GB423932A - Improvements in and relating to thermionic valves - Google Patents

Abstract

423,932. Discharge apparatus. ELECTRIC & MUSICAL INDUSTRIES, Ltd., Blyth Road, Hayes, Middlesex, SHOENBERG, 1., 202, Willesden Lane, Kilburn, London, BULL, C. S., 33, Micawber Avenue, Hillingdon, and RODDA, S., 15, Osterley Park Road, Southall, both in Middlesex. Aug. 2, 1933, Nos. 21653 /33, 21654 /33, 21655 /33, and 13169 /34. [Class 39 (i)] A screen-grid tube has an auxiliary electrode located at least mainly clear of the path of the electron stream and adapted when maintained at a low potential to modify the field in the space between the anode and the screening electrode so that with the control grid and auxiliary electrode at cathode potential and the screen grid at a positive potential equal to the mean anode potential the anode voltageanode current characteristic exhibits no inflexion. In one form, Fig. 1, a rectangular cathode a is surrounded by control grids b and screen grids c spaced from each other and from the cathode above and below by insulating strips k. The auxiliary electrode consists of a box-like structure e having internal fins l and portions u in the place of the anodes d. The distance between the anode and the screening grid should not be less than twice the pitch of the screen grid. In a modification, the auxiliary electrode is continued round the back of the anodes d and the portions z are omitted, being replaced by screens connected to the screening grid. In another modification, the fins l are omitted. In another form, Fig. 8, the cathode a is surrounded by control grid b, screen grid c and a two part anode d, the parts being separated by a two-part auxiliary electrode l which is connected to the cathode or furnished with an external lead. Metal or insulating shields t prevent secondary electrons from reaching the screen grid in the shadow of the supports s. The anode and auxiliary electrode may consist each of more than two parts and may be secured to upper and lower mica sheets, into which the grid posts fit, by bent-over lugs. In a modification, cylindrical anode members alternate with cylindrical auxiliary electrode members along the length of the cathode. In another modification the auxiliary electrode e consists of extensions of the screens t. As shown in Fig. 18, an anode d may be supported from auxiliary electrode parts e by an insulating bar x engaged by a bar w fixed to the anode d and clamped by tongues v<1>, v<2> struck out of the electrodes e<1>, e<2>. In a modification the anode d is riveted to a thin bar x. The arrangement shown in Fig. 1 may be modified by omitting the side portions z and by substituting for the fins l rectangular apertured sheets which are spaced from the screen grid c by insulating spacers. The grid posts are then secured to upper and lower mica sheets to which the anodes are secured by bentover tongues. The auxiliary electrodes are tied together by welded straps. The anodes and control grids may be connected together or brought out separately if push-pull amplification is desired.