An output circuit for a microwave tube is provided that has generally high interaction impedance for good efficiency, has high average power capability, and is physically large for a given operating frequency. The output circuit is designed to operate in conjunction with an off-axis, bunched electron beam. Electromagnetic fields are applied to the region in which the electron beam propagates to impart an azimuthal velocity to the bunched electron beam. The electron bunches then interact synchronously with a resonant output structure to excite radio-frequency modes from which energy can be extracted and applied to a load.