Just finished adding a upgrade to my dummy load. I had picked up a DA-458/URM (Bird 6733) a while back. I mounted it on the wall in the shack with a coax jumper over to the bench.
The addition was a solenoid valve and a Klixon 4344 thermostat mounted on the fin. When the fin temperature hit 120 degrees, it opens the valve and runs domestic water through the heat sink. The water is regulated to 30 PSI to avoid damage to the loop in the 6733. 200W for 15 minutes did not even get the 6733 warm enough to activate the klixon. I had to test it by aiming a heat gun at the sensor.
