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Galvin Motorola Model 61 Automotive Receiver
October 1932 Radio-Craft

October 1932 Radio-Craft

October 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.

Mallory-Elkon "Elkonode" B-battery eliminator - RF Cafe

Mallory-Elkon "Elkonode" B-battery eliminator.

What the heck is an Elkonode? That was my response to its mention in this Radio Service Data Sheet for the Galvin Motorola Model 61 Automotive Receiver. The Mallory-Elkon Elkonode was an electromechanical vibrator device for DC-DC conversion. An oscillating circuit opened and closed a set of contacts being fed with the automobile's DC supply, thereby creating a chopped waveform which was applied to a step-up transformer, then rectified and filtered to provide the high plate voltage for the radio's vacuum tubes. A Google search turned up a datasheet on the Mallory Elkonode. Per the info, "The series 60, 70, and 80 Mallory Elkonodes (scroll down a couple screens) are described as single-reed, full-wave inverters, with self-contained synchronous rectifiers. These units within themselves supply direct current, high voltage for radio receiver plate supply. No tube rectifiers are required with these types." This 1932 Radio−Craft magazine article recommends against attempting self-repair of Elkonodes (aka interrupters), so restoration buffs will appreciate the instructions offered in the datasheet (I had Archive.org save a copy).

Galvin Motorola Model 61 Automotive Receiver
Radio Service Data Sheet

Schematic: Galvin Motorola Model 61 Automotive Receiver, October 1932 Radio Craft - RF CafeIncorporating a type 85 duodiode-triode tube as a combination second-detector, automatic volume control and first A.F. amplifier.)

This automotive receiver incorporates the following tube combination: Tube V1, type '36 screen-grid as an R.F. amplifier; V2, type '39 variable-mu R.F. pentode as a combination oscillator and first-detector; V3, type '36 screen-grid I.F. amplifier; V4, type 85 duodiode-triode as a combination second-detector, automatic volume control and A.F. amplifier; V5, type 41 high-mu special automotive pentode second A.F.

High voltages are obtained from the storage battery of the car by means of an interrupter system and step-up transformer, in the manner described in the Sept. 1932 issue of Radio-Craft, pg. 152.

Following are the values of the components of this modern radio set: Condensers C1, C2, C3, tuning condenser gang; C4, C8, coupling condensers; C5, C6, C7, I.F. trimmers; C9, C13, C17 (buffer), .05-mf.; C10, 0.5-mf.; C-11, 0.25-mf.; C12, 500 mmf.; C14, .002-mf.; C15, .01-mf.; C16, 1. mf.; C18, C19, 8 mf.; C20, C21, 0.1-mf.

Resistor R1, volume control potentiometer, 0.5-meg.; R2, R4, R7, R8, 0.1-meg.; R3, 75,000 ohms; R5, 5,000 ohms; R6, 500 ohms; R9, 0.2-meg.; R10, 50,000 ohms; R11, 0.7-meg.

It is not recommended that any repairs be made to a defective Elkonode (interrupter.) All such units should be returned to the factory (Galvin Mfg. Corp., Chicago, Ill.), or to the manufacturers of the Elkonode (see label on unit).

An open buffer condenser, C17, will be indicated by failure of the rectifier tube V6 to stay ionized. A purple glow in the tube is an indication of correct operation of this type of rectifier; a shorted C17 condenser will be indicated by spasmodic operation of the Elkonode, as well as failure of V6 to glow. As a general rule, when spasmodic operation of the Elkonode is observed it is an indication that the Elkonode is not feeding in to the correct load; it either is underloaded or overloaded; two undesirable conditions.

After the Elkonode has been removed, it may be tested by applying 6 volts to the large terminals, with positive polarity to the brown wire; it is also necessary to connect a 5,000-ohm resistor across the red (or green) and black wires, together with an 8 mf. electrolytic condenser and a voltmeter. With this setup, the Elkonode should consume not more than 2.25 A.; the voltage drop across the 5,000-ohm load should he between 160 and 170 volts, provided the battery voltage is exactly 6.3.

The following precautions should be observed: Do not remove the receiver section of the set from the power pack, with the set turned on; the BR tube, V6, should not be removed from its socket unless the set is turned off. Since the "A" supply is polarized, it is necessary to make certain that the red wire connects to the positive terminal and the white wire to the negative terminal of the battery; do not operate the set with the "A" leads reversed, otherwise the Elkonode will be damaged beyond repair. For this reason, the polarity of the car battery should be double-checked by means of a voltmeter before the set is put into operation. (Reversed connection to the "A" battery will be indicated by low "B" voltage, spasmodic operation of the Elkonode and erratic flashing of V6.)

An ideal place for the reproducer is face-out, with the reproducer flush with the instrument board, but such a position is undesirable because of the space factor. Therefore, the first alternative is to leave it at the same level but to move it back to the bulk-head, for good operation.

If there is not room to mount the reproducer in that position, a second method is to face the reproducer toward the floorboards, with the front-edge of the reproducer against the instrument board and the side against the side of the car, a position available in most cars.

It generally necessitates two holes being drilled through the instrument board to hold the reproducer and an additional bracket run from the adjacent side of the reproducer to the side of the car. This location is rather new to some installation men, but its acoustic properties are superior because of the additional baffle effect which results from the close proximity to the instrument board.

Following is a listing of the preferred location for automotive radio receivers to be used in the 1931 car models specified:

Ford, Model A: Motor compartment on the left side;

Chevrolet: Motor compartment on the left side or below the cowl on the right inside; (For 1932 model, remove carburetor and air cleaner, temporarily.);

Buick: Below the cowl on the right inside;

Chrysler: Right side of car under cowl;

Pontiac: Left side of motor compartment or right side of car under cowl;

DeSoto: Ditto;

Plymouth: Left motor compartment or right side of car, under cowl;

Cadillac: Ditto;

Lincoln: Center of motor compartment or right side of car, under cowl;

Packard: Ditto; (Light Eight, left side of motor compartment.);

Oakland, V8: Below cowl on right side or right side of car, under cowl;

Studebaker: Left motor compartment or right side of car, under cowl;

Oldsmobile: Right motor compartment or right side of car, under cowl;

Auburn: Right motor compartment or right side of car, under cowl.

(The "bulkhead" is the partition in the car which separates the motor compartment from the driver's compartment.)

Car manufacturers have furnished the following data regarding their provisions, in 1932 models, concerning automotive radio antennas:

Chrysler: Roof antenna with lead-in and provisions for "B" battery box;

Dodge: Ditto;

DeSoto: Ditto;

Plymouth: Ditto;

Reo: Equipped with roof antenna and lead-in;

Rockne: Ditto;

Studebaker: Ditto;

Buick: All models, $6.00 additional for antenna installation;

Franklin: Roof antenna but no lead-in;

Ford: Ditto;

Cunningham: All models, additional charge for antenna installation.

Check the proposed antenna for ground by means of a 0-200 V. meter, of 1,000 ohms-per-volt type, and a 200 V. battery. Even on damp days the leakage should not exceed 2 V. Lack of peak resonance on the antenna trimmer indicates a leaky antenna, or one having too great capacity; in general, an antenna screen area of about 9 sq. ft. will be satisfactory.

The dynamic reproducer may be checked for a rubbing voice coil by applying 50 V., 60 cycles. to the two outside or "B" terminals of the output transformer; instead of a clear, steady hum, a rubbing noise will be heard, if the voice coil is not floating entirely clear.



Posted March 23, 2023
(updated from original post on 1/9/2015)

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.

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