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)))
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.
My Strat/Modded '69 RI Mustang
Ovation 1117-4 c. '75
Fender Blues Jr. [JJ Power Tubes, White Grille, Warehouse Speakers Greenback Clone]

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