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WTB: Sprague Black Beauty Caps

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Jeff Stapleton

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Oct 26, 2002, 10:52:00 PM10/26/02
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Looking for some NOS or even used in good shape Sprague Black Beuty caps in
the following values:

- .02uF / .022uF either 400 or 600V
- .01uF / .015uF either 400 or 600V
- .033uF either 400V or 600V

Let me know what you have and your asking price.

--
Jeff Stapleton
j...@megsinet.net


Jimmie Stewart

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Oct 27, 2002, 1:57:20 AM10/27/02
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Can you tell me WHY even NOS ones are bad.

Jimmie

Jeff Stapleton <j...@megsinet.net> wrote in message
news:3dbb54ca$0$1458$1dc6...@news.corecomm.net...


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michael Mueller

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Oct 27, 2002, 12:30:00 PM10/27/02
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I have a dozen pulls from my st-70 and Mk3 rebuild's
make offer???
Mike M

Chuck Harris

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Oct 27, 2002, 2:53:10 PM10/27/02
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Tektronix scopes were the first place I ever came across
Black Beauty caps. I was rehabing a 513D scope,
and EVERY ONE WAS BAD!. They all leaked oil, and they all
had high DC leakage.

I asked an engineer at Tektronix why they used such junk,
and they said it was because Mallory did something to make
one of the owners mad, and he swore that Tektronix would never
ever buy anything made by Mallory.

He explained to me why the BB caps fail.

If you look carefully at the banded end of the
BB cap, you will see a thicker area of the lead right up
against the black body. That is actually a piece of brass
tubing. When the caps are made, the oil is injected into
that tube, and then the lead is fitted in the hole, and soldered
to form the seal. When you solder the leads on the cap, if you
don't use a heatsink, enough heat travels up the lead to melt
the solder, and make a cold joint. The oil will then leak
out. The capacitor will then fail at some future point.

Tek used the caps on terminal boards, and the solder joints
were 1/4" or so from the ends of the caps, so all of their older
scopes failed this way, until they learned to heat sink the leads.

Even if you didn't kill the cap by soldering, the plastic will
eventually shrink a little bit, breaking the seal between the tube
and the body creating a leak. This makes NOS caps a problem.

I wouldn't even consider even for one minute using a NOS Black Beauty cap.
There are so many vastly superior caps available.

-Chuck

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