180,655. British Thomson-Houston Co., Ltd., (Assignees of Hull, A. W.). May 24,1921, [Convention date]. Vacuum tubes.-A valve has an incandescent cathode, an anode, and one or more intermediate grids consisting of one or more flat conducting members arranged parallel with or at an acute angle to the normal path of the electrons, and a magnetic field acting at right angles to their path deflects the electrons and causes them to strike the conducting members, which may act as cathodes emiting secondary electrons. As shown in Fig. 1, the grid consists of a number of flat strips, spaced in radial planes about an incandescent cathode 2, and mounted on two conducting bands 11, for instance, by welding. A cylindrical molybdenum anode 6 is spaced from the bulb by coiled-wire springs 7, and anchored by a spring-cushioned stem 8. The grid is carried by wires 13 secured by collars 14 to re-entrant tubes. The grid may be stamped with radial strips from a sheet, and bent to cylindrical shape, or a helix of flat strip wound edgewise may be used. The strips may extend at an angle to the radii, or may be bent so as to produce a maximum electrostatic shielding of the flament without interfering with the production and escape of secondary electrons. In an arrangement, Fig. 2, for use as a negative resistance device for producing oscillations, the grid 10 is connected with a point on a battery 22, through an oscillating circuit, consisting of a condenser 31 and inductance 29 coupled with the aerial inductance, the anode 6 being maintained at a higher potential than the grid by means of the battery 22. A winding around the tube is energized by a battery 26, and produces a magnetic field which causes electrons from the fila. ment to be deflected towards the strip of the grid, thereby producing secondary electrons which are attracted towards the anode. The potential of the grid and the strength of the magnetic field are so chosen that the emission of secondary electrons exceeds the reception of primary electrons, thereby enabling oscillations to be produced. The condenser 31 may be omitted and the inductance 29 tightly coupled with the aerial inductance. In another arrangement, Fig. 3, for producing oscillations, the grid 10 acts as a control electrode, and as a cathode for emitting secondary electrons, and is connected through variable inductance 34 with the negative terminal of a source of current 35, the positive terminal of which is connected through a load, such as an aerial transformer 36, with the anode. A variable condenser 38 is connected between the anode and the grid. In tho wireless transmitting system shown in Fig. 7, the anode-cathode circuit 6, 2 includes a direct current generator 60, and one winding of an aerial transformer 59. The grid-cathode circuit 10, 2 includes a signalling key 66 and a tuned circuit 65, 67, and has a negative resistance characteristic owing to secondary emission of electrons from the grid. In the frequency-changing arrangement shown in Fig. 8, the anode 6 is siotted longitudinally to prevent the formation of induced currents, and is connected through a load, such as an aerial transformer, with a battery 72. A winding producing a polarizing field 71 is provided, and another winding 69 is connected with an alternator 70. The field strength is adjusted so that the secondary electron emission is cut off when the field is at a. maximum depending on the voltage in the grid. If the polarizing winding is omitted, the frequency of the current in the circuit 73 will be double that of the alternator. In another wireless signalling arrangement, Fig. 9, an additional strip grid 81, interposed between the grid 80 and the anode 6, is maintained at a higher potential than the grid 80. The anode is connected with a battery c through one winding of a transformer 88 in parallel with a condenser 90. The grid 80 is connected through a signalling key 91, and a tuned circuit 83, 84, with an intermediate point of the battery b. The grid-cathode circuit 80, 2 has a negative resistance characteristic. The magnetic field due to the winding 23 causes secondary electrons emitted from the grid 80 to strike the radial strips of the outer grid 81, producing further secondary electrons which pass to the anode. The tuned circuit 83, 84 determines the frequency of the oscillations, and the inductance in the circuit 88 determines the phase, so that the plate voltage is low when the current passes. In another arrangement having a field winding, the grid acts only as a secondary cathode for the emission of secondary electrons, and is connected with an intermediate point of a transformer secondary winding, the ends of which are connected with the cathode and the anode through a load such as a discharge device for smoke preci. pitation.