Here's the underside of the audio amp:
The capacitors circled in green have been replaced. They are an older sealed Mylar
capacitor, reliable and correctly sized and installed so I'll leave them in. Once the amp
is ready to power up, I will be able to tell if they need to be replaced. The capacitors circled
in red will need to be replaced. They are made from metal foil with paper dielectric, dipped in beeswax.
These will eventually deteriorate from age and either short out or open up, requiring replacement.
The black capacitor with stripes is a paper capacitor in a plastic shell and will need to be replaced.