[Boatanchors] Micamold Recovery

[Jim Wilhite]

From: Mike Hanz 



> I don't believe Dave suggested anything like "a cure for all of them", but perhaps I misunderstood his experimental goals.

I believe Dave acquired a “batch” that he tested.  He discarded those that failed the test but then tried the heat treatment on some of the others that resulted in them reaching leakage specs and value.  

What I don’t know is if they were used and removed or Old Stock that had never been used.  

I happened on a electronics parts store in the late 90s that had a stock of the pink postage stamp caps of various values that were never used.  I have a Sprague TO-6 and so I check the value then ran them through the insulation resistance test on it.  Some of them failed so I tried what Dave attempted and found they met specs in most cases after extended heating at a lower temperature than Dave used.  

Now the problem with sealing them is I don’t know where they will be installed, so I cannot speculate on the heat exposure they will see.  Also I don’t know the melting point of varnish or poly coating but I do know that bee’s wax is quite low, so the answer there is obvious.  As for value change, Dave promised to post any results, so we should see.  At my age I hope I live long enough to find out his results

As for the capacitors that I have, I dissected some of the bad ones and found the connections to the mica bad so that is obvious and cannot be repaired, I didn’t even try on the paper ones.

Another thing I did not see in Dave’s post was the voltage rating of the caps in question nor his test parameters or how he performed the tests.  That is a moot point for I know Dave and he is quite competent.  So that is all speculation, but in the installations I did,  I had to replace most of the ones I used on equipment that saw regular operation within a short period of time, not 30-50 years.  I hate doing things two times so I quit trying. 

Back in the early 90s I had a tank radio that I baked caps under a heat lamp for several days.   They were of the larger 1 KV mica types and 4-5 of them caused the problems in the radio.  One would think after that failure I would learn and not try it in the late 90s again, but they were never used.  Learned another lesson.

Jim
W5JO