[Milsurplus] Re: [The WS No19] Diode Effect in Cap's.

[J. Forster]

I'm inclined to agree about the mechanism, namely a chemical rectifier, but I
think it's likely that the effect only occurs in capacitors that have become
damp inside and then had high voltage applied causing an electrolytic action. I
think it'd be less likely in dry capacitors.

If this is correct, it implied that radios with these type of caps should be
very thoroughly dried out before any voltage is applied to forestall this kind
of failure. Perhaps a week or two in a warm, dry place?

-John

John Berry. wrote:

> Hi Keith.This is a good one, personally I've never really checked it
> out,BUT it does not suprise me.Looking at the nature of the leakage
> ie silver foil between waxed paper "printing through" effects etc,etc
> it's probably making a "Chemical Rectifier".Think of all those really
> ODD ONE'S from the DAWN of radio.I wonder if there is any detectable
> VOLTAGE developed in these cap's....

> .John G1WOS.

Has anyone ever come across the effect of a non-polarised waxed paper cap
testing like a diode?

I have found numerous waxed paper capacitors with the values of 0.01 and 0.047
uf that are used
to couple the 1st AF amp to the second or main AF amp in radio circuits that
when tested they
show little or no leakage in one direction and significant leakage in the other
direction. The
result of this is obviously very distorted audio on receive.

Does anyone have any theories how this kind of problem can happen with an old
wax paper
capacitor?

Keith Watt RN (Rtd.)