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Delco 32-Volt Radio Receiver Chasses
Radio Service Data Sheet
January 1932 Radio-Craft

January 1932 Radio-Craft

January 1932 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.

Delco 32-Volt Vacuum Tube Radio (philcoradio.com) - RF Cafe

32 -volt Delco radio (philcoradio.com)

Here is the Delco 32-Volt Radio Receiver Chassis schematic and parts list as featured in a 1933 edition of Radio-Craft magazine. The only example I could find is the one shown to the left, on the PhilcoRadio.com website. The schematic shows six vacuum tubes, and there appears to be six in the photo. Battery-powered radios were common in the era before AC electric service was available in rural locations, and a lot of homes even in the cities did not have service either. A look through a Sears, Roebuck & Co. catalog in the early part of the last century showed many electricity generator systems for use on farms, including windmills and water-powered generators for placing in streams and rivers. Life was tough. As mentioned many times in the past, I post these online for the benefit of hobbyists looking for information to assist in repairing or restoring vintage communication equipment. Even with the availability of SAMS Photofacts, there are some models that cannot be found anywhere other than in these vintage magazines.

Delco 32-Volt Radio Receiver Chassis Models RA-3, RB-3 and RC-3 Radio Service Data Sheet

Delco 32-Volt Radio Receiver Chasses Radio Service Data Sheet, January 1932 Radio-Craft - RF CafeThese three cabinet model receivers, designed for farm districts powered by 32-volt supply systems, are manufactured by the Delco Appliance Corp., Rochester, N. Y., and employ the same chassis, the schematic circuit of which is shown below. The 32-volt or "farm lighting" power line supplies only the filament potential, as shown; the plate potentials must be obtained from a block of "E" batteries or from a Delco Power Unit.

Before connecting the power unit, turn the power switch to the "off" position. The power switch is incorporated in the volume control and is turned off by turning the left-hand knob to the left or in a counter -clockwise direction as far as it will go. Connect the power unit to the chassis by means of the 3-lead cable according to the following color code: red, "Plus 135 V." connection on the Delco power unit; maroon, "Plus 67.5 V." tap; black, the negative lead. The "A" lead on the receiver chassis is plugged into. the 32-volt power line; reversing the position of the plug in some instances may, improve reception a little.

As indicated in the diagram, this 32-volt chassis employs four type '36 or 2-volt screen-grid tubes and two type '38 or 2-volt pentacles; these '38's are connected in parallel, plate-to-plate, grid-to-grid, etc.

In shunt with each of the tuning condensers in the gang is a trimmer. The nuts of these small condensers are accessible for adjustment through four holes in the top of the condenser shield. A bakelite aligning tool must be used, in order to prevent injury to the inductances within their respective shield cans. The frequency at which it is recommended that this chassis be aligned is 1400 kc. Adjust the volume by means of the volume control until the station signals can be heard faintly but clearly.

If the pointers on the dial window do not correctly indicate the frequency of the stations, the dial may be rotated to the correct position. To do this, it will be necessary to remove the chassis from the cabinet.

After the chassis is removed from the cabinet, measure the vertical distance from the bottom of the cabinet to the indicating points on the dial window (inside the cabinet). Tune in a station of known frequency and loosen the two square-head set screws which hold the dial and hub assembly to the tuning condenser shaft. Hold the condenser rotor stationary and turn the selector dial on the condenser shaft until the frequency shown on the selector dial at that particular station is the same vertical distance from the bottom of the chassis as that previously measured from the bottom of the cabinet to the indicating points on the dial window inside the cabinet.

Lock the selector dial assembly on the shaft by tightening the two square-head screws and reassemble the chassis in the cabinet.

The dial light is rated at 6 volts and has a standard flash-light base. It can be removed or replaced easily by lifting the dial light, socket and bracket assembly up and off the dial light mounting bracket.

A good ground connection is necessary for best operation. Use an approved ground clamp to make a connection to a cold water pipe or a six-foot iron rod driven into moist ground. The antenna may be 100 to 150 feet long.

The knob at the left of the station selector dial window operates the combination volume control and off-on switch. The toggle switch located on the left-hand side of the cabinet is the local-distance switch shown in the schematic circuit as shown. The large knob at the right is the tuning control and the central one is the tone selector.

Note that when the local-distance switch is in the up or "distance" position, the receiver is adjusted for maximum sensitivity. However, when the switch is in the down or "local" position battery power is conserved, as described below. In this position the volume on distant stations is very greatly reduced, and satisfactory reception is possible only from local stations. Incidentally, this provides better control of volume on local stations and, as will be observed by reference to the schematic circuit, there is conservation of the battery current.

Tubes for these 32-volt receivers are available from the Delco company, and are somewhat special in their characteristics, although, in lieu of these, the more standard types may be used; they carry the designations D-236 for the Screen-grid type; and D-238 for the pentode.



Posted October 24, 2023
(updated from original post on 3/11/2016)

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.


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