US2420345A - Electron discharge device - Google Patents

Description

y 1947- G. H. P. ALMA 511m.

ELECTRON DISCHARGE DEVICE Filed March 22, 1945 Patented May 13, 1947 UNITED STATES PATENT OFFICE ELEQTRON DISCHARGE DEVICE Application March 22, 1943, Serial No. 480,161 in the Netherlands December 30, 1946 3 Claims.

This invention relates to an electric discharge tube particularly suitable as a mixer tube utilized in superheterody'ne circuits and having an electrode system constituted by at least two control grids, such as, for example, in a hexode, a pentagrid tube or an octode.

In these discharge tubes, which may be used, for example, as mixing tubes, at least one positive auxiliary electrode is provided between the two control grids. Before the second control grid, reckoned from the cathode, and behind the said positive auxiliary electrode a space charge is generally formed which is controlled by the second control grid.

One of the difficulties which most occur when using the discharge tubes concerned is that electrons can return from the space between the positive auxiliary electrode and the second control grid, hence from the said space charge, which electrons can impinge in the vicinity of the cathode and the first control electrode. An un desirable reaction of the second upon the first control grid is thus produced.

Different means have previously been proposed to eliminate the stated difiiculty. Thus, a discharge tube has been described, comprising an electrode system having two control grids and a virtual cathode, the electrons which have such a low speed that they will return in front of the second control grid as soon as they are deflected, being intercepted by a special electrode. In another known construction of the tube a screen electrode provided between two control electrodes is so shaped and the space between these screen electrodes and the second control electrode is so dimensioned that returning electrons, after being first deflected from their original path, are intercepted by this screen electrode.

It is also known to join the electrodes to a tube having two control grids into two groups which are so arranged in the tube relatively to each other that the axes of these two groups jointly form an angle which may be, for example, 120. In this case the cathode, the first control electrode and the screen electrode provided intermediate the two control electrodes form one group and the second control electrode, the anode and any intermediate electrodes form the second group. The returning electrons are then intercepted by a separate electrode arranged aside from the electrode system.

It is also known by means of a magnetic field to influence the paths of going and returning electrons in such manner that, either by the use of a slanting arrangement as stated before the returning electrons are collected on a separate electrode, or these electrons impinge on a definite part of one of the electrodes, for example on a solid part of the first screen grid; in this case the electrodes are arranged in the normal manner about the cathode and a slanting arrangement as stated above is not utilized.

In the latter case, in which the electrodes are arranged in the usual manner about the oathode, a special magnetic or electrostatic field must be utilized which renders the construction of the device utilizing such a tube more complicated. In the former case, in which a slanting arrangement of part of the electrode system isutilized, a separate electrode is required, while diniculties occur due to the first screen grid forming part of the group of the cathode and the first control grid and, due to the large space which exists between the first screen grid and the second control grid, induction effects upon this second control grid are produced.

The object of my invention is to provide an improved electron discharge device particularly suitable as a mixer in a superheterodyne circuit.

The difficulties set out above may be obviated by utilizing the improvement provided by the device the tube according to the present invention. This device utilizes a tube comprising an electrode system, the electrodes of which are divided'into two groups, of which the. axes jointly form an angle, for example, of about 45 degrees and in which the screen grid provided between the two control grids forms part of the group which comprises the second control grid and the anode. To this end, this screen gridmay be arranged comparatively closely in front of the second control grid so that a large space between these electrodes and consequently the occurrence of induction effects is avoided. Besides, the returning electrons may be easily intercepted without utilizing additional means. In one definite embodiment of the present invention this may be effected by making the first screen grid partly solid, which solid part intercepts the returning electrons, while in another embodiment this screen grid is provided with comparatively thick supports so that the removal of the returning electrons is promoted.

The invention will now be explained more fully with reference to the accompanying drawing showing diagrammatically the electrode system of a discharge tube according to the invention.

As shown in the drawing, the cathode l of the tube is rectangular in cross-section with the ends uncoated and non-emitting so that the electron emission coming only from the coated sides forms two oppositely directed electron beams. The cathode is surrounded by a control grid 2 with its side rods 2 opposite the non-emitting ends of the cathode to assist in forming the electron discharge from the coated sides of the cathode into beams. These electrodes jointly form one group whose axis forms an angle with the second group of electrodes which is constituted by a second control grid 3 having side rods 3, a screen grid 4 and an anode 5. In front or the second control grid is the first screen electrode 6 which is provided with comparatively thick supports 1 which because of their size act to some extent as shields between the two groups of electrodes, so that the electrons which return before the grid 4 can be easily intercepted. All of the electrodes are enclosed in evacuated envelope 8.

It is evident that the invention is not limited to the above-stated example, but that still other applicaions are possible. If, for example, the tube is constructed as a mixing tube of which the oscillator electrodes are closer to the cathode than the input control grid, the electrode group to which the cathode pertains is not constituted by the cathode and one grid, but by the cathode and two grids. In this case the oscillator anode may consist of a few rods arranged in the space between the first control grid and the screen grid.

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 employed, it will be apparent that our invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of our invention as set forth in the appended claims.

We claim:

1. An electron discharge device having a cathode surrounded by a control grid having a pair of oppositely disposed side rods lying in a common plane, a screen grid and second control grid surrounding said cathode, each of said grids having oppositely disposed side rods, the side rods of said screen grid and second control grid lying in a common plane passing at an angle through the first plane, and an anode surrounding said cathode, screen grid and control grids, the electrons from said cathode being formed into oppositely directed beams, each beam passing close to one of the screen grid side rods, the side rods of said screen grid having a larger diameter than the other side rods, and a second screen grid positioned between the anode and second control 4 grid, said screen grid side rods absorbing electrons returned by said second control grid during operation of said electron discharge device.

2. An electron discharge device having a cathode surrounded by a control grid having a pair of oppositely disposed side rods lying in a common plane, a screen grid and second control grid surrounding said cathode, each of said grids having oppositely disposed side rods; the side rods of said screen grid and second control grid lying in a common plane passing at an angle through the first plane, the side rods of said screen grid having a larger diameter than the other side rods, and an anode surrounding said cathode, screen grid and control grids, the electrons from said cathode being formed into oppositely directed beams, each beam passing between and close to the screen grid side rods, said screen grid side rods absorbing electrons returned by said second control grid during operation of said electron discharge device.

3, An electron discharge device having a cathode of rectangular cross section, only the opposite faces of which are coated with emitting material with the ends uncoated and non-emitting and providing a pair of oppositely disposed electron beams, a first control grid surrounding said cathode and provided with oppositely disposed side rods, one of each of said side rods being disposed opposite each non-emitting portion of the cathode, said side rods and the longitudinal axis of said cathode lying in a common plane, a screen grid and a second control grid surrounding said cathode and first control grid and of elliptical shape, and each grid being provided with side rods, said side rods lying in a common plane disposed at an angle of about degrees to the plane of said first control grid, whereby the electron beams are directed between the screen grid side rods, said screen grid side rods having an enlarged diameter for absorbing electrons returned by said second control grid during operation of said electron discharge device.

GERRIT HENDRIK PETRUS ALMA. BERNHARDUS GERHARDUS DAMMERS.

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

UNITED STATES PATENTS Number Name Date 2,159,765 Jonker May 23, 1939 2,198,340 Harris Apr. 23, 1940 2,219,102 Herold Oct. 22, 1940 2,256,335 Aldous Sept. 16, 1941

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