This thread has been quiet for a while now. It's very difficult to just say which tubes you should use in an MP-3. But I've experimented extensively with 6SN7 tubes in a friend's MP-3, and even more so in my own MP-1 (the latest version with three 6SN7s per channel) and MA-1. In my opinion, there are no "best tubes," and it all depends on musical preference, the overall audio setup, acoustics, and whether you prefer high engagement or a more laid-back presentation.
Furthermore, many manufacturers have produced various versions that, in some cases, offer significant differences in sound, spaciousness, engagement, etc. My focus is on the GT tubes because I generally don't consider the later GTA/GTB tubes to be the best audio tubes, but take that comment with a grain of salt. Of course, I haven't heard everything, and I'm happy to be surprised by the opposite.
I'll start with a tube that I find particularly beautiful in certain positions: the Russian Melz 6H8C. Melz has produced non-holed, holed, and holed anodes with an additional metal support. All versions are fantastic, in my opinion, but you have to be very careful about which combinations you make with them. The holed version combines beautifully in the second position with my favorite musical Sylvania GT Bottom Getter in the first position (viewed from the front) in the preamp. It's as if the Sylvania gets a shot of nitroglycerin. You retain the many advantages of the Sylvania combined with the warm and full sound of this Melz. Incidentally, I find that too cool in my setup, so I use a particularly warm tube in the third position, such as the RCA gray/black fully coated version from '40 (first version). For me, this provides a nice balance as a starting position for the MA-1. In my MA-1, a Linlai E on the left rear works wonders. If you're looking for engagement, this is a really great tube. This tube simply does a lot well, at least that's my opinion. I thought I'd never say that about a new production tube. (Ralph, thanks for the tip). In the MP-1, I couldn't get the Linlai to work properly, but that might just be me. Back to the Melz; don't think for a moment that the Melz-hole version would be suitable on the right rear for the same trick as in the MP-1. This combination really produces too much bloom in the midrange/low end, completely destroying the transparency and detail. This combination isn't a 1+1=2. A Melz '50 (Short Bottle) without gun holes does exactly what it should. This tube is much more linear, detailed, and also powerful, and keeps the low end nicely under control. Starting from this foundation, you can then further refine things in the third position (center left in my version). If you want a 3D image (great for classical music), plug in a Sylvania GT Bottom Getter or a genuine Chrome Top from the same manufacturer. If you're looking for more engagement (great for jazz/singer-songwriters), you can try the various Tung Sol GTs with T-plates here. The TS Short Bottle T-plates Grey is hot; for me, it clearly reveals the transients. Sometimes right up to the edge and sometimes just over the edge with percussion like bongos, congas, and piano with lots of hard hits on the right side. I've managed to track down about 9-10 versions of the TS, of which I just bought 5 to try and reach the "sweet spot," which, like the Holy Grail, obviously doesn't exist. I'm right there, and with a bit more warmth and pressure in the midrange and a bit less high notes, the system would sound even more homogeneous. If you want to have Jimi Hendrix playing your ear off for an evening, try a Foton '50 with ribbed anodes. It's a rough guy, but on some nights with a bottle of whiskey...
In short, there are many combinations, but first of all, don't believe all the general rumors on the internet. Some tubes suddenly get hyped, and the next year, the same "super" tube falls from grace, as I saw with the TS GT Roundplate. I read in several places that the Sylvania VT231 doesn't sound as good as a regular Sylvania GT with a Bottom Getter, or even worse than the version with three holes in the anode. It's all bullshit; they're structurally the same and sound virtually identical, and if there are even small, insignificant differences, they can be attributed to, for example, batch variations. Make sure you have a wide selection of tubes and work systematically, keeping track of the "logical" configurations you've tried in a spreadsheet or notepad. Use your ears, don't pay too much attention to the forums, and put in several months of generous passion, and you'll be rewarded with a satisfying result. Don't let bad-sounding combinations hold you back, because you're guaranteed to encounter them, but one day that aha moment will come!
