Which 12AX7 ?

[mulveling]

Telefunken 12ax7 are pricey from the primary NOS tube dealers, yes. They are not expensive, and are plentiful, on the used market - if you are willing to accept "used, test strong or like NOS". I think this is a good way to go, since the quality of Telefunkens were produced in large quantity and in pretty consistently good quality. Both varieties (smooth plate, ribbed plate) are excellent tubes that will bring notable improvements to most 12ax7 slots. The ribbed plates have a little bit more zip up top; preferable in some systems but not others.

I've bought these kind of "pulled" Telefunkens, say $50 - $70 per tube, and you'll get an occasional dud but the overall savings makes them an awesome value for the money.