US2045526A - Multielectrode tube apparatus - Google Patents

Description

June 23, 1936. J. H. o. HARRIES 2,045,526

MULTIELECTRODE TUBE APPARATUS Filed March 18, 1932 2 Sheets-Sheet l ATToRNeys .Bune 23, 1936. J. H. o. HARRIES MULTIELECTRODE TUBE APPARATUS Filed March 18, 1932 I 2 Sheets-Sheet 2 mill- Esf=-X Ey -2x Eg=4x Fly 40 Patented June 23, 1936 PATENT OFFICE MULTIELECTBODE TUBE APPARATUS John Henry Owen Harries, Frinton-on-Sca, England Application March 18,

In G

1932,- Serial No. 599,653

feat Britain, April 2, 1931 11 Claims.

This invention relates to the production and control of electronic streams and more particularly, though not exclusively, to electron discharge devices where the current is varied in intensity and these variations are employed to energize a load usually connected in the anode circuit of the device.

In electric discharge vacuum tubes, streams of electrons, the lengths of which are great in proportion to their cross-section have the advantage that the capacities between electrodes can be greatly reduced, and the undesirable retrograde movement of secondary electrons from the anode is prevented. Furthermore, such streams of electrons can, in contradistinction to shorter streams, be deflected to a considerable degree and consequently can be used in tubes which are worked by deflection of the stream of electrons therein, for the purpose, for instance, of multiplying frequencies. (For this purpose, for example, a stream of electrons may be periodically moved by means of an alternating current over a perforated plate acting as the anode, so that a series of current impulses is produced in a closed output circuit connected to this plate). Hitherto, however, the ratio between the voltage used to produce the space current, and the intensity of the current, in such streams of electrons which are long and small in cross-section, has been so high that known apparatus worked by such streamsof electrons have been unsuitable for practical use in incandescent cathode tubes and the like. Therefore, previous practice has been confined to the use of tubes with streams of electrons. the lengths of which were comparatively short in proportion to their cross-sections, (and which were produced by voltages which were comparatively small in proportion to the intensity of the current), although such tubes exhibited disadvantageously high capacities between the electrodes, a tendency towards the undesirable retrograde movement of secondary electrons; and the streams therein cannot be deflected to any useful extent.

An object of the present invention is the production of streams of electrons in which the ratio of the voltage to the intensity of the current is small, and the length in proportion to the cross-section is great, whereby the disadvantages of the two kinds of streams hereinbefore mentioned are' avoided; the intensity of the curother controlling electrode or control grid or grids of such configuration and position the potentia1 variations thereon have a substantial controlling eifect on the intensity of the stream.

Referring now to the accompanying drawings, 5 which in some instances are diagrammatic:-

Figures 1 to 7 illustrate one form of the present invention, and in these:-

Figure 1 shows a completed tube in part sectional plan; 10

Figure 2 diagrammatically illustrates the legs of a cathode filament;

Figures 3 and 3A in elevation and plan respeotively show a control grid;

Figure 4 illustrates an accelerating electrode;

Figure 5 shows a second accelerating electrode;

Figure 6 shows a third accelerating electrode;

Figure '7 shows the anode;

Figures 8 and 8A show in part sectional plan and in part sectional elevation respectively a modified form of tube;

Figure 9 is a diagram showing the relationship I between anode voltage and anode current for various negative values of control grid voltage;

Figure 10 shows suitable circuit arrangements 5 for the tube of Figure 1 when connected to act as a high frequency amplifier;

Figure 11 is a side elevation partially broken away of an electrode assembly in which the cathode is enclosed by circumferentially complete electrodes.

In carrying the invention into effect in the form illustrated by way of example in Figures 1 to 7, a highly exhausted glass bulb I contains accelerating electrodes 2, 3, and-4, anode 5, control grid 6 and cathode filament l.

The anode 5 is movable, and is supported so as to be adjustable toward and away from the remaining electrodes. The anode is placed at a distance d from an accelerating electrode 4. The distance between the anode and accelerating electrode may be adjusted to be equal to the critical anode distance (see my co-pending patent application, Serial No. 595,339) at which the 45 anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood .of the minimum whereby secondary electrons radiated by said anode are prevented from reaching the accelerating electrode 4. Two further accelerating electrodes 2 and 3 are positioned as shown, and acontrol grid 6 is arranged to surround three cathode filament V legs 1, so as the electron stream from the filament to the accelerating electrodes and anode may be controlled in accordance with the potentials of the control grid 6.

Figures 2, 3, 4, 5, 6, and 7 respectively show the details of the various electrodes in the tube. In Figure 2 the three legs 1 of the filament are shown; in Figure 3 the control grid is shown in end elevation and in plan view. The control grid 6 consists of ameshB. The wires forming the mesh may be spaced 8 per centimeter. The grid contains three compartments 9, in each one of which a leg of the filamentwhich legs may be in series or in paralle1-is inserted. Separate partitions I divide the control grid 6, but they may be omitted if desired, and an ordinary control grid such as that commonly used in thermionic valves may be employed. In Figure 4 the first accelerating electrode 2 is illustrated and consists of a mesh I2 stretched across a wire frame I3. The mesh may consist of 10 wires per centimeter. Figure illustrates the second accelerating electrode 3 which consists of a fiat plate I4 having a mesh [5. The mesh may consist of 5 wires per centimeter. In Figure 6 the third accelerating electrode 4 is shown, and consists of a mesh l6, comprising for example 10 wires per centimeter, and wound on a Wire frame I! similarly to the first accelerating electrode 2. Figure '7 illustrates the anode 5 which consists of a fiat nickel plate. The electrodes may be of nickel with molybdenum wire meshes.

Figures 1 to 7 illustrate an arrangement for determining the correct distancing of the various electrodes in a valve made in accordance with the present invention, the tube being for example about 23 centimeters long, and about 5% centimeters in external diameter.

The tube illustrated in Figure 1 of the present specification contains an electrode assembly primarily for use at potentials similar to that explained in the prior specification with reference to Figure 13 or 15 therein. The accelerating electrode 3 is suitably connected to the cathode for example, although not preferably, by a connection outside the tube, for instance, as illustrated in Figure 10. The distance d in Figure 1 is arranged to be at the critical anode distance above explained and the meshes of the accelerating electrodes 2, 3, and 4 and the spacing between them are arranged'to reduce the capacity between the anode 5 and control grid 6 to as low a value as possible.

As an example, the distance between the accelerating electrodes 2 and 3 may be 5 millimeters; and the distance between the accelerating electrodes 3 and 4 may be 1 millimeter; the mesh I2 of the accelerating electrode 2 being, for instance, 10 wires per centimeter length, that of the second accelerating electrode 3 being, for instance, 5 wires per centimeter, and the mesh of the third accelerating electrode 4 being, for example, 10 wires per centimeter; the wires being, for example, 0.1 millimeter diameter, and the distance d in Figure 1 equalling, for instance, about 2 centimeters. With these values the capacity of the anode to the control grid is a suitably small fraction of a micro-micro-farad.

The anode 5 may conveniently have a matt or roughened surface to reduce the effects of secondary radiation.

In Figure 3 the separate compartments into which the control grid 6 is divided tend to cause this to exercise a focusing action upon the electrons because this is usually worked at a negative potential in respect of the filament. sing action is due to the plates l0, and the control This focusgrid 6 therefore exerts a focussing action as well as a control ing effect on the stream.

The meshes of the adjacent electrodes, such as those of the control grid 6 and. the accelerating electrode 2 in Figure 1, are preferably arranged to run at right angles to one another as shown in Figures 3 and 4.

Referring now to the modification shown in Figures 8 and 8A, this employs, as is preferred, an arrangement of anodes at both sides of the filament, with a corresponding series of accelerating electrodes on each side, the anode distance and other electrode spacings being of fixed type. In these figures the glass bulb I contains two anodes 5 which are supported from the top of the bulb I at the seal 18. By means of a wire 25 through the seal l8 the connection to the anodes may be made from outside the tube. Between the two anodes 5, the cathode and accelerating electrodes are supported on a press l9. They are numbered as in the previous figure. The filament 7 and control grid 6 are arranged inside the three accelerating electrodes 2, 3, and 4. For the sake of clarity the relative spacing between the electrodes has not been shown to scale, and the details of construction are omitted. The metal plate portion l4 in Figure 5 of the accelerating electrode 3 is arranged so as totally or nearly totally to enclose the other electrodes (except the accelerating electrode 4 and the anode 5), and thus as far as possible electrostatically shield the control grid 6 from the anode 5. Preferably the top and sides 2| of the plate portion l4 of the accelerating electrode 3 are closed over so as to form a hood enclosing the filament I, control grid 6 r and accelerating electrode 2.

The pitch of the wires on electrode 2 may equal 2 mm. the pitch of the wires to electrode 3 may equal 6 mm. The shape and area 01 the aperture in electrode 3 may approximately equal the shape and area of the control grid (compare Figures 3 and 5) the pitch of the wires of electrode 4 may equal 1.5 mm. The distance between the anodes 5 and electrode 4 may equal 13 mm. approximately and the anode may be 24 x 28 mm.

Referring now to Figure 9, the form of the curves showing the relationship between anode voltage Es and anode current Ia for various negative values of the voltage Eg on the control grid 6 is illustrated. As the control grid is made more negative and the space current thereby reduced, the anode current becomes substantially saturated at progressively lower values of the anode voltage, and, the saturation point is arranged to occur at an anode voltage very much less than the voltage of the accelerating electrodes.

The point at which the anode current becomes substantially saturated is not always very sharply defined, and is usually of the nature of a region rather than a point, as shown in Figure 9. If the curves of that figure are continued to the origin they may overlap, that is to say, that whereas it is usual with thermionic valves on the application of an increasing negative bias to the control grid for the anode current to become progressively less, in the case of the valves described above, an increase in the negative voltage on the control grid may cause the anode current to become greater over a portion of the range of control grid voltages.

Because the valve is to work at anode voltages over saturation, the lower the anode voltage at which saturation occurs the greater will be the undistorted output" of the valve.

The slope of the curves after saturation has occurred is small.

Due to the long distance which may be em-; ployed by means of the present invention in a thermionic valve, between the anode and the control grid, the intervening electrodes may be made to have a very large shielding action (thus reducing the plate/control grid capacity) without having to place the first accelerating electrode very far from the control grid and without employing very close meshed or thick wire grids. The latter point enables there to be comparatively little waste of space current to the various accelerating electrodes, which tends to make the mutual conductance of the valve higher than would be the case if the various accelerating electrodes had a large area in the path of the stream. In Figure 1, for instance, the anode/control grid capacity is very small, and at the same time the current intercepted by the accelerating electrodes is not too great, Because the accelerating electrode 2 is close to the control grid 6 and filament l a large anode current may be obtained for a given potential on the accelerating electrode 2. Due to the low anode voltage at which .the saturation may be obtained with the anode at the critical distance, the efliciency of conversion of the direct current anode input power into alternating current output with a negligible harmonic distortion may be at least as good as 30 per cent to per cent. The resulting combination of good mutual conductance and direct current to alternating current conversion efliciency of valves made as indicated herein, results in the provision of valves which are applicable for both high frequency and low frequency working. By suitable spacing of the I anode from other electrodes an extremely low anode to earth capacity may also be obtained if desired.

The forms illustrated may be regarded as small receiving valves in which a reasonable compromise has been obtained with reference to the factors involved. For other tubes, for instance, high power or very short wave tubes, suitable alterations in respect of electrode configuration and mountings should be made, and these should be made bearing in mind the principles in-- dicated above.

The stream need only be made as long as is necessary to give the desired value of anode/control grid capacity, and to obtain the anode critical distance effect, therefore, tubes made in accordance with the present specification will not, in general have as long a stream as many of those made in accordance with my prior application Serial No. 595,339.

Referring now to Figure 10, this diagrammatically illustrates circuit connections suitable for using the valve of Figure 1 and the valve of Figures 8 and 8A as high frequency amplifiers. Like parts are numbered with like numerals to those previously employed. In Figure 10 the tuned circuit L1, C1 is tuned to a high frequency current which is injected therein, and whichis to be amplified by the valve l. The control grid 6 and filament 1. are connected across the circuit L1, C1. The output tuned circuit L2, C2 is connected in series with the anode 5, and a high tension battery 22 which is arranged to apply a positive voltage to the anode. The grid 6 is given a steady negative potential by means of a further battery 23. The filament of the valve is heated by means of the battery 24. The accelerating electrode .2 is connected to the same high tension voltage as the anode. The grid 3 is connected to the filament, and decelerates the electrons as already explained with reference to Figure 15 of my co-pending application. The voltage of the third accelerating electrode 4 may be the same as that of the first accelerating electrode 2., unless this latter voltage is so high as to produce secondary radiation eifects, and to cause the anode current to lose saturation when the voltage of the first accelerating electrode is higher than that of the anode, as explained in my co-pending' specification. When the high tension voltage is as high as this, secondary radiation effects are eliminated by connecting the third accelerating electrode 4 to a lower voltage on the battery 22 than the anode 5 (see Figure 10). Alternatively the velocity changing electrodes may be connected together, provided that the voltage thereon is not toohigh. In these circumstances the arrangement becomes similar to that illustrated in Figure 13 of my co-pending application Serial No. 595,339. The characteristic curves of the tube or valve in both cases, that is to say, the tube of Figures 1 to 7 and the tube of Figures 8 and 8A, are substantially similar to those illustrated in Figure 9.

In Fig. 11 the cathode la is of the circular unipotential type and is enclosed by circumferentially complete control grid 6a, auxiliary electrode 4a and anode 5a successively arranged concentric with said cathode. In this modification, the fullest possible area of the cathode is utilized by virtue of the concentric arrangement of the remaining electrodes and the maximum mutual conductance is obtained. The juxtaposition of the supports of the control grid to the cathode exercise focussing or directory eifect on the electron stream, tending to' confine it to a narrow segment from the surface of the cathode to the anode thereby improving the linearity of the characteristics and tending to compactness of the assembly as a whole. In this modification the effective anode area is spaced from the auxiliary or accelerating electrode 4a. by a distance about equal to the critical distance.

Instead of being used as a high frequency amplifier, the valve shown in Figure 10 may be used for other purposes, for example, the inductances L1 and L2 may be magnetically coupled so that the whole apparatus acts as an oscillator. Alternatively the tuned circuit L1, C1 may be omitted and speech frequency voltages may be applied across the grid and filament of the valve and utilized in a pair of telephones connected in the place of the tuned circuit L2, C2. Instead of telephones, a resistance may be substituted, so that the valve acts as a resistance/capacity amplifier. The steady anode voltage is dropped considerably due to this resistance, but the higher the value of this resistance, the greater will be the stage magnification. To make the resistance as large as possible without causing the anode voltage to go below the saturated part of the characteristics the negative grid biasbattery 23 may be increased in I generalconsiderations are to be borne in mind with reference to the present invention. 1

Any known method of controlling the intensity of a stream of electrons may be employed, and more than one such controlling means. may be employed in different parts of the stream to simultaneously control the current flow. The control may be bymeans of electric or magneticflelds i is) acting on the stream. Apparatus to carry out the invention may include many difi'erent devices, for-example, electhat-variations in the applied potential have a substantial effect upon the intensity of the stream of electrons, as distinct from the relatively slight I variations which may be found in the intensity of the stream by varying the potential of almost any electrode in the tube.

It should be borne in mind that the principal requirements of aneflicient valve are a high value of mutual conductance and a low interelectrode .capacityiin particular between the anode and control grid). The efllciency of conversion of alternating current input voltage into output undistorted power should also be high and the in-- put/output characteristics should have a long straight portion to'give linear amplification over 8.

- wide range of amplitude.

. Generally speaking; a space charge control grid or the like may be employed to control the inten sity of the stream. As is well known it is desirable to utilize the'full area of the cathode of the valve, and for this reason more than one side of the cathode may be employed to produce a stream of electrons.

anode and control grid they are spaced some distance "apart. To obtain linear amplification the valve is worked at a suitable part of its characteristic, and very low interelectrode capacities are obtained by spacing the electrodes, and because this spacing may be made wide without reducing the space current, a large power output efliciency and linear amplification over a wider range may be obtained without difliculty. Electrodes may be interconnected as described in my prior patent application to produce a lower anode impedance than would otherwise be the case, but it is pointed out that'in any valve the maximum value of stage gain for a given output impedance will beproduced when the anode current is substantially saturated over the working range of the anode voltage.

The stream may be decelerated by suitably arranged electrodes at more than one part of the stream. If decelerated sufliciently. it will not be saturated, and the control of the intensity by means of a control grid or the like may be performed at more than one point in the length of the stream.

By suitably arranging the electrodes or the like and the potentials acting on the stream, various useful mathematical functions may be obtained between applied forces and output currents or voltages, for example, rectification efiects and negative resistance efiects and the like. .A

The invention may be applied to many other shapes and forms of the electrodes commonly employed for various purposes. For instance, a circular unlpotential cathode or tubular electrode assembly may be used and the other electrodes To reduce the capacity between ing or decelerating,

aocaaac',

shaped accordingly, or circular concentrically arranged electrodes might be used.

Secondary radiation from the electrodes placed in the path of the stream may be employed in the usual mannerto increase the anode current and mutual conductance of the tube.

The terms critical anode distanceVand anode breakdown voltage referred to in this specification and appendedclaims are explained fully in my co-pending application, Ser. No. 595,339. The

anode breakdown voltage may be defined as the anode voltage at which the anode current becomes substantially saturated.

The critical distance referred to in this specification and appended claims may be defined as the distance between the anode and an auxiliary electrode at which the anode breakdown voltage is in the neighborhoodof theminimum; when the distance is shorter than this value a substantial amount of secondary radiation, when produced at the anode, tends to pass to the auxiliary electrode (when the anode potential is less than that of the auxiliary electrode) tending to produce a negative resistancecharacteristic; when the distance is longer than this value then there is a range of anode voltagesfrom zero upwards over which substantially no anode current tends to be produced and immediately above. this range. the

anode current rises abruptly to a saturated value. The term "auxiliary electrode and anode in this specification and the appended claims are intended to refer to any two electrodes having po- It; is pointed out that though the critical dis- 7 tance is distinguished from shorter distances by its eifect in preventing thepassage of secondary radiation (which passes at shorter distances), my invention is not limited to the use of electrodes of material which produce secondary electrons copiously.

By secondary radiation or the like referred to in this specification is meant both reflected and emitted secondary electrons.

According to the invention the grid, acceleratelectrodes is mentioned heretofore are formed so as to intercept as little of the electron stream as possible. To do this they preferably are in the shape of a mesh or grid. The sizes of the apertures in the electrodes are not made too large and there are preferably more than one aperture. For example, for the satisfactory operation of the tube illustrated in Figure 1, an electrode of the kind shown in Figure 4 is necessary. An important part of my invention is in the fact that I have shown that such mesh electrodes may be made to give satisfactory results in the production of streams of electrons which are of the jet type, i. e. are of comparatively great length in comparison with their cross-section. Previously it appears to have been thought essential in endeavors to produce such jets to employ electron guns or the like of, for instance, tubular, and similar formations. They intercept almost all the space current, or only produce a very small space current, and therefore make the anode current too small to be of use.

The characteristics of means employed to transfer potential variations from one part of a stream to another as in Figures 10 and 12, may

also be arranged to change the characteristics of the said variations when transferred (e. g. change the phase, amplitude and/or wave form thereof). The characteristics of the said means may be a 3 function of other factors, e. g. the frequency of the variations. The potential variations when transferred to different parts of the length of stream may have relatively different characteristics. Therefore, by means of the present invention the differential resistance may be given a series of values including vector forms and complex values which may be dependent on variables which are changeable over a very wide range.

The potential variations across a stream or pori tion thereof may be transferred to sources of potential in other parts of the stream by suitable electrical circuits, e. g. potentiometer devices, reactive networks, inductive coupling, relaying devices, or the like. Or, if an output circuit is used in conjunction with the tube, potentials may be tapped off thereacross for this purpose. For example, if this coupling circuit is inductive and the potentials transferred to the unsaturated part of the stream are tapped off therefrom, a phase difference may exist between the original potential changes and those transferred and if potentials' of another phase are applied from the load to another electrode also acting on an unsaturated part of the stream, the current phase will depend on the result of all three phases, i. e. the differential resistance will possess a phase angle. If the frequency is varied the phase angles will change, hence the phase angle of the difierential resistance will change also.

Electrostatic screening devices, e. g. metal grids, may be interposed between the electrodes in the tube if required.

The explanation of the production of the critical distance effect is that a negative gradient is formed in the space between the anode and the auxiliary electrode (or equivalent to such electrodes) and because where such a negative potential gradient exists the passage of comparatively low velocity secondary radiation between the two 5 electrodes is prevented. The electrodes may be worked at a, sufliciently long distance apart for the stream to be readily deflectable and capacities between electrodes in the tube will be substantially less at these distances than would be the case when employing shorter distances.

It is to be understood that the various methods of discharge tube control above described are merely by way of illustrating the invention and 5 that the invention is not limited thereto, but is limited only by the scope of the appended claims.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

a 1. An electron discharge device comprising an anode, a cathode, a plurality of auxiliary grid-like electrodes therebetween and a grid-like control electrode for controlling the intensity of the electron stream fiowing from the cathode to the anode, the auxiliary electrode nearest the anode being spaced therefrom'by a distance at least equal to about the critical distance at which the anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode even though the voltage of the anode becores less than the voltage of the auxiliary electrode, circuits connecting said cathode and each of the remaining electrodes, means included in such circuits for applying different potentials to the va rious electrodes, an accelerating voltage being applied to at least one auxiliary electrode and a lower decelerating 'voltage being applied to the 5 auxiliary electrode nearest to the anode, and an auxiliary electrode immediately preceding the auxiliary electrode nearest the anode being at or near cathode potential, the said grid-like control electrode being electrostatically shielded from the anode and having its connecting lead led out of the discharge device at the opposite end to the end at which the lead connected to the anode is led out, and input and output circuits being connected respectively to the said grid-like control electrode and to said anode.

2. An electron discharge device in accordance with claim 1 wherein the auxiliary electrode nearest the anode is spaced therefrom by approximately the critical distance.

3. An electron discharge device comprising an anode, a cathode, means for energizing said cathode to produce primary electrons, means for applying potentials to said anode to direct said electrons thereto in the form of a stream, a plurality of auxiliary grid-like electrodes between said cathode and anode, a grid-like control electrode for controlling the intensity of the electron stream flowing from the cathode to the anode, and confining said electron stream to a path of limited cross section and means for impressing potentials on said control electrode, the auxiliary electrode nearest the anode being spaced therefrom by a distance at least equal to about the critical distance at which the anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode even though the voltage of the anode becomes less than the. voltage of the auxiliary electrode, the said grid-like control electrode he'- ing electrostatically shielded from the said anode and the lead to the anode passing out of the dis.-. charge device at the opposite end to that at which the lead to the grid-like control electrode is led out.

4. An electron discharge device in accordance with claim 3 wherein the auxiliary electrode nearest the anode, is spaced therefrom by approximately the critical distance.

5. An electron discharge device comprising a cathode, an anode, a first and a second grid elec-' trode between said cathode and anode, said grid electrodes and anode enclosing said cathode and being circumferentially complete, means for energizing said cathode to produce primary electrons, means for applying potentials to said second grid electrode and anode to direct said electrons in the form of a stream to said anode, means for impressing voltages on said first grid electrode to vary the intensity of said electron stream, and means incorporated in said first grid electrode to confine said electron stream to a path of limited cross section, said anode being spaced from said second grid electrode by a distance at least equal to about the critical distance at which the anode break down voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said second grid electrode even though the voltage of the anode becomes less than the voltage of said second grid electrode.

. trons in the form of a stream to said anode, and

means for impressing voltage on said first grid electrode to vary the intensity of said electron stream, said anode being spaced from saidsecond grid electrode by a distance at least equal to about the critical distance at which the anode break down voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum whereby any secondary electrons radiated by said anode are prevented from reaching said second grid electrode even though the voltage of the anode becomes less than the voltage of said second grid electrode.

8. An electron discharge device according to claim 7 in which said anode is spaced from said second grid electrode approximately the critical distance.

9. An electron discharge device comprising a cathode, ananode having sections between which said cathode is interposed, a first and a second grid electrode having sections arranged between said cathode and anode sections, means for energizing said cathode to produce primary electrons, means for applying potentials to said second grid electrode and anode to direct said electrons in the form of streams to said anode sections, means for impressing voltages on said first grid electrode sections to vary the intensity of said electron streams, and means incorporated in said first grid electrode for confining said electron streams to paths having limited cross sections, said anode sections being spaced from said second grid electrode sections by a distance at least equal to about the critical distance at which the anode break down voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum and secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode even'though the voltage of the anode becomes less than the voltage of said second grid electrode.

10. An electron discharge device in accordance with claim 9 wherein said anode sections are spaced from said grid electrode by approximately the-critical distance.

- 11. An electron discharge device comprising an anode, a cathode, a control electrode, a plurality oi. auxiliary electrodes between said control electrode and anode, means for energizing the oathode to produce primary electrons, means for applying positive potentials to said anode and the auxiliary electrode nearest to the anode to direct such electrons in the form of an electron stream to the anode, said anode being spaced from said auxiliary electrode nearest to it by a distance approximately the critical distance at which the anode breakdown voltage at which the anode current becomes substantially saturated is in the neighborhood of the minimum, whereby any secondary electrons radiated by said anode are prevented from reaching said auxiliary electrode nearest the anode even though the voltage of the anode becomes less than the voltage of the auxiliary electrode, one of the remaining auxiliary electrodes partially enclosing the oathode and at least one of the other remaining auxiliary electrodes and having members forming an aperture restricting the path of the stream of electrons flowing to the anode, and means for maintaining said enclosing electrode substantially at cathode potential.

JOHN HENRY OWEN HARRIES.

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