Abstract: An electrode of an inductive output tube (IOT) is provided with channels for guiding cooling fluid. In one aspect of the invention, the channels are in a confronting relationship with a jacket surrounding the electrode and spaced from the electrode so as to define an interior region. Cooling fluid such as oil is circulated in the channels in fluid communication with the interior region, providing an escape mechanism for trapped bubbles in order to prevent localized heating of the electrode. In another aspect of the invention, the channels form multiple intersecting helical patterns of different pitches, with the steeper-pitched channels providing a more direct escape route for the bubbles.