Pooh Bear said:

So don't anyone start about bad quality Russkies :-)

I've seen some Zaerix 6L6GCs go zero emission. Took some believing for all
4 to have gone but they sure did. That's more than 20 yrs ago though.

Zaerix was just a brand name, they got their valves from everywhere.
Could have been the USSR at the time you mention, but not likely IMO.
Most of their stock was RFT (DDR) at that time, and they were actually
good valves.
If you can read German, a very interesting piece on valve history can
be found he
http://www.jogis-roehrenbude.de/
Click on "Rohren Geschichtiches".

BTW: how long did it take for those to go "zero emission"?
I've never seen this happen with power valves, actually. They might
get weak after many years, but *zero* ? Cathode blasted away?
Rectifiers, yes, like Carys with 1200 uF at the cathode of a GZ37!

--
Sander deWaal
"SOA of a KT88? Sufficient."