GB274514A - Improvements relating to multiple thermionic valves - Google Patents

Abstract

274,514. Loewe, S. July 19, 1926, [Convention date]. Vacuum tubes. - In multiple thermionic valves with several amplifier stages, each comprising a separate incandescent cathode, a grid and an anode, enclosed in a common envelope usually together with coupling elements, screens separated from the wall of the envelope are provided to prevent periodic disturbances apparently due to periodic charges on the envelope and condensers produced by the streams of electrons and ions. The electrode system of the final stage 10, Fig. 2, may be enclosed in an electrostatic metallic screen 18, which is cylindrical with closed ends when the electrodes are cylindrical. The screen 18 comprises halves secured together by wires 23, 24 through eyes at the joints. It is made from sheet nickel or nickel alloy and has apertures 29 for the electrode leads and supports. In modifications, the screens limit the movement of electrons and ions mechanically and are of insulating material. A cylindrical screen with ends closed by discs may be made from mica or the screen may comprise glass or mica discs. The mica discs may be coated with magnesium in the usual vaporization. The metallic screens may be connected inside the envelope to a point of constant potential, positive when the vacuum is high and negative when there are traces of gas, for example, to an anode, lead or to the negative end of the filament. Alternatively the earlier electrode systems or the coupling elements may be surrounded or masked by screens which do not enclose them hermetically. Periodic charges on the glass walls may be prevented by connecting the magnesium deposit on the walls to a point of constant potential, preferably inside the envelope, through a wire fused to the envelope. The Specification as open to inspection under Sect. 91 (3) (a) comprises also the following constructions. Several amplifier stages 8 - - 10, Fig. 3 (Cancelled), with coupling condensers 15, 16 and grid leaks 13, 14 are mounted in one envelope and the anode of one of the stages other than the last 10, for example, of stage 8, is connected directly to lead-in 18<1> without any anode resistance, the other stages having anode resistances 12. A tuned circuit or back-coupling coil can be connected to the lead 18' to increase selectivity or an ohmic resistance can be used to obtain the usual aperiodic amplification produced by multiple valves. Filaments 2 - - 4 of the stages 8 - - 10, Fig. 4 (Cancelled), are connected in series with resistance 19<1>, and correct grid-bias is obtained by connecting the grid circuits to points of the filament circuit. The grid leak 13 of stage. 9 is connected to the negative end of the filament 2 of stage 8. The grid-leak 14 of stage 10 may be connected to the same point or to the resistance 19<1>. This multiple valve thus has only five lead-in wires and is suitable for apparatus connected to electric mains. This subject-matter does not appear in the Specification as accepted.