Radio Broadcast (May 1929-Apr 1930)

THE SERVICEMAN'S CORNER Hints on Majestic Sets The Majestic receiver is one of the season's most popular sets, and the following points on their servicing will be of assistance to many of our professional readers. Short by-pass condensers: Art Hughes, of Newark, N. J., writes: "I have been servicing Majestic Sets since they first made their appearance. "The troubles with Majesties are very few and simple, but for a man who does not understand the set they may appear many and serious. "When he goes to answer a service call and finds, through his Weston or Jewell, he gets only 50 volts on his r.f. and first a.f. and about 10 volts on his detector plate, first thing he blames is the power pack, takes it out, and puts same on bench for test. He is all wrong, the pack is ok., the trouble is in the chassis. "The trouble invariably is a shorted twin by-pass condenser in the r.f. B-plus lead located near the volume control. Do not take chassis out, just take a 100volt a.c. pair, put one wire on the chassis and touch the other on the outside terminals of the loud speaker connections. Before doing this remove the ground wire from the set, also the loud speaker from the terminal strip. " The resul t of applying the a.c. is simply this: the short is cleared, due to the heavy current burning the condenser wide enough so that the comparatively low current and voltage used by the set will not jump the punctured section. "To test a power pack on the bench you have to connect either the loud speaker field or a suitable choke across the 96-volt and 220-volt terminals on the connection block in power pack." Poor connection through eyelets: "This trouble was encountered in a Majestic set. The set would play satisfactorily and then suddenly cut out. As usual the set would play all right when the serviceman arrived. Continuity test showed all connections apparently ok. It was found that upon pressing the speaker and speaker-field-coil connection strip that the machine would cut out. This strip was removed and to all appearances seemed to be in good condition. However, upon reconnecting, it acted the same as before. The lugs for the connections on this strip are held by eyelets punched through the bakelite. These eyelets are not soldered to the lugs so they form a possible chance for a poor connection. After the lugs were soldered to the eyelets, the receiver performed satisfactorily. This trouble was not due to failure to tighten the binding posts as might be suspected." H. Weimar, Appleton, Wis. Adjusting gang condensers: Robert Freeman, dealer in Majestic and Everready receivers, of Adel, Iowa, helps the cause along as follows: "In servicing Majestic radio receivers The well-arranged and equipped service department of the Electric Service Company, Inc., of Allston, Mass. we required a method to adjust the gang condensers to resonance. A modulated oscillator and a 0-125 milliammeter across the input to the loud speaker did the trick. Each trimmer screw was adjusted to give a maximum reading on the meter. "A fraction of a turn made a decided difference in the reading of the meter." Hum — Its Cause and Cure In a generous response to our request for data on hum, radio servicemen have contributed the following suggestions on this all important subject: Hum in dynamic speakers: "The use of dry rectifiers in popular-priced dynamic We like to think that Radio Broadcast is to the serviceman what the medical journals are to the physician. We endeavor to cover general and specific considerations involved in the servicing of all radio receivers. However, there are additional publications, in the nature of books, radio courses, and special pamphlets issued by manufacturers and other publishing sources that should not be neglected by the efficient serviceman. We review these from time to time in this department, staling specifically where they may be obtained, and the price, if any. loud speakers has been discovered the source of hum in many instances. "The hum which is common in a.c. dynamic loud speakers, can be eliminated almost entirely by connecting dry C batteries or flashlight batteries across the rectifier output. The positive terminal of the battery should connect to the positive side of the rectifier. As the voltage supplied to the field coil varies in different types of loud speakers, it should be measured before connecting the batteries. If no voltmeter is available, try various battery voltages, with the current turned on, until no spark is seen when the battery connection is made or broken. It is best to have the battery voltage slightly lower than the rectified output, so that no current will be drawn from the battery. A switch must be used to disconnect the battery when the loud speaker is not in use in order to prevent the battery from discharging into the rectifier. This arrangement makes a very effective filter, and is much cheaper than a lowvoltage condenser." A. H. Goud, South Portland, Me. Hum from rectifier discs: "When determining the cause of hum or extraneous noise in an a.c. outfit, if there is a dry disc metallic-type rectifier in the installation it should not be overlooked as a possible offender. The Elkon type as used on some dynamic loud speakers and A-power units seems to radiate, producing a peculiar grind which may be likened to the 'static' created by a large Tungar-type charging unit. "In a Fada 70 receiver I traced this noise to the Elkon rectifier used on the 174 • • JULY -1 9 2 9 •