Audible difference with old but hum-free PSU caps in tube amps?

[KT88]

How long do PSU electrolytic capacitors last in tube amplifiers? I mean two points of view. One is obvious because when a cap fails you can clearly hear a hum even when the amp is idle. Mostly twice the frequency of the mains frequency. But I mean the second aspect, namely whether there can be a weakening of the sound even if still nothing hums?
From transistor amps I know that old caps should be replaced in some cases. I have a British Quad 306 sandamp and although nothing hummed (but audible pumping when switching on and off) with 35 year old caps that were also visually bulging in their tops, the sound and sovereign power was much better with new PSU caps, and the pumping noise when switching on was gone.
How is this effect with tube amps? I have a 20+ year old MC275 MK4 that does not hum. But would it make a difference sonically if this amp gets new PSU caps, or do you wait until it hums with tube amps?

The background of the question is (as a technical layman) whether it makes a difference whether with a transistor amp the power supply transforms say down to +/- 40 V but with a tube amp transforms up to e.g. 500V. Could this influence the extent to which a PSU cap is involved in the sound?

[henry4841]

Tubes or SS makes no difference in cap life if they were rated properly to begin with. Life expectancy is in a capacitor spec sheet. In a 20 year old piece of electronics it would sure not hurt to replace the caps but then they could very well last another decade before giving a problem. 

 

The caps that are subjected to the extreme high voltage is in the power supply section. They are the most likely cause of hum when they get tired. Again it depends on the quality of the capacitor, it's rating and not so much on whether tube or SS. One thing for sure those high voltage caps are more expensive.