US1917963A - Hot cathode electron discharge tube - Google Patents

Description

July 11, 1933. H. M. FREEMAN ET AL HOT CATHODE ELECTRON DISCHARGE TUBE Original Filed Jan. 1925 5/35 'T' INVENTO R5 f/uer/ /7 fieeman 3 WITNESSES [xx/W fifii-MAM Wa//a:e 6 Node.

ATTORNEY Patented July 11, 1933 UNITED STATES PATENT OFFICE HUBERT M. FREEMAN, OF EAST P ITTSBUBGH, PENNSYLVANIA, AND WALLACE G.

WADE, OF NEW YORK, N. Y., ASSIGNORS TO WESTINGHOUSE ELECTBIC- AND MANU- FACTURING COMPANY, A CORPORATION OF PENNSYLVANIA HOT CATHODE ELECTRON DISCHARGE TUBE Original application filed January 8, 1923, Serial No 611,263. Divided and this application filed July 8,

1926. Serial No. 120,579. Renewed April 24, 1931.

; ending application, erial No. 611,263, filed an. 8, 1923 and of which this application is a division.

The principal object of the present invention is to provide an improved cathode structure for electron discharge tubes, in

which alternating current is utilized to heat the cathode to a temperature at which it emits electrons.

Another object of our invention is to provide a simple cathode structure of the above described character and having good mechanical qualities so arranged as to eliminate as much as possible the undesirable effects of the pulsations of the heating current on the flow of the electrons from the cathode without impairing the high cathode eficiency.

A cathode construction constituting a preferred embodiment of the invention, comprises two tubular refractory members disposed in side-by-side relation and having therearound a wrapping or coating of conducting material adapted to emit electrons when heated. A hairpin shaped heater wire has its two sides threaded through the perforations of the two refractory tubes and is arranged to be supplied by alternating current for heating the refractory members and the electron emitting material on the surface thereof.

The foregoing construction permits very close spacing between the two wires of the hairpin-shaped heater element, thus reducing the magnetic field produced by the alternating heating current to a minimum and eliminating the undesirable influence that such currents may have on the flow of electrons from the electron emitting surface of the cathode. At the same time, the improved construction utilizes a minimum of refractory material requiring little time for heating it, and the electron emitting surface material thereof, to the desired operating temperature. The improved structure has also the further advantage that it gives a relatively large emitting surface with a minimum amount of material.

Our invention will be best understood from the accompanying drawing, in which Figure 1 is a view partially in elevation and partially in section of a radio tube embodying the invention, with a diagrammatic view of the circuits associated therewith,

Fi 2 is a horizontal sectional view along the line IIII of the cathode structure of the tube shown in Fig. 1,

Fig. 3 is an elevational view of a modified catiode structure embodying our invention, an

Fig. 4 is a horizontal enlar ed sectional view of the cathode structure s own in Fig. 3, along the line IVIV.

Referring to Fig. 1, a radio receiving tube embodying the invention is shown comprising an elongated, suitably evacuated envelope 2, having a reentrant stem 3, terminating in a press 4. Five leading-in wires 6 to 10, are fused into the press and serve to support, and to make connections to, a cathode structure 12 and concentrically mounted grid and anode structures 13 and 14:.

The cathode structure 12, which constitutes the distinct feature of the invention, comprises two tubular members 15 and 16, in the shape of slender solid cylinders of refractory material, disposed in side-by-side relation and having longitudinal, central perforations 17. A heater element or wire 21, which is bent in the shape of a hairpin, is threaded through the two perforations 17 the two sides or sections 22 of the heater element being insulatingly spaced from each other by the walls of the refractory cylinders 15 and 16, which thus constitute a refractory body in which the heater element is completely embedded. The thickness of the walls of the refractory cylinders is made as small as is feasible, in order to reduce the spacing between the parallel sides 22, of the heater element, to a minimum. Such construction has been found to substantially eliminate the fluctuating magnetic field that would otherwise be established by the alternating current with which this heater wire is being supplied.

The two tubular members 15 and 16 are made of an insulating refractory material, which does not chemically or otherwise react with the heater element embedded therein. Zircon has been found very suitable for this urpose.

The cathode element proper, from which the electron flow in the tube is obtained, consists of a wrapping 25 of conducting mate rial, surrounding the two refractory members 15 and 16. In the form of our invention shown in Figs. 1 and 2, the wrapping 25 is formed by helically winding an oxide coated platinum strip around the outer surfaces of the two refractory cylinders, the platinum strip being heated to the electron emitting temperature-through the medium of the refractory bodies, which thus perform the double function of insulating the electron emitting cathode surface from the alternating-current energized heating element, and, at the same time, conveying thereto the heat generated inside the heating element.

The oxide coating on the platinum strip 25, which is utilized as the cathode surface, may be made in any of the familiar ways. Very good results are obtained when a coating of the oxides of barium, strontium or the like is used.

The cathode structure consists thus of a tubular envelope or sheath, surrounding a pair of heating wires and insulatingly spaced therefrom by an elongated heater body which surrounds the heater wires, the cathode sheath conforming in its outer con tour to the shape of the heater element. The cathode element itself has the shape of a flattened tubular member of oblong cross section corresponding to the shape of the body constituted by the two adjacently disposed refractory heater elements.

The above-described cathode structure may be supported by means of a carrier rod 26 extending from the lead-in wire 6 and holding the bent portion of the heater wire 21 at its upper end.. The electron emitting wrapping 25 has a suitable electrical connection to the carrier rod 26, which also serves as an external terminal connection to the cathode surface.

The lower end of the cathode structure 12 is held in place by the leadein wires 7 and 8, which are welded to the lower ends of the heater wire 15 to make electrical connection thereto. The tube is provided with -a suitable base having five contact pins 28, which are connected to the five lead-in wires 6 to 10 in the usual manner. The improved tube a may be utilized in any of the familiar circuits, the principal distinction being the means for heating the cathode to maintain the surface thereof at an electron emitting condition.

Inplace of the ordinary storage batteries,

or direct-current sources, which are required in the prior art tubes for heating the cathode, alternating current may be utilized with the tubes made according to the invention, the two terminals 7 and 8 of the heater wire 21 being shown connected to a source of alternating current in the form of a transformer 31. The remainder of the circuit in which the tube is shown to be utilized, comprises input leads, in the form of conductors 32 and 33 connected to the grid 13 and the cathode element 25, respectively, the output circuit of the tube comprising a detecting or'other load device 34 connected in series with a source of plate energy 35 between the anode 14 and the cathode 25 of the tube.

In Figs. 3 and 4 is shown a cathode construction embodying a modification of the invention in which more direct transmission of heat from the heater element 21 to the electron emitting cathode surface is secured. To this end the tubular cathode element 36 is placed substantially in direct contact with the heater wires 22 of the heater element, being insulated therefrom either by an insulating oxide coating 37 covering the interior surface of the tubular cathod element 36, or a similar coating 38 on the surface of the heater wires 22, or by insulating coatings on both. The tubular cathode element 31 may be made by wrapping an oxide coated platinum strip around the two wires 22 of the heater element or in any other suitable manner. The finished cathode structure has the shape of an elongated flat tubular member, the outer surfaces of which is adapted to give large electron emission. The insulating coating 38 on the heater wires 22 may comprise magnesium oxide, or a similar substance.

Tubes embodying cathode constructions of the type described hereinabove, and distinguished by the features more particularly pointed out in the appended claims, have proved very efiicient and it is desired that the appended claims be accorded a broad construction commensurate with the invention disclosed in the application.

IVe claim as our invention:

1. In a thermionic device, a discharge tube having a cathode structure comprising a plurality of heater Wire sections arranged in a row, refractory means surrounding said sections and conforming substantially to the shape of the envelope of said row, and electron emitting means on the surface of said refractory means. a

2. In a thermionic device comprising a hot-cathode electron discharge tube, a cat11- odc member in said tube comprising elongated refractory insulating means, a pair of substantially parallel heater wire sections embedded in said refractory member, said refractory member having an oblong cross alternating heating current thereto, a re fractory substantially insulating means surrounding the sides ofsaid heater wire and holding the same inspaced relation, said .means constituting an elongated body having an oblong cross section in a plane perpendicular to the wire sides, an electronemittin sheath surrounding the surface of said refi'actory body and conforming to the shape thereof, and a terminal connection to said sheath.

4. In a hot-cathode electron-discharge tube, a cathode structure comprisinga pair of parallel disposed heater wire sections having terminals for conveying current thereto, and an electron-emitting sheath surrounding said -wires and heated thereby, said sheath constituting an elongated tubular body having flattened side surfaces substantially parallel to the plane of said Wires.

5. In a hot-cathode electron-discharge tube, a cathode structure comprising a tubular elongated member having an electronemitting conducting cathode surface, said member having flattened sides, and heating means in the interior of said member and substantially insulated from the adjacent portions thereof.

6. In a hot-cathode electron-discharge tube, a cathode member comprising a tubular elongated member having an electronemitting conducting cathode surface, said member having an oblong cross section, an insulating material inthe interior of said member a heater element insulatingly embedded in said material, terminal connections for said heating element, and an independent terminal connection for said cathode surface.

7. In a hot-cathode electron-discharge tube, a cathode structure comprising a tubular elongated member having an electronernitting conducting cathode surface, said member'having an oblong cross section, an insulating material in the interior of said member, a pair of serially connected wire sections constituting a hair-pin shaped heating element insulatingly embedded in said material, terminal connections for said heating element and an independent terminal connection for said cathode surface.

8. In a hot-cathode electron-discharge tube, a cathode structure comprising an elongated refractory insulating "member electrical heating-means embedded in the in-- terior of said member and a wrapping of conducting material on the surface of said member, said wrapping having an electron emitting terminal connection.

9. In -a hot-cathode electron-discharge tube, a cathode structure comprising a pluralit of elongated members of substantially insu ating refractory material disposed in side-b -side relation, astrip of conducting material tightly wrappedaround said members and constituting an electron emitting cathode surface, and means embedded within said refractory members for heating the same.

10. In a hot-cathode electron-discharge tube, a cathode structure comprising two parallel disposed heating wire sections, tubular refractory insulating members surrounding said wires and spacing the same from each other, a conducting wrapping tying said tubular members together, said wrapping having a surface that emits large quantities of electrons when heated.

11. In a thermionic device, a discharge tube having a cathode structure comprisin a plurality of heater-wire sections arrange in a row, refractory means surrounding, but mechanically separate from, said sections and conforming substantially to the shape of the envelope of said row, and electronemitting means on the surface of said refractory means.

12. An electron-discharge tube, comprising a cathode structure comprising an elec trically conducting heat-ing element, an electrically conducting strip having an electronemitting surface wound about and supported by said heating element and electrically insulated therefrom except that said strip is connected to said heating element at substantially the mid-point of said heating element.

13. A thermionic cathode electron-discharge tube comprising a cathode structure comprising a U-shape heating wire havin closely disposed parallel heater sections an a tubular sheath of conducting material embracing said heater sections, such sheath comprising a helix of conducting material wound around said sections, the outer surface of said helix having a coating of electron-emitting oxides.

14. An electron discharge tube, comprising a cathode structure comprising an electrically conducting heating element, an electrically conducting strip having an electronemitting surface wound about and supportcharge tube comprising a cathode structure comprising a U-shape heating wire having closely disposed parallel heater sections havcathode member having a continuous outer surface adapted to emit electrons when heated, a U-shape heater wire longitudinally disposed in said tubular casing and refractory tubular members individually surrounding the sides of said heater members for insulating the same with respect to each other and to the Walls of said outer casing.

In testimony whereof, we have hereunto subscribed our names this 26th day of June, 1926, and this 23rd day of June, 1926, respectively.

HUBERT M. FREEMAN. WALLACE G. WADE.

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