Mullard EL84s are among the best I've heard. Granted that was in a hifi power amp, not a guitar amp...YMMV. Cheers,
el-84s are not a swap in those amps so the mullards are not in the works for you for the power tubes and they really are not worth the money in an everynight gig amp. I tried NOS phillips in My Dr z and they sounded great but a bit pricey compared to the stock sovtechs, and the folks at the bar didn't seem to notice the difference..including the bandmembers. The guts of the Dr Z are all point to point hand wired with propriatary caps and trannies so it is pretty close to high fi but the listening setting just isn't critical enough to warrent the cost.
Groove Tubes is the place to look for replacements. They QA the tubes and match the sets. They seperate their tubes according to break-up character so you can fine tune your amp to some degree. They also have mullard design 12ax7s you can try if you want to tweak the tone some. Replace the power tubes first since they are the ones likely to actually need it. If you want to clean up the tone and get a little more headroom before the amp breaks up try a 12AU7 in the first gain stage (the AU 7 has less gain than the AX7)
I have not worked with the Fender, but the Peavey does not react all that much to tube choice. I think you could swap the EL84s with some JJs or EIs and have a slightly cleaner, tighter sound, but it will not be fundamentally different. Bob at Eurotubes can pick out a hot set of EL84s that will make the amp go into power tube overdrive a little bit faster, but you are talking about having the amp turned up very loud to hear it.
As for preamp tubes, you should consider an NOS tube for V1 (12AX7 or 5751, but I would shy away from a 12AU7 or 12AT7), like an RCA or a Philips, or possibly an Electro Harmonix, a European tube for V2 (JJ, EI, or Mullard or Brimar if you are feeling crazy), and a high gain, low noise Chinese or Electro Harmonix tube for V3.
www.kcanostubes.com is a good resource for these kinds of preamp tubes.
If you are fundamentally unhappy with the Classic 50 tone, sell it or trade it toward something else. You are not going to get it to sound different without drastic modification, and there are people out there who like them stock. Steve Ahola has such mods on the web, but you are looking at a virtual rebuild of the circuit.
looks like i read too fast, i ment to say the el-84s are not a swap for the 6l6's...i always thought that's what the peavy had as well...I should pay more attention i guess.
Mrpapa why the adversion to 12au7
if you want to get into power tube saturation without having ear splitting volume try an attnuator. The Dr Z airbrake designed by ken Fisher is the most transparent i've used, a tad pricey but worth every dime
Generaly speaking the small preamp tubes make the bigger impact on sound, try rca,ge or sylvania for 12ax7 they sound good, are durable and cheaper than nos european. 12at7 and 5751 are the usual lower mu sub for 12ax7 not the 12au or 12ay. JAN phillips is the bargain 12ax7 and cost about the same as sovtec which I prefer to chinese. Having said that, smooth plate telefunken and mullard made my ampeg sound its best. I play harps and the sound was rounder harmonius and I finally got rid of this terrible glare that kept popping out on the lower highs, hi c i think it was. If the amp squeals or distorts check the power tubes first. Mullards and ge seem to be favored by a lot of guitar rollers and I'm looking for some to try. Go with what you like to hear, way to often people in the bars are treating live music like background music-that is a shame so fellow music lovers appluad, cheer whistle and show the bands some more love.