I bought a used Dsl50 several months ago and finally got around to testing the bias with the probes in back. One side is reading 52 mv, and the other side is reading virtually nothing-like .3 mv. I switched them and now the other side is reading nothing. I messed a little with the bias screws so now it's not 52 anymore, but he other side didn't rise much if any. Is it a bad power tube? Should I take it in or just try two new tubes? I should mention that it seems to work fine, which is why I haven't tested it until now. It is a little noisy at idle, which actually diminishes when I turn one of the screws down, but so was my Jcm800 I used to have so it's not out of the ordinary, but it does change when I turn one of the screws (I think the one that controls the bad tube, it got quieter). Can an amp function nearly normal with a bad tube? They both glow a light orange and look the same.