US2415349A - Electron discharge tube for ultra high frequencies - Google Patents

Description

1947' J. H. o. HARRIES 2,415,349

ELECTRON DISCHARGE TUBES FOR ULTRA HIGH FREQUENCIES Filed Sept. 4, 1941 4 Sheets-Sheet l lA/VEA/TOR nrrmA/gg 9 .1. H. o. HARRIES 1 ELECTRON DISCHARGE TUBES FOR ULTRA HIGH FREQUENCIES Filed Sept, 4, 1941 4 Sheets-Sheet 2 7" God :ZTTORNE F Feb. 4, 1941.

J. H. o. HARRIES 2,415,349

EEECfIRON DISCHARGE TUBES FOR ULTRA HIGH FREQUENCIES Filed Sept. 4, 1941 4 Sheets-Sheet 3 ll Ti Fig.3.

V .514 5 J s T J T 1 l II E BL L D2 J. H. o. HARRlES 2,415,39

ELECTRON DISCHARGE TUBES FOR ULTRA HIGH FREQUENCIES Filed Sept. 4, 1941 4 Sheecs-Sheet 4 Patented Feb. 4, 1947 ELECTRGN DISCHARGE TUBE FOR ULTRA HIGIEFREQUENCKES John Henry Owen Harriea'Clrtphatrh Park, London S, W. 4, England Application September 4, 1941, Serial No. 409,587 In Great Britain September 5, 1940 16 Claims; 1

This invention relates to electron discharge tubes, and more particularly to the production of beams of electrons and the control of the same in electron discharge tubes; the invention has ap-- plication to, but is not limited to, electron dis" charge tubes, as set forth in the specificationsof British Patents Nos. 380,429, 385,968 and 521,l99.

Electron discharge tubes are known in which a beam or jet of electrons is deflected over a series of contacts or the like. Such tubes may be used as relaysor frequency multipliers. Thebeam may be deflected by input currents or voltages applied, for instance, to electrostatic deflecting plates or magnetic deflecting coils and the output current produced in circuits connected to the contacts upon which the beam impinges. Pulsating currents or amplified currents maybe produced in these circuits in accordance with the movement of the beam, which is in turn proportionalto the variation of the deflecting voltages or currents applied to the deflectingplatesor deflection coils. Electron discharge tubes of this kind are sometimes known as deflection valves. One particularly important application of the. present invention is the production of a beam of electrons for use in a deflection valve.

Certain difficulties arise, particularly if. such valves are operated at very short wave lengths. One of these is that if the valves are to have a high velocity of beam current (such as will give a desirably short transit time), then a fairly high voltage has to be applied along the length of the beam. It is, however, fundamental to the operation of thermionic devices, thatif energy is to be withdrawn eficiently from such a beam of .electrons for operation of an output device (e. g., for wireless transmission), then the potential of the output or target electrode must be able to, fall to a potential approaching zero without substantially reducing (in this case) the beam current.

A further problem consists in providinganoutput circuit and output target system which has a very low loss at extremely short wave lengths, but which is also capable of operating eficiently in withdrawing energy from the electron beam.

Thus, the present invention in the main aims at providing an arrangement which enablesa beam of electrons to be decelerated'during operation without substantially reducing the beam current flowing to an output or target electrode, and to provide a construction of deflection valve capable of overcoming generally the above difiicul ties.

The usual method of enablingthe output anode electrode to take up a lower potential than that of adjacent electrodes without resulting in the loss of anode current, is to insert an electrode operated as a suppressor grid between the anode and the said adjacent electrodes. It is found, however, that at very high frequencies it is extremely diflicult to design-such a suppressor grid and its associated circuit so that it" does not acquire a high frequency potential which lies between that of the anode and of the adjacent electrode which therefore preventscorrect operation of the suppressor grid. Therefore, the present invention is also directed to enable efiicient operation to be obtained without inserting. an electrode of the nature of a suppressor grid in the high frequency field of the anode.

When a-deflection valve is to bev operated on a very short wave length, say below 1 meter, circuits for use for output purposes at suchra very short wave length in general consist of an enclosed metallic structure, such as the well-known shielded concentric quarter-wave transmission line; The losses in such. a transmission line circuit become very considerable if the continuity of its outer conductor or shield is broken, and it is not easy to devise a construction of valve such as a de fiection valve, by means of which an electron beaminay give energy to such an output' circuit, while at the same time preserving a low value of loss in the circuit. Therefore, the present invention also aims at solving this dificulty.

According to the present inventioinin anelectron discharge tube inwhich a beam of electrons is deflected ormodulated in order to enable alternating energy to be taken from an output electrode system, the latter consists of an output electrode or anode and another output electrode or sub-anode which is maintained at zero alternating current potential and shields the alternating fielcl' of the output anode from the other electrodes of thetube, while an accelerating electrode is provided maintained at a positive potential and mounted further from the cathode than the device used for deflecting or modulating the beam; furthermore, a retarding electrode maintained at a relatively low potential is mounted next to the accelerating electrode and between it andthe output system, so that the sub-anode may be set 'at a direct current potential lower than that of the accelerating electrode so that the potential of the output anode may assume an'instantaneous value, during operation, lower than that of the'accelerating electrode'without reduction of current to the output electrode, or appreciable loss of focus of the electron beam This arrangement enables the output system to include,

in addition to one Or more output targets or anodes, an electrode or sub-anode consisting of a transverse metallic partition Which divides the tube into two parts and is formed with one or more apertures through which the electron beam may pass from the part of the tube containing the cathode and the beam deflecting or modulating device, to the part of the tube in which the output target or targets is mounted. The sub-anode and the output target or targets may then extend outside the envelope of the tube and be fitted directly to an outer shield and a high potential pole or poles of an output circuit The sub-anode is then maintained at a potential between that of the retarding grid and the mean potential of the output target or targets.

The sub-anode referred to and the target or targets are preferably made of copper sealed into the envelope of the tube, the sub-anode being a copper disc which electrically and mechanically separates the output target from the other electrodes. The output circuit employed may be of the shielded concentric line or similar type, which is suitable for very short wave operation.

Since the potential of the sub-anode is low compared with the steady direct potential of the output target or targets, the potential of the latter may decrease substantially without substantially reducing the beam current, thus providing for efficient transfer of energy from the electron beam to the output circuit. At the same time, the transit time of the beam in that part of the tube in which it is acted upon by the deflecting or modulating device, is short because of the comparatively high potential on the accelerating electrode. Nevertheless, undesirable transfer of secondary radiation from the low potential subanode to the high potential accelerating electrode is prevented by the insertion between them of the comparatively low potential retarding electrode. Furthermore, the electric field of the output circuit may even, in the case of an extremely short wave length, be confined entirely to the target side of the sub-anode, that is to say, if a concentric line output circuit is used, the field is entirely confined to the inside of this circuit. This condition, as is well known, is necessary if severe losses are to be avoided in such a circuit. The losses are also very low because the connection of the internal electrodes of the tube to the external output circuit themselves form part of that circuit.

The invention may also be combined with that set forth in patent application Serial No. 409,588, filed September 4, 1941.

In order that the invention may be more clearly understood and readily carried into effect, a form of electron discharge tube in accordance therewith will now be described by way of example with reference to the accompanying drawings, in which-- Figure 1 is a central longitudinal section of the tube;

Figure 2 is a so-called exploded view in perspective showing the electrodes from the deflecting cylinder to the output target in detail but spaced further apart than they are in the actual tube;

Figure 3 is a longitudinal section at righteangles to Figure 1 and showing the same electrodes as Figure 2;

Figure 4 is a cross-section of the tube taken on the line IVIV in Figure 1;

Figure 5 is a central section showing the mounting of the tube and the mechanical details of the output circuit; while Figure 6 is a fragmentary section showing in detail a method of securing the tube on its mount- The electron discharge tube illustrated is the same as shown in application Serial No. 409,585, filed September 4, 1941 and the complete sequence of electrodes is shown in Figure 1 comprising the spiral cathode C, the negative grid G mounted close to the cathode C, the positive grid G and the deflection electrode of cylindrical shape D D seen in Figures 1 to 3. The electrodes so far mentioned are not specially concerned with the present invention and need not be further described in detail.

However, the next electrode is the high potential electrode L and then the retarding electrode or suppressor grid S. These are followed by the sub-anode SA and finally the anode or output target T. The dimensions and spacings of the electrode C, G G D D are exactly as set forth in application Serial No. 409,585.

The electrode L is a disc of molybdenum 0.5 mm. thick and spaced from the end of the deflecting cylinder D D by a distance of 0.5 mm. The electrode L has an aperture of the shape seen in Figure 2, which is 14 mm. across the flats and has a diameter of 16 mm. for the areshaped part.

The suppressor electrode S is spaced 9. distance of 2.5 mm. from the electrode L and is a disc similar to the latter but having an aperture 0.5 mm. larger all round than the electrode L The lead-in wires to the electrode L are shown at 9, 9', and that for the suppressor electrode S at I 0 in Figure 4.

The sub-anode SA is a massive copper disc sealed to the glass of the envelope E and with its nearest surface spaced 3.5 mm. from that of the suppressor electrode S. As can be seen in Figures 1 and 3, the sub-anode SA extends outside the envelope of the tube, and as will be explained later, is adapted to be fitted directly to the output circuit. It also divides the tube into two parts separating the lower part of the tube containing the cathode C from the upper part of the tube containing the output target T. The electrode SA has a single rectangular slot 8 through which the electron beam passes When it is not deflected. It will be evident, however, that if more than one output target such as T is provided, more than one rectangular slot .9 could be provided each associated with one of the output targets. In the form shown the slot 3 is 4 mm. wide and 20 mm. long. The sealing of the sub-anode SA to the two parts of the glass envelope E is effected by means of annular fin- like flanges 5, 5, extending from opposite surfaces of the electrode SA, and in order to avoid the glass breaking away, the section of these flanges has a pronounced taper towards the root, but the points are thin with practically parallel sides.

All of the electrodes except the cathode C and the deflection cylinder D D so far described are each provided with a pair of spaced apertures l, as is also the mica disc m. These apertures are in alignment with two screw-threaded holes 8 in the sub-anode SA for use in assembling and aligning the electrodes, as described in Patent Application Serial No. 409,589, filed September 4, 1941. This method preserves perfect alignment which is very important indeed since unless it is preserved, very indifferent results are obtained.

The anode or output target T has its front surface spaced 10 mm. from the nearest surface of the sub-anode SA. The target is of the shape shown, being sealed into the glass, as shown in Figure 1, by an annular fin 11, so that its rear surface is accessible from outside the envelope and is formed with a screw-threaded socket t for receiving the conductor by means of which connection is made to it. As already explained, the target T is placed behind the slot 8 in the subanode SA.

As an example of potentials which may be applied to the different electrodes, the following may be mentioned. The grid G is at the same potential as or a few volts negative to the cathode C. The positive grid G is held at 1000 volts positive, The mean potential of the deflection and focussing cylinder D D is 300 volts. The electrode L is at the same voltage as the anode T which is 2500 volts. The suppressor electrode S is at cathode potential and the sub-anode SA is maintained at 1200 to 1500 volts positive with respect to the cathode C.

The beam of electrons is drawn from the oathode C by the positive potential on the positive grid G and passes through the deflecting and focussing cylinder D D When there are no deflecting potentials, it passes entirely through the slot 5 in the sub-anode and strikes the target T. For the reasons already explained, under the above working conditions, a focussed beam is produced of rectangular or ribbon shape in crosssection so as to conform to the slot 5, and is consequently deflected by the electrode D D in the direction of the smaller dimension of its crosssection. In this way, a greater sensitivity is obtained and a greater current change .per unit of deflecting force than would be the case if the beam were deflected in another direction with respect to its cross-section.

It can now be appreciated that since the subanode SA is kept at a potential low compared with the steady potential of the output tar et T, the potential of the latter may decrease substantially without substantially reducing the beam current and thereby provide an efficient transfer of energy from the beam to the output circuit. At the same time, the transit time of the beam in that part of the tube where it passes through the deflecting cylinder D D is short because of the comparatively high potential on the positive accelerating electrode L At the same time, undesirable transfer of secondary radiation from the sub-anode SA, which is at relatively low potential to the high potential accelerating electrode L is prevented by the presence between them of the low potential retarding electrode S. Furthermore, even when operating on extremely short wave lengths, the electric field of the output circuit may be confined entirely to the target side of the sub-anode SA, and if a concentric line output circuit is used, as will be described with reference to Figures 5 and 6, the field is entirely confined to the inside of this circuit which is necessary if severe losses are to be avoided in the circuit.

The mechanical details of the output circuit are shown in Figures 5 and 6. The tube is mounted by bedding the sub-anode SA on to a seating on a brass ring Sii with a thin silver ring 3i interposed to make good contact. The subanode SA is pressed on to the seating in the ring Ell by three equally spaced screws 32 (Figure 6) screwed radially into the ring 33 and formed with conical points which press the sub-anode SA on to the seating, as can be seen in Figure 6. The voltage of 1500 volts for the sub-anode SA is applied to a ring 38a which is in direct metallic contact with the ring 3% As already mentioned,

the target T has a screw-threaded socket in its outer or rear surface and connection is made to it by a rod l2 screwed into that socket and is actually tubular as shown, and is perforated at its lower end so that air can be forced in at the top of the tubular rod I2 and can escape through the perforations for the purposes of cooling the output target T. The tubular rod i2, being screwed into the output target T, is fixed relatively to the brass ring 36. A sheet metal casing 33 open at the top is soldered to a further brass ring 34 secured by screws (t5 to yet a further brass ring A sheet metal cap 3'! with its lower end slit at 38 telescopes into the casing and has vent holes 40a in its top wall it to allow of the escape of the cooling air. The wall Aid is also secured to a tubular sleeve 39 which is capable of sliding on the tubular rod 22. The result of this is that the rod i2, the sleeve as, and end wall ie, and the sheet metal casings 3i and 33, and the brass rings 34 and 3'5, are all subject to the voltage of 2500 volts applied to the output target T. Consequently, hese parts have to be insulated from the rings 3% and 39a which receive toe sub-anode voltage of 1500 volts. this purpose, a sheet of mica it about mm. in thickness is interposed between the rings Etta and 36, but these rings are mechanically fastened together by screws d2 which pass through the ring 36 and through large holes in the ring 38a and screw into nuts 43 which are ins lated from the brass ring 35a by mica washers Thus, the parts subjected to the two different voltages of the target T and subanode SA are insulated from one another, and the forms the dielectric of the condenser through which the two sets of parts are electrically connected. The whole output structure will be recognised as a concentric line type of tuned output circuit. In order to reduce losses while enabling sufiicient mechanical strength to be provided, the casings 33, Si, 16, and the rings t l, should be made or" brass and should be silver-plated since goodcontact surfaces must'be maintained.

For tuning purposes the metal cap 31 can slide relatively to the metal casing 33 and to the brass rings which are fixed to the sub-anode SA. For this purpose, a sleeve 45 is secured by set screws 5 .3 to the sleeve 39 and is provided with a righthand screw-thread ll on its outer surface. This screw-thread engages an internal right-hand thread in a nut 43 fixed within an ebonite adjusting disc d9. On the other side of this disc, there is a nut till having an internal left-hand screw engaged by a threaded sleeve 5| fixed by set screws 52 to the upper part of the rod 12. Now if, for example, the ebonite disc 29 is rotated so as to screw the nut 58 up onthe screw-thread of the sleeve 5! which, of course, is fixed to the rod l2, and therefore also fixed relatively to the subanode SA, owing to the fact that the sleeves 5| and 45 have threads of opposite hand, the sleeve 55 will be drawn upwards into the nut 48 at double the rate assuming the pitches of the screwthreads to be the same. As a result, the sleeve 35 and the sheet-metal cap 3'5 are drawn up relatively to the metal casing 33. Also, if the disc id is rotated in the opposite direction, the cap ii is forced down into the casing 33 and by this means the tuning of the concentric conductors i2 and 3'! is efiected.

The loop is is a pick-up loop connected to twin-shielded conductors 53 for connection to a di-pole transmitting aerial. The loop 55 is a tuning loop connected directly to a small lamp 55 which by its brilliance indicates the tuning point.

I claim:

1. Electronic apparatus comprising an electron discharge tube including an electron-emitting cathode for producing a beam of electrons, an output electrode comprising a target anode for receiving electrons from said beam and adapted to alternately vary above and below a mean potential, a control electrode mounted between said cathode and said anode, a high potential accelcrating electrode mounted between said control electrode and said anode, a retarding electrode mounted between said accelerating electrode and said anode and to be maintained at a relatively low potential with respect to said accelerating electrode, and a shielding sub-anode interposed between said retarding electrode and said anode, said sub-anode to be maintained at the same alternating potential as said cathode and constituting a shield to prevent the alternating field of said anode from influencing the electrodes of said tube located on the opposite side of said sub-anode from said anode.

2. Electronic apparatus comprising an electron discharge tube including an electron-emitting cathode for producing a beam of electrons, an output electrode comprising a target anode for receiving electrons from said beam and adapted to alternately vary above and below a mean potential, a beam-deflecting element mounted between said cathode and said anode, a high potential accelerating electrode mounted between said deflecting element and said anode, a retarding electrode mounted between said accelerating electrode and said anode and to be maintained at a relatively low potential with respect to said accelerating electrode, and a shielding sub-anode interposed between said retarding electrode and said anode, said sub-anode to be maintained at the same alternating potential as said cathode and constituting a shield to prevent the alternating field of said anode from influencing the electrodes and elements of said tube located on the opposite side of said sub-anode from said anode.

3. An electron discharge tube comprising an electrode system including an electron-emitting cathode for producing a beam of electrons, an output electrode system including a target anode for receiving electrons from said beam and adapted to alternately vary above and below a mean potential and a shielding sub-anode to be maintained at zero alternating current potential and being formed as a transverse metallic partition dividing the space within the envelope of the tube into two parts one containing the oathode, and one the anode and having an aperture through which the beam of electrons may pass from the space containing said cathode to the space containing said anode and a control electrode mounted between said cathode and said output electrode system, said anode and said subanode having surfaces outside the envelope of the tube adapted to fit mechanically two poles of an output circuit. 7

4. An electron discharge tube comprising an electrode system including an electron-emitting cathode for producing a beam of electrons, an output electrode system including a target anode for receiving electrons from said beam and adapted to alternately vary above and below a mean potential and a shielding sub-anode to be maintained at zero alternating current potential and being formed as a transverse metallic partition dividing the space within the envelope of the tube into two parts one containing the cathode, and

one the anode and having an aperture through which the beam of electrons may pass from the space containing said cathode to the space containing said anode and a beam-deflecting element mounted between said cathode and said output electrode system, said anode and said subanode having surfaces outside the envelope of the tube adapted to fit mechanically two poles of an output circuit.

5. An electron discharge tube comprising an electron beam-forming system including an electron-emitting cathode, a control electrode for the electron beam, a high potential accelerating electrode mounted on the side of said control electrode remote from said cathode, a retarding electrode to be maintained at a relatively low potential with respect to said accelerating electrode and mounted next to said accelerating electrode and on the side therefor remote from said cathode, and an output electrode system including a target anode for receiving electrons from said cathode and adapted to alternately vary above and below a mean potential and a shielding subanode mounted immediately next to said retarding electrode and between same and said anode and having an aperture through which part of the electron beam may pass to said anode on its way from said cathode, said sub-anode also to be maintained at a potential between that of said retarding electrode and the mean potential of said anode.

6. An electron discharge tube comprising an electron beam-forming system including an electron-emitting cathode, a beam-deflecting element for the electron beam, a high potential accelerating electrode mounted on the side of said beamdefiecting element remote from said cathode, a retarding electrode to be maintained at a relatively low potential with respect to said accelerating electrode and mounted next to said accelcrating electrode and on the side thereof remote from said cathode, and an output electrode system including a target anode for receiving electrons from said cathode and adapted to alternately vary above and below a mean potential and a shielding sub-anode mounted immediately next to said retarding electrode and between same and said anode, and having an aperture through which part of the electron beam may pass to said anode on its Way from said cathode, said subanode also to be maintained at a potential between that of said retarding electrode and the mean potential of said anode.

7. An electron discharge tube comprising an envelope consisting in part of vitreous material, an electrode system including an electron-emitting cathode for producing a beam of electrons, an output electrode system including an anode of copper for receiving electrons from said beam and adapted to alternately vary above and below a mean potential, said anode being sealed into a vitreous portion of said envelope and presenting a surface outside said envelope, and a shielding sub-anode in the form of a transverse copper partition dividing the space within said envelope into two parts, having an aperture for afiording the electron beam access to said anode and sealed into a vitreous portion of said envelope and extending outside said envelope, and a beam-deflecting element mounted between said cathode and said output electrode system.

8. An electron discharge tube installation com prising an electrode system including an electronemitting cathode for producing a beam of electrons, a target anode for receiving electrons from said beam and adapted to vary alternately above and below a mean potential, a shielding sub-anode in the form of a transverse metallic partition dividing the space within the envelope of the tube into two parts one containing the cathode, and one the anode and having an aperture through which electrons from said beam pass to said anode and having an annular portion extending to the outside of said envelope, a concentric line having an inner conductor connected with said anode and a tubular outer conductor surrounding that part of the tube envelope which includes said anode and being electrically connected with the outer annular portion of said sub-anode.

9. An electron discharge tube installation according to claim 8 wherein said sub-anode is to be maintained at zero alternating current potential and at a mean direct current potential lower than the mean potential of said anode.

10. An electron discharge tube comprising an electrode system including an electron-emitting cathode for producing a beam of electrons, an output electrode system including an anode for receiving electrons from said beam and adapted to alternately vary above and below a mean po. tential and a shielded sub-anode to be maintained at the alternating potential of said cathode and interposed between said anode and the remaining electrodes of the tube, a beam-deflecting element mounted between said cathode and said output electrode system, an accelerating electrode mounted further from said cathode than said beam-deflecting element and a retarding electrode the form of a disc with a central aperture for the passage of the electron beam and to be maintained at a relatively low potential with respect to said accelerating electrode and mounted next to said accelerating electrode and between same said output electrode systern.

11. An electron discharge tube comprising an electron beam-forming system including an electron-emitting cathode, a control electrode for the electron beam. an accelerating electrode mounted on the side of said control electrode remote from cathode, a retarding electrode in the form of a disc with a central aperture for the passage of the electron beam and to be maintained at a relatively low potential with respect to accelerating electrode, and mounted next to said accelerating electrode and on the side thereof remote from said cathode, and an output electrode system including a target anode for receiving electrons from said beam and adapted to alternately vary above and below a mean potential and a shielding sub-anode mounted immediately next to said retarding electrode and between same and said anode and having an aperture through which part of th electron beam may pass to said anode on its way from said cathode, said sub-anode also to be maintained at a potential between that of said retarding electrode and the mean potential of said anode.

12. An electron discharge tube installation comprising an electrode system including an electron-emitting cathode for producing a beam of electrons, a control electrode for the electron beam, anoutput electrode system including an anode for receiving electrons from said beam and adapted to alternately vary above and below a mean potential and having a portion extending outside of the envelope of the tube and a subanode in the form of a transverse metallic partition dividing the space within the envelope of the tube into two parts and having an aperture to afford the electron beam access to said anode and extending to the outside of the said envelope, a retarding electrode in the form of a disc with a central aperture for the passage of the electron and to be maintained at a relatively low potential with respect to said anode and mounted between said control electrode and said output electrode system, and an output circuit including a concentric line having a tubular outer conductor surrounding that portion of the tube envelope which contains said anode and being electrically connected with said sub-anode, said concentric line including an inner conductor electrically connected with said outer surface of said anode.

13. An electron discharge tube comprising an electrode system including an electron-emitting cathode for producing a beam of electrons, an output electrode system including an anode for receiving electrons from said beam and adapted to alternately vary above and below a mean potential and a shielding sub-anode to be maintained at the alternating potential of said cathode and interposed between said anode and the remaining electrodes of the tube, a beam-deflecting element mounted between said cathode and said output electrode system, an accelerating electrode in the form of a disc with a central aperture for the passage of the electron beam and mounted further from said cathode than said beam-deflecting element and a retarding element in the form of a disc with a central aperture slightly larger all round than the aperture in said accelerating electrode for the passage of the electron beam and to be maintained at a relatively low potential with respect to said accelerating electrode and mounted next to said accelcrating electrode and between same and said output electrode system.

14. An electron discharge tube comprising an electron beam-forming system including an electron-emitting cathode, a control electrode for the electron beam, an accelerating electrode in the form of a disc with a central aperture for the passage of the electron beam and, mounted on the side of said control electrode remote from said cathode, a retarding electrode in the form of a disc with a central aperture slightly larger all round than the aperture in said accelerating electrode for the passage of the electron beam and to be maintained at a relatively low potential with respect to said accelerating electrode and mounted next to said accelerating electrode and on the side thereof remote from said cathode and output electrode system including a target anode for receiving electrons from said beam and adapted to alternately vary above and below a mean potential and a shielding subanode mounted immediately next to said retarding electrode and between same and said anode and having an aperture through which part of the electron beam may pass to said anode on its vay from said cathode, said sub-anode also to be maintained at a potential between that of said retarding electrode and the mean potential of said anode.

15. An electron discharge tube installation comprising an el ctrode system including an electron-emitting cathode for producing a beam of electrons, a control electrode for the electron beam, an output electrode system including an anode for receiving electrons from said beam and adapted to alternately vary above and below a mean potential and having a surface outside the envelope of the tube and a shielding sub-anode in the form of a transverse metallic partition dividing the space within the envelope of the tube into two parts and having an aperture to afford the electron beam access to said anode and extending to the outside of the said envelope, an accelerating electrode in the form of a disc with a central aperture for the passage of the electron beam and mounted further from said cathode than said control electrode, a retarding electrode in the form of a disc with a central aperture slightly larger all round than the aperture in said accelerating electrode for the passage of the electron beam and to be maintained at a relatively low potential with respect to said accelcrating electrode and mounted next to said accelerating electrode and between same and said output electrode system.

16. Electronic apparatus comprising an electron discharge tube including an electron-emitting cathode for producing a beam of electrons, an output electrode comprising a target anode for receiving electrons from said beam and adapted to alternatel vary above and below a mean potential, an apertured shielding sub-anode positioned in front of said anode and to be maintained at zero alternating current potential and at a direct current potential lower than the mean potential of said anode, and an apertured suppres- 12 sor electrode positioned in front of said subanode and to be maintained at a lower potential than said sub-anode.

JOHN HENRY OWEN HARRIES.

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

UNITED STATES PATENTS Number Name Date 2,167,431 Bowie July 25, 1939 1,779,794 Ackermann Oct. 28, 1930 2,140,707 Lee Dec. 20, 1938 1,814,805 Hitchcock July 14, 1931 1,893,887 Giard Jan, 10, 1933 2,254,090 Power Aug. 26, 1941 2,232,098 Deichman Feb. 18, 1941 2,189,261 Bowie Feb, 6, 1940 2,284,829 Ludi June 2, 1942 2,250,511 Varian July 29, 1941 2,303,166 Laico Nov. 24, 1942 2,309,966 Litton Feb. 2, 1943 2,281,935 Hansen et al May 5, 1942 2,272,165 Varian et a1 Feb. 3, 1942 2,275,480 Varian et a1 Mar. 10, 1942 1,942,596 Hentschel Jan. 9, 1934 2,084,867 Prinz et al June 22, 1937 2,207,846 W011i July 16, 1940 2,284,733 Haefi June 2, 1942

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