[Amps] Indirectly heated cathodes

[Steve Thompson]

> ##  dunno abt   Indirectly  heated tubes.  I don't think you can drop the V  
> very much ['dark heat'] 
> I believe, even if that's  done... you still  have to wait XXX  minutes, which 
> might be slightly less than
> the  normal 3 mins.   I believe there is a very  narrow window  for  fil v on 
> INdirectly heated tubes. 
> Too low, and you contaminate the fil.   Although the  YC-156  has a 6 min warm 
> up, Eimac tell's
> me to use 8 mins. 
> 
> later... Jim   VE7RF
> 
To avoid confusuon, it's the oxide cathode rather than the 
fil(ament) that can suffer from too low a heater voltage in an 
indirectly heated tube.

I'm not sure about the 'narrow window'. Most tubes I can think of 
specify something like 10% tolerance on the heater voltage, 
similar to many directly heated ones.

Steve