Hi All,
I have a friend who was telling me how he keeps a fan turned on, facing towards his amplifier, to keep it from getting too hot. I told him that it doesn't matter because the only heat that will affect his amplifier comes from internally. I'm now wondering if I could be wrong. So I'm wondering, if a stereo is in an attic during the summer and it's being played to the point of getting hot, will the temperature in the attic effect the amplifier?
I use two computer fans underneath 845 SET amp, tremendous current and heat from these transmitter tubes. Don't bother with my other tube amps and pre.
Then if the room is cooler, the heat s being drawn through the heat sinks with greater efficiency?
Then if the room is cooler, the heat s being drawn through the heat sinks with greater efficiency?

Yes. Cold air consumes more energy (heat) from the cooling than warmer air can. 

Two factors come into play. 1.) The colder the air, the more heat it can absorb before it reaches a temperature where it will no longer absorb heat from the sinks. 2.)The faster the rate you can replace the air that has already absorbed heat from the sinks with cold (room temperature) air, the faster the rate that heat can be transferred away from your amp.
Theoretical, or actual amp in an attic? Summer attic temperatures are like this


Pushing hot air at a hot thing ain’t gonna do much. Attic exhaust fans can avoid extreme temperatures, but not enough IMO.

A box with small personal ac unit can work, however, power on/off, settings, and importantly condensation needs to be dealt with.

Some floor standing room units have ducts to vents like a clothes dryer, that would work if that could be worked, again, an enclosure to retain the cooler/block the hotter air would be wise. I used one of them to cool the V Berth in a boat in Florida I inherited (thankfully sold) found one with self evaporation, pvc pipe for heat exhaust.
Very simply, the operating temperature of electrical equipment is X deg F above whatever is the ambient w/o forced cooling such as a fan.  If X deg F is say 25F, and the ambient temperature is 75F, the internal operating temp is then 25F + 75F = 100F.  If the attic reaches 95F, the equipment operating temp increases to 25F + 95F = 120F.  In reality,  X deg F above whatever is the ambient is somewhat variable for the static condition, but for the range we are generally talking about its relatively constant. 

As @millercarbon has detailed, forced air can increase the heat transfer lowering the equipment internal operating temp.  But for forced air to lower the equipment operating temp (to remove heat) there has to be a temperature difference - the ambient air temp has to be less than the equipment internal operating temp (or the external heat sinks).

The easiest example for what happens at elevated operating temps is to look at a capacitor.  The average capacitor in home audio equipment is rated for an operating temp of 85C (185F) for 1000-hrs.  For every 10C(18F) less that it operates, the service life doubles.  So, operate at 75C, the life is ~2000hrs.  Operate at 65C, the life is ~4000hrs, and so-on.  But, operate at 95C and the life drops in half to ~500hrs.  

Quick examples:  If in a 25C(77F) room & an equipment operating temp of 40C (104F), the service life of the 85C/1000-hr capacitor is ~22,000-hrs.  In an attic at 35C (95F), and an equipment internal operating temp of 50C (122F), the service life of the  85C/1000-hr capacitor is now only ~11,000-hrs.

Some of the better audio capacitors such as  Mundorf are rated 105C while Teflon capacitors are generally rated 125C. Industrial power capacitors may be rated 85C/10,000-hrs - they are designed for 30-yrs continuous service.