GB441849A - Improvements in and relating to electron discharge devices - Google Patents

Abstract

441,849. Discharge apparatus. BULL, C. S., 33, Micawber Avenue, Hillingdon, and KEYSTON, J. E., Holly Cottage, Wood End Green, Hayes, both in Middlesex. June 26, 1934, No. 18876. [Class 39 (i)] The invention relates to electron discharge devices of the kind having a cathode, a control grid, a screen grid surrounding the cathode, and an anode surrounding the screening grid, the anode potential being so positive that a substantial amount of secondary emission takes place, and the anode being spaced at such a distance from the screen grid that owing to the space charge of primary and secondary electrons a potential minimum is produced in the anode - screen space which prevents secondary electrons from reaching the screen under operating conditions. Such devices exhibit no inflexion of the anode current-anode voltage characteristic with the screen grid potential equal to the mean anode potential. According to the invention, either the control grid has no supports which extend into the electron stream, or else the thickness of such supports is not substantially greater than the thickness of the wire or the like of which the grid is made. The screening grid supports are preferably arranged in a similar way. By this means electron shadows cast by the grid supports are made too small to allow substantial leakage of secondary electrons to the screen grid. The thickness of the supports in the electron stream should not be greater than three times that of the grid wires, the effective thickness being that measured perpendicular to the electron stream. The grid shown in Fig. 2 is composed of parallel wires 6 joined at their ends to supporting rings 7, 8 which are outside the electron stream. In another form, Fig. 6, the grid is of perforated metal, the perforations 12 being produced by etching or punching. Wire gauze grids may also be used. In an alternative construction, Fig. 5, the grid is a helix 10 wound on supports 9 of the same diameter;. two or more intermeshed helices may be employed. Dimensions and spacing of electrodes in an example are given. Specification 423,932 is referred to.