> From: Rich Measures <measures@vc.net>
To: <amps@contesting.com>
> Date: Fri, 18 Jul 97 14:23:25 +0000
> >> True, Peter. However, since the RF peak V rating of vacuum variable
> >> capacitors is 60% of the DC/60Hz rating...
> >Interesting; I've never heard of this derating requirement.
>
> It's in the Jenning Radio Co. catalog.
Another case of improperly reading the text Peter.
Here's what the text says on page 8 of my brand new Jennings catalog:
"RF working voltage is the maximum peak RF voltage that can be
applied continuously to the capacitor without affecting its ability
to withstand instantaneous overloads. The difference between the 60
Hz test rating and the RF working voltage rating is the recommended
SAFETY FACTOR of the capacitor."
Had Rich read on, he would have found this....
" DC- Vacuum capacitors should not be operated in DC
applications above the peak RF working voltage rating."
"DC plus RF- The sum of DC and RF peak voltage shall not
exceed the capacitors peak RF working voltage."
The applications notes plainly say for ANY frequency, DC through
RF, the peak applied voltage should not exceed the RF rating, and the
RF rating is 60% of the 60 Hz peak TEST voltage.
> >What
> >causes the change in breakdown voltage with frequency?
> >
> I am not certain
The correct answer is NOTHING. The reason the ratings are different
is this.
The 60 Hz test rating is the minimum production test pass-fail
criteria using a 60 Hz hypot machine, while the DC and RF ratings
include a simple normal safety factor to insure reliability.
Of course the correct answer would never help sell suppressor kits.
;-)
73, Tom W8JI
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