Patent GB-578620-A (GB)
Title: Improvements in electron discharge devices of the electron velocity modulation type
IPC: H01J25/02
Filed: 1942-01-02
Abstract: 578,620. Velocity modulated electron discharge devices and circuits therefor. STANDARD TELEPHONES & CABLES, Ltd. Jan. 2, 1942, No. 69. Convention date, Jan. 7, 1941. [Classes 39 (i) and 40 (v)] In an electron discharge device, a constant density primary electron stream is velocity modulated and then impacts a secondary emitting electrode, the varying velocity primaries resulting in density modulated secondaries. The constant density stream is obtained from (i) a cathode 4, Fig. 2, working at saturation with an anode 5 which is also the secondary emitter, the cathode heater current being' supplied from a source 8 through an adjustable resistance and chokes 9 ; or (ii) a cathode 52, Fig. 4, with control grid 53 and screen grid 54, all surrounded by a focusing electrode 55; a a resistance 45 is connected between the cathode and control grid to help maintain constant the primary stream leaving the screen grid 54. The input signal is applied between the cathode 4, Fig. 2, and the secondary emitting anode 5 or between the screen grid 54, Fig. 4, and the secondary emitting anode 56, both anodes being earthed; the varying output of secondaries is collected by the electrode 6, Fig. 2, or 57, Fig. 4, the output circuit being across the anode and collector electrodes. A screen grid 105, Fig. 2, may be used to prevent feed-back from the varying secondary stream and a choke 14 is placed in the biassing circuit between anode and collector. The cathode control grid and screen grid 54, Fig. 4, are connected together for A.C. by byepass condensers. In a modification, the primary stream from a temperature limited cathode 18, Fig. 3, is focused to pass through the gap 27 in an input resonator 21 to which the signal is applied by a loop ; the velocity modulated stream passes through a guide electrode 31 to impact the secondary emitter 34, the guide electrode being extended by a grid 36 and sheet end 41. The varying secondaries flow to a collector electrode 37 through the grid 36 and a second grid 44, which terminating at the envelope wall is capacitycoupled to one side wall of the output resonator ; this flow of secondaries sustains oscillations in the output resonator 22 to which the load is coupled by a loop 38. The guide 31, grid 36, extension 41 are all connected to one wall of the resonator 22. The collector 37 is at the same or at a higher potential than the secondary emitter 34. In a modification, the input and output resonators 87, 88, Fig. 5, have passing through the discharge envelope 86 a common wall 89 in which is a grid 96; connected to this wall 89 is a cylinder 101 with integral grid 102 and enclosing a screen grid 97 and the insulated, conical secondary-emitter 98. The varying secondaries pass to the collector 103 and energize the resonator 88. A temperature limited cathode is used, but in another similar arrangement (Fig. 6, not shown) constant density primary current is obtained by a construction as described with reference to Fig. 4. In another amplifier (Fig. 9, not shown), a multi-stage electron multiplier is used with a temperature limited cathode as shown in Fig. 2, the input signal being applied through a circuit connected to the first emitter and a grid in front of the multiplier electrodes. In a further construction, the primary beam is velocity modulated at the gap 126, Fig. 10, in the input resonator 127 ; this beam is focused on to two secondary emitters 133, 134, part only of the primaries grazing and being collected by the first emitter. The two emitters are carried by plates 130, 131 at lower bias potential than the resonator ; a gapped, central, conducting plate 136 is arranged between the plates 130, 131, grids 138 being formed in the plate 136 at the gaps opposite the emitters. Behind the grids are collector electrodes 139, the secondary currents to which pass through the primary 140 of the output transformer 141. In an oscillator, the electron gun 113, Fig. 8, may be of the type described with reference to Fig. 3, and the cathode is connected to the mid-point 119 of the primary 120 of the output transformer, which primary is connected to the secondary emitting anode 114 and collector 115. To keep the secondary emitting surfaces clean, they may be of pure copper or silver and heated in use.