I don't know when Raytheon last made subminiature tubes, but do know
that they were going into new-manufacture missile warhead guidance
electronics until the early-mid 1970's.

Production line shut down in 1983, I think. That factory now only makes
magnetrons and travelling wave tubes.

Sonotone did have their own line for subminiature tubes, but I don't
know whether that was set up during WWII or afterward. Their first
"transistorized" hearing aid hit the market in 1953, but it was a
hybrid that still used tubes plus one transistor in a cigarette-pack
amplifier.

The Japanese made the things too, and there were other companies like Hy-Vac
making them.


BUT... as far as the original poster's tube goes, I got a couple from him
in the mail and it looks to be a pentode with a 5J pinout. My guess without
putting it on the curve tracer is that it is likely to be a CK531DX. I'll
try and test it more carefully this weekend.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."