From the AM Press Exchange, October 1981
Audio Conversion for Johnson Viking I and II Transmitters
| Shown above 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
(For improved low frequency response increase the interstage coupling
caps to .05 uF, the cathode bypass caps to 20 or 50 uF, and the two 8 uF
decoupling caps to 20 or 50 uF. - WB3HUZ).
Back to the Modifications Page
2 August 1997