Hi, Tom

Thanks for the hint about gas in large glass tubes.
Also thanks for the link to your web site, plenty of wonderful info!

One question please - I have 8 type 3-500Z which
have not been used for 20 years. You mentioned operating
them at low plate voltage and positive grid voltage,
so that the plates show color (for gettering action).

What range of plate voltage/ grid voltage do you recommend,
and what current limiting resistor would you suggest
in the plate circuit?
Do you use a current limiting resistor in the grid circuit also?
I plan a test fixture to recussitate
the 3-500Z tubes before risking them in an amplifier.

73,
Ed Knobloch

wrote:
snip
As for cooling, seal cooling is critical in glass tubes. So is periodic
operation to keep the tubes gettered.

http://www.w8ji.com/vacuum_tubes_and...e_failures.htm

73 Tom