Patent GB-435933-A (GB)
Title: Improvements in and relating to electron discharge devices
IPC: H01J21/20
Filed: 1934-03-27
Abstract: 435,933. Thermionic valves and valve circuits. BULL, C. S., 33, Micawber Avenue, Hillingdon, Middlesex, and AGATE, C. S., 33, Dornton Road, South Croydon. March 27, 1934, Nos. 9616 and 9616. [Classes 39 (i) and 40 (v)] A circuit arrangement comprises an electron-discharge device, which consists of a cathode structure, two control grids and two anodes, each of which co-operates with the cathode structure and with a grid, and electrostatic coupling between the grids is prevented by screening members located in the plane of the cathode structure or is prevented by the cathode structure itself, wherein television and sound signals are fed respectively to each control grid and means are provided for feeding the signals from the two anodes into different channels. The screening may be such that when one grid is at cathode potential and when the potential of the other grid relative to the cathode is changed from zero to a value corresponding to zero anode current, the change in the discharge current through the first-mentioned grid is less than ten per cent. A double triode comprises anodes 6, Fig. 1, grids 3 and a cathode filament 1 between the wires of which are arranged screening plates 2 which may be connected together and to earth. Alternatively, the plates 2 may be replaced by a slotted plate and the cathode wires are arranged to lie in, or close to and opposite, the slots. The plate may be bent to bring the portions between the slots into the plane of the cathode which may consist of indirectly-heated rods. A flatsided screening grid, or separate screening grids which may be connected together, are provided between the control grids and anodes. Suppressor grids also may be provided. Each grid may consist of a wire helix, the turns of which are spot-welded to two support rods. The wires on one side of the rods are removed and the remaining wires may be pressed into or beyond the plane which contains the rods. An indirectly-heated cathode 1, Fig. 3, consists of a flat shallow box, of which the sides 11, 1<11> are coated with electron-emitting material. The cathode itself may form the screen either wholly or in conjunction with members 8. When separate biassing resistances are used for the grids, the cathode structure may consist of two separate cathodes, e.g. formed respectively by the plates 1<1>, 1<11>, Fig. 4, which co-operate with the same heater or are provided with separate heaters. T-shaped screening members 2 may be provided. Alternatively, the cathodes may each be formed by L-shaped members arranged to form a box which contains the heater. Interfering fields from the heater may be reduced by a metal tube which surrounds the heater and is arranged within and insulated from the plates. The screening effected by the cathode structure, which consists of one or two cathodes, may be supplemented by T-shaped members 14, Fig. 8, and is arranged, together with flat control grids 4 and screen grids 10, within a metal shield which comprises portions 12, connected together and to a fixed potential, e.g. earth, and comprises slats 13 which assist in the formation of a space charge between the screening grids and the anodes and reduces secondary emission therebetween. In another form, a double tetrode comprises a screening cylindrical or flat cathode 1, Fig. 10, control grids 3, 4, a screening grid 9, anodes 6, 7 and shields 12. Metal or insulating shields 15 screen the space which is located between the screening grid and the shield 12 and in the electron shadow cast by the grid supporting rods. Tuned circuits 16, 17, Fig. 11, are provided respectively for sound and television carriers, and are connected to the control grids of a valve 18, the common screening grid of which is connected to the oscillator 22. One or more intermediate-frequency amplifying valves 24, a detector 27 and an output valve 28 are provided. The anode circuit of the upper half of the valve 28 comprises a loudspeaker 29 and that of the lower half of the valve comprises a cathode-ray tube 30. The received carriers may be amplified before being applied to the first detector. When the number of amplifying stages for the two signals are different, the circuit connections of the double valves are modified, e.g. with four double valves, five " half valves " may be used for the television signals and three "half valves" for the sound signals. Specification 423,932 is referred to.