Patent GB-546771-A (GB)
Title: Velocity modulated electrical discharge tube
IPC: H01J25/10
Filed: 1941-05-02
Abstract: 546,771. Velocity-modulation electron discharge apparatus. STANDARD TELEPHONES & CABLES, Ltd. May 2, 1941, No. 5722. Convention date, July 13, 1940. [Class 39 (i)] An electron-discharge tube having a velocitymodulation and an extraction chamber which are traversed by the electron stream and have flexible walls for tuning is provided with means for flexing the walls such that both chambers may be tuned simultaneously by the same manual operation, or separately. As shown, the device comprises resonance chambers formed by cup-shaped members 1, 2 with their bases connected and traversed by a drift-tube 5 having a grid 6 at each end. The outer end walls of the resonance chambers are formed by flexible diaphragms 7, 8. A metal tube 10 is secured in an aperture in the diaphragm 7, and is surrounded by a metal tube 11 which is sealed to a glass thimble 13 carrying the press 17 through which pass leading-in wires connected to pins mounted in a ceramic base 52 sealed to the thimble 13. A tube 27 is welded in a central aperture in the diaphragm 8 and carries the target electrode 29. Grids 24, 28 are arranged in the inner ends of the tubes 10, 27 respectively. The unit is carried in an outer casing formed by a ring 42 formed in two parts which are joined at 44 and each of which carries fingers 43 engaging the edge of one of the diaphragms 7, 8, so that the resonance chambers are clamped between them. End-caps 45, 47 are secured to the ring 42. The chamber 1 is adjusted by deflecting the diaphragm 7, for which purpose the spindle of a knob 60 engages a threaded spike 56 connected by rods 55 to fingers 54 on a split-ring 53 clamped to the tube 11. Ribs 15 formed in or attached to the wall of the tube 11 prevent the clamping from distorting it and breaking the seal with the glass thimble 13. The diaphragm 8 is similarly deflected to tune the chamber 8 by means of a knob 64 into which is threaded a rod 62 secured to the target electrode 29. When the chambers have been brought into resonance by independent tuning they may be simultaneously adjusted to operate on a different wave length by turning the knobs 60 and 64 together. The grids 6, 24, 28 are preferably formed of radially-disposed vanes 6, preferably of tantalum, placed edge-on to the electron stream. As shown, their ends are bent and welded to form, in conjunction, inner and outer rings, and the grid is secured in the drift tube 5 by pressed-up portions 69. The low thermal conductivity between the grid and the tube 5 allows the former to be easily heated by electronic bombardment to drive out gases during manufacture. The cathode 19 is surrounded by a cylindrical control electrode 20 in which is a grid 20a of tantalum wire mesh or other material. The chambers 1 and 2 are coupled by a wire 71 forming a loop in each of them, and an output conductor 36 is secured to the inside of the chamber 2 so as to form a loop 37. A protective sleeve 41 surrounds a glass seal 39 through which the conductor 36 passes, and may form the outer conductor of a concentric line coupling. To test whether the tube is oscillating a meter is connected to a wire electrode 31 extending through an aperture in the target 29 and to the target. The valve is cooled by air which is admitted through a pipe 48 and passes between fins 35 secured to the cylindrical members 27.