GB464977A - Improvements in and relating to electron discharge devices - Google Patents

Abstract

464,977. Thermionic valves and valve circuits. PERCIVAL, W. S. July 24, 1935, Nos. 21077 and 35039. [Classes 39 (i), 40 (iii), and 40 (v)] Various arrangements are described comprising an electron discharge device having two electrodes, one electron-emitting, which together form an electrical transmission line ; the line is provided at or near one end with an input circuit feeding electric oscillations into the line and at or near the other end with a terminating impedance so matched to the characteristics of the line that substantially no reflexion of waves, set up in operation on the line, occurs. One or both electrodes may be formed wholly or in part as an inductance coil, or lumped inductances may be inserted at intervals along their length. A diode detector comprises a filamentary or indirectly heated cathode 1, Fig. 1, surrounded by a helical anode 2 woundon insulating supports 6. Modulated oscillations from circuit 3 are applied to one end of the transmission line formed by the electrodes and are absorbed in impedance 51. A further impedance 5 applied to the input end prevents reflexion of rectified modulation frequencies travelling backwards. The inductance of anode 2 and hence the characteristic impedance of the line should be as high as possible, to reduce the damping on input circuit 3. In a screen grid amplifying valve shown in Fig. 2, an inductive grid 7 forms with cathode 1 one transmission line, and inductive anode 9 forms with mesh screen grid 8 a second transmission line. Non-reflecting terminating impedances 5, 12 are applied to the ends of the lines remote from input terminals 10 and output terminals 11 respectively. The velocity of propagation of waves along each line is preferably made the same. The valve may also act as an anode bend detector. Secondary emission from the anode may be prevented by a suppressor grid, or its effects minimized by reducing the anode-screen separation. In a modification, the screen grid valve may be connected up as a dynatron, when it acts as a line with negative shunt conductance. The control grid may be omitted if no control of the anode current is required. An electron multiplier comprises two helical electrodes 16, 17, Fig. 4, preferably rectangular in cross-section, arranged parallel to one another and on either side of a mesh accelerating and collecting electrode 18. Oscillations are applied to one end of the line thus formed and are absorbed in a terminating impedance 25. Electrons are liberated from a photo-electric or thermionic portion of the input end of one of electrodes 16, 17 and travel in zigzag fashion between these electrodes, under the influence of the progressive wave and of accelerating electrode 18. Multipli. cation occurs at each impact and the output current is taken from electrode 18. The electrodes 16, 17 may be supplied with potentials in opposite phase, as shown, or may be connected together to one end of circuit 22 so as to be in phase. The modification shown in Fig. 7 is intended to increase the diameter and hence the inductance of the control grid of a screen grid valve of the type shown in Fig. 2, by provision of a virtual cathode. Between the inductive control grid 29 and the cathode are interposed two mesh grids 27, 28 ; the positive grid 28 controls the velocity of the electron stream and hence the distance of the virtual cathode from the control grid, while the negative grid 27 controls its intensity and may be omitted. A mesh screen grid 30 and inductive anode 31 are similar to those shown in Fig. 2. Non-reflective terminating impedances 35, 41 are provided. Two or more valves may be connected in series ; valves so connected may be mounted in the same envelope. The terminating resistances may also be mounted within the envelope. The simple resistances shown may be replaced by complex terminations giving greater accuracy over an extended range of frequency.