US3221201A

US3221201A - Getter assembly for electron tubes

Info

Publication number: US3221201A
Application number: US238680A
Authority: US
Inventors: Free Jerome Joseph; John W Gaylord
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1962-11-19
Filing date: 1962-11-19
Publication date: 1965-11-30
Anticipated expiration: 1982-11-30

Description

Nov. 30, 1965 J. J. FREE ETAL 3,

GETTER ASSEMBLY FOR ELECTRON TUBES Filed Nov. 19. 1962 EAR/0M 2041 (MI/MUM) 4 6f 67 INVENTORS JOHN W- GAYLORD, AND JEROME J. FREE United States Patent 3,221,201 GETTER ASSEMBLY FOR ELECTRON TUBES Jerome Joseph Free and John W. Gaylord, Lancaster, Pa.,

assignors to Radio Corporation of America, a corporation of Delaware Filed Nov. 19, 1962, Ser. No. 238,680 6 Claims. (Cl. 313177) The present invention relates to improved getter assemblies of the type in which a flashable getter is raised to flashing temperature by the passage of electrical current therethrough.

The invention finds particular utility in electron tubes having ceramic-metal parts. The manufacture of tubes of this type usually involves loosely assembling on a jig ceramic and metal parts with the ceramic parts suitably metalized and baking the parts so assembled in an oven having suitable temperature and atmosphere ambient for mutually fixing the parts. Oven baking for fixing the parts has been found desirable because the fixed junctures between the parts formed by the oven heating are characterized by greater freedom from strains than if performed by techniques involving localized heating of the parts.

The parts involved in the assembly and baking operations referred to, include electrode sub-assemblies and envelope parts. The envelope parts employed form an enclosure that is complete except for an exhaust opening and an opening through which a cathode sub-assembly later may be extended and sealedacross by localized heat.

It is found that after the envelope has been initially evacuated through the exhaust opening to a desirably low gas pressure, and the exhaust opening sealed, gases oceluded in the metal and ceramic parts within the envelope are released to an extent that is objectionable in certain applications. While this problem is solved in other tube types by means of getters that chemically combine with the released gases, the use .of getters in tubes of the type under consideration has not been fully satisfactory.

One type of getter that is highly efficient to take up gases released after evacuation of a tube comprises barium suitably sheathed for protection from the atmosphere. The sheath is made of electrically conductive material, such as nickel or aluminum, and may be provided with a relatively thin portion constituting a zone of Weakness. When the sheath is heated, the barium therein provides a pressure sufficiently high to rupture the sheath at its zone of weakness, and to liberate barium in the form of a flash.

Difiiculty has been experienced in using this type of highly eficient getter in ceramic metal tubes of the type discussed. Incorporation of the getter in the tube structure prior to the oven baking thereof has not been found feasible because the temperature employed is high enough to flash the getter prematurely. Subsequent introduction of the getter involves difficulty because the only available openings in the tube envelope after baking are inadequate -for this purpose. For example, the exhaust opening is too small to permit extension of a getter therethrough and a fixing of a getter within the envelope. Furthermore, the opening for receiving the cathode sub-assembly is not suitable for getter introduction. If the getter is introduced through the opening provided for the cathode sub-assembly, prior to extension of this sub-assembly into the envelope, a flashing of the getter will deposit getter material on the adjacent electrodes, which is harmful to their operation. If the getter is mounted within the cathode sub-assembly and introduced into the tube envelope with this sub-assembly, the flash from the getter may be shielded from regions of the interiorof the tube envelope other than that encompassed by the cathode subassembly. This is particularly true in tube types employing the cathode-heater sub-assembly described in co-pending application Serial No. 199,404 filed June 1, 1962, by F. R. Ragland, Jr., and assigned to the same assignee as the present application.

Moreover, in tube types having ceramic-metal envelopes, it is not readily feasible to heat the getter to flashing temperature by exteriorly positioned means for inducing electrical currents in the getter structure nor by directly connecting spaced portions of the getter structure across a suitable electrical current supply.

Accordingly, it is an object of the present invention to provide an improved electron tube.

It is a further object to provide an electron tube having an improved getter assembly.

Another object is to provide an improved getter structure for the use in association with an electron tube having an envelope that is subjected to a brazing operation prior to evacuation, at a temperature higher than the temperature at which the getter flashes.

A further object is to provide a getter structure of the type in which the getter is heated to flashing temperature by electric current losses therein, in association with an electron tube having a ceramic-metal envelope.

Another object is to provide a novel getter-exhausttubulation assembly wherein the exhaust tubulation is spaced from the tube envelope and constitutes an electrical lead to a getter structure.

A further object is to provide an electron tube in which a getter structure is electrically connected across an anode and an exhaust tubulation of the tube for flashing by establishing a suitable potential diiference between the anode and the exhaust tubulation.

In one example of the invention, an electron tube having a ceramic-metal envelope, is provided with an exhaust opening in one end of the envelope. A chamber having walls fixed to the envelope end referred to, and provided with an opening communicating with the exhaust opening, supports an exhaust tubulation in spaced coaxial relation with respect to the exhaust opening. The chamber walls include an insulating member electrically isolating a portion thereof including the exhaust tubulation, from other wall portions including those in engagement with the tube envelope. In the example discussed, the tube envelope portionengaging the aforementioned chamber, comprises an external anode. An elongated getterstructure has one end fixed to the aforementioned wall portions engaging the anode, and the other end fixed to the wall portion that includes the exhaust tubulation. The getter structure includes a metal sheath made of a aluminum or nickel and having a relatively thin zone of weakness therein. Within the sheath is disposed a body or slug of substantially pure barium intermixed with particles of aluminum. When the exhaust tubulation and anode are connected across a suitable electrical power suuply the sheath and barium will become heated by electrical losses therein to a temperature sufficiently high to cause the barium to develop .a pressure within the sheath of such magnitude as to rupture the zone of weakness in the sheath and to result in a flash of barium vapor. The portion of sheath having the zone Weakness is oriented in the chamber in such a way as to direct the barium flash to a region where its electrically conductive character will result in least harm. The resultant barium coating deposited in this region will serve as a continuing take-up agent for gases liberated within the tube. This function is facilitated because of the displacement of the exhaust tube from the exhaust opening in the anode.

Further features and objects of the invention will become evident as the :present description continues.

In the drawing:

FIG. 1 is an elevation, partly in section, of an electron tube and getter assembly incorporating the invention;

FIG. 2 is an exploded elevational view in section showing the sequence in which the parts constituting the structure shown in FIG. 1, are assembled;

FIG. 3 is a longitudinal sectional view of a getter structure employed in the tube shown in FIG. 1; and

FIG. 4 is a sectional view taken along the line 44 of FIG. 3, and shows the zone of weakness in the sheath of the getter structure depicted in FIG. 3.

The electron tube structure shown in FIG. 1 comprises an electron tube having a getter and exhaust tube assem bly 12. The electron tube 10 may be of the tetrode type described in co-pending application Serial No. 182,908 filed March 27, 1962, by J. W. Gaylord, and assigned to the same assignee as the present application. The tube 10 includes a heater 14, a cathode 16, a control grid 18, a screen grid 20, and an external anode 22. These electrodes, with the exception of the heater 14, terminate in downwardly turned flanges comprising anode flange 24, screen grid flange 26, control grid flange 28 and cathode flange 30. These flanges are insulated from each other as shown in the aforementioned Gaylord application, by means of ceramic rings. The upper end of the anode 22 has an exhaust opening 32. The tube 10 may be made and assembled in accordance with the method described in US. Patent 2,980,984 to M. B. Shrader et al. issued April 25, 1961, and assigned to the same assignee as the present application.

The getter and exhaust tube assembly 12 includes a dish-shaped metallic member 34 fixed as by brazing to the outer top wall of the anode 22. Member 34 is provided with an opening 36 communicating with the exhaust opening 32. The member 34 is also provided with an outwardly extending radial flange 38, to which is fixed as by welding, an outwardly extending radial flange 40 of an inverted dish-shaped metallic member 42 having an opening 44 in register with

openings

32 and 36. To the inner surface of member 42 is brazed one metallized surface of a ceramic ring 46 which is in coaxial relation with opening 44. To the other surface of the ceramic ring 46, is brazed a metal eyelet 48 including an outwardly extending flange 50 engaging the ring, and a tubular portion 52. The tubular portion 52 has an inner diameter for snugly receiving an exhaust tubulation 54 in coaxial relation with

openings

32, 36. The exhaust tubulation 54 is suitably fixed to the eyelet 48, as by brazing in a position to provide an appreciable space between the lower end 56 of the tubulation and the dish shaped member 34 This space provides desired communication between interior of the getter chamber defined by the dish-shaped members 34, 42 and the interior of the envelope of tube 10, for a purpose to be described. The exhaust tubulation 54 is pinched off at 58 in a vacuum-type seal.

Within the chamber defined by the dish-shaped members 34, 42 is positioned an elongated getter structure 60 having one end tab 62 fixed as by spot welding to the inner wall of the upper dish-shaped member 42, and another end tab 64 fixed as by spot welding to the eyelet 48. It will be noted that in this arrangement, the elements to which the end tabs of the getter structure are fixed, are in electrically insulated relation. Thus by connecting a suitable electrical potential across the exhaust tubulation 54 and the anode 22, electric will follow through the getter structure 60 for heating it to a flashing temperature.

The getter structure as shown in FIGS. 3 and 4 comprises a sheath 65 having a thinned down portion 66 constituting a zone of weakness. Within the sheath 65 is disposed at body or slug 67 of substantially pure barium mixed with particles of aluminum. This getter structure is so oriented in the space or chamber defined by the dishs'haped members 34, 42 that the flash will occur in a direction where it will be least harmful to tube operation.

Such orientation may include positioning the getter structure 60 in such a way that its relatively thin wall portion 66 (FIGS. 3 and 4) extends downwardly so that the flash will be directed to the lower left-hand corner portion 68 (FIG. 1) of the aforementioned chamber. In this way, the flash will be directed away from the opening 32 to prevent contamination of the electrodes of tube 10. The Zone of weakness in an alternative arrangement, may be positioned to face upwardly. In this position most of the getter flash will impinge upon the lower surface of flange 50 of the eyelet 48. Since there is a likelihood that some portion of the flash will coat the edge of ceramic ring 46 and thereby provide a parallel and more conductive path for electrical energy, than that provided by the getter structure 60, and thereby prevent a complete flash of the getter, it is preferred to mount the getter in such a manner that its zone of weakness 66 faces the lower left hand corner 68 of the chamber defined by members 34, 42, as viewed in FIG. 1.

The barium deposited in the corner region 68 (FIG. 1) will serve a continuing gas absorbing function with respect to gases evolved within the tube 10. This is rendered feasible because of the spaced mounting of the exhaust tubulation 54 from the opening 32, as a consequence of which a free path is provided between the corner portion 68 and the interior of tube 10.

In one example, a getter structure comprising a sheath 65 made of nickel and containing about 0.012 gram of a mixture of pure barium and aluminum was successfully flashed by connecting the anode 22 and exhaust tubulation 54 across a potential source of alternating current at a voltage of about 0.7 volt and a current of about 12 amperes, for 8 seconds. Suitable connections to the anode and exhaust tubulation were effected by means of metal clamps embracing these elements.

In assembling the parts constituting the electron tube shown in FIG. 1 care must be taken to avoid a premature flashing of the getter 60. To this end, the parts comprising the tube 10 and the dish-shaped member 34 are assembled and mutually fixed apart from the sub-assembly 70 (FIG. 2) which includes the getter 60.

The assembling and fixing of the parts of the tube 10 and the dish-shaped member 34 may be effected in accordance with the method described in the aforementioned Patent Number 2,980,984. Thus the control grid 18 and screen grid 20 may be first mutally fixed in imperforate tubular blank form, with an insulating ring disposed between radially extending

flanges

26, 28 thereof. Radial openings are then cut in the tubular portions of the blanks by an erosion technique such as electrical discharge machining. In fixing the two grid blanks to the suitably metalized insulating rings, a relatively high melting point solder should be used, such as commercially available BT solder having a flow point of 780 C. This is because the operation of mutally fixing the two grid blanks and the later operation of fixing the anode 22 and dish-shaped number 34 to the grid assembly, are performed in an oven in order to prevent the development of objectionable strains in the regions of the joints. This multiple-step fixing operation requires that the brazing material or solder initially employed, have a higher melting point than the solder employed in subsequent brazing operations. Otherwise, a later brazing operation would result in a loosening and displacement of the parts previously jigged and brazed.

To reduce the number of later oven operations involving oven heating and thereby permit the final oven operation to be carried out using a solder that has a melting point only slightly lower than that of BT solder, the later operation may involve jigging the grid assembly into coaxial relation to the anode 22, a cathode fixing flange 30, and suitably metallized insulating rings disposed between the previously formed grid assembly and the anode, and between the cathode fixing flange 30 and the grid assembly. The solder used in this final brazing operation may be RTSN solder which is commercially available and has flow point temperature of 720 C.

After the parts have been brazed in accordance with the foregoing, a sub-assembly comprising the cathode 16 and the heater 14 is telescoped into the control grid 18. This sub-assembly has a flange which nests in the cathode flange 30 (FIG. 1) as shown in the aforementioned Patent 2,980,984, when the sub-assembly is in coaxial relation with the control grid 16. The flange of the cathode heater sub-assemblly is fixed to the cathode flange 30 by means of localized heat, such as heliarc welding. This completes the assembling and fixing of parts comprising the tube and the dish-shaped member 34.

The parts comprising the sub-assembly 70 (FIG. 2) with the exception of the getter 60 are then jigged into coaxial relation. BT solder is interposed between the two opposite metalized surfaces of ceramic ring 46 and the surface portions of the cup-shaped member 42 and eyelet flange 50 engaged by the ring 46. BT solder is also interposed between the exhaust tubulation and the eyelet. While so jigged the assembly is brazed in an oven at a temperature of 820 C. Thereafter, the tabs 62, 64 (FIG. 3) of the getter structure 60 are spot-welded across the cup-shaped member 42 and the eyelet 48. This subsequence in assembling the parts of sub-assembly 70 preserves the getter structure 60 from harmful heat.

The final assembling step comprises jigging assembly 70 into coaxial relation with respect to the tube 10 and the dish-shaped member 34 fixed thereto (FIG. 1) to dispose the

flanges

38, 40 of the two dish-shaped members in abutting relation. In this relation the two flanges are mutually fixed by localized heat such as that involved in heliarc welding.

The envelope of the tube structure formed by the aforementioned assembling and fixing operations is evacuated through exhaust tubulation 54 and thereafter the tubulation is sealed in a pressure weld 58 formed without the deliberate application of heat.

After the evacuation of the tube envelope, the getter structure is flashed by connecting a suitable power source across the portion of the exhaust tubulation 54 remaining after sealing, and the anode 22, as described in the foregoing.

We claim:

1. An electron tube comprising:

(a) an envelope having electrodes therein, said envelope having an exhaust opening in a wall thereof,

(b) a chamber fixed to an outer surface of said wall and having an opening communicating with said exhaust opening,

(c) an exhaust tubulation supported in said chamber in coaxial relation with said exhaust opening and having a free end portion extending into said chamber,

(d) and a getter structure supported in said chamber.

2. An electron tube comprising:

(a) an envelope having an exhaust opening therein,

(b) a chamber having a metal wall mounted upon an outside surface of said envelope, said chamber having an opening communicating with said exhaust opening,

(0) metallic means supported in said chamber and insulatingly extending through said wall for mechanically evacuating the interior of said envelope and chamber,

((1) and an elgonated getter positioned in said chamber to direct a flash of gettering material away from said exhaust opening, one end of said getter being fixed to said means and the other end being fixed to said metal wall.

3. An electron tube having:

(a) a first envelope,

(b) electrodes supported in said first envelope,

(c) a second envelope joined to said first envelope,

(d) said first and second envelopes having registering openings,

(e) said second envelope including two metallic wall portions electrically insulated from each other,

(f) and a getter in said second envelope connected across said portions, whereby said getter may be flashed by impressing a predetermined voltage difference on said two portions, said getter comprising a material including barium and aluminum and having a structure for directing the flashed barium to a region within said second envelope remote from said openings.

4. An electron tube having:

(a) an envelope having metallic walls,

(b) a partition wall within said envelope forming two chambers, said wall having an opening providing communication between said chambers,

(c) a plurality of electrodes in one of said chambers,

((1) structure including a metallic exhaust tubulation insulatingly supported in the other of said chambers, said exhaust tubulation being spaced from said opening, said other of said chambers having one of said metallic Walls,

(e) and an elongated flashable getter structure having one end fixed to said exhaust tubulation structure and the other end fixed to said one of said metallic Walls of said other of said chambers electrically insulated from said exhaust tubulation structure.

5. An electron tube having:

(a) an envelope forming two compartments having a common wall,

(b) said Wall having a relatively small opening therein,

(0) one of'said compartments being defined by two metal wall portions,

(d) an insulating member interposed between said wall portions,

(e) a flashable getter structure connected across said wall portions,

(f) an exhaust tubulation mounted on one of said wall portions and having a free end in closely spaced relation with respect to said opening, the other of the said wall portions comprising a portion of said wall,

(g) and a plurality of electrodes positioned in the other of said compartments.

6. An electron tube having:

(a) an envelope forming two compartments having a common wall,

(b) said wall having a relatively small opening therein,

(c) one of said compartments being defined by two spaced metallic wall portions,

(d) an insulating member interposed between said wall portions,

(e) a flashable getter structure connected across said wall portions,

(f) an exhaust tubulation mounted on one of said wall portions and having a free end in closely spaced relation with respect to said opening and another end extending outside of said envelope,

(g) and a plurality of electrodes positioned in the other of said compartments,

(b) said getter structure being positioned to direct a getter flash to a region remote from said opening, whereby said electrodes are free from contamination by flashed getter material.

References Cited by the Examiner UNITED STATES PATENTS GEORGE N. WESTBY, Primary Examiner.

Claims

1. AN ELECTRON TUBE COMPRISING: (A) AN ENVELOPE HAVING ELECTRODES THEREIN, SAID ENVELOPE HAVING AN EXHAUST OPENING IN A WALL THEREOF, (B) A CHAMBER FIXED TO AN OUTER SURFACE OF SAID WALL AND HAVING AN OPENING COMMUNICATING WITH SAID EXHAUST OPENING, (C) AN EXHAUST TUBULATION SUPPORTED IN SAID CHAMBER IN COAXIAL RELATION WITH SAID EXHAUST OPENING AND HAVING A FREE END PORTION EXTENDING INTO SAID CHAMBER, (D) AND A GETTER STRUCTURE SUPPORTED IN SAID CHAMBER.