Re: air variable capacitor

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Sharpe by way of Terry Fritz <twftesla-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>

Jesse

It sounds like and is the right size to be a transmitter tuning capacitor.
Check the frame of the capacitor carefully.   There should be marking
on frame as to capacitance and maximum operating voltage for capacitor
(usually expressed as DC voltage).  If this info is not there, measure
clearance apacing between fixed and moving plates, this will give
some idea to hold off voltage capability.  Another option would be
power cap up with a _current-limited_  supply (like a NST) powered
by a variac while monitoring _LV_Input_  voltage with a AC voltmeter
(digital). Turns ratio of transformer (15kV as example, divided by
120V) would be 125:1.  If cap flashed over at 50V, peak voltage at flashover
would be 50*125* sqrt(2) or about 8800V. Adjust voltage back quickly
to limit arcing to plates or over body.  BE CAREFUL while performing
this test.  In VTTC service, would limit maximum applied tank voltage to
60-80% of what was calculated from test.  Test should be performed with
capacitor tuned for _maximum_ capacitance.

Capacitance can be directly measured of course with a LCR meter.

Regards
Dave Sharpe, TCBOR
Chesterfield, VA. USA

Tesla list wrote:

> Original poster: "jesse hampton by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <zetoyoc-at-yahoo-dot-com>
>
> Hello,
>
> I have a large (18" X 6" X 6" aprox.) air variable
> capacitor.  My question is, how would this perform in
> TC operation as the main cap?  By the way this is not
> my coil it's going into but a vttc I know very little
> about. Could this variable cap handle the job? or do
> you need a bit more info and if so what?
>
> Thanks.
>
> Jesse
>
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