What is a Direct Radiating Collector Amplifier?
It is a TWT (Traveling Wave Tube). It is a kind of the vacuum tube technology. It has a cathode and an anode (forming an electron gun), a helical amplification structure, and a collector. [It's not a collector of a transistor]. However, instead of standard way to dissipate the collector's heat into spacecraft body by conduction, the collector is designed to cool additionally by direct radiation into outer space. This technique allows to unload the heat transfer into spacecraft body by 50%, see this L-3 publication. Some mentioning of "DRC" advantage can be found in this US patent application, paragraph [0044].