US2898501A - Getters for electron tubes - Google Patents

Description

Aug. 4, 1959 B. H. WADIA ETAL 2,898,501

GETTERS FOB ELECTRON TUBES Filed Aug. 13, 1956 INVENTOR.

, BEHRAM H. WADIA BY EUGENE J.. NAILL United. Sta es Pa 0.-."

GETTERS FOR ELECTRON TUBES Behram H. Wadia, Darien, and Eugene J. Naill, New

Canaan, Conn., assignors to Machlett Laboratories, Incorporated, Springdale, Conn., a corporation of Connecticut Application August 13, 1956, Serial No. 603,659 3 Claims. (Cl. 313-174) This invention relates to improvements in high frequency electron discharge devices and has particular reference to novel gettering means for electron tubes.

In the development and manufacture of electron tubes, particularly of the coaxial high frequency type, 1t 1s common practice to provide a cathode structure which embodies a disc-like emitter supported on one end of a tubular foil member of low thermal conductivity and carried by the cathode terminal structure. The present invention is directed to the provision of such a cathode structure wherein gettering means is provided in the form of a second tubular foil member which is mounted within and in spaced relation to the supporting foil member. The getter is also supported by the cathode terminal structure and extends toward the emitter and terminates in closely spaced relation to the emitter whereby 'it is heated by radiation at the proper temperatures in order to perform its gettering function. g

In known prior art types of structures it has been conventional practice to provide a gettering device in the form of a source of gettering material secured to one of the inner or outer surfaces of the supporting foil. One 'of the more common types of getters has been a semi-circular shaped metal device which was usually mounted on the inner walls of the foil. Barium was usually selected for such getters and was provided as a component a thin-walled sheath of a suitable soft metal such as iron on nickel-iron alloy. In operating the tube, the temperature in the area of the getter rose to a point where the barium would vaporize and rupture the sheath and dispose on adjacent parts of the tube to perform its gettering function.

Such devices have not been entirely satisfactory, however, because the temperatures of the cathode structures become greater than optimum temperatures at which barium getters operate efliciently. Another undesirable feature is that after prolonged periods of operation, or short periods of operation at elevated temperatures, deposits of the barium getter material appear on the surface of the parts interiorly of the tube. Such deposits sometimes form loose particles and also sometimes accumulate sufiiciently to provide undesired conductive paths and discolor the inside of the tube structure.

It is desirable to use titanium or the like as the preferred getter material in such tubes. The use, however, of titanium has not been entirely successful because titanium requires a relatively high temperature, at least 500 C. for operation as a getter. This requires that the titanium must be placed close to the parts of the cathode which normally operate at elevated temperatures. Since titanium alloys rather easily with nickel, it has been difficult to position the titanium in any form in direct contact with the parts of the cathode which are formed of nickel and which operate at high temperatures.

It is, accordingly, a primary object of this invention to provide an electron tube with an 'efiiciently functioning getter of titanium or other suitable gettering material.

2,898,501 f V Patented Aug. 4, 1959 Another object is to provide a radiantly heated getter which is individually supported within the cathode structure in close proximity to the parts thereof which operate at relatively high temperatures.

Other objects and advantages of this invention will become apparent from the following description taken'in connection with the accompanying drawings, in which:

. Fig. 1 is a front elevational view partly in axial section of an electron tube embodying a preferred form of the invention; and

Fig. 2 is an enlarged sectional view of the cathode structure of the tube shown in Fig. 1.

Referring more particularly to the drawings, the tube embodying the invention comprises a gas-tight envelope generally designated by numeral 10* and having metal portion 11 at one end connected by a suitable vacuum seal to one end of a glass or similar dielectric bulb portion 12. Within the envelope and supported by portion 11, which functions as a terminal therefor, is an axially disposed anode 13. Concentric with anode 13 is a tubular 1 grid terminal 14 which is sealed throughout one end to the other end of the dielectric portion 12 of the envelope. A tubular grid support 15 is sealed at one end to the inner wall of grid terminal 14 and carries on its other end a grid 16. The grid 16 is maintained in position 1 on a flange formed on the inner end of the support 15 by a retainer 17 and disposed in predetermined spaced relation from the anode 13 and from a cathode structure '18 located coaxially therewith within the grid support 15.

The cathode structure 18 includes a first terminal formed by a pair of coaxial tubular members, an inner member 19 and an outer member 20, which are joined together adjacent the end of the tube and form a portion of the envelope 10. Outer member 20 is flared outwardly at 21 and is sealed by an annular dielectric insulating ring 22 to one end of an annular metal ring 23 which is in turn sealed throughout its opposite peripheral end to the inner surface of the grid support 15.

' The inner tubular member 19 encircles and is sealed to the outer surface of a substantially tubular cathode supporting ring 24. The supporting ring 24 is in turn sealed by an annular insulating member 25 to the inner end of a second tubular terminal 26 which extends coaxially within and in spaced relation to the first cathode terminal 1920.

Theinner end of the cathode supporting ring 24 has secured to it one end of a cathode support member 27 which consists of a tubular foil formed of Kovar or other selected material having relatively low thermal conductivity. The opposite end of the support member 27 is secured throughout its periphery to and supports a disc-like cathode emitter 28 formed of nickel or like material which carries either thereon or therein a material which is capable when heated of emitting a copious supply of electrons. The emitter is connected adjacent its periphery to the support foil 27 and is disposed with its eifective electron emitting surface adjacent and parallel to the grid 16 and in coaxial predetermined spaced relation thereto. i

It is apparent that the terminal 1920 and foil 27 2 form one side of a circuit to the emitter 28. The circuit is completed to the second terminal 26 through a filament'or heater coil 29 which is positioned in close proximity to the emitter 28, preferably within a cup-shaped portion 30 thereof. The heater coil has one end connected by a metal supporting conductor 31 to a metal disc 32 which is sealed throughout its periphery to the inner wall of the second terminal 26 and thus also forms a portion of the envelope 10. The other end of the heater coil 29 is connected by a supporting conductor 33 to the cathode supporting ring 24 and thereby to the first cathode terminal 19-40. Thus, a circuit is completed through both the emitter 28 and the heater coil 29. Upon application of suitable electrical energy to the cathode terminal, the heater 29. will raise. the temperature of, the emitter lit-whereupon a copious supply of electronswill be produced, the electrons flowing totthe anode 13 under control of the grid 16 in thenormal operation of a tube. of this type. t e

In'the conventional manufacture. of electron tubes,v it has been found to be practically impossible 'to. cojnpletely ontgas a tube, that is, remove all the gas from all the elements within the envelope. Therefore, gettering means is required for removing gases that mayappear during operation ofthe tube. a

It is known that the cathode areas of tubes of the presently described type become extremely hotduring operation, usually reaching the vicinityof 800 C. The temperatures'of the parts of the cathode structure 111 the vicinity of the emitter attain the highest levels and are progressively lower toward the terminal end of the structure. Therefore, it is desirable to provide a getter which will operate'satisfactorily at the relatively high temperatures reached by parts of the tube structure as well as throughout the range of operating temperatures of the cathode structure, for example, approximately between 3.00700 C. Material such as titanium, zirconium and tantalum are known to function satisfactorily as gettering materials at such relatively high temperatures and can be readily manufactured in the form of thin foils which, when used in the manner taught herein, extend to some extent into the areas of the cathode which operate at the highest temperatures and also into the cooler areas of the structure. Therefore, the present invention relates to the use of a foil 34 of such gettering material which is mounted within the cathode structure interiorly of the cylinder formed by the supporting foil 27. Getter foil 34 is formed to a tubular shape and has one end secured to the cathode supporting ring 24. In the preferred structure the foil 34 is secured throughout its outer peripheral surface to the inner surface of the cathode supporting ring 24'. The foil 34 extends toward the emitter 28 and terminates in proximity thereto so that it is readily and efficiently radiantly heated by the emitter and adjacent parts of the cathode structure. The foil 34, furthermore, is also spaced slightly from the supporting foil- 27 nd, thus does not become alloyed with the material of the emitter 28 when the foil 27 is spot welded to the emitter. In the manufacture of an electron tube embodying the presently described getter structure, the heater conductor 33 is generally secured to the ring 24 before the getter foil, 34 is welded into place. Therefore, the foil 34. is provided with an elongated notch 35 for receiving the conductor, as shown clearly in Fig. 2.

It will be noted that the foil 34 extends longitudinally of the cathode structure and, because of its length, has

""asasnoi a portion lying within the hottest area of the structure and also has portions lying within cooler areas. In this way the getter is able to perform its gettering function throughout a wide range of temperatures, such as approximately from 300 C. to 800 0., since some portionof the foil willalways be positioned in an area having a temperature at which the gettering occurs most etficiently.

An additional advantage of a structure of this typev is that the getter foil 34 also provides a heat shield for the inner surface of the supporting foil 27, which further improves the overall cathode operation.

It will be apparent from the foregoing description that all of the objects and advantages of this invention have been accomplished by the provision of the novel gettering device described hereinbefore. It is also apparent, however, that one skilled in the art may conceive of changes and modifications which will come within the scope of, this invention. The matter shown and de, scribed herein is, therefore, to be considered as illustrativeand not in a limiting sense.

We claim:

1. A cathode structurefor electron tubes, said structure comprising an annular terminal member, a substantially tubular support having its inner surface at one end encircling and mounted upon the outer surface of one end of the terminal member, a disclike emitter secured to and closing the opposite end of the support, a, heating element within the support and adjacent the inner surface of the emitter, a tubular getter within the support and having its outer surface adjacent one end; secured to the inner surface of the terminal memher, the. getter being, a foil of gettering material extending toward the emitter between the support and heater and terminating relatively close to the emitter.

2., A cathode structure for electron tubes, said structure comprising an annular terminal member, a substantially tubular, supporting foil having its inner surface at. one end encircling and mounted upon the outer surface ofi one end of the terminal member, a disclike emitter secured to and closing the opposite end of the foil, a. heating element within the foil and adjacent the inner surface of the emitter, a tubular getter within the foil and.- having its outer surface adjacent one end secured to the inner surface of the terminal member, the getter being a foil of gettering material extending toward the emitter between the foil and heater and terminating in relatively closely spaced relation to the emitter. 3.: An electron tube embodying an anode and a cathode within a gas-tight. envelope, the cathode comprising a, cathode. terminal extending exteriorly of the envelope and. having an annular inner end, a disclike emitter positioned. in predetermined spaced relation to the anode, and supporting means for the emitter comprising a substantially tubular conductive member having its inner surfaceat oneend. encircling and mounted on the outer surface of the annular end of the cathode terminal and closed at its other end by the emitter, a heating element adjacent the'emitter and within the conductive member, and a tubular foil of gettering material having its outer surface at one end secured to they inner surface of the annular: end of the cathode terminal and extending toward. the emitter in substantially parallel spaced relation to the conductive member, the foil encircling the heating element and terminating, adjacent and closely spaced fromthe emitter.

References Citedin the file of this patent UNITED STATES PATENTS Germany May 4, 1953 2,455,381 Morton et al Dec. 7, 194a 2,716,199 Diemor et a1 Aug. 23, 1955 2,722,624 Doolittle Nov. 1, 1955 2,741,717 Katz Apr. 10, 1956 1 FOREIGN PATENTS

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