I am using a 1981 JCM 800 2003 marshall and a digitech rp-7 effects processor. I play guitar in a heavy metal band. I am running my effects processor directly to my effects loop return on my amp(I added a tube effects loop). I am currently running a quad of E.H. EL34s and my pre-amp tubes are RFT. It's about time to change my power tubes to be on the safe side. Since I am getting my heavy metal gain sound from my processor, would it be a good idea to get a very clean sounding set? I was thinking about getting some NOS tubes, but maybe that wouldn't be a good idea in this situation as it may muddy things up. I want a clean and tight heavy metal sound. I was thinking about a quad of RFTs or Siemens, but ???. What do you guys think?
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if your satisfied with your tone and want it to change as little as possible you should get another quad of EH EL34's

Ouch on drilling holes in your '81 2203 though....ouch
^+1 i LOVE JCM 800 Gain. You're not using one of the greatest things ever invented.
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Yea, use the JCM800's gain by cranking the hell out of it (or using an attenuator).

But if you're really happy with the tone just get some more EL34s.
"Breathe, breathe in the air
Don't be afraid to care"

Fender Strat/Tokai LS80>few pedals>Orange Rocker 30

yeah crank the JCM800 or if it's still not yet enough
then get an OD ped to spice things up a bit...