US2428610A

US2428610A - Method and apparatus for manufacturing electric discharge devices

Info

Publication number: US2428610A
Application number: US501791A
Authority: US
Inventors: James E Beggs
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1943-09-10
Filing date: 1943-09-10
Publication date: 1947-10-07
Anticipated expiration: 1964-10-07

Description

Oct. 7, 1947. J. E. BEGGS #3180!) AND APPARATUS FOR muFACTURING ELECTRIC DISCHARGE DEVICES Filed Sept. 10, 1943 I i I E x-- I Q -42 :y-J/ I 3 'f 1 y I w Ill v n 11 a 0 S 01 a .9 A if a 78 7 62 9 S M v u .57 E a f A/ z I I): 71 2 7 7 92 a Qacuun i PUMP -70 z a 74'" Inventor:

James EBeg s, bg W;

is ttorneg.

Patented Oct. 1, 1947 2,428,610

METHOD AND APPARATUS FOR MANUFAC- TUBING ELECTRIC DISCHARGE DEVICES James E. Beggs, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application September 10, 1943, Serial No. 501,791

34 Claims. (Cl. 316-32) 1 My invention relates to electric discharge devices and, in particular, to methods and apparatus for manufacturing such devices.

It is an object of my invention to provide a new and improved method for manufacturing an 5 the position of an electrode of the device. To electric discharge device. insure that the device will operat with desired It is another object 01' my invention to provide electrical characteristics the output currents of a new and improved apparatus for manufacturthe device are utilized to measure the spacing of ing electric discharge devices. the electrode whose position is being adjusted. I; is a further object of my invention to pro- Means are also provided to seal hermetically the vide a new and improved method of manufacturelectrode to be adjusted in an approximate opering electric discharge devices in which the charating position, which means includes a molten acteristics ofthe devices are established during metallic seal. A final gas pressure within the the period while the devices are being evacuated. sealed device is obtained while the device is being It is still another object of my invention to proevacuated and after the molten metallic seal has vide a new and improved method of controlling been formed. the physical spacing of the electrodes of an elec- For a better understanding of my invention, tric discharge device. reference may be had to the following descrip- It is a still further object of my invention to tion taken in connection with the accompanying provide a new and improved apparatus for addrawing and its scope will be pointed out in the justing the electrical characteristic of an elecappended claims. Fig. l of the drawing is an 'tric discharge device during the manufacture of elevational view of a section of apparatus for that device. manufacturing an electric discharge device in It is another object of my invention to provide accordance with my invention; and Fig. 2 illusa new and improved method for manufacturing trates an alternative electric circuit which may an electric discharge device in which, during the be employed with the apparatus of Fig. l. manufacture thereof, the electrical characteris- In Fig. 1 of the drawing, my invention is there tics of the device are established under normal shown as embodied in apparatus comprising an operating conditions. electric discharge device I to be exhausted and A further object of my invention is to provide hermetically sealed, an enclosed chamber 2 which zproved method of sealing an eleois evacuated by means of a vacuum pump 3, and device. apparatus t for adjusting the position of the object of my invention is to procathode of the electric discharge device i during proved apparatus for controlling the the period that the device is being exhausted. physical s icing of the electrodes in an electric 35. The discharge device i is described and claimed. in discharge a. my copending application, Serial No. 561,790, filed Another 0?),JGE of my invention is to provide September it, 1 and assigned to the assi ne improved method and apparatus for evacuating of this application. an electric discharge device. Electric discharge device i comprises a cylin- Briefry stated, in accordance with one aspect 40 drical anode it, a composite cylindrical cathode of my invention, I provide new and improved tructure it, and may vin a pair of control methods and apparatus for constructing an elecelectrodes or grids l2, l3. Concentrically surtrie discharge device in which, while the device is rounding the cylindrical anode ill is a metallic- Supported n a v cu ted chamber, the electrlsleeve having inwardly and outwardly directed cal characteristics of the device are adjusted unflanges at its opposite ends. Hermetically sealed der normal operating conditions and while the between the anode i0 and the inwardly directed device is hermetically but not mechanically flange of sleeve ll at a point spaced longitudinally sealed, Alternatively, in accordance with anfrom the electron receiving surface of the anode other aspect of my invention, physical spacing of is a 'disk l5 constituted of a material having a any desired pair of electrodes of the device may thermal coeilicient of expansion substantially be adjusted precisely while the device is being evacuated, at operating temperatures, and after the device has been hermetically sealed, but before all joints are made mechanically rigid. The final sealing of the electric discharge device is accomplished within an evacuated chamber and means are provided external of the chamber for supplying operating potentials to the electrodes of the device and for making final adjustment of equal to that of the metallic members to which it is connected and also, preferably, having a low dielectric loss at high frequencies. Concentrically surrounding the composite cathode structure H is a hollow metal cylinder ll. A metal centrically aligned with the' hollow cylinder I1 and the inwardly directed flange of sleeve I8- ishermetically sealed to the hollow cylinder I! at a. pointnear its upper end by means of a glass disk--|9, similar to previously described disk l5. The grids l2 and 3 are conductively connected to and supported by a pair of metal rings or washers 20, 2| which are located between the outwardly directed flanges or the sleeves l4, I8, being insulated from each other by means of a ring 22 of suitable insulating material. The joint between the sleeves l4, I8 and the rings 20, 2| is hermetically sealed by means of a circular bead 24 of glass, constituted similar to the glass used for the disks l5, l9.

The composite cathode structure U is described and claimed in my copending application S. N, 522,097, filed February 2, 1944, and assi ned to the assignee of the present invention. The structure comprises a hollow' metal tube 25, inwardly flanged at its upper end, and a tubular conductive member 26 of a thin metal foil, such as iernico, across the upper endof which is welded an emissive disk 21 constituted of a suitable electron emitting material, such as nickel coated with barium and strontium carbonates. A heating element or filament 28, disposed below the disk 21, has one of its terminals connected to the metal tube 25 and its other terminal conductively connected to and supported by a substantially rigid conductor 29 which passes through a glass disk 30 hermetically sealed across the lower end of tube 25. Surrounding the filament 28 is an eyelet or heat conducting member 3| welded to and supported from the flange portion of the fernico foil 26 and disk 21. In this composite structure, the fernico foil 26, Welded to the upper flange of tube 25, serves thermally to isolate, the emissive disk 27 from metal tube 25. The eyelet 3|, constituted of a suitable heat conducting material such as nickel, serves to conduct to disk 21 any heat radiating outwardly from filament 28. Supported by and conductively connected to another substantially rigid conductor 33 sealed to the glass disk 38 is a getter 34 of suitable material. This getter is conductively connected at its opposite end to the conductor 29.

The evacuated chamber 2 comprises a removable envelope or bell jar 36 of glass or metal seated on a rubber member 31 vulcanized or otherwise bonded to the upper surface 38 of a table of suitable material, such as steel or aluminum. The table has a, second metal plate or surface '48 spaced vertically below the surface 38 and connected therewith by means of an end wall 4| to define a duct for exhausting or evacuating the chamber defined by the bell jar 36..

This duct is connected by. means of a valve 42 to a large exhaust chamber or reservoir 43, which is evacuated by the vacuum pump 3, and serves as means rapidly to exhaust the bell jar 36, when the latter is connected to the exhaust chamber 43 by operation of the valve 42. Instead of being formed as a separate chamber, the reservoir 43 may comprise an extension pipe or conduit system.

The upper plate or surface 38 has an opening 45 centrally located below the bell jar 36. A plurality of vertical rods 46 secured to the upper surface 38 of the table serve to support a disk 41 of suitable insulating material to which is attached a plurality of spring clamps 48 for engaging the upper metal sleeve 4 of the electric discharge device I. Disk-4'! also carries a second set of metal spring clamps 49 for engaging the lower metallic sleeve |8 of the discharge device. These clamps 48, 49 thusserve to support in a vertical position the upper portion of the electric discharge device comprising anode l0, metallic sleeves l8, l4, the grids I2, l3 sealed therebetween, and the lower metal tube H.

The composite cathode structure U is supported within the sleeve I! by means of the substantially rigid conductors 29, 33 clamped respectively to a pair of vertical rods 5|, 52 by means of spring clamps 53, 54. At their lower ends, the rods 5|, 52 are secured to a disk 55 of a suitable insulating material. An opening 58 in the lower wall 46 of the exhaust duct is sealed by means of a circular rubber gasket 51. At its perimeter, asket 51 has a circular bead 58 which fits into corresponding grooves 59, 60 located, respectively, in the lower wall and a metallic clamping ring 6| secured to this lower wall by any suitable means, such as screws (not shown). When the ring 6| is attached to the lower wall 40, the bead 58 is clamped in the grooves 59, 60 to prevent the rubber gasket 51 from being removed from the seat thus formed. The gasket 51 has a relatively thick central portion 62 connected to the bead 58 by means of a thin flexible section 63.

A metal plate 64 lies over the upper p i n f central section 62 of the gasket and another metal plate 65 is located below this central section of the gasket. These metal plates are clamped to this central portion of the gasket by means of a metallic rod 66 having a shoulder 61 engaging the lower surface of plate 65 and extending through aligned holes in plate 65, gasket 51, upper plate 64, and insulating disk 55. The upper plate 64 is spaced from the disk 55 by means of a metal collar 68. A nut 69 engaging threads at the upper end of rod 66, serves to clamp together the members 55, 64, 65. By this structure, the vertical rods 5|, 52 and the composite cathode structure U supported thereby are clamped to the rubber sealing gasket 51, the thin section 63 of that gasket stretched across the opening 56 in the lower plate 49 serving as a flexible support for these rods.

In order to provide means to adjust the position of the composite cathode structure U within the metal tube H, the member 65 has external threads engaged by an adjusting nut 1|. vA

shoulder 12 on adjusting nut abuts against the on metallic member 65 so that the nut serves as a micrometer arrangement for adjusting the vertical position of the cathode structure I The table 38, 48 may also be provided with suitable legs 15 to serve as supports therefor.

I also provide means for applying operating potentials to the electrodes of the device I while it is in position within the exhaust chamrber 2. This'means comprises the leads l6, l1, l8, 19 connected, respectively, to a spring clamp 8|) which engages the anode III, a spring clamp 8| which engages the metal sleeve l1 surrounding the cathode structure, the clamp 48 connected to the upper metallic sleeve l4 and grid I2, and clamp 49 connected to the lower metallic sleeve l8 and grid l3. These leads may pass through the end wall 4| of the exhaust duct, an airtight seal between the side wall and the leads being maintained by a rubber disk 83 sealed across an open- .5 ing in wall 4|. For purposes to be pointed out later, the lead I8, which contacts the anode I0, is connected to the positive terminal-of a source of potential, such as .the battery 84, through a resistance 88; the negative terminal of battery 84' being grounded. The lead 11, conductively joined to sleeve ll surrounding the cathode structure, is connected directly to ground. Lead 18, connected to the screen grid [2 of the discharge device i, is supplied with proper operating poe tential from a tap 81 on battery 84. Lead 18, connected to the control grid of discharge device I, may be connected to ground through a bias battery 88 and, when required, a resistor 89.

Current for heating the filament 28 of the cathode structure may be supplied over a conductor 80 connected to the bottom of the vertical metal post SI and insulatingly sealed at its point of pass ge through metal plates 64, 65 by means of rubber washers 8|, 82 which may be formed integral with gasket 82. A conductor 94 similarly sealed at its point of passage through metal members 64, G8 is connected to the bottom point of the vertical metal post 82 and, in conjunction with lead 90, may serve to supply potential for flashing the getter 34.

In the manufacture of an electric discharge device of the type described, the anode l and the metal ferrule H are sealed in concentric relation by means of the glass disk l5. Similarly, the metal tube I1 and the ferrule l8 are sealed in concentric, relation by means of the glass disk It. Thereafter, the rings 20, 2| supporting the two grids and the ring of insulation 22 are clamped between the opposed outwardly directed flanges of the two ferrules and the glass bead 24 is hermetically sealed across these flanges. The cathode structure II is formed by welding the eyelet ii, the tube 28 of fernico foil, and the disk 21 together, after which the fernico foil is welded to the inwardly flanged upper end of the hollow metal tube 25 in which has been previously sealed the filament structure 28 and the getter 34, the glass disk 30 hermetically sealing the lower end of the hollow tube 25. The filament structure is then supported from the vertical posts 52 by clamping the substantially rigid conductors 29, 33 to these posts by means of spring clamps 53, 54. Thereafter. a ring 96 of solder is placed about the inwardly flanged upper end of the hollow tube 25. The unitary structure comprising the grid-anode assembly portion of the electric discharge device is then supported from the ring of insulating material 41, the sleeve I! being slipped over the hollow metal tube 25 and spring clamps 48, 49 being adjusted to hold the gridanode assembly in a vertical position. The bell jar 36 is placed over the assembly of the electric discharge device and its supporting structure so that the device may be evacuated.

As previously stated, the enclosed chamber 2 is connected to a large vacuum chamber l3, or any suitable reservoir, by means of a conduit defined by the metal plates 38, 48 and the side walls associated therewith. Preferably, the vacuum chamber 43 is considerably larger than the shame ber 2 so that, when these chambers are connected together by operation of the valve 42, the pressure within the bell jar 86 is rapidly reduced to a very low value, such a system facilitating manufacture of the electronic tube to the extent that only a very short period of time is required to evacuate the device. While the discharge device is being evacuated, the filament 28 is heated by means of current supplied thereto over the conductor and conductor. 11 and spring contact 8|, the connection between the filament and the sleeve ll being made through the ring of solder and the metallic contact between sleeves I1 and 25. Preferably, the current supplied to the filament is larger than that used in normal operation of the electric discharge device and is of suillcient value efiectively to sinter the cathode or emissive disk 21 and to degas the electrodes of the discharge device. Due to the fact that this degassing takes place within the evacuated bell jar 36, substantially no gas ions are present in the discharge device and a high voltage of the order of twice the normal voltage may be impressed across the filament with no fear of producing arcing and injuring the filament or electrodes. By this means, therefore, more effective and more rapid degassing of the electrodes is permitted. At the same time, the high temperatures thus produced may be used to melt the ring of solder 96 causing it to flow between sleeves i1 and 25 and hermetically seal the region within the discharge device from the evacuated region within bell jar 36.

Operating potentials may be supplied also to the anode, cathode, and grids of the device through the previously described electrical connections made over conductors lBl9 and clamps 48; 49, 8|] and BI.

After the pressure within the enclosed region 2 has been reduced to a low value, for example of the order of 10 microns, by means of the vacuum chamber 43 and the vacuum pump 3, the ring of solder 96, if not already melted by the heat produced by the excess currents in filament 28, is melted by means of high frequency currents supplied thereto inductively from a coil 98 connected to any suitable source (not shown) of high frequency currents. The melted solder forms a molten metallic seal between the two sleeves ll, 25, sealing the region within the electric discharge device from the region within the bell jar 36. To this end, the sleeves IT and 25, as well as other metallic parts of the electric discharge device, preferably are made of a material to which molten solder easily adheres, such a material being, for example, silver-plated steel, a suitable solder being used to form the ring of solder 96.

When the inner region of the device has been thus sealed from the remainder of the evacuated chamber, if additional time is required to degas or remove occluded gases from the electrodes, the molten solder may be allowed to cool. The tube is removed from the bell jar to continue the degassing operation according to the method normally used in manufacturing such tubes and thereafter is replaced in the bell jar and the latter exhausted. If all occluded gases have been removed by the time the tube and bell jar are exhausted and the ring of solder 96 is melted, suitable potentials may be impressed across the leads 9D, 94 to flash the getter material 34. A small hole or orifice 91 in the upper end of the metal sleeve 25 provides communication between the interior of the composite cathode I l and the region between the electrodes of the electric discharge device so that the getter 34, after vaporization, may further reduce the gas pressure Within the device to a value, for example, of the order of .01 micron, creating a final vacuum conditon within the device. The surfacetension of the molten seal of solder between the sleeves 11, 25 maintains the differential pressures between the inner and outer surfaces of the electric discharge rent of the discharge device.

In order to permit the manufacture of an electric discharge device having predetermined characteristics, either physical or electrical, the molten metallic seal between the sleeves I1, 25 provides means whereby the spacing of the emissive surface 21 from the anode III or the electrode 13 may be adjusted either to a desired physical value or to a distance which gives a desired electrical characteristic to the electric discharge device. In the case of tubes which have been removed from the bell jar for completion of the degassing operation, the tube is replaced in the chamber 2 and the solder seal remelted prior to the electrode spacing operation. For tubeswhich do not require additional time for degassing, the tube is allowed to cool to normal operating temperature and the,

electrodes are spaced without removing the tube from the evacuated bell jar. Where a particular spacing between electrodes is desired, such a spacing is obtained by adjustment of the micrometer screw II until the cathode 21 contacts the grid I3. It is apparent that due to the differential pressures on the opposite sides of the thin section 63 of the rubber gasket 51, this gasket is flexed inwardly toward the bell jar, tending to raise the position of the cathode within the sleeve l1. Such inward movement of the cathode supporting structure is limited by shoulder 12 on the micrometer screw ll. Contact of the emissive disk 2l with the grid l3 may be indicated by a suitable instrument used to show a current flow between these electrodes when direct electrical connection is made. Thereafter, the micrometer screw II is adjusted to lower the disk 21 exactly to the desired distance below the grid iii, the scale 13 indicating this distance. By such means, very small distances and very close spacing of electrodes may be obtained in an electric discharge device, distances for example of the order of .001 inch or less. Moreover, since the physical spacing is made with the tube elements heated to operating temperatures, assurance is had that such a spacing is obtained when the tube is used subsequently.

When it is desired to manufacture an electric discharge device having particular electrical characteristics, for example a particular grid voltage-plate current characteristic, the electrical connection shown in Fig. 1 of the drawing may be used. An ammeter 99 connected in series between the cathode and ground indicates the plate cur- By adjusting the spacing of the electrodes by means of the micrometer screw H, the position of the cathode with respect tov the anode and control electrodes may be varied until a proper plate current reading is obtained. In this way, any errors due to previous inaccuracies in assembly may be compensated and all tubes manufactured may be given substantially identical characteristics.

In Fig. 2, there is shown an alternative circuit which may be used'in spacing the electrodes of a discharge device manufactured in accordance with my invention. In the circuit of Fig. 2, the

discharge device I is represented diagrammatically, with the leads Hi-I9 being connected to the same electrodes as shown in the circuit of Fig. 1. A source of high frequency oscillations Hill is connected across an inductance Illl through an ammeter l02. The leads IE-J9 may be connected in any desired arrangement to connect the cathode any any other electrode as a capacitance in parallel with the inductance llll, the lead 'I'i from the position of the composite cathode structure ll within the tube II, the capacitance connected in parallel with the inductance l0! may be varied to tune this inductance to a reso'nance condition at the frequency of the source I", such a condition being indicated by a minimum current reading on ammeter I02. This method of adjusting the position of the electrodes is of value, especially where a desired value of interelectrode capacitance is desired for electronic tubes of special characteristics.

From the foregoing, it is seen that my invention provides an improved technique for manufacturing electric discharge devices, by means of which tubes having closely spaced electrodes may be manufactured, the spacing being adjusted to a desired value while the tube is being exhausted in an evacuated chamber. Also, tubes having nearly 'identical characteristics may be constructed since the grid-to-cathode spacing may be adjusted to compensate for small errors in the spacing of'the other electrodes. While I have described the method and apparatus as being employed in the manufacture of a tube of the tetrode type, it is apparent that they'may be employed to manufacture diodes, triodes, or tubes having any other desired combination of electrodes. Likewise, although I have illustrated and described a particular type of electric discharge device, namely, one in which the anode of the device extends in a direction opposite to the cathode and is supported by the metallic sleeves H, II which serve as external connections for the grids. it is apparent that my method and apparatus may be employed to manufacture any type of disthrough a metallic sleeve to which it is subsequently soldered. Thus, a glass envelope may, be employed and external connections to the electrodes may extend from the bottom of the device according to the usual technique.

Furthermore, in certain of the above descriptive matter and in the accompanying claims where the terms characteristic," characteristics, or dimension are used, it is understood that these terms are used in the sense of electrical characteristics or physical characteristics of a predeterminable nature, that is, which are determined through measurements, electrical or physical, during the manufacture of the device, the physical characteristics or dimensions excluding the gas pressure within the electric discharge device being manufactured.

While I have shown and described my invention as applied to particular systems embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention and I,'therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secureby Letters Patent of the United States is:

1. The method of manufacturing an electric discharge device whichincludes exhausting said device and positioning one electrode thereof to establish a predetermined characteristic of said device during said exhausting.

2. The method of manufacturing an electric of said device by moving an electrode thereof after said device is exhausted.

3. The method of manufacturing an electric discharge device which includes exhausting said device and adjusting the grid voltage-plate current characteristic of said device durin the exhausting thereof.

4. The method of manufacturing an electric discharge device which includes exhausting said device and adjusting the grid voltage-plate current characteristic of said device at normal operating temperatures during the exhausting thereof.

5. The method of manufacturing an electric discharge device which includes exhausting said device and adjusting the spacing between a pair of the electrodes thereof during the period of exhausting the device.

6. The method of manufacturing an electric discharge device which includes heating said device to normal operating temperatures and adjusting the spacing between a pair of the electrodes thereof at said temperatures.

'7. Th method of manufacturing an electric discharge device which includes heating the electrodes thereof to normal operating temperatures and adjusting the spacing between a pair of said electrodes during the exhausting of said device and at said temperatures.

8. The method of manufacturing an electric discharge device which includes applying operating potentials across the electrodes of said device during the exhausting thereof and adjusting the spacing between a pair of said electrodes with said potentials thereacross and during said exhausting.

9.,The method of manufacturing an electric discharge device which includes supporting said device within an evacuated chamber, supplying operating potentials across the electrodes of said device, and adjusting the spacing between a pair of said electrodes with the potentials thereacross and while said device is in said chamber.

10. The method of manufacturing an electric discharge device which includes exhausting said device, heating the electrodes thereof to abnormal temperatures, cooling said electrodes to normal operating temperatures, and then adjusting the spacing between a pair of said electrodes at said normal operating temperatures.

11. The method of manufacturing an electric di charge device of the type having an envelope with an aperture and an electrode stem wh ch projects through said aperture which includes forming a ring of molten metal about said electrode stem to establish a vacuum seal for said device and sliding said stem through the ring of molten metal to adjust the position of said electrode within said device.

12. The method of manufacturing an electric discharge device of the type having an entrance through which the device may be evacuated which comprises evacuating said device, establishing a molten metallic seal over said entrance, and then adjusting the position of an electrode within said device through said seal.

13. The method of adjusting the spacing of an electrode within an evacuated vessel, said electrode having a stem portion projecting through a wall of said vessel which comprises forming a molten metal seal about said stem, sliding said stem through said seal to a desired position, and

allowing said molten metal to harden to fix said position.

14. The method of manufacturing an electric discharge device having an entrance through which the device may be evacuated comprising establishing a primary vacuum within said device, using molten metal to seal said entrance, reducing still further the gas pressure within said device, and thereafter adjusting the position of an electrode in said device.

15. The method of manufacturing an electric discharge device which includes connecting a. reactive circuit across a pair of the electrodes of said device, exhausting said device, and adjusting the spacing of said electrodes to tune said circuit to resonance during said exhausting.

16. The method of manufacturing an electric discharge device of the type having an anode, a control electrode; and a cathode in spaced relation, which comprises establishing said electrodes in proximate positions, exhausting said device, and spacing said electrodes to a final position while said device is being exhausted.

17. The method of manufacturing an electric discharge device of the enclosed type and having a substantially cylindrical cathode structure closely surrounded by a metallic sleeve which comprises placing a ring of solder about said cylindrical cathode, supporting said device within a closed chamber, evacuating said device and said chamber, and melting said solder hermetically to seal the space between said sleeve and said cathode.

18. The method of manufacturing an electric discharge device of the enclosed type and having a substantially cylindrical cathode structure closely surrounded by a metallic sleeve which comprises placing a. ring of solder about said cylindrical cathode, supporting said device within a. closed chamber, evacuating said device and. said chamber, heating said cathode to abnormal temperatures to melt said solder hermetically to seal the space between said sleeve and said cathode, and adjusting the position of said cathode structure within said device while said solder is in a molten condition and said device is supported .within said evacuated chamber.

19. The method of manufacturing an electric discharge device of the type having a cylindri cal anode and a cylindrical cathode in alignment, said cathode being surrounded by a cylindrical tube, which comprises insulatingly sealing said said cathode being surrounded by a cylindrical tube, which comprises insulatingly sealing said tube to said anode and in concentric alignment therewith, inserting said cathode within said tube, establishing a vacuum within said device and in a region external to said device, forming a seal of molten metal between said tube and said cathode, heating the electrodes of said device to normal operating temperatures, applying operating potentials-between said electrodes, and adjusting the spacing between said electrodes to obtain a 11 desired electrical characteristic of said device, said spacing being accomplished while the vacuum of said region is maintained.

21. In combination, a closed chamber, means for exhausting said chamber, means for supporting an electric discharge device within said chamber, and means accessible from the exterior of said chamber for varying the spacing between a pair of the electrodes of said device within said chamber. v

22. In combination, a closed chamber, means for establishing a vacuum within said chamber, means within said chamber for supporting an electric discharge device to be evacuated, means for hermetically sealing said device after evacuation without removing said device from said chamber, and means accessible from the exterior of said chamber for adjusting the position of an electrode of said device after said device has been hermetically sealed.

23. Apparatus for manufacturing an electric discharge device comprising an exhaust cham-. ber, an exhaust reservoir having a large volume relative to the volume of said chamber, means for supporting said device within said small chamber, valve means-for connecting said chamber to said reservoir to effect rapid exhausting of said device upon operation of said valve means,

and means for adjusting the position of an electrode of said device without removing said device from said chamber.

24. In combination, a vessel adapted to be evacuated having a flexible wall, means adapted to support an electron discharge device in fixed position in said vessel, means connecting an electrode within said discharge device for mechanical movement with said wall, and micrometer means for moving said wall to position said electrode within said device without disturbing the vacum condition within said vessel.

25. Apparatus for manufacturing an electric discharge device comprising a closed chamber,

means for exhausting said chamber, means for supporting said device within said chamber, means for heating said device within said chamber to normal operating temperatures, and means for spacing a pair of electrodes of said device at said temperatures and without removing said device from said chamber.

26. In combination,-a closed chamber, means for supporting an electric discharge device to be evacuated within said chamber, means for supplying operating potentials to the electrodes of said device, means for evacuating said chamber to establish a desired gas pressure within said device, and means for adjusting the relative position of said electrodes to obtain a desired electrical characteristic of said device without removing said device from said evacuated chamber.

27. Apparatus for manufacturing an electric discharge device comprising a closed chamber, means for supporting said device within said chamber, means for evacuating said chamber, means for hermetically sealing said device while said device is within said chamber, and means for moving an electrode within said device after said sealing thereof.

28. Apparatus for manufacturing an electric discharge device of the type having an anode, a grid, and a cathode in spaced alignment and including a metallic sleeve surrounding a portion of said cathode and formed as a unitary structure with said anode comprising, a closed chamber, means for supporting said unitary structure within said chamber, additional means for Supporting said cathode within said sleeve, means for evacuating said chamber to establish a de sired gas pressure within said device, means for forming a molten metallic seal between said sleeve and said cathode, and means external of said chamber for adjusting the spacing of said cathode and said grid without removing said device from said chamber.

29. Apparatus for manufacturing an electric discharge device of the type having an anode, a grid, and a cathode in spaced alignment and including a metallic sleeve surrounding a portion of said cathode and formed as a unitary struc-' ture with said anode comprising, a closed chamber, means for supporting said unitary structure within said chamber, additional means for supporting said cathode within said sleeve, means for evacuatingsaid chamber to establish a desired gas pressure within said device, means for forming a molten metallic seal between said sleeve and said cathode, means for supplying operating potentials to the electrodes of said de- I within said device, means for hermetically sealing said device, and means for adjusting the electric characteristics of said device,after said device has been hermetically sealed and while said device is in said evacuated chamber.

31; Apparatus for manufacturing an electric discharge device having a pair of electrodes, said apparatus comprising 'a closed chamber, means for supporting a discharge device in said chamber, means for evacuating said chamber, means for supplying operating potentials to the electrodes of a device supported in said chamber, and means for effecting relative movement of the electrodes while the device is in said evacuated chamber.

32. The method of manufacturing an electric discharge device which comprises supporting said device within a closed chamber, evacuating said chamber and said device, using a molten metal to seal said device, allowing said seal to harden, removing said device from said chamber and degasifying said device, supporting said device in an evacuated chamber and melting said seal, and adjusting the position of an electrode of said device while said device is in said evacuated,

chamber.

33. Apparatus for manufacturing an electric discharge device including an anode and cathode in spaced relation, said apparatus comprising a chamber to be evacuated, means for supporting a discharge device within said chamber, means for hermetically sealing a discharge device supported within said chamber, means for evacuating said chamber and the device, and means accessible from the exterior of said chamber for adjusting the relative position of said anode and cathode without disturbing th vacuum condition within said chamber.

34. Apparatus for manufacturing an electric discharge device including a plurality of electrodes, said apparatus comprising a chamber, means for supporting a discharge device within said chamber, means for evacuating said cham- 13 ing a seal to hermetically seal the envelope of a device in said chamber and means for eflecting relative movement of said electrodes to determine a characteristic of the device without disturbing the vacuum condition within the device.

JAMES E. BEGGS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,006,818 Zimber July 2, 1935 2,058,105 Pohl Oct. 20, 1936 1,559,714 Lilieni'eld Nov. 3, 1925 Number