I bought an eBay Spectrian 75W amplifier for 13cm to go with the Kuhne transverter. Spec says 26V at 16A, so the efficiency is extremely low, but it was cheap. 7 amps or so standing current. Thinking of watercooling it. It has a thin copper heat spreader bonded to the underside of the PCB, so maybe OK just mounting it on an aluminium cooling plate, but I have a bit of copper bar that I can solder the water pipe to directly, so might go for that instead. Transverter has not arrived yet, so having to test it with a CW signal from my Agilent E4421B