The inductive output tube or IOT is a variety of vacuum tube which evolved in the 1980s to meet increasing efficiency requirements for high-power RF amplifiers. IOTs have been described as a cross between a klystron and a triode, and have their primary commercial use in UHF television transmitters, in which application they have mostly replaced klystrons. Because the control grid of an IOT is located so close to its high-voltage, high-current cathode, arcing was a serious problem in design and development of the technology. This problem is now mitigated after-the-fact by equipping each IOT with an arc detector, which triggers a crowbar circuit based on a hydrogen thyratron in the high-voltage supply. IOTs are also used in particle accelerators.
