired on C.O.D. Orders CANNON- FREE: Send for Catalog C Phones have kept in the NEWTR ÄDD ÌTÖ2i lead -o v e r twenty -five Sims In your Docket Wt. my , Complete. RISCO SALES CO. READY TO as years through real per- self-contained personal durable WHOLESALE RADIO DISTRIBUTORS formance. Write f o r ilversilver plastic Has patented Crystal - NO 224 E. 65th ST., NEW YORK 21, N. Y. R -9, TUNES. BATTERIES OR 73.F:C- Folder illustrat- TRIC PLUG IS REQUIRED. USUALLY RECEIVES LOCAI, ing complete line of BROADCASTS CLEARLY without aerial felwelneally unusually sen- GUARANTEED TO WORK when 72C40 Plsota Eleatic Zeit rugged, connected .I !Teary ° bar men ntructioons eused theach iradioo.. For nrnrow control l. °lit sitive, dependable Can - Can e4° homes. offices. Purple. alarms, ndmb fo sore,, controls, 'b.. hotels. cabin.. bed. houras. r,e1" m- non -Ball Headsets. the kl d SEND ONLY S1.0Ó 4`.4.,'".6:11;473"27117: slue or bene lo of F. CANNON COMPANY or send 33.9y for delivery persons and soh ,,., Fo. AC IDEAL a ObFT FOR ADULTS dALIKE! Complu. .alb oil lob, SPRINGWATER, N. Y. Get your PA -BETTE RADIO TODAY -NOW. Dealers In most allies. and b,,l' -in SPOT color $11.95 PA -KETTE RADIO COMPANY ADSON RADIO CO. lie adi t #eadivattat! DEPT. RC.9 KEARNEY. NEBRASKA 221 FULTON ST., NEW TORM 7. N. T.

882 RADIO -CRAFT for SEPTEMBER, I946 BOOK REVIEWS MATHEMATICS ELECTRONICS F(JR ENGINEERS, by ELECTRICAL AND RADIO DIC- John Markus and Vin Zeluff. Published TIONARY, by Dunlap and Haan. Pub- FOR by McGraw -Hill Book Company. Stiff lished by American Technical Society. RADIO Two volumes, cloth covers, 9 x 11 inches, 390 pages. Stiff cloth covers, 6 x 8'/2 inches, 114 prepared for home study. Price $6.00. pages, plus page index. Price $1.00. Book I (314 pp.) covers the algebra, arithmetic, and geometry; Book 11 (329 This book contains a wealth of tech- This dictionary of words and terms pp.) covers the advanced algebra, trigo- nical information and data for radio used in electrical and radio fields is nometry, and complex numbers neces- and electronic engineers and engineer- useful to the student or engineer. The sary to read technical books and articles ing students. It is a compilation of 142 words and terms are divided into two on radio. papers that have been printed in Elec- sections. In the first, words are defined tronics magazine since April 1930. The as they apply to general electricity, in MAEDEL PUBLISHING HOUSE Room 117 articles selected for this book have been the second, definitions are given as used 593 East 38 Street, Brooklyn, New York in great demand as reference material in radio. Send me MATHEMATICS FOR RADIO AND COMMUNICATION as checked below. I enclose for engineers. Elsewhere in the book are numerous payment therefor with the understanding that The material is presented in the form tables, I may return the book(s) within 5 days in good charts, diagrams, formulas and condition and my money will be refunded. of papers, data sheets, design charts symbols containing information and and graphs. There are design charts data most often sought by the student and graphs covering all phases of com- and engineer. Name munication work as well as electronic heating, mathematics and permanent THE RADIO AMATEUR'S HAND- Address magnets. BOOK (Twenty -third Edition-1946), All material of a similar nature has by the Headquarters Staff of the Amer- been grouped together in a single chap- ican Radio Relay League. Published by D Book I at 33.75 plus he postage ter for easy reference. There are 28 the American Radio Relay League. Hard D Beek II at 34.00 plus 6c postage chapters with the heading at the top D Books I and II at 57.75 postage prepaid paper covers, 6 %2 x 9 %2 inches, 688 of each page, so that it is not neces- pages. Price $1.00 in continental Foreign and Canadian prices 25c per volume higher to U.S.A.; sary resort to the index to find the $1.50 elsewhere. . necessary references. The AREL Handbook, one of the most widely -read radio publications, needs no WHY SMASH ATOMS? by Arthur K. review Solomon, Research Fellow in Physics or introduction to the radio - OSCILLOSCOPE and Chemistry, Harvard University; minded public. For years it has been a "must" on the bookshelf of radio engi- FOUNDATION KIT Staff Member, Radiation Laboratory, 5 INCH Massachusetts Institute of Technology. neers, operators and experimenters and anyone who has Consisting of Case, Chassis, two Published by Harvard University Press. read or owned a copy invariably purchases the latest edition shelves (right & left), tube shield and Size 6 %2 by 91/4 inches, stiff cloth covers, as soon as it leaves the presses. bracket, front panel, screen window 204 pages, illustrated. Price $3.00. This, the first frame, handle, plastic window socket, peacetime edition in with 5CP1 Cathode four years, is Ray tube - The author has presented the sub- very similar in many re- Special $18.95 ject of atomic reaction in a most in- spects to the 1945 edition. The close teresting and lucid manner-we might similarity between these editions is almost say in a grand manner. He gives probably caused by lack of amateur the names of men in science who made experiment and development during the important discoveries along the upward war years. The chapters on WERS and path which culminated in the atomic carrier-current communication have bomb and the dawn of a new era in been omitted and more space given to e physics. material on antenna construction and One valuable feature of the book is v.h.f. equipment. that the important ground work on sim- More than 200 pages are devoted to pie electron and nuclear theory is ex- catalog section, listing the complete plained in a clear and interesting style. line of more than one manufacturer. A The first chapter starts with the elec- complete index, 10- pages, adds much to tron; then we learn something about the utility of The Handbook. -R.P.S. the nature of the proton, the neutron, KIT without Cathode Ray tube 511.95 the nucleus and atomic number. Follow- 5CP1 Cathode Ray tube only.... 7.10 Tube shield and bracket, only 1.98 ing chapters -with beautiful illustra- 38P1-Cathode Ray Tubes 5.25 tions -are devoted to atom smashers, PHONO including the voltage HIGHBRIDGE RADIO-TELEVISION doubler, the Van AND APPLIANCE CO. AMPLIFIER 340 Canal der Graff electrostatic generator, the Street New York 13. N. Y. Cyclotron and others. 3 -Tube, A.C. -D.C.Completely Wired Geiger counters and cloud chambers Ready to Operate are explained clearly, as is the subject of uranium fission. Other chapters cover atomic energy, uranium, plutonium, ap- $375 MARCOT KEY MACHINE plication of nuclear energy in medicine, M 1,0( No. 8 Key Ma- the atomic bomb, etc. chine Mount- (leas tubes) ed on Cab- The excellent line illustrations by inet s 75.06 Katherine Book on Campbell Duff lend an air M o d e r n of charm and a clear interpretation of Uses 50L6- 35Z5 -12SQ7 Lockamlth- 1ng 3.95 the various actions in the new world of Auto Cade Bonk and Auto Depth Keys 12.50 nuclear physics. An excellent glossary N. J. INDUSTRIAL CO. 162 Dos. popular Key Blanks 77.79 of atomic energy terms is provided, to- 11 HILL STREET get Key Files, Tools. Pins, Springs. Thimble 1050 gether with a complete index of 9179.71 the sub- NEWARK 2, NEW JERSEY jects covered in the book.-H.W.S. A. J. MARCOTTE CO. peoetp aC ca 400se^Ìn:

RADIO -CRAFT for SEPTEMBER, 1946 883 Despite the high operating potential, DIRECTORY the 4100-volt power unit is less than liDIO SCI11ODL ;=' two pounds in weight. Two battery - operated models were produced, one PREPARE NOW FOR SKILLED JOBS IN RADIO AND ELECTRONICS using a small vibrator interrupter and one an impulse closely resem- a place for yourself in a new world of radio and electronics -a world in which breaker MARErevolutionary electronic developments will require highly specialized technical bling the hairspring assembly of a knowledge. Take a good course now to fit yourself for a good paying job. The training watch. you need can be supplied by one of the schools advertised in this publication. Powered by a single storage cell, the size of a flashlight cell, battery life is RADIO from one to two hours of operation in SERVICING RADIO- the first -mentioned type of.supply, 50 Train with professionals. Com- in BROADCAST ENGINEERING plete, intensified courses; Re- hours the second. pair a Maintenance. Communi- A third model employed a relaxation COMMERCIAL OPERATING cations, High -speed telegraphy, slip transcription. FCC exams. oscillator as the source of high voltage TELEVISION etc FM- High School Students ac- powered from the 117 -volt line, rectified SHOP MATH cepted for training as Mer- by chant Marine Radio Officers. another product of wartime research, HOME APPLIANCE Gov't sponsorship available to a minute tube consuming but five hun- REPAIRING veterans. dredths of watt in filament. PA /radio School managed by radio men." a the October Classes Now Forming 45 W. 45th St., Dept. RC, New York 19. N.Y. The 1P25 tube being a recently-de- MELVILLE RADIO INSTITUTE veloped contribution to the art of elec- Baltimore Technical Institute tronics, mass production of the quanti- 1425 EUTAW PLACE BALTIMORE 17, MARYLAND ties necessary to supply the needs of our COMMERCIAL RADIO INSTITUTE armed forces has presented countless Veterans Accepted Under G.I. Bill A Resident Courses Only radio training center for problems in manufacture. twenty -five years. THOSE e liNs SriTi RADIO COURSES RESIDENT COURSES ONLY RADIO OPERATING CODE Broadcast, Service, Aeronautical. Television and Marine RADIO SERVICING ELECTRONICS telegraphy classes mwY forming. Literature upon request. - Veteran training. Classes now forming for Oct. 1st. REFRIGERATION SERVICING Dept. C. 38 West Biddle St., Baltimore 1, Md. Personal CounsellIno Serviese for Veterans Writs for Latest Trade & Technical Catalog I.M.C.A. THROE & TECHNICAL SCHOOLS 4 W. bath street New York City RADIO RADIO Technician and Radio Communications courses. Register now for new cluses starting first MONDAY 100-{ el euh month. Day and Evening Classes. 600 4100

AMERICAN RADIO INSTITUTE I P25 electron lens assembly, with voltages. 101 West 63rd St.. New York 33. N. Y. APPROVED UNDER SI RILL OF RIGHTS. Defective operation occurs if, in the Rea "Lq" man. Learn how to end and assembly and processing operations, ill RIIIOIIIIII 111111Ili I111111II11RIIIIIIIIili111IIIOIa ndr °radio.e Cognmerce need thousands Jlllllllllli IUI1111IIIIIIIIIIH II III of men for Job.. Good pay adventure. even a slight contamination is intro- Interesting k. Learn at home Culck. ly through famous Candler System. duced in the form of oils or vapors, Write for FREE BOOK. LEARN RAPID CANDLER SYSTEM CO. metallic compounds or dirt. Therefore, Dept. 3 -K, Sox SSS. Denver 1. COI...U.S.A. RADIO SERVICING Send for Free Information. "3 Ways to Learn extreme precautions toward cleanliness Radio." Approved for Training Veterans. of parts and purity of atmosphere are RCA INSTITUTES, Inc. WESTERN RADIO INSTITUTE observed. - 11 Offer thorough training 1457 Glenarm. Denver 2. Colo. Astigmatism in the completed tube courses in all technical phases of l 11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111 I I I Æ Radio and Television appears as the result of misalignment DAYS- EVENINGS WEEKLY RATES of the electron lens assembly and mem- VETERANS: RCA Institutes is approved bers of the lens system being slightly under G. I. 8111 of Rights ELECTRONICS out of round. This in tends to limit For Free Catalog Write Dept. RC -46 Electronic Technician Training Course. Quail?, for turn RCA INSTITUTES, Inc. Radin Communication (Commercial Government Li- resolution. A nose): Radio Repair Service: or be an Industrial Radio Corporation of America Seretee Electronic Technician. Register 110,V for new dunes However, the engineering staff of the 75 VARICK STREET NEW YORK 15. N. Y. staring etely (our weeks. Approved under G. I. Bill of Right;. Itesidence day and evening school Write to corporation designed equipment and in- ELECTRONICS INSTITUTE, INC. itiated specialized procedures and tech- 21 HENRY. DETROIT 1. MICH. niques so that during the war an aver- L Eti Correspondence Courses In age of over 1000 tubes per month wer.e VETERANS can complete work supplied by the production division of here in shortest possible time. RADIO dnd ELECTRICAL ENGINEERING their vacuum tube laboratories. Courses also in Civil. Electrical. II ELECTRICAL ENGINEERING ";7w;; ;;,c Mechanical, Chemical. Aeronautical In addition, large quantities of the Engineering: futur.°cio ° u ` u ôkiV Business Administration, Accounting, Secretarial h complete unit, consisting of a Schmidt RAD EeGINËËRINGz^ 1e p° o°o -vnacuum o Science. 63rd year. Enter Sept., Jan., Mar., June. Trains you super-service man. real v in- technician. badly. comple- optics system for projection of the School now filled to capacity. No applications can . tion.t itio n $25. eitherit cou al maeetá;en olñ fra-red image upon the tube, an ocular 1 be accepted until further notice. eß r i magasnes. ptr enti,e SdE.N NOwt SlI FREE lens system for image magnification and } TRI -STATE COLLEGE AN OLA INDIANA LINCOLN ENGINEERING SCHOOL i7nsos?,,s.°'rai:er. power supply, also a product of the engineering division, were supplied by the BLACK -LIGHT TELESCOPE company. The entire assembly is con- (Continued from page 826) tained within a sealed nitrogen -filled case for protection against moisture and submersion ow current density, fine grain for high the phosphor screen and the water is dirt. Even in water is not resolution, high voltage and vacuum decanted off. detrimental to operation. operation, and insensitivity to caesium The completed tube, together with an contamination, willemite has been used ocular lens and infra-red optics, has A studio for radio and television is one as the fluorescent material. In the prep - unity magnification. Resolution is such of the features of the modernization aration of the screen material, precau- as to resolve nearly 400 lines per inch. plans of New York's Metropolitan Mu- tions are observed to insure an efficient A star of the fifth magnitude may be seum of Art, which include reconstruc- screen of fine texture. detected by the tube. This is equivalent tion of the present buildings. Below the Willemite, in water suspension, is to one -tenth of a candle -power at a dis- studios will be an auditorium seating placed on the glass surface to be coated. tance of one mile-a very small amount 1200 people, in which programs can ei- A centrifuge is employed to lay down of infra -red radiation, indeed. ther be originated or received.

884 Printed In the U.S.A. RADIO -CRAFT for SEPTEMBER, 1946 . Portrait of a nary Happy Man

Sjwra.--- *am

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