I have a Peavey 6505+ and I blew one powertube (if looking at the front of the amp, the one on the very right). I can see that it's burnt out but the other 3 work fine. I've removed the outer two tubes to test the middle two and it works fine at 60 watts but I would like to have the full 120. Do you guys think I should just retube the whole thing or is it possible to buy a single powertube replacement without losing sound quality/tone/whatever?
tubes usually go out in succession. So it is best to replace them all.
Buy a matched quartet of power tubes. Replacing just one means that the tubes wont be matched and can cause some biasing problems.
Ah alright, awesome. I guess I will do that, thanks guys.