I admit to being a bit of a 12AX7 snob, and I also admit that this is a marginal, not essential, pursuit.
That being said, I put some old pre-war Yugo EI 12AX7s in the 3 slots in my Synergy 50 head (running TDLX & Bogner Ecstasy Modules) and the smoothness and lushness just reached another level over the 2 ARS China and 1 ARS JJ that were in there.
I'd also put NOS in the Bogner module (that wasn't fun, sheesh).
Anyway, not to send anyone down the rabbit hole, but if you so choose, you might enjoy the results.
That being said, I put some old pre-war Yugo EI 12AX7s in the 3 slots in my Synergy 50 head (running TDLX & Bogner Ecstasy Modules) and the smoothness and lushness just reached another level over the 2 ARS China and 1 ARS JJ that were in there.
I'd also put NOS in the Bogner module (that wasn't fun, sheesh).
Anyway, not to send anyone down the rabbit hole, but if you so choose, you might enjoy the results.