If the filament supply can handle extra current, and if the filament voltage is 12V (not 6V), then a great upgrade from the 12AU7 and its congeners is the 12FQ7. Even as a cathode follower, the 12FQ7 can be heard to be an improvement on the 12AU7.
Primaluna signal tube replacement
I need to replace my small signal tubes in my 2 year old Dialogue Premium. The 2 middle tubes are good. I had replaced those with GL 12au7. The outer tubes are stock Primaluna. Left channel got “scratchy” and I replaced with some backups.
Do I go cheap? Doesn’t affect audio quality,,right? Or pay more for longevity? Love the amp and it’s on a lot. Thanks for your advice.