I have tried just about every 12AU7 variation out there, and the best match to bring about the qualities of dynamics, transient attack, detail and energy would be the Amperex 7316. More lively than the Amperex 12au7 you are using now, with even better detail and soundstage too. Steer clear of the Mullards if you do not want a warmer sound than your current Amperex. The RCA cleartops are very lively and energetic on the top end, but are very lacking in lower midrange and bass weight.
12AU7 for DeHavilland 50A Amplifier
To all those "in the know"... I have a pair of DeHavilland 50A mono blocks which use a 12au7 input tube. The amps are a bit "soft" sounding in my system, lacking some of the leading edge transients which I had grown accustom to with my prior solid state amplifier. I was curious as to whether replacing the current Amperex NOS 12au7's with the Gold Lion reissue 12au7's (the amps were designed around, and use, the Gold Lion KT88 power tubes) would give a bit more of a well defined transient type of presentation, or would I be giving up too much sonic beauty that the Amperex tubes provide? FWIW, I tried (with Kara's OK) substituting the KT88's with KT150's, and wound up returning to the KT88's as the KT150's proved to be a little too lean.
Thanks for all your input on this...
Thanks for all your input on this...