I got tons of unloved 12AU7 because everyone wants all the 12AX7 tubes. Which I have much less of. I also have a moderately substantial stash of 6SN7. But few identical ones to make matched pairs. Those were often used for lots of non audio apps so they are numerous. Until you start trying to specify "special" versions that everyone wants. The "magic" tubes they say.
I got tons of unloved 12AU7 because everyone wants all the 12AX7 tubes. Which I have much less of. I also have a moderately substantial stash of 6SN7. But few identical ones to make matched pairs. Those were often used for lots of non audio apps so they are numerous. Until you start trying to specify "special" versions that everyone wants. The "magic" tubes they say.