"Chuck Harris" wrote in
message ...
Richard Knoppow wrote:

All the BBs I've seen had colored stripes indicating
the capacitance value and other data. These were dry
caps. Not dried out oil-filled, there was no trace of oil
or means of adding it.

Richard, All BB's with color bands made in the late 40's,
through the '50s were oil filled. The filler was not all
that obvious unless you knew what you were looking at. It
looks like a little solder ball on the banded lead where
it enters the case. The cases look like bakelite, but I
am
not sure that they are. Bakelite requires high
temperature
and high pressure to cure (hence the "bake"). I don't
think
that would be good for a plastic dielectric capacitor.

By the early '60s Sprague had thoroughly taken a drubbing
over
the failures of the BB's, and changed them to be a plastic
dielectric, like the OD's.

I don't think I have ever found a bad OD; nor have I ever
found
a bad BB that wasn't of the oil filled variety.

-Chuck

Well, I don't know. The BB's I've gotten from Hammarlund
receivers and some other equipment date from the mid 1950's
and are definitely not oil-filled nor do they have the
filler tubes. I've taken them apart: the dielectric is paper
impregnated with plastic. It looks a little like the very
fine paper used in Chinese cooking, thin and translucent.
These all have stripes on them and no printing. Some of
these have a thick end from the way the end leads are
fastened to the foil. I really think there must have been
two versions of the BB series. Perhaps the plastic type was
a replacement for the oil-filled kind. They would have been
easier to make and free from leakage.
All the BBs I've check on a capacitance bridge, even
those which appear new, have somewhat low capacitance and
somewhat high dissipation factor. Of course, both could be
accounted for if they were actually oil filled and the oil
is gone to the extent of leaving no trace whatever. It would
be interesting to know what the molded cases were actually
made of. The material does not quite look like Bakelite but
there were many variations of resins sold as Bakelite and
under other names like Durez. Old catalogue date could
answer some of these questions.


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Richard Knoppow
Los Angeles, CA, USA