Capacitors: Who is Right? What ages them faster?

Sean: I don't know if you are correct about the caps being exposed to high heat. Nelson said that he has always run the caps considerably below the rated temps. He mentioned 55 degrees C, while ratings are 85 C. The heat sinks may be absorbing the bulk of the heat, while the internal components remain cooler. I'm not sure on this, though.

Hi guys, very interesting subject. My system uses four Linn Klouts in an active mode (electronic crossover inside the amp), each amp has eight 63DCV/10,000uf capacitors. This amps run very hot, I have always wondered if the heat or age would damage or wear them. Could someone please advise me on how to check them? Can it be done with a digital multimeter? Thanks.

All the time, and to allow a minimum of 48 hours for settling prior to listening??

This is in the Threshold owners manual. Just a thought.

loontoon

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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Sean - 130* at the heatsink is WAY too high for any amp to operate. Most transistors can't operate above 120*C without burning up. Including thermal impedance effects, 130* at the heatsink means about 150*C at the junction (in a good design) which is impossible. Your temp measurement needs to be verified.

Capacitors are even worse: many can't function over 85*C. This is a problem I face nearly every day in my applications. the darn caps are typically the thermal limiter in many designs and so they must be kept as far away from the transistors as possible. Caps have a low loss character so they aren't too affected by the load - time is the bigger problem since the heat present around them exacerbates the drying process.

Also, the temperature rise caused by cranking the volume cannot be overlooked as may have here. The initial temp rise at turn-on is only half the battle (less than that even in class B designs) - the other half is when you turn the volume up due to I^2*R conduction losses in transistors. Since current is squared, the volume control results in non-linear heating which can overcome initial turn-on effects rather easily. A much lower time constant driven by high power supply energy in this case is also to blame.

Anyway, I haven't seen my buddy yet but I will start a thread after I talk to him. Cheers! Arthur