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MECA Electronics Attenuators

International Radio Corp. Model 90 4-Tube Set and Power Supply
Radio Service Data Sheet
March 1936 Radio-Craft

March 1936 Radio-Craft

March 1936 Radio-Craft Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Craft, published 1929 - 1953. All copyrights are hereby acknowledged.

This is another Radio Service Data Sheet that appeared in the March 1936 edition of Radio-Craft magazine. I post this schematic and functional description of the International Radio Corp. Model 90 4-Tube Set and Power Supply radio manufacturers' publications for the benefit of hobbyists and archivists who might be searching for such information either in a effort to restore a radio to working condition, or to collect archival information.

International Radio Corp. Model 90 4-Tube Set and Power Supply Radio Service Data Sheet

(110 V. A.C.; and 6 V. or 32 V. D.C. service; 6-tube operation; A.V.C.; small size)

The following table gives voltages as measured between points indicated and ground:

International Radio Corp. Model 90 4-Tube Set and Power Supply Radio Service Data Sheet, March 1936 Radio-Craft - RF Cafe

*Depends on applied signal. The above table holds true only when the line voltage is 115 V.

A standard type of output meter should be used and is connected between the amplifier section plate prong of V4 and ground. The signal from the service oscillator must be kept at a low level in order to get below the A.V.C. action.

To align the I.F., first turn the tuning condenser to about 600 kc. - do not ground the oscillator section of the gang condenser. Set service oscillator to correct frequency and attach to antenna of set. Adjust primary and secondary of both I.F. transformers for maximum gain. Insulated screwdriver and socket wrench are necessary for this operation.

Next, set oscillator at 1,500 kc. Turn gang condenser of set so that the plates are slightly meshed (about 1/8-in.). Adjust trimmers on both sections for maximum signal.

If the coils have been changed it may be necessary to bend plates at 1,000 kc. and 550 kc, Do not bend oscillator plates (rear section) unless absolutely necessary.

The power supply of the set is designed for use on 110 V. A.C. but separate power units are made which supply 110 V. A.C. when connected to 6 V. or 32 V. D.C.

Keep the green wire on the antenna section of the gang condenser as far as possible from the oscillator. Keep antenna coil as far as possible from sockets. Keep A.C. power cord clear at the end of chassis. If the set becomes microphonic, push a piece of rubber between speaker and chassis base.

If the D.C. power supply does not deliver the proper voltage (between 110 and 120 V., under the load of the set) the trouble is usually a defective vibrator or the set is drawing abnormal current.

To adjust the speaker remove cover plate from unit. There are 2 screws at each end of the unit within the magnets. When adjusting either pair of screws, one is to he loosened slightly and the other tightened. You will notice that this moves the armature slightly to one side. The air gap at both sides should be the same.

 

 

Posted July 13, 2015

Radio Service Data Sheets

These schematics, tuning instructions, and other data are reproduced from my collection of vintage radio and electronics magazines. As back in the era, similar schematic and service info was available for purchase from sources such as SAMS Photofacts, but these printings were a no-cost bonus for readers. There are 220 Radio Service Data Sheets as of February 2, 2018.

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