US2107519A - Electron discharge device - Google Patents

Description

Feb. 8, 1938. SHQENBERG AL 2,107,519

ELECTRON DISCHARGE DEVICE Original Filed July 27,' 1934 3 Sheets-Sheet 1 Lwz wanna (,4 3 7 4641011 41 l- Smiy H "up To 15 n'rmn- In Ill/(Air 1938. I. .SHOENBERG ET AL ,1

ELECTRON DISCHARGE DEVICE Origin al Filed July 27, 1934 S Sheets-Sheet 2 5 14; 610618513 M1 sun" a .17.

A Trauij/ 714 M Febjs, 1938. SHOENBERG ET AL 2,107,519

ELECTRON DISCHARGE DEVICE Original Filed July 27, 1934 3 Sheets-Shed 3 Amy's ne M 5 more than a 2,101,519 ELECTRON DISCHARGE nnvrcn UNITED STATES" Isaac Shoenbcrg, London,

Hillingdon, and Sidney d, minors to Elect tries Limited, Middlcsex,

tain

of Great Brl Original application 1935, Serial No. 24,482.

In Great BritainAugust 2,

The present invention relates to electron discharge devices of the course of its oscillation, the anode voltage falls certain small amount below the fixed voltage of the screening electrode. For many purposes the flow of such secondary emission current from the anode to the screen is undesirable and proposals have been made to pre- 'ven t it.

In one known arrangement a third grid, usually connected to the cathode, is arranged between the screening electrode and the anode.

It is the principal object of the present invention to provide an electron discharge device of the kind above referred to in which the flow of secondary emission current from the anode to the screening electrode can be prevented with the a normal operating potential the anode voltageanode current characteristic exhibits no inflexion. The space charge itself electrostatic field may be insufiicient.

Although in some forms of discharge devices according to the present invention the distortion of the electrostatic field produced by the auxil- July 27, 1934, Divided and this application June 1,

Cabot Seaton Bull, Rodda, Enfield, Engric and Musical Indus- England, a'company Serial No.

Renewed June 12, 1937.

According to the present invention a discharge device comprises a cathode surrounded by a con trol grid and a screening grid, the screening grid being surrounded in part by an anode and in to the accompanying drawings, in which Figures 1, 6 and 7 are diagrammatic views in plan of certain forms of discharge devices according to the present invention, I

Figures 2 to are curve diagrams serving to explain certain characteristics of discharge devices according to the invention,

' Figures 8, 9 and 12 are diagrammatic views in plan of further forms of devices according to the invention,

Figures 10 and 11 are diagrammatic views in elevation and plan, respectively, of a further form of the invention,

Figures 13, 14, 15 and 16 are views in side elevation, front elevation, sectional elevation and plan, respectively, of a preferred constructional embodiment of the invention,

Figure 17 is a perspective view of an anode of the device of Figures 13 to 16,

Figures 18 and 19 are perspective views showing methods of supporting anodes in arrangements according to the present invention, and

Figures 20, 21, 22 and 23 are views in elevation, sectional plan, sectional elevation and underside plan, respectively, oi a second preferred constructional embodiment of the invention.

Like parts are indicated in the various figures by the same references. I

Referring to Figure 1, there is shown diagrammatically the electrede arrangement of one form of device according to the present invention. A cathode a is of rectangular cross-section and is elongated (in a direction perpendicular to the paper). Two control grids b1 and be are arranged one on each side of the cathode 'a and are spaced therefrom by means of insulating strips 10, one strip being arranged near one end of the cathode and another near the opposite end. Thus the strips k are located substantialiy out side the electron stream. Two screening grids c1 and c: are arranged outside the control grid andare spaced therefrom by means of further insulators k. This assemhly may be clamped together in any convenient way and mounted within a casing e which constitutes an auxiliary electrode. This auxiliary electrode has portions 1 extending towards but not to any great extent into the discharge space. Anodes d1 and (12 are provided as shown. It will be assumed for the present that the anodes d1 and are electrically connected together and that the two grids bl and b: on the-one hand and c1 and 02 on the other hand are also connected together.

If the anodes d1, dz be maintained at a positive 'potential relatively to the cathode a and if the screens 01 and c: be maintained at a potentiai which is higher than the anode, the potential distribution in the space between each anode section d1 and (Z2 and the corresponding screen section or or 02 along lines-normal to the screen and anode will be somewhat as represented in Figure 2, where voltages are plotted as ordinates against distances as abscissa. The position of the anode is represented by the line D and the position of the screen by the line C, the heights of these lines representing the potentials at the anode and screen respectively. The dotted curve go shows the distribution of potential along lines between the anode and screen approximately normal to these electrodes in the absence of eiectron flow and without the auxiliary electrodes. In the case of infinite plane parallel anode and screen this curve 90 is a straight line. In other cases it is curved somewhat as shown. Owing to the action of the auxiliary electrode including theportions 1 thereof, it will be seen that the distribution of potential between the anode and screen represented by the curve 9 is such that (I: is made more positive proceeding from the anode to the screen, where V is the potential at any point and a: is the distance of this point from'the anode. That is to say the rate oE change of the potential gradient is more positive, the poten-.

tial gradient being of course It will be seen also that the potential gradient in the neighbourhood of the anode is very small and for this reason very little further drop in potential in the anode-screen space is necessary to produce a potential minimum in the space as shown in Figure 3 where the curve 9 of Figure 2 is shown'dotted and the curve It shows the effect I tential.

of a further drop in potential in the space. Such a further drop can of course be produced by space charge due to the primary electrons from the cathode and the secondary electrons from the anode. It has been found however that unless, in the absence of electron emission, the value of 1 dz is positive to a substantial degree, the space charge is incapable of forming the potential minimum at least in those cases which have so far been investigated, with normal working currents. In Figure 2 there is shown in dotted lines the distribution of potential g1 when the screen indicated by C1 is closer to the anode. it will be seen that the potential gradient close to the anode is much higher than in the case above considered and consequently a greater additional drop in potential will be required to produce the desired potential minimum. This curve indicates the importance of arranging the anode at a sufiicient distance from the screen taking into account the voltages and currents at which the electrodes are to work.

Figure 4 shows the distribution of potential when the anode and screen are at the same po- Here also is positive and therefore This minimum, produced electro-staticaliy when the anode voltage is equal to that of the screen, if it be of sufiicient depth, prevents the flow of secondary electrons between the anode and screen in both directions under conditions in which the depression due to space charge alone, owing to high electron velocities, is insuflicient. When the anode voltage is much lower than that of the screen, the increase in space charge effects due to reduction in eiectron velocities causes such an increase in the depression in potential that although there is now no electrostatic potential minimum, there is suflicient total depression of the potential below that of the anode to prevent the flow of secondary electrons from the anode to the screen.

Along a line in a the direction 'of the electron stream '(that is parallel to the anode surfaces) the distri iition oftion in the space is thus in the form of a saddle' The modification of the potential distribution in the anode-screen space produced by the aux iliary electrode has afocusing or concentrating efiect upon the electron stream in the screen to anode space. The result of this concentration of the electrons is that the space charge developed is considerably increased and the formation of a potential minimum by space charge is assisted. Thus if secondary electrons are emitted by the anode at a velocity of about 20 volts, for example, they may travel some distance towards the screening grid until they reach a position in which, if the space charge is suii'iciently dense, they are brought to rest by the potentials arising from the space charge and the electrostatic field. They then return to the anode and give rise to more secondaries. The process may be repeated so that it may be expected that in the direction at right angles to a potential minimum is produced even in the absence of electron flow.

creased or if the neighbourhood of the anode surface there will be in the neighbourhood of the anode produced by modification of the electrostatic field will be accentuated by the space charge due to the primary electrons and also by the space charge due to the secondary electrons, and the electrostatic and space charge modifications are arranged together For most purposes a tetrode is required to have an anode voltage-anode current characteristic of the kind shown in Figure 5 wherein the anode voltage EA is shown plotted against anode current In for various values of the control grid voltage Eg- It is usually desirable that the knee m should be as sharp as possible and should oc-.

cur at as low a voltage as possible, and that there should be no.inflexion or kink, or at least no marked infiexion, in the characteristic. A kink such as appears at n in the curve Eg=4 and to a less extent in the curve Ey=--3 is not material because it isat a point away from any practical working point. However, it has been found possible to produce devices according to this invention in which no noticeable kink is present in A practical load line for a resistive load is shown at o and in the case of an inductive load the load line may have the form shown dotted at 01. In neither case do appreciably inflected portions fall within the working range of anode voltages and currents. It will be assumed that the type of characteristic shown in Figure 5 is desired (although it will be understood that for certain purposes other forms of characteristic may be preferred) and certain ways in which departures from the desired characteristic are obtained will be explained in order.

that the eifects of the several variables may be appreciated.

If either the anode d1, d: is too small in area, the auxiliary electrodes e are too close to the electron stream or the projections or slats Z extend too far into the electron stream, the characteristic has a knee m of'large radius of curvature and the value of anode voltage above which the current is nearly constant is not well defined and rather high. If the area of the anode is in.

auxiliary electrodes are arranged i'urther away from the electron stream, thedesired form of characteristic can be obtained. Further increase in area of the anode or in the distance of the auxiliary electrodes from the electron stream gives rise to a characteristic in which the knee m is very sharp and the anode current falls beyond the knee and then rises again so that the curve exhibits an. inflexion. This form of characteristic indicates that secondary emission is reaching the screening grid. I

The way in which the device with what has been referred to as the desired characteristic is believed to operate will now be described.

The screening grid will be assumed to be held at some suitable positive potential relative to the cathode, the auxiliary electrode will be assumed to be at cathode potential and the anode voltage will be regarded in the first place as at cathode potential. Under these conditions the electrons projected towards the anode will come to rest before reaching the anode on account of the elec trostatic field, the low anode potential and the portion flowing to anode potential increases.

Above the knee voltage there is still a potential minimum along the electron path but this minizero potential, substantially simultaneously over the whole area of the virtual cathode. If the size voltage around the edges of the beam than in the centre, thus giving rise to a knee of lai'ger radius of curvature.

If the anode be unduly large, the secondary space charge consisting of electrons moving slowly in random directions can diffuse to the por- I tions of the anode not struck by primary electrons or at least not struck by any considerable number of primary electrons. The space charge is in this case reduced in intensity and may be insuflicient to prevent the flow of secondary electrons to the screening grid. Even if the anode is not unduly large it is usually necessary to take steps to prevent the secondary electrons from diifusing around to the back of the anode with similar results to those produced by an unduly large anode. For this purpose the auxiliary electrodes already described are arranged to extend to points close to the edges of the anode. With anodes'of small size it may be found unnecessary to extend the auxiliary electrodes so .close to the anode.

Unless the anode is of considerably greater length the anode only.

If it is required that the knee voltage should be reduced, it is necessary to reduce the primary primary space charge, with the assistance of the secondary space charge and the electrostatic field, to maintain a sufiiciently pronounced potential minimum to prevent the secondary electrons from travelling to the screening grid and, in the 75 latter case, upon the fineness of structure of the screening grid.

It has been found that if the anode and the screening the distance between grid be too small in comparison with the pitch of the screening grid, for example about four times or less, the electron distribution over the surface of the anode is markedly non-uniform. The effect of this is that secondary electrons can return to the screening grid through those parts of the space which lie in front of the screening grid wires because in these parts there is very little primary space charge and consequently only a small screening effect due to space charge.

This effect of the non-uniformity of the electron stream can be reduced or removed by dividing the anode into a plurality of parts and preferably by inserting auxiliary electrode plates, which may be connected to the auxiliary electrodes already described, between the two or more parts of the anode. v I

So far as it has been assumed that the auxiliary electrodes by which the electrostatic potential minimum are produced'were maintained at a fixed potential equal to that of the cathode. This is not necessarily the case. In the first place it may be found desirable or convenient to arrange the auxiliary electrodes at fixed potentials difiering from the cathode potential. An

auxiliary electrode at cathode potential in a given position can often be replaced, with equivalent results, by an auxiliary electrode located closer to the electron stream and having a potential above that of the cathode or by an auxiliary electrode located further from the electron stream and having a potential lower than that of the cathode.

Further it is not necessary that the auxiliary electrode potential should be. maintained constant. In some cases the auxiliary electrode potential may be allowed to vary with the potential of the anode or control grid.

In addition to the feature of this invention, namely the provision of means whereby an electrostatic potential minimum can be developed at some region in the space between the screening grid and the anode, at least trodes are at the same potential, it is usually desirable to arrange that (1) A region between the screening grid and anode which constitutes a virtual cathode at low anode potential should become a region of minimum potential, exceeding zero potential, sub1- stantially simultaneously over the greater part of the region as the anode potential is increased, and

(2)The distance between the anode and the screening grid should not be less than about twice the pitch of the screening grid, that is to say the mesh of this grid or the equivalent structure size.

Condition (1) is not essential since if it is not fulfilled the principal effect is to influence the shape of the knee of the characteristic. The efiect of this may only be that the amplification obtainable is not so free from distortion as with a sharper knee. A knee which is slightly more rounded than it need be may be advantageous in some cases as it has been found possible to obtain a higher impedance above the knee voltage under these conditions.

Instead of allowing the auxiliary electrodes e to extend alongside of the grids and cathode as shown in Figure 1, the auxiliary electrodes may be terminated just short of the screening grid, for example at the inwardly projecting slats l as when these two elecshown in Figure 6. The electrostatic field in the space between the'anode and screening grid is not affected by this shortening of the auxiliary electrodes. Auxiliary electrodes 11, preferably electrically connected and ca, may then be provided around the grids and cathode. In the construction shown in Figure 6, the auxiliary electrode is extended around the back of theanode as shown at q.

A modification of the arrangement of Figure 1 is shown in Figure 7 where the projections l are omitted and the auxiliary electrode e is shaped so as to influence the electrostatic field in the anode-screen space in the desired manner. As in Figure 6, the auxiliary electrode is continued behind the anode at q and it also acts as a clamp for the grid and cathode assembly. For this purpose the electrode e is formed in two halves with flanges 1' which can be bolted or otherwise fixed together, suitable insulating means In being provided between the electrode 6 and the grids c1 and 02.

Another construction according to the invention is shown diagrammatically in Figure 8. In Figure 8; the elongated cathode a is surrounded by a control grid b which is in turn surrounded by a screening grid 0. Around the screening grid c is arranged an anode in two sections (11 and dz each of part cylindrical shape and between the anode sections (ii and (12 are arranged further part cylindrical electrodes e1 and e: constituting sections of the auxiliary electrode. The two grids b and c are of cylindrical shape and these two electrodes together wi the anode and auxiliary electrode preferably extend over substantially the whole length of the cathode a. In this case it will be seen that the sections 1 and. e2 of the auxiliary electrode constitute continuations of the anode sections di and (l2 and lie in the same cylindrical surface as the anode sections, this surface being coaxial with the cathode a and the two grids b and c. The sections of the auxiliary electrode are connected electrically together and are either connected to the cathode, for example within the envelope 1 of the device, or else they are brought out to a suitable external terminal by which-they can be maintained at a low potential usually not difiering greatly from cathode potential.

The auxiliary electrodes e1 and ez serve to modify the electrostatic field in the anode-screen space in such a way that is sufliciently positive proceeding from the anode to the screen and when electron current is flowing between the cathode and the anode a space charge is set up in the space as already described. In the regions of the space opposite the rods s which support the grids,.however, an electron shadow is cast and in these regions what may be termed the electron screen which serves to stop secondary electrons is absent or insufficiently dense. To overcome this difficulty there are provided shield members t which are so placed that they stop secondary electrons which might otherwise reach the screening grid 0.

The shields t may be of metal or of insulating material. In the former case they may be of solid metal or in the form of a metal coating on an insulating backing. The metal surface may be connected to the auxiliary electrodes e1 and e2 or to some other point of relatively low potential to the screening grids 0i i where insulating shields are used they may be of fixed to the anode d, for example with the aid of glass or mica for example and in operation each rivets, near to the top and bottom thereof. These to that of the cathode. placed in position upon tongues v1, 122, v: and D4 5 In a modification of the arrangement of Figure bent outward from the plane of the auxiliary 8 shown in Figure 9, the anode and auxiliary elecelectrodes as above described and these tongues trode are still further subdivided into parts d1, are bent over the projecting ends of the strips as (Z2, (Z3 etc. and 81, ea, ea respectively the former shown at or and 112 to hold them in position.

10 parts being interspersed with the latter. Instead of bending tongues out from the body 10 cathode. Thus each anode section a1, a2 and also be applied to the securing of a plurality of each section of the auxiliary electrode e1, e2, e; is anode elements to one another in cases, such as 15 in the form of a short cylinder. have been described above, in which the anode Figure 12 illustrates a modification of the aris divided into a plurality of parts. When-the rangement of Figure 8 in which the shields t anode elements are separated by an auxiliary and the auxiliary electrodes e1, e: are combined electrode the adjacent sections of the auxiliary and the whole electrode e1, 62, t may be regarded electrode can also be supported Irom'one another 20 as the auxiliary electrode.

In the arrangements of Figures 1, 6, 8, 9 and a similar way any one electrode can be supported 10, the auxiliary electrodes are themselves or from any other electrode so long as these elec- 'have parts it (Figures 1 and 6) which form controdes have parts extending sufliciently near totinuations of the anode. gether. 25 In Figure 12 the auxiliary electrode although Referring now to the constructional embodinot constituting a continuation of the anode surment of the invention shown in Figures 13 to 17, face nevertheless has edgeslocated close to edges two control grids b1 and b2 and two screening of the anode so that the anode sections d1 and d2 grids c1 and c: are mounted in suitably spaced retogetherwith the auxiliary electrodes form sublation from one another and from the cathode a by 30 tially square or circular shape. When these elecof mica. Two anodes 111 and dz are fixed t th trodes have a much greater length (in the direcmica strips 2 by means of tongues 3 which protion of the length of the cathode) than breadth, ject through the mica, and are bent over.v As- .40

In discharge devices of the kind described in projecting portions 6 extending close to the edges which the auxiliary electrodes extendclose to the of the anode. In the rectangular apertures in 45 in which this may be done are illustrated in Figof the auxiliary electrodes are caused to bear 50 the top of the two auxiliary electrodes. Two the cathode and grid assembly is thus held firmly 55 0 plate, has a rod 20 preferably of square section ed so that together with the screening grid 0 ends. The rod 10 which projects from the upper engaging in the notches in theends ofthe msw may be connectedto the cathode within the en- 70 to holdthem in position, at any desired low potential. The potential of the In a, modified construction shown, in Figure 19 auxiliary electrode is usually fixed but 88 al 7 thin strips of insulating material 21 and z: are ready stated need not necessarily be so as it may between twio discs e'f insulating material Si and Ill for example of 'mica which have serrated edg es adapted to bear against the inner walls of the envelope f. The anodes 1o auxiliary electrodes of and e: are mounted npon the mica dies 9 and III with the aid of lugs II which pass through holesjin the discs and are bent over. Thus the electrodes (11,42, e1, ez serve to form a'rigid structure with the discs 9 and I0. I The cathode a is lecated in apertures in the centres of the discs 9 and Ill and the grid supporting reds s also pass through holes in the discs 9 v aiid I0. The cathode is of the indirectly heated type and the heater is brought out through leads I2 and I3, the cathode itself being connected to lead I. The anode parts di and (12 are connected together by a wife l5 and to a lead l6.f

The auxiliary electrode partsei. and e: are connected together and to shields t by a wire l1 and to a lead l8 and also to the cathode a. The gridsE "b and c 'e-re connected respectively to leads ,l9 and: 20. The shields t are provided in the shadow "cast by the rods .9, for the purpose described in connection with Figure 8. These shields are fixed to the mica'discs 9 andjill with the aid of lugs 2|. f

The anode @ctions a; and 112 may be provided as shown with' slats or projections 22 in the form of small part annular members of sheet material.

5 Theseislats are preferably arranged fairly nee;

i to the upper and lower end of each ,section 51' and 112. In one example they aredis'tant from the ends of the sections (21 and (12 by about one fifth the whole length of the sections. The pur- 40 pose of these slats is :to intercept electrons travelling obliqueiy in the anode-screen space which might in the absence of the slats reach the screen around the outside of the space charge area.

Iti' has found that in addition to the various factors influencing the behavior of discharge devices according to this invention aiready mentioned, there are certain other points which should be taken 5 to consideration. If the 50 screening grid be ariranged too close to the control grid or be too open, the control grid may produce a reduction in potential in the anodescr'een spagie. )This reduction in potential enhances the'effect of the auxiliary electrode and 55 must be taken into account when designing the device or eise firstly the knee of the characteristic may be of unduly large radius of curvature and secondly the impedance of the device above the knee voltage inay be lowered. The former effect is believed" to arise because the virtual cathode disappears at different voltages at different paints in the anode-screen space, latter effect is believed to arise from the influence of the control grid in preventing the removal of 65 secondary space charge from the screen by the anode. g

In some constructions it is desirable to align the apertures it? the control grid with the apertures iii the screen in the direction of the electron stream and if a device is designed to operfate satisfactorily in accordance with the present invention with aligned grids it may be found to operate unsatisfactorily if the grids are not 75 aligned. The effect produced is equivalent to that produced by the use of a screen which is too open. 1

We claim: r 1? 1. An electron discharge device comprising, within an evacuated envelope, a cathode surrounded by a control grid, a screeninggrid surrounding said control grid, an anode having surfaces coextensive withand disposed oppgisite to longitudinal portions of said screening gricFand an.

auxiliary electrode insulated frem said anode and having surfaces coextensive with and disposed opposite to other ilongitudinal portions of said screening girji'd, said anode and said auxiliary electrode being 'jeach' in a plurality of sections, the sections of said anode being interspersed with ,the sections of said auxiliary electrode.

2. An electron discharge device comprising an elongated cathode surrounded by a control grid, a screening grid surrounding said control grid, an anode having surfacesgcoextensive withrand disposed opposite to longitudinal portions of said screening grid and an auxiliary electrode insulated from said fanode and having'surfaces coextensive with and disposed opposite to other longitudinal portions of said screening grid, said anode and said auxiliary electrode being each in a plurality of sections, the sections of said anode being interspersed with the sections of said auxiliary electrode, and each of said sections extending over substantially the whole length of said cathode. i I 7 3. An electron discharge device comprising, within an evacuated envelope, a cathode surrounded by a control grid, a screening grid surrounding said control grid, an anode having surfaces coextensive with and disposed opposite to other longitudinal portions of said screening grid and an auxiliary electrode insulated from said anode and having surfaces icoextensive with and disposed opposite to other longitudinal portions of said screening grid, said anode and said auxiliary electrede being each in a plurality of sectie fns, the sections of said anode being interspersed with the sections of said auxiliary? electrode and each of said sections being of part cyrespect to said cathode. 7

4. An electron discharge device comprising, within an evacuated envelope, a cathode surrounded joy a coritrol grid, a screening grid surroundingfjsaid control grid, an anode having sur" faces coextensive with and disposed opposite to iongitudinal portions of said screening g'iid and an auxiliary electrode insulated irom said anode and having surfaces coextensive with and disposed opposite to otherjlongitufinal portions of said screening grid, said anode and said auxiliary electrode being each in a plurality of sections, the sections of said anode being interspersed with the sections of said auxiliary electrode and each or said seetions being ofpart cylindrical shape and- The being disposed in a single cylindrical surface coaxial with said cathode. 7

5. An electron discharge device comprising, within an evacuated envelope, a cathode surrounded by a control grid, a screening grid surrounding saidfcontrol grid, an anode having surfaces coexteneive with and disposed opposite to longitudinal portions of said screening grid, an auxiliary electrode insulated from said anode and having surfaces coextensive with and disposed opposite to other longitudinal portions of said screening grid, said anode and said auxiliary electrodebeing each in a piurality of sections,

the sections of saidanode being interspersed with lindrical shape and being disposed so-axially with a part of said screening grid and an auxiliary the Space around d a hode, wherein said 10 5 tions, t sections of said anode being t to said cathode for substantially preventing the 60 named a cathode a control grid a screening g id sections Of said anode lying between the sections 60 will 5 which form a region of electron shadow in the d control grid Surrounding the Cathode, 75

2,107,510 r 7 the sections of said auxiliary electrode, and inspace between said anode and said screening grid sulating means connected between said anode and conducting shield means for substantially said auxiliary electrode sections. said region. 5 6. An electron discharge device comprising, An l ctron discharge device havin withwithin an evacuated envelope, a cathode surm an evacuated envelope arranged in the Order rounding said control grid, an anode surrounding and an an d said an de xtendin v a pa electrode electrically connected to aid cathode device also has Within S d pe means which within the envelope and surrounding another part form a region electron ad in t e pa of said screening grid, said anode and said auxilbetween Sald anode and Said Screening d a d spersed with the sections of said auxiliary elec- P ss e of secondary electrons from said anode trode, to said screening grid through said region.

tions having their edges disposed close to adjatolsaid Screening gri d through said legl'on- 30 cent edges of said auxiliary electrode sections. An electron discharge device ha g, Withgrid and an anode, Said anode having a pluralof the space around said cathode, wherein said n having an equal number of c rcumfe space hetween said anode and said screening grid allel to adjacent edges of said auxiliary electrode connected electrically to said cathode' seething 15 An electron discharge device comprising, 9. An electron discharge device having, with- Wlthm an evacuated @Q a cathode grid and an anode, said anode extending over a sald control grid and screening grid disposed subsaid anode electrode being each in two sections, the sections 10. An electron discharge device having, withauxlljary electrode and shield being in an evacuated envelope arranged in the rder disposed to be intersected Sald plane and the between said anode and said screening grid and anode including plurality u e entia -11y in an evacuated envelope arranged in the order P D electrode m d of a plurality of said device also has within said envelope means n e t n s h ge d vice comprising a a screen grid surrounding the control grid, an anode including a plurality of circumierentially spaced sections disposed around the screen grid, and means whereby an electrostatic potential minimum is developed in a region in the space between the screen-grid and anode, said means comprising low potential electrodes arranged bea screen grid surrounding the control grid, a pluralityof circumferentially spaced members arranged about the cathode and coextensive therewith, alternate ones of said members being electrically connected together and constituting the anode electrode, the remaining alternate members beingelectrically connected together and to the cathode and constituting an auxiliary electrode;

20. An electron discharge device as defined in claim 19 wherein there are provided means which form a region of electron shadow in the space between the anode and the screen grid, and shield means for substantially preventing the passage of secondary electrons from the anode to the screen grid through said region, said shield means being electrically connected to both the cathode and to the auxiliary electrode.

21. An electron dischargedevice including an evacuated envelope and having arranged in the order named within-the envelope, a cathode, a control grid, a screening grid, and an anode, said device comprising a rods lying in a common screening grid and anode being spaced from ,eachother to provide during operation or said electron discharge device a space charge between said screening gridand anode, said control grid and screening grid being provided with side rods lying in a common plane, said side rods forming a region of electron shadow in the space between said anode and said screening grid, and shield means for substantially preventing the passageof'secondary electrons from said anode to said screening grid through said region.

22. An electron discharge device including an evacuated envelope having within the envelope and arranged in the order named 'a cathode, a

control grid, a screeninggrid and an anode, said screening grid and anode being spaced from each other to provide during operation of the tube a space charge between said anode and said cathode, saidcontrol grid and screening grid having side rods lying in a common plane, said side rods -forming' a region of electron shadow in the space between said anode and said screening grid, and. a conducting shield means for substantially preventing passage of secondary electrons from said anode to said screening grid through said region.

23. An electron discharge device having an evacuated envelope containing in the order named a cathode, a control grid, a screening grid, and anode, said screening grid and anode being spaced to provide during operation of the device a space charge between said screening grid and anode, said control grid and screening grid having side plane, said side rods forming a region of electron shadow in the space betweensaid anode and said screening grid, and conducting shield means electrically connected to said cathode for substantially preventing passage of secondary electrons from said anode to 'said screening grid through said region.

' v I. SHOENBERG. SIDNEY RODDA.

c. s. BULL.

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