SB-610 follow up

[Bill Turner]

On Wed, 13 Aug 2003 17:11:06 -0400, Steve <steveac at CHARTER.NET> wrote:

>I understand that electrolytic capacitors deteriorate with the passing
>of years, hence their replacement. Wonder what happens to the tubular,
>disc and mica caps that are used in the SB-610 over 30 years?

_________________________________________________________

My experience over 45+ years of hamming is that disc and mica caps are
pretty much eternal.  The tubular types however, are not, especially
the older ones which used actual paper for the dielectric.  Paper
absorbs moisture and degrades eventually.  The later ones using
dielectrics like polyethylene and mylar are much better.

If you come across any of the really old tubular style which have a
black plastic case and are marked with color bands only (no
lettering), try this:  With the capacitor removed from the circuit,
connect a high-impedance voltmeter across it and observe the reading.
Some kind of chemical reaction in the dielectric is actually
generating a small amount of voltage, just like a battery.  Hard to
believe, but true.  I've seen them get as high as two volts with no
load.  Not exactly a desirable condition in circuit!

-- 
73, Bill W7TI

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