August 1939 Radio-Craft
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 Radio Service Data Sheet is from the series published by Radio-Craft magazine in the 1920s and 1930s.
I am posting them for the benefit of people who restore those vintage models to working order. It is still possible
to buy Sam's Photofacts packages that include schematics
and alignment data, but these info sheets fill the gap for ones either not available, or for someone needing to
get a feeling for what he/she is up against before making a full commitment to the task.
RCA Victor Model M-70 2-Unit Auto-Radio (Chassis No. RC-394) Radio Service Data Sheet
This is No. 259 in a series of Radio Service Data Sheets within Radio-Craft instituted with the October, 1929
issue. During this time the manner of presenting these Data Sheets has undergone considerable modification in accordance
with comments by readers. Can you suggest any changes which will make these Data Sheets of greater value to the
majority of the Servicemen who read Radio-Craft?
Test Oscillator. - For all alignment operations, connect the low side of the test oscilla-tor to the receiver
chassis, and keep the output signal as low as possible to avoid A. V .C. action.
Cathode-Ray Alignment is the preferable method. Connections for the oscilloscope are as follows: Vertical "H1"
to terminal "C" on 2nd I-F transformer; vertical "0" to chassis.
Output Meter. - Connect the output meter across the speaker voice-coil and turn the receiver volume control to
maximum (fully clockwise) and the tone control to middle of range.
Dial Calibration. - Rotate the gang condenser to its full-mesh (maximum-capacity) position and then adjust dial
scale so that the pointer is aligned to the last calibration mark at the low-frequency end of the scale.
It is very important that these instructions be followed when installing' the M-70 receiver.
The antenna circuit is designed to work with an antenna having a total capacity including the shielded lead-in
not to exceed 150 mmf. If an antenna having a larger capacity is to be used, it will be necessary to add a condenser
in series with the lead from the antenna filter L1 to the antenna coil terminal ("A"). Where a "Doublet Under the
Running Board" type of antenna is to be used having a capacity of approximately 200 mmf., the condenser added should
be approximately 500 mmf. The insulated running board type having an approx. capacity of 550 mmf. will require a
condenser of approximately 150 mmf. Cars using an insulated steel top of approximately 3,500 mmf. will require a
series condenser of 150 mmf.
Posted December 19, 2014