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!

Twinbugles would you kindly share where it was that you found $5 12AX7s US made in the 1960s. I would like to expand my search to places offering such bargains. Can you Help me out? If they also have RCA 1950s triple mica blackplate 5751s for a similar price please pass that along as well. Actually prefer Sylvania but any brand of 5751 would be fine Thanks in advance.

i have c.a.l. sigma 2 dac that has a 12ax7a stock. so far i have tried a JJ 12ax7 ( a bigger sound stage, more detail but not as smooth) a phillips 5751(didn't really notice much of a drop considering the gain difference, less detailed and not really as coherent). i bought a psvane 12ax7 from grant fidelity here in calgary, and have about 20 hours on it so far. it seems to have most of the qualities i was looking for-smooth with a nice big soundstage. so far it's my favorite, with the stock tube second. i'm gonna give the psvane a bunch more hours and see what happens, all the tubes so far are relatively cheap-$10.00-$37.00. if i'm still searchin', i may pay some big bucks for some nos mullards or the like for $100.00 plus for a single tube!

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

Thank you Twinbugles-
I have heard of Hamfests but I am afraid they will peg me as an audio guy not a radio guy and jack up the prices. What do you do with all the odd tubes. I have bought lots like that in the past and don't have the heart or mindset to throw them out. I am in southwest Ct. near Danbury and the NY border for the time being. You can use the email feature they have to look me up . If you know a hamfest is happening in my area or a couple of hours by car please let me know Thanks again.