US1951216A - Cathode for electric discharge devices - Google Patents

Description

March 13, 1934. H, SIMON CATHODE FOR ELECTRIC DISCHARGE DEVICES Filed Aug. 12, 1931 Inventor. Hellrnut Simon,

by 1 His Attorney.

Patented Mar. 13, 1934 STAT Z 1 S PATE T OFFICE CATHODE FOR ELECTRIC DISCHARGE DEVICES Hellrnut Simon,

Berlin-Charlottenburg,

Ger-

many, assignor to General Electric Company, a corporation of New York Application August 12, 1931, Serial No. 556,709 In Germany August 25, 1930 6 Claims.

. The present invention relates to cathodes for electric discharge devices and more particularly to cathodes designed to carry large current at relatively low voltage.

Heavy current cathodes of large power tubes are sometimes constituted of metallic strips having a serpentine, looped or spiral configuration and presented edgewise to the anode. These shapes are desirable in order to obtain large cathode surfaces in relatively small spaces and to minimize radiation of heat. It is found in practice that when cathodes of this character are heated, the folds or convolutions, upon expansion, sometimes tend to distort in shape and change the relative position of the various portions of the cathode with respect to one another, which causes deleterious operating effects.

An object of the present invention is to pro- :vide an improved arrangement for holding a cathode structure of the type referred to rigidly in shape under heated and unheated conditions. This object is attained in brief by bracing the various parts of the cathode with tie wires constituted of refractory material, also of high mechanical strength and high resistance, so as not to cause excessive current loss. The invention will be better understood when reference is made to the following description and accompanying drawing in which Fig. 1 represents a View in perspective of the improved cathode; Figs. and 3 show modified structures, and Fig. 4 is cross-section taken on line 4-4 of Fig. 3.

Referring to Fig. l, numeral 1 designates a strip form of cathode constituted of a number of parallelly aligned portions folded or bent back on one another and terminating in loops 2. The cathode may be fabricated of any suitable metal, for example, nickel, and, if desired, coated with an electronically active material in any well known and suitable manner. The loops 2 grip metal uprights 3 which are bent at the top to form horizontal members i extending in opposite directions, as shown. The members 4 are tied rigidly together by means of one or more wires 5 pulled or stretched sufficiently tight so as to cause horizontal members 4 to rest against the vertical surfaces of the two outer portions of the cathode.

The wires 5 are preferably made of a tough, high refractory metal, such as tungsten, in order that sufficient tension may be applied under heated conditions without breakage. The wires are also of small gauge and of high resistance in order to introduce sufficient resistance to the current which flows in parallel to the current through the cathode proper. There are metals, including the nickel referred to, out of which the cathode can advantageously be made,

which produce ample electron emission at low temperatures so that suitable materials, such as iii) tungsten are abundantly available for the bracing wires which have sufficient and dependable strength at the operating temperature of the cathode.

It is evident that the is such as to preclude cathode as a whole, or

structural arrangement any movement of the the individual portions thereof, in a direction normal to the length of each convolution because the distance between the support members 4 is rigidly fixed by the As the cathode is heated, the resulting wires 5.

expansion is taken up by a lengthening of the individual convolutions along their greatest dimension and to some extent by a change in the distance between the juxtaposed portions of the However, the general shape of strip material.

the electron emission surface remains substantially the same after heating as before and the electrical characteristics of the tube in which such a cathode is used remain constant under 80 variable operating conditions. It is evident that the wires 5 also impart considerable mechanical strength to the cathode as a whole, and if de sired, may be secured in any suitable manner as by welding, to intermediate portions thereof in order to provide additional support. The uprights 3 may be extended through the of the tube in order to support the cathode metal press Withtrons are emanated from both sides of the strip,

thereby to provide a tube of very low impedance in the current-carrying direction.

In Fig. 2 the arrangement is somewhat similar to that shown and described in connection with Fig. 1, except that the uprights 3 terminate in vertical portions and lack the horizontal bers 4. and supported between the two outermost The wires 5 in this case are stretched memedges of the cathode and, as in the case of Fig. 1, may be welded or otherwise secured to intermediate portions of the cathode, if desired.

Figs. 3 and i show an arrangement particularly suitable for heavy and long cathode strips. In this arrangement, the individual lengths of the strip are braced between two or more oppositely extending diagonal wires 5, which present a strong lateral supporting network.

These braces conveniently may be formed from a continuous length of wire, wound tightly and bent over the diagonally adjacent edges of the strip portions. are shown as metal members of rectangular cross-section which are rigidly secured as by weldingQto the face of the outermost convolutions of the strip. It is apparent in this embodiment, that the wires 5 are bent sharply about the edges of the strip so that it is not necessary to weld the wires to the edges, as in the case of the two preceding figures, altho the welds may be employed, if desired. It is also evident that more than one brace wire may be employed in any of the embodiments and if desired, such wires may start and terminate at both edges of'the strips. Thus in Fig. 2, there are shown two pairs of wires, one pair lying along the upper edge of thestrip cathode and the other pair secured to the lower edge thereof. In Figs. 3 and 4, one pair of support wires starts at the upper'edge of one of the outermost portions of the cathode and terminates at the upper edge of the. other outermost portion, while a second pair of support wires starts at the lower edge of one of said portions and terminates at the lower edge of the other of said portions.

While I have described my invention in connection with a serpentine or looped form of cathode, it is to be understood that the bracing wires may advantageously be used with cathodes of all configurations where two or more portions of a strip are in juxtaposed relation. Thus, the invention has application to the spiral as well as to the helical type of cathode, in which the bracing or support wire may be secured in any suitable manner to one or more pairs of the con volutions.

What I claim as new and desire to secure by Letters Patent of the United States, is: 1. A cathode for an electron discharge device comprising a metallic strip member bent back on itself to constitute a plurality of juxtaposed portions and means for holding said portions rigidly in place whereby the cathode as a whole is precluded from distortion during operation and manufacture, said means comprising a wire stretched between the extreme end portions of the cathode.

2. A cathode for an electron discharge device comprising a metallic strip member bent back on The vertical uprights 6 in this figure I itself to constitute a plurality of juxtaposed poitions, and means for holding said portions rigidly in place whereby the cathode as a whole is precluded from distortion during operation and manufacture, said means comprising a wire stretched between the extreme end portions of the cathode and secured to intermediate portions thereof.

3. A cathode for an electron discharge device comprising a metallic strip member bent back on itself to constitute a plurality of juxtaposed portions adapted to emit electrons, a pair of rigidsupport rods, the extreme end portions of the cathode being provided with loops which embrace the rods, and means, comprising a wire stretched between said rods, for rigidly .holding said juxtaposed portions in place.

4. A cathode for an electron discharge device comprisingia metallic strip member bent back on itself to constitute a plurality of juxtaposed portions adapted to emit electrons, a pair of rigid support rods, the extreme end portions of the cathode beingprovided with loops which embrace the rods, and means, comprising a Wire stretched between said rods, for rigidly holding said juxtaposed portions in place, said means comprising a wire stretched between diagonally opposite edges of the respective portions.

5. A cathode for an electron discharge device comprising a metallic strip member constituted of a plurality of convolutions in juxtaposed fiatwise relation, and means for holding said convolutions rigidly in place whereby the cathode as a whole is precluded from distortion during operation and manufacture, said means comprising an elongated member of refractory metal and of relatively high resistance secured to all of said ccnvolutions.

6. A cathodefor an electron discharge device comprising a nickel strip member constituted of a plurality of convolutions in juxtaposed fiatwise relation, said member being coated with an electronically active material, and means for holding the convolutions rigid with respect to one another whereby the cathode as a whole is precluded from distortion during operation and manufacture, said means comprising a tungsten wire'oi relatively small gauge secured to all of said ccnvolutions.

HELLMUT SIMON.

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