[Amps] Ceramic capacitor ratings

[Tom W8JI]

> Now take the maximum RF RMS voltage at the tube plate. It 
> will be quite
> close to the DC plate voltage, so for simplicity you might 
> even cheat
> and use the DC voltage.


The dc plate voltage is the peak RF voltage in a very hard 
switched PA, so RMS plate voltage would be about .71 times 
anode voltage but this ignores harmonics.

In linear PA's it less, since the anode cannot swing from 
full HV rail to zero.

So it seems the DC rail would probably be a very 
conservative estimate when the PA is properly loaded.

When the PA is not properly loaded the circulating currents 
can be higher, and the peak voltage can be higher than the 
anode voltage!

I also agree the unloaded Q has little to do with the 
problem, neither does the operating Q. It is strictly the 
amount of RF voltage across the capacitor and the capacitive 
reactance that causes the current....but we have to be 
careful of ignoring harmonics and also careful of situations 
with improper loading.

73 Tom