[ARC5] Re-stuffed cap

[J. Forster]

> Later this evening, I'll post the article and photos of my latest
> re-stuffing job
> to my website.
>
> Although this first attempt looks "acceptable" and works well, it does not
> look
> as good as I think I can make them. I would like to make them look
> identical
> with the originals, but may not be able to.
>
> I am working on another one, which, by the way, was made by Aerovox. The
> previous one was made by Sprague. Both appear to have been built
> identically, probably according to either A.R.C. or military
> specifications.
>
> However, the Aerovox cap was MUCH more deteriorated, both internally and
> externally, than the Sprague. All the individual caps in the Aerovox cap
> were
> completely "soaked" in green corrosion, and the connections to the ends
> were all loose. They ALL came loose with a very slight tug on the leads,
> and
> the interior of the brass pot was covered in green corrosion, which was
> very
> difficult to clean out.
>
> I have tested the Sprague cap that I finished, and have found some
> interesting things:
>
> 1) there is considerable capacitance measurable BETWEEN each of the
> three disk ceramics, even the "outside" two, in the restuffed cap: about
> 0.025
> mfd between EACH 0.05 mfd cap, almost exactly 1/2 of the capacitance of
> each individual cap. I installed all three disc ceramics "facing" the same
> way.
> In the next one, I'll reverse the center one to see if that makes any
> difference.

It won't. The capacitors are in series. You are not measuring stray
capacitance, but the two caps in series, and it's entirely predictable the
value should be C/2.

> 2) When measuring the originals, there was ALSO just about 1/2 the rated
> capacitance between each of the paper caps. I wonder if this was a
> "designed-in" feature of the original circuitry? If it was, i wonder what
> its purpose was intended to be? Maybe it doesn't matter?

See above. Entirely predictable.

> 3) There is no measurable leakage at 450 VDC (the upper limit for my C-3)
> between any of the three caps. The capacitances between them, again
> 0.025 mfd, have identical leakage as that of each individual
> cap....essentially none.

So, why re-stuff them?

> 4) Although I did this first job in several sessions, I suspect that if I
> were to sit
> down and complete one, from start to finish, it would take a little over 1
> hour
> apiece.
>
> Does anyone know that these brass pots were plated with? Zinc? Some
> other metal?

Cadmium, most likely.

-John

============

> Is it worth it? I don't know, but it is certainly interesting...
>
> Ken W7EKB