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Re: Capacitor construction



Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

> I was wondering if anyone has
>  experimented with glass plates with aluminum foil or brass sheets for the
>  electrodes. Both of these are in abundant supply in my shop and I'm trying 
> to save a buck :)

>  TIA,
>  db

DB,

Glass will work, but it's lossy, and must be placed in oil for
best results.  The dielectric constant is high at about 6, but
the Q depends on the dissipation factor which is rather poor
for glass.  You'll probably lose about 15% in spark output
length using a glass plate cap vs. a low loss cap.  The 
primary tank in a Tesla coil runs in a low Q mode anyway,
but glass caps increase the overall losses.  If you want to
insist on building your own caps, an alternative would be
to used rolled polyethylene, or flat layers of polyethylene.
Such construction gives good results and low losses,
and can be built very cheaply if you can obtain the parts
for free, or almost so.  Such caps are bulky however.
Glass caps, despite their shortcomings do work, and that's
what Tesla himself used.  He used glass bottles which used
to fail on a regular basis.  

John Freau