US2090006A - Electron discharge tube - Google Patents

Description

Aug. 17, 1937. M. KNOLL ET AL ELECTRON DISCHARGE TUBE Filed March 6, 1954 36 INVENTOR MAX ff/VOLL BY? OLF HULK/4 W TORNEY Patented Aug. 17, 1937 PATENT OFFICE ELECTRON DISCHARGE TUBE Max Knoll and Rudolf Rzehulka, Berlin, Germany, assignors to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. 11., Berlin, Germany, a corporation of Germany Application March 6, 1934, Serial No. 714,261 In Germany November 5, 1932 1 Claim.

The present invention relates to anelectron discharge tube for the rectification, amplification and production of oscillations, and is provided with a fiat cathode surface as the electron source. A fiat cathode is understood to be an incandes- -cent cathode of rectangular, square-shaped, or similarly formed section such as an elliptical section, the electron emitting surface of which forms a plane or nearly plane surface. Discharge tubes provided with such cathodes, due to the relatively simple mounting of the cathode and of the electrode system cooperating therewith, offer essential constructive advantages, and furthermore afford obtaining of great steepness due to the relatively large cathode surface.

In such tubes it is advantageous to arrange the auxiliary electrodes, such as control grid and anode, in planesparallel to the cathode surface.

Tests have proven that the actual steepness ofsuch arrangements is less than that when calculated from the emitting surface, and that the characteristic at its upward course does not reveal the required sharp bend (Flg. 1) but a smooth course (Fig. 2) so that the expected height of the mutual conductance is not attained. The cause of this behavior is to be seen in the fact that with a definite control voltage of the electrode system there corresponds respective locally different field intensities at the flat and curved or end portions of the cathode surface.

- of the electrodes (for instance bars of a control This invention resides in the fact that the electron emission from the narrow sides or edges of the cathode is suppressed, so that the emission is limited to the plane or nearly plane parts of the cathode surface. In this manner the maximum steepness corresponding with the size of the emitting surface, and a very sharp bend in the characteristic curve are obtained. The main object of the invention can best be accomplished by shielding the emission from the cathode edges or borders, by suitably shaping the cathode itself,

grid( opposite the cathode edges that the field intensity at the cathode edges is greatly reduced or becomes negative in comparison with the field intensity at the remaining cathode surfaces.

The accompanying figures show embodiments of the invention by way of example.

Figures 3 and 4 show front and plan views, respectively, of an embodiment of a triode in which the support rods 4 and 5 of the control grid serve as screens and simultaneously to reduce the field intensity at the cathode edges. The fiat cathode l which is of the indirectly heated type, is fixedly secured in openings of insulating bridges l3 and I 4 by means of extensions 8, 9 and I0, I l at the upper and lower ends of the cathode, respectively. The grid support rods or bars 4 and 5 and the anode supports I5 and I8 are also threaded through suitable openings in the insulating bridges. The grid bars 4 and 5 are wide enough to cover the narrow sides 2, 3 of the cathode; the diameter of the rods and their distance from the narrow sides of the cathode is suitably approximately equal to the inner diameter of the grid.

Figure 5 shows a section through a pentode whose fiat cathode I1 is not covered at the edges 21 and 31 by emitting substance. Only the wide surfaces of the cathode are provided with layers l2 of emitting substance. successively surrounding the cathode are control grid 51, screen grid 62, suppressor grid 63 and anode 11.

Figure 6 shows the section of a triode having a fiat cathode 2| whose electrical field in the direction of its two narrow sides or edges 22 and 23 is extended by means of two auxiliary electrodes 24 and 25. The cathode 2| and the auxiliary electrodes 24 and 25 are maintained at a suitable equal potential and are surrounded by control grid 26 and anode 21.

Figure 7 represents a plan view of a triode having a square-shaped cathode 3i. Adjacent to the four corners 32', 33, 34 and 35 of cathode 3| are the shields 31, 38, 39 and 40 which are connected to and serve to support the control electrode 36 placed between the anode 4| and thecathode.

What we claim is:

An electron discharge tube comprising an elongated indirectly heated, fiat-shaped cathode, substantially rectangular in cross section, a plurality of cooperating electrodes completely surrounding the cathode and having their support rods in alignmentwith the narrower side edges of the cathode, the support rods of the electrode immediately adjacent the cathode being spaced from said cathode edges a distance equal to substantially the diameter of said rods, which diameter is substantially wider than the cathode side edges, whereby to effectively shield the cooperating electrodes from electrons emitted from the

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