12ax7 tubes can be enterchanged with xxx tubes?

IMO:
So many really good choices in vintage 12ax7 that I would recommend trying:
Almost any 50's or 60's vintage USA made 12ax7 will sound better than current production ones. Try RCA or GE or Sylvania grey plates also...not quite as refined as the soo sweet black plates of that era, but still very good, and don't command the premium prices either.

Holy grail 12ax7 for me: Telefunken smooth plate, closely followed by the ribbed plate:

Any Mullard or Amperex from that era:

I have 15 12AX7WA Sylvania, USAF stamped mil spec tubes dated 12-64 that are some of the finest tubes I have...absolutely smooth, very quiet, with very fine detail that I paid $5/ea. for....so you can find super tubes for fair prices if you just broaden your search field a bit.
Good Luck....tube rolling is great fun!

Hi, Mechans:
The 12ax7 Sylvania USAF tubes I bought locally, friend-of-a-friend type deal. Almost all of my other tube purchases were made by going to vintage radio shows and an event called a "Hamfest" which is a swap meet for ham radio collectors. These are where I have found my best deals, when some elderly gentleman has a box of unsorted tubes he is selling for $20. I buy the box, plus any others I can find, and go home and sort the tubes and test the ones I decide to keep (I have a tube tester also). The majirity are tubes I cant use or have no need for, but I always end up with some I am looking for.
Just check your local paper, or go to a local electronic shop and ask around.
Good luck!
PS:
If you are interested in contacting me regarding tubes, my email is
Twinbugles52@comcast.net