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 covers the
[Montgomery] Ward 10-tube all-wave, high-fidelity superheterodyne, Series ODM receiver. Most - if not all - electronics servicemen
had subscriptions to these magazines because they were a ready source of not just these service sheets, but because of the extensive
articles offering advice on servicing radios and televisions. In fact, many electronics manufacturers had a policy of supplying
service data only to bona fide shops. A large list is included at the bottom of the page of similar documents from vintage receiver
schematics, troubleshooting tips, and alignment procedures. They were originally published in magazines like Radio-Craft,
Radio and Television News, Radio News, etc. I scan and post them for the benefit of hobbyists who restore
and service vintage electronics equipment.
Ward 10-Tube All-Wave High-Fidelity Superhet, Series ODM Radio Service Data Sheet
(Features: undistorted power output, 5 W.; ranges, 535-1,730, 1,715-5,800, and 5,750-18,000 kc.; variable band width intermediate;
metal tubes; available for any power supply; dual volume control)
The socket voltages of this receiver are as shown in the table:
These readings are taken with antenna shorted to ground and volume control at maximum. The line voltage should be 115 V.
Heater voltages are read across the heater or filament prongs, all other voltages from prong to ground. The total power consumption
of this outfit is 90 W. at 115 V.
The circuit alignment is accomplished according to standard practice. Alignment frequencies are: 456, 1,730, 1,500, 600,
5,800. 5,000, 18,300, 15,000, and 6,000 kc. It is absolutely necessary to use a signal generator and an output meter for alignment
work. The selectivity control should be turned to the "sharp" position and left there for all adjustments. The band switch must
be in the "B" range or broadcast position when aligning the I.F., and the volume control at maximum point. Care must be exercised
to set the attenuator of the service oscillator at the minimum position necessary to secure a satisfactory reading on the output
indicator, in order to prevent A.V.C. action from causing false readings.
It will be noted that a dual volume control is used, and that section R3 is shorted out when the band switch is turned to
the second short-wave position. When not shorted, this control functions to lower the sensitivity of the receiver at low-volume
settings, to cut down the noise pick-up between stations.
The average sensitivity of this set on the various bands is as follows: "B" range, 7-microvolt, absolute; "C" range, 1 microvolt,
absolute; "D" range, 2 microvolts, absolute. It may be found in certain cases that when a station is tuned in with the selectivity
control in the "broad" position, the station will disappear when the control is turned to the "sharp" position. This is normal
and does not indicate any fault or misalignment of the receiver.
The locations of the various trimmers in the receiver are shown on the small diagram. The "C" numbers correspond with those
on the main diagram.
Another small diagram is given showing the necessary connection to be made for the use of a phonograph pickup. A good quality,
high-impedance pickup must be used. A low-impedance pickup will necessitate the use of a matching transformer.
On some early models of this receiver. the tone control was connected as a series resistor, rather than as a potentiometer.
The resistor, R18, was not used in early models. The 6K7 metal tubes replace the 6D6 tubes. Condenser C35 is not used in all
models.
The resistance values of all inductances are shown on the diagram in the form of small figures in parentheses. Those marked
(X) are too low for accurate measurement.
Posted June 17, 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
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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
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