"COLIN LAMB" wrote in message
...
And, Phil's website is as good and concise as it gets
about replacing capacitors. See
http://antiqueradio.org/recap.htm

Even if you have been doing it for years, you will
appreciate Phil's nice writing style and useful
information.

And, a big fat A for taking the time to help spread his
wisdom, learned from years of experience.

Even after years of repairing radios, we learn that we can
do it better. A few years ago I was going to replace a
paper cap in a 17 tube receiver. I do them one at a time.
I clipped the old one out, got a phone call and dinner
call and shut the soldering iron off and left. I was not
able to return to the work for about a month. By then, I
knew there was a capacitor out - but I had clipped the old
leads off and it took me an hour of tracing and schematic
reading before I could determine where the missing
capacitor was. Now, I am more methodical and make notes
before I clip the capacitor. A notebook and pencil are
always nearby to document before I start work. Life has
been much simpler since then. And, it really is a good
idea to test the radio after a maximum number of changes.

Colin K7FM
I will add to what is on this page that the flat molded
caps are often also mica types, however, they are not
silvered micas. They are simply stacks of alternating mica
dielectric and foil plates. They are not as reliable or high
performance as silvered micas and should be checked. These
were used mostly in high voltage applications or where waxed
paper had too much loss.
Black Beauty caps are not exactly paper dielectric but
used paper impregnated with a polyester. They _should_ have
been low loss and quite reliable but became notorious within
a few years of their manufacture for developing high losses.
I suspect this may have been due to some problem with the
molded casing because Sprague sold capacotors with a similar
construction but in dipped epoxy casing as Orange Drops and
I have not heard that they shared the same short life
problems.
BTW, while silvered mica caps are generally very
reliable they can still go bad. I've had to replace quite a
few in rebuilding a couple of SP-600-JX's due to
instability. Here again all were molded bakelite cases so I
suspect either the case or perhaps end connections. Again,
the dipped epoxy mica caps do not seem to suffer from this
problem.


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Richard Knoppow
Los Angeles, CA, USA