GB307856A - Improvements in vacuum electric tube devices - Google Patents

Abstract

307,856. Robinson, E. Y., and Associated Electrical Industries, Ltd. Dec. 13, 1927. Vacuum tubes.-In thermionic valves having indirectly-heated cathodes, screens are arranged to shield the electrode system either from the heater leads which proceed from one stem and are connected to the heater at the opposite ends of the electrode system, or from a resistance which is arranged in series with the heater to enable the valve to be fed from the mains. The first arrangement is shown in Figs. 1 and 2, in connection with a valve of the kind described in Specification 195,691, wherein the space current is confined to a small inter-electrode space, and a carbon heater is wound on a porcelain rod 2 which is secured by clips 3 as described in Specification 297,966, one of the heater leads 14 being passed outside the electrode system to the top of the cathode and enclosed in metal screening tubes 15. These are connected at 17 to a cylindrical screen 9 that surrounds a network anode and the other electrodes and is connected electrically at 11 to the cathode as described in Specification 307,857. The ends of the cathode tube are left non-emissive so as to act as screens, and washers 12 that centre the cathode at the top and optionally also at the bottom may also act as screens. The second arrangement (Fig. 4, not shown) is obtained by extending the screen 9, Figs. 1 and 2, to support the series resistance above the screening washer 12, the resistance being placed in the return lead 14. In a modification, the heater leads are sealed in a stem 28, Fig. 5, at the top of the valve, and a resistance 25 is placed in series with the heater. A screening disc 30, and optionally also a screening cylinder mounted on the wires 29, shield the resistance from the electrode system.