[R-390] silver-mica capacitor failures

[Charles Steinmetz]

David wrote:

> Do the dipped parts have a crimp joint between the lead and the assembly, like the molded ones?

Generally, the ones I've seen the insides of are put together like 
multi-layer ceramic caps or stacked film capacitors -- stacks of 
metalized dielectric sheets, every other sheet offset, with sprayed 
metalization at the two ends (connecting all even sheets and all odd 
sheets together), with radial lead wires attached by the metalization 
(often with metal end caps for structural reinforcement).  I'm sure 
there are a variety of ways (and proprietary processes) it is done by 
different manufacturers.

> I'm not used to thinking of bakelite as a plastic.

The general usage of that term includes the various phenol/formaldehyde 
resin systems like Bakelite and Catalin.  Bakelite itself used the trade 
name "Bakelite Plastics" for many years.

What information do you have that the bodies of postage-stamp mica caps 
were made of it?  The ones I've destroyed in the interests of science 
appeared to me to be some other plastic material.

Best regards,

Charles