Design of Lens-Mask Three-Gun Color Television Tubes

This paper discusses a modification of the shadow-mask three-gun color television tube. By applying an electron accelerating field between the mask and the fluorescent screen, the mask apertures act as individual electron lenses causing the individual electron beams to converge. This permits the apertures to be increased in area resulting in improved utilization of the electron beam current and reduced mask heating. The added voltage is applied after beam deflection and therefore increases the energy in the beam without requiring increased scanning power. Design formulas pertaining to lens effects at the mask and electron beam refraction effects between the mask and the fluorescent screen are given for both planar mask and curved mask designs. The effects of fluorescent screen bombardment by secondary electrons produced at the lens mask is described and means for suppressing these effects are discussed.