What does a rectifier tube do? Is it necessary?
They convert the electricity running through the amp from AC (alternating current) to DC (Direct Current). So yeah, it's pretty important. Most amps these days have Solid State rectifiers, the only difference is that Valve rectifiers give a slight "sag" in the signal. It's very slight though, and most people don't notice it.
Sag good or bad? (very little experiance with tube amps)((sorry))(((Thanks though)))
From what I've read most people say good. Valve rectifiers are mostly in vintage amps (and vintage gear is quite sought after/liked these days) so it contributes to getting that sound.
A rectifier tube allows voltage to be changed from ac to dc like was said. If i am thinking right sag occurs because the voltage to the power tubes changes and can drop from time to time giving it that "tube mojo"
unless you're trying to get a really tight sound for metal (I'm talking absolutely punishing amounts of gain) then a rectifier tube will do your sound good.