Patent GB-616870-A (GB)
Title: Improvements in or relating to electron discharge tubes
IPC: H01J21/06
Filed: 1946-09-19
Abstract: 616,870. Thermionic valves. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Sept. 19, 1946, No. 28158. Convention date, Oct. 25, 1945. [Class 39 (i)] An electron discharge device comprises a cathode structure consisting of a plurality of parallel coplanar electron emitting members 25, Fig. 7, each member being situated in but out of contact with the walls of a slot 26 formed in a focusing member 27, a control grid including a plurality of coplanar flat members 28, a screen grid including a plurality of coplanar members 29, the members of each grid registering with the portions of the focusing member between the slots, and an anode 30. The cathode elements may be planar or concave, and the structure provides substantially equal transit times for electrons emitted simultaneously from various parts of the cathode surface. The surfaces 31 of the portions of the focusing member between the slots are preferably concave to reduce the grid-focusing member capacity. The grid elements are of rectangular or bevelled rectangular crosssection, mounted with the widest face towards the cathode. In a high power push-pull double tetrode for use at ultra-high-frequencies, the cathode and focusing electrode assembly comprises focusing electrode blocks 35 and 36, Figs. 10, 11, insulated from each other by a mica spacer 38, and provided with rectangular slots 37. The focusing blocks 35, 36 are supported between liquid-cooled blocks 39, 40 insulated from each other by a mica spacer 41<1>. The cathode comprises parallel U-shaped elements 47 positioned within the slots 37. The ends of the legs of the cathode members are secured together with cathode shields 50, 51 to the focusing blocks. A shield 52, Fig. 11, mounted on one of the focusing blocks 35, 36 prevents emission from the closed ends of the U-shaped cathode elements, and a shield 53 is positioned below the focusing blocks to prevent bombardment of the glass envelope. The control grid assembly comprises metallic cooling pipes 56, 56<1> supporting the grid slats 55, 55<1>. The pipes 56 have lugs 58, 58<1> carrying the L- shaped studs 59, 59<1> extending towards the anodes to provide neutralizing capacitance. Surrounding the cathode assembly and the control grids is a screen grid comprising a boxlike frame 60, 61 supporting grid elements 71, 72 in its side walls, and which is fluid cooled. The members 60, 61 are secured to the cathode supporting blocks 39, 40, but insulated from them by mica spacers 76, 77 to form byepass condensers. The anode comprises multichannelled blocks 81, 81<1> through which a coolant is circulated. Passageway 89, 89<1> in the anode extensions 85, 85<1> convey the coolant which is introduced through the outer tubular member 87 and directed out of the anode through the inner tubular member 88, the cross-sectional area of which is smaller than the area between the two tubes to build up the static pressure of the coolant within the anode. The inner tubular member 88 has a slip joint to prevent deformation of the tube during baking and processing. The cathode, control grids and screen grid are assembled, aligned and spaced on a header plate 90 which is then bolted to a metal portion 93 of the envelope. The header plate is adjustable laterally with respect to the'metal collar 93. The cathode blocks 39 and 40 are provided with passageways in which are inserted the cooling pipes 101 and 102 which serve also as the cathode leads. The cooling pipes 101 and 102 are sealed through the header plate 90. Each member 60, 61 of the screen grid assembly has passageways such as 110, Fig. 8, communicating with the cooling pipes 112 and 113 and joined together by the coupling tube 114. The pipes 112 and 113 are sealed through the header plate 90 by the plug 115 and serve also as leads for the screen grids. The control grids supporting and cooling pipes 56, 56<1> are sealed through a dome-shaped insulating member 121, sealed to a collar 120. A skirt-shaped shield 127 connected to the screen electrode extends between the screen electrode and the header and shields the control grids and their leads from the anodes and their leads.