I was absolutely confused regarding what kind of “tubes” this guy talks about. But when I saw 6N1P and recognized it immediately. Not the exact name, but the numbering scheme - each owner of a Russian TV would learn a numbering scheme for “tubes” sooner or later.

It’s interesting that Russia became (or remained as) an almost single supplier of this “outdated” technology.

But still, these “tubes” are rather a niche product in the audio equipment market, no? We probably can’t get a good enough insight looking just at them.