[R-390] Capacitors in R390 (non "A") vs those in R390A

[Jack Sullivan]

I have noted the type/brand of condensors (we now call
them capacitors) in R390 and in R390A, and I have been
reading original data from manufacturers of those
condensors, mostly from Spraque,that was in MA at the
time.  Clearly, a huge difference in caps between
original R390 and later cheapened up "A" version (I
will probably hear nasty words from you "A" lovers,
but "A" version was indeed cheapened up, for that was
objective of the revamp).  However, some improvements
were made in "A" version, as you probably already
know.  Anyway, the caps used in the original R390 were
about the best available at the time, many of them
being Vitamin Q type, with insulation resistance of
200,000 to 300,000 megs.  Too bad that they didn't
keep using those vastly superior caps in "A" version. 
Now, after 50 years, leakage is common with most paper
caps, but the super caps in original R390 seem to
still be doing well, based on my tests anyway.  Even
the oil filled electrolytics in R390 are in great
shape, if my set is any indication.  However, I did
find the 50 mf, 50 volt small elect. one to be bad,
but that is no problem to replace.  Nice to put new
one in old case, so it all looks as it originally did.
Hope this all doesn't sound like I know it all. I am
just trying to share what I have been testing and
reading, regarding caps in R390/R390A.


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