[Boatanchors] Micamold Recovery- The Sweat Test

[David Stinson]

"Micamold" Recovery- The Sweat Test.

As most of you remember, I've been working with a batch of
NOS "Micamold-type" capacitors, which had been stored in 
an un-airconditioned Texas barn since about 1954.
For what has been done so far, see my earlier posts.
(Note:  I think the high temp treatment worked better
then the low-temp, slow cycle method because 
I got the caps above the boiling point of water 
so the moisture out-gassing was more complete).

I divided the 20 "baked and dipped" capacitors into two lots 
of 10 and selected another lot of 10 "modern" silver mica 
and disc ceramic capacitors.
Put one lot of the "Micamolds" into a Zip-Lock bag
with a wet rag, sealed it and set  it in the Texas sun 
for two days and two nights of cycling temperature,
pressure and humidity.  
For controls, I did the same with the "modern" capacitors and
left the second lot of "Micamolds" undisturbed on my bench.

I removed the caps from the "wet" bags and allowed them to 
dry, then tested them for leakage and value on the ZM-11.
Nine of the ten "Micamold" caps retained their "good" status,
one failing for 0.4 mA leakage at 250 VDC.
All the other caps showed no changes.

I examined the "bad" cap under magnification and discovered
one lead where it entered the case was not sealed by the wax.
I'm guessing trapped air in the space kept the wax out.
That was enough to let the water in and spoil the cap.

My next test will really torture them.
I am going to put them in series with a 60-watt light bulb
and plug them into 120 VAC (170 VAC PTP), measure
the voltage across the lamp as a "baseline" and leave them
like that for a few days.  If the light comes on,
one or more have leaked or shorted.
We'll see.

73 DE Dave AB5S