[Amps] HV Turn On Delay

[Vic K2VCO]

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