Subject:Re: Topband: Submerging variable caps in oil as substitute for vacuum
variables
The author points out (correctly) the tempco issues with oil dielectric.
Still I am intrigued by the thought of a remote tuning capacitor via hydraulic
tubing :-). The capacitor plates could be as simple as two concentric cylinder
conductors with appropriate spacers. I betcha crud collecting on the top of the
oil would set voltage limit.
Tim N3QE
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The omega match for my shunt fed tower uses two 300 uF roughly 3000-volt
variables I bought from Henry radio a few years ago. I think
occasionally about running more than 100 watts on 160, but the cost of
the vacuum variables is a real issue. February QST has an article on
using mineral oil immersion to increase the voltage capability of
variables in a 600M amplifier. The article does not include any hi-pot
data, but indicates that the maximum capacitance went up a lot.
Opinions?
Tim,
I have an oil filled variable capacitor that I picked up surplus many years
ago. The spacing is about 0.01 inch, capacitance 1000 pF and
if I remember correctly it hi-potted to around 5kV. I still have it.
I am using 2 X 500pF @ 7.5kV vacuum variables in my Omega Shunt feed. I
normally run 1500 watts out on 160. Top loaded 80 feet of Rohn 45G.
Guyed with 6700 lb Phillystran.
73 de Price W0RI and Club Station W0CKC
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