Patent GB-217552-A (GB)
Title: Improvements in radio transmission systems
IPC: H03F1/13
Filed: 1924-02-11
Abstract: 217,552. Western Electric Co., Ltd., (Assignees of Oswald, A. A., and Schelleng, J. C.). June 13, 1923, [Convention date]. Thermionic generators and amplifiers, of the kind in which a number of high-power valves are connected in parallel, are provided with means for preventing the production of undesired or parasitic oscillations. Fig. 1 shows a circuit arrangement., and Fig. 4 a constructional arrangement of the apparatus. A number of valves 2 .. 11 are arranged in two parallel rows, their anodes being connected in parallel to a bus-bar 26 which is connected through a choke-coil 25 to a high-potential source 24 of say 10,000 volts. Between the bus-bar and each anode is interposed an inductance coil 30 of about 0.1 millihenrv and a resistance 29 of about 1,200 ohms, connected in parallel. The filaments are all connected in parallel to the secondary of supply transformer 20, the middle point of which is earthed. Condensers 22 are provided for bypassing high-frequency currents from the two halves of the secondary coil. The anode supply circuits are completed by earthing the negative side of the high-potential source 24. The tuned anode circuit 12 is coupled to the aerial 13 and a blocking condenser 27<A> is interposed between the circuit 12 and the anode lead 26. Resistances 34 of about 100 ohms are connected between the anode of each valve 2 and the opposite valve 7 in the other row, and similar resistances 31 are connected between adjacent anodes in each row. Similar resistances 32, 33 are connected symmetrically between anodes at opposite ends of the same row. The grids of the valves are connected in parallel to a bus-bar 17, which is connected to one side of the secondary coil of an input transformer 14, the primary of which is connected to a source' of high-frequency oscillations. The other end of the secondary coil is connected through a ripple-eliminating filter 15 to a source 16 supplying a biassing potential of about 250 volts. A resistance 14<a> connected across the secondary coil reduces distortion of the input waves. Between the various grids, and between each grid and the common bus-bar 17, impedances may be connected in precisely the same manner as described above for the anodes. The impedances may be omitted from either the grid circuits or the plate circuits. The inductance coils 30 in the anode circuits of the valves offer low impedance to the carrier frequency, but high impedance to the parasitic oscillations which tend to be set up by the inherent reactions in the circuits. The impedances 29, 30 and the leads for the various valves are carefully designed to offer equal impedance to the carrier frequency so that no difference of potential occurs between the various anodes so far as the carrier frequency is concerned, and therefore no current of this frequency flows through the low resistances 31 - - 34. Undesired oscillations will however be suppressed by, or dissipated in, these resistances. Fig. 4 is an end view of a bank of valves. The anodes 27<c> are enclosed in water jackets 27a connected to supply pipes 44 through insulating sections 45. Water is supplied from a main 41 through a coiled insulating tube 42 to a pipe 43 branching into the separate pipes 44. Discharge is effected through insulating sleeves 49, pipes 50, 51, flexible insulating tube 142 to the sewers. The coiled; tubes 42, 142 are wound on a spool 53 supported on insulators 54. The water jackets 27<a> are supported in frames 56, themselves insulated from the supporting frame by insulators 57. The resistances 31, 34 interconnecting the various anodes are mounted in a box 59. Between each anode and the bus-bar 26 is connected an inductance coil 30 wound on the outside of an insulating cylinder 62, within which are mounted two resistance elements 65, constituting the resistance 29 of Fig. 1. The elements 65 are in parallel with the coil 30, and a switch 71 is provided for connecting each unit separately to the bus-bar 26. The grids are connected through leads 18 to the bus-bar 17, and the filaments are supplied with heating-current by leads 21.