The best 12AX7 is not a 12AX7. The best 12AX7 is a 7058. There is just one rub. The 7058 is an extremely ruggedized 12AX7 substitute that was designed for automotive use. The rub is that it only operates with center tapped heaters and will not operate with series connected heaters. If it works in your phono stage, it will be an excellent contender for best 12AX7. As a bonus, it's cheap. 6681 is a very nice instrumentation grade 12AX7 that is a direct sub, no caveats.
The best 12AT7 is a 6201. There are many great makes of this instrumentation grade 12AT7 to choose from. Mullard, Tele. I like the Sylvania Gold tubes. On the plus side, they are a direct sub for 12AT7 on the negative side of the ledger, they are spendy.
Good luck with the hunt.
The best 12AT7 is a 6201. There are many great makes of this instrumentation grade 12AT7 to choose from. Mullard, Tele. I like the Sylvania Gold tubes. On the plus side, they are a direct sub for 12AT7 on the negative side of the ledger, they are spendy.
Good luck with the hunt.