mica capacitor substitutes

Discussion in 'Electronic Repair' started by Johan Wagener, May 4, 2004.

  1. 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?
    Johan Wagener, May 4, 2004
    #1
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  2. Johan Wagener

    Joerg Guest

    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
    http://www.analogconsultants.com
    Joerg, May 4, 2004
    #2
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  3. On Tue, 04 May 2004 20:19:33 GMT, Joerg
    <> wrote:

    >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??
    --

    The BBC: licenced at public expense to spread lies.
    Paul Burridge, May 4, 2004
    #3
  4. Johan Wagener

    Ken Smith Guest

    In article <>,
    Johan Wagener <> wrote:
    >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?


    --
    --
    forging knowledge
    Ken Smith, May 5, 2004
    #4
  5. Johan Wagener

    John Larkin Guest

    On Tue, 04 May 2004 23:52:19 +0100, Paul Burridge
    <1.co.uk> wrote:

    >On Tue, 04 May 2004 20:19:33 GMT, Joerg
    ><> wrote:
    >
    >>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??


    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
    John Larkin, May 5, 2004
    #5
  6. Johan Wagener

    Joerg Guest

    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
    http://www.analogconsultants.com
    Joerg, May 5, 2004
    #6
  7. Johan Wagener

    Joerg Guest

    Joerg, May 5, 2004
    #7
  8. Johan Wagener

    Tom Bruhns Guest

    (Johan Wagener) wrote in message news:<>...
    > 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
    Tom Bruhns, May 5, 2004
    #8
  9. Johan Wagener

    Frank Miles Guest

    In article <>,
    Paul Burridge <1.co.uk> wrote:
    >On Tue, 04 May 2004 20:19:33 GMT, Joerg
    ><> wrote:
    >
    >>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??


    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
    --
    Frank Miles, May 5, 2004
    #9
  10. Johan Wagener

    Jim Adney Guest

    On 4 May 2004 12:44:09 -0700 (Johan
    Wagener) wrote:

    >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.

    -
    -----------------------------------------------
    Jim Adney
    Madison, WI 53711 USA
    -----------------------------------------------
    Jim Adney, May 6, 2004
    #10
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