Re: Tube watts & volts

"Max plate voltage is normally given in DC and for an 811A that is

For an RF amplifier tube like the 811, the DC voltage rating is usually
for Class C RF amplifier applications, where the peak AC voltage is very
close to twice the DC plate voltage.  Thus, 1500 VDC is equivalent to
3000 VAC.  As long as the tubes have good insulation and vacuum,
applying higher voltage is not necessarily harmful.  Exceeding the plate
dissipation, on the other hand, can lead to gas formation or melting of
the plate, both of which are swiftly destructive.    I've used a small
receiving pentode (6AU6) for a series regulator on a 3000 volt DC supply
(very small current) and never had a failure after a few hundred hours
of operation. Suspect that with time the insulation would fail as the
tube became gassy and metallic deposits from the heater coated the
glass.  In TC work one would probably never pile up that much time.