[R-390] silver-mica capacitor failures

[David Wise]

Thanks for describing dipped-mica construction.

I don't know what the molded mica bodies are made of; I just guessed.  It's hard and breaks with a grainy texture, which made me think of Bakelite.  What do you think it is?

________________________________________
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> on behalf of Charles Steinmetz <csteinmetz at yandex.com>
Sent: Tuesday, March 31, 2020 1:24 AM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] silver-mica capacitor failures

David wrote:

> Do the dipped parts have a crimp joint between the lead and the assembly, like the molded ones?

Generally, the ones I've seen the insides of are put together like
multi-layer ceramic caps or stacked film capacitors -- stacks of
metalized dielectric sheets, every other sheet offset, with sprayed
metalization at the two ends (connecting all even sheets and all odd
sheets together), with radial lead wires attached by the metalization
(often with metal end caps for structural reinforcement).  I'm sure
there are a variety of ways (and proprietary processes) it is done by
different manufacturers.

> I'm not used to thinking of bakelite as a plastic.

The general usage of that term includes the various phenol/formaldehyde
resin systems like Bakelite and Catalin.  Bakelite itself used the trade
name "Bakelite Plastics" for many years.

What information do you have that the bodies of postage-stamp mica caps
were made of it?  The ones I've destroyed in the interests of science
appeared to me to be some other plastic material.

Best regards,

Charles