Triode electron gun with positive control grid, with emitting cathode, and with acceleration anode, providing a concentration and emission of electrons directed along straight and parallel paths. Thus gun includes several elementary guns distributed around a single axis, the axes of the guns converging toward one and the same point on the axis situated at the entrance to an axial conical conduit drilled in the anode. The electrons produced in each elementary gun by an emitting pellet go through a concentrator and then through a conduit in alignment with the axis of each gun and perforated in a single thick grid. The invention can be applied in metallurgy for melting and heating.