[AMPS] Re:HV on tube w/o filament voltage

[Rich Measures]

>
>Dick says:
>
>>Don't you  think the HV filter will generally discharge much faster than 
>>the cathode will  cool down & lose emissivity, Peter...?  
>
>It's all going to depend, isn't it? The relative time constants of screen
>and bias supplies, the time constant of the HV supply..........you could get
>the case where the tube is cut off and cooling  and then the bias supply
>falls before the HV has. It's a bit academic, though - the probability of it
>giving a problem is pretty remote. If you're running multiple amps and
>switching the heaters as you change band, leaving the other voltages on,
>it's possible. X ray tubes have back bombardment which heats the cathode, I
>believe, but I don't think anyone on this reflector is running B+ voltages
>up in 100kV region - not in amateur service, anyhow.

€  I have heard about amateurs in Italy and Japan that have 
8349/4CX35000C amplifiers.  The rated anode potential is 20kV, which is 
close to the limit for thoriated tungsten cathodes.  .  X-ray shielding 
is definitely not optional.    
>
-  later, Peter


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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