Patent GB-435559-A (GB)
Title: Improvements in and relating to electron discharge devices
IPC: H01J21/02
Filed: 1934-03-23
Abstract: 435,559. Thermionic valves. BULL, C. S.. 33, Micawber Avenue, Hillingdon, Middlesex. March 23, 1934, No. 9219. [Class 39 (i)] A valve comprises two or more grids which are located between the anode and cathode, and each of which is provided with apertures in such manner that the apertures in one grid may be brought into alignment with those in the other grid, wherein one or more members extend between, and register with portions of, the grids and serve to locate the apertures thereof in predetermined relation to one another with respect to the election stream. A flat grid may be formed of wire which is wound in a flat helix on, and welded to, two supports 3, 4, Fig. 1, and the wires 2 on one side of the supports are cut away ; the wires 1 may be pressed towards, or into, or beyond the plane which contains the supports 3, 4. The turns per inch of one grid may be the same as, or may be an integral multiple of, that of the other grid. A flat rectangular cathode 5, Fig. 4, is placed between two pairs of grids 6, 6<1>, 7, 7<1> and glass, silica, mica or steatite rods 8 or strips are threaded through corresponding points on each grid, e.g. between the two adjacent wires at the ends thereof. The thickness of the rods or strips is equal to the distance between adjacent wires and the width of the strips is equal to the distance between the supports 3, 4. The cathode may be located, and made slideable, in holes in the strips. Nuts may be screwed on to the ends of the rods to secure the electrode assembly. As shown in Fig. 8, the rods may pass between the outer wires of grids 7 and above and below each outer wire of grids 6. In another form, a screeen grid valve comprises an indirectlyheated box-like cathode 5, Fig. 10, the ends of which are not electron-emitting, pairs of grids 6, 7 and 6<1>, 7<1> on opposite sides thereof, and aperture-aligning strips 10. The grid rods 3, 4 are spaced from one another by members 12, from the cathode by members 13 and from a metal casing 15 by members 14. The casing consists of two members bolted together at flanges 16 to clamp the electrode assembly, and holes are provided in opposite sides thereof for the passage of electrons to the anodes. The strips 10 may support the anodes and may be so dimensioned that they engage the inner walls of the casing 15 or project through, and fit tightly, the holes in opposite sides thereof. The spacing members 12, 13 may, as shown, pass between adjacent grid wires which project from the plane containing the supports 3, 4. The grids may be so arranged that the apertures are not in alignment. Thus a member 10, Fig. 14, is formed with two portions, both of which pass between adjacent wires of grids 23, 25 but which pass on opposite sides of a wire in grid 24. Alternatively, a straight rod passes through all the grids, one of which has two adjacent wires displaced to the extent of half the normal distance between adjacent wires. In another form, the grids, which may consist of wire helices, are registered with respect to one another by mica strips which engage notches in grid support rods. The grids may consist of gauze or etched plates and are registered with respect to one another by rods which pass through holes therein, the holes being formed by drilling the imperforate portion of the plate, or by enlarging the apertures, or by removing the material between adjacent apertures. When the grids have been suitably registered, the grid rods may, at each end of the assembly, be clamped by means of parallel metal strips which are lined with mica, joined together at the ends of semicircular parts and are pressed towards each other to hold the rods. Shallow nicks may be provided on the ends of the rods to facilitate clamping.