Multi-digit luminescence display tube having means for supplying a positive or zero voltage to a selected grid to suppress luminescence of anode segments covered thereby

Claim 1

In a multi-digit luminescence display tube comprising an evacuated sealed envelope having a light transparent portion, an anode assembly within said envelope disposed in a facing relationship with said envelope transparent portion, said anode assembly including an insulating substrate and a plurality of luminescent anode segments formed on said substrate for each of a plurality of digits, cathode means disposed in front of said anode assembly for emitting thermal electrons, a plurality of grids disposed between said cathode means and the anode segments in substantial registration with the anode segments of the respective digits, first means for supplying first electric voltages between said cathode means and said grids and between said cathode means and at least a selected one of said anode segments for distributing the thermal electrons substantially uniformly on the selected anode segment to make said electron-irradiated segment luminesce, and second means for superposing a second electric voltage on the first voltage supplied between said cathode means and at least a selected one of said grids for preventing those anode segments from luminescing which are in substantial registration with the selected grid, the improvement being wherein said cathode means comprises a common filament for the anode segments of all digits, and further comprising third means for rendering said second voltage non-negative and greater than zero such that the luminescence of that selected anode segment which is not in substantial registration with the selected grid is not adversely affected.