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Re: Glass Caps
Hi Nick,
Glass plates are like any other HV cap. The air space will ionize and
cause a little loss. Glass stands up to ozone and ultraviolet much
better than plastics.
What you have is a electrostatic loudspeaker also (probably makes more
noise than the spark gap). Put it in oil if possible.
Paraffin wax works as well, and is less messy if something breaks.
Unless you are careful to remove all the air, and maintain insulation
margins, an internal arc will cause tracking on the glass and burn a
conductive (carbon track) path in the glass. Oil is more forgiving in
that respect.
Since paraffin has to be worked in the molten state, things like
adhesive tapes tend to come loose when you pour the wax. Use cotton
twine (synthetics stretch when hot) stay away from electrical tape
(ditto stretch) masking tape works, if reinforced with twine. I use
wooden boxes to hold glass plate caps. Masking tape on the outside of
the box is good enough to prevent leaks through small cracks. Wax
shrinks, you have to keep toping it off with more wax, as it cools.
Oil is less hassle, and works better. Wax is safer.
Glass works very well as a dielectric in practice, if not on paper.
One of the old books mentions putting down a layer of varnish on the
glass then laying foil against the varnish and waiting for it to dry
(forever probably) then coating over the foils with varnish. (this was
in a single plate of glass which comprised the whole cap - only two
plates) All this was done in an effort to eliminate corona and adhere
the foil to the glass.
Hang onto the glass plate cap if you decide to try rolled poly cap
construction. Bypassing a rolled cap, with a stacked foil cap, works
wonders with TC output.
take care
bob misiura