GB211551A - Improvements in vacuum tubes - Google Patents

Abstract

211,551. Robinson, E. Y. Nov. 17, 1922. Vacuum tubes. - Tubular shields of smail internal crosssection are provided around at least the major portion of the ends of a filament cathode so as to prevent the emission of electrons to the anode from the ends. By this means the upper bend of the characteristic curve may be made very sharp or otherwise modified. The shields may be insulated or connected to the electrodes or their supports. As shown in Fig. 3, the filament 9 is surrounded at the ends by tubular shields 13, 14 mounted on the filament supports, the shield 14 being cut away ,as shown and pinched on to the end of the filament. A helical grid 10 .is preferably longer than the active portion of the filament. The shields may be of conical shape. In a modification a single shield or ellipsoidal shape surrounds the ends of a U-shaped filament, the grid and anode being of ellipsoidal shape. In the arrangement shown in Fig. 5, the end turns 22 of a helical grid 10 are closely wound to form shields having a diameter of about 2 mms. The grid is secured between the parts of a wire 23 by binding wire 24. The shields may be spaced by a stem and may support a helical grid. Perforated shields may be used. The valve may be of the type described in Specification 195,691 having a small inter-electrode space, and the shields may serve to confine the discharge. According to the Provisional Specification the shields may be in the form of discs. Specification 164,175 also is referred to.