Hi all. My nephew was given a well-kept 135w Twin. While going through it, we noticed a 120 Hz hum, even with the PI pulled. Since the ser. # dates it to 1979, I figured filter caps should be replaced anyway, so I just put in the new ones I got from Doug Hoffman. Plate voltage is about 505. I measure 38 to 42 ma average on the original 6L6s (using a Weber bias adaptor). As you know, the bias voltage on this thing is not easily adjustable, so I haven't tried my newer 6L6s that might not handle that. I've poked around with a Sharpie, listening as I lift wires, tap on things, etc. No change. Do we have a bad tranny? Thanks in advance.