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What can you tell me about paper capacitors?

Discussion in 'General Electronics Discussion' started by {cog}, Sep 15, 2016.

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  1. {cog}

    {cog}

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    Sep 5, 2015
    So, recently I acquired an old synth organ from the 70's. A lot of the features aren't working but I'm hoping I can fix it up. Anyways, I vaguely remember hearing about paper capacitors becoming acidic with age and losing their capacitance. So I'm thinking they may be the culprit.

    Could I just go through and replace them all with film or electrolytic capacitors of equal capacitance? I tested one and it seems to be way off on its capacitance, should I just assume all of them are bad or is there a chance some are still good? Is there anything else I should know?
     

    Attached Files:

  2. alfa88

    alfa88

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    4
    Dec 1, 2010
    If it were my project I'd bite the bullet and replace all the caps. 40 years is a long time. Don't expect miracles but it's definitely a good start. Hopefully you have a schematic.
     
    davenn likes this.
  3. 73's de Edd

    73's de Edd

    2,944
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    Aug 21, 2015
    Sir {cog} . . . . . . .

    That which you show, I find to be a DAMN good capacitor,
    HOWEVER, if you find any of THESE.
    They are at the top of the list of the ROGUES GALLERY of bad capacitors . . . .they DEFINE
    the conditions of bad capacitors of their type.

    EXAMPLES:

    bad capacitors.png


    73's de Edd
     
    Last edited by a moderator: Sep 16, 2016
    hevans1944 likes this.
  4. davenn

    davenn Moderator

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    1,892
    Sep 5, 2009
    that isn't a paper capacitor and you cannot replace that style with electro's
    paper caps are like the three you see at the bottom of pic in Edd's post

    there shouldn't be anything wrong with the style you have shown, their failure is pretty rare
    show us a photo or 2 of the circuit boards and we can point out the likely suspects


    Dave
     
    hevans1944 likes this.
  5. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Actually, ALL the capacitors in Edd's post are wax-impregnated paper capacitors. Don't be fooled by their encapsulation in plastic.
     
  6. davenn

    davenn Moderator

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    Sep 5, 2009
    most probably, I was pointing out the obvious ones for the OP ;)

    tho the 4 top left ones more remind me of the old resistors or inductors :)
     
  7. Chemelec

    Chemelec

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    Jul 12, 2016

    That looks like a Polystyrene capacitor.

    They are Best for High end Audio equipment.
     
  8. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Geez, Dave... you are OLD!:D I remember my first encounter with molded inductors, too. Couldn't make out head nor tails of what the markings meant, so probably just "filed" them away as miscellaneous as I was salvaging parts from discarded radios and televisions in the 1950s to pursue my "electronics hobby". It was many years later that I discovered the discarded parts were actually inductors. Still haven't learned how to read their color-codes though... easier to just whip out an LCR meter and measure,

    Many thanks to @73's de Edd for posting the image. It does bring back memories, mostly long forgotten until now.

    Here is a quote from this website:

    • Old paper/wax capacitors are one of the most unreliable parts in an old radio. Don't let "molded" paper capacitors fool you. They are just paper capacitors in plastic cases and are just as unreliable as the ones coated in wax. Molded paper caps were sold under trade-names such as Bumble Bee, Black Cats, Black Beauty, Pyamid, Goodall, etc.

    I looked this up because, until Edd posted his images, I was under the mistaken impression that Sprague Black Beauty capacitors were "a cut above" the others of their genre. Nope, just better protected from the environment... until they "crack open like a peanut" or, in some cases apparently, explode.

    Avoid, and/or replace, all paper capacitors. Ignore the audiophiles with "golden ears" who think it's worth paying big bux for ancient, new old-stock (NOS), Black Beauty, Bumblebee, and the like paper capacitors. See also this 2004 EDN article.

    73 de AC8NS
    Hop
     
    davenn likes this.
  9. BobK

    BobK

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    Jan 5, 2010
    Wow, I am picturing the old TVs (B&W) that I picked up by the side of the road to either repair or harvest parts. Harvesting was easier in those days, with point-to-point wiring, just snip them off.

    Bob
     
    davenn and hevans1944 like this.
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