GB1463349A - Electron gun having extended field electrostatic focus lens - Google Patents

Abstract

1463349 Electron guns ZENITH RADIO CORP 14 Oct 1974 [23 Oct 1973] 44475/74 Heading H1D To minimize spherical aberration the focusing lens of each gun in a C.R.T. comprises tubular electrodes, the initial and final ones at relatively high voltages bracketing a low voltage electrode with at least one intermediate electrode between the low and at least one of the high voltage electrodes at intermediate voltage. The five sections 52, 53, 54, 55, 56, preferably of equal diameter, have potentials (above cathode) of the first and last equal to that of the tube screen 14, that of the second 53 and fourth 55 being set equal at some intermediate value and the central section 54 at the lowest level, the potentials preferably falling from each end geometrically, e.g. with a common ratio of 2. The inter-section gaps should be only sufficient to prevent arcing, with edges 58 curled to reduce stress. The section lengths need not be symmetrical; if not symmetrical then in a five section lens the second 53 should be shorter than the fourth 55, being eliminated completely in a four section lens. The diameter should be as large as geometry permits; in a multi-gun tube corresponding sections may be combined in multi-aperture elements. The sections may be further subdivided, with minor potential differences between the subdivisions, so long as the monotonic use of potential in each direction from the lowest voltage electrode is maintained.