Electronic – How long do electrolytic capacitors last in seldom-used equipment

capacitorelectrolytic-capacitorlifetime

I have a Fender solid-state amplifier nearing its 40th birthday. I've been going through it, replacing some failed logic chips and updating some of the op-amps (gaining about 10dB in S/N ratio!).

The low-voltage (±18V) DC supply has typical 220µF 25V electrolytics. I haven't tried to test them but they seem to work OK. But they're almost 40 years old! The amp has been used only sporadically over its lifetime—I wouldn't hazard a guess as to total hours but it's not many.

Should I replace them? I'm thinking yes, but if total hours are low, is it necessary?

Best Answer

If you're already in there messing with it all over the place, I'd replace all the big ones for sure. All of them if you like. With replacements from a top-tier manufacturer.

Otherwise, no need to break something that isn't broken (broken would be excessive hum or possibly intermittent oscillation).

Lifetime is related to time and temperature mostly, and temperature goes up when in use, so the lifetime is reduced. 40 years is not uncommon for good capacitors kept cool, but it's also possible some have excessive ESR. It's usually not a catastrophic failure, just an increase in ESR (equivalent series resistance) as the electrolyte dries out. At some point the circuit doesn't work well enough. In the case of your power supply that would be excessive ripple and probably some resulting hum. If there is regulation in the power supply the onset of hum might be more sudden than gradual.

As a rule of thumb life is halved for every 10°C temperature rise, so it's usually good to buy 105°C-rated capacitors rather than 85°C, all other things being equal. The lifetime ratings at full temperature are very short (thousands of hours only). Higher voltage rating than the original is also better. Since capacitors have gotten smaller over time for the same ratings you can definitely substitute a really good part that fits in the same space as the original.