Audio Conversion for Johnson Viking I and II Transmitters

[Steve - K4HX]

Audio Conversion for Johnson Viking I and II Transmitters

From the AM Press Exchange, October 1981

 
Attached is a schematic that gives you improved gain and audio quality.

Remove the two 6AU6 audio tubes and the associated circuitry.

Remove the first 7 pin socket (1st audio stage).

Punch a hole for a nine pin socket.  

The second 7 pin socket remains, as the 6C4 is a 7 pin tube.

Rewire the first three stages as shown in the schematic above.  

Replace the driver transformer with a larger one.  

You now have two audio stages, 12AX7a drives 12AX7b. The 12AX7B drives the 6C4 driver which delivers extra drive to the 807 modulators.