There are several things that could be fishflopping since you got it.
First off - the Rectifier tubes are the big Coke bottle ones to the far right near your Power Transformer - they supply voltage ONLY OR you can use silicone diodes mode. Pull out just one if you're using rec tubes mode.
BOLD power on variac in back.
Second, pull the outside two (don't know if it matters) power tubes or replace the broken tube if it's on the inside with a good one.
Third, make sure the orange channel mode (in back) is set to clean rythm.
Put your gain on orange to @ 10:30-11:00 o'clock, Master @ 12 NOON, EQ to taste. Should be fairly clean, tweek it as needed.
There's a lot more to your DR also using channel cloning, efx loop..etc..
Do you have a parallel (mix/send controls) or series (one knob) loop?
There are a few tricks you can try tweeking these with loop engaged on orange and red.
ie...using Loop Active Master in front as main volume !
I would try to get a new matched set of power tubes asap so you can enjoy your 2 ch Dual Rec thoroughly !