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Old July 17th 05, 07:22 PM
Z.Z.
 
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Default 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...

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Old July 17th 05, 07:36 PM
Henry Kolesnik
 
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Silver micas cost more and had a better spec for capacitance, temperature as
well as aging and are used in circuits where you want to minimize frequency
drift.
IIRC silver was plated somehow onto the higher grade mica whereas ordinary
micas used a lower grade o f mica and weren't plated or plated as well.

--

73
Hank WD5JFR
"Z.Z." wrote in message
...
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...



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Old July 18th 05, 05:18 AM
Jim Adney
 
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On Sun, 17 Jul 2005 18:22:54 GMT "Z.Z." 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.

The little mica compression variables would be an exception, as those
are not plated, but I suspect you're not asking about those.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
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Old July 18th 05, 06:15 AM
-ex-
 
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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
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Old July 18th 05, 02:39 PM
straydog
 
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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






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Old July 21st 05, 02:06 AM
Jim Adney
 
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On Mon, 18 Jul 2005 01:15:24 -0400 -ex- wrote:

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?


They are plated, but I don't know for sure that there is any sliver in
the process. Perhaps there never was....

I share your confidence, but only time will tell for sure.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------
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Old July 23rd 05, 11:03 AM
doug dwyer
 
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In message , Jim Adney
writes
On Mon, 18 Jul 2005 01:15:24 -0400 -ex- wrote:

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?


They are plated, but I don't know for sure that there is any sliver in
the process. Perhaps there never was....

I share your confidence, but only time will tell for sure.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

Mica used to be cleaved and plated then a lower costt mica reconstituted
was employed all were silver evaporated.
Dipped refers to the encapsulation.
Low values had their tc altered by the encapsulation material.
Modern npo ceramic chips are Much? Better. Also some porcelain are the
best for Q ie loss.
--
dd
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Old July 24th 05, 05:10 PM
Jim Adney
 
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On Sat, 23 Jul 2005 11:03:55 +0100 doug dwyer
wrote:

then a lower costt mica reconstituted
was employed all were silver evaporated.


Was that "Microy?"

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------


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