281 Ch= R-1A

General Motors Radio Corp.

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  • Year
  • 1931
  • Category
  • Pre-stage (adaptor for SW/FM/VHF/UHF incl. built-in), Frequency converter
  • Radiomuseum.org ID
  • 42778

Click on the schematic thumbnail to request the schematic as a free document.

 Technical Specifications

  • Number of Tubes
  • 2
  • Valves / Tubes
  • 36 37
  • Main principle
  • RF Converter/Adapter (not voltage converter); ZF/IF 535 kHz
  • Wave bands
  • Broadcast only (MW).
  • Power type and voltage
  • AC/DC-set / 110 Volt
  • Loudspeaker
  • - - No sound reproduction output.
  • Material
  • Metal case
  • from Radiomuseum.org
  • Model: 281 Ch= R-1A - General Motors Radio Corp.
  • Shape
  • Miscellaneous shapes - described under notes.
  • Notes

  • This converter had an output frequency of 535 kHz.

    This operational explanation came from Ebay Item number: 111073448105.

    "This 1931 device has probably caused more confusion as to its real purpose than any other radio item. Most importantly, the 281 is not a radio receiver - it is a converter. A converter receives an incoming radio signal at that signal's frequency and then converts that frequency to another frequency by heterodyning the signal with a local oscillator. This intermediate frequency can then be connected to the antenna input of a radio receiver and amplified and detected, resulting in better selectivity, stability and sensitivity. The GM 281 is a heterodyning-type converter which was designed to be connected to any receiver to provide several different functions. First, as a converter, when used with a TRF (Tuned Radio Frequency - a non-superheterodyne) receiver, that receiver would then become a superheterodyne - providing the advantages of better sensitivity and selectivity. If used with a superhet receiver, that radio would then become a double-conversion superhet - advantages were better image rejection. An added advantage to the 281 installation was that it allowed for remote control of any receiver it was used with, providing remote tuning and remote volume control. Finally, it was also a floor-type ash stand. The IF frequency was 535Kc - so the receiver used with the 281 had to be tuned to 535Kc in order for the combination to work together. The 281 AC plug was to provide the 6.3vac heater voltage for the two tubes in the converter but B+ (high voltage) had to be supplied by the receiver (connecting wires were from the metal "coupler unit" which was mounted in the receiver cabinet.) A 25' cable allowed the 281 to be placed anyw in the room, preferably next to the "over-stuffed" easy chair and the pipe. Today, many GM 281 converters are encountered with the cables removed and the seller trying to convince the buyer that the 281 is a radio receiver - it isn't. Neither was it ever intended to be set up in GM automobile dealerships for customer entertainment. The erroneous auto-related story variations are endless. The 281 was designed for home use and was to provide the user a way to upgrade his older TRF console radio into a remotely controlled superheterodyne radio. "

  • Price in first year of sale
  • 49.00 $
  • External source of data
  • Ernst Erb
  • Circuit diagram reference
  • Rider's Perpetual, Volume 3 = 1933 and before

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