DEpends on amp. If it is self bias no problem, if not you need to bias the power tubes eveytime you change.
4 responses Add your response
I think it's a good idea to periodically check tube bias to ensure that the tubes still function. Further, as Ryriken says, if a tube amp does not self-bias, occasional adjustments are required. Maybe because I'm OCD or just bored, I check tube bias every 2 or 3 weeks just because .... More frequently if I hear distortion.