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, 50 separate electrolytic caps in the amp and power supply sections.
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.”
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. In our complete vintage component service, we replace all small electrolytics in the audio amplifier and power supply, often resulting in changing over 50 separate components, which means 100 desolder operations and 100 solder operations. 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.