Radio today (Sept 1935-Dec 1936)

SERVICE NOTES {From 'preceding page) hand has been invented by Carl Evans, Concord, N. H., serviceman. Instrument as shown by sketch is simple but effective. Condenser shaft is slipped through hole in center and made fast by set screw. Two side bearing screws are turned up against panel front which locks shaft from turning. Block is made from piece of V2 inch bakelite (or very hard wood). The holes in the block are drilled and tapped for machine WEBBER'S OFFICIAL! RADIO SERVICE LABORATORY • Write for details about this new radio service STAR — this modern, complete, compact and impressive SERVICE LABORATORY. Has everything for speedy and efficient handling of all radio problems. Makes more business for you — creates good will. Pays out within a short time. Get full facts. Made by the same experts who designed and engineered other Webber Radio Testing Instruments. Write today for catalog. EARL WEBBER COMPANY, Mfrs. 1313 W. Randolph St. Chicago, III. screws, which may be picked up around the shop. With this, your dial band and cable troubles are over. STUDY REQUIRED * With all the new circuits that are continually being introduced, it is essential that the serviceman spend a number of hours each week studying the new developments. Here is what the foreman of Philco-New York's service department, Mr. Wellman, has to say about study. "I find that a serviceman must devote an average of two or three evenings a week to read about and become acquainted with the new sets and circuits. Unless he does this, it is not long before he is hopelessly in a fog as far as servicing new models is concerned." Never before has there been so much need for study — in the past year there have been such developments as AFC, AVE, automatic tuning, tone compensated circuits, new biasing methods, cathode-ray alignment, high-fidelity, new tuning indicators and tubes. If the serviceman is not familiar with these and other new developments, he should spend more time studying. And in view of the fact that study is required after business hours, the service charges should reflect this item. SERVICE TIPS' Silver Marshall A Low Volume, Distortion * The cathode circuit of the 47 output tube is unable to recover from voltage fluctuations due to signal current flow. This in turn is due to the use of too small a condenser across the •Service tips are selected from the flies of H. K. Bradford, President, Capitol Radio Research Labs., "Washington. D. C. cathode resistor to take care of the matter. Remove the .1 mfd. condenser and wire a 10 mfd. 25 volt electrolytic (dry type) in its place. The positive lead goes to the filament centertap and the negative to ground. This will permanently cure the trouble. General Electric K-64 Intermittent While Tuning * A bare wire connects to wave band switch to the condenser gang stators. Within the cabinet this is often forced in contact with another bare grounded wire close to it, due to downward pressure put on It from the condenser gang shaft. Remove the chassis and separate the wires as far as conveniently possible. Silvertone 42 Poor Low Frequency Reception * If reception up to 950 Kc. is attended by noise, heterodyne and instability, a suggestion is made to ground one side of the antenna coil. In addition to this grounding the chassis externally will reduce or entirely eliminate hum from that cause. The chassis is thus prevented from picking up voltage variations from the line and power apparatus within the receiver. Adding a ground to a receiver which is not supplied with one, is always helpful in this end. RCA Victor 220, 222 Motorboating ■*: Usually occurs in connection with the grid circuit of the 2A5 tube. Bombardment of the grid due to heavy emission of the cathode will force the grid negative to a point where it will unload itself through secondary emission when the grid resistor is too high to carry electrons off of the grid at the same rate that they are deposited on it. Reduce the grid resistor value to 250,000 ohms from its original value of 500,000 ohms. Crosley 8H1 Noise, Intermittent Reception * Carefully check the mechanical condition of the balancing condensers mounted on top of the i-f coil cans. The plates of these condensers often get out of line vertically and short to the mounting pillars which are grounded. If the condition is permanent the set will of course be dead, but the conditions mentioned as the symptom will give the forwarning to this trouble. 60 Radio Today