Title:
Electron discharge device
United States Patent 2107519


Abstract:
23 Claims The present invention relates to electron d charge devices of the kind comprising a catho( a control grid and an anode and, between t control grid and the anode, a screening electroc It is known that when valves of this kind a Operated with large anode voltage swings ar with a fixed...



Inventors:
Isaac, Shoenberg
Seaton, Bull Cabot
Sidney, Rodda
Application Number:
US2448235A
Publication Date:
02/08/1938
Filing Date:
06/01/1935
Assignee:
EMI LTD
Primary Class:
International Classes:
H01J19/02
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Description:

23 Claims The present invention relates to electron d charge devices of the kind comprising a catho( a control grid and an anode and, between t control grid and the anode, a screening electroc It is known that when valves of this kind a Operated with large anode voltage swings ar with a fixed positive voltage on the screenir electrode, secondary emission tends to occur fro the anode to the screening grid when, in ti course of its oscillation, the anode voltage fal more than a certain small amount below th fixed voltage of the screening electrode. Fe many Purposes the flow of such secondary emis sion current from the anode to the screen is un desirable and proposals have been made to pre vent it.

In one known arrangement a third grid, us ualy connected to the cathode, is arranged be tween the screening eluctrode and the anode. It is the principal object of the present inven. tion to provide an electron discharge device or the kind above referred to in which the flow oi secondary emission current from the anode to the screening electrode can be prevented with the aid of an electrode located at least mainly clear of the electron stream between the cathode and the 'anode and in such position that when it is maintained at a low potential such for example as cathode potential, it can modify the electrostatic field in the space between the screening electrode and the anode, this modification being such that, even in the absence of electron flow between the cathode and the anode, the rate of change of potential gradient from the anode to the screening electrode is made positive or has its otherwise positive value increased over substantially the whole anode surface when the anode potential is lower than that of the screening electrode, and in such a manner that under operating conditions with the control grid at cathode potential and the screening electrode at a normal operating potential the anode voltageanode current Characteristic exhibits no infiexion. The space charge itself also modifies the electrostatic field in the space between the anode and the screening electrode and this modification together with that produced by the auxiliary electrode has been found sufficient, under operative conditions, to prevent the flow of secondary ro electrons from the anode to the screening electrode, even though that due to space charge alone may be insufficient.

Although in some forms of discharge devices according to the present invention the distortion 5, of the electrostatic field produced by the auxilS(Cl. 250-27.5) is- lary electrode may not be such as to Produce an de, actual Potential minimum n the space between he the anode and the screen, in the absence of elecle. tron flow, over the whole range of working volre tages and corresponding working anode currents, d nevertheless the combined effect of the means for ig modifying the electrostatic field and the space m charge is always to produce a combined potenoe tial minimum throughout the whole range of s working anode voltages and corresponding worke ing anode currents over which secondary emis)r sion to the screening electrode might take place. - This is usually regarded as the range over which - the anode voltage is less than the screen voltage.

- 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 Part by an auxiliary electrode insulated from - said anode, wherein said anode and said auxiliary f electrode are each in a lurality of sections, the 20 Ssections of the anode being interspersed with the sections of the auxiliary electrode.

Various forms of discharge devices which can be made to exhibit the feature of the present Sinvention will be described hereinafter and the theory which is at present considered to explain the observed phenomena will be set forth. It is to be understood, however, that this theory may require modification in the light of further 3 knowledge.

The invention will be described with reference 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, Figures 2 to 5 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 eleva2 1, tion, sectional plan, sectional elevation and underside plan, respectively, of a second preferred constructional embodiment of the invention.

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

Referring to Figure 1, there is shown diagrammatically the electrode arrangement of one form of device according to the present invention. A cathode a is of rectangular cross-section and is elongated tin a direction perpendicular to the ranged one on each side of the cathode a and are spaced therefrom by means of insulating strips k, one strip being arranged near one end of the 15 cathode and another near the opposite end. side the electron stream. Two screening grids ci and C2 are arranged outside the control grid and are spaced therefrom by means of further 20 insulators c. This assembly may be clamped to-gether in any convenient way and mounted within a casing e which constitutes an auxiliary electrode. This auxiliary electrode has portions I extending towards but not to any great extent into the discharge space. Anodes di and cl are provided as shown. It will be assumed for the present that the anodes di and dc are electrically connected together and that the two grids bi and b2 on the, one hand and ci and c2 on the other hand are also connected together.

If the anodes di d2 be maintained at a positive potential relatively to the cathode a and if the screens ci and C be maintained at a potential which is higher than the anode, the potential distribution in the space between eact anode section di and td and the coriespondint screen section ci or c2 along lines normal to th4 screen and anode will be somewhat as repre sented in Figure 2, where voltages are plotted a ordinates against distances as abscissa. Th position of the anode is represented b the lin D and the position of the screen by the line C the heights of these lines representing the pa tentials at the anode and screen respectivelo The dotted curve go shows the distribution c potential along lines between the anode an screen approximately normal to these electrodi in the absence of electron flow and without t1 auxiliary electrodes. In the case of infinite plar parallel anode and screen this curve go is straight line. In other cases it is curved som what as shown. Owing to the action of the au iliary electrode including the portions 1 therec it will be seen that the distribution of potenti between the anode and screen represented the curve g is such that d2V dx2 60 is made more positive proceeding from the anc to the screen, where V is the potential at a point and x is the distance of this point from I anode. That is to say the rate of change of 1 potential gradient is more positive, the poti tial gradient being of course dV It will be seen also that the potential gradieni 70 the neighbourhood of the anode is very sr and for this reason very little further drop in tential in the anode-screen space is necessar: produce a potential minimum in the spacE shown in Figure 3 where the curve g of Figu 75 is shown dotted and the curve h shows the el 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 d2-/ is\ positive to a substantial degree, te 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 15 distribution of potential 9i when the screen indicated by Ci 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 20 drop in potential will be required to produce the desired potential minimum. This curve indicates the importance of arranging the anode at a sufficient distance from the screen taking into account the voltages and currents at which the 25 electrodes are to work.

Figure 4 shows the distribution of potential when the anode and screen are at the same potential. Here also is positive and therefore a potential minimum is produced even in the absence of electron flow.

This minimum, produced electro-statically when the anode voltage is equal to that of the 35 screen, if it be of sufficient 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 insuffi- 40 cient. When the anode voltage is much lower than that of the screen, the increase in space charge effects due to reduction in electron velocities causes such an increase in the depression in potential that although there is now no electro- 45 static potential minimum, there is sufficient 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 direction at right angles to 50 the direction of the electron stream (that is parallel to the anode surfaces) the distribution of potential in the space between the anode and the screen will of course be such that there is a maximum about midway along the line and low 55 values at the two ends. The potential distribution 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 auxiliary electrode has a focusing or concentrating 60 effect 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. 65 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 i screening grid until they reach a position in 1 which, if the space charge is sufficiently dense, 70 they are brought to rest by the potentials arisD ing from the space charge and the electrostatic s field. They then return to the anode and give 2 rise to more secondaries. The process may be 4t repeated so that it may be expected that in the 75 neighbourhood of the anode surface there will a very dense space charge of comparati, slowly moving electrons. Consequently any al braic decrease of dV dx in the neighbourhood of the anode produced modification of the electrostatic field will be I1) centuated by the space charge due to the primn electrons and also by the space charge due to t secondary electrons, and the electrostatic a space charge modifications are arranged togeth to give rise to a combined potential minimu It is this combined potential minimum which capable of preventing the flow of secondary ele tron current from the anode to the screenli grid.

For most purposes a tetrode is required have an anode voltage-anode current chara, teristic of the kind shown in Figure 5 wherein ti anode voltage EA is shown plotted against ano{ current IA for various values of the control gr voltage Eg. It is usually desirable that the kne m should be as sharp as possible and should oc cur at as low a voltage as possible, and that ther should be no inflexion or kink, or at least n marked inflexion, in the characteristic. A kin such as appears at n in the curve Eg=-4 an to a less extent in the curve Eg=-3 is not mate rial because it is at a point away from any prac tical working point. However, it -has been founi possible to produce devices according to this in vention in which no noticeable kink is present ih 33 any characteristic. A practical load line for resistive load is shown at o and in the case of ar inductive load the load line may have the fore shown dotted at oi. 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 (lthough it will be understood that for certain Purposes other forms of characteristic may be preferred) and certain 43 ways in which departures from the desired characteristic are obtained will be explained in order that the effects of the several variables may be appreciated.

If either the anode di, f2 is too small in area, the auxiliary electrodes e are too close to the electron stream or the projections or slats I 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 increased or if the auxiliary electrodes are arranged further away from the electron stream, the desired form of characteristic can be obtained.

Go 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 63 so that the curve exhibits an infiexion. This form of characteristic indicates that secondary emission is reaching the screening grid.

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 F5 will be regarded in the first place as at cathode be potential. Under these conditions the electrons rely projected towards the anode will come to rest ge- before reaching the anode on account of the electrostatic field, the low anode otential and the space charge. If the anode voltage be now increased to a value equal to say one half the knee voltage, the spaqe charge will still be sufficient to by produce zero potential in the space between the ac- anode and the screening grid. In this region of Lry zero potential all electrons are brought to rest he and the region may be regarded as a virtual nd cathode. The number of electrons flowing from ier the virtual cathode to the anode or to the screen n. is determined by the anode potential and the proIs portion flowing-to the anode increases as the c- anode potential increases.

Ig Above the knee voltage there is still a potential minimum along the electron path but this minito mum Is no longer zero and any electrons proc- jected by the screening grid towards the anode ie can only travel forward and eventually strike the le anode even though they are retarded by the poid tential minimum. The knee is sharp because, )e as the anode voltage is increased, the virtual Scathode becomes a region of minimum, but not 'e zero potential, substantially simultaneously over o. the whole area of the virtual cathode. If the size k of the anode is decreased, or if the auxiliary d electrodes are -placed closer to the stream, the - virtual cathode will persist at a greater anode - voltage around the edges of the beam than In the I centre, thus giving rise to a knee of lafger radius - of curvature.

n If the anode be unduly large, the secondary a space charge consisting of electrons moving slowSly in random directions can diffuse to the portions 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 insufficient 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 diffusing 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 than breadth it is usually desirable to provide the auxiliary electrodes, as already mentioned, close to both pairs of opposite edges.

With long and narrow anodes, or where less perfect screening from secondary emission is permissible, it may be ufficient to provide the auxiliary electrodes close to the longer edges of the anode only.

If it is required that the knee voltage should be reduced, it is necessary to reduce the primary space charge so that the virtual cathode formed thereby may collapse at a lower anode voltage. This can be done by increasing the screefiing grid voltage or by reducing the distance between the anode and the screening grid. The limit to which these two changes can be taken depends, in the case of the former, upon the ability of the Primary space charge, with the assistance of the secondary space charge and the electrostatic field, to maintain a sufficiently pronounced Potential minimum to prevent the secondary electrons from travelling to the screening grid and, in the latter case, upon the fineness of structure of the screening grid.

It has been found that if the distance between the anode and the screening grid be too small 6 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.

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 differing from the cathode potential. An 80 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 potentia of the anode or control grid.

In addition to the feature of this invention namely the provision of means whereby an elec trostatic potential minimum can be developed a some region in the space between the screeninl grid and the anode, at least when these two elec trodes are at the same potential, it is usually de sirable to arrange that ;*j (1) A region between the screening grid an anode which constitutes a virtual cathode at lo1 anode potential should become a region of mm imum potential, exceeding zero potential, su stantially simultaneously over the greater part ( ., the region as the anode potential is increase! and (2) The distance between the anode and ti screening grid should not be less than about twi( the pitch of the screening grid, that is to say ti Smesh of this grid or the equivalent structure si2 Condition (1) is not essential since if it is n fulfilled the principal effect is to influence tl shape of the knee of the characteristic. T] effect of this may only be that the amplificati( obtainable is not so free from distortion as wi a sharper knee. A knee which is slightly mc rounded than it need be may be advantageo in some cases as it has been found possible obtain a higher impedance above the knee vo age under these conditions.

Instead of allowing the auxiliary electrodel to extend alongside of the grids and cathode shown in Figure 1, the auxiliary electrodes nr be terminated just short of the screening gi for example at the inwardly projecting slats I shown 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 p, preferably electrically connected to the screening grids ci and c2, 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 the anode as shown at q.

A modification of the arrangement of Figure 1 is shown in Figure 7 where the projections I 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 r which can be bolted or otherwise fixed together, suitable insulating means ki being provided between the electrode e and the grids ci and C2.

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 c. Around the screening grid c is arranged an anode in two sections di and d2 each of part cylindrical shape and between the anode sections di and d2 are arranged further part cylindrical electrodes ei and e2 constituting sections of the auxiliary electrode. The two grids b and c are of cylindrical shape and these two electrodes together with 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 el and. e2 of the auxiliary electrode constitute continuations of the anode sections di and d2 and lie in the same cylindrical surface as the anode sections, this 1 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 Sare either connected to the cathode, for example t within the envelope f of the device, or else they g are brought out to a suitable external terminal - by which they can be maintained at a low potential usually not differing greatly from cathode potential.

d The auxiliary electrodes ei and ez serve to w modify the electrostatic field in the anode-screen - space in such a way that is sufficiently 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 60 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 65 are provided shield members t which are so placed that they stop secondary electrons which might otherwise reach the screening grid c.

The shields t may be of metal or of insulating material. In the former case they may be of solid 70 metal or in the form of a metal coating on an insulating backing. The metal surface may be connected to the auxiliary electrodes ei and e2 or to some other point of relatively low potential or they may be left unconnected. In the case 75 where insulating shields are used they may glass or mica for example and in operation shield acquires a charge upon its surface cient to make its potential approximately to that of the cathode.

In a modification of the arrangement of Fi 8 shown in Figure 9, the anode and auxiliary4 trode are still further subdivided into part, d2, d3 etc. and e, e, e3 respectively the foi parts being interspersed with the latter.

In Figures 10 and 11 there. is shown a mo cation of the arrangement of Figures 8 an, the subdivision being along the length of cathode. Thus each anode section at, a2 each section of the auxiliary electrode ei, e2, £ in the form of a short cylinder. Figure 12 illustrates a modification of the rangement of Figure 8 in which the shield and the auxiliary electrodes ei, e2 are combli and the whole electrode el, e2, t may be regar as the auxiliary electrode.

In the arrangements of Figures 1, 6, 8, 9 10, the auxiliary electrodes are themselves have parts u (Figures 1 and 6) which form cc tinuations of the anode.

In Figure 12 the auxiliary electrode althou not constituting a continuation of the anode st face nevertheless has edges-located close to edc of the anode so that the anode sections di and together with the auxiliary electrodes form su stantially a box-like structure extending aromu the grids and the cathode. It will be understo( that the auxiliary electrode e of Figures 1, 6 at 7 may extend completely around the anode ar grids, that is around the edges thereof parallel the plane of the paper and this is usually desih able when the anode and grids are of substar tially square or circular shape. When these elec trodes have a much greater length (in the direc tion of the length of the cathode) than breadtl however, it is often unnecessary to arrange tha the auxiliary electrode completely surrounds th grids and anode.

In discharge devices of the kind described ii which the auxiliary electrodes extend close to thi edges of the anode, it is often convenient to sup. port the anode from the auxiliary electrodes witl the aid of suitable insulators which may be o1 mica or ceramic material for example. Two ways in which this may be done are illustrated in Figures 18 and 19. Referring to Figure 18, the inner edges of the auxiliary electrodes ei and e2 are slit in such a way that two tongues vh and v2 can be bent outwardly into a horizontal plane near the top of the two auxiliary electrodes. Two similar tongues are also bent out into a horizontal plane near to the bottom of the two auxiliary electrodes but this is not shown in the drawings.

The anode (, in the form of a flat rectangular plate, has a rod w Preferably of square section fixed along the centre line. Two insulators in the form of rectangular bars of which the upper is shown at x are each Provided at their centres with a square hole and have notches cut in their ends. The rod w which projects from the upper and lower ends of the anode is inserted in the holes in the insulators x and the insulators are slipped into Position along the auxiliary electrodes, the inner edges of the auxiliary electrodes engaging in the notches in the-ends of the insulators. The tongues v, and v2 are then bent outwardly and around the insulators as showri at vt to hold them in Position.

In a modified construction shown in Figure 19 thin strips of insulating material zs and z2 are u0 nfxed to the anode d, for example with the aid of each rivets, near to the top and bottom thereof. These sum- strips are arranged to project outwardly beyond equal the vertical edges of the anode. The anode is placed in position upon tongues vi, v2, v and v4 gure bent outward from the plane of the auxiliary elec- electrodes as above described and these tongues s di, are bent over the projecting ends of the strips as mer shown at vi and V2 to hold them in position.

Instead of bending tongues out from the body lo difi- of the shields, suitable tongues may of course be d 9, fixed to the shields, for example by welding. the The method of assembly above described can and also be applied to the securing of a Plurality of e3 is anode elements to one another in cases, such as have been described above, in which the anode ar- is divided into a plurality of parts. When the Is t anode elements are separated by an auxiliary ned electrode the adjacent sections of the auxiliary ded electrode can also be supported from one another by the use of insulators as abovedescribed. In ond a similar way any one electrode can be supported or from any other electrode so long as these elecn- trodes have Parts extending sufficiently near together. gh Referring now to the constructional embodi- 25 e- m cnt of the invention shown in Figures 13 to 17, res two control grids bi and b2 and two screening d2 grids ci and c2 are mounted in suitably spaced reb- lation from one another and from the cathode a by nd means of suitable insulators k. The two control od grids are connected together and to a lead Z id passing through the top of the envelope f. The id grids are composed of thin wires extending beto tween supporting rods and between the two upr- Per and between the two lower wires of each L- grid are passed insulating. trips 2 for example of mica. Two anodes di and d2 are fixed to the mica strips 2 by means of tongues 3 which prot, ject through the mica and are bent over. Aset sociated with each anode is an auxiliary electrode e composed of a flat portion 4 having a large rectangular aperture, side portions 5 and inwardly 1 Projecting portions 6 extending close to the edges e of the anode. In the rectang ularpertures in Sthe auxiliary electrodes are arranged shields 25 and 26 of channel shape having their edges fixed to the screen grids cg and c and therefore elecStrically connected thereto. The flat portions 5 of the auxiliary electrodes are caused to bear through insulating strips r upon the grid and cathode assembly and the two auxiliary electrodes are then united by metal cross straps , which may be attached by spot welding, and the cathode and grid assembly is thus held firmly in position. Four metal members 8 are then spot welded to the auxiliary electrode and serve to revent movement of the mica strips 2.

The shields 25 and 26 may if desired be extended so that together with the screening grid c they completely envelop the control grid b excepting for apertures for the Passage of the cathode and control grid leads.

The two anodes di and d2 and the two control grids bi and b2 may be connected together or if 5 desired they may be brought out to separate terminals so that the device can be used as a pushpull amplifier. The auxiliary electrode structure may be connected to the cathode within the envelope or if desired may be brought out to a separate terminal so that it can be maintained at any desired low Potential. The potential of the auxiliary electrode is usually fixed but as already stated need not necessarily be so as it may be caused to vary with the anode potential for example.

Referring to Figures 20-23, there is shown a constructional embodiment of the type of device shown in Figure 8. The electrodes are mounted between two discs of insulating material 91 and 10 for example of mica which have serrated edges adapted to bear against the inner walls of the envelope f. The anodes di and d2 and auxiliarY electrodes ei and e2 are mounted upon the mica dics 9 and I0 with the aid of lugs II which pass through holesin the discs and are bent over. Thus the electrodes di, d2, ei, e serve to form a rigid structure with the discs 9 and ID. The cathode a is located in apertures in the centres of the discs 9 and ID and the grid supporting rods s also pass through holescin the discs 9 and 1O. The cathode is of the indirectly heated type and the heater is brought out through leads 12 and 13, the cathode itself being connected to lead II. The anode parts d and d2 are connected together by a wire 15 and to a lead 16. The auxiliary electrode parts ei, and e2 are connected together and to shields t by a wire II and to a lead IS and also to the cathode a. The grids b and c ore connected respectively to leads 19 and 20. The shields t are provided in the shadow cast by the rods s for the purpose described in connection with Figure 8. These shields are fixed to the mica discs 9 and 10 with the aid of lugs 21. , The anode sections di and d2 may be provided as shown with slats or projections 22 in the form1 of small part annular members of sheet material These slats are preferably arranged fairly neal to the upper and lower end of each section d and d2. In one example they are distant fron the ends of the sections di and d2 by about on fifth the whole length of the sections. The pur pose of these slats is to intercept electrons tray elling obliquely in the anode-screen space whic. might in the absence of the slats reach th screen around the outside of the space charg areaIt has been found that in addition to the va. ous factors influencing the behavior of discharE devices according to this invention already mer tioned, there are certain other points whic should be taken into consideration. If tl screening grid be arranged too close to the coi trol grid or be too open, the control grid mr produce a reduction in potential in the anod screen space. )his reduction in potential e hances the effect of the auxiliary electrode ai must be taken into account when designing t device or else firstly the knee of the character tic may be of unduly large radius of curvatt and secondly the impedance of the device aix the knee voltage may be lowered. The forn effect is believed to arise because the virti cathode disappears at different voltages at d ferent points in the anode-screen space. '1 latter effect is believed to arise from the influe: of the control grid in preventing the removal 5 secondary space charge from the screen by anode.

In some constructions it is desirable to a the apertures in the control grid with the al tures in the screen in the direction of the e tron stream and if a device is designed to oi ate satisfactorily in accordance with the pre invention with aligned grids it may be-foun operate unsatisfactorily if the grids are ....  ^ ,.nii+ -nP is equivalent to la igned. The e e c p produced by the use of a screen which is too open.

We claim: 1. 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 auxiliary electrode insulated from said anode 10 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.

2. An electron discharge device comprising an elongated cathode surrounded by a conarol grid, a screening grid surrounding said control grid, an anode having surfaces coextensive with and disposed opposite to longitudinal portions of said screening grid and 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 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 30-cathode.

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 n other longitudinal portions of said screening grid e and an auxiliary electrode insulated from said Sanode and having surfaces coextensive with and Sdisposed opposite to other longitudinal portions oh f said screening grid, said anode and said auxil.e iary electrode being each in a plurality of sece tions, the sections of said anode being interspersed with the sections of said auxiliary elecL- trode and each of said sections being of part cylindrical shape and being disposed co-axially with respect to said cathode.

-h 4. An electron discharge device comprising, ih within an evacuated envelope, a cathode sur- rounded by a control grid, a screening grid sury rounding-said control grid, an anode having sure- faces coextensive with and disposed opposite to n- longitudinal portions of said screening grid and nd an auxiliary electrode insulated from said anode he and having surfaces coextensive with and disis- posed opposite to other longitudinal portions of ire said screening grid, said anode and said auxiliary )ve electrode being each in a plurality of sections, the ter sections of said anode being interspersed with the ial sections of said auxiliary electrode and each of Ssaid sections being ofpart cylindrical shape and hf- being disposed in a single cylindrical surface coahe axial with said cathode.

[ of 5. An electron discharge device comprising, S within an evacuated envelope, a cathode sur- 6 the rounded by a control grid, a screening grid surrounding said control grid, an anode having surlign faces coextensive with and disposed opposite to per- longitudinal portions of said screening grid, an lec- auxilfary electrode insulated from said anode 7 per-ý and having surfaces coextensive with and digsent posed opposite to other longitudinal portions of d to said screening grid, said anode and said auxiliary not electrode being each in a plurality of sections, that the sections of said anode being interspersed with the sections of said auxiliary electrode, and Insulating means connected between said anode sections and said auxiliary electrode sections whereby said anode sections are supported by said auxiliary electrode sections.

6. 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 surrounding a part of said screening grid and an auxiliary electrode electrically connected to haid cathode within the envelope and surrounding another part 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.

7. An electron discharge device having, within an evacuated envelope arranged in the order named, a cathode, a control grid, a screening grid and an anode, said anode having a Plurality of circumferentially spaced sections, each extending longitudinally over a different part of the space around said cathode, wherein said device also has within said envelope, an auxiliary electrode having an equal number of circumferen. tially spaced sections which alternate with the anode sections around the cathode and are insulated from said anode sections, said anode sections having their edges disposed close to adjacent edges of said auxiliary electrode sections.

8. An electron discharge device having, within i an evacuated envelope arranged in the order named, a cathode, a control grid, a screening grid and an anode, said anode having a plural- c ity of circumferentially spaced sections, each ex- d tending longitudinally over a different part of the e space around said cathode, wherein said device s also has within said envelope, an auxiliary electrode having an equal number of circumferen. s] tially spaced sections which alternate with the a: anode sections around the cathode and are insu- P lated from said anode sections, said anode sec- tc tions having their edges disposed close and par- ai allel to adjacent edges of said auxiliary electrode cc sections.

9. An electron discharge device having, with- wi in an evacuated envelope arranged in the order ro named, a cathode, a control grid, a screening ro o50 grid and an anode, said anode extending over a sa part of the space around said cathode, wherein stl said device also has within said envelope, an auxil- pa iary electrode extending over a further part of su said space and insulated from said anode, said an auxiliary electrode having a flat portion disposed dis close and parallel to a portion of the surface of sai said anode. ele 10. An electron discharge device having, with- of in an evacuated envelope arranged in the order dis named, a cathode, a control grid, a screening grid sec and an anode, said anode extending over a part of of the space around said cathode, wherein said 1 device also has within said envelope means which cat] form a region of electron shadow in the space a s 5 between said anode and said screening grid and ano shield means for substantially Preventing the spai passage of secondary electrons from said anode and to said screening grid through said region. min 11. An electron discharge device having, with- betv 0 in an evacuated envelope arranged in the order cor named, a cathode, a control grid, a screening circi grid and an anode, said anode extending over a is in part of the space around said cathode, wherein sectj said device also has within said envelope means 17 5 which form a region of electron shadow in the cath space between said anode and said screening grid and conducting shield means for substantially preventing the passage of secondary electrons from said anode to said screening grid through said region.

12 An electron discharge device having, within an evacuated envelope arranged in the order named, a cathode, a control grid, a screening grid evice also has within said envelope means which form a region of electron shadow in the space between said anode and said screening grid and conducting shield means electrically connected to said cathode for substantially Preventing the 15 Passage of secondary electrons from said anode to said screening grid through said region.

13. An electron discharge device having, within an evacuated envelope arranged in the order named, a cathod , a control grid, a screening grid and an anode, said anode extending overma part of the space around said cathode, wherein said device also has within said envelope, an auxiliary electrode extending over a further part of said space and insulated from said anode, means which form a region of electron shadow in the space between said anode and said screening grid and shield means for substantially Preventing the passage of secondary electrons from said anode to, said screening grid through said region. 14. An electron discharge device having, withn an evacuated envelope arranged in the order named, a cathode, a control grid, a screening grid lnd an anode, said anode extending over a part f the space around said cathode, wherein said levice also has within said envelope, an auxiliary lectrode extending over a further part of said pace and insulated from said anode, means rhich form a region of electron shadow in the pace between said anode and said screening grid nd shield means for substantially Preventing the assage of secondary electrons from said anode said screening grid through said region, said uxiliary electrode and said shield means being )nnected electrically to said cathode. 15. An electron discharge device comprising, thin an evacuated envelope, a cathode surunded by a control grid, a screening grid surunding said control grid, rods for supporting id control grid and screening grid disposed subantially in a plane, an anode surrounding a rt of said screening grid, an auxiliary electrode rrounding a further part of said screening grid d insulated from said anode and shield means posed between said auxiliary electrode and d screening grid, said anode and said auxiliary ctrode being each in two sections, the sections ýaid auxiliary electrode and said shield being posed to be intersected by Said plane and the tions of said anode lying between the sections aid auxiliary electrode.

6. An electron discharge device comprising a bode, a control grid surrounding the cathode, creen grid surrounding the control grid, an de including a Plurality of circumferentially ced sections disposed around the screen grid, means whereby an electrostatic potential imum is developed in a region in the space veen the screen grid and anode, said means prising an electrode formed of a Plurality of umferentially spaced sections, each of which terspersed between a pair of adjacent anode ions.

SAn electron discharge device comprising a ode, a control grid surrounding the cathode, 8 , a screen grid surrounding the control grid, an sc anode including a plurality of circumferentially e: spaced sections disposed around the screen grid, e: and means whereby an electrostatic potential s minimum is developed in a region in the space a between the screen grid and anode, said means I: comprising low potential electrodes arranged be- a tween adjacent anode sections and outside the space discharge path between cathode and anode. -8. An electron discharge device comprising a cathode, a control grid surrounding the cathode, a screen grid surrounding the control grid, a plurality of 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 being electrically connected together and constituting an auxiliary electrode.

19. An electron discharge device comprising a cathode, a control grid surrounding the cathode, a screen grid surrounding the control grid, a plurality of 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 being electrically 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 discharge device 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 cr'eening grid and anode being spaced from ach other to provide during operation of said lectron discharge device a space charge between aid screening gridand anode, said control grid nd screening grid being provided with side rods ying in a common plane, said side rods forming region of electron shadow in the space between aid anode and said screening grid, and shield neans for substantially preventing the passage of secondary electrons from said anode to said i0 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 screening grid 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, said control 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 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 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. I. SHOENBERG.

SIDNEY RODDA.

C. S. BULL.