April 1932 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 for the RCA-Victor Radiola Model
M-30 Automotive Radio Set is an example of the dozens of similar
schematic and alignment instruction sheets that have been posted
on RF Cafe over the years. Obtaining technical information on
most things, even readily available items, prior to the Internet
era was often very difficult - if not impossible. Service centers
had what was need provided by manufacturers and distributors,
but if you wanted to find a part number or service data on a
refrigerator, radio, lawn mower, garage door opener, etc., and
did not have the original paperwork, you were usually out of
luck. Nowadays a Web search will quite often get you what you
need thanks to people (like me)
who go to the trouble of making the information available. The
stuff doesn't just magically appear or get posted by benevolent
governmental entities. You're welcome.
RCA-Victor Radiola Model M-30 Automotive Radio Set Radio
Service Data Sheet
(Automatic Volume-Control - Push-Push Power Amplification
- 9 Tubes)
Automotive radio receivers have been undergoing a change,
with the primary objective of obtaining in automobiles comparatively
the same over-all efficiency which exists in the less mobile
"home" installation. A close approach to this degree of perfection
is obtained from the Radiola Model M-30 receiver, manufactured
by RCA-Victor Co., Camden, N. J.
The values of the components of this receiver model are as
Condensers Ct , C2, C3, tuning condensers, 18-325 mmf.; C1A,
C2A, C3A, trimmers, 4-50 mmf.; C4, padding condenser, 720 mmf.;
C4A, padding trimmer, 10-75 mm£.; C5, trimmers, 15-75 mmf.;
C6, trimmers, 140-220 mmf.; C7, 745 mmf.; C8, C10, 0.25-mf.;
C9, C11, C12, 0.1-mf.; C13, C14, 0.0024-mf.; C15, C16, 0.5-mf.;
C17, 4 mf.; C18, C19, 0.018-mf.
Resistor R1, 10,000 ohms; R2, 6,000 ohms; R3, 40,000 ohms;
R4, R5, 30,000 ohms; R6, 170 ohms; R7, 0.5-meg.; R8, 28,000
ohms; R9, 0.1-meg.; R10, 1.0 meg.; R11, 3,500 ohms; R12, 4 ohms;
R13, R14, 270 ohms; R15, 1,200 ohms; R16, 70,000 ohms; R17,
The Model M-30 receiver has been designed with particular
regard to ease of installation and service. Properly installed,
freedom from interference should be experienced with the receiver
operating at full sensitivity. Approximate operating voltage
and current values (obtained on a Weston Model 547 test set),
taken with the volume control set at the "minimum" and "maximum"
(maximum values shown in parentheses) positions are as follows:
Filament potential, V1 to V6, V9, 6 volts; V7, V8, 4.5 volts.
Cathode-to-heater potential, V1, V4, 18 volts; V2, 1.0 volt;
V3, 6 volts; V5, 12 volts; V6, 15 volts; V9, 10 (5) volts. Control-grid-to-cathode
(or filament) potential, V1, 0.5-volt; V2, 3 volts; V3, zero;
V4, 1.0 (0.5) volt; V5, 10 volts; V6, 2 volts; V7, V8, 20 volts;
V9, 1.0 (9) volts. Screen-grid-to-cathode potential, V1, V4,
100 (70) volts; V2, 42 volts. Plate-to-cathode (or filament)
potential, V1, V4, 136 (135) volts; V2, 150 volts; V3, 45 volts;
V5, 110 volts; V6, 165 volts; V7, V8, 155 volts; V9, 15 volts.
Plate current, V1 ,V4, zero (4 ma.); V2, 0.25-ma.; V3, V6, 3.5
ma., V5, 0.5·ma.; V7, V8, 1.5 ma.; V9, zero. Screen-grid current,
V1, V4, zero (1.0 ma.); V2, 0.1-ma.
Automatic volume-control tube V9 is connected to the cathode
circuit of second-detector V5. The change in the bias voltage
of V5, due to fluctuation of the signal, is applied to the control-grid
of V9, resulting in a drop across plate resistor R7 which constitutes
the control-grid bias for the R. F. and I.F. tubes. As the value
of the plate current in a tube is a direct result of the voltage
applied to the grid, a greater plate current in V9 gives a greater
voltage drop across the resistor in its plate circuit and therefore
a higher bias on the I.F. and R.F. stages, resulting in less
sensitivity, and vice versa; previous A. V.C. systems have operated
on different principles. Manual volume-control resistor R17
varies the bias on the control-grid of V9.
The total "A" current is 2.85 amps.; "B," 12 ma. min., and
25 average max. The power output rating of' this receiver is
2 watts. This high rating is a result of "push-push" (or class
B") power output, which has been described in detail in past
issues of Radio-Craft; notably, the January and February, 1932
To adjust these circuits, dismount the chassis but do not
remove its connections or the flexible cable. Balance the R.F.
circuits at 1400 and 600 kc., using a No. 5 Spintite, and an
insulated screw driver. When the dial indicates 150, the tuning
condensers should be fully meshed. Padding condenser C4 comes
into consideration when the 600-kc. adjustments are being made;
its trimmer C4A is then adjusted, while the main condenser gang
is rocked back and forth for maximum deflection on the output
test meter. During these adjustments, V9 must be removed from
For the I.F. adjustments, at 175 kc., it is also necessary to
remove the chassis from its mounting brackets.
Insufficient volume-control by means of R17 may be due to
the use of a tube of wrong constants for V9.
In the receiver, the tubes are arranged in two rows. In one
(left to right) they are:
V3, V2, V1, V4, V5, V8; in the other: V9, V6, V7.
Posted August 7, 2015