US2219117A - Electron discharge device - Google Patents

Description

Oct. 22, 1940.- o. SCHADE ELECTRON DISCHARGE DEVICE 4 Sheets-Sheet 1 Filed June 29, 1937 viii/4 35/1/14 .INVENTOR 0770 SCI/ADE B ATTORNEY Oct. 22, 1940.

0. H. sc -mum:

ELECTRON DISCHARGE DEVICE 4 Sheets-Sheet 2 Filed June 29, 1937 'INVE NTOR 077'0 H. SCHADE %aa mar ATTORNEY Oct. 22, 1940. Q, ge E 2,219,117

ELECTRON DIS CHARGE DEVI CE 4 Sheets-Sheet 3 Filed June 29, 1937 1940. o. H. SCHADE 2, 19,117

' ELECTRON DISCHARGE DEVICE Fi led June 29, 1951 4 Sheets-Sheet 4 E5 VOLTS INVENTOR 0770 H. SCHADE /25 2'50 375 ATTORNEY Patented 0a. 22, 1940 Delaware 1 I '5 may -be*'op'erat'e'd'either at the comparatively low' voltages generallyused in conventional receiving "r at considerablyhi'glier voltages.

t f7 e h 10 v cathodejray -tii s, such as X-ray tubes and cathood ifay oscillographswhich operate atcomp'arativ'ely' h i'g 'vbi age's; in some cases several thou- Tliere arealsoat the I I II A I iiicharge devices making use of the conventional .wound "grids which are aligned to reduce sometimes; desired: i In this typef'of t dii'ficulty ncreasesi as the number of turns creased; initheicont rol grid 'In "this type or le'c- 40 trohvdischa'rge: deviee the charactri'stics for 'op' timumcoperaitioriidict'ate the shape andjposition I the positive grid is substantially currentless durn5 Whidhl'ifll utilizediinf-noveli and effective waysm lit I ELncTRoNprsoHARGE DEVICE I ott n; 'Schade; West Caldwell, N. J., assignor, by

mesne assignments; to Radio Corporation of America, New York, N. Y., a corporation of his, usually small and circular 'in ave'"been' utilized. principally in present" time electron dis- I "an electron discharge device having a plurality ent'takeri by the control ele'ct'rode's during n ofthe- -d "vices; While iii-effect lindjup grids-produce mor'e' orle'ss Well defined beams", the iiicoritr'ol over me-team is limitedand: the" current .los to the control electrodes while" small mcam: I

' to 'other typesof tubes'is still greater asrflahe umber: of grids increases 'it'becomes in 1; ,o'rea'sing-ly3 difficult to *aligii' --"g rids and his" I i electrode which may be operated over a partly or GSi'lOf' one; grid necessitates changing the herwi'se the"beanis would b'e i'n-fj other" grid wiresi Furthermore, I

" cathode provided with a plurality of emitting sur- I pehaving high plate current' and a am electron beams, and an anode for receiving the On dbje'ct l of my invention' is' 'to'iiprovide "el'cso tronscl chargeide'vices of the beam type which ar'i officient Elli-Utilize 5 substantially all df "the i t1missionefitbnraiithermioniccathode and in which theetotahidischarge; tromr-the catho'de'J -i's' formed: in-t'o aiplurality ofr -more'orsless avelledefined beams'az tential or at a slightly positive potential, the slots 55 iP 'lArENT omce 'l t licatibar neze,1937, semi No. 150,891

19 Claims (01-. 250-27) obtain improved tubeshaving advantages unobtainable with the conventional types of structure used in electron discharge devices.

Another object of my invention is to provide improved electron discharge devices which-are of much the same dimensions and are operated at much the same voltages as the conventionalreceiving tube, but which can be also effectively operated at higher voltages, and in which various desirablecharacteristics are obtained by segregating the space current into an electron beam or beamsand utilizing the properties of the beam to advantage.

Astill further object is to provide an electron discharge device of the electron beam type which 15 I is of greater efliciency and operates at lower voltages than the beam type devices heretofore used. Another object of my invention is to provide an improved form of electron discharge device in which" the characteristics for optimum operation 0 do not entirely dictate the shape and position of theelectrodes, and in which a change in aperture in one control electrode will not necessarily require a corresponding change in the apertures in other control electrodes.

Itis another object of my invention to provide faces and formed to assist inthe formation of beams of electrons from the cathode. Between the cathode and anode are positioned in succession three slat type grids, that is, flat sheet grids having slots and including a zero or negatively biased grid near the cathode, a positively biased grid; and a third grid which may be at zero poof each of the grids registering with the slots in the other grids and with the emitting surfaces of the cathode. The cathode may comprise a plurality of individual cathode members in registry with the grid slots or a specially formed cathode which provides a plurality of beams. By properly shaping the slots or apertures in the grids and supplying the proper potentials to the various electrodes, I am able to obtain a highly efficient, high current, low mu tube which is particularly suitable for amplifying and power output purposes, and which has the other desirable characteristics referred to in the objects of the invention.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawings in which Figure 1 is a diagrammatic representation of the electrode arrangement of a simple form of electron discharge device made according to my invention and a circuit connected thereto, Figures 2 to 7 inclusive are diagrammatic representations illustrating the action of an electron in various types of electric fields formed by different types of electrodes, Figure 8 is a perspective partly in section to show details of construction of an electron discharge device made according to my invention, Figure 8a is a bottom view of the mount showing details of construction, Figure 9 is a transverse section taken along the line 9-9 of Figure 8, Figure 10 is a detailed showing in perspective of a modified form of cathode construction, Figure 11 is a detailed showing in perspective of a form of grid used in the construction shown in Figure 8, Figure 12 shows the details of a mica spacer used in connection with the grid shown in Figure 11 and the mount of the tube shown in Figure 8, Figure 13 is a diagrammatic representation of the electrode arrangement of another simple form of electron discharge device made according to my invention and a circuit connected thereto, and Figures 14 and 15 are curves showing the anode voltage-anode current characteristics of tubes made according to my invention.

In- Figure 1 is diagrammatically shown the electrode arrangement of a simple form of an electron discharge device employing the principles of my invention. The cathode l which may be of the indirectly heated type has on a restricted area, an electron emitting coating ll.-

Following in succession are grids I2, l3 and 14 having apertures l2, l3 and I4 which are aligned, and an anode l suitably positioned which, receives the beam of electrons from the cathode III. The cathode I0 is shown as a square tubular member indirectly heated but it may be of the directly heated filament type and the grids l2, I3 and i4 rectangular plates provided with rectangular apertures or slots coextensive with the coating H on the cathode Hi. The anode or plate l5 may be an imperforated rectangular electrode. It is understood of course that the electrode system may be duplicated on the other sides of the cathode so that a plurality of beams are formed. The electrode i2 may be at zero or negative potential with respect to the cathode and may be used as the control electrode. As shown, it is biased negatively with respect to the cathode. The second electrode, which is at a higher positive potential may be used as an accelerating rid or screen grid, or as a positively biased control grid in which case grid l2 acts as a beam forming and current adjusting electrode to form the electrons from the cathode into a beam of desired intensity. Grid IB is shown used as a control grid, the input circuit Ill being connected between it and the cathode ID. Grid H may be termed a suppressor grid or shield for controlling the formation of the beam between the grid l3 and anode l5 and to prevent the return of primary electrons and for suppressing secondary electrons. Anode l5 may be connected to the output circuit I5. The broken lines having the arrow heads represent the outline of the beam of electron, and the other lighter lines transverse to the broken lines represent equipotential surfaces or field force lines of the electric field between the various electrodes. The formation of the beam and the effect of the field on the electrons moving from the cathode to the anode will be discussed in greater detail after consideration of some of the fundamental principles governing the movement of electrons in electric fields.

In Figure 2 is represented an electric field in which the voltage increases in the direction of the movement of electrons from to Such a field is termed an accelerating field. The broken lines represent the path of electrons and the straight lines transverse to the broken lines represent the points in space of the same potential. These last lines may be termed field force lines. An electron moving perpendicularly to the field force lines continues to move in a straight line. This is represented by broken line a. If, however, the electron enters the field at some angle as indicated by lines D, c, d, or e, the electron is deflected from its original direction so that it travels on a curved path as shown. The greater the field gradient, that is the greater the change in the field in the direction of the movement of the electron, the greater will be the curvature of the path of the electron until it assumes a direction at right angle to the field force lines.

In Figure 3 is representedan electric field in which the gradient decreases, in other words one in which the potential decreases in the direction of the movement of an electron in the electric field. This is termed. a decelerating field. Here again as shown by the broken line a. an electron will continue to travel in a straight path perpendicular to the field force lines if this is its initial direction with respect to the field. If the electron enters the field at an angle as represented by b, c, d and e the electric forces tend to reverse the electron direction of movement in the same way that the opposing gravitational force tends to reverse the direction of a projectile shot into the air. If the angle is great enough and the field strong enough the electron will make a complete reversal as is inspaced fromit and at a lowe beam disperses.

.electron beam from cathode I6 is focused at some point i beyond the electrode l8 after which the Thus in an accelerating field,

. that is one which increases in potential in the direction of travel of the electron, an apertured electrode atless than space potential, that is, less than the potential which the field would nor-. mally have at the position of the electrode acts like a condensing'lens which focuses the electron beam at some point beyond the electrode in the direction of the movementof electrons.

Because the space potential is increasing in, the direction of electron flight, the lens efiectproduced may be referred to as an accelerating condensing lens.

In Figure 5 the electrode J8 is above space potential. Here the action of the'field is to disperse the beam and increase its width so that v and along the field gradient.

i tential.

no focusing results. In both. Figures '4 and 5 it will be seen that the electrons'tend to move in paths at right angles to the field force lines The resulting lens effect of thearran'gement in Figure 5 may be referred to as an accelerating dispersing lens.

In Figure 6 there is shown an'apertured electrode in a decelerating field and below space p0- Here again the action of the field on the electron beam is to focus the beam as indicated by the broken lines toward a point beyond the electrode in the direction of the travel of the electron. The resulting lens effect may be referred to as a decelerating condensing lens.

In Figure '7 the electrode I9 is in a decelerating field and above space potential, causing dis! persion of the electron beam as indicated by the broken lines. The resulting lens eifect may be referred to as a decelerating dispersing lens.

Various combinations can thus be formed and'by the application of the proper voltages either a condensing lens or a dispersing lens can be provided for effecting the electron beam either to converge the beam to a point or to disperse the beam. Thus an apertured electrode at a potential lower than space potential produces a focusing action while an electrode at a potential higher! than space potential produces a dispersing action.

The field distribution and movement of the electrons as shown in Figure 1 can. now be better understood. The electrode I2 is at a potential which is that of the cathode or at some lower potential, while electrode I3 is at a higher potential than the cathode. This produces conditions equivalent to the condition shown in Figure 4 so that a focusing action results. trode l3 also functions to accelerate-the electrons-toward the electrodes l4 and I5. The aperture l3 in electrode I3 is sufiiciently large to permit the beam to pass through without any substantial number of the electrons directly hitting this electrode. The third electrode I4, which is at a lower potential than electrode l3, but

Elec-- 0nd condensing .lens to prevent excessive dispersion of the beam which diverges beyond the point 9. The results at this point are similar to the condition shown in Figure 6. The beam of course doesnot focus to. a point but has some width at the cross-over or focus a.

The prevention of electron dispersion by insertion of element I4 is desirable to prevent the undesirable consequences of a too divergent beam, which would permit many primary electrons to be returned to the grid, see for example path 'e in Figure 3.

To obtain an efiicient beam tube it is necessary first that the beam width should be smaller than any slot width of any positive element,.to prevent the interception of electrons, and secondly, that the electrons should not be permitted to return to auxiliary positive electrodes. These conditions are satisfied by the construc-- tion shown in Figure 1 in which the electrons are so focused that they are not intercepted by the electrodes l3 or l8, and the potential on electrode l4 and consequently the space potential between H and I5 is sufiiciently less than that of the anode I5 so that secondaries produced at the plate 15 are prevented from returning to any of the positive grids.

Where the potential on grid i4 is less than that on grid l3, being only slightly higher than that of the cathode I0 and lower than that on the anode [5, as is the case in Figure 1, a. high currenttube is obtained with substantially no grid currentp Substantially complete suppres sion of secondary emission is also obtained. In this case, where I4 is at a lower 'potentialthan !3, the slot width I4 must be larger than i3 as shown in Figure 1. I I

By decreasing the width of the slot in electrode I2, the other conditions remaining the same, the distancefrom the cathode of the focal point of the beam is decreased. This increases the dispersion beyond the positive screen and ,may result in undesirable grid current due to 'the greater number of electrons returned to the positive grids after passing through. A short tocal length is desirable to get a narrow beam at cross-over or focus, so that small apertures can be used in the grids andas a result better control over the beam. The most desirable focal length is one that gives the best balance between the control effect of applied potentials and waste current percentage.

I have found that the structure shown in Fig ure 1 is the simplest and produces substantially optimum results. It is of course possible by the introduction of other grids between grid 14 and the anode l5 to produce other results. The plate-impedance in tubesof this type can be controlled entirely by the beam formation in the structure and it may have any value, even negative values regardless of the electrostatic mu values of the grid or control electrode structures. The structure shown in Figure 1 might be described as a lens system having one accelerating lens produced by positively biased grid I3 and has been found quite effective 'in preventing the returnof-electrons having wide angle paths. The

No. 3 grid shields the divergent decelerated beam of primary electrons from the accelerating grid member 2, simultaneously serving as suppressor for secondary electrons, thus'reducing the num- Figure 1 is used with small plate currents as for example in radio frequency operation, it may be desirable to use a fourth or a suppressor grid to decrease the plate to control grid capacity and prevent secondary emission as the space charge in the beam which helps in suppression of secondary electrons becomes too small with small anode currents.

By means of the arrangement described in Figure 1 it is possible to collect with a very low voltage applied on the anode l5 substantially all of the available current from the cathode l0 without loss of current to any of the positive control electrodes. This results in a low control-to-screen grid mu, high current output power tube which is of simple construction and easily made. A reasonable change in the slot width of one electrode need not materially affect the arrangement or construction of the other electrodes in the tube since it is possible by the proper application of potentials to the electrodes to obtain the desired field and electron beam formation, which could not be done in conventional tubes using the conventional helically wound grids. For best results the slot in grid l2 should be coextensive with the emitting surface H on the cathode I8. The slot in grid l3 should be smaller than that in grid 2 but not so small as to intercept electrons. The slot l4 in grid I4 is wider than that in the other grids but not so wide that the grid loses its shielding ability and permits secondary electrons or returned primary electrons to reach grid l3. It is possible with this arrangement, because of the small beam width formed, to obtain effective control over the current and to reduce the loss within the tube to a very small value. Furthermore the positive electrode 3 can be used as a control grid with, very low grid current losses, because the beam is focused through the slot l3.

In Figure 13 I show another simple form of electrode arrangement made according to my invention. The electrode arrangement comprises a cathode having an emitting coating 80' and grids 8|, 82, 83 and 84 positioned between the cathode and the anode and having registering apertures 8|, 82', 83 and 84'. In this arrangement positive voltages are applied to both grids 82 and 83, the grid 83 being at the higher positive potential. With this arrangement I provide a high current tube of similar characteristics to that shown in Figure 1 and having a low first to second grid mu. In this case the slot width in grid 83 is reduced to or made less than the slot width 82' in grid 82 to obtain a good electron lens. Without the grid 84, the high voltage on the second accelerating grid, however, would cause slightly more grid current and increased power loss although still considerably smaller than in conventional tubes. In order to remedy this last condition I use another .or fourth grid 84 between grid 83 and the anode 85 to act as a suppressor for secondary electrons.

A proper balance should be reached between the various factors and it has been found that with the structure shown in Figure 13 where grids 82 and 83 are at a positive potential, grid 83 being at the higher potential, the best results are obtained when the ratio of the voltage on grid 83 with respect to the voltage on grid 82 is equal to 2.5, with the slot 83' being reduced to the width of slot 82' and with the additional suppressor electrode 84 having a slot width greater than the slots in any of the other grid electrodes but not so large that it loses its shielding and suppressing ability. With a higher ratio than 2.5 the beam divergence beyond the focus It is smaller than the convergence angle before the focus. The beam, however, is dispersed again to some extent near grid 83 which would result in increased grid current. This, however, is neutralized by increasing the voltage on the anode or decreasing the slot width of gird 83 or both. However, the slot must not be made such that it interferes with the beam. Where the voltages are applied to grid 82 and 83, as just described, the additional suppressor grid 84 is necessary to prevent return of secondaries. Grid 82 may, however, be shaped with a narrow deep aperture and thus have the combined effect of grids 82 and 83, making it possible to eliminate grid 83. The addition of another electrode complicates the structure although it does increase the tube plate impedance and reduce the waste current. The second method of forming a narrow slot requires a well corrected first electron lens to prevent interception of electrons and thus requires high mechanical accuracy to form the grids. In this case grid 82 is the control grid, the input circuit 86 being connected between the cathode 80 and control grid 82. The output circuit 81 is connected to anode 85.

In Figures 14 and 15 are shown characteristic curves of tubes using the electrode arrangements just described. Figure 14 is the characteristic of a tube incorporating the electrode arrangement shown in Figure 1 and having six beams, and Figure 15 shows the characteristic of a tube incorporating the electrode arrangement shown in Figure 13 and having two beams. It will be observed that in tubes of this type the platevoltage anode-current characteristics have a sharp knee at a very low anode voltage, a very desirable characteristic for amplifying tubes, particularly power amplifying tubes and oscillators.

The arrangement of electrodes shown in Figure 1 is incorporated in a practical embodiment of my invention which is shown in Figures 8 and 9, a plurality of cathodes being used'instead of a single cathode as shown in Figure 1, the grids being provided with a plurality of slots registering with the cathode so that in effect the tube is a multiple unit of the construction shown in Figure 1.

The tube in Figures 8 and 9 includes an envelope 20 having a base 2| and a conventional stem and press 22. A mount assembly is supported on the stem by means of the collar 23 having the upright supporting rods 24 and 25.

In accordance with my invention the mount includes a plurality of tubular indirectly heated cathode elements 28 (heaters not shown) coated only on opposite sides with emitting coatings 21. This limited application of the emitting material and the use of the-bracing fins 28 assist in the formation of beams of electrons from the cathode. Mounted in succession on opposite sides of the cathode are a plurality of slotted rectangular shaped grids including the control grid 29 having rectangular apertures orslots 38 registering with the emitting portions on the cathode elements. This in turn is followed by the screen or accelerating grid 3| having registering apertures 32 and the shield grid 33 provided with apertures 34, the aperture in the grid 3| being the smallest and that in the shield grid 33 the largest. These grids which are of the so-called slat type and best shown in Fig- I8 ures and 9, and in modified formin Figure 11, are mounted on a plurality of insulating rods 40 extending through each of the corners of the grid as shown inFigures 8 and 9, the grids being spaced from each other by means of insulating collars or washers 4| and 4|". The grid assembly is locked in position and the open ends closed by meansof the shield members 42 which are welded by means of the ears 43 to thesupporting uprights 24 and 25.' As best shown in I Figure 8a showing the bottom of the mount, the grids on either side of the cathode are electrically connected together in pairs as by means of jumpers 35, 36 and 31, the grids being pro vided with leads 38, 39 and 31'. Mounted around the cathodes and grids is anode member 44 provided with coolingfins 45. v

The grid and cathode element assembly is maintained in spaced relation by means of upper and lower mica spacers 46 and 41 through .which the cathodes and the ears on the outer grids 33 extend. Longitudinal movement of the micas is prevented by ears 42 on the shield members 42 extending through and bent down against the surface of the micas as best shown in Figures 8 and 8a. The ceramic rods and collars 4| and 4| could be eliminated and ears placed on each of the grids to extend through micafspacers 46 and 41 to space the cathode and grids but the disclosed construction increases the voltage necessary to cause breakdown between i the electrodes due to the better insulating properties of the ceramics at high temperatures and removing high voltages from the mica. This grid and cathode assembly and the anode are in turn maintained in spaced relation by means of the ceramic spacer members 48 at the bottom of the mount and 49 at the top of the mount; the

anodes being supported on the anode side rods 50 which are secured to the ceramic spacer rality of long spring spacers 52 contacting theinterior'of the envelope to resiliently support the upper end of the mount in the envelope. The anode is connected by meansof a lead 53 connected to one of the anode side rods 50 and to the cap 54 at the top of the envelope. Cathode heater wires 55 are electrically connected to the cathodeconnecting bars 56 which are connected and 25 are electrically connected to each other by collar 23. I

-The spacing between the grids, the size of the apertures and other factors. influencing the operation of the tube shown in Figures 8 and 9 are in accordance with the principles set forth above ing to my invention, the first grid is usually the control grid and is at either cathode potential'or negativelybiased with respect to the cathode.

The second grid is positively biased and maybe used as a screen or a positively biased control respect to the cathode, .but at a lower potential tube.

,tom'of the" grid [to a thin lip orledge 'l4 atfithe other bars.

The shield members 42 according to my inventioml provid yidedwith the 'ars pointed. The mica in discussing Figures 1 to 7 inclusive, the'con- ,struction shown diagrammatically in Figure 1 sh'ownat "is provided ati being the construction used in the practicalembodiment of the tubeshown in Figures 8 and 9.

In the preferred operation of a tube made accord- *enlarged central portions ""19 cult t'o nsert-imaged cause of the 'narrowwmtn o machinery in a fixture with remove.

than the anode which is: normally operated at a. lower potential than the-numberftwo grid. The number one or controlgrid should notabe closer to the cathodethan one-half the widthof-tlie slots for best-results. 'Close'spacing of the-elec- 5 trodes is desirable to obtain a tube lnwhichilow voltages can beused; By dividing the total cur! rent into a number of. beams, the current ineach beam is made small enough so that excessive space charge does not build up between the grids and anode and interferes .with the beam and limits the anode current. Because alow anode voltage canbe used and stillobtain high anode current a tube of high efliciency results since little power is dissipated within the tube itself.

A modified form ofcathodeis shown in Figure 10 and comprises a pair of punched and formed stampings 60 and BI provided with slots 52 and raised portions 63 which form a plurality oftubular cathode sleeves. These raised portions are provided with anemitting coating 64. .Mounted within the cathode is the insulated heater 55 having the separate loops 66.61 and. which are inserted within the tubular. members. This cathode is rigid, strong and conserves heat, and is usually made-to provide a plurality of separate emitting sections which help in the formation of a beam. The cathode is easy to assemble and reduces the time required for assembly in the I v I so,

When handling high voltages and high currents it is advisable to have a grid structure in which the separate bars or slats betweenfthe slots can contract or expand independently of each other. in case of uneven heating. A /grid of this kind is shown inFigure 11. The punched and formedgrid 10 provided with theslots; II and the positioning "ears "l2 and "I3 is formed so that the slots ll' extend all the way to the bot bottom of "the grid. If for any reasonthe' different bars intermediate these'slots shoul be heated to different levels so that expansion-is uneven the thin lip which is flexiblejpermitsthei individual bars to movewithoutailecting the Uneven expansion of" onefoifthe bars does not then cause buckling offtliegjrid bars and short circuiting the various grids: If it is desired to increase the transcohducta of the grid, grid wires may be mounted'flin the grid transversely of the slotslj Suchj tubes with grid wires on the number one gridfirairieonly have been made and gavevery mgnit njsfqen ductance values having negligible screenf'grid v E w, .J-Y .a.

In order to iacilitatei'asseinbly ota tu f and mica spacer arrangement for X As best shown in Figure 12 the 'gri an-enlargedop'ningf s wil r T i permits q ears; The elements-may be starte b possible in conventional tube mounts. 1

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is:

1. An electron discharge device including a thermionic cathode, an apertured control electrode for forming the electron discharge from said cathode into a focused beam and means for maintaining said control electrode at a voltage not greater than that of the cathode, a second grid electrode having an aperture registering with the aperture in said control electrode and means for maintaining said second electrode at a positive voltage, and a single anode for receiving electrons in said beam, and means for maintaining said anode at a lower positive potential than said second grid electrode, and a third grid electrode between said anode and said second grid electrode and having an aperture registering with the apertures in the other electrodes, and means for maintaining said third grid electrode at a potential greater than that of the cathode but less than that of the second grid electrode and anode.

2. An electron discharge device having a cathode formed to assist in the formation of a beam of electrons, a control electrode having an aperture coextensive with said cathode and through which electrons pass for forming a focused beam, and means for maintaining said control electrode at a voltage not greater than that of the cathode, a second electrode having an aperture registering with the aperture in the control electrode and positioned so that the beam is focused near the aperture of said second electrode and means for maintaining said second electrode at a positive potential with respect to said cathode, a single anode for receiving the beam of electrons from said cathode, and means for maintaining said anode at a positive potential less than that of said second electrode, and a third electrode between said anode and said second electrode and having an aperture registering with the apertures in the other grids, and means for maintaining said third electrode at a positive potential less than that of said second electrode and said anode.

3. An electron discharge device including a thermionic cathode having a plurality of parallel longitudinally extending emitting surfaces, means for forming the electron discharge from said cathode surfaces into a plurality of beams and including a control electrode of sheet material and provided with a plurality of apertures registering with said coated areas on the cathode and coextensive therewith, and a second electrode of sheet material parallel to said first electrode and spaced therefrom and provided with apertures coextensive and registering with the apertures in said first electrode and of larger cross section area than said beams, a single anode for receiving said beams of electrons, and a third electrode positioned between said second electrode and said anode and having apertures registering and coextensive with the apertures in the other electrodes and of an area greater than the width of the beam passing through said last electrode, the

width of the aperture in the first electrode being greater than the aperture in said second but less than that of the aperture in the third electrode.

4. An electron discharge device having means for forming the electron discharge from a cathode into beams of rectangular cross section and including a cathode having a plurality of rectangular shaped parallel coated areas for providing a pluralityof electron emitting areas, a single anode for receiving the electrons from said cathode and at least three electrodes positioned between the cathode and the anode and comprising sheet metal electrodes provided with apertures coextensive and in registry with the electron emitting areas of said cathode, the electrode nearest to said cathode being spaced from said cathode not less than one-half the width of the aperature in the electrode nearest to said cathode and forming focused beams which pass through the apertures of the other apertured electrodes to said anode.

5. An electron discharge device having a plurality of beam forming cathode elements, each of said elements comprising a tubular member provided on opposite sides with fins extending beyond the surface of said tubular members, said cathode elements being coated with emitting material only on the surface lying between said fins whereby a beam is formed, a control electrode adjacent said cathode elements and comprising a sheet metal member provided with a plurality of rectangular shaped apertures coextensive and registering with the emitting surfaces of said cathode elements for forming the electrons into focused beams, a single anode for receiving said electrons and a plurality of other sheet metal electrodes positioned between said first control electrode and said anode and provided with a plurality of rectangular shaped apertures in registry with and coextensive with the apertures in said first control electrode, the apertures in said plurality of grids being larger than the cross section of the beams passing through said electrode.

6. An electron discharge device including a cathode for emitting electrons and an anode for receiving said electrons, a control electrode positioned between said cathode and said anode and comprising a sheet metal electrode, one edge of which lies in a plane at an angle to the remainder of said sheet electrode to provide a lip, and apertures in said electrode extending substantially the length of said electrode to said lip whereby the portions of the grid between the apertures may expand and contract independently of each other.

7. An electron discharge device including a cathode, an anode and a control electrode positioned therebetween, said control electrode being of sheet metal and provided at one end with a pointed ear, and an insulating spacer member at one end of said cathode, anode and electrode and having a slot for receiving said pointed ear, said slot being enlarged at that part which registers with the point on said ear to permit quick assembly of said insulating spacer and said control electrode.

8. An electron discharge device including a cathode having a plurality of longitudinally extending electron emitting areas, a control electrode having a plurality of apertures registering with the emitting areas on said cathode for forming a plurality of beams, a second electrode coextensive with said first electrode and spaced therefrom and provided with a plurality of apertures registering with the apertures in said control electrode, asingle anode for receiving the beams of and a voltage source for maintaining said third tial with respect to said cathode, a voltage source for biasing said second electrode to a positive potential with respect tov said cathode, a voltage I source for maintaining said anode at a positive potential less than that of the second electrode.

' electrode at a positive potentialless than that of said second electrode and said anode.

9. An electron discharge device including a thermionic cathode, a control electrode having an elongated aperture for forming the electron discharge from said cathode into a beam, a second electrode having an aperture in registry with the aperture in said control electrode and of an area greater than thecross section of the beam, a third grid electrode having an aperture registering with the apertures in the other grids and a single anode for receiving electrons in said beam, a voltage source for biasing said control electrode to negative potential with respect to said cathode, a voltage source for biasing said second electrode to a positive potential with respect to said cathode, a voltage source for maintaining said anode at a positive potential less than that of the second electrode, and a voltage source for maintaining said third electrode at a positive potential less than that of said second electrode and said anode.

10. An electron discharge device having a cathode formed to provide a beam of electrons, a control electrode having an aperture coextensive with said cathode and an aperture through which the electrons pass for forming a focused beam, a second electrode having an aperture registering with the aperture in said first electrode and positioned so that the beam is focused near the aperture of said second electrode and a third electrode having an aperture registering with the apertures to a negative potential with respect to said cath-.

coatings on said tubular sections, and a conin the other electrodes, a single anode for receiving the electron beam from said cathode, a. source 01' voltagefor biasing said control electrode ode, a source of voltage for biasing said second electrode to a positive potential with respect to said cathode, a voltage source for maintaining said anode at a positive potential less than that of the second electrode, and means for main- :taining said third electrode at a positive poten-- tial less than that of said second electrode and said anode. I

' 11. An indirectly heated cathode having a plurality of spaced parallel emitting surfaces and including aflat member provided with a plurality of longitudinally extending tubular sections with slots in between said sections, electron emitting tinuous insulated heater wire extending within each of the tubular sections.

. 12. An indirectly heated cathode having a p1u-' rality of spaced parallel emitting surfaces and and secured together with the longitudinally extending channel shaped sections in registry and cooperating to provide a plurality of tubular sec- 'ments, a plurality of fiat slat type grids and in-- sulating bars extending through said grids for ,tions, an emittingcoating on said tubular sections and an insulated heaterwire extending within each of the tubular sections.

13. An electron discharge device comprising a plurality of longitudinally extending cathode elepositioning said grids with respectlto each other, andinsulating washer members carried by said insulating bar for, maintaining said grids in spaced relation, U-shaped shieldmembers at opposite longitudinal edges of said grid members for maintaining said grid membersassembled on said bars, mica spacer members at the oppositeends of said cathodes, grids and shields for maintaining said cathodes, grids and shields in spaced relation, an anode having side rods surrounding said cathode and grids, ceramic members at opposite ends of said anode and secured to the anode side rods, and supporting rods to which said shield members are secured and to which said ceramic members are secured for maintaining said cathode, grids, shields and anode in spaced relation.

14. An electrode assembly having a cathode and grids and-insulating members at opposite ends of said cathode and grids for maintaining grids in spaced relation, insulating spacers at opposite ends of said cathodes and grids formain taining said cathodes and grids in spaced relation, oppositely disposed shield members adjacent said grids and secured to said insulating spacers for maintaining said cathodes, grids and shield in fixed relationship, a pair of support rods, said shield members being secured to said support rods, an anode surrounding said cathodes and grids, ceramic members secured to opposite ends of said anode and to said support rods for maintaining said cathodes, grids, shields and anode in spaced relation.

16. An electron discharge device having cathode formed to assist in the formation of abeam of electrons, a first electrode having an "aperture co-extensive with the cathode and through which electrons pass for forming a said cathode and grids in spaced relation, shield focused beam, a second and third electrode each having an aperture registering with the aperture in the first electrode and positioned so that the beam is focused through the last two apertures, and a fourth electrode having an aperture registering with the apertures in the other electrodes, and a single anode for receiving the electrons from said cathode, the aperture in the first electrode being greater than the apertures in the second and third electrodes but less'than that in the fourth apertured electrode.

17. An electron discharge device having a cathode formed to assist in the formation of a beam of electrons, afirst electrode having an aperture co-extensive with the cathode and throughwhich electronspass for forming a focusedbeam, a second and third electrode each having an aperture registering with the aperturein the first electrode and positioned so that the beam is focused through the last two apertures, and a fourth electrode having an aperture registering with the apertures in the other electrodes, and a single anode forreceiving the' electrons from said cathode, a voltage source for applying a negative potential to the first electrode with respect to the cathode, a voltage source for applying a positive potential to the second and third electrodes with respect to the cathode, and a voltage source for applying a voltage to the anode less than that applied to the second and. third electrodes, and means for applying a voltage not greater than that of the cathode to the fourth apertured electrode.

18. An electron discharge device having a cathode formed to assist in the formation of a beam of electrons, a first electrode having an aperture co-extensive with the cathode and through which electrons pass for forming a focused beam, a second and third electrode each having an aperture registering with the aperture in the first electrode and positioned so that the beam is focused through the last two apertures, and a fourth electrode having an aperture registering with the apertures in the other electrodes, and a single anode for receiving the electrons from said cathode, a voltage source for applying a negative potential to the first electrode with respect to the cathode, a voltage source for applying a positive potential to the second and third electrodes with respect to the cathode, and a voltage source for applying a voltage to the anode less than that applied to the second and third electrodes, and meansfor applying a voltage not greater than that of the cathode to the fourth apertured electrode, the ratio of the positive voltages on the third grid to that on the second grid being 2.5 to 1.

19. An electron discharge device including a cathode, an anode and a control electrode positioned therebetween, said control electrode being of sheet material and provided at one end with a plurality of pointed extensions, and an insulating spacer member at one end of said cathode, anode and control electrode and having slots into which said extensions fit snugly, said slots having an enlarged portion at that part which registers with the points on said extensions to permit quick assembly of the insulating spacer and said control electrode.

OTTO H. SCHADE.

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