US3504213A - Nonemissive carbide elements for grids for power tubes - Google Patents

Description

P. HlX ET AL March 31, 1970 NONEMISSIVE CARBIDE ELEMENTS FOR GRIDS FOR POWER TUBES Filed Jan. 16, 1967 Fly. 1

O INVENTORS /e7r 7992; .7871' fc me/dek BY Wan/Q United States Patent NONEMISSIVE CARBIDE ELEMENTS FOR GRIDS FOR POWER TUBES Petr Hix and Petr Schneider, Prague, Czechoslovakia, assignors to Tesla narodni podnik, Prague, Czechoslovakia Filed Jan. 16, 1967, Ser. No. 609,649 Claims priority, application Czechoslovakia, Aug. 17, 1966, 5,403/66 Int. Cl. H01j 43/04 US. Cl. 313-106 6 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a grid for power tubes, more particularly for short-wave operation.

It is a general object of this invention to eliminate thermal grid emission of tubes of the above mentioned type because this emission is a source of serious difficulties in the design and operation of such tubes.

Though the causes of thermal emission from grids of power tubes are already sufficiently known, they could not yet be efiiciently eliminated. So far, no metal or alloy has been found which would not emit electrons at the grid temperatures of power tubes in short-wave operation due to the vicinity of a heated cathode or due to grid dissipation.

Various methods of treating the surfaces of such grids have already been proposed with a view towards elimination of thermal emission. Under practical operational conditions, however, none of the proposed methods could completely eliminate thermal emission from the grid. The only result achieved was a certain reduction of this emission. Suitable for this purpose are coating materials which bind the material evaporated from the cathode during operation of the tube and deposited on all parts of the tube, and therefore also on the grid. Such coating materials reduce the emission from the grid and increase its loading capacity.

The higher the operating frequency of the tube, the more difiicult becomes the problem of the loading capacity of the grid. This problem could be solved by employing a material with good electric conductivity and a high work function which could withstand a relatively high temperature and which is dark so that it radiates heat well. This material should also combine with the material evaporated from the cathode at temperatures occurring in the tube during operation.

These properties can be found in graphite. Practical test proved that a graphite grid can withstand a 3 to 5 times higher power dissipation in comparison with a metal grid of the same dimensions. Graphite can also withstand without difiiculties a relatively high temperature at which metal evaporated from the cathode is deposited on such a grid only to a small extent and is chemically bound to the grid. But pure graphite is not suitable for the production of tube grids because of manufacturing difficulties.

In accordance with the invention, graphite is combined with other materials having similar properties as graphite to strengthen the grid construction. It is of primary importance to increase the strength of the various active elements of which the grid is made up.

The invention also relates to the form of the active elements or members of the grid, and means for holding these active members in their position in the grid structure to achieve a cage-type grid.

This invention is characterized by the feature that its active portion consists of individual members consisting of a non-metallic material with electric and thermal conductivity.

A suitable non-metallic material for use in the invention is a carbide of a metal of the Group IV, Vb 0r VIb of the periodic system of elements with carbon bound in the carbide and an excess of graphite not bound therein. This excess lies between 0.3 and 40% of the weight of the carbon bound in the carbide. Particularly suitable are carbides of molybdenum or tungsten.

In accordance with the invention the active portion of the grid consists of members made from the mentioned non-metallic material, for example in the form of rods of circular or rectangular cross-section elongated parallel to the axis of the cathode and circumferentially spaced about the same. If the rods are of rectangular cross-section, the narrower side faces the cathode. A tubular grid body is created in both cases.

The carrier system of the non-active portion is made in any known manner.

The above and other features will be best understood with the following specification to be read in conjunction with the accompanying drawing which illustrates preferred embodiments. In the drawing:

FIG. 1 shows a grid of the invention for an otherwise conventional power tube, not shown; and FIG. 2 shows a modified grid both figures being fragmentary perspective views.

Twelve cylindrical rod 1 in FIG. 1 form a cylindrical grid surrounding a non-illustrated cathode and interposed between the cathode and a non-illustrated anode. These rods are conductively connected in parallel alignment and in spaced circumferential relationship between two, coaxial, circularly annular holders 2, 3 of metal, metallized ceramic, or carbon containing material, having a rectangular cross-section. The spacing of the rods 1 is selected in accordance with the required .grid transparency of the tube, not otherwise shown. If a small transparency is required, rods 5 shown in FIG. 2. and having a rectangular cross-section may be used, and their smaller side faces the cathode in the axis of the tube. The individual rods are soldered together with suitably profiled metal sleeves. The grid surface subjected to bombardment by electrons is smaller than in the grid of FIG. 1, but the total radiating surface of the grid is substantially increased.

The grid may be assembled, for example, in the following manner: One end of each rod 1 is covered with rhodium, gold or nickel by galvanic deposition. The metallized rods are then inserted first in blind openings or a groove of one of the holders 2, 3. The distance between the openings determines the density of the grid. The assembled holder and rods 1 are heated in a vacuum or hydrogen oven until the metallized ends of the rods 1 are soldered to the metal of the holder. Then the free second ends of the rods 1 are also provided with a metal layer and are soldered to the second holder. The grid may of course also be completed by a single soldering step.

In comparison with metallic grids, the non-metallic grids have the advantage that the admissible grid dissipation is at least three times larger.

What we claim is:

1. A grid for an electron tube, comprising:

(a) a portion formed of a plurality of spaced elements,

said elements being conductively connected with each other,

(1) each of said elements consisting throughout of a carbide of a metal from Group IVb, Vb, or

VIb of the periodic system, and graphite, said carbide having its carbon bound therein, and said graphite being unbound or free in the body of said carbide,

(2) the Weight of said unbound graphite being between 0.3 and 40% of the carbon bound in said carbide.

2. In a tube as set forth in claim 1, said elements being rods elongated in a common direction and spaced from each other transversely of said direction. Y

3. In a tube as set forth in claim 2, said rods being of circular cross section.

4. In a tube as set forth in claim 2, said rods being of rectangular cross section. one ofthe narrow longitudinal faces of each rod being directed toward said cathode.

5. In a. tube as set forth in claim 2, an annular conductor member, said rods having respective longitudinal end portions conductively engaging said conductor member in circumferentially spaced relationship for connecting said elements.

in claim 1, said metal being tungsten or molybdenum.

References Cited UNITED STATES PATENTS Holdaway, et a1. 313-107 Becker 313-107 X Williams 313-107 X Holst 313-107 X Wei 313-107 Peri 313-107 X Thomson 313-107 Widell 313-107 X Kern 313-107 X Wooten 313-107 X Holst 313-107 X Schonhuber et al. 313-348 X JOHN W. HUCKERT, Primary Examiner A. .1. JAMES, Assistant Examiner U.S. c1. X.R. 313-107, 311, 348, 350, 355

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