The 12AU7 driver tubes make a larger difference in sound than do the 12AX7 phase splitters in my experience and according to Mark O'Brien of Rogue.
My preference is for NOS Mullard CV4003s. I use an RT 6189 in the pre-amp spot and either NOS Mullards or RCA black-plates in the phase splitter positions.
My preference is for NOS Mullard CV4003s. I use an RT 6189 in the pre-amp spot and either NOS Mullards or RCA black-plates in the phase splitter positions.