US2939990A

US2939990A - Oxide cathode for amplifier tubes

Info

Publication number: US2939990A
Application number: US586045A
Authority: US
Inventors: Schmidt-Brucken Heinrich
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1956-05-21
Filing date: 1956-05-21
Publication date: 1960-06-07
Anticipated expiration: 1977-06-07

Description

June 7, 1960 H. SCHMIDT-BRUCKEN 2,939,990

OXIDE CATHODE FOR AMPLIFIER TUBES Filed May 21, 1956 Fig. 1

WWW/WW Fig. 2

Control INVENTOR H. SCHMIDT-BRUCKEN ATTORNEY om CATHODE FOR AMPLIFIER TUBES Heinrich Schmidt-Briicken, Darmstadt, Germany, as-

signor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed May 21, 1956, Ser. No. 586,045

12 Claims. (Cl. 313-346) This invention relates to improvements in or relating to electric discharge tubes and more particularly to cathodes for such tubes, of the oxide type and a novel manner of: controlling emission current therefrom. The emission current of the cathodes of amplifier tubes can be controlled externally of the tube by means of the grid voltage or the plate voltage. A change in the degree heating the cathode is not employed for control purposes due to the considerable inertia necessarily involved. Oxide cathodes are electrodes which have been coated with oxides of alkaline earth metals to improve electron emission at moderate temperatures. It is well-known that in oxide cathodes there are likely to be formed intermediate layers between the alkaline earth oxide and the core metal. These layers are the reaction product between the alkaline earth oxide and components resulting from the core metal. Thus it is known, for instance, that in the case of nickel containing silicon there is formed a thin intermediate layer of alkaline earth orthd silicates at the bottom of the alkaline earth oxide layer. The formation of the intermediate layer is only effected on a heated cathode and very slowly, because the reacting component (e.g. the Si), only diffuses slowly out of the nickel and into thelayer of alkaline earth oxide. This may take up to a thousand hours.

It is an object of this invention to provide a novel means to control emission of a cathode by the interposition of an intermediate layer between the cathode support and the electron emissive coating.

It is a further object of the invention to control the emission of a cathode by means of a barrier layer on said cathode.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which:

Fig. l is a schematic diagram of the cathode circuit of an amplifier tube;

Fig. 2 is a cross section of a cathode made in accordance with my invention;

Fig. 3 is a cross section of another cathode comprising another embodiment of my invention;

Fig. 4 is a schematic diagram of a tube containing a cathode according to the invention; and

Fig. 5 is a schematic diagram of a circuit utilizing a tube containing a cathode according to my invention, with input, output and modulating circuits.

The particular electrical effect of this intermediate layer is featured by a deterioration of the conductivity of the emitting layer. Hence it acts like an electric resistance R inserted in the cathode lead. As is well known, an un-bypassed resistance in series with a cathode produces a degenerative or negative current feedback, that is, it reduces the efiective transconductance of the tube. Since the intermediate layer is very thin, the limiting surfaces thereof also have a noticeable capacity with renited States Patent 0 2,939,990 Patented June 7, 1960 spect to one another, and constitute a by-pass condenser for resistance R by means of which a path for high hequencies is produced. In the equivalent circuit diagram (Fig. 1), therefore, the resistance R inserted in the cathode lead is shown shunted by a condenser C The value of the resistance is of the order of about 40 ohms and [that of the layer capacity about 500 micromicrofarads, as regards 1 cm. surface. As has become known recently, this intermediate layer does not represent a common poorly-conductive layer such as an ohmic type resistance layer, but a barrier layer as exists in semiconductors with a rectifier characteristic.

The barrier layer action of this intermediate layer is successfully utilized with the oxide cathode according to the invention. On the cathode carrier there is provided, in accordance with the invention, an intermediate layer serving to control the emission current. Hence in a predetermined manner there is produced an intermediate layer on a suitably arranged cathode carrier which layer is utilized for controlling the emission current. Thus, the cathode according to the invention represents a tram sistor cathode, because the barrier layer, similar as in a transistor, is atfected by an ancillary electrode and is used for control purposes. In this case, however, unlike the normal type transistor, there is not utilized and controlled the unidirectional conductivity of the layer, but the emissive power of the cathode is alfected in a controllable manner. With the transistor there are required at least three electrodes in contact with the semiconductor. One of such electrodes is replaced in this case by the emitting surface of the cathode. The base metal of the cathode may act as the second electrode and for the third one an additional contact is introduced to the alkaline earth oxide, that is, appropriately at a small distance (e.g. 50 from the base metal surface but, of course, without touching the metals.

However, the second and the third electrode may also be obtained by splitting the base metal into two surfaces separated from each other, for example, in such a way that two thin Wires are double-wound closely next to one another on an insulated heatable carrier (made for example, of ceramic material), but in such a Way that the two wires do not touch each other. Thereafter the emitting layer would then have to be applied over this arrangement of wires.

In order then to enable the formation of the intermediate layer, suitable wires would have to be employed. To this end there could be used eg. a wire of silicon-containing nickel, or also wires of pure nickel which are coated with a silicon-containing lacquer. A material known under the trade name of Silikon, consisting ofa high polymer silicon-organic compound which is formed by groups of [R SiO] is suitable for the purpose. In this compound R is a radical hydrocarbon residual, e.g. CH The formation of a barrier layer in the emission substance near the metal wires can also be effected by means of a suitable previous treatment of the emitting layer itself. To this end, for instance, the cathode may be dipped during 'the preliminary treatment into the aqueous solution of an electrolyte, and the wires serving as base metal, may be connected during the electrolysis either individually or in common as the cathode or the anode. By means of the ions which are ten formed on the surface, the emitting layer surrounding the wire may then be converted into an intermediate layer such as illustrated in Figs. 2 and 3. The single lead-in via the base metal of the cathode of a normal type of tube has thus been split up into a two-terminal connection, so that the emission of the cathode can be controlled by a voltage applied to these feeder terminals.

The subject matter of the invention will be described nickel wires.

more particularly inthefollowing with reference to the exemplified embodiments schematically showniuthefig: ures; of the accompanying drawings.

Fig. 2 shows a cross-section of a tube cathode having an'emitting: layer B arranged on the baser-metalt G;-

Withinthe emitting layer, but spaced a; small-1 distance di from the'surface of the base metal G, thereis: ar-

ranged the third electrode, Ni, which;is;formed egg. of

In this embodiment,- the first; electrode is constituted, bythe emitting surface: and thefi second stituted by twothinwiresNiland NiZ made,. for instance, of nickel, and which are; bifilar: wound: closely next to each other onto the insulatedesupport K made of. ceramic material. In this e'rnbodiment;there= no necessity for spacing the; Wires: Nil and:.from-.the surface of supportK.

There is shown in Fig. 4a, circuitidiagram ofia dischargetube utilizing. my novel cathode whereby the arrow P of the second lead-in denotes-.the barrier-layer character of the arrangement, while the lead-in C forms the; cathode conductor. is not:,shown in the drawing,,but:is presumed to lie beneath'the tube cathode. The employmentof such acontrollable cathode do not in-general? eliminate the needfor a. special control grid. In a tube according toiFig. 4 there will be -btained control possibilities via the control grid (or via a: plurality of. grids-),, as.well asalso viav the cathode. Hence the signal modulation may be applied via the control grid, but, the amplitude level or' the dynamic level may, be controlled via'the cathode. .By utilizing my improved cathode. the two control voltages arewidely shielded: from each other by the sandwiched emitting layer. lying in betweenwithrespect toa mutual capacitative interaction. Since by the control of: cathode emission thetransconductance of. the-tube is modified, this arrangement lends itself? suitably for. mixing or modulating purposes. The tube employing atransistor-cathode in: accordance with my invention, for example, could'be employedwithan arrangementzaccording to 'Fig. 5 where trolling means, said'tube comprising 'an envelope, cathode base means within saidenvelope, a layer of electron emissive material mountedon'said base means, a thin barrier having semiconductive properties located interelectrode isconstituted by thebasemetal G; Ah'eating mediate said base means and said emissive material, means for causing electron emission from said emissive layer, and an emission-controlling conductor disposed in electrical contact with said thin barrier.

2. A: device as claimed in:claim:1,;whereinj said layer comprises earth alkaline oxides and saidbase means comprises an element made ofmetal containing silicon.

3. A device asrclaimedin claim- 2 wherein said emissioncontrolling conductors comprise a second element made of metal, spacedfromsaid; basemeans a predetermined distance.

4. A device as claimed'in'clainr l further comprising a non-conductive support for saidbase means.

5. A device as claimed in claim 4, wherein said base means includesffirst wires, saidcmissiomcontrolling,conductor comprising second wires, and said two wires being wound about the surface ofsaid. non-conducting support inbifilar relationship. r

6. A deviceas' claimed in claim 5, wherein said wires are coated with a lacquercontaining silicon.

As usual, the" heating filament in a grid input may be applied throughan-inpu't-trans- 'formerTi and the output of the tube may be derived via. To; both transformers being of conventionaltypes "andzhaving windings substantially matching theimpedances of the circuits they interconnect. A voltage having a-frequency lower than that applied: to the grid may be'applied between ground and'the lead'P.

The invention as illustrated is shown applied to hard vacuum tubes, but it should be understood that the invention is broadlyapplicable to any other type of tube where it is desirable to control electron emission, e.g., such asin gas-filled tubes.

. What is claimed is:

1. An electron tube having cathode emission con- 7. A device as claimed in clairnS, wherein said wires consist ofa nickel-silicon alloy.

8. A cathode as claimed in, claim 1, wherein said emission-controlling conductor comprises a Wire helix em: bedded in the layer.

9. A cathode as claimed in; claim 1, wherein said emission-controlling conductor is embedded within said layer.

10.- A circuit arrangement for a device as claimed in claim 1, further comprising a control gridandan anode, meansfor applying a signal of. first fiequency-to said control grid, means for applying a signal ofsecondfrequency tosaid emission-controlling conductor, whereby said first signal modulated by said second signal, will appear at said anode.

11. A. circuit arrangement. as in claim 10, wherein said" second signalhas aptrequency lowerthansaidfirst signal 12. A method of producing abarrierlayer ona cathfode for an electron discharge tube comprisingthe steps of winding a pair ofwiresin abifilar. manner; aboutan electrically nonsconductive support; coveringsaidwires with a layer of, alkaline. earth oxide material, dipping the assembly into an aqueous solution of. antelectrolyte while applying. an electric. current betweenrsaid. pair. of wires, whereby ions are formed on the surface of 'said Wires and a thin intermediate barrier layerv having. semiconductive properties is produced;

References Cited in the file of this patent UNITED STATES PATENTS 2,121,589 Espe June 21, '1938 2,186,013 Edgerton V Y Jan. 9,- 1940 2,249,672 Spanner July 15, 1941 2,716,716v Hughes Aug.- 30, 1955 2,718,607 Katz -e Sept. 20, 1955 2,750,527 Katz a June 12, 1956 2,786,957 Huber Mar. 26, 1 957

Claims

1. AN ELECTRON TUBE HAVING CATHODE EMISSION CONTROLLING MEANS, SAID TUBE COMPRISING AN ENVELOPE, CATHODE BASE MEANS WITHIN SAID ENVELOPE, A LAYER OF ELECTRON EMISSIVE MATERIAL MOUNTED ON SAID BASE MEANS, A THIN BARRIER HAVING SEMICONDUCTIVE PROPERTIES LOCATED INTERMEDIATE SAID BASE MEANS AND SAID EMISSIVE MATERIAL, MEANS FOR CAUSING ELECTRON EMISSION FROM SAID EMISSIVE LAYER, AND AN EMISSION-CONTROLLING CONDUCTOR DISPOSED IN ELECTRICAL CONTACT WITH SAID THIN BARRIER.