I've got a Shuguang (long plate) in V2 now and I find it's a decent compromise between gain and brightness. I found the JJ
maybe to be a little thinner... same with the Marshall (which
is a Shuguang), but that could be an 'illusion' because of the Tung-Sol's higher gain. The surprise to me is the Tung-Sol - it very noticeably has more gain and is much fatter than the other tubes I've tried in V2. I'm still surprised that such a difference would be so apparent.
I do like the Mullard RI in V1 though. I'd like to get something that's halfway between the thickness and gain of the Tung-Sol, but perhaps dialed back just enough to get some of the clarity of the JJ and Shugaung. Or perhaps I'll just decide to use a certain set of guitars with the MP-1 and use the tubes that suit those guitars best.
Hey... while typing this message I just looked in my Marshall JVM and found another Mullard RI that I forgot about. I swapped it into the MP-1 and put the Shuguang in the Marshall. I don't find the JVM that sensitive to tube swaps (at least not like the MP-1) and it sounds good with just about anything, so I'll give the MP-1 a run through with the two Mullards tomorrow.
I bought one of my MP-1s new in 1989 and it still has the original battery and tubes as well. Works great!
Isn't that crazy??? The MP-1 mustn't draw much current, or only use the battery intermittently, on demand.
It's crazy how well some of the gear from back then has held up. I have a bunch of stuff from the '80s - from Boss pedals to a Fender amp to an ART Power Plant preamp - and some of this stuff is practically like the day it was made. Not just to look at, but functionally too. I got the ART Power Plant on Ebay for $13.16 U.S. ...and the thing is dead quiet, no hiss, and the pots aren't even scratchy. It needed a cleaning and some new knobs, but now it's like new. My MP-1 is just silly... it's like NOS, inside and out.