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Wax covered capacitors from the 1950s

Discussion in 'Electronic Repair' started by n cook, Jul 17, 2006.

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  1. n cook

    n cook Guest

    Proudly stating "British Made"
    What makes all those yellow tubular wax covered caps, Dubilier type 460, TCC
    type 343, 645 etc 300V to 750V caps in range 1 to 100nF go so leaky ? Is it
    the wax is actually hygroscopic and absorbs water vapour over time. ?
    On DVM resistance scale in Meg ohms but on a Megger then as low as 50Kohm.
  2. These were the start of planned obsolescence :)
    My guess is the wax as you say or bad manufacturing process.
  3. Steven

    Steven Guest

    You can't top my nym of Dr. Antichrist PhD though. Well it could be fun
    to make a dash at it...

    The concept of planned obsolescence was made feasible and completely
    successful by the last 40 years of my life.
  4. Paul Sherwin

    Paul Sherwin Guest

    Yes, the wax is hygroscopic. The problem isn't restricted to British caps,
    most non-tropicalised consumer grade paper caps from the 40s and 50s will
    be leaky now.

  5. n cook

    n cook Guest

    If they were not wax covered would they still have been be problematic ?
    Understandable in a damp environment but indoors would dampness get in the
    paper and not evaporate again if not waxed, the use of wax sealing the
    dampness/vapour/condensate insde each cap?
  6. Syl

    Syl Guest

    ALL paper caps go bad with time, whether they are "tropicalized" or sealed
    like the infamous Black Beauty.

    Oil caps on the other hand have a pretty good lifetime. I have a Russian
    made radio and the sealed oil caps are still good.
    There are no paper/wax caps in that radio. Parts are military grade, and I
    mean military grade.


  7. Some of the wax boils away over time, and they made the capacitors
    out of what was available at the time. Thermal cycling will let
    moisture into the capacitor as the coating starts to break down.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  8. nesesu

    nesesu Guest

    The leakage is not an issue of moisture migrating into the capacitor
    'jellyroll' slug directly, but once there is some moisture in the slug
    in combination with the sulphites in the kraft paper, they promote
    aluminum ions of the foil in the slug to begin to migrate into the
    paper dielectric. These ions eventually cause leakage paths to form
    through the paper, or worse, cause a moderately high conductive path
    that, with a high bias voltage, will cause it to carbonize and cause a
    high leakage path or full short. If the cap moves to a dry location the
    moisture theoretically will migrate out again, but the ionic migration
    does not reverse--just slows down.
    The "tropical" wax that I use in paper cap rebuilding may be somewhat
    better than the 'filled' potting and slug waxes of consumer grade paper
    caps, but it's main difference is the anti-fungicides it contains to
    delay the formation of molds and mill-dew on the organic components.

    Neil S.
  9. n cook

    n cook Guest

  10. N. Cook-

    Neil pegged it. It isn't the wax that is hygroscopic as much as the paper
    used as a dielectric in such capacitors made until the late 50s.

    As a teenager, I had collected boxes of components by canibalizing
    equipment from a local Radio-TV repairman's trash bin. When I saved up
    enough money to buy a multimeter, I found that over 90 percent of the
    paper capacitors were leaky, and may have been the cause of the equipment
    failure. I learned quickly that the first step in repairing old radios,
    was to replace all the paper capacitors.

    Somewhere around 1957, the capacitor companys started using plastic
    dielectric, sometimes in combination with paper. Names like "Mylar",
    "Dipped Mylar" and "Paper-Mylar" were used to describe these newer
    capacitors. From my viewpoint, that marked a turning point in the
    reliability of electronic circuits.

    I understand that some people who restore antique radios, will use the
    case of a paper capacitor, replace the core with a mylar capacitor and
    seal it again with wax.

  11. I wonder if this is part of what kills a supposedly better-sealed
    "Black Beauty" (paper cap sealed in a molded plastic capsule)?
  12. Phil Nelson

    Phil Nelson Guest

    I understand that some people who restore antique radios, will use the
    For more details on capacitor replacement (including restuffing), you can


    Phil Nelson
    Phil's Old Radios
  13. nesesu

    nesesu Guest

    Fred, if you are interested, I can send a series of photos showing the
    process I use in restuffing old cardboard cased paper caps and a new
    process I use to make brand new cardboard cases, since I am running out
    of old cap cases in some sizes, to restuff.
    It is really annoying when recapping a worthwhile set to find that 3 or
    4 original cardboard cased caps have been replaced with plastic or
    ceramic cased replacements that are bad, but cannot easily be cleaned
    out for restuffing and are, in any case, non-OEM, so I developed a
    simple method of making new shells of any regular size.

    Neil S.
  14. n cook

    n cook Guest

  15. Gary Tayman

    Gary Tayman Guest

    In regards to these "cottage industries", is there anybody out there selling
    "new" OEM resistors and capacitors?

    Among my many, many future projects is my Atwater Kent 60. In the process
    of fixing it up, just about all the carbon resistors have been replaced.
    These are white ceramic with soldered ends. I've kept the old ones, with
    the high hopes that one day I'll try to make some sort of reproduction that
    can go back in the radio. If somebody is selling these I may be interested.
  16. nesesu

    nesesu Guest

    Actually, I usually paint them with the BED colour code after bending
    the leads at a sharp right angle and adding some epoxy on each end to
    give the 'dogbone' radial leaded shape.
    [BED= Body-End-Dot coding that was common just before the colourbanding
    became common.]

    Neil S.

  17. Yo Syl ... what happened to your website?.. went to look at your bit about
    making new old resistors.. the tech stuff won't work on the site..

    John k9uwa

  18. Our own Syl Vanier did that. I saw the procedure documented on his

    That right there convinced me he had totally lost his mind. ;)
  19. Syl

    Syl Guest

    Hi John,

    Restructuring the website. Will be done in a few dayz. You can still access
    previous interface here:

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