I had one of these but traded it to my brother for a T50C. We spent lots of hours experimenting with lots of different power tubes, pre-amp tubes and combinations.
Stick to 6L6s, but go with SEDs. We experimented with Sovteks, EHs, Shuguang, SEDs, JJs, etc. and came to the conclusion that the SEDs were best. Groove Tube 6L6GEs sounded good too, but they are pricey.
Three other suggestions: (1) use a JAN Philips or JAN GE 5751 in V1 instead of a 12AX7; (2) use a JAN Philips 12AT7 for the reverb driver; and (3) use a JAN GE 5751 for your phase inverter.
This set up sounded excellent. Hope our experience helps you out.