Abstract: A tungsten filament intended as a thermionic source, made from a wire of which the zone defining the point is of a diameter smaller than that of the basal zone and where the diameter of the transitory part of the wire changes progressively. This filament is contained in the same plane and its lower legs are welded to rigid posts in a ceramic base. A novel electrolytic sharpening process is used for the reduction of the diameter of the filament wire, and this process, which permits the progressive reduction of the dimension of a workpiece, can be used in other applications. An apparatus is used for the manufacturing of such a filament by cyclic electrolytic sharpening, as well as means enabling the bending of the wire and its positioning during the welding operation.