[AMRadio] old round aluminum filter Capacitors

Joe A. Taylor n4nas1 at hotmail.com
Wed Nov 1 11:07:39 EST 2006

   I worked for P. R. Mallory Capacitor Company about 45 years ago and we
   made  all  sorts  of  capacitors including the extruded aluminum cans,
   both  AC and DC units.  I don't remember any screen material in any of
   them.    Inside  was  etched aluminum foil rated at specific voltages.
   The  foil  was split into needed widths, cut to needed length and tabs
   attached.  This was matched with slightly wider paper and a non-etched
   aluminum   foil   length   added  to  the  other  side  of  the  paper
   insulations.  "Rollers" would roll this foil and paper sandwich into a
   roll.   The  raw  roll was then immersed in electrolyte solution, ours
   was  glycol  based,  akin to car antifreeze, and once saturated, a low
   voltage  was applied with voltage increasing over time until the units
   were  "aged".   Faulty units were trashed.   Good units were canned in
   aluminum  cans  using  black  tar to hold them in place.  Bottoms were
   sealed  and  tabs soldered or spot-welded to terminals.  I was part of
   Quality  control  so I got to "blow them up".    Maybe this summary is

   Joe Taylor  N4NAS,  Glasgow, KY

     From:  Jack Schmidling <jack at schmidling.com>
     Reply-To:  Discussion   of   AM   Radio   in  the  Amateur  Service
     <amradio at mailman.qth.net>
     To:  Discussion    of    AM    Radio   in   the   Amateur   Service
     <amradio at mailman.qth.net>
     Subject:  Re: [AMRadio] old round aluminum filter Capacitors
     Date:  Wed, 01 Nov 2006 09:44:00 -0600
     >John E. Coleman (ARS WA5BXO) wrote:
     >>What was in these things?  The inside of the can is lined with a
     >>brittle screen perhaps some carbon stuff. The center post is
     >>connected to a
     >>foil which is wound in a spiral.  I don't think it is laminated
     >Not sure just what you have but electrolytics are/were made by a
     >process that produced the dielectric when fired up.  The foil was
     >uninsulated and immersed in a chemical soup that coated the foil
     >with a very thin layer of dielectric when activated.  It's
     >electro/chemical magic.

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