US1974448A - Indirectly heated cathode and insulator assembly - Google Patents

Description

Patented Sept. 25, 1934 UNITED STATES INDIRECTLY HEATED CATHODE AND INSULATOR ASSEIWBLY Henry L. Crowley, West Orange, N. J., assigner to Henry L. Crowley vz Co., Inc., West Orange, N, J., a corporation of New Jersey Applicationnpril 5, 1930, serial No. 441,744

6 Claims.

This invention relates to a cathode assembly, especially as is employed in thermionic vacuum tubes, electron discharge devices, audions, etc.

The object of the invention is to provide a cathlode structure and insulator assembly which is economical in manufacture and easy to assemble.

A further object of the invention is to provide an assembly of this-nature which is highly eicient in operation.

A further object of the invention is to provide an assembly of this nature which is not only novel in itself, but utilizes novel structure of filaments and insulators.

Further objects of the invention will appear Imore 'fully hereinafter. The invention consists substantially in the construction, combination and relative arrangement of parts, all as will be more fully hereinafter set forth and finally pointed out in the appended claims.

Referring to the drawing:

Figure 1 is a top plan View in horizontal section of a cathode and insulator assembly;

Fig. 2 is a sectional View taken on the line 2-2 of Fig. l and looking in the direction of the arrows.

Similar reference characters refer to similar parts throughout the several views of the drawing. 1

In the art of thermionic vacuum tubes employed in electrical communications and allied arts, notably in radio sets, it is customary to use so-called indirectly heated cathodes, especially where alternating current from lighting mains are utilized for vitalizingthe tubes in use. In essence, these structures comprise a resistor element adapted to be heated by a passage of current therethrough, which is usually in the form of a filament similar to a lament employed in an incandescent lamp or the filament employed in the standard audion constructions. The heat from the filament is utijlized to render active an electron emissive element usually employed as a shield surrounding, or otherwise intimately associated with the filament, so that the heat from the filament may be most efficiently utilized. One great defect in the in- .directly heated cathode tubes heretofore used has been Well recognized to be the length of time consumed between the switching on of the current to the filament and the necessary electronic activity of the element heated thereby, in order to render lthe tube operative. So Well recognized has been this disadvantage in indirectly heated tubes that intensive research has been conducted in the Vacuum tube industry and concentrated effort been made to minimize the required time.

The problem has been diflicult of solution due (Cl. Z50-27.5)

to a number of extraneous causes.` In the first place, it has been necessary to employ carefully designed and produced insulators for the heating element. The constructions for elimination of microphonie noises due to relative thermal ex-y pension between the nlament and insulator, the cost of the insulator, the strength and rigidity thereof, have materially added to the difnculties of a practical solution of the problem of minimizing the length of time between the turning on of current to the Vacuum tube and the time that it actually functions for its intended purpose. Different types of hairpin filament have been employed and are universally employed at the present time, and to prevent electric contact between one leg of the filament and the other leg thereof, as well as the necessity of avoiding short-circuiting, it has been necessary to completely insulate the respective legs ofthe filament 'from each other, as Well as from the electronic emissive element.

Having in mind that the two important factors in -minimizing the inactive period of the vacuum tube comprises the lamount of heat available and the directness of radiation from the heat source to the element to be heated, I have created an assembly of novel construction in itself, as well as of the important parts thereof, which has solved the problem and enabled the provision of an indirectly heated cathode tube structure of maximum efciency-'a'nd minimum inactivity.

' Referring to the drawing, where I have shown in exceedingly enlarged size the assemblyr and parts comprising my invention,referencecharacter l designates what is usually" known V:in the art as the shield and which contains, either as a constituent or as a surface layer, the electron emissive material. While I have shown the shield in the form of a cylinder, it is to be understood that I do not desire to be limited or restricted in this respect, as its particular shape or type forms no part of my invention. The insulator is illustrated at 2 and is in the form of what may be termed a double anchor, viz., it has a central portion 3 at each end of which are provided arms 4 and 5 extending therefrom. This insulator may be formed of any suitable material commonly employed for such purpose and may be of any desired length, depending upon the dimensional requirements of the completed vacuum tube structure as dictated by the filament, power, size, etc. The insulator 2 is shaped so as to be positioned within the shield 1, and its position may be Varied as conditions permit or may be desired. While I have shown the insulator as out of contact with the shield 1, I do not desire to be limited in this respect as it may be positioned in contact with shield 1 or spaced therefrom evenly or unliability of breakage materiallyreduced; j I t will be understood, of course, in the form illustrated,

that the lament is of the hairpin type, i. e., is formed of one piece, looped at the uppere'nd The legs 6 and '7 projecting on opposite sidesV of the ends of the central portion 3 of the insulator 2` may be of any desired shape and may extendany desired distance. The importantA factor is that a substantial space is provided between adjacent ends of the respective legs so that the heat radiated from thelegs and 7 of the lilament will directly impinge onthe inner surface 0f the shield 1. Thus, direct heat radiation is secured from a-heating surface extremely large as compared tothe hairpin filament heretofore employed. 1

.From the foregoing, it will be seen that both factors, viz., increased heat source and effective direct heating radiation, are present in the struc-v ture and assembly of my invention and inactivity,

due to insufficient heating of the emissive elementafter supply of curr-ent is effected, is minimized, f n i Many modifications and changes indetails'and construction will readily occur to those skilled in the art-without departing from the spirit and scope of my invention as defined in the claims, but having now'set forth the nature of my invention and having shown and described a structure embodyingY theprinciples thereof, what I claim as new and useful and desire to secure by Letters Patent is: I

`1. The combination with an insulating member formed of one piece and open on opposite sides,V

a ribbon conductor for producing heat and provided with a leg extending longitudinally on each sideof said insulator and opposite the said open sides, and an electron emitting member surrounding said conductor to be heated by direct-heat radiation from said conductor through the open L sides ,of said insulator.

2. A unitary insulator member Vshaped in cross section substantially like a double anchor with a central connecting portion and open sides on each side thereof, a at ribbon shaped conductor with a leg positioned on each side of the central por- A tion of said insulator and opposite the open sides thereof to permit unobstructed radiation of heat from said conductor therethrough, and an electron emitting member surrounding said insulatOrand adapted to be heated in part at least by vdirect radiation of heat from said conductor through the opensides of said insulator.

3.' -A vcathode for electron discharge devices comprising a longitudinal rib of insulation, a pair` of transversev ribs attached to the longitudinal edges o f said rib said transverse members be- -ingsubstantially cylindrical in shape and having their-longitudinaliedges spaced apart, a metallic sleeve, embracing said curved transverse members, a coating of emissive material on the face of said sleeve, and means within saidV sleeve for heating the same.Y Y

4. The combination with an electrical vconduc-lA tor for creating'V heat having two substantially parallel ribbon legs, means for velectrically insu,-l lating said legs from each Votherat adjacent sidesthroughout their length, and anl electron emitting member surrounding said'heating,member` and directly exposed thereto so` asto be heated by direct-,radiation from said heating member-` 5. Anelectron discharge device comprising` an anode and a cathode, said cathode includinganf` element having a surface adapted to emit-elec,-V

trons when heated, an insulator within-said element having av plurality of ,relatively wide and shallow undercut slots onthe sides ofsaid insulator and a resistance element held inL position` in said undercut portions. Y A y 6. A cathode for electron discharge devices comprising a longitudinalrib of insulation, a pair oftransverse` ribs attachedqto the longitudinal edges of said rib, said transverse members being,-

substantially cylindrical in shape and having their longitudinal edges ,spaced apart, a metallic sleeve embracing said curved transverse members, a coating of emissive material on the face of said sleeve, and means within said sleeve for heating the samesaid heating meansv being Yin the form of a looped filament having lportions extending longitudinally on opposite sides ofsaid rib, and

in registry with the Vspaced ends of said transverse members. u f i HENRY L.y CROWLEY.

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