Electron transmission of mesh lenses for scan magnification in television picture tubes

Battery operated transistorized television receivers require low power consumption. The magnetic deflection system of a display tube absorbs considerable energy; thus, scan magnification as means for power saving gains increasing importance in modern display tube design. The principles of scan magnification and scan conservation are outlined. Magnetic and electrostatic lenses showing a diverging action and thus applicable to scan magnification, are discussed. Divergent electrostatic lenses employing mesh electrodes are presently being applied to scan magnification. The use of such beam-intercepting electrodes reduces the brightness obtainable even though the electron transmission of such a structure may be higher than its optical transmission. The question of the electron optical mesh transmission is investigated both theoretically and experimentally. Numerical integration of the paraxial ray equation and its analytic solution indicate that the electron optical transmission of these mesh electrodes increases with increasing strength of the interstitial lenses. However, appreciable increases are obtained only in very strong lenses. Methods of determining experimentally a possible change of mesh transmission with changing strength of the interstitial lenses are discussed. It is shown that the mesh transmission may increase with increasing lens strength, but the increase thus obtained is not a substantial one.