In traveling wave tubes with broad bandwidth, such as an octave or more, the gain varies by many dB across the band. One or more lossy circuits inside the tube coupled to the interaction helix-type slow-wave circuit are resonant at frequencies within the operating band. They provide a loss varying with frequency to compensate for the gain variation. The resonant circuits are typically metallized patterns on a dielectric rod which may be a support rod for the interaction circuit. Compared to an external gain equilizer in the drive circuit of the TWT, the internal equalizer is cheaper and provides a better noise figure.