Patent GB-596291-A (GB)
Title: Improvements in cathode structures for magnetrons
IPC: H01J23/05
Filed: 1944-08-08
Abstract: 596,291. Magnetrons. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and YOUNG, A. J. Aug. 8, 1944, No. 15094. [Class 39 (i)] A magnetron cathode structure comprises a coated conductive cylinder 1, Fig. 1, having at one or both ends an insulating centrally-apertured closure member 2, 2a of magnesia or steatite which is or are held against axial movement relatively thereto, a conductive, e.g. molybdenum rod 8 inside and extending from end to end of the cylinder 1 and held by the insulating closure member or members 2, 2a against axial movement relative to the cylinder 1, and a heater 5 in electrical connection at one end with the rod 8 and at the other end with the cylinder 1. The insulating washers 2, 2a are held in place by collars 6, 6a and by metal discs 4, 4a welded to the ends of the cylinder 1, and the rod 8 is fastened to the cupshaped washer 2 by collars 9, 9a. One end of the heater 5 is threaded through an off-central aperture in the washer 2 and attached to the rod 8, and the other end is threaded through an off central aperture in the members 2a, 4a and is connected to the outer face of the disc 4a. Support wires 7, 7a are attached to the disc 4 and to the protruding right-hand end of the rod 8 respectively. The sleeve 1 is flared at both ends, as shown. In a modification, Fig. 2 (not shown), one end of the heater 5 is connected to the rod 8 without being passed through an aperture in the washer 2, and the left-hand end of the rod protrudes through a central aperture in the disc 4 but is not electrically connected thereto. In another form, Fig. 3, the left-hand end of the cylinder 1 is provided with tags 11 which are bent over to hold the washer 2 firmly in place and which replace the metal disc 4, and the right-hand end, . unprovided with closure members, is attached to a copper cylinder 3 having therein an insulating washer 2a held in place by a collar 6a. The free end of the heater 5 is threaded through an off-central aperture in the washer 2 and is connected to one of the tags 11. The cylinder 3 and the protruding right-hand end of the rod 8 provide the electrical connections to the cathode structure ; two polepieces 10, 10a are driven on to opposite ends of the cylinder 1. In a further form, Fig. 4 (not shown) the cathode cylinder is closed at each end by an insulating washer which is held in place solely by a metal disc welded to the outer flared end of the cylinder and by a collar attached to the conductive rod, the collars 6, 6a, of Fig. 1 being omitted. The left-hand end of the heater is threaded through off-central holes in the corresponding washer and metal disc and is connected to the outer face of the disc, and the right-hand end of the heater is connected to one of the collars attached to the conductive rod. The right-hand end of the rod protrudes from the structure, as in Fig. 1. in all cases the cylinder 1 is preferably of "O Nickel," i.e. nickel containing 1 per cent magnesium, coated with carbonates on a nickel gauze base or on a porous nickel deposit on the cylinder. The Specification also refers in detail to prior art constructions comprising : (a) a cylindrical conductive sleeve closed at each end with an apertured ceramic plug over which is fitted an apertured metallic cup and disc, and enclosing a heater, and (b) a cylindrical conductive flared sleeve closed at one end by an apertured metal disc and at the other end by a centrally apertured ceramic washer fitted with a nickel eyelet and seated on a collar attached to the inner surface of the sleeve, and by a second centrally apertured metallic disc through which the shank of the eyelet extends but without making contact therewith, and enclosing a heater.