US2000695A - Hot cathode electron discharge tube - Google Patents

Description

H. M. FREEMAN ET AL HOT CATHODE ELECTRON DISCHARGE TUBE Original Filed Jan.

May 7, 1935.

ESSES n s www v ATTO'RNEY Patented May 7, 1935 UNITED STATES HOT CATHODE ELECTBON DISCHARGE TUBE Hubert M. Freeman. deceased, late of East Pitteburgh, Pa., by Max F. neges, administrator, Bloomfield, N. J., and Wallace G. Wade, Philadelphia, Pa., assignors to Westinghouse Electric and Manufacturing Company, a corporation o! Pennsylvania Original application January 8, 1923. Serial No. 611,263. Divided and this application Jnnezl, 1932, Serial No. 619,600

9 Claims.

The invention relates to hot-cathode electron discharge tubes and it has particular relation to grid-controlled discharge tubes in which the electron-emitting cathode is so heated from a source of alternating; or fluctuating, current as to substantially eliminate the undesirable effects of the varying heating current upon the electron flow in the tube.

Several cathode structures embodying the foregoing features have been disclosed in our copending application, Serial No. 611,263, filed January 8, 1923, of which the present application is a division. This application is also a substitute for a divisional application Serial No. 120,580, led July 6, 1926.

.Among the objects of the invention is the provision of a cathode element comprising an electron-emitting cathode surface element and an electrically distinct heating element so associated therewith that the fluctuations of the current in the heating element, whenv energized from an alternating-current source or the like, do not interfere, or otherwise exert a controlling action, upon the ilow of electrons from the cathode element to the other space-current electrodes of the tube. v

According to the invention, a heater element which may be in the form of a U-shape wire, or the like, with its two legs placed close together, so as to render it substantially non-inductive, is encased in a tubular heat-conducting sheath, the surface of which is adapted to emit electrons when heated. In order to secure prompt electron emission upon turning on the heating current for the cathode, the body of the cathode structure is made relatively small, eliminating excess material that is to be heated. To this end,l the cathode sheath is secured directly upon the U shape heating wires and is insulated therefrom by an oxide coating which is provided either on the surface of the electron-emitting sheath or on the heating wire disposed therein, or on both.

Our invention will be best understood from the accompanying drawing, in which Fig. 1 is a view, partially in elevation and par? tially in section, of a thermionic tube, with the associated circuits shown in diagrammatic form, embodying the invention, and Fig. 2 is an enlarged horizontal sectional view along the line II--II of the cathode of Fig. 1.

Referring to the drawing, which illustrates the invention as applied/to a radio-receiving tube of a familiar type, an elongated envelope i of glass or the like, has a re-entrant stem 3 termi- '3 mating in a press 4 into which are welded ve (ci. 25o-21.5),

lead-in wires l to Il, which serve to support, and to provide connections to, a cathode member II, a grid I2 and a plate Il arranged concentrically In the usual way.

'I'he cathode member II, to which this invention particularly relates, comprises a pair of parallel-disposed wires I5 bent to form a substantially U-shape heater element supported at its two ends by the ends oi.' the two lead-in wires 1 and 8, which serve to supply thereto the heating current. The bent portion connecting the two wires I5 is supported at the top of the tube by means of a carrier rod II extending from leadin wire 6, the latter serving also to make connection to the electron emitting surface of the cathode element, as will be described hereinafter. 'I'he electron-emitting cathode element of the tube is constituted by an oxide coated platinum wrapping 2l surrounding the two heating wires I5. The Wrapping is formed by helically winding an oxide-coated strip of platinum, or other suitable material, around the two sections of the heater element I5. The turns of the helix thus constitute an equi-potential sheath or tube en- In the form of the invention shown in Figs. 1 Y

and 2, the insulation is provided by the oxide coating 22 on the strip constituting the wrapping 2|, thus securing a very good heat exchange between the wires of the heating element and the body which is to be heated to the temperature of electron emission. If additional insulation is necessary, the wires l5 of the heating element itself may be covered by a layer 23 of some insulating material, for instance in the form of an oxide, such as magnesium oxide. which may be made to adhere to the surface of the heating wire in a way similar to the oxides on the platinum strip, of which the wrapping 2i is made.

As stated before, the connection to the electronemitting surface element of the cathode is made independently of the connection to the heating carrier rod I1.

wires il, for instance, by means of a strip 24 extending from the platinum wrapping 2| to the which is connected to the terminals of the heating wires I5, thus eliminating the diiiiculties incident to the heating-current supply of prior art tubes. v

The cathode, grid and anode terminal wires t, 9 and I0 may be connected in the usual way. When operating as an ampliner, for instance, the connections may comprise input leads 26 connected to the grid and cathode element, while the output circuit may comprise a detecting or load device 21 connected in series with a source of plate voltage 2l between the cathode lead-in wire Il and the cathode lead-'in wire I. Y

The novel features of the invention, which are based on the idea of securing a compact and efcient cathode structure for alternating-current heated tubes by adheringlv uniting the insulating spacing member interposed between the outer cathode sheath and the heating wires embodied therein with the surfaces of the sheath or heating wire may be embodied in a variety of other structures which will readily suggest themselves to those skilled in the art.

We claim as our invention:

1. A thermionic cathodeA electron-discharge tube comprising a cathode structure comprising a U-shape heating wire having closely disposed parallel heater sections and a tubular sheath comprising platinum strip wound about said heater sections, the outer surface of said sheath being adapted to emit electrons when heated, and a surface layer of insulating oxide intervening between said heater sections and said sheath.

2. A thermionic cathode electron-discharge tube comprising a cathode member comprising a U-sha'pe heating wire'havingclosely disposed parallel heater sections and a tubular sheath of` tions, the outer surface of said sheath being -adapted to emit electrons when heated, said sheath comprising a helically wound strip of conducting material having an oxide coated surface engaging the surface of said heater sections.

' 4. An electron-discharge tube, comprising a cathode structure comprising an electrically conducting heating element, an electrically conducting strip having an electron-emitting surface of strontium oxide wound about said heating element and electrically insulated therefrom by means of magnesium oxide.

5. An equipotential cathode structure comprising an equipotential surface, a substantially non-inductive electrical heater for rendering said surface thermionically active, said non-inductive heater having an insulating layer adhering to its outer surface.

6. An equipotential cathode structure comprising an equipotential surface, a two leg heating wire having closely disposed heater sections within said equipotential surfaceand an insulating heat-resisting coating formed on said heater sections and adhesively bound thereto.

7. An electron discharge device comprising a plurality of cooperating electrodes, at least one of said electrodes being an indirectly heated electron-emitting cathode comprising a metallic sleeve serving as an electron-emitter and a heater surrounded substantially by said sleeve, but maintained out of direct electrical contact therewith, said heater comprising a two-leg electric conductor anchored about its center and connected l at its ends to lead-in conductors and comprising rectly heated cathode comprising a metallic cath-r ode sleeve serving as an electron-emitter, a filamentary heating element having a plurality of legs for heating said cathode sleeve and adjacent thereto, and an insulating, refractory coating, containing an insulating compound of an element having' a low atomic number, on said heating element and being normally substantially non-conductive and solid at the operating temperatures of said heating element and adhesively bowed to at least a part of said heating element.

, MAX F. REGES. Administrator of the Estate of Hubert M. Freeman, Deceased.

WALLACE G. WADE.

Cyl

Images