Hi Scooter, when I had my Mc275 MkIV I found the combination of NOS Mullard 12AT7 and 12AX7 plus reissue Genalex Gold Lion KT88 to be very musical and satisfying in my system. The Mullards were from Upscale Audio. This was, however, a number of years ago and prices of NOS Mullards may make this combination prohibitively expensive at this point.