[R-390] A question about silver-mica capacitors failures.

[David Wise]

Great summary, Charles.  Do the dipped parts have a crimp joint between the lead and the assembly, like the molded ones?

Dave Wise

(PS: I'm not used to thinking of bakelite as a plastic.  It is, though, isn't it?  Strictly speaking?)
________________________________________
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: Sunday, March 29, 2020 11:57 PM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] A question about silver-mica capacitors failures.

Jacques wrote:

> It was flagged by many contributors to this site that the number of silver
> mica capacitors failures is rising.
>
> As the failure mechanism seems to be understood (silver migration within the
> capacitor package), it is not clear for me if this occurs only when a
> potential difference is applied to these capacitors, or if it can be
> triggered only by the time, even if the radio containing those capacitors
> was left unpowered for years.

First, note that two common types of silver mica capacitors are found in
boatanchor radios.  First came molded mica capacitors, mostly seen as
the "postage-stamp" type.  As their name implies, a plastic body was
molded over a naked capacitor assembly (generally, with leads arranged
axially).

<snip>