The Graymavox superheterodyne was designed from information culled from Ric Havyatt's library and other places, I aimed to maintain authenticity as much as possible by using:

  1. Triodes throughout.
  2. Leaky grids for 1st and 2nd detectors
  3. A separate local oscillator.
  4. A low IF frequency - 55 Kcs.
  5. Inductor coupling to audio stages.
  6. The cabinet should be coffin style, bakelite front panel and breadboard and enough shielding of the early stages to eliminate "joeys" and other interference and instability problems.

    graymavox.jpg - 55356 Bytes

    The valve lineup: neutralised RF amp., 1st detector, local osc., 1st IF amp., 2nd IF amp., 2nd detector, 1st audio amp and output stage.

    To eliminate TPTG instability in the IF stages resistive coupling was used between these two valves. Ric has also constructed one of these and both are good performers. For more information refer HRSA "Radiowaves" July 1998   No. 65 and also 66

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