US2104816A - Electron discharge device - Google Patents

Description

Jan. 11, 1938. H. ROTHE 2,104,816

ELECTRON DISCHARGE DEVICE Filed Feb. 19, 1955 INVENTOR. HORST ROTHE BY I wqaa;

ATTORNEY.

Patented Jan. 11, 1938 UNITED STATES PATENT OFFICE ELECTRON DISCHARGE DEVICE Horst Rothe, Berlin,-Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application February 19, 1935, Serial No. 7,181 In Germany March 1, 1934 4 Claims. (01. 250-215) electrodes and useful as an amplifier, which has more desirable characteristics and particularly a more nearly constant amplification factor than such devices constructed in the usual way.

In modern radio sets supplied from power supplylines, tubes having indirectlyheated cathodes are commonly used. These cathodes comprise an insulating body or tube in which a heater element is positioned, and on the exterior of which is placed a metallic shell or tube coated or covered with a substance capable of electron emission. In the conventional tube, the cathode as well as the other electrodes, has a cylindrical form. For tubes of more than average power, especially so-called power tubes, the anodes or plates are either of box-shape or of oval-cylindrical form to provide a larger heat-dissipating surface. In these latter cases it is customary to provide the cathode with a cross-sectional shape other than circular, more particularly a rectangular, elliptical, or oval form. While it has been previously proposed to dispose the grid close to the cathode and equidistant from the cathode at all points to provide a tube in which the amplification factor characteristic is as uniform as possible around the entire circumference of the cathode, the forms of cathode and electrode system heretofore employed were not such as to provide a uniform field, distribution between the electrodes which is essential to obtain a uniform amplification factor. Where the cathode is other than circular in cross section,

the radius of curvature of. the cathode cross section is not equal along the whole surface thereof. This disturbs the uniformity of field distribution. In addition, the uniformity of the field distribution is affected by the stay wires or side rods supporting the grid electrodes. As a result all portions of the cathode surface are not equally effective in supplying electrons to the anode of the electrode system.

According to a preferred embodiment of my invention, I use a straight indirectly heated cathode which is lenticular in cross section. With respect to the other electrodes, at least the one which is nearest the cathode, and which is usually a grid, is formed so that it lies equidistant from the cathode surface at all points and is also lenticular in cross section. The supporting stays or side rods of this electrode as well as of all the other electrodes are positioned in a plane passing thru the two edges of and longitudinally thru the cathode. V

The novel features which I believe to be char-' acteristic of my 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 drawing in which the single figure in the drawing is a cross section transverse to the longitudinal axis of an electron dis- 0' charge device made in accordance with my invention. 7

Referring to the drawing, the indirectly heated cathode includes a body I of insulating material, the cross section of which is in the shape of 15 a lens, the contour lines of the cross section being formed, for example, by arcs having centers 0, O. The insulating body has two bores 2 whose axes are parallel and in which a looped or helical heater wire 3 is embedded. The surface of the insulating body may be coated with a metallic layer or provided with a metallic sleeve 4, upon which is placed any well-known electron emissive substance 4'. The grid electrode 5 may consist of a perforatedsheet, a metallic gauze or helically wound wires which may be welded to stays or side rods 6. The anode I supported on stays or side rods 8 surrounds the other two electrodes. The grid is lenticular in cross section so that it is equidistant at all points from the cathode surface, that is so that the distance (I measured perpendicularly to the surface of the cathode be-- tween the cathode and grid is the same at all points. In the present case it will thus be seen that the grid cross section consists of two arcs described about the centers indicated at O and 0'.

It can be readily seen that the radius 'of curvature of the grid has a constant value along the entire cathode surface. As a consequence, the density of the force-lines upon the surface of 40 the cathode or the field distribution will be uniform. In other words, there is obtained a substantially ideal condition where the entire cathode surface is equally effective and is thus utilized under optimum conditions. Moreover, the amplification factor characteristic over the whole surface of the cathode is constant, insuring a desirable grid voltage plate current characteristic, the curve representing this characteristic having a sharply curved bottom knee, the rest of the 5 curve following the well-known 3/2 law. Tubes of the usual construction in which theamplification factor diifers for different parts of the oathode surface may be pictured as composed of a plurality of components or partial electron discharge systems each having a characteristic of different form. The resulting characteristic curve has a more gradual slope, the lower end of the curve gradually tapering off instead of being sharply curved. Conventional tubes of this kind do not have desirable rectifying properties, and when used, for amplification they do not permit high degree of modulation (large grid swings) without distortion. Another desirable feature of an electron discharge device made in accordance with my inventionis that the grid stays or side rods 6 are placed at a point where they will not appreciably disturb the uniform shape of the field.

The anode I is also formed and positioned so that it is equidistant from the cathode surface at all points, and may also be lenticular in shape. It would be sufficient if the anodes were to com-' prise only those portions determined by the angles whose apices lie at the points and O, that is those portions of the anode lying between planes passing thru the edges of the cathode and the centers 0, O of the arcs defining the surfaces of the cathode, for even in this case substantially the entire electron emission from the cathode surface would be utilized. In order to avoid marginal unsteadiness or irregularity, however, the anode is preferably formed as shown and supported by the stays or side rods 8. The electrode system is contained within an evacuated envelope 9. V

The utilization of the whole cathode surface is an advantage of the cross sectional shape of the cathode of this invention as compared with the so-called fiat type of cathode of rectangular cross section. Whereas in the case of box-type cathodes the emission of the narrow ends of necessity is lost because the ends of the cathode are shielded by the grid side rods, and because the field is very much distorted at the side rods, it, is possible by my invention to avoid all losses of electron emission current. Hence, the cathode contains no surface portions that are left unutilized, and the consequence is that minimum cathode volume and minimum heating energy are combined with maximum electron emission.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed,

it will be apparent that my 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 purposefor which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is:-

1. An electron discharge device having an envelope and containing a straight thermionic cathode, a grid and another electrode, said cathode, grid and other electrode being lenticular in a transverse cross section and defined by intersecting cylindrical surfaces, the surfaces on one side having one common center of curvature and the surfaces on the other side having another common center of curvature oppositely disposed to said one common. center of curvature, side rods for supporting said grid and other electrode, said side rods lying in a plane passing longitudinally thru the intersections of said cylindrical surfaces.

2. An electron discharge device having an envelope and containing a straight thermionic cathode, a grid and. another electrode surrounding said cathode, said cathode being lenticular in a transverse cross section, all portions of the grid lying between planes passing thru the longitudinal edges of the cathode and the centers of the intersecting arcs defining the surfaces of the cathode being substantially equidistant from the surfaces of the cathode at all points, said grid having side rods positioned opposite the longitudinal edges of the cathode and lying in a plane passing longitudinally through the longitudinal edges of said cathode and all portions of said other electrode lying between planes passing thru the edges of the cathode and the centers of the arcs defining the surface of the cathode being equidistant from the surface of the cathode.

3. An electron-discharge device having an envelope and containing a straight thermionic cathode, a grid and another electrode surrounding said thermionic cathode, said cathode, grid and other electrode being lenticular in cross section, the surfaces of one side of said grid, cathode and other electrode being defined by cylindrical surfaces having the same center of curvature and the surfaces of the other side of said cathode, grid and other electrode being defined by cylindrical surfacesv having a center of curvature different from and oppositely disposed to the first center of curvature, and side rods for supporting said grid at the points of intersection of the cylindrical surfaces defining said grid.

4. An electron discharge device having an envelope and containing a straight thermionic cathode, agrid. and another electrode surrounding said thermionic cathode, said cathode, grid and other electrode being lenticular in cross section, the surfaces of one side of said cathode, grid and other electrode being defined by arcs having one center and the surfaces of the other side of said cathode, grid and other electrode being defined by arcs having another center oppositely disposed to said one center and side rods for supporting said grid positioned at the intersections of the surfaces defining said grid.

HORST ROTI-IE.

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