Capacitors: Who is Right? What ages them faster?

My educated guess is that none of 1, 2, or 3 are correct, and that what really causes cap aging is thermal cycling. Krells tend to run hot (never owned one, but they have huge heatsinks for a reason), so this might shorten the life.

Leaving equipment off for a long period is probably OK, leaving it on for a long period is probably OK, but switching on and off every day is probably not so good due to the thermal cycling, which causes mechanical stresses (expansion and contraction).

The lifetime will also vary with the quality of the parts.

So if I were you I'd leave all solid state stuff on all the time to minimize temperature variations and condensation problems.

Another thing to bear in mind is that some manufacturers and repair houses make a lot of money swapping caps, and so it pays them to put fear into the audio community that their caps are bad and need changing. By analogy, try to find a car mechanic who'll tell you that oil really doesn't need to be changed every 3000 miles.

I have seen data sheets that give operational life as much as 300,000 hours (34 years), with a shelf life as high as 10 to 15 years "...without deterioration of quality". What will affect the life span is the ambient temperature (if too high, the caps will start leaking current), the ripple current frequency and the initial temperature rise (on/off operation). If you leave the amps off, then you increase the life span by virture of zero frequency but lose it when you turn on the amps (high initial temp rise). If you leave the amps on, then the reverse is true - so, to me, it's a wash whether you keep the amp on or off.

But 8 years to a ps filter cap? Doesn't sound right to me, nor have I heard that Krell caps have such a problem; however 34 plus years for a cap is, IMO, a bit on the optimistic side. I would guess that 15 to 20 yrs would be in the ballpark. Then again, my ML 20.6 pc boards were replaced twice in 15 years. Because of bad caps.

What does this mean with regard to those amps that use few large value caps as opposed to those amps that use more smaller value caps?

One of my collegues does research on capacitor reliability (for aircraft systems) and he agrees that thermal cycling is the main problem. I will ask him again now that he has had time to look more into the issue and let you know. In my experience with using caps in designs is that 10 to 15 years is typical in 55C ambient conditions (for electrolytics).

As for the on/off bit, I have thought about it at length since I am a thermal guy by education and have decided that off once a week and when I leave town is the best balance.

For large value caps, the thermal lag time is longer so perhaps they normally last longer than smaller (physically and value) ones. I will ask my buddy tomorrow about this too if I see him. Arthur

Arthur,
I spoke to Nelson Pass today. He said that, over time, the fluid in the cap slowly dissipates from the cap, until it eventually dries out. He believes that if the amp is left on, the higher ambient temperature is accelerating the process, but by how much, he didn't seem sure.

Your colleague is probably more knowledgeable than Pass is on this issue, since this is his profession. I'll be very interested in his answers......