On Sun, 17 Jul 2005, Z.Z. wrote:

Date: Sun, 17 Jul 2005 18:22:54 GMT
From: Z.Z.
Newsgroups: rec.radio.amateur.homebrew
Subject: Silver Mica vs Mica Caps

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?

Thanks...


Yes, there is a difference and catalogs should say "silver mica" and if
they don't then they are not silver mica. Today's sales people may not be
techie literate and so today's catalogs may be less accurate. Silver micas
were a little more expensive, too.

Besides a higher price, the overall performance specs were better besides
haveing lower losses and better accuracy. Most of the time, silver micas
were meant for free-running VFO circuits (IIRC) because you wanted thermal
stability and as little losses to lead to heat which would cause drift.

However, if you wanted to be clever, you would get a set of negative
temperature coefficient capacitors and use them to balance out the (all
the rest of them) positive temperature coefficient capacitors and thus
arive at a very low warm-up drift free running VFO.

I'm from the old days. Today, its all phase-locked-loop VFOs and "throw
away" rigs when they break (nobody fixes stuff anymore [pardon my
exageration]).

Art, W4PON