Richard Knoppow wrote:
"Chuck Harris" wrote in

The BB's are all bad by now, and should be replaced on
sight, but when
they were new, they were a nice high performance
capacitor.

-Chuck

OK about the ceramics. I think there must have been two
series of Black Beauty caps. Not all are oil filled. The
ones I removed from an SP-600-JX for instance, are paper
impregnated with polyester plastic. They are dry and don't
have filler tubes. I suspect the main failure mode for these
is due to the incapsulation. Many seem to have cracked and
even those which have not cracked often have low capacitance
and high dissipation factor. The capacitor winding is
usually physically distorted, flattened for instance. I
suspect that the case shrinks distoring it and also may
allow moisture to enter. These caps were supposed to be much
better than the wax coated paper caps of the time.
Sprague also made a similar capacitor, that is a dry
polyester impregnated paper cap, but in epoxy-dipped casings
called Orange Drops. AFAIK, these have proven quite reliable
and long lived, giving some support to my idea that it was
the molded cases of the BBs that failed.
BBs are found in a lot of high-quality equipment,
General Radio, Hewlett-Packard, etc, used a lot of them.

There are Black Beauties, and there are Black Beauties!

The oil filled Black Beauties, in my experience, always have
color coded bands that tell the ratings. They were a premium
capacitor, and as such were quite expensive.

The polyester dielectric capacitors have black bodies, with
red lettering. I recall that they came out after the oil
filled capacitors.

Orange drops were a step up from the waxed paper capacitors,
and a step down from the molded polyester black beauties.
They were designed especially for printed circuit board use.
Orange drops were a relatively cheap "jobber" capacitor, but
they have certainly withstood the test of time quite well.

-Chuck