to add to what Traveller said...when you get new power tubes, if you dont buy from Mesa, make sure you say theyre for a Dual Rec. that way they will be within spec for the amps bias.
i have a single rectifier, and im running EL34s...love it. one suggestion i have is DONT use a boost! i know, some will say its heresy, especially for a metal tone. but IMO the amp is tight enough and gainy enough on its own, but you have to have a good, precise right hand to make it work. when i first got the amp i couldnt play crap on it. hell, its only the 3rd amp ive ever really owned, and for most of the time i had an amp it was a 5150. the saturation on a 5150 makes everything so easy to play...on a Rec that isnt the case. you really have to whip you playing into shape, the amp is much less compressed and it takes work. using a boost will saturate the tone, and it sounds awesome, no denying that! but i decided to go without and it works for me. im starting to incorporate it back into my rig (self modded SD-1), but only as a lead boost to fatten single notes up and make them cut more.
heres my settings on channel 2 (i only have two...lol) in o'clock
modern
gain 1-1:30
treble 1
mids 11:30
bass 11
presence 11
master and output will be personal preference, but the louder you go, the better it sounds. i still do tweak occasionally, but dont we all?
and the clean tone on my Single is actually really awesome. i loved my 5150, and i love my Ultra Plus, but getting a good clean out of those amps...no chance compared to the Recto.
have fun, and crank that sucker! they only sound passable at low volumes, but nothing comes close when you get the speakers moving and power tubes cooking!