Heat

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. 

So a fan doesn't hurt anything, this is probably common sense. And this is basically what I told my friend. My thought would be that if the amp had an internal power supply, that this would increase heat inside the unit. My friend has a Rega amp so it doesn't have visible heat sinks. The heat sinks on my amp however probably weigh 40 pounds on each side and my power supply is external. However, my amp is in my attic so I don't play it much in during summer.