My favorite 12AX7 compatible tube is the 5751 triple mica black plate from the 1950s by RCA and GE, in that order. There are several versions of these. The older silver clip versions are the very best.
Prices are all over the board on these. I have an abundance of the GE version if you want to give them a try.
Prices are all over the board on these. I have an abundance of the GE version if you want to give them a try.