Heat

You are right about heat being generated internally. From there it flows into other things such as the heat sinks by a process of conduction. When you put a spoon in a cup of hot tea and the handle starts to get warm this is conduction. So the amp heats the heat sinks and this takes some of the internal heat away. But what if the outside temperature is higher? Then less heat flows out. That's conduction.

Now on the outside some of the heat simply radiates away. If you've ever seen infra-red images that is from this radiation. Some heat also warms the air. Warm air rises being replaced by fresh cool air. This is convection. This is why heat sinks are vertical, to maximize convection. 

Convection can be increased with a cooling fan. The more air the more convection and the greater the cooling. Always depending of course on the temperature of the air. A heat gun is after all blowing heated air. 

So yes your amp will get hot and run hotter in a hot attic. Most all SS amps have thermal cutoff for heat protection. It is best to avoid this. If it does happen however simply let it cool and resume. Then look for a better cooler location for your amp.

Thanks millercarbon, that's a great explanation!

Heat is the enemy of audio equipment. The lower and more constant you can keep equipment, the longer it usually lasts. Failures primarily occur from thermal cycling. I'm not saying to keep your equipment on all the time and I don't like the noise a fan makes. But when you listen at moderately loud to loud volumes, a fan will help extend the life. I use Rotron whisper fans.

Ambient temperature will effect how much heat you amplifier can dissipate. The warmer the ambient temperature the less it will be able to. Airflow will greatly enhance an amplifiers ability to dissipate heat.

I use 12" computer cooling fans on my preamp - on both the power supply unit and the line level unit. I've mounted them in butcher blocks which I have laid flat on top of both the chassis'. The blocks are cut to the same dimensions as the pre-amp chassis' and the fans are orientated to extract air from the pre amp units. Both units are now cool to the touch no matter what the ambient temperature is, where before they were noticeably warm.

I cannot say if it will extend the life of the amp or the tubes, but I'm sure it doesn't hurt. It helps to dampen any chassis vibration and I definitely think the noise floor is a little lower.