I have a Mark V 35 i did some NOS tube swapping in V1/V2/V3 positions.
I'm using:
V1 Early 61 Amperex White Label
V2 Early 61 Amperex White Label
V3 CV4004 60's Brimar
It seems to have warmed up the low end a bit, and has given it a bit more character. The mids sound great, and overall the amp...