I wanted a simple way to keep my two GM`s cooler without having to fabricate anything. I went and got two 60mm computer fans (these particular ones are 60x25, are sub 18db noise and flow 18cfm of air). I have an infrared thermometer, and tested with and without fans on with the power soak at 1 watt to generate the most heat.
Without the fans I got a max temp on the cover right over the tubes of about 125 degrees F (which is really nothing in the big picture). With the fans on, the same spot is right about 103 degrees. That`s roughly 18% less heat, a substantial reduction. What is more exciting was the difference in chassis temp. I measured right next to the DI out, and without the fans was at roughly 110 degrees. With the fans it`s down to 98. That means that everything inside the chassis has experienced a 10% drop in operating temperature. And mind you this was with only one fan per amp, and a small one at that. The 50mm fan actually fits the vents better but the 60`s flowed significantly more air than the 50`s that were available.
I got both fans and a power supply for $20 and it required no fabricating or even tools. The fans came wit these little rubber insulator mounts that fit perfectly between the vent slots. I might take one of the fans and move it to the other amp to test what difference two will make, but I`m honestly 100% satisfied with what I`m working with now.
A cheap and very simple solution for those who just want to keep their amp a little cooler for safety`s sake. The folks at H&K were tickled with the setup.