I had a job in the Summer of 1971 repairing tape recorders and
special phonographs in our state's Visual Services department.
The phonographs were special in that they played records that
ran at 8-and-1/3 RPM and contained Talking Books for the blind
but the electronics were much like any low-end phonograph of the
day, a piezoelectric pickup and a 2-watt or so audio amplifier.

	During that Summer, all of the solid-state phonographs
which had been issued to patrons of the agency were recalled
because the electrolytic caps which were rated at 1000uF at 35
volts were exploding like popcorn.

	In fact, the recall was almost not necessary as the
customers were more than glad to send in their machines after
the big bang, a buzzing from the loudspeaker, and the inability
to play the Talking Books.

	When I started working there, there were boxes of the
now removed bad caps and each machine was given new life by
replacing the bad one with a better cap.

	Interestingly enough, the bad ones were not all bad.
They were going to discard all of them and I asked if I could
have some with the idea of running them at a lower voltage. I
used many of them in various projects, some for almost 40 years,
and didn't have a bit of trouble but my luck finally ran out one
day.

	I think now, the problem was probably some sort of
manufacturing defect that caused holes in the dielectric so one
would randomly get hold of one of those caps that was shorted to
begin with and, boy, did things go down hill fast.

	I had built a power supply with two of these caps and
had just switched it on. The output voltage was about half what
it should be. I had about enough time to say to myself, "Hmm.
Why is the voltage---!"

	At that moment, this thumb-sized capacitor popped like a
shotgun shell and disgorged more aluminum foil than one would
think could have even fit in that case.

	It even looked like a spent shotgun shell and I found
pieces of it as much as 6 months later. That's what I get for
being cheap. When you're a student, one tends to do such things.

	When you are grown and mature, you remove good
electrolytics from stuff that failed for some other reason.

Martin

Joe McCauley writes:
> A good find Russell. I was trying to explain this to some students last=20
> week, but could tell they were sceptical.
--=20
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