Topband: Submerging variable caps in oil as substitute for vacuum variables

[Shoppa, Tim]

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

----- Original Message -----
From: Pete Smith N4ZR [mailto:n4zr at contesting.com]
Sent: Wednesday, January 29, 2014 05:42 PM
To: topband at contesting.com <topband at contesting.com>
Subject: Topband: Submerging variable caps in oil as substitute for vacuum	variables

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?

-- 
73, Pete N4ZR
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