Patent GB-382638-A (GB)
Title: Improvements in or relating to electrical oscillation generators
IPC: H01J31/04
Filed: 1931-07-28
Abstract: 382,638. Thermionic valves; valve generating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Strand, London, and BRETT, G. F., 23, Cross Flatts Avenue, Dewsbury Road, Leeds. July 28, 1931, No. 21591. [Classes 39 (i) and 40 (v).] A high frequency electrical oscillation generator comprises an electron gun or other source of an electron beam, an electrode system situated relatively near to the source of electrons, a second electrode system consisting of at least two anodes, means for subjecting the electron beam to a magnetic or electrostatic field whereby the beam is caused to take a path passing adjacent to the first electrode system to the second electrode system, and means operable in dependence upon the occurrence of current flow through an anode as a result of the electron beam striking that anode, for altering the anode potential and thus altering the speed of the electrons in the beam, whereby the beam is caused to be incident upon another anode, thereby causing the velocity of the electrons to be again changed whereby the beam again becomes incident on the first anode. In one form a hot cathode or filament F, Fig. 1, is arranged near to a slitted electrode system S positioned so that the electron beam passes' through the slit, a potential difference between the cathode and system S being applied by a battery or other source H.T. An anode A<2> is connected directly to the slit electrode S, and to the source H.T. through an impedance consisting of chokes C<1>, C<2> and a preferably non- inductive and non-capacitative resistance R, the other anode A<1> being connected directly to a tapping upon the source H.T. The electrodes are housed within an envelope, not shown, which is evacuated and then filled with inert gas. A preferably uniform magnetic field is provided, of such magnitude and arrangement that the beam of electrons from F passing through the slit in the electrode S passes in an arcuate path and strikes the anode A<2>, whereupon the electron current passing through the impedance produces a fall in the potential between the electrode S and the cathode F, the electron speed is decreased, and the electron beam strikes the anode A<1>. This results in a rise of the potential of the anode A<2> and the electrode S connected thereto, and the beam shifts back to the anode A<2>. The cycle of operations is repeated indefinitely, and an oscillatory current of very high frequency is tapped off across the ends of the resistance R. Preferably the impedance is constituted by a low capacity diode arrangement designed to operate over the linear portion of its currentvoltage characteristic. As shown in Fig. 2 the diode D is connected to a duplicated choke C<1>, and the diode filament is heated by a battery DB. The diode arrangement may be incorporated in the same envelope as the electrodes of the oscillating system, thereby reducing losses due to connecting-leads. In another form the impedance between the first electrode system and the source of anode potential consists of a rejector circuit of suitable values of capacity and inductance. Instead of subjecting the electron beam to a magnetic field a constant electrostatic force may be applied thereto by arranging a pair of deflecting-plates, at a constant potential difference, adjacent to the slit through which the beam issues. Preferably a screen or grid electrode connected to the anode A<1> is provided adjacent to the surface of the anode A<2> in order to ensure a substantially unvarying field being presented to oncoming electrons, so that the arrival point of the electrons will be almost entirely dependent upon their initial velocity. In tubes designed for very high frequency operation the radius of curvature of the electron beam is made as small as possible, and in one form to achieve this the slit electrode S, Fig. 4, and the anode A<2>, which is directly connected thereto may be made integrally from a single piece of metal having a slit adjacent to the cathode F and another aperture behind which the anode A<1> is placed. A screen or grid electrode G connected to the anode A<1> extends over and close to the anode A<2> and slit electrode S. The cathode system consists of a small tungsten helix or oxide-coated wire inside an apertured cylinder. The impedance between the first electrode system and the source of anode potential may be provided by a diode comprising an additional cathode behind the anode A<1>, one of the cathode leads being connected to the slit electrode system.. For lower frequency operation the slit electrode S, Fig. 5, adjacent to the cathode may be joined to the anode A<2> by a wire connection either within or external to the containing envelope. In this form the screen G connected to the anode A<1> extends only over the anode A<2>. The bulbs containing the electrodes shown in Figs. 4 and 5 are adapted to be inserted in a solenoid or between the poles of an electromagnet to provide the required electromagnetic force upon the electron stream.