An inductive output tube (IOT) operates in a frequency range above 1000 MHz. An output window may be provided to separate a vacuum portion of the IOT from an atmospheric pressure portion of the IOT, the output window being surrounded by a cooling air manifold, the manifold including an air input port and a plurality of apertures permitting cooling air to move from the port, through the manifold and into the atmospheric pressure portion of the IOT. The output cavity may include a liquid coolant input port; a lower circular coolant channel coupled to receive liquid coolant from the liquid coolant input port; a vertical coolant channel coupled to receive liquid coolant from the lower circular coolant channel; an upper circular coolant channel coupled to receive liquid coolant from the vertical coolant channel; and a liquid coolant exhaust port coupled to receive liquid coolant from the upper circular coolant channel.