GB624009A - Improvements in or relating to electric discharge tubes - Google Patents

Abstract

624,009. Making electrodes for discharge tubes. PHILIPS LAMPS, Ltd. Aug. 22, 1946, No. 25083. Convention date, Nov. 14, 1942. [Class 83 (ii)] [Also in Group XL (a)] An electrode system comprising a cathode and one or more other electrodes is formed by starting with two or more concentric conductors 1, 2, 3, Fig. 1, separated by insulating material 4, hammering and/or drawing the structure, and then removing one or more of the conductors and if necessary one or more intermediate layers of insulating material over part of the circumference, e.g. by grinding. In one form, Fig. 1, the inner conductor 1 is finally coated with emissive material 5 over its exposed surface and the exposed edges of conductors 2 and 3 form grids. In another form, Fig. 2, none of the insulating layer 13 is removed and this layer is also electron emissive. In modifications of the arrangement of Fig. 1, the cathode may be indirectly heated in which case it is made up of either two concentric conductors separated by insulating material, the inner conductor acting as a heater, or alternatively the heater itself may be made up of two concentric conductors separated by insulating material so as to nullify the magnetic field associated with the heater current. To strengthen the structure the outer conductor or conductors in all cases need not be entirely removed over the section of the circumference, small " bridges " 15, Fig. 1 being left. An anode (not shown) surrounds the electrode structure or may be included in the structure as well as or instead of the grids. The conductors may be of nickel, tungsten, or molybdenum, and the insulating material may be of magnesia, alumina, beryllia, zirconium oxide, a mixture of silica, alumina, magnesia, or an alkaline earth oxide such as barium oxide which is also electron emissive.