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Title: Audio Conversion for Johnson Viking I and II Transmitters Post by: Steve - K4HX on December 15, 2012, 11:32:53 AM Audio Conversion for Johnson Viking I and II Transmitters AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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. |