[Heathkit] SB-301 hum

[wb8jkr@juno.com]

  Well guys, I'm thinking maybe the audio tube may
have leakage, I'll try subbing it and see what happens.
The measured ripple at the first filter section is 1% 
and temporarily adding an additional 100 uf made
no difference whatsoever. All circuit board grounds
are fine, and just to make sure I put a small buss wire
from the ground trace to a circuitboard hold down screw.
 I also put a tube shield over the audio tube. Nothing made
any change at all. I'll try a new 6HF8 and see what happens.

Mark  WB8JKR