To tell you the truth, it's usually the other way around. The DR's at one time were the end-all be-all of thick distortion. The Mark IV was built with less gain as people were starting to demand more clarity out of Mesas after the whole down-tuned Nu-Metal faze when DR's and TR's were flying off the shelves. DR's nowadays are used mainly by Rhythm guitarists for their low end chunk.
In all honesty, a DR is much easier to tailor with NOS tubes because the preamp section is wired in a straight chain.
V1- 1st gain stage/ (second half not used)
V2- 2nd & 3rd gain stage
V3- 4th & 5th gain stage
V4- Effects loop send
V5- Effects loop return
V6- Phase inverter
Each 12ax7 slot serves 2 functions of the amlpifier. They're split in halves. When you re-tube with NOS tubes there's an order that should be followed with the gain stages. There are NOS tubes that are known for their Bass tones, mid tones and highs. Also clarity or grittiness. If you only play the distortion channel for example, you can get tubes that really gain out the dist. Channel very well, however, that characteristic will also follow suit in the clean channel. So if you use both, or just the Clean channel, you'd be better opting for clarity. Mesas always have a good amount of gain in them.
So in a DR you would want to look at it like this:
V1- Highs
V2- Mids
V3- Bass
V4- 12at7 (for quietness and more clarity)
V5- 12at7
V6- This will shape the overall sound of the previous slots, so it's all about a personal preference.
If you were to put a Bassy 12ax7 like a long-plate tube in front of a Middy or trebly tube, you'll get mud. So this kind of order is key to the process.
Here's why I went through all of that. I know you're not asking about how to re-tube a DR. But it's the basic concept I wanted to explain first. The reason being, that a Mark IV has a more complicated preamp structure.
A Mark IV is wired like this:
V1a- Input stage
V1b- Tone recovery stage (post tone controls)
V2a- 3rd gain stage (rhythm modes) and 5th gain stage
V2b- Effects return
V3a- 1st lead high gain stage
V3b- Reverb return
V4a- 2nd lead high gain stage
V4b- Reverb send
V5- phase inverter
Holy crap!! See how intertwined and all over the place the halves are split? Not to worry though, I've re-tubed these before. It took a whole lot of experimentation, but yes, you can find some middle ground here.
What I really don't like about a Mark IV is the way they split gain stages with the effects loop and reverb. Whatever you put in the gain stages is going to follow suit in the reverb and effects loop. If you wanted a trebly gain in the lead high gain stage (whaich a lot of people like to do to tame the bassiness of a Mesa as a whole) , guess what? Your reverb just became very trebly as well. A LOT of Mesa users like to use 12at7's for their reverb slots. Do that and guess what again? You just lowered the Gain of your 1st lead high gain stage. So a lot of middle ground is in order when re-tubing a Mark IV if it's to be done the right way.
Due to adding reverb to the amp and minus one tube specifically for a reverb function, the amp becomes a lot more complicated. As a result most people will buy all of the same NOS preamp tubes and call it a day. Which I don't blame them for doing. You can really get a headache trying to figure it out.
I have some things I have to do right now, so I'll have to come back to this Jeff. But just a few things to think about.
1. Re-tubing with NOS usually isn't a quick process. The reason is, there are limited amounts. And you have to shop for the right ones. You can't just go to the store and buy them.
2. They can be expensive. Usually buying 1 or 2 at a time makes the cost seem like a smaller gradual dent to your wallet, rather than one big one. When you buy your pedals, do you buy 5 at once or 1 at a time. The same can apply here.
But I will say this. Once is all said and done, you'll be amazed by your amp like you never thought you would. If you're running modern GT or Sovtek, Tung Sol, JJ, etc.. The swap to NOS will make your amp sound 10Xs better. The clarity will be astonishing. That's the biggest difference with NOS tubes. They are a LOT more clean and clear sounding. Secondly, they can last usually about 10-years if they're true NOS. So you don't have to re-tube as much as you do modern tubes. If you think your BB sounds good now, you haven't even heard IT'S full potential yet. I would still continue to use it. I like those pedals as well.
