US2543739A - Electron discharge device - Google Patents

Description

Filed Feb. 12, 1946 2 Sheets-Sheet l IN VEN TOR. 11'. H. BurneTT H15 ATTORNEY.

'2 Sheets-Sheet 2 Leg 5OVOLT5 e iOOVOLTS ,eq =15 OVOLTO C) O -a J- H. BURNETT 6q KOOVOL-TS 8 (D ANODE VOLTS ELECTRON DISCHARGE DEVICE oow ANODE CURRENT-VOLTAGE CHARACTERISTICS Feb. 27, 1951 Filed Feb. 12, 1946 FIG. 4.

A-8p 200 vows 4 42 100 VOLTS ZOO INVENTOR. J. H. B urneTT 8p 50 vows H115 ATTORNEY ANODE CURRENT- CONTROL ELECTRODE CHARACTERISTICS CONTROL ELEMENT VOLTS M50150 Lo IozH mum OMKMQZ SJHZ PZMEIDU MDOZ Patented Feb. 27, 1951 ELECTRON DISCHARGE DEVICE James H2 Burnett, Upper Montclair, N. J., as-

sianor,,,by mesneassignments, to, General-Rail: way Signal, Company, a, corporation; of New York 1.

Application February 12, 1946; Serial No; 64?;007

3 Claims. (01. 2505-5215.)

This invention relates to electronicdevices; and more particular-1v toucontrollable;electron discharge devices suitable: for amplifiers oscillators, and the. like.

In the usual type of controllable electron discharge tubes, such as exemplified bythe ordinary and well known triode, electrons are. attracted: to the grid: whenever it assumes a positive potential with respect to the. cathode and the, resultant grid current: imposes limitations upon the efiicient and effective usexof" such tubes-in various. applications. In power amplifiersand. oscillators, for example, the grid current flowing duringthe; time thegrid is DOSltlVGJSBPIBSBIItS a. substantial part: ofthe electron space current: and; is; aiwaste-q ful'power loss. In voltage amplifiers and similar applications of the conventional triodeu where: it is desired to have thegoutput vary within close limits with the variations; ofitheinput; voltage. impressed on thegrid, the fiowof' grid; current: when the grid assumes a positive potential tends to modify the potential on thegrid; and-cause distortion of the-output. Al'soyi-n various; applica tions of the usualtriode, the gri'dgcurrentexisting while the. grid. is positive 118151.21. tendency tooverheat the grid; and cause. undesirable; thermionic or secondary emission of electronsfrom the rid-, particularly where thoriatedj tungsten or oxide coated cathodesare usedin the interests: of emission efiiciency and the grid may accumulate: a depositof emissivermaterial evaporated or sputteredfrom the'cathode. "These and other limis tati'ons in the efficiency and, use of the usual; type of grid controlled. electrondischarge tube, are due primarilyto the: attraction of electrons to the grid when it assumes positive potential withrespect to. the cathode;- andthese, limitations can be'mitigated and in many respects-entirely. over-: come and the efficiency and utility of such tubes clearly'increased;if the flDWriQf eleotronsrto th positive grid can Ice-effectively prevented.

With these considerations in mind, one of the objects of the presentminvention is to; provide a' controllable electron discharge: device--which maybe proportioned to 'havesthe desirableopera ating characteristics of; the: usual: grid :control; triode or similar multiple electrode tubes, but which does not have, any appreciable electron current to the grid-or control electroda; evenwhen this grid or control-1 electrodeassumes rela-- tively high positive, potentialsxwithrespectpto the; cathode;

A further object of: the; invention is tov attain this desirable obj ective by' a" simpler-and effective structural organization, in which theloomponent parts may be readily proportioned and arranged to. obtain anydesired rating and operating characteristiQS.

Various other-objects, attributes and characteristic features-of the'invention will be in part apparent, and in part pointed out, as the nature of the inventionand certain specific embodiments are hereinafter described.

Generally-speaking, and without attemptingto define the natureand scope of the invention, it is proposed to combine a: magnetic field with a cathode, anode, and'a control electrode in such a, Way that, although the control electrode may perform its usual functionofcontrolling the electron space current in accordance with variations in its-impressedpotential, the electrons emitted by the cathode and formingthe electron or space current; are; influenced, by the magnetic field, so asnot to reach the control electrode or grid, even thoughit. assumes a, relatively high positive potentialwith respect to thecathode in the operation of the tubes Considering thegeneral attributes of the invention from another viewpoint, the control element-or electrode, instead of being the conventional grid with'spaces between its wires for, the passage of electrons and located'between the cathode and anode in the path of direct movement of electrons from thecathode to the anode, is. disposed to one side of the direct or normal path of electrons emitted by the cathode and attracted to the anode, butin such a position that variations in the electrostatic field due to potentials on the control electrode may influence the intensity of the electron-current and exercise the same controlling function as the grid of the conventional' triode; and thisarr-angement or disposition of cathode, anode and control electrode is supplemented by a magnetic field acting in a direction and with-such intensity as to confine the movement of electrons emitted from the cathode-into, a beam or stream over a discharge pathof the appropriatearea which does not touch the control electrode; even though it assumes a.

relatively high positive potential with respect to ent, in explaining the nature and attributes of the invention, to refer to the specific embodiments of the invention illustrated in the accompanying drawings in a schematic and diagrammatic manner, the parts being shown in these drawings more with a view of facilitating an explanation and'understanding of the invention than for the purpose of illustrating the details of any particular construction and arrangement of parts that may be advantageously employed in practice.

In the accompanying drawings,

Fig. 1 is a general view, partly in section and partly in perspective, of one elemental form of controllable electron discharge tube embodying the invention;

Fig. 2 is a diagrammatic representation of the relationship and function of the component elements of the tube of Fig. 1, with a schematic representation of associated circuit connections;

Fig. 3 illustrates diagrammatically a variation in the disposition of the elements of the tube of Fig. 1 in connection with a magnetic field provided by a permanent magnet; and

Figs. 4 and 5 illustrate, for explanatory purposes, typical curves of the operating characteristics of one form of tube embodying the invention.

Considering first the structural organization of what may be said to be an elemental form of an electron discharge tube of this invention as shown in Fig. 1, this tube comprises a thermionic emissive cathode C of the filamentary type, which may be a directly heated wire of tungsten or other emissive metal, a wire thoriated or oxide coated, or a cathode of the oxide coated indirectly heated type, the particular type of the cathode not being material to the present invention.

The cathode shown is assumed to be a nickel core wire spirally wound with a fine nickel wire to aid adherence of the emissive coating and to help in maintaining a uniform temperature.

In the interests of efficiency of low operating temperature, it is considered preferable for ordinary applications to employ an oxide coated cathode formed and treated in the manner disclosed in the prior patents to D. V. Edwards, et al., No. 1,985,855, December 25,1934, and No. 2,- 081,864, May 25, 1937, because it is found that such a cathode has superior qualities in the way of life and durability, as well as high emissivity at relatively low temperatures.

In the simplified arrangement illustrated, this cathode C is welded or otherwise suitably attached at its ends to non-emissive supports 5, 6 sealed in the reentrant stem or press I of the glass envelope E for the tube, said supports 5, 6 being connected by leads in the usual way to pins 8, 9 of a base I0 cemented to the glass envelope in accordance with the usual practice.

In the elemental type of tube shown in Fig. 1, the anode comprises two like flat plates A, A located on oppositesides of the cathode C in planes substantially parallel to the linear axis of the cathode, with the edges of said plates parallel with the cathode at substantially equal distances from the cathode. As shown in Fig. 1, these anode plates A, A are located parallel with each other above and below the cathode C at equal distances in conformity with the desired voltage and current characteristics of the tube.

In the simplified construction illustrated, the two anode plates A and A are electrically connected and held in the-proper relative positions by a support or brace H welded to these plates,

4 and the upper anode plate A is supported by a rigid support I2 extending through a seal l3 in the upper end of the envelope E and connected to a terminal cap M in accordance with the usual practice. These anode plates A, A are preferably formed from sheet stock of the appropriate thickness for stiifn'ess or rigidity, with stiffening flanges or ribs (not shown) if desired, of tantalum, or a like non-magnetic material capable f 'ofoperating at a high temperature with low emissivityv and having characteristics suitable for the plates of electron discharge tubes.

In the elemental tube shown in Fig. 1, the control electrode, having the function of the grid in the conventional 'triode, comprises two like fiat plates G, G located parallel to each other on opposite sides of the cathode C substantially parallel with the cathode and in planes substantially parallel with the straight line between the anode plates A, A through the. cathode, which may be considered to be .the axis of the tube.

As shown, these control electrodes G, G which may conveniently be termed grids, are assumed to be in the form of fiat sheets of tantalum, or a like non-magnetic material, without any grid wires or openings characteristic of the usual grid structure employed in electron discharge tubes, although it should be understood that these control electrodes may be plates with openings therein, or some form of a reticulate or striated structure, although such openings are not necessary for the passage of electrons as in the conventional grid.

In the simplified structure illustrated in Fig. 1, the control electrodes or grids G, G are electrically connected and supported in the desired relationship by a cross support or brace l5 welded thereto; and this brace is welded to a support l6 sealed in the reentrant stem 1 of the envelope E and connected to a pin I! on the base H) in accordance with the usual practice.

In addition to the electrodes in an evacuated envelope as described,'the electron discharge tube of this invention further includes suitable means for providing a steady magnetic field of the appropriate strength directed in a proper direction with respect to the electrodes to influence the movement of the electrons in a way to prevent them reaching the control electrodes. In the simplified form of the" elemental tube shown in Fig. 1, this magnetic field is assumed to be provided by a coil or solenoid M energized with unidirectional current, as indicated by the arrows and symbols and This magnetostatic field is directed along the axis of the tube substantially at right angles to the surfaces of the anode plates A, A and parallel to the surfaces of the control electrodes G, G as indicated by the arrow I-I, so that the magnetic lines of force act along the straight and normaljpath for movement of electrons from the cathode C to the anodes A, A

Fig. 3 illustrates schematically a modified organization in which the filamentary cathode C is disposed vertically in the tube envelope E, shown broken away and partially in section, with the anode plates A, A disposed vertically on opposite sides of the-cathode. and the control electrode plates G, G disposed vertically on opposite sides of the cathode in planes substantially at right angles to the planes of the anodes. In this form of the invention, the steady magnetic field is illustrated as provided by a permanent magnet PM of any one of the well-known permanent magnet materials, preferably analloy of a manac iron; nickel :andaluminumwommonly fES .Alnico: This-permanentzmagnet PM is positioned asrindicated: diagrammatically .inf'Fig'QaB to pro- 'vide :magnetic: lines. :of :iorce the? rdirfidtiDI'IlIldicatedt by: the arrow TH substantial'ly'at right angles irto the. planes of: the." anodes :A, :A and parallel :tothesurfaces :of the :control electrodes Thisipermanent magnet PM is preferably provided-:1 withcsoftciron pole; pieces it to give a :more I effective flux d'istributi-on.

Sincethe total anodercurrent .:.dependsupon the area of r the anode -surfac e-,"- aswell :as the cathode to .anodedistance:andtheaeifective anode voltage; it is contemplatedthat.the effective area of the anode may be increased to obtain desired 'currentwreadings by -elongation;=-of the anode plates A,-'A .in Fig-sail. andi3, 1i-n.-a direction par allel .-to [the filament axis. which have their. .-.-width determined-by the spacingof the-control electrodes. G,-.'G .-selected tor the desired control characteristics. -.Also;--i.t is contemplated that a plurality of elemental tubeunits, such. as .shown in-Eigs.-l and-3 may=beassembled in the-same envelope and. have their-anodesan-d rcon-trol elec trodesinterconnected, or employaanodes anclcontrol electrodes .common to adjacent units-, by any suitable disposition-tor relationship otthe par-ts adaptable .for effectual-mountingand. support of the electrodes :inthe. tube envelope Various arrangements. of .expanding. thesurtace. area of the electrodes of the elemental tube. -unit, .or packinga plurality of tube. elements in some cellularelike organization the same envelope may be employed withoutdeparting. iromethe fundamental. attributes -andadvaLn-tages of .this

invention.

The particular organizations. illustrated. in Fi s. 1 nd-3 re m ly typical otthe various other geometrical arrangements and disposition of the cathode, anode vland control electrode, to-

gether with means. providinga magnetic field characteristic of this invention; and it is contemplated, that these organizations illustrated may be. modified. and adapted in other ways, in

additionto varying the space relation and dimen- -4 evacuatedof all air and gases; in accordance 65 with recognized practice to provide what is known as a hard tube;

Consideringnow the function and operation of the controllable .electron discharge tube of this invention, it is foundthata disposition of electrodes, together with a magnetic "field, such'as illustrated and described; provides a control of theelectron-or 'spacecurrent to the anodes in accordance with the variations in "the "potential of the control electrodes with 'respeot'to the cathode, and that thereis noappreciable movement of electrons to the control electrodes and a resultant'electron current, even though the control electrodes assume a relatively high'positive potential with respect to the cathode; 'retical consideration indicates that this action or performance of the device of this invention may be attiibuted to certain recognized phenomena in connection with I the emission and magnetic fields; butit should be understood that therollowing; discussionxof a theory-of operation is not comprehensive, nor necessarily. applicable in all. details to the various forms which the tube of this invention may take.-

With regard to the controlling effect of the potentialon the control-electrodes, it may be said that the numberof electrons emitted from the. cathode and attractedto the anodes in an electron discharge tube is dependent upon the potential gradient to the cathode, and primarily the electrostatic field adjacent the cathode. In the tube ofthis. invention, the electrostatic field of the existing potential. on the control electrodes acts to modify this potential. gradient provided by the space charge and anode voltage in such a Way as to control the electron current'actually flowing to the anodes and through the external output circuit. It may beassumed that the control electrodes of the tube of this invention act inz-this respect much like the grid of the conventional triode, -.negative potentials tending to reduce and cut oif electron current to the anodes, and positive potentials acting to neutralize. the effect of the spacecharge and also supplement the anode potentials tending to draw electrons from the cathode. In. this connection, the relative spacing of the elements as well as the voltages involved, are factors in determining the intensity of the anode current and the efiectiveness and-range of control of thepotentials on the control electrodes.

Speakinggenerally, it is contemplated for-ordinary uses of the. tube thatthe. cathode willbe capableof emitting a surplus of .electronsat the maximum anodeoperating voltage, so that the anodecurrent is limited by space charge etlects. Under such conditions, the. anode. current for a given anode voltage increases .with a decrease in anode.to cathode spacing; and in general the anode to cathodespacing may be choserrfor certain anode voltages to provide the. desired anode current.

With respect to the dimensions and space relation of the control electrodes, the effective area of the control electrodes and their distance from the. cathode depending in g n al pon th o trol potentials to-be usedfor the control electrodes, amplification factor, and control characteristics desired, since it may be considered that the control exercised bythe grid is dependent in general upon the potential or" the electrostatic field created adjacent the cathode emitting surface by the combined action of the potentials on the control electrodes G,.G and on the anode plates A, A When the control electrodes G, G are spaced closer to thecathode C than the anodes A, A as shown in Fig. 2, in general there is an increase in the ratio of the effectiveness of the control electrode and. anode voltages in producing an electrostatic field .near the cathode; and while such relative spacing is generally favorable for many applicationswhere a range of controtvolt'a'geslower'th'an the anode voltage are desirable, it should be'understo'od that other relative spacings "of the :control electrodes and the anode plates withtrespect to the cathode may be employed without I departing from the invention. Similarly; the'contro'lelectrodes G indicated in Fig.2 as extending most of the distance be-- tween-theano'de 'platesA and A may extend over anydesired part of thisdist'anc'e, dependent upon the control characteristics desired; or even project beyond the-anodeplates'if desired for movement-ofelectrons in dischargetubesandin 75"s't'ructural "purposes; 'In "short; the dimensions and relationship of the tube elements indicated in the accompanying drawings are merely typical and may be materially changed without departing from the functions and mode of operation characterizing this invention.

Investigations indicate that the operating characteristics of the tubes of this invention are dependent upon the proportioning and spacing of the tube elements in much the same way as in erally speaking, the cathode and anode spacing determines the space charge effect, and the proximity of the control electrodes to the cathode, as well as their area and potential as compared with the anodes, determines the effectiveness of variations in potentials onthe control electrode upon the flow of anode current. Theoretical considerations, as well as investigations, indicate that various parts may be proportioned and spaced and a tube geometry selected to obtain a wide variety of operating characteristics.

Considering now the important feature of this invention of utilizing the magnetic field in a way 'to minimize or eleminate electron current to the control electrodes at positive potentials, it is a familiar phenomena that a magnetic field will influence the path of movement of an electron.

More specifically, an electron as a negatively charged particle while moving in a magnetic field is acted upon by a force which is perpendicular to the direction of movement of the electron as of a given instant and also perpendicular to the direction of the magneticfield. This force is dependent upon the strength of the magnetic field, and also upon the component of the instantaneous velocity of the electron which is perpendicular to the direction of the magnetic lines of force. In this respect an electron in motion in a magnetic field may be said to be subjected to forces similar to those acting on a current carrying conductor moving in a magnetic field; and the same quantitative relations apply. While an electric field, such as produced by voltages on electrodes in the tube, exerts a force on an electron whether at rest or in motion, and in the direction of the field, a magnetic field exerts force on an electron only when it is in motion, and in a direction at right angles to the direction of such magnetic field. Consequently, a magnetic field does not accelerate or retard the motion of an electron under the influence of an electric field, but merely changes its direction of movement.

Referring to the diagrammatic illustration in Fig. 2, and assuming the magnetic field acts either up or down in the direction indicated by the arrow H along the axis of the tube extending through the cathode and parallel with an imaginary line indicated by the dash lines IE, it can be seen that electrons leaving the surface of the cathode with an initial velocity eithe up or down towards an anode plate A or A and in the same direction as the magnetic lines of force, are not effected by the magnetic field and move in straight lines toward such anode under the infiuence of the electric field of the anode voltage. In the case of electrons leaving the surface of the cathode with a component of velocity at right angles to the magnetic lines of force, however, such electrons will be deflected by the magnetic field in accordance with well known principles; and since these electrons are subject to the infiuence of the electric field as well as the magnetic field, they will move in what may be called a spiral path toward one of the anodes. In other words, it may be said that the magnetic field acts to converge or focus the electrons leaving the cathode into a beam or stream directed toward each of the anodes, as indicated by the dotted lines in Fig. 2.

Generally speaking, the path of movement of the electrons emitted from the cathode is dependent upon their velocity and the intensity of the magnetic lines of force; and the tube elements may be arranged and proportioned, and anode voltages and magnetic field strength chosen or selected, such that the forces acting on the electrons to confine them into a prescribed beam, as compared with the forces exerted on the electrons by positive potentials on control electrodes, will cause all or substantially all of the electrons emitted from the cathode to be focused into a discharge path to the anodes and escape the control electrodes. In other words, the strength of the magnetic lines of force, in connection with the proportioning and spacing of the electrodes and voltages employed, may be such that there is no appreciable electron current to the control electrode, even though said control electrode assumes a high positive potential with respect to the cathode.

Since the tube of this invention involves the influence of a magnetic field upon the electrons moving from the cathode to the anode, it is desirable to avoid any weakening or distortion of this magnetic field by employing non-magnetic metals for the electrodes and many of the supporting elements. For ordinary purposes it is considered preferable to employ tant lum for the electrodes, on account of the facility with which this metal gives up occluded gases and its tendency to absorb gases given off during operation. Molybdenum, or other non-magnetic metals of similar characteristics, are preferably employed for the mounting and supporting elements of the tube, except at the glass seals, rather than nickel, commonly employed for such purpose, in order that the magnetic qualities of nickel may not adversely affect the magnetic flux distribution.

To illustrate this characteristic of the tube of this invention, as compared with the conven tional triode, Fig. 4 shows curves of anode current plotted against anode voltage for different control element potentials per unit of cathode length for a typical tube of this invention; and Fig. 5 illustrates similar curves of anode current against control element potential for different anode voltages of another typical tube. It should be understood that these curves are merely representative of one specific form of a tube, but they serve to illustrate how this invention provides a tube in which the control may be provided by positive control element potentials without any appreciable or readily measurable electron current to the control electrode.

Referring to curves of Fig. 4 for the particular tube under consideration, it will be noted that there is no appreciable anode current for a zero potential on thescontrol electrode. untilzthe anode has a voltage of some 5.00- V'ol-ts and thattheincrease inanod'e current-for increaseslin anode voltage is very slight.

As indicated by the curves of Fig. 5, this particular organization gives an electron discharge tube controlled in effect primarily by positive potentialsof' the control electrode thereby showing a marked contrast with i the I conventional triode. In this connection, it-- should be understood that for the conditions of voltage and cur-- rent shown Figs. 4 and 5 there isnoreadily measurable electron current to the control electrode; i e

The characteristic curves of Figs. 4 and 5 are merely typicalor=representative of one specific organization of. the invention, and it should be understood that the dimensions and spacing of the electrodes may be varied and chosen to-give quite different operating characteristics.

From this illustration and explanation of specific embodiments of the invention, it can be seen that a magnetic field may be combined with a disposition of electrodes,- constituting a thermionic cathode, anodeand a control electrode, and included in anevacuated envelope, in such a way that the anode current-may be effectively controlled in accordance with potentials on the control' electrode, without having any substantial or objectionable electron current to the control electrode when it assumes positive potentials with respect to the cathode. A controllable electron discharge tube of this type, characterized by the absence of any electron current to the control electrode when positive, may be advantageously employed in various applications, where the conventional triode or similar multiple electrode tube is used, more particularly in poweramplifiers and oscillators, where the grid current existing with positive grid potentials and characteristic of the ordinary triode, is a limitation upon efiiciency and performance. Aside from indicating schematically in Fig. 2 typical connections for input and output circuits for the tube of this invention, no attempt has been made to illustrate the circuits for applying a tube of this invention to the field of amplifiers and oscillators, since the tube of this invention is applicable to any one of the various types of circuit organizations, commonly used with triodes for such purposes. In short, a tube of this invention, which may be termed a magna-triode, is in effect an improved or equivalent form of the well known conventional triode, and in general is applicable to all the uses to which such triodes are now applied.

In the particular embodiments of the invention illustrated and described, a filamentary type of cathode has been assumed, and since such a cathode provides electron emission in all directions from its axis, it is considered expedient to provide anodes on opposite sides of such cathode, and. similarly two control electrodes. It should be understood, however, that this is merely a typical or illustrative organization, and that the same principles and mode of operation characterizing the invention may be applied to other forms of cathodes, number and arrangement of electrodes. Similarly, while the anodes have been illustrated as flat plates, it should be understood that these anodes may have curved surfaces, as may be best adapted to the operating characteristics of the tube desired.

The current for energizing the coils shown in Figs. Land" zi -for providing-ether magneticfield characteristic of this invention maybe 1 derived from any suitable: source;.and' on. account of the. power requirements for such an electroemagnetic field, it isdesirable tousapermanentmagnets to.provideuthis,magnetic field when the,.current. and voltage ratings of the..tube,. or other: operating characteristics, .permitipermanent magnets: to. be-used effectively. within the :spacelimitations desired. L The. term magnet isnusedlforfcom venienceintheclaims; as a generic expression: to include a-ipermanent magnet, a.solenoid, or any other type of .like device whichv constitutes. a source, of magneto-motive-forceh .Various adaptations, modifications, andradditions may be made to the specific embodiments of. the invention. illustrated and described .without departing from itsunderlying principles, functions,:and mode of operation; and I desire, to have itunderstood that theinvention isnotjimited to. the specific structural. organizationsilluse trated or described, but may take atwid'e: variety of other forms.

What I claim is:

1. A controllable electron. dischargev tubecomprising, an evacuated envelope, a straightfilamentary thermionicv :emissive cathode 11.11.58.161 envelope, supporting. elements sealed in said envelope for supportingsaid cathode atiits .ends' and supplying heating current thereto, an anode within said envelope having opposing surfaces of substantial area on opposite sides of said cathode substantially parallel with its axis, said anode surfaces being interconnected within said envelope to operate at the same potential, 3, pair of flat control electrodes in said envelope connected together within said envelope and disposed one on each side of said cathode in planes substantially at right angles to said anode surfaces, elements sealed in said envelope for providing separate lead-in connections for said anode and control electrodes, said anode and control electrodes being of a readily degassed but nonmagnetic material, and a magnet outside of said envelope providing magnetic lines of force directed substantially at right angles to the axis of said cathode and the surfaces of said anode, said magnet providing a magnetic field strong enough to prevent significant electron current flow to said control electrodes when the positive potentials applied thereto are relatively high and have a substantial effect upon the electrostatic field at the emissive surface of the cathode and the space current drawn from said cathode.

2. A controllable electron discharge tube comprising a highly evacuated envelope, 2. straight filamentary thermionic emissive cathode supported at its ends by a pair of supporting elements sealed in one end of said envelope, an anode of sheet metal within the envelope having opposing surfaces on opposite sides of said cathode generally parallel with its axis and equidistant therefrom, a rigid connection Within said envelope between said anode surfaces to maintain them in their space relationship and at the same operating potential, a connection for said anode sealed in the other end of said envelope, a control electrode having surfaces on opposite sides of said cathode substantially at right angles to said anode surfaces, a supporting element for said control electrode sealed in the same end of said envelope as said cathode supporting elements, said anode and control electrodes being of a non-magnetic material, and a magnet outside of said envelope providing a strong magnetic field directed transversely of said cathode and substantially at right angles to said anode surfaces, said magnetic field acting to direct electrons emitted from said cathode under the combined influence of positive potentials on said control electrode and anode along paths escaping the surface of said control electrode in spite of a relatively high positive potential applied thereto, said'magnetic field cooperating with said control electrode to provide beams of space current extending to said anode surfaces of an intensity dependent primarily upon the positive potential of said control electrode and without having significant electron current flow to said control electrode.

3. A controllable electron discharge tubecomprising a linear thermionic emissive cathode, an anode comprising surfaces extending throughout the length of said cathode on opposite sides thereof in planes substantially parallel with the axis of said cathode, a rigid metallic connection within said envelope between said anode surfaces to maintain them at the same operating potential, a control electrode comprising a pair of fiat plates electrically connected together within said envelope and disposed one on each side of said cathode, said control electrode having its surfaces extending throughout the length of the emissive surface of said cathode in planessubstantially at right angles to said anode surfaces, a magnet providing a magnetic field acting in a direction substantially at right angles to the axis of said cathode and said anode surfaces, said magnetic field having a strength with relation to the spacing of said control electrodes to permit a, relatively high positive potential to be applied to said control electrodes without having significant electron current flow to said control electrodes, said control electrodes and anodes being made of a readily degassed but non-magnetic material to avoid weakening or distortion of the magnetic field acting upon the electrons emitted from the cathode.

JAMES H. BURNETT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,132,946 Fritz Oct. 11, 1938 2,177,065 Hollmann Oct. 24, 1939 2,187,171 Okabe Jan. 16, 1940 2,227,078 Gerhard Dec. 31, 1940 2,248,712 Litton July 8, 1941 2,259,549 Braden Oct. 21, 1941

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