mica capacitor substitutes

[Johan Wagener]

I simply can't buy silvered mica caps in south africa. They cost more
than the output transistors.

I need them for an amplifier project.

What do I do?

 

[Joerg]

Hi Johan,

Can't you use polyester or other film type caps? Or maybe if you need a
lot of them order internationally from Digikey or one of those places?
When I lived in Europe I sometimes had stuff shipped from the US and it
wasn't a big deal unless you want fast airmail service, but even then it
was ok for smaller parts.

For small qties my solution was very often to scavenge them out of an old
radio or TV. One that was at least 20 years old because the new ones only
have ceramics and electrolytics.

Regards, Joerg

 

[Paul Burridge]

Hi Johan,

Can't you use polyester or other film type caps? Or maybe if you need a
lot of them order internationally from Digikey or one of those places?
When I lived in Europe I sometimes had stuff shipped from the US and it
wasn't a big deal unless you want fast airmail service, but even then it
was ok for smaller parts.

For small qties my solution was very often to scavenge them out of an old
radio or TV. One that was at least 20 years old because the new ones only
have ceramics and electrolytics.

Anyone know why it is that mica and polystyrene types are becoming so
hard to find? Is there a shortage of mica and polystyrene??

 

[Ken Smith]

I simply can't buy silvered mica caps in south africa. They cost more
than the output transistors.

I need them for an amplifier project.

What do I do?

Move?

Use NPO ceramic?

 

[John Larkin]

Anyone know why it is that mica and polystyrene types are becoming so
hard to find? Is there a shortage of mica and polystyrene??

Somebody in Japan, I think, quit making the polystyrene film. There's
still lots of mica in the ground, but these caps are labor-intensive
to fabricate, and NPO ceramics work as well (better, maybe: mica has
nasty dielectric absorption.) I think some big transmitting caps may
still be mica.

Mica is still used to insulate the heater elements in toasters, last
time I looked. Somebody does make surface-mount mica caps, I think!

John

 

[Joerg]

Hi Paul,

Besides Japan there had also been a rumor or maybe even story in the press
that Bayer might discontinue some type of film. But there are alternatives.

Regards, Joerg

 

[Joerg]

Hi Paul,

This is an older article but it seems the folks from Bayer and others are
instilling some hope here:

http://www.manufacturing.net/pur/article/CA139284

Regards, Joerg

 

[Tom Bruhns]

I simply can't buy silvered mica caps in south africa. They cost more
than the output transistors.

I need them for an amplifier project.

What do I do?

You didn't mention why you're looking specifically for silvered mica,
nor what ratings (capacitance, voltage, tolerance). Likely candidates
are C0G (NPO) ceramics and polypropylenes. The ceramics give very
good stability, but that's not likely needed in an amplifier. If it's
for frequencies less than a couple MHz, polypropylene should work
well; they have low dissipation factor and can handle fairly high
currents. If they will be handling much current, the polyprops should
be much better than polyester (Mylar). If it's for high RF current,
there are transmitting-type capacitors that can do the job, but they
won't be cheap, most likely.

Paul: Polystyrene are absolutely awful to deal with in automated
assembly processes. They can't take the heat. And there are other
caps that work fine that cover what needs to be done. That's why.

Cheers,
Tom

 

[Frank Miles]

Anyone know why it is that mica and polystyrene types are becoming so
hard to find? Is there a shortage of mica and polystyrene??

The low melting temperature has a lot to do with polystyrene's demise.
Too bad, they have some nice properties. Can't put those through the
machines, though -- have to be hand-soldered.

Mica, which pricy, is still available from places like DigiKey.

-frank
--

 

[Jim Adney]

I simply can't buy silvered mica caps in south africa. They cost more
than the output transistors.

I need them for an amplifier project.

If this is just an amplifier, then any kind of plastic film capacitor
would work just as well.

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