What's the best sounding replacement for 12AX7A and 12AT7?

For 12ax7, try a 7058 (RCA made good ones). They are cheap and sound amazing.

For 12at7, try a GE or Sylvania 6201.

A very good tube equivalency resource is:

http://www.duncanamps.co.uk/

Talk with Andy Bowman at Vintage Tube Services (www.vintagetubeservices.com). This guy is the real deal! His supply, service, knowledge, testing expertise and equipment, and experience make you realize that all of the other so called "experts" really don't have a clue...and I've dealt with most of 'em.

I would suggest that you talk to Andy at Vintage Tube Services. He has been in the business (his only business) since the mid 80's and this has been an avocation for him virtually his whole life. His web page is www.vintagetubeservices.com or better yet call him at 616-454-3467.

His suggestions regarding replacing my 12AX7's from my Aronov preamp worked magic...much more musical and detailed. I also hate to burst your bubble but there are many grades of 6550's and what is currently out there is definitely substandard compared to the NOS Tungsols and Sylvanias. I should know. Andy put together some NOS Sylvanias and WOW!

At any rate it would definitely be to your benefit to call him.

I also use 1 pair 12ax7 and 1pair 12at7. Thor (line stage) I purchased a pair of mullards 12at7s from kevin at Upscale Audio. Tubes marked 6201 mullard gold pins. Great base very nuetral also. I think they were about $60 pair. The other pair i purchased to compliment them were, Tungsrams 12ax7s. Good combo! About the same price per pair.good luck!

Imust agree. Andy is the man to talk to when you want tube info.But there really are only 2 great tubes out there when
it comes to a 12ax7 and 12at7. for 12ax7 the telefunken
smooth plates are it.although the bugle boy 12ax7 is great
also.depends on your taste.for 12at7 only telefunken will do.hope this helps.