Abstract: An electron beam tube (1) having an input resonator cavity (2) through which a high-frequency control voltage is applied between cathode (15) and grid (17) of the tube (1), while an annular electrode (8) connected in an electrically conducting manner to the grid (17) of the tube is arranged opposite a metal wall (9) of the input resonator cavity (2) and is connected to a DC power supply lead (11). Interference oscillations are suppressed in that a high-frequency damping material (14) is associated with the DC power supply lead (11) on a part of the length located proximate to the annular electrode.