[Milsurplus] [Boatanchors] Mica compression trimmers?

[Mike Feher]

Yes, mica indeed increases the operating voltage for the same plate spacing.
That is why it was used in early spark transmitters along with glass. It is
called a mica compression trimmer because mica is used as an insulator
between plates so they do not short. Obviously, mica is not compressed.
Neither is air in air variables. 73 - Mike 

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell NJ 07731
848-245-9115

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net
<milsurplus-bounces at mailman.qth.net> On Behalf Of KD7JYK DM09
Sent: Sunday, November 8, 2020 3:20 PM
To: 'milsurplus listserv' <milsurplus at mailman.qth.net>
Subject: Re: [Milsurplus] [Boatanchors] Mica compression trimmers?

> I believe your observation is wrong. Mica compression trimmers indeed 
> do have mica between the plates, so the compression is on the mica and 
> not air. Consequently you can obtain a higher capacitance for the same 
> size as the dielectric constant for air is 1 and for mica it is about 3 to
6.

And here I though rock didn't compress, and only the air-gap between the
plates was changing relatively electrically, until the plates stopped. 
I do however, recall a saying of squeezing blood from a stone, so maybe
that's how they work, but I can't imagine it designed to shatter eisenglass,
bend plates, strip screws, and crack the body, for that last little uuF.  I
figured the mica was the dielectric to increase the operating voltage...

Kurt

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