SummerTime and Amp Heat

I agree with Bombaywalla. Heatsinks get hot because they are doing what they were intended to do.

Cannot assume that power supply are automatically hot if the heatsink is hot.....
Bombaywalla (System | Reviews | Threads | Answers | This Thread)

There are plenty of resistors close enough to the coupling, and other caps inside the amp to soak up the heat from those resistors. A lot of the time when I buy something, I look inside and see the caps or resistors leaning toward each other on one side of the amp (one channel), and not the other channel. This is quite common, and on upper end gear, not just mid-fi. I've seen this in all kinds of electronics, more so with PC boards. A lot of heat inside some of them. That's why I said it depends on the design. I have some stuff with a lot of clearance that needs nothing in the way of extra cooling. When some people buy this type of gear, they'll say it's just a big box of nothing. Maybe the designers did this for heat and other beneficial reasons.

No one seems to have mentioned the associated load on the amp and its output stage[s]. As a corollary, one sometimes sees ads that say "drove my Thiels/Apogees/'stats with aplomb". That's all good and well but it would seem that driving the amp to its upper limits might shorten its useful life and perhaps wear it out faster than one would with an easier load. Just wondering...

05-30-11: Tripper
No one seems to have mentioned the associated load on the amp and its output stage[s]. As a corollary, one sometimes sees ads that say "drove my Thiels/Apogees/'stats with aplomb". That's all good and well but it would seem that driving the amp to its upper limits might shorten its useful life and perhaps wear it out faster than one would with an easier load. Just wondering...

all (larger) power amps have output protection circuitry ( that kicks in if there is unusually high DC offset) + thermal shut-down circuitry that cuts off the output power stage if the heatsink temp goes too high (this is often monitored by transistors attached directly to the heatsink & the bias running thru these transistors is set to the upper limit of the heatsink temp that the designer thinks is safe) + the power transformer is also designed to provide lower current than the transistor's max so that the transistors always operate in their SOA. All these safety checks (idiot-proofing) ensure that (unless you short the speaker binding posts) the amp will operate safely & within its limits 99% of the time.
So, if the amp is driving somebody's Thiels/Apogees/'stats with aplomb then it is doing so within the SOA region of the output transistors (otherwise it'd be shutting down time & again & the owner would not make such a statement).

By "a matter of degree" I meant (along with a lame pun) the degree to which you're using the amp...running into a 4 ohm load to get 115db peaks for 5 hours might cause more heat than a day of light background music. I have a later MOSFET Forte' A/B that get toasty-ish only when I play something kinda loud for a while, but unless you have the amp in a VERY hot room I'd think excessive heat (risking shut down) is a design flaw, and the amp designer should have included fans. I'm amazed that some "all Class A" amps don't melt in "normal" use...but maybe I'm easily amazed.