[Amps] Capacitor Recommendation Needed

[George & Marijke Guerin]

Dennis, etc.,

I would try to find vacuum padders, or even a vacuum variable.  Padders are
regularly available in 50, 100 and 250 pfd cheap at hamfests.
I would not try ceramic door knobs unless you find some rated for high
current.  I think many small value ones in parallel might be OK.  We tried
to make an 80 meter trap using a big high voltage 150 or 200 pfd door knob
and blew it up on the first test with power!!  Three 75 pfd door knobs in
parallel or four 50 pfd door knobs worked OK for that trap with the
inductance trimmed to 80 CW

Good luck    George    K8GG

----- Original Message -----
From: "Dennis Ashworth" <K7FL at ARRL.NET>
To: <amps at contesting.com>
Sent: Saturday, October 04, 2003 7:27 PM
Subject: [Amps] Capacitor Recommendation Needed


> I need to insert a 1000pf of capacitance in series with my 80M vertical to
> move the resonant frequency up to the phone band. I have been using a
> vacuum variable, but would like to use it in another project - and change
> to a fixed capacitor. The logical choice would be a fixed 1000 pf vacuum
> capacitor. Failing to locate a fixed vacuum cap, what low loss dielectric
> materials should I be considering given the frequency, voltage and current
> involved. The driving impedance is 40 ohms and I run the legal limit.
> Therefore, currents will be in the 6-8A range ... voltages probably less
> than 500 V.
>
> Thoughts on dielectric materials and sources would be most appreciated.
> Although this is not AMP related, I suspect you folks know the answer(s).
>
> Dennis, K7FL
>
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