Todd:
I have a number of tricks that I have developed over the years for
building up capacitors. Perhaps I will reveal some of them soon -
unfortunately some of my data is proprietary since I am in the electronics
business. However, I try to share what I can with fellow hobbyists.
My purpose in this last posting was simply to help stamp out another of
those myths that seem to have no known origin, either in fact or in
authorship. Let's just see if anybody comes up with anything for real that
supports the negative comments about mica that have been seen here. I don't
believe it will happen - I consider mica to be the best overall dielectric
for capacitors that mother nature has seen fit to bless us with. And if
somebody knows about a better one, I would be one of the first to embrace it.
The particular problem which you stated has an obvious cause.
You cannot maintain good pressure near the center of your 'plates' with
clamps on the edges. When you are working with very thin dielectrics, every
little bit of air gap becomes enormously significant. You will have to put
additional screws (like, maybe every 1-2 inches or so.) As you know from
your experience so far, this is easier said than done. The main advice I can
offer is to be very careful around the screw holes since there is a
substantial fringing field at every sharp edge.
Eric von Valtier K8LV
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