12ax7 tubes can be enterchanged with xxx tubes?

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.

I know this is stating the obvious - but any ECC-83 is a direct sub for a 12AX7.