I ran into problems with an air variable that I had increased the plate
seperation to handle more power at that higher Z on a 4-1000A.. I calculated
that the max RF peak voltage would be 4.5KV. When I used the amplifier it
would
arc over on voice peaks. I hi potted the capacitor and sure enough it broke
down
at 4.5 KV
I would say it would be best to hi pot the one you have so you know what you
really have. If it is not 25% higher than what you calculate for peak RF
voltage
I would look for another.
Regards
Denis VE6AQ
William Fuqua wrote:
> Looking at Jenning's data on Vacuum Variable capacitors I noticed that
> the
> voltage rating on the capacitor is the Test Voltage and the working voltage
> is less.
> For example a 3000volt cap Cxxx-300-3 has a test peak voltage rating of
> 3Kv and a working peak voltage rating
> of 1.8KV. A 5Kv one has working voltage of 3KV and a 7.5 has working peak
> voltage of 5KV.
> So if I am running a 4-1000A with 5K plate resistance and 1500 watts out
> the RMS Plate voltage would be 2740 Vrms or 3872V peak. I can't use a
> 3000V cap based on those
> figures but must use at least a 7.5KV cap.
> So what gives. I expect most of us are pushing these caps beyond their
> working voltage limits.
>
> 73
> Bill wa4lav
>
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