[Milsurplus] Micamold Recovery

[John Vendely]

Interesting observations.  I assume there was some level of residual 
leakage, even in those capacitors which were considered to be free of 
leakage.  Everything leaks a little bit, and I'm curious just how good 
the "good" capacitors were compared to more modern types, especially 
after the heat treatment.  Regarding a sealant, perhaps ordinary Q-dope 
would work?

73,

John K9WT

On 6/4/2014 12:12 PM, David Stinson wrote:
> 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
>
>
>
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>