Patent GB-544232-A (GB)
Title: Improvements in or relating to electron discharge devices and arrangements including such devices
IPC: H01J21/18
Filed: 1940-09-30
Abstract: 544,232. Thermionic valves and valve circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Sept. 30, 1940, No. 14713. Convention date, Sept. 30, 1939. [Classes 39 (i) and 40 (v)] An electron discharge device, particularly for volume or tone control purposes, comprises a slotted mask between the cathode and anode, a magnetic field for forming the electrons into a beam, and means for rotating the magnetic field so as to cause the electron stream to be intercepted to varying degrees by the mask. The electron beam may be modulated by a control electrode, which may be of the variable-mu type, and the slots in the mask may be so shaped and arranged that a modulated part of the beam may be varied while the direct current component of the beam remains constant. For tone control, the anode may be made in two or more parts each separately connected to an output of a particular frequency, and the current to the several anode parts adjustably regulated by suitable formation and arrangement of the slots in the mask. As shown in Fig. 2, a cylindrical cathode 3, preferably indirectly heated, is placed concentrically in an anode 4, with a mask 5 having diametrically apposite slots 8, 9. The electrons are formed into two beams 6, 7 by a magnetic field, represented by the poles 2, and rotation of the field causes more or less of the beams to be intercepted by the mask. A control electrode may surround the cathode so as to modulate the anode current, and the mask slots may be variously shaped so as to provide any desired variation of the anode current. The arrangement in Fig. 12 comprises a control grid 25 of the variable mu type and the slots 26 in the mask are V-shaped so that rotation of the beam produces varying trans-conductance, while maintaining a constant volume level. Another arrangement whereby varying signal amplitude with constant volume is shown in Fig. 13. This comprises a long cathode 3 and anode 4, and a masking device in two end-to-end parts 26, 27. The current from the upper part of the cathode is modulated by a control grid 28, while a grid 29 with a steady biasing potential surrounds the lower part of the cathode. The slots 5 in the masking device are triangular in shape and oppositely disposed, so that rotation of the beam varies the anode current in the lower and upper parts of the device to equal extents in opposite directions. A modification consists in separately controlling the beams from opposite sides of the cathode. Tone control is effected in a device as shown in Fig. 9 comprising an anode made in two parts 14, 15 connected to output of different frequency bands, represented by the circuits 16, 17. The slots 5a in the mask are of triangular shape and oppositely disposed so that increase of the current to one anode segment is accompanied by a decrease of the current to. the other, and vice-versa. Fig. 8 shows the valve, with a control grid 13, coupled to the load circuit 12 of a dioderectifier, and the masking electrode 5 connected to a source of steady positive potential. In a modification, Fig. 6 (not shown), the masking electrode is coupled to the detector load circuit through a resistor and condenser.