Originally Posted by Wilder Amplification

Bullshit. It just means it has a non-adjustable bias, which means that it cannot be adjusted without swapping resistor values in the bias supply circuit. There's even a way to mod them so that they are adjustable. No amp can compensate its own bias based on what valve type/batch happens to be in it.

Not to be rude (I'm actually trying to help you here) but this is again one of those areas where you need to just not post up about things you have no clue about. You even indicated above that you had no idea what a fuse was...let alone a valve. This speaks volumes about the scope of your knowledge as it pertains to amplifiers. Just ask questions...we'll give you the answers and I promise they'll all be correct.