Jim Adney wrote:



What's the difference between a silver mica cap and a plain old mica cap?
Is there any? I mean with respect to size, performance, stability, voltage
ratings, etc. Where would one be used instead of the other?


I believe these are just 2 different names for the same thing. Silver
mica caps come in various cases, and those cases have varied over the
decades, but they've always consisted of a mica wafer plated on each
side.

I've never seen a manufacturer's catalog that made this distinction.

Oh, no. Not at all true. Before about say 1940, mica caps were truly a
sandwich of simple alternating metal plates and mica insulators. About
1950-ish they began 'plating' the mica.
Silvering is a mixed blessing. Many of the original silvered-mica caps
now exhibit migration (leakage) problems.
It doesn't go without noting that in the 50s mica caps were not at all
en vogue. Precision caps went thru an era where the ceramic (silvered)
dogbone style were the most common.

Nowadays, I'm not sure exactly what it is I'm buying when I buy the
"dipped mica" caps. I'm confident to say they are better than the
old-timers but are they silver plated onto mica or what?

-Bill