US2124428A - Metal vacuum tube - Google Patents

Description

July 19, 1938. H. J, NoL'rE METAL VACUUM TUBE Fig. Z.

Filed sept. 15, 1934 Fig. I.

Ffg.

- Inventor: Hem-g J. Nolte,

Attorr'weg.

basis.

Patented July 19, 1938 PATENT orf-ica METAL VACUUM TUBE Henry J. Nolte, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application September 13, 1934, Serial No. 743,832

2 Claims. (Cl. Z50-275),

'I'he present invention relates to electron discharge apparatus, and more particularly to thermionic devices employing metal envelopes.'

Metal oifers many advantages over' vitreous substances, such as glass, quartz, etc. for envelope material of electric discharge devices. When the envelope is constituted substantially entirely of' metal, the tube is extremely rugged, which promotes long life. 'I'he metal envelope not only offers electrostatic and magnetic shielding to the contained electrodes but in addition, may serve as' one of the electrodes of the device, thus eliminating one element and its leading-in conductor. In the case of a metal envelope, which constitutes l one of the electrodes, electrical connection may be made direct to the exterior surface of the tube. In addition to these advantages, metal 'envelopes may often be made more cheaply' than "glass envelopes due to the fact that highly skilled -labor,-

, such as glass blowing,- etc., is unnecessary-and the' envelopesmay be fabricated on automatic machines. Envelopes of-'this character may be made' of inexpensive metal, such as iron or nickel, and readily shaped to form on a quantity production Some of these advantages have long been recognized by the'art, but the successful development of an all-'metal tube, particularly one of small size, has'been beset'by many difficulties, among which are the leakage at thepositions where the leading-in conductors pass through the envelope, and the lack of an effective method for sealing off such a tube from the pump after the required high vacuum has been obtained.

The primary object of my invention is to provide an electron discharge device of simple design and rugged construction and which may be made entirely out of metal, except for the necessary seals about the leading-in conductors. Another object is to provide a tube which employs a metal seal-off communicating with the interior of the tube and one which provides a strictly hermetic seal so that the tube may be permanently disconnected from the pump.

The invention will be better understood when reference is made to the following specication and accompanying drawing in which Fig. l is a view partly in section of an electron discharge device improved in accordance with the present invention; Fig. 2 is a sectional view of a typical form of cathode employed in the tube shown in Fig. 1; Fig. 3 is a fragmentary view of the lower end of the envelope and header member showing the metal seal-oil in section; Fig. 4 is a view similar,` to Fig. 3 but illustrating a different type of metal seal-off, while Fig. is a cross-sectional View of a typical form of leading-in conductor seal. Referring more particularly to Fig. 1, numeral I designates a cylinder consisting of any workable, inexpensive metal such as iron, nickel, etc., closed at the top (as shown) by a transverse member 2 andat the bottom by a metal header 3 which may consist of the same metal as the cylinder. The header conveniently takes the form of areentrant cylindrical member, tting snugly within the interior of the cylinder l, to which it may be secured in any suitable and well-known manner, such as by welding. The member 2 preferably is formed integral with the cylinder l so that the entire structure, apart from the header member and electrodes, may be made from sheet metal and formed by a deep drawing process. As stated hereinbefore, the members i, 2, and 3 consist of an inexpensive metal having a surface which necessitates no treatment other than to remove surface contamination, such as oil, water, etc. The metal preferably should be reasonably smooth, although not polished. The ordinary commercial grade of sheet metal serves this pur-- pose satisfactorily. The reentrant member 3 is provided with a Wide flange and extends for a considerable distance into the envelope l so as to provide a relatively large contacting surface with the interior of the envelope, sumcient for an adequate weld between the flange and envelope. In forming the weld, one of the welding electrodes may be positioned on the exterior of the envelope t and the other electrode on the interior of the flanged header, and the electrodes moved as a unit, in a circular path around the periphery of the envelope. or if desired, the electrodes may be maintained stationary and the envelope and header members moved, in order to produce a stitch or line weld.

Before the header member is welded or otherwise secured to the envelope Il, one or more electrodes are mounted on top of the header. 'I'here are two electrodes shown, the center electrode 4 constituting an indirectly heated cathode and the other electrode 5 taking the form of a grid which surrounds the cathode. It will be apparent that I have exemplified my invention in connection with a three-electrode device consisting of a cathode t, an electrostatic control member 5 and an anode which is constituted of the envelope i. This general arrangement of electrodes and their application and proper circuits therefor are well known in the art. Obviously, the invention is not limited to any particular number of electrodes er kind of electrodes contained within the enveiope.

The cathode l is shown in detail in r'ig. 2 consists preferably of a hairpin iilamentary lheater member ii insulatingly mounted within a Leads 8 are taken from both ends of the heater,

and a lead 9 taken 4from the lower end (as shown) of the cathode cylinder l.

The grid or control member 5 may consist of a wire helix wound on a pair of metal uprights i0. A leading-in conductor il may be taken from either one of the uprights.

In order to maintain the proper spacing between the cathode, the control member and the envelope, disks i2 of insulating material, such as mica or alumina, are provided at each end of the electrode structure. These disks are of a shape and size to iit snugly within the envelope and are provided with openings to receive the ends of the electrode structure.

For bringing out the various leading-in conductors through the metal header 3, specially designed seals are employed, an example of which is shown in Fig. 5. The metal header is iirst provided with openings at the positions where it is desired to pass the leading-in conductors and secured to the header at each of these openings, for example, by welding, there is an eyelet i3 provided at the bottom with an outwardlyextending flange for securing to the under side or if desired, to the upper side, of the header member. Fitted snugly within the eyelet i3, there is a cylinder i4 of glass or other vitreous material which may carry any one of the leading-in conductors and is provided with an annular groove i5 which serves to increase the leakage distance or path between the conductor and the eyelet. A hermetic seal is formed between the conductor, the surrounding glass member and eyelet, conveniently by means of a gas flame which is directed at the proper position on the eyelet after the conductor and glass have been assembled of the seal or during any subsequent heat treat- Iment of the tube which contains the seal.

While various metals and glasses may be employed for this purpose, the freedom from strain and stress at the seal being dependent upon the respective differences of thermal expansion at the various temperatures reached during the manufacture of the tube, I prefer to employ materials which have (B263), 7% sodium oxide (NazO) and 5% aiuminurn oxide (A1203). Under certain conditions, particularly when the manufacturing temperature is relatively low and the thickness of the eyelet is relatively small, it is possible to obtain a satisfactory seal when employing metals such as molybdenum, nickel and copper in connection with certain well-known glasses.

As stated hereinbefore, when the eyelet i3 is Weldedto the at portion of the header member 3, either on the under side thereof` as shown in Fig. 5, or on the upper side, and further, when the glass member id and the metal member i3 are of the proper materials, examples of which are given hereinbefore, the leading-in conductor is carried through the metal header in an insulating manner and at the same time is hermetically sealed. A sufcient number of these seals are provided to accommodate the various leading-in conductors.

The improved seal shown in Fig. 5, including the use of a metal eyelet and glass bead, has been disclosed and broadly claimed in the Elder and Gable application, Serial No. 746,808, led October 4, 1934 entitled Electric discharge devices and seals therefor, and in a limited aspect has been disclosed and claimed in the Beggs application, Serial No. 744,165, filed September l5, 1934 and entitled Glass-to-metal seals. The Elder and Gable application and the Beggs application referred to are assigned to the same assignee as the present invention.

In addition to these seals, the metal header 3 carries a metal seal-off tube i t, examples of which are shown in Figs. 3 and 4'. The seal-olf tubulation is preferably constituted of a readily workable metal, such as steel, which may be hermetically secured to the header member in any suitable and well-known manner. As illustrated, the header is provided at the center with an opening of a size snugly to receive the tube l 6. The tubulation may extend through the opening for a small distance in order to provide suiiicient surface at the upper side (as shown) of the header member to insure a good joint. The tubulation may be welded to the header in order to provide a hermetic joint or if desired, may be brazed or soldered, and for this purpose, a ring of solder is dropped over the upper end of the tube IS so as to rest on the upper surface of the header member. The header is then heated in a hydrogen furnace to a temperature below the melting temperature of the glass but above the melting temperature of the solder which then iiows and forms a firm uniting material between the tubulation and header, suciently tight to constitute a hermetic seal. If desired, the eyelets i3 may also be brazed to the header member during the time when the tubulation is being secured and in substantially the same mannen'although it has been found preferable to weld the flanges of the eyelets, either to the lower surface or upper surface of the header member as explained hereinbefore.

An excess length of tabulation may be provided, as indicated by the dotted lines in Fig. 1, the additional length being out off during the seal-off process, as will be described presently.

When the leading-in conductor seals and the metal seal-off tube have been properly secured to the metal header, connections are taken from the various leading-in conductors to their respective electrodes which previously have been tted within the openings in the disks l2. Thus the metal header and the electrode structure which together constitute the entire structure contained within the envelope are assembled and mounted in place. The next step in the manufacturing process is to secure the header member and associated elements to the envelope I. It is apparent that the header member and the disks l2 position and rigidly support the electrode structure within the envelope container. The header member may then be welded to the envelope as explained hereinbefore.

After the electrode assembly has been placed in position and the header member 3 welded or otherwise secured thereto, the tube is placed on an exhaust system and the interior of the envelope evacuated through the metal tubulation I6. During this time, the metal envelope is heated by high frequency or by a gasor electrically-operated oven to a. temperature of approximately 1000 C., the source of heat being so positioned that the seal end of the envelope runs somewhat cooler, for example, approximately '700 C., which is just below the melting point of the glass employed in the leading-in conductor seals. If the tube is heated with the header member and seal structure at the lower end, as illustrated in Fig. 1, and a high frequency coil placed about the midsection of the envelope, the top member 2 of the envelope will be heated much hotter than the cylindrical portion, and the header member will necessarily runmuch cooler than the remaining portion of the envelope.

The evacuation should preferably be conducted at a fast rate, something of the order of one minute if possible and if a. high frequency coil is immediately lowered over the container, it takes about ten seconds for an envelope of radio-receiving tube size to acquire the necessary temperature and the heating process may be continued for approximately forty seconds, which leaves about ten seconds for the envelope to cool down at the end of the exhaust. It has been found that if the heat treatment does not extend for any considerable length of time, the various insulating materials contained within the envelope are not damaged thereby and yet the deleterious gases occluded in the material of the envelope, also in the electrode and insulating materials, such as water vapor, etc., are eiectively removed by the pump. The tube may be getter-ed in any suitable and well-known manner.

When a suiiiciently high degree of vacuum has been obtained, and assuming that no gas is to be introduced, the tube is sealed ofi the pump by closing the tubulation i6. The preferred manner of doing this is by the use of a weld which is applied to the tubulation through a pair of electrodal jaws of suitable shape connected to a source of direct or alternating current. A welding machine suitable for this purpose is well known in the art, as are also satisfactory energizing circuits for the welder. The jaws of the machine are preferably operated by a foot pedal which causes the jaws to press together with considerable force so that when placed on opposite sides of the tubulation l5, the latter is completely collapsed to form a flattened welded portion at any suitable position along the length of the tubulation. If desired, more than one attened and welded portion may be employed and the length of the seal-off tubulation increased accordingly. The distance between the header member and the position at which the Weld is produced should be as short as possible but yet sufciently long to permit ready access to the welding electrodes. After the weld has been made, the surplus length of tubulation may be snipped od by cutting pliers whereupon the tube is removed from the evacuating system.

I have found that when a suitable welding apparatus is employed and suiiicient pressure applied to the welding electrodes so as completely to flatten the tubulation I6 at the welding position and thereby provide a line weld, the end of the tubulation is hermetically sealed most effectively. In fact, such a sealV compares very favorably with seals produced between glasses.

Instead of producing the seal by a weld, a hermetic joint may also be obtained by the use of solder. For this purpose, the tubulation I6 is preferably made of copper and before being secured to the header member 3, is tinned on the inside and outside by immersing the end in liquid solder, leaving an excess of solder sticking to the interior of the tubulation. The tubulation may then be secured to the header member in the manner explained hereinbefore, and after evacuation ofthe envelope, a pair of parallel jaw pliers and a ame is employed to effect the seal-01T. The name is applied, while the tubulation is held compressed by the pliers, at a position about 2" above the constriction and gradually lowered along the tubulation until it is directed immediately above the constriction. This portion is thoroughly heated to insure complete formation of a solder pool which collects at the constriction. The tubulation must be compressed suiiciently tight to prevent iiow of solder through the constriction and this may be accomplished by the use of pliers with rounded inserts in the jaws. The solder seal-olf is quite effective from the hermetic standpoint but as stated hereinbefore, the welded seal-oli is preferred since, obviously, it may be more quickly done and the choice o metal for the tubulation i6 may be greater.

After the tube has been sealed oi, if desired, a base may be applied to the lower or header end of the envelope and the various leading-in conductors taken to the usual contact pins. However, I have found that a base of this character is not necessary because the metal seal-off is so rugged as not to require mechanical protection and to this extent, when the improved tube is mounted in a radio set, a cheaper installation is possible.

It is apparent that the entire tube structure, except for the small glass cylinders I4 and the insulating disks l2 which are employed for supporting the electrode structure within the envelope, is made oi metal. The manufacturing -processes employed in shaping and securing the various parts together lend themselves to automatic machines so that the improved tubes may be cheaply fabricated. Moreover, the material out of which the envelope o such a tube is constructed, Winch for the most part is an ordinary grade of iron or nickel, is relatively inexpensive. Finally, a tube oi this character is extremely rugged in construction and the only glass or other' fragile elements employed is the member lil which'is so protected by the metal eyelet i3 and the reentrant form of header and furthermore, issc constituted oi thick material, as to be practically unbreakable and shatterprooi. It is apparent that when effective joints and seals are provided in the manner described hereinbefore, the possibility of tube failure by reason of leakage or breakage is substantially eliminated.

in operation, the container or envelope l may serve as one of the electrodes, since the remaining electrodes are insulated therefrom, and ccn fris .e

sequently, the improved construction pemits the elimination of at least one electrode and its associated leading-ln conductor which are normally found in tubes provided with glass envelopes. The elimination of this electrode adds simplicity to the tube construction as Well as assisting in lowering the cost of manufacture. The improved construction is adapted to the design of tubes of all sizes, not only small radio receiver tubes made on a quantity production basis but also large transmitter tubes employed with high voltage.

While l have illustrated and described my invention as applying to a three-electrode highvacuum device in which the envelope constitutes the anode, it is apparent that if desired, the construction may be employed in connection with gas or vapor tubes of the arc or glow discharge type. Furthermore, any number of electrodes, one or more, may be contained `within the envelope and the envelope take on the role of any of the electrodes, depending upon the circuits employed. lt is also apparent that the metal seal-o tubulation disclosed herein may be employed in connection with tubes having envelopes made entirely o glass except for a metal portion to which. the metal seal-on is secured.

What l claim as new and desire to secure by Letters atent of the United States s:

l. in electric discharge device comprising an envelope containing a plurality of electrones, said envelope including a cylinder closed by a hanged metal header member secured at the ange to said cylinder, said header being substantially at except for the ange, leading-in conductors for said electrodes passing through the header member and insulated therefrom, an all-metal evacuating tubulation secured to the dat portion of said header member and closed. by a Weld at the end remote from the envelope.

2. An electric discharge device comprising an envelope containing a plurality of electrodes, said envelope including a cylinder closed by a metal header member of substantially dat conguration, leading-in conductors for said electrodes passing through the header member and insulated therefrom, an all-metal evacuating tubulation secured to said header and hermetcally closed by the fusion of metal.

mi? J. NOLTE.

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