An inductive output tube (IOT) provides improved efficiency and larger bandwidth. In one embodiment, an IOT is provided with an electron gun that generates an electron beam, a tube body, a collector for collecting the electron beam, and an extended-interaction output circuit. The electron beam travels through the tube body and the extended-interaction output circuit. The extended-interaction output circuit is located within the tube body. The extended-interaction output circuit comprises a short-circuited resonant structure. The extended-interaction output circuit is used for reducing undesired components of a radio frequency (RF) wave, increasing desired components of the RF wave, and slowing down the propagation of the RF wave. (That is the circuit increases the integral of the electric field along the path of the beam electrons while decreasing the stored energy associated with those fields.) The extended-interaction output circuit also provides the IOT with larger bandwidth operation. The collector may be a multi-stage depressed collector having voltages on the collector to result in a constant efficiency characteristic. The radio-frequency drive power to the tube is connected by means of a broadband impedance matching transformer, and the grid to cathode capacitance may be reduced by depressions in the surface of the cathode directly underneath the grid structure.