Tom W8JI wrote:
> Whenever cathode current demand exceeds emission capability
> for the cathode operating temperature or surface area, the
> cathode can be chemically poisoned. This is why
> indirectly-heated tubes or oxide-cathode tubes must have
> long controlled warm-up times before any cathode current is
> drawn.
I believe that a similar issue can arise with directly-heated cathodes,
although the delay is much shorter. I had a 3-500Z amplifier with a
step start arrangement that took about 1 second to apply full filament
voltage. On one occasion I stupidly threw the switch and immediately
started sending CW, without waiting for the step start to kick in.
Immediately thereafter the tube produced significantly less output for a
given amount of drive. In time it recovered a bit, but I ultimately
replaced the tube. Next time I'll interlock the step start with the ptt
line.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|