Capacitors age over time and thermals play the biggest part. Can seal leakage is another big failure point and the next aging aspect is the level of current that is modulated through it, over time, with regard to peak long term transient levels, or sine levels (sine wave...in-out, at high levels, over time)
Leaving an amplifier on is probably the fastest way to age the capacitors, as the thermal levels are generally much higher if the amplifier is on, compared to being off and in cool dry storage. Each small plastic skinned aluminum can has the materials inside and then two leads coming out. What the end cap of the can is, is a shaped/molded rubber bung. The bung must seal the outer rim of the can, and then seal the capacitor metal connection legs.
The capacitors are filled with layers of thin metal sheet, coiled along with dielectric separators. The capacitor is infused with a fluid or slurry that is called the electrolyte. This electrolyte, when heated, can have an out-gassing issue tied to the seal quality, and general overall micro leakage, over time. The thermal and natural long term leakage or drying out of the fluids in the electrolyte..slowly ages the capacitor until it finally reaches a failure point.
The failure point is impossible to avoid and WILL happen like gravity and the sun coming up. This failure point is not guaranteed to happen all at the same times on identical capacitors due to the mentioned point that all capacitors are stressed differently and not all seals on all capacitors are created equal. The biggest metal can capacitors in most audio (power supply) gear are generally, if utilized correctly (not electrically over-stressed or thermally stressed) ..they are generally the least likely to fail, and the longest lived.
The failure mode of an electrolytic capacitor that is drying out..is to have no remaining capacitance value, it’s like running a gasoline engine dry with no oil. The end result, is messy for the engine at best. The next thing they do, is to internally short with internal arcs, and the residual electrolytic fluid is converted to gas and can ignite. The infamous capacitor *bang!* we hear about and sometimes get to witness. Much amplifier circuitry or general circuitry carnage can ensue in this scenario.
In general terms, most gear over 10 years old should have a general capacitor quality and wear inspection.
Anything that is Class D or has a pulse power supply should likely be inspected at least at the 5 year age point and then maybe every two years or earlier, after that first 5 year period. The stressing that their capacitors are under is much higher than a standard fully analog system that is built with transformers and rectifiers.
I had to explain all of that so I could say that the continually running GAS amp mentioned in this thread, is quite seriously in the hardcore red zone of imminent failure modes.
If the ampzilla has never been recapped since 1977, as a technical type, I would never even turn it on without a full inspection and some critical level recapping, before taking it even further in the recapping realm.
Please do not take to heart such advice about leaving the amplifier on, ok?
One does also..not want to thermally over stress any plastic aspects in the given design which might be exposed to heat..., as heat over time is what stresses plastic components that may be in use. These plastic bits which can be in the given gear will discolor, harden and become embrittled, fragile..as time goes by. Generally, this is stuff that is (or can be) a problem in the 20 year age range and greater.
