Homebrew Variable Condensers

[Dick Blaney]

Sometime last week there was a thread to the Glowbugs List concerning
the scarcity of variables and homebrewing variable capacitors.  I
remembered that there was an article in QST some years back on the
same thing.  I found it in the November, 1975, issue, page 22.  Jay
Rusgrove, WA1LNQ, then Novice Editor, built one using 2 sizes of
tubing, one copper & one aluminum, taking advantage of the fact that
copper tube is specified by ID, while aluminum tubing is sized by OD.
This resulted in a smooth variable cap insulated with 10 mil teflon,
with the capacity of 5 to 368 pF, a VERY wide range, wider than most
conventional caps.  The 10 mil Teflon, at 1-2 kV/mil, should easily be
good for at least 6kV peak with comfortable safety margin.  The result
was a tubular variable, high capacity, high Voltage rating, and quite
smaller in physical size than a similarilly rated conventional "bacon
slicer", and one that should be easily replicated on the "kitchen
table" with ordinary hand tools.  He used it successfully in an "L
network" antenna tuner.  Anyone interested in trying their hand at
such a progect would, I think, be well served to get a copy of that
article.  Any thoughts?
73 de
Dick, WB8MHE
wb8mhe at bright.net

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