On a sunny day (Sun, 16 May 2004 21:16:23 +0100) it happened Joe McElvenney
wrote in :

Hi,

Have a look at the 'Mica' section of this -

http://my.execpc.com/~endlr/misc__dielectrics.html

It won't answer your question but should give you an idea as to
why that particular dielectric should be avoided in certain
situations.


Cheers - Joe


Nice page, I like these oldies, remind me of the past:
http://www.orenelliottproducts.com/capacito.htm
JP

"Steve Kavanagh" wrote in message
om...
A year or so ago I was working on a microwave local oscillator (at
about 2.5 GHz) multiplied up from a crystal oscillator near 40 MHz.
The output was found to jump in frequency by tens or hundreds of Hz
many times as the LO chain was warming up. I was able to reduce this
jumping by replacing all the dipped silver mica capacitors [...snip]

The capacitors used in both cases are from unknown sources and were
probably manufactured in the early 1980's.
Has anyone else experienced this behaviour ?
Steve (VE3SMA)

Steve,
Although I didn't figure it out at the time, my Knight-Kit Space Spanner
circa 1960 had terrible microphonics - very noisy. I cleaned the entire
chassis & rewired it to no avail. Today I suspect a mica cap, the old
square type, since I heard of same thing this some time ago.

"Steve Kavanagh" wrote in message
om...
A year or so ago I was working on a microwave local oscillator (at
about 2.5 GHz) multiplied up from a crystal oscillator near 40 MHz.
The output was found to jump in frequency by tens or hundreds of Hz
many times as the LO chain was warming up. I was able to reduce this
jumping by replacing all the dipped silver mica capacitors [...snip]

The capacitors used in both cases are from unknown sources and were
probably manufactured in the early 1980's.
Has anyone else experienced this behaviour ?
Steve (VE3SMA)

Steve,
Although I didn't figure it out at the time, my Knight-Kit Space Spanner
circa 1960 had terrible microphonics - very noisy. I cleaned the entire
chassis & rewired it to no avail. Today I suspect a mica cap, the old
square type, since I heard of same thing this some time ago.

In article ,
Steve Kavanagh wrote:
[...]
I have just been observing the same sort of frequent jumping behaviour
(up to a kHz or so at a time) in another local oscillator (output at
about 10.5 GHz, phase locked to a crystal oscillator around 100 MHz).
I note that this one also has dipped silver mica caps in the crystal
oscillator and I wonder if it too would be improved by replacing them
with NP0 ceramics.

Do the silver mica caps say "made in china" on them? Are they a light tan
color? If either of these are true chances are you will get a better cap
made from ear wax and tin foil. Somewhere in China there was, and perhaps
still is a factory, that made silver mica caps that change value if you
squeeze them between your fingers and go open if you heat cycle them.

I've never had much trouble with CDE caps.

--
--
forging knowledge

In article ,
Steve Kavanagh wrote:
[...]
I have just been observing the same sort of frequent jumping behaviour
(up to a kHz or so at a time) in another local oscillator (output at
about 10.5 GHz, phase locked to a crystal oscillator around 100 MHz).
I note that this one also has dipped silver mica caps in the crystal
oscillator and I wonder if it too would be improved by replacing them
with NP0 ceramics.

Do the silver mica caps say "made in china" on them? Are they a light tan
color? If either of these are true chances are you will get a better cap
made from ear wax and tin foil. Somewhere in China there was, and perhaps
still is a factory, that made silver mica caps that change value if you
squeeze them between your fingers and go open if you heat cycle them.

I've never had much trouble with CDE caps.

--
--
forging knowledge

On 16 May 2004 07:06:24 -0700 (Steve
Kavanagh) wrote:

The capacitors used in both cases are from unknown sources and were
probably manufactured in the early 1980's.

That may be the secret here. In the past, I've used silver mica caps
in a number of applications with positive results. The only problem
I've ever seen with good quality ones was a single one in a 40 year
old HP amplifier that had become leaky.

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

On 16 May 2004 07:06:24 -0700 (Steve
Kavanagh) wrote:

The capacitors used in both cases are from unknown sources and were
probably manufactured in the early 1980's.

That may be the secret here. In the past, I've used silver mica caps
in a number of applications with positive results. The only problem
I've ever seen with good quality ones was a single one in a 40 year
old HP amplifier that had become leaky.

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

"Jim Adney" wrote in message
...
On 16 May 2004 07:06:24 -0700 (Steve
Kavanagh) wrote:

The capacitors used in both cases are from unknown sources and were
probably manufactured in the early 1980's.

That may be the secret here. In the past, I've used silver mica caps
in a number of applications with positive results. The only problem
I've ever seen with good quality ones was a single one in a 40 year
old HP amplifier that had become leaky.

If silvered mica caps are so crappy, why did they ever use them in
the first place?

Thanks,
Rich

"Jim Adney" wrote in message
...
On 16 May 2004 07:06:24 -0700 (Steve
Kavanagh) wrote:

The capacitors used in both cases are from unknown sources and were
probably manufactured in the early 1980's.

That may be the secret here. In the past, I've used silver mica caps
in a number of applications with positive results. The only problem
I've ever seen with good quality ones was a single one in a 40 year
old HP amplifier that had become leaky.

If silvered mica caps are so crappy, why did they ever use them in
the first place?

Thanks,
Rich

Space Spanner.. O'Man, I could only afford the Ocean Hopper.. Man, them
were the days!

Joel AG4QC

"Steve Nosko" wrote in message
...

Steve,
Although I didn't figure it out at the time, my Knight-Kit Space
Spanner
circa 1960 had terrible microphonics - very noisy. I cleaned the entire
chassis & rewired it to no avail. Today I suspect a mica cap, the old
square type, since I heard of same thing this some time ago.