[Amps] HV Turn On Delay

[Tom W8JI]

> 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.

I've never heard of that problem. Thoriated tungsten tubes 
are not subject to these problems Vic. They can tolerate 
much higher anode voltages and be operated with full 
emission saturation without degradation.

There are some oxide directly heated tubes, but the 3-500 is 
not one of them.

Sometimes we just have a part fail and relate it to a 
situation that didn't actually cause it. For a long time I 
wouldn't fill the gas tank of my car because I filled it 
twice in a row and every time right after filling it someone 
ran into it. That's actually a true event. It took me six 
months to get over it.

73 Tom