Radio Broadcast (May 1929-Apr 1930)

THE SERVICEMAN'S CORNER Points on the Victor Hum Potentiometer: "A Victor 32 operated satisfactory if the hum control in the R. P. A. unit was not adjusted to balance out the hum perfectly. Operation ceased when the hum was perfectly balanced out. The contact arm was deformed in such a manner as to permit it to make contact with the resistor strip at all points except at the exact center where the hum should have been negligible. As this resistor is the means of providing the grid return to the first a.f. tube, an open effectively disables the unit." R. L. Minor, 0. K. Houck Piano Co., Little Rock, Ark. No Plate Voltage "I had a Victor 'Micro-etc' with no plate voltage on the 226's. All the dope in the service notes and the diagram didn't help a lot. "Another set was torn down to obtain actual values of resistors and other parts. This didn't do much good either and we went into a huddle with the circuit. Hey! Where's that other choke the service notes don't mention? It's the loud speaker! Absolutely right the first time. Another loud speaker did the trick. "Another Victor oddity that will give a bad five minutes is two wire-wound volume controls ganged to one shaft. Maybe they are tracking together and then again — well look 'em over if volume seems spotty." P. E. Robinson, Augusta, Me. Mechanical Hints Arthur E. Starkweather, of Starkweather Radio, dealer in Rrunswick, Fada and Philco, of Chatham, Mass., still finds time to service Victors. He remarks: "Just a word to servicemen who might be called to service Victor 'Combs.' " First: I want to say that it is not necessary to remove the tuning knobs or a.c. switch from panel to remove the set chassis as the panel pulls back with the chassis when the two wood strips are removed from in back. "Second: Sometimes the tuning knob will only cover either the higher or the lower range of the dial and then will stick about one third the way across. This may be corrected by removing the tuning knob, taking a pair of heavy pliers and giving the tuning shaft a slight pull. This will allow the groove on the tuning shaft to snap into place on the tuning raceway." Short Cuts to Neutralization Balancing The Majestic Chassis: "I often run across a Majestic chassis that is very obstinate to balance. This is the way I go about it. "First remove shield housing over the condenser gang. Remove all trimmer adjusting screws, and, with a pair of longnosed pliers buckle the trimmer plate in the middle so that when the trimmer screws are replaced the center of the plate will come about £ inch away from its other plate. Proceed to balance set in usual manner with oscillator and resonance indicator, R. L. Minor, of the radio service department of O. K. Houck Piano Co., Little Rock, Ark., sends this photo of his laboratory with his contribution. and by taking out the r.f . tubes stage by stage it is very easy to peak each stage. "I have found this method to be very effective and it results in a highly efficient receiver." H. A. Gratdc, Electric Service Laboratory, South Portland, Me. Rapid Neutralization Yern Peters, radio technician of Havre, Montana, contributes the following generalities on the technique of rapid neutralization: "Most servicemen possess a diagnoser similar to the Weston Model 537. A set analyzer of this type may be used for neutralization, and for the lining up of condensers in a single-dial set. This is accomplished by using the tester as a In the Department this month we publish a short article describing how an alarm clock can be used to turn a receiver on and off automatically. This clock device is an elementary remote-control proposition. The problems of remote control should be cropping up in the serviceman s routine more and more consistently this radio season. In their more simple ramifications, remote-control jobs include turning a receiver on and off from different rooms, and adjusting volume, generally with two or more loud speakers operated simultaneously or singly from one receiver. The more complicated problems involve remote tuning. We solicit contributions from servicemen whose efforts have been applied in this direction. — The Editor. vacuum-tube voltmeter in the first a.f. or the output stage. "The lead to the grid connection on the analyzer is broken, two leads are brought out, and clips are put on the end of them. Ry clipping the two leads together the tester may be used in the ordinary manner. On the Weston 537 the green wire is the grid lead. "To use the tester as a vacuum-tube voltmeter, the leads brought out are connected to a C battery to place an additional bias on the tube so that it will act as a detector. On the 171a and the 245 tube I find 19| volts the proper additional C voltage required when they are used in push pull, and 22| volts when they are used singly. When the measurement is taken in the first a.f. stage 4£ volts negative additional is satisfactory. Care should be taken not to overload the tube from which the reading is being taken. The plug from the set analyzer is inserted in the first or second a.f. socket and the switch on the tester is set to measure plate current. The tube is put into the socket on the tester. "A modulated oscillator is necessary to furnish a signal. To line up sets with compensating condensers it is only necessary to adjust for the highest reading on the plate milliammeter. For neutralizing the conventional dummy tube and lowest reading method is employed. For accurate results use the lowest scale possible on the plate meter." Sparton Sets "The Sparton models 62, 63 and AC7 which were built about two years ago, have a radio-frequency amplifier system which is so much different from the general run of T. R. F. sets, that a serviceman must understand the principles of its operation before he can successfully resonate the tuned circuits or neutralize the set. "I have seen a serviceman work steadily for three hours with an oscillator trying (Continued on page 228) 226 • • FEBRUARY 1 930 •