Re: May I be the first to say...
"...which are copies of RCA Nuvistors. I used to have some of these. EMP resistant before anybody needed it."
No they were not. The Nuvistor was much later and completely different construction. The Russians developed "Rod Pentodes", which are not even remotely similar to the USA "Pencil tubes" used in missiles and hearing aids.
The Rod Pentodes used in Sputnik and MiG fighters as well as other early space stuff.
Superior to Germanium transistors. Much lower power and easier to make than the later RCA Nuvistors which were a last gasp dead end for USA tube industry (In Domestic products, only used in USA VHF & UHF tuner heads. Some Professional condenser microphones and hardly at all in Military).