Recapping Audio Equipment
Electrolytic capacitors (“caps”) are electronic components that perform a several important functions in amplifier and receiver circuits. Eliminating hum among others. The electrolytic compound in a capacitor decays over time. A typical receiver has on somewhere around 30 to 40 separate electrolytic caps in the amp and power supply sections. Some of the largest receivers have over around twice that number of individual capacitors. Integrated amplifiers typically have a smaller number of capacitors.
Quoted directly from a manufacturer of electrolytic capacitors. “The aluminum electrolytic capacitor has a limited life span. This occurs because the electrolyte in the element eventually dissipates.”
Symptoms included degraded performance in either channel or both, hum, sporadic noises, and eventually, failure to operate. In some cases, damage to other components that are irreplaceable can occur.
In the image to the right, the electrolytic capacitors are the larger blue cylinders. In some cases, you can actually see physical evidence that the capacitor has failed. The fact is that most of the time there is no visual indication of degradation or failure at all.
In earlier electronics, primarily vacuum tube amplifiers, non polar capacitors are also replaced. This depends on the composition, as some types decay with age, while other types are known for long term reliability, and are of very high quality. In these cases, we leave those capacitors in place.
It is of course possible to isolate the failing capacitors in a circuit, but this is not only a lot of work, it is the beginning of a never ending loop of replacing one after the other. A fool's errand in our view.
If you would like to know more, or just need help falling asleep at night, here is some data on electrolytic capacitor reliability.