I've only used long plate tubes. Short plates make them sound too brittle.
Ok, some other tubes rolling.
I started from a very good point:
1) TAD 7025 --> V1
2) Ruby's 12AX7ACZHG --> V2
The first test was with the Ruby's 12AX7ACZHG+ in V2.
Result = WOW!!!
Punch, very very low noise, more gainy than with the 12AX7ACZHG in V2, better bass response and more overall clarity.
Very articulated and 3-D clean tones.
Absolutely the best.
Then I swapped the 12AX7ACZHG+ with the 12AX7AC5HG+ (TAD 7025 still in V1) : another nice combination...a little less gain and less "bassy", but very good.
Third test: Ruby's 12AX7AC5HG+ in V1 and 12AX7ACZHG+ in V2.
Very close to the starting point with the TAD 7025 in V1, maybe just a slightly different eq....little less basses, little more mids.
Another very good combination.....very hard to choose what's the best.
Next and last step was to swap V1 and V2: I don't liked it at all.
I think, to my taste, those Ruby's JJs are very good tubes for V2, but I don't like them in V1 in the MP-1: the sound looses gain and 3-D.
I've to say I love one thing of all these tubes (Ruby's and TADs): they are not noisy.
I assume this comes from Highgrade selection...they seem reliable and have good tones.
Having less noise, I can push my MP-1's output level some more and I increased OD1 and OD2 levels on my main distortion patch from 7.0 to 7.5 without adding any noise (I also tested with 8.0...same result....but I preferred a .5 less value).
Yes, MP-1 is the best preamp on this planet.
I cannot wait to send mine to MJMP for the mods and have it back...ready to rock for the next 30 years.
More tubes rolling will follow.