I changed my V1 and V2 to Tung Sol 12AX7 and it was a huge improvement for the low end and reduced the fizziness in the preamp (it seems the newer Mesa 12AX7 highgrade are quite thin and fizzy).
The MKI mode in channel two is more or less useless now (bass overkill), but the IIC+ in the third channel is more or less spot on and the MKIV mode has the same amount of bass as the original Mark IV lead channel...
I played the MKIV mode at band volumes with the 80Hz slider all the way up before I changed the tubes. Now I have to take it under the upper line, because otherwise the bass-volume would kill my speakers (2x12 Recto vertical cab w/ V30s). :evil: