Hey Max,
I've had a few Mullard RI's in my MP-1, Groove Tubes, (12AX7M), and the New Sensor Mullards, and found the New Sensor to not have as much punch as the GTs. I have found a pair of NOS Mullards, made in Great Britain, but they are very expensive. I am considering it though, since the MP-1 really came to life with those GTs in it.
Harley
I had a couple of 7025/12AX7A GT Tubes in my previous, old 1.38 MP-1 many years ago.
I bought it from a friend who replaced original tubes with some chinese PM tubes...
They were not so bad, but GTs were better.
So, you prefer GTs to Mullards RI in MP-1?
I've some more results from my tests...
1) TAD 7025 Highgrade in V1 is a real WINNER: very good gain, punch, low noise, firm basses and very good overall detail
2) TungSol 12AX7 is not so bad in V2 combined with TAD 7025 in V1, but is not so good in V1...less gain and flat tone...
3) TAD 7025s Highgrade in V2 has very good gain and low noise, but basses are too "gummy" and confused, specially with high gain settings (I paid about 20 euros for it some years ago...and now TAD sells that tube for more than 50 euros...
)
4) a 5751 in V2, combined with TAD 7025 in V1, is a very good solution...good tones....but slightly less gain, of course
5) the chinese tube from the Zoom 9150 looks like original MP-1 tubes but it doesn't have the same sound and tone...similar, ok...but not the same at all
6) the best combination is still the TAD 7025 in V1 with an original 12AX7A chinese tube in V2: very good gain, not so noisy, very detailed sound, perfect basses, thick 3-D sound
I cannot wait to test a TAD 12AX7A-C in V2...
About NOS Mullards...an average price is 180-200 euros for 2 of them...
Too much, IMHO.