Crosley Model 120 Senior Superheterodyne (Pliodynatron) Chassis
Radio Service Data Sheet
June 1931 Radio-Craft

June 1931 Radio-Craft

[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.

In the diagram below is shown the foundation chassis incorporated in a number of superheterodyne receivers manufactured by the Crosley Radio Corp., Cincinnati, Ohio. It was common for original equipment manufacturers (OEMs) and third-party companies to offer decorative cabinets (aka consoles) into which the electronics (chassis, speaker, front panel controls, etc.) are installed. In the case of this Model 120, is never had a cabinet and was meant to be integrated into custom cabinets. No photo of the chassis could be found. Note the relative simplicity of the circuit since there were no accommodations for fancy push-button tuning and tonal adjustments. Standard consoles are the models Super-Administrator and Super-Rondeau; while the Super-Sondo console is a radio and phonograph combination. The "pliodynatron" was a special vacuum combining the pliotron and the dynatron, as detailed in "The Saga of the Vacuum Tube - Part 14," published in the November 1944 issue of Radio News magazine. Vacuum tube V3 performs the pliodynatron function here.

Crosley Model 120 Senior Superheterodyne (Pliodynatron) Chassis

If, when the receiver is carefully turned to the middle of the band, the dial reading does not correspond to the frequency of the signal, but is not more than two channels off, set the dial at the correct frequency, and adjust the trimming condenser C3A (the control farthest toward the rear of the chassis) until the signal is loudest. Check the tuning by readjusting the station selector. It may be impossible to regulate the oscillator trimming condenser C3 so that the oscillator condenser is properly aligned with the exact dial setting; in which case align the trimming condenser with a dial setting as close to the actual frequency as. practicable.

Oscillator V-3 is a screen-grid tube connected as an oscillator of the dynatron type (more correctly, a "pliodynatron'"; the generic term applied by Dr. Hull to a 4-element or screen-grid oscillator as differentiated from the dynatron or 3-element oscillator). Its plate potential is lower (20 volts) than its screen-grid, which is at a positive potential of 90 volts. It may be necessary to try two or three tubes in this position to obtain a satisfactory one. The volume-control resistor R1 performs the dual functions of increasing the control-grid bias of amplifiers V1 and V4, and grounding the antenna - that is, when reducing volume - and vice versa. The tone-control circuit is ingenious and should be carefully noted as to electrical values and arrangement.

If, when receiving some signals, the volume control is turned up so far that the first detector is overloaded, a whistling note will be heard. This is a perfectly normal characteristic of superheterodynes, and does not mean that anything is wrong with the receiver: when the volume is adjusted for normal reception, the whistle does not occur.

Posted November 10, 2023
(updated from original post on 8/31/2016)

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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Crosley Model 120 Senior Superheterodyne (Pliodynatron) ChassisRadio Service Data SheetJune 1931 Radio-Craft

Crosley Model 120 Senior Superheterodyne (Pliodynatron) Chassis
Radio Service Data Sheet
June 1931 Radio-Craft