[R-390] Working on the R-392

[Charles Steinmetz]

David wrote:

> So all the Sprague Vitamin-Q caps were fine, and it was a silver mica
> postage stamp type capacitor  inside an RF transformer that was giving
> me grief!

In the ~60 years I've been playing with radios and other electronic 
gear, I can only recall finding one bad Vitamin-Q -- and there is a very 
good chance that one was damaged by the hoe who tried to fix the radio 
before me.  [For those who haven't heard the term before, "hoe" refers 
to someone who leaves electronic equipment looking like it was worked on 
with garden tools.]

By contrast, postage-stamp micas are dying like flies now.  The time is 
nearing -- if it isn't here already -- when they should be replaced 
shotgun-style, like plastic-cased paper caps.

Epoxy-dipped silver micas have generally been very reliable unless they 
had spent time underwater, but old ones have started to show EOL 
failures over the last 20 years or so.  I expect this trend to 
accelerate as they age further.

Best regards,

Charles