Hi Amarin,

You are right about the caps too. All of them have a finite age, and temperature is the biggest factor, both internally generated by their electrical duty and ambient.

I wouldn't be so confident about those sealed with epoxy, based on what I think are the most notorious capacitor failures among those used in our Volvos. The clocks use electrolytic caps with epoxy-sealed bases. But, rather than construction, the use of the capacitor (its electrical duty) has a lot to do with our perception of its life.

Choosing the right part for a design has to take this duty into consideration, for the selection process is more than just quality vs. price. The automotive temperature range is somewhere between that for consumer products and satellite electronics.

For example, if the capacity in a part used for timing reduces by 50%, the instrument panel clock will stop, but if the same reduction occurs in a part which smooths the speedometer needle or decouples the power supply, you won't notice it. Even if it fails completely open, the effect is subtle.

Maybe in your pre-amp, the electrolytic caps are used to decouple power line frequency hum. Like with the car's shock absorbers, the damping function can reduce gradually without notice as we humans just adapt to the subtle decline in performance.

When I said I wasn't convinced, I was opposing the tendency of folks who have just learned of the "great capacitor plague" of the early 2000's and feel they could repair any device by replacing the caps.



PS, I hope I didn't spoil your dinner with that old picture of lentil soup. :)

--
Art Benstein near Baltimore

A Local Area Network in Australia is the LAN down under.