The present invention relates to an electronic tube with cylindrical electrodes. In tubes of this kind, where the cathode generally consisting of a wire mesh 1, the space located within same is tightly coupled with the other inter-electrode spaces of the tube. The invention, in order to avert parasitic resonances at the harmonics closest to the operating frequency, which can occur in said space in operation, provides for the arrangement in said space of a certain number of metal sleeves 8, 9 and 10 coaxial with the electrodes, constituting low-inductance coaxial line sections.Application to high-power, short-wave (20 MHz) triodes for transmitting applications.