Capacitors: Who is Right? What ages them faster?

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

Ah, perhaps Sean meant 130*F... I had long forgotten about Fahrenheit so I didn't think of it till now. Otherwise, see my reply above.

Aball: Celsius is for use by "fureners", not us folks here in the USA : ) Sean
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Sean, in my conversation with Nelson, he indicated that the caps would probably dry out faster when the amp is on all the time, probably due to the heat, as you suggest. Yet, he seemed to feel that you shouldn't worry about life span for probably 15 years, in his designs, anyway. How much of this is conjecture on his part, I don't know. That's why I eagerly await Aball's buddy's opinion.