What does it mean to rebias an amp?

Question

I brought in my Sovtek MIG 100 tube amp to be maintenanced (change the tubes, clean it out, the usual stuff). He said that he would also rebias it. I've been playing music forever, but I've never been much of a gearhead - so I have no idea what this really means. Can someone explain it? Thanks!!!

Answer 1

The bias determines the centerpoint of the range.
If the bias gets out of whack, the sound will be distorted or the controls will have to be in a more extreme position to create the desired effect.
What he is doing is recalibratring it to work properly