What is the effect of age on audio components?

I have a 1978 year power amp. It seems to be ok, but do old components degrade gradually, or do they just fail all at once. In order words, how do I know I am still getting all that the spec sheet says is avalible. Talk about old components. Thank you.
In addition to Mlsstl's excellent response, you may find the following thread to be of interest. The bottom line: it's very unpredictable.


-- Al
For an amp of 1978 that has seen regular use, the dominant factor will be how hot it runs. A high-bias amp will dry out the capacitors much quicker than one that runs cool. They will degrade slowly, but then can short out all of a sudden.

But there are many other factors that also contribute to longevity, like the quality of the caps, their ratings and type, how much voltage stress they see in operation, where they are located in the chassis, chassis cooling, if the amp wasn't used for long periods of time, the available space around the amp when it is used, if something was stacked on top of it, the typical ambient temperature in the room, the humidity, etc. This is why generalizations lead to unpredictability.