US1881644A - Electron discharge cathode - Google Patents

Description

Oct. 1l, 1932. 1 -loNEs ELECTRON DISCHARGE CATHODE Filed Feb. 28. 1929 oxxDE EMU-TER coATnNG (la) ELECTRO-PLATED OUTER SHELL (H) CENTRAL CORE or- METAL l(to) lNVENToR Lesfer 1 Jon es RNEYS Patented Oct. 11, 1932 ffUNr LESTER L. JONES, F ORADELL, NEW ERSEY :ernennen Dieci-:meen cnrnonn Application led February 28, 1929. Serial No. 343,255.

This invention relates to electron discharge devices or tubes and has special reference to the provision of a novel cathode structure for electron discharge devices or tubes.

The problem of constructing cathode elements embodying heaters for the oxide emitters in Velectron Vdischarge tubes has been fraught with many difficulties and has led to severe limitations in the design of electron 2 discharge devices or vacuum tubes. It is def slrable, for'eizample, to coat the thermionicallyactive material or oxide emitter on a metal such as nickel, molybdenum or tungsten.

V' [lhejresistanc'es ofthese metals are too low,

however, to generate the required amount of heatinthe current and voltage ranges desirable unless the metal be Vdrawn into eX- tremely fine wire, or unless long lengths be used. The drawing of these metals'into filamentsgives rise to the necessity for providing filament supporting structures to prevent the sagging and vibrational motions of the iine filaments and such filament supporting structures undesirably occupy considerable space in the vacuum tube.

Where thecathodes are of the so-called uni-potential heated type, it'has been necessary to provide a considerable mass of insulating material between the heater and the electron emitting cathode surface, the heater comprising vin such uni-potential cathode structures an element electrically distinct from the electron emitting cathode surface. This type of uni-potential cathode gives rise to heater burnouts and is especially troublesome in the construction' of relay tubes for broadcast receivers due tothe relatively long time required to heat up the cathode to the emitting temperature. y

In the construction of electron discharge tubes in which the heaters are energized by alternating current, another problem resides in the importance of confining the electrostaticfield due to the voltages in the heater into a region outsi de the path of the electron flow. It is also important to minimize the magnetic field due to the heater currents especially in the region of the electron current flow.

The prime desideratum of my present invention centers about the provision of a new cathode structure in which the above disadvantages incident either to the filamentary or indirectly heated prior art types of cathode structures lare edectively obviated and which is characterized by new advantages and by the opening up of a new field of design in the electron discharge tube and allied arts. Amongthese new advantages which comprise objects of the present invention are the con- 0U struction of acathode element including a heater which defines a rigid self-supporting structure devoid of any insulating material, the further provision of a heater which is eX- tremely compact and preferably of a long cylindrical form, the further provision of a heater in which all of the parts are mechanically integral, are in intimate Contact with one another and therefore free from any loose parts, the still further provision of a cathode heater in which the heat distribution is uniform tothe surface of application, and the construction of a heater in which the magnetic and capacitive fieldsl due to the heater n current and voltage are at a minimum. These advantages and the accomplishments of these objects lead to important results in many fields; and in the present application I will relate the especial advantages which appertain to the production of cathodes for use in electron discharge devices or vacuum tubes. -To the accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consists in the elements and their relation one to the other, as herein- 8 afterv more particularly described and sought to be dened in the claims; reference being had to the accompanying drawing which shows the preferred embodiments of my invention, and in which:

' Fig. l is a circuit diagrammatic view of an electron discharge device embodying my invention and showing one manner of its use:

Fig. 2 is a generalized structural view of an electron discharge tube showing my invention applied thereto; and

Fig. 3 is a view taken on an enlarged scale and showing in detail the cathode structure nf the present invention.

Having reference now more in detail to 10 resistance layer. Due lto this Construction,

the drawing and referring first.. to lFig. 3 thereof, the cathode structure of the invention comprises a unitary element embodying spaced conduct- ing electrodes 10 and 11, one o-f which provides the electron emitting surface and a resistor element l12 defining the V heater disposed between and conductively inter-gral with .the electrodes 10 and 11. VIn the preferred embodiment of the invention, theV electrode 10 comprises a Vfairly rigid central core made, forexample, kofcopper,niclel, tungsten, etc., having a diameter approximately 1/100 vof its length, the 4resistorv'element 12 comprises a coating of a high resistance material coated over and covering the core :10, andthe electrode 11 comprises a conductive 'fllm'of such-a metal as silver, copper or nickel which` preferably .is electroplated over the resista-nce coatingV 12 and forms a cylindrical shell Whichreceivesthe outer lcoating 13 of .a thermionically active preparation or oxide emitter.

In the design and construction of 'this cathodefelementit iscontemplatedythat the conductivity ofthe core 10 and of the electro-` plated shell 11 be yvery .high as compared 'to the conductivity of therresistance layer or coating'` 12 therebetween. Heat is ltherefore generated vin the' resistance Alayerland substantially the entire y.voltage dropy 'occurs in Vfthe the electrostaticr field incident-to the heater voltage is thereforeconfined lto Within the heater element and therefore toa Vregion out.- side the path of theelectron flow. If the current be led in and :from the electrodes 10 and Y 11 by vmeansof the conductors 141: and 15fat-` tached to the electrodes, as shown in'Fig. 3

Y of the drawing, substantially no magnetic field is created vbecausethe return current is ledba-ck to the point oforigin along the path in extremelyclose spacial relationship to the outgoing path. Thus the magnetic field due to theheater currents is minimized especially in the regionof the electronY current flow. It Will also be noted thatthat part of thefcurrent Which is used for heating near the heater terminals does not travel through .themore remote portions of the heater, and therefore the-remote portions have lesser currents and thefresidual'magnetic field' intheir. vicinity ode unitsor heatersof the prior art. The constructionof a self-supportingtheater in this fashion gives rise to a minimum of miaterial to be heated and therefore to extremely fast heating of the cathode and permits the '-taryltypes ofscathodeof the prior art. The

compacting of the cathode confining the same into a minimum of space, permits ofthe use of muchV smaller grids `and plates with consequent advantages in the reduction of interelectrode capacities vof the electron discharge device. All ofthe parts of theheater .being conductively integral are in intimate contact, and `therefore lthe unit as Ia Whole 1s free from any looseparts. lIt will be apparent, moreover, that the heat distributionris uniformto thesurface ofapplication,

In lthe preferred construction, `the resistor element 12 comprises la high resistance .material of the kind described vandfclaimed in the'application of Lester L. Jones, et al.,

Serial No.167,588, 'filed February 1927, and theelectroplated outerjshell 11,1sapplied to` the resistor coating 12 preferablym the manner described and claimed in the ,application ofjLester LJones and Joseph A. Flanzer, SerialNo'. 260,987, filed March v12, 1928. set-'forthvinsaid application, V.the resistance coating 12 is composed ,ofa finely divided graphite mixed With a binder .and vehicle consisting of a `metallic phosphate. In compounding, they resist-ance material, the graphite, preferably a colloidal graphite, is vmixed With a solution of aluminum in phosphoric acid to form a. freely flowing paint. AThe aluminum in the phosphoric acid produces an aluminum phosphate; and in theY preparation Vof the aluminuml .phosphate it has been found desirable .to Aadd aluminum to the phosphoric acid in such ,an amount as just fails to produce :a precipitate. Addition'of ymore than this amount, Which would .produce .a precipitate, is .undesirable because'of the-presence inthe paint of large particles Yformed bythe precipitate Whichinterferevvith the productionof a smooth uniform tilm.' On the other hand, the addition ofan insufficient quantity of aluminum .or aluminum phosphate is .undesirablemainly because -of theumore highly*k acid condition of the resulting paint, Which tends to destroy the colloidal knature of the graphite, cause ing clotting of the paint With streahiness in the film. It kis therefore .preferred pto. use a solution .of aluminum in phosphoric acid in a slight excess 4of phosphoric acid, aluminum being added'v in suchan amountas just fails'toproduce a precipitate. y'The aluminum phosphate may also be preparedfby the addition 4of C. vAP...aluminum phosphate to phosphoric acid in suiiicient quantity to just copper or nickel. 15

avoid the formation of any precipitate.

The paint thus compounded is then applied to the conductive core 10 by means of a brush or by dipping or by any other method. After being applied the embryo unit thus formed is subjected to a heat treatment which produces a tough and durable coating or film having a relatively high resistance. This coating (12) is thenelectroplated to the required thickness, usually of the order of several thousandths of an inch of conducting metal which may be silver, The paint coating 12 is found to adhere very firmly to the conductive core 10 and forms a firm basis or support for the deposited or plated metal film. In afixing the terminals 14- and 15 to the electrodes of the cathode unit, it is preferred to reinforce one end of the electrode shell 11 with a ring 16 of additional thickness and this may be accomplished by the method of spot electroplating the shell 11, as kkdescribed and claimed in the copending application of Joseph A. Flanzer, Serial No. 228,-

264, led October 1, 1927. The lead wires or conductors 14 andl may then be spot welded, one to the end of the core 1() and the other to the reinforced spot plated ring 16. In some 'cases the reinforcement may be placed at the middle of the heater instead of at one end thereof. l

In F ig. 2 of the drawing, I show diagrammatically the structural inter-relation between the cathode unit of my invention and the other elements of an electron discharge device illustrating some of the advantages hereinbefore outlined when the heater is used in an electron discharge tube. This electron discharge device comprises the usual evacuated vessell 17 provided with the cathode C of the present invention, the said cathode being surrounded by the grid structure Gr which is interposed between the cathode and the plate P.

In F ig. 1 of the drawing, I show diagrammatically a vacuum tube embodying the cathode of the present invention depicting the manner of connecting such a vacuum tube in a relay circuit.v As shown, the electrodes 10 and 11 of the cathode unit are connected to a battery A, the electrode 11 and the grid Gr comprising the electrodes of an input circuit I which is fed from a transformer T, said input circuit being provided, for example, with a battery C. The electrode 11 and the plate P form the electrodes of an output circuit O which in turn is connected to a transformer T', and which output circuit is supplied with a battery B. The use and operation of such amplifier or relay circuits, as shown in Fig. 1 of the drawf ing, is well known to the art and need not be further detailed. c

The manner of making cathodes or heaters of the present invention and the making of electron discharge devices embodying such cathodes or heaters, and the many advantages in the manufacture and use thereof will in the main be fully apparent from the above detailed description thereof. It will be further apparent that while I have shown and described my invention in the preferred forms, many changes and modifications may be kmade in the structure disclosed without departing from the spirit of the invention, defined in the following claims. i

I claim:

, 1. kA heater comprising a conductive core, aiconductive shell having one closed end and surrounding said core, a resistor element disposed between and forming the sole conductive path between said core and shell, and lead-in wires connected to the core and the shell at one end only of the said heater.

2. A unitary heater structure comprising a rigid highly conductive metallic core and support, a thin film or coating of high resistance material over said core, a highly conductive film of metal over said` resistance coating, the resistance film forming the sole conductive path between the support and the metallic film, an electron emitter coating over said film, and lead-in wires connecten"- to the metallic core and the metallic film at one end only of said heater.

3. An electron emitting cathode comprising a conductive core defining one cathode electrode, a resistor coating thereon forming the cathode heater, and a conductive shell having one closed end surrounding said resistor coating and defining the other cathode electrode, said resistor forming the sole conductive path between the core and the shell.

4. A unit-potential cathode for low powered electron emission tubes comprising a central highly conductive wire or rod, a thin heater resistance surrounding the rod, a thin highly conductive metallic shell surrounding the heater resistance, the resistance material forming the sole conductive path between the rod and the shell, and lead-in wires connected to the rod and the shell at one end only of said rod and shell whereby a selfsupporting rigid cathode is provided having a small diameter and small mass for low heat radiation loss and quick heating.

5. A cathode for low powered electron emission tubes comprising a highly conductive wire or rod, a high resistance film coated on the rod, a highly conductive metallic shell plated over the resulting resistance coating, the resistance material forming the sole conductive path between the rod and the shell, a thermionically active material applied to the said metallic shell, and lead-in wires connected to the rod and the shell at one end only of said rod and shell.

6. A uni-potential cathode for low powered electron emission tubes comprising a y central highly conductive wire or rod, a carly bona'ceous high resistanceilm coated on the rod7` a'highly conductive metallic shell plated;

y. over theV resulting resista-nce film, the resista ance material formingjthe sole 'conductive path between the rod and the'shell, a ther.-`

In'ionically activematerial applied to the said metallic shell, and lead-in WiresV connected Il, to the rod and the shell at one end only of i saidfrod and shell, wherebya self-supportf ing rigid cathode is'provided having, a small diameter and small mass lor low heat radiay'tion loss and quick heating. f

' 7. *Acathod'e comprising a highly` conducg tive wire or rod, a heater resistance surround ing the walls and one end of the rod, and4 a highly conductive metallic shell placed over the' walls and end of the heater resist- K. ance, said resistance being in intimate con- 0 tact with said conductors and forming an electricalv path therebetween.

' 8. A cathode for low powered electron Y emission tubes comprising a highlycon'ductive wire or rod7 a highl resistance film coated entirely around the walls and one fend of the rod, a highly conductive metallic shellplated onthe walls and end of 'the resulting resistance coating, and a therinionically active inaterial applied to the said metallic shell.v-

' `9. A cathode for low powered Yelectron emission tubesV comprising a highly conductivewire or rod, a carbonaceous high resist'- ance film" coated entirely VaroundA the walls ,4 and one Ae'ndof the rod, and a highly conduc- A tive metallic shell plated on the walls and end of the resulting resistance coating. Y

10. A non-magneti uni-potential cathode for' low powered electron emission tubes com- 4 prising a central highly conductive wire or V23;() rod, a carbonaceous high resistance Vfilm coated entirely aroundthe walls and one end of the rod, a highly conductive metallic shell plated on the walls and end of the "resulting resistancecoating;and a thermionically active material applied to the said metallic shell,y whereby a self-supporting rigid cathrode is provided having a small diameter and small mass for low heat radiation loss ,andy

`. quick heating.V l

` Signed at New York in the county of New York and VState of New York this 26th day of February A. 1929.

i LESTER L. JONES.

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