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:
*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 227 Radio Service Data Sheets as of
December 28, 2020.
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while typing up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
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and text used on the RF Cafe website are hereby acknowledged.
