[Milsurplus] Micamold Recovery

[J. Forster]

Yes.

I'd bake them at a lower temperature, more like 150F, for a lot longer,
maybe 12 to 24 hours. Possibly even 48 hours. Getting the moisture out is
a diffusion process.

I've always been a fan of 'drying out' vintage gear for several days at
about 150F before applying power.

IMO, a higher temperature for ashorter time is NOT a good idea.

A wax bath is not unreasonable, but I'd leave a few out in the air w/o it.
My guess is it'll take a long time for the leakage to increase,if they are
thoroughly dried out.

YMMV,

-John

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


> I recently acquired a lot of NOS, unused "Micamold"-like
> capacitors with varying values- most around .01 uFd
> at 250-600 Volts.
> Most are the square and rectangular Micamolds
> with some Cornell and Sprague in the mix.
> I randomly selected 50 for testing.  21 of the lot displayed
> varying amounts of leakage current and were set aside.
> Two tested "open" and were discarded.
> I subjected 7 of the "tested good" caps to 250 VDC
> for 12 hours.  None developed leakage.  They and
> the remaining "good" ones went into my parts stock.
>
> I placed the remaining 21 "leaky" caps in a disposable
> pie pan and put them in a 300-degree electric oven
>  for 1.5 hours, then turned the oven off and let them
> cool undisturbed for two hours.
> The larger rectangular caps leaked some oil.
> A couple of the square caps had a slight "bulge"
> in the center from (I assume) gas or steam pressure.
> After cleaning them with a disposable towel,
> I retested the capacitors and all save *one* now
> tests "good."  No leakage and all but three are within
> "earshot" of their marked value.
> The three test a bit low (i.e a .01 that tests .006)
> but still "good" as-in no leakage at that value.
> Have three of these caps sitting at 500V and
> three of them at 250 V and will keep them there
> for 12 hours to see if they start leaking again.
>
> If they hold-up, I'd like to coat them with something
> to keep the water out for another 70 years.
> A friend suggested boiling them in clean beeswax,
> which sounds messy, LOL.
>
> Thoughts?
> 73 DE Dave AB5S
>
>
>
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