US2173267A - Electron discharge device - Google Patents

Description

Sept. 19, 1939. M. J. '0. STRUTT ET AL ELECTRON DISCHARGE DEVICE Filed April 21, 1938 2 Sheets-Sheet 1 INVENTORS MAXIMILIAAN J. O. STRUTT.

ALDERT VAN DER ZIEL Sept. 19, 1939.

M. J. O. STRUTT ET AL ELECTRON DI S CHARGE DEVIC E Filed April 21, 1938 2 Sheets-Sheet 2 I NV EN TORS MAXIMILIA'AN .1. o. STRUTT. ALDERT VAN DER ZlEL.

ATTORNEY.

Patented Sept. 19, 1939 PATENT OFFICE ELECTRON DISCHARGE DEVICE Maximiliaan Julius Otto Strutt and Aldert van der Ziel, Eindhoven, Netherlands, assignors to N. V. Philips Gloeilampeniabrieken,

hoven, Netherlands Eind- Application April 21, 1938, Serial No. 203,280 In Germany May 14, 1937 4 Claims. (Cl. 250-174) This invention relates to electron discharge devices having a multiple control of the stream oi electrons emerging from the cathode, and particularly suitable for use as mixers or convertors 5 in superheterodyne circuits.

In such tubes a stream of electrons emerging from a cathode is usually supplied through a plurality of grids to an anode inside the tube and influenced by two controlgrids on its travel to the anode. Sucha tube may be used as a mixing tube in which the input oscillations are supplied to one of the grids, whereas the local oscillations produced by a local oscillator are applied to another grid. The tube may also be used as aself-oscillating mixing tube or so-called convertor in which the local oscillations are produced between two grids of the tube itself.

The operation of the tube is as follows. The electrons emerging from the cathode fly through the first control electrode and after traversing generally a positive grid they approach the second control electrode. Since this second electrode usually has a lower voltage than the preceding positive grid, a space charge is formed in front of the second control grid which charge may be considered as a virtual cathode. The second control grid controls the electrons emanating from this cathode. However, this space charge is also subject to the influence of the pre- 06 ceding electrodes. In response to the voltage on these electrodes and of the second control grid,

electrons from the space charge are returned toward the first control grid where in the case of a.

mixing tube and in splite of the negative voltage n,- on this control grid, they will produce a control must be applied to the first control grid which involves difficulties particularly when such a tube is used as a mixing tube and the second control 40 grid is used as an oscillator grid. In addition,

the returning electrons affect the input damping. These undesirable characteristics might be avoided by using cathode ray tubes for this purpose. In this case the first control may be affected by an electrode provided in the neighgrid current. Consequently a high negative bias.

struction of mixing tubes is not suitable in normal receiving arrangements.

The principal object of our invention is to provide an improved electron dischargedevice particularly suitable for use as a mixer or convertor 5 tube in radio circuits and making use of controlled beams at low voltages.

In electron discharge devices made according to the present invention the undesirable characteristics noted above can be avoided. In one form 10 of tube having a double control and made according to our invention the electrons emanating from the cathode are supplied in the form of beams and along curved paths through a control and screen electrode arranged in the immediate vicin- 15 ity of the cathode. One control occurs on the control grid arranged in the immediate vicinity,

whereas the other control occurs in that part of the space from which the electrons can substantially not return to the first-mentioned electrodes, 20 the paths over which the electrons are influenced by the voltages applied to this second control electrode being larger than the paths over which they are influenced by the first control electrode.

When the electrons are directed in the form of 5 beams along curved paths it is possible on one hand to effect the second control at such a point of the space charge that the electrons can substantially not return to the vicinity of the first control grid, whereas on the other hand it is possible, without rendering the construction of the tube too complicated or its size too large, to give the paths such a length that the electrons can be controlled also by electrodes having a lower alternating voltage supplied to them. It is found 5 that by such a construction the current to the first control grid can almost entirely be suppressed, and that the input damping of such a tube is very much reduced.

In one form of construction a discharge tube according to the present invention may be built as follows. A= control grid and a screen grid are arranged one behind the other around an indirectly heated cathode. Between the two electrodes, members may be provided for focusing into 5 a beam the electrons emerging from the cathode. For this purpose it is also possible however, to provide the control grid with a solid portion, and this control grid may also consist of rod-shaped members by which the focusing of the electrons is efiected at the same time.

These electrodes are surrounded by an electrode which, for instance together with oneor more other electrodes of the tube, determines the form of the paths of the electron beams, the

' reach either one or the other electrode. The form of the paths of the electrons need not absolutely be determined by the second control grid. It is also possible to control the form of these curved paths, which form is quite immaterial, by means of other electrostatic or magnetic means provided in the tube. The output circuit of the tube may be connected to one of the two intercepting electrodes.

In another form of construction of the present invention the intercepting electrodes are ar-. ranged one behind the other and the electrode which is first reached by the arriving electrons is furnished with one or more apertures so that in accordance with the voltage of the second controlthe electron beams fall either on the front electrode or pass through the apertures provided therein to the back electrode.

Particularly in the last mentioned form of example the mutual conductance of the tube can be increased by making use of secondary emission. For this purpose the apertured electrode on the side facing the arriving electrons is coated with a material which readily emits secondary electrons when struck by a stream of electrons. The anode proper of the tube is provided in opposition thereto. Thus the beam of electrons falls either on the secondary emission electrode from which secondary electrons go to the anode, or passes through apertures of this secondary emission electrode to a suppressor or collector electrode placed behind it.

In another form of construction the tube is so built that the electrons impinge either on a secondary emission electrode arranged behind a grid-shaped anode, or are intercepted by the supporting rods of this grid-shaped anode, thus directly striking the anode.

If in the forms of construction described above it is desired to use a tube according to the present invention as a mixing tube the oscillator voltage may besupplied from the outside to the second grid. As an alternative, however, a tube according to the invention may be constructed as a self-oscillating mixing tube which according to another form of construction is effected by applying to an electrode arranged behind an apertured secondary emission electrode a voltage corresponding to cathode potential or being negative so that the electrons traversing these apertures do not impinge on the intercepting electrode, but on the inner side of the secondary emission electrode. In this case the second control grid and the second emission electrode work together as electrodes of the local oscillator, whereas the amplifying anode proper is arranged opposite the secondary emission electrode.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawings in.

which Figure 1 is a transverse section of an electron discharge device embodying our invention, Figure 2 is a circuit diagram utilizing the device shown in Figure 1,. Figures 3 and 4 are tubes shown in Figures 3 and 4, Figure 6 is a still further modification of an electron discharge device made according to our invention, and Figure 7 is a circuit diagram utilizing the tube shown in Figure 6.

Figure 1 shows a transverse section of an electron discharge device made according to our invention and having a straight indirectly heated cathode l, which cathode is surrounded by a control grid '2 wound on supporting members or side rods 3 and by a screen grid 4. Between the two electrodes are arranged two members, preferably fiat members, 5 used for focusing the electrons emerging from the cathode. The electrons pass in the form of beams along the paths approrximately indicated by the dotted lines 6 and finally reach a region of two more or less opposed V-shaped intercepting electrodes 1 and 8. The whole of the system is surrounded by an electrode 9 determining the form of the electron paths and acting as a second control grid at the same time. In accordance with the alternating voltage applied to this electrode the electron beams can be shifted so that the electrons go to either the electrode 1 along paths III or to the electrode 8 along paths ll. Electrodes 5, l, 8 and 9 may be of sheet metal and coextensive with each other and the cathode and grids. These electrodes are housed within an evacuated envelope 9'.

As appears from the circuit arranged in Figure 2 the output circuit l2 may be connected between the two electrodes I and 8. In this figure and in Figure 1 the indirectly heated cathode, control grid and screen grid are denoted by the same numbers as are the other electrodes. The input circuit I3 is connected between cathode I and control grid 2, the resistances H and I5 providing the biases on the electrodes 2 and 9. The oscillations of a local oscillator are supplied to the electrode 9 through transformer I6.

Figure 3 shows a slightly different form of construction of an electron discharge device made according to our invention. In this figure an indirectly heated cathode I 'l is surrounded by a control grid l8 wound on two rods I 9, and a screen grid 20. Between the two last mentioned electrodes are provided two preferably fiat members 2| by which the electron beams are formed. The course of these beams is indicated by the dotted lines 22, 23 and 2|. As appears from the drawings the electrons finally reach an electrode 25 and may either reach this electrode or gain access through apertures 26 to an electrode 21 arranged behind it. On the side facing the arriving electrons the electrode 25 is coated with a material which readily emits secondary electrons so that the electrons upon reaching the surface 'of the electrode 25 along paths 24 dislodge secondary electrons from this surface which electrons impinge on the anode 29 proper of the tube along paths 28. When the electrons pass through the apertures of the electrode 25 under the influence of the voltages applied to the elec trode 30 acting as a second control grid they strike an auxiliary electrode 21.

Figure 4 shows a tube construction which may be considered as a variation of the construction shown in Figure 3. As appears from the figure the members 2| for forming the beam are ar ranged outside the screen grid in this case. The second control grid consists of plate-shaped metal members 30 surrounding part of the system, whereas the intercepting electrode consists of supporting rods 21' for the anode 29' which consists of wire or gauze. The last mentioned electrode is arranged in front of the secondary emission electrode 25'.

Figure shows a circuit arrangement in which a tube as shown in Figure 3 or 4 may be used. In this figure an indirectly heated cathode H is surrounded by the first control grid l8, the screen grid 20, and the second control grid 30. The anode 29 is connected to the output circuit 3 I, the secondary emission electrode 25 and the intercepting electrode by 21 to the source of biasing voltage. The input circuit 32 is connected between cathode ll and grid 18, the resistances 33 and 34 determining the bias-es of the grid l8 and electrode 30. The oscillator not shown is coupled to electrode 30 by transformer 35.

In Figure 6, which represents another form of construction of the present invention, an indirectly heated cathode 36 is surrounded by a control grid 31 wound on supporting rods 38 and by the screen grid 39, members 40 for forming the electron beams being provided between the control and the screen grids.

The beams follow paths approximately indicated by the dotted line ll, 42 and 43 and reach an electrode 44 which on the side facing the arriving electrons is coated with a material emitting secondary electrons. When in accordance with the voltages applied to the electrode 45 the electrons strike the secondary electron emitting material, secondary electrons are dislodged from the latter which electrons reach the anode 41 proper of the tube along paths 46. However, the arriving electrons can also pass through apertures 48 of the electrode 44 and then reach the inner side of the electrode 44 under the influence of a negative or zero voltage applied to the electrode 49. Thus such a tube may also be used as a self-oscillating mixing tube, which appears more clearly from Figure 7.

In Figure 7 which represents a circuit arrangement together with a tube as shown in Figure 6,

the cathode 36 is surrounded by the first control grid 31 and the screen grid 39'properly biased. The auxiliary electrode is connected either to a point of negative voltage or to the cathode.

The electrodes 44 and 41 together constitute the oscillator electrodes of the self-oscillating mixing tube and are connected to the oscillator circuit 50. Furthermore the figure shows the output circuit 5i, the input circuit 52 and the resistances 53 and 54 by means of which the biases for the grid 36 and electrode 40 are determined.

While we have indicated the preferred embodiments of our invention of which we are now aware and have also indicated only one specific application for which our invention may be emand the purpose for which it is employed without departing from the scope of our invention as set forth in the appended claims.

What we claim as new is:

1. An electron discharge device including an envelope containing the cathode surrounded by a control grid and a screen grid, means for forming the electrons from said cathode into a beam, means including a second control electrode adjacent the beam of electrons for causing said beam to travel along a curved path, an anode positioned in the path of said beam and coated with secondary electron emitting material on the side facing the arriving electrons and lz ving an aperture, and an electrode adjacent said anode for receiving secondary electrons emitted from said secondary emitting surface.

2. An electron discharge device including an envelope containing a cathode surrounded'by a control grid and a screen grid and means for forming the electrons from said cathode into a beam, means including a second control electrode adjacent the said beam of electrons for causing said beam to travel along a curved path, an anode positioned in the path of said beam and coated with secondary electron emitting material on the side facing the arriving electrons and having an aperture and an electrode adjacent said anode for receiving secondary electrons emitted from said secondary emitting surface, and a second electrode in registry with said aperture, said second control electrode shifting said beam whereby said beam may pass through said aperture to said second electrode.

3. An electron discharge device having an envelope enclosing a cathode surrounded by a control grid and a screen grid and means for forming the electrons from the cathode into a pair of oppositely disposed beams, electrodes in the path of said beams for causing said beams to follow curved paths, an anode electrode in the path of said beams and covered with electron emitting material and a foraminous electrode adjacent said anode for receiving electrons emitted by said anode.

4. An electron discharge device having an envelope containing a straight thermionic cathode, a control grid and a screen grid surrounding said cathode, means for forming the electrons from said cathode into oppositely disposed electron beams,a pair of curved electrodes having concave surfaces facing said beams, for causing said beams to travel along curved paths, oppositely disposed anodes in the path 01' said beams and coated with secondary emitting material on the side receiving the electrons and a mesh like auxiliary electrode adjacent each anode and between the anodes and said cathode for receiving secondary electrons emitted from said anodes.

MAXIMILIAAN JULIUS O'I'IO S'I'RU'I'I. AIDERT VAN on ZIEL.

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