GB662550A - Improvements in multi-grid electric discharge tubes - Google Patents

Abstract

662,550. Discharge tubes. PHILIPS ELECTRICAL, Ltd. March 9,1949 [March 12, 1948], No. 6434/49. Class 39 (i). A discharge tube of the kind having a cathode, first control grid, first screen grid, second control grid, an anode, in that order, and a collector electrode 4 connected to the first screen grid and serving to collect electrons which return from the second control grid, is so constructed that when used as a variable-Á tube, which application requires a high screengrid voltage, only a low second-control-grid voltage is necessary. Accordingly, the cathode 1 emits, under the control of the first control grid 2, two oppositely-directed wedge-shaped electron beams whose apex angles do not exceed 20 degrees, and the surface of the second control grid 5 intersects the transverse plane I (the electrode system being symmetrical about the axial plane II) at an angle not less than 75 degrees, e.g. 82 degrees, and the distance between the first screen-grid 3 and second control grid 5 measured in the plane I is between <SP>2</SP>/ 3 and “ of the radius of curvature of the second control grid 5 at its intersection with the plane I, and is at least 1¢ times the width of the active surfaces of the cathode. A second screen grid 6 may be interposed between the second control grid 5 and the anode 7, the latter comprising a strip having a width less than 2¢ times that of the active cathode surfaces and being displaced to that side of the plane I in the direction in which the distance between the grids 3, 5 increases. In Fig. 2 (not shown), the anode is replaced by a concave secondaryemissive electrode which faces a convex anode in such manner that the distance between them decreases in the direction of the electron travel. The anode is provided with a cooling fin. Actual dimensions of the electrodes and the potentials applied thereto, are given in the Specification.