Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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Temperature.

Posted by Al Sekela (A) on May 8, 2007 at 15:00:30

In Reply to: What factors degrade electrolytic filter caps? posted by DaveD on May 8, 2007 at 13:42:04:

Electrolytic caps lose the water from their electrolyte paste. Heat from other circuit elements in a poorly-ventilated cabinet, or internal heat from large amounts of ripple current, can raise the temperature and cause the water to be lost.

This is the general reason for the limited life-span of electrolytic caps, but each unit will age at a slightly different rate. There are two ways to tell if your units are near death. Measuring the equivalent series resistance (esr) with a specialized meter is one. Another is to weigh them. All caps of the same model number should weigh the same. If one or more are significantly lighter than the others, then these have lost a lot of water and are closer to death.

I've found that a big electrolytic cap can lose a lot of weight and still show a low esr, so I consider the weight test to be more sensitive.

If your amp does not have a soft-start circuit, the hum you hear is the transformer being overloaded upon start-up. It would be worth checking to see if there is a surge-limiting device (a specialized thermistor) at or near the AC input. I don't know if these things fail to a short-circuit, but what you hear suggests that your amp has one and that it is failing.

• ATP Surge Current Limiter thermistor page   (Open in New Window)

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