[murf]

HI guy's,
Have not been on here for a while, so its about time I bugged some of you zenith fans.
Picked up a 1941 10 tube console that had been restored around the year 2000 by a pro.
He did a very nice clean looking job and did not miss anything.
He even put a cord on it so you can play your music from another source.
Question is, I noticed a low frequency humm that got louder as the volume increases.
Whether on radio or Ipod hookup.
First checked tubes and replaced a couple 6V6 tubes that showed marginal.
No difference.
Next, replaced the filter caps thinking maybe one is out of spec.
No difference.
I did notice that I could almost eliminate the humm by pushing in the lower right bass tone control.
Could there be something going on in the tone control circuit that could cause this?
Otherwise, it is in immaculate condition.
murf