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Viking Audio Mods from KS3K




 
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Steve - K4HX
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« on: December 15, 2012, 11:36:10 AM »

Audio Conversion for Johnson Viking I and II Transmitters

by
Ed Patrucci, KS3K


These modifications do not require any changing of sockets in the audio speech amplifier section. The 6AH6 is a plug-in replacement for the original 6AU6, first audio amplifier.

Although the driver tube now uses a 6C4, which is a seven pin tube, the socket will need to be rewired, except for the filaments. Be sure to compare the schematic above to the original schematic because some components have been changed, others removed and others remain the same.

After the mods have been made, adjust the resting current of the modulators to 60 milliamps by adjusting the variable tap of R13.

For proper audio equalization, use an unamplified crystal microphone such as an Astatic D-104.

See attached schematic.


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