Recapping Audio Equipment
Electrolytic capacitors (“caps”) are electronic components that perform a critical function in amplifier and receiver circuits. The electrolytic compound decays over time. A typical receiver has on average, 40 to 50 separate electrolytic caps in the amp and power supply sections. Some of the largest amplifiers and receivers have over 100 individual 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.”
The image to the right shows several forms of the electrolytic capacitor. The larger cylinder shaped ones are more typical in mid century audio. The very smallest ones are "chip" type SMD components used in many modern amplifiers and receivers. These are very difficult to replace, and are one of a number of factors that made modern electronics impractical to service.
In earlier electronics, primarity vacuum tube amplifiers, non polar capacitors are also replaced. This depends on the composition, as some types are known to decay, and other types are known for long term reliability.
It is possible to isolate the failing capacitors in a circuit, but this is not only laborious, it is the beginning of a never ending loop of replacing one after the other when they are all 35 years old or older. We replace all of them in the preamp, power amp, and power supply stages. For mid century vintage audio, it is the only approach that makes sense.
If you would like to know more, or just need help falling asleep at night, here is some data on electrolytic capacitor reliability.