Capacitors: Who is Right? What ages them faster?

Kevziek: Most of Nelson Pass' amps are of a high bias design and run hot. Leaving them on exposes the caps to a greater amount of heat, so they will end up "cooking" themselves and drying out. Then again, if one turns the amp off and on as needed, the caps are exposed to big temperature swings from the amp being stone cold and then coming up to operating temperature. Doing this repeatedly stresses the caps more than leaving them turned on all the time. That is, so long as the amp has proper ventilation both internally and externally to begin with.

This is not to mention that leaving them on reduces the amount of exposure to high levels of in-rush current. It is in-rush current that damages equipment the most due to the huge surges involved and the rapid internal temperature changes that take place when this occurs. This is why light bulbs typically blow when turning them on, not once they are already on.

Other than that, Seandtaylor did a nice job. GS's comments are right in the ball park too, but one has to realize that not all caps are made the same or have the same spec's and reliability. For that matter, caps from the same manufacturer and of the same product line may differ due to variances in the dielectrics used from batch to batch. Some batch's of products are much better / reliable than others.

As a side note, just a while back i pulled some caps from an amp that Nelson designed and released in appr 1990. While this amp is 13 years old and idles at about 130* at the heatsink, it has been on 24/7 for over three years. With all of that in mind, the electrolytics in the power supply actually tested above their rated values by almost 20%. Needless to say, i didn't replace them as there was no need. Sean
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Kevziek: While the heatsinks and output devices will obviously get hotter than anything else, the ambient temperature inside of the amp is also raised as the amp comes up to temperature. I'm not claiming that ANY amp runs the caps too hot, because if they did, that would be an underdesigned product. We all know that we don't have any of those floating around and that i would be the last to comment on something like that : )

What i am getting at is that the caps "cooking to death" will be a long, slow process. While the caps are heated, they aren't heated enough to exagerate their failure rate. In effect, Nelson verified this with his comments saying that their operating temp was measurably below their rated specs.

As such, you've now heard the answer to the question, albeit in a confused and round-about manner, directly from Nelson himself. That is, the caps aren't run up against their thermal limits when turned on. This means that they aren't stressed. At the same time and using common sense, leaving them on keeps them stabilized in terms of thermal shock AND reduces the potential for blowing holes in the dielectric via removing in-rush current from the equation. Sean
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Aball: Celsius is for use by "fureners", not us folks here in the USA : ) Sean
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