Bias of a Blackstar Amp !

escargotomy wrote:OK, my amp guy, who has been doing this for over 40 years and is actually very well known in the amp community as the designer of several well-regarded tube amps, told me this. There is a tremendous amount of variation of current flow from brand to brand, model to model, and NOS and new generation tubes. Therefore while it is possible that you could be replacing a tube with one of approximately same values in which biasing is not necessary, it is much more likely that the one you are replacing does not have sufficiently equivalent charcteristics and so biasing is necessary. You could actually have a same brand, same class tube which came off the line minutes after the one you are replacing and it could potentially need biasing too. Certainly if you are replacing a new generation tube with a NOS tube, biasing is a given because manufacturing standards have changed significantly over the years. While the Blackstar schematics have not been made available, most amp technicians with even moderate exprience know what they are looking at and don't need them. I guess the trick is to find someone with a good reputation as an amp technician. Incidentally, these guys are usually specialists in a music shop and don't typically do guitar maintenance, just amp work. It is its own discipline, apart from luthiery/guitar repair. I hope that helps.

MusashiChan wrote:blackstar amps are cathode bias and NOT fixed bias. So...they all need to be rebiased