any ideas on fan cooling of a high powered amp?

4" square muffin fans, one on each side of the amp works well for me, using a variac to slow them down to a tolarably quiet noise level. Do not use a noise-generating dimmer for this, not even the motor control variety.
and orient the fans such that they draw heat away from the heatsinks vs. blowing cool air directly onto them, in order to reduce thermal stresses & uneven temperatures

Obviously, one should take into consideration that any amp needs adequate ventilation. This means that air needs to be able to flow on ALL sides of the amp AND there has to be enough space above the amp for heat to naturally convect up and away from it.

Other than that, forced fan cooling is the next step. Depending on the shape and design of the amp, you may need multiple fans to do this. Just bare in mind that the fans blowing will increase the noise floor in the room, so you may want to look for fans that are both quiet and move a good amount of air. A "secret trick" is to select a fan that moves a lot of air and then run it at reduced voltage. You end up with reduced air flow but the fan is also much quieter due to reduced turbulence. Just remember that heated air tends to rise, so make sure that you orient the fan(s) are oriented to blow cool air into the heatsinks, not force hot air back over them. Sean
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Whisperfan with thermostatic switch.