Pretty simple, really. Better tubes equal better sound.
For these variants, with few exceptions, you need to look toward old production. Not necessarily NOS, though so many aspire to that. I found you can do VERY well for yourself buying tubes others sneer at as they come up measuring as having obviously miles on their clocks. Old tubes often play quite a long time, and pretty much sound great until they give out.
As has been mentioned the best 12AX7 tubes are 5751. What I can add is the best 12AU7 are 7316. Both tubes will cost you deep in the purse. Both tubes instantly convince you that you won't go back.
If you do want to buy new production tubes, Shuguang triple mica 12AX7B aka Silver Dragon and Psvane 12AX7 and 12AU7 stack up surprisingly well
For these variants, with few exceptions, you need to look toward old production. Not necessarily NOS, though so many aspire to that. I found you can do VERY well for yourself buying tubes others sneer at as they come up measuring as having obviously miles on their clocks. Old tubes often play quite a long time, and pretty much sound great until they give out.
As has been mentioned the best 12AX7 tubes are 5751. What I can add is the best 12AU7 are 7316. Both tubes will cost you deep in the purse. Both tubes instantly convince you that you won't go back.
If you do want to buy new production tubes, Shuguang triple mica 12AX7B aka Silver Dragon and Psvane 12AX7 and 12AU7 stack up surprisingly well