#1
alright so was just wondering what that term means, because i was reading up some info on my amp and the article said, it has a set bias for all 6V6 brands. does that mean i could replace the sovteks(6V6) and use Tung Sol instead?
#2
does "set" mean "fixed"?

There a 2 ways an amp works with a fixed bias, there can be fixed adjustable bias, and fixed non-adjustable bias..

Fixed adjustable means there is a bias pot that you can adjust to provide the correct plate current for different tubes you use. Fenders and Marshalls have used this method for a long time.

Fixed non adjustable, means you can't change the bias without modding it or adding/removing resistors. Amps like Mesa use this. It's great in that you don't have to mess with bias adjustments, but it also limits you to using tubes tested to work with the fixed bias of the amp. That's why Mesa sells their own rebranded/tested tubes, but you can also order from a dealer that tests tubes for Mesa's fixed bias.

There can also be cathode bias, which is more self adjusting. Does the article say specifically what method your amp uses?
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#3
well the guy who i bought i from said he set the bias so i am pretty sure it is adjustable