Radio age (Jan 1927-Jan 1928)

40 RADIO AGE for March, 1927 TTBATTERY ELIMINATOR MONEY-BACK GUARANTEE No more worry with "B" Batteries I Hook up a Roll-O "B" Battery Eliminator and forget battery troubles forever. This wonderful new invention means better reception, sharper tuning. Gives you more real pleasure from your set. Completely Equipped — No "Extras" to Buy Operates perfectly on direct or alternating current, giving up to 90 volts current, and using the full wave of the power supply. Simple directions enclosed — anyone can plug it in to any kind of set up to sis tubes. Constant voltage gives set more power. Costs no mora ,«k than set of good "B" Batteries. SolSIOV Idly built in beautifully finished metal Don't blame your set because run down "B" Batteries won't let it work right. Order your Eliminator NOW. Write name and address on a piece of paper, pin a dollar bill to it, and mail It TODAY. Pay postman balance (S6.95 plus a few cents postage) when he delivers your Eliminator. Use It ten days. If not more than satis a_ fied, return it and get your money back. *& THE ROLL-0 RADIO CO. Dept. T-2 3d &. Sycamore, Cincinnati, 0. Amazing New 5-Tube Radio At Very Small Cost Improves Reception 100% Lieut. Sterling G. Sears of the U. S. Naval Reserves has perfected a marvelous new 5-tube Radio that improves average home reception about 100%. Due to special features, this Radio is extraordinarily selective and powerful, easy to operate, very economical on Battery consumption — and costs only about one-third of the usual price of 5-tube machines. Perfect satisfaction absolutely guaranteed, and a 10day Free Trial offered to all who wish to try it. Full information together with reports of tests made by experts will be sent FREE to all who write at once to Geo. W. Naylor, Jr., Dept. 316N, 161 Chambers St., New York City. Write today — no obligation! CHELSEA Chelsea Models $26 to $99.50. Write to-day! Chelsea Radio Co., Chelsea, Mass. Shield Your Radio Cabinet Make jour set selective and cut nut your local stations. Our METALLIZED PAPER does the work better than individual shielding. It is easy to put on with ordinary g!ue. Enough for the inside of the largest cabinet, sent prepaid with full instructions for $1.00. GUN METAL CO., Ave. K, MAR-CO Illuminated back-panel controls set the 1927 style. Mailing Lists ,se sales thoasaDClB~ of classified est proroectlve itateandLocal; Professions. Business O Guaranteed £ £ Radio Is Used to Find Auto Noises WHAT does the voice look like? Of course you have never seen it. But visitors to the General Motors building in Detroit recently were able to see projected upon a screen the sound waves their voices made. They saw, also, how General Motors has harnessed radio and put it to work to make better automobiles. It was a demonstration in popular form of the more delicate and elaborate apparatus used in the G. M. Research Laboratories for finding automobile noises. What the microphone tells about a motor. Upper pattern shows a tuning fork vibrating at a pitch of 512 cycles. The lower pattern is that produced by striking on the pan of the car with a hammer. Note the change in the pattern at the moment of impact Noises are sounds having irregular and complex waves. To study them, it is necessary to reproduce them faithfully on a photographic film, where they may be measured. The resulting data are used to trace the offending noise to its source. The apparatus used in the General Motors Laboratories consists of three distinct units: 1. The microphone. 2. The vacuum amplifier. 3. In the oscillograph a tiny spot of light reflected from the moving element vibrates back and forth across the photographic film revolving on a drum. After development the film shows a trace representing the wave form, intensity and pitch of the sound picked up by the microphone. Ordinary radio equipment is not accurate enough for this work, and each of these devices must be specially built. Noise hunting in cars is difficult because vibrations may be Locating a vibrating tuning fork in front of a microphone as shown in this picture, gives the effect shown in the oscillaograph pattern shown at the top of the smaller photo "telegraphed" from one member to another. There is always the danger that the wrong member will be accused of making the noise. It often happens, too, that when the real source is found, the changes necessary to remove it cannot be made. In such cases one or more of the members, through which the noise is being "telegraphed" to the air and the passenger's ears, must be changed so that they will no longer respond to the vibrations of the offending part. MAKE YOUR OWN CONE OR ROLL SPEAKER GENUINE ENSCO KIT Only $10 The Sensation of 1926-27 MAKE TOUR OWN THREE FOOT CONE SPEAKER IN LESS THAN AN HOUR. Complete parts furnished In kit form. We guarantee thi« speaker the equal of any manufactured cone speaker at any price. With this THREE FOOT CONE SPEAKER you near all the tones. It brings out the true depth and oeauty of orchestral and instrumental music. Can oe operated softly for living Room Music or Full volume for dancing, and without trace of distortion. Kit includes famuus '-ENSCO" cone unit, the only direct-drive, dlsturtlnnless unit for large cones: Alhambra Fonotex for big cone, with brass apexes, blueprints showing five different types of cone and roll speaker construction. All necessary instructions. Buy this wonderful speaker under our absolute guarantee. Your monoy back if you are not convinced that it is the finest reproducing medium obtainable at any price. It works on any get. with ordinary Tubes or with Power Output. Send No Money! Write your name plainly as indicated below, then mall and complete kit will be forwarded to you. Just pay postman $10.00 upon delivery. ENGINEERS' SERVICE CO. 25 Church Si (Desk A). New York City WESTERN DISTRICT OFFICE AND STUDIO 911 Steger Building Chicago, 111. Please Mention Radio Age When Writting to Advertisers.