Just a shot in the dark but I remember reading somewhere that the audio driver transformer is a common failure mode in these rigs... Check for an open secondary perhaps?
Last night my Valiant had no modulation after warm up. Worked ok before shutting
down the night before. Alll meter readings normal except only a very small kick upward
when tapping the D-104. Hmmm... Mod idle bias is normal... Carrier and loading normal...
Pull it out of the case... whew!... 12AX7 weak. Replaced it with a good one... Readings the
same and still no audio. All other tubes check good... Ran the Mod bias up and down and
got normal meter swing on the Mod currant... Have to go to work, now. Will keep you
posted. Maybe my D-104 crapped out. Cant find my spare. I'll have to get out the Audio
generator, Monday.
