US2093303A - Screen grid metal tube - Google Patents

Description

J. E. BEGGS Inventor James E. E ggf9 bg His Atbovheg.

SCREEN GRID METAL TUBE Original Filed Sept. l. y1.93

@epm M? E937.

Patented Sept. 14, `193,7

UNITED STATES PATENT OFFICE soaEEN cmo METAL TUBE James E. Boggs, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Original application September 1, 1934, Serial 8 Claims.

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

This application is a division of my application duction basis and in which the metal container serves the function of one of the screen electrodes. Other objects and features will be apparent as the speciilcation is perused in connection with the accompanying drawingv in which Fig. 1 is a view, partly in section, of a thermionic device improved in accordance with the present invention and embodying the improved screen electrode; Fig. 2 is a view of the tube shown in Fig. 1 but with the envelope removed and the anode cut away to show the interior electrodes; Fig. 3 is an enlarged sectional view of a preferred form of cathode employed in the tube shown in Figs. 1 and 2; Fig. 4 is an enlarged fragmentary sectional view oi' a typical seal employed in the tube shown in Figs. 1 and 2; Fig. 5 is a modified form of metal tube employing a screen electrode, while Fig. 6 is a view similar to Fig. 5 except that the upper seal and the metal seal-off are shown in section and the anode is cut away to show the interior electrode structure more clearly.

Referring more particularly to Fig. l, numeral i designates a cylinder consisting of any readily workable, inexpensive metal such as iron, nickel, etc., which is closed at the top (as shown) by a metal header member 2 and at the bottom by a metal header member 3. These headers conveniently take the form of a reentrant cylindrical member fitting snugly within the interior of the envelope l to which they may be secured in any suitable and well-known manner, as by welding.

l'lhe interior assembly of the tube, as illustrated more clearly in Fig. 2, takes the form of a four-electrode device having a cathode d, an electrostatic control grid 5, a screen grid t, all preferably of cylindrical configuration and surrounding one another. While any suitable form of cathode may -be used, I prefer to employ an indirectly heated cathode of the type shown in Fig. 3. In this iigure, numeral 8 designates a tungsten heater which may take the form of a hairpin, insulatingly mounted Within the cylinder 4 which is preferably of nickel and constitutes the cathode proper, The cylinder t advan- Divided and this application December 17, 1936, Serial No. 116,398

(ci. 25o-21.5)

tageously may be coated with electronically active material S such as barium and strontium oxide obtained initially from the carbonate as is well known in the art. Leads I@ may be taken from both ends of the heater and a lead Il connected to the lower end (as shown) oi the cathode cylinder.

The gridV or electrostatic control member 5 may consist of a circular wire helix, woundon a pair of metal uprights l2, one of which, the extreme right-hand member as shown, is extended and joined to a leading-in conductor I3 taken out through the upper end of the tube. The screen grid may also consist of a wire helix but of larger diameter than the control grid, and wound on a pair of metal uprights lll. One of these uprights may be extended to make suitable connection with the container by means of a transverse conductor l5 as will be explained hereinafter.

The anode 'l may consist of a metal cylinder, preferably of nickel, and provided at diametral positions with a pair of rod uprights I6, one ci which, the left-hand rod as shown, being extended and connected to a leading-ln conductor il.

The electrode structure as a whole is mounted on a frame constituted of a pair of metal uprights il@ which are secured by flanged metal collars 2l to the upper and lower headers 2, 3. It is apparent that the uprlghts 2G serve to maintain the proper spacing between the headers and together with the latter constitute a rigid rectangular frame.

The control grid uprights l2 and the screen 1.

grid uprights lil are spaced .and maintained in proper position by means oi' a pair of disks 22, of insulating material such as mica, which contain openings for snugly receiving the uprights. On the upper side of the upper disk 22 and the lower side of the lower disk 22, there is a pair of disks 23, also of mica but of larger diameter than the disk 22. The disks 23 have openings about the periphery to receive the anode uprights i6. The upper disk 23 is of a diametral size such as to ilt snugly Within the metal cap member 2d, the purpose of which will be explained hereinafter. The cap 24 is provided with a slot (not shown but indicated by the lack of cross-sectional lines along the flattened portion of the mernber), sufliciently large to permit the control grid leading-in conductor and the cathode to pass through without touching. The frame members 20 also pass through the slot and are rigidly secured to the cap member 24 by angle pieces 25.

In order to maintain the mica disks 22 and 2l perfectly flat, i. e. to prevent warp, and in order to oil'er more rigidity to the supporting framework, I have provided at each end of the electrode structure, transverse metal bars 26 which are respectively secured to each pair of mica disks 22, 2l, for example by riveting and also secured as by welding, to the frame uprights 20. Each of these bars is provided with a transverse slot corresponding to the slot in the cap 2l in order to permit the upper ends of the control 4grid uprights i2, also the upper end of the cathode cylinder 4 and the lower ends of the screen grid uprights il, and thelower end of the cathode l, to pass through without contacting with the bars.

The control grid leading-in conductor I3 is taken out through the upper header 2 by means of an improved seal shown more completely in Fig. 4 which constitutes the subject matter of my application Serial No. 744,165, filed September 15, 1934 and entitled Glass-to-metal seals, and is disclosed and claimed in broader scope in the Elder and Gable application Serial No. 746,808, filed October 4, 1934, and entitled Electricdischarge devices and seals therefor. These applications are assigned to the same assignee as the present invention.

Leading-in conductor I1 of the anode, conductor Ii of the cathode, and conductors I0 of the heater member are taken out through the opposite header 3, also by means of improved seals. There is no leading-in conductor for the screen grid 6 because the conductor i5 between the screen grid and frame upright 20 connects the screen grid to the headers 2, l, and thus to the envelope i.

The flattened portion of the header member is provided with an opening at the position where it is desired to pass the leading-in conductor through. Secured to the header at the opening, for example, by welding, there is a metal eyelet 28 which is provided at one end (at the bottom as shown) with an outwardly extending flange in order to be secured either to the under side or the upper side of the header member. A cylinder 29 of glass or other vitreous material within the eyelet may support and insulate any one of the leading-in conductors from the eyelet and hence from the header member. A hermetic seal is formed between the conductor, the glass and the eyelet, preferably by means of a gas flame which is directed at the proper position on the eyelet after the conductor and glass have been assembled in the eyelet. The seal,'including the conductor, glass and eyelet members, is completed as a unit, apart from the header member after which the eyelet isvsecured to the header.

In order to insure an absolutely vacuum-tight seal between the glass 29 and the eyelet 20, these members should preferably have substantially the same thermal expansion characteristic over the entire temperature range between 0 C. and the softening temperature of the glass. Thus no stress or strain is introduced at the various joints during fabrication of the seal or during any subsequent heat treatment of the tube which contains the seal. While various metals and glasses may be employed for this purpose, the freedom from stress and strain at the seal being dependent upon the amount of materials involved and the respective differences of thermal expansion at the various temperatures reached during the manufacture of the tube, I prefer to employ materials which have been disclosed and claimed in the Burger and Hull application Serial No.

2 a,oos,sos

705,250, nled January 4, 1934 and entitled Glassto-metal seals, assigned to the sameassignee as the vpresent invention. This application has matured into Patent 2,071,196. As pointed out in the Burger and Hull patent, a metal which may be advantageously employed for a substantially strain-free seal, regardless of the amount of metal and glass used or regardless of the temperatures reached during manufacture, consists approximately of 18% cobalt (Co), 28% nickel (Ni), 54% iron (Fe), and the glass in this case may have the following approximate composition: 65% silica (SiOs), 23% boric oxide (B201), 7% sodium oxide (NazO) and 5% aluminum oxide (A1201). v

As stated hereinbefore, when the eyelet is welded to the fiat portion of the header member, either on the under or the upper side thereof, and when the glass member 2l and the metal member 28 are of the proper materials, the leading-in conductor is carried through the metal header in an insulating manner and is hermetically sealed. A sumcient number of these seals are provided to accommodate the various leading-in-conductors. e

In addition to these seals, the lower header member 3 carries a seal-oi! tube 20, constituted of a readily workable metal such as steel, which is hermetically secured to the header member in any suitable and well-knownl manner, for example by welding or copper brazing in a hydrogen furnace. An excess of tubulation III is provided, the additional length being cut on during the seal-off process as will be described presently.

When the leading-in conductor seals and the metal seal-off have been secured to the proper headers. and the electrode assembly, including the frame uprights 20, has been assembled and secured between the headers, connections are made between the various leading-in conductors and their respective electrodes, as has been explained hereinbefore. Thus the metal headers and the electrode structure together with the supporting framework and elements, constitute the entire structure contained within the envelope i. The structure as a whole is extremely rigid in view of the support offered by the header members and the frame uprights 20. I'he feature of providing a pair of metal headers connected together by a rigid framework which supports the electrodes and constitutes a complete assembly unit is disclosed and claimed in my application Serial No. 742,407 flled September 1, 1934 entitled Electrode structures for metal tubes and assigned to the same assignee as the present invention. This application has matured into United States Letters Patent No. 2,056,035.

The next step in the process of manufacture is to secure the header members and associated elements to the envelope. 'I'he headers are of such a diameter as to ilt snugly within the envelope I, and are so spaced that their outer edges align themselves with the edges of the cylinder i. The entire unit may be slipped into place and the headers welded or otherwise permanently and metallically secured to the envelope. The tube is then placed on an exhaust system and the interior of the envelope evacuated through the tubulation 30. During this time, the metal envelope is heated by high frequency or by a gas or electrically operated oven, to a temperature. for example, of approximately 700 C., sufficiently high to remove the occluded gases from the envelope material and yet not high enough to cause the glass members 29 to `melt in Fig. 6 and comprises an indirectly heated or otherwise to cause damage to the non-metallic elements. The evacuation should preferably be cor. lucted at a fast rate, after which the tube is gettered in any suitable and well-known manner.

When a sufilciently high vacuum has been obtained, the tube is sealed from the pump by closing the tubulation 30 in any suitable manner, for example by simultaneousiycollapsing the tubulation and welding the sides thereof. After the weld has been made. the surplus length of tubulation may be snipped of! by cutting pliers, whereupon the tube is removed from the evacuating system. A base may be provided, ii desired, and the various leading-in conductors colinected to the usual contact pins.

As stated hereinbefore, the screen grid 8 is connected to the envelope through the short transverse conductor I5 and the frame uprights consequently, the metal envelope serves not only as a rugged container for the electrodes but also as a part of the screening system for intercepting electrostatic lines of force which tend to pass between the control grid and the inner or outer surfaces of the plate. While I am awarethat screen grids having a portion interposed between the control grid and the anode and another portion positioned on the opposite side of the anode have been employed heretofore in tubes, it should be noted that in the case of the prior tubes, an outer screen electrode is utilized in addition to the envelope. However, in accordance with the present invention, the screen electrode has been combined with the envelope so that one less element is necessary under these conditions. Furthermore, by connecting the inner screen electrode with the metal envelope, an external connection may be effectively made with the inner screen electrode by simply making contact with the envelope, thus eliminating the usual leading-in conductor for the inner screen electrode.

The cap 24 is provided in order more effectively to shield the anode from the control member and more particularly for'the purpose o'f intercepting the electrostatic lines of force which pass between the leading-in conductor I3 of the control grid and the outer upper surface of the anode. It ls apparent that any lin'e drawn between the conductor I3 and the exterior surface of the anode will be intercepted either by the cap member 2C or by the envelope I or by both.

Figs. .5 and 6 show a modified type of screen grid tube, illustrated in the form of a pentode. The parts in these figures which correspond to the elements shown and described in connection with Figs. l, 2, 3 and 4 have been given similar reference characters. It will be noted that the tube shown in Figs. 5 and 6 employs only one metal header, namely the element 3, because the upper end of the envelope 3| ls closed by a portion integral with the envelope and' produced by a deep-drawing process. member consists of a reentrant wall portion 32 which terminates in a rectilinear wall portion 33 forming a closed compartment 34. A ledge 35 is formed vwithin this compartment and resting against the ledge there is a mica disk 3 8, the function of which is to support the upper ends of the electrodes. For this purpose, the disk 36 is provided with openings snugly to receive the various electrode uprights and the upper end of the cathode l.

The electrode structure is shown more clearly The upper closure cathode 8 which may be similar to that shown and described in connection with Fig. 3, a helical control grid 5, a helical screen grid B, an anode 1 and In addition, a secondary emission suppression grid 31, Vtermed a suppressor grid," positioned between the anode and the screen grid. The various grids 5'. B and 31 are wound around their respective uprights I2, i4 and 38, these uprights fitting snugly at the top, in openings provided in the mica disk 38 and having their lower ends supported within openings provided in a mica disk 38. The disk 38 is contained within a plate member 40 of circular configuration and provided at the upper edge with a flange in order to receive the disk 39. The plate member 40 is provided at the lower edge with a metalbar 4I which carries a longitudinal slot of sufficient size so that the various leading-in conductors for the electrodes may pass through without touching.

The plate member l0-is supported from the header member 3 by means of a pair of rigid up- 'rights 82, at diametral positions, which are secured to the header by means of hanged metal members 2l. A leading-in conductor I3 for the control member is taken out through the top of the envelope and may constitute an extension of one of the control grid uprights. The cathode 4 is connected to the longitudinal bar 42 by means of a conductor 43 and the suppressor grid is also effectively connected to the same bar by means of the conductor M. It is apparent that the cathode and the suppressor 'grid are effectively connected to the envelope 3i through the uprights 42 and the header member 3.

'Leading-in conductors 45, 48 and 41 are provided respectively for the anode 1, the heater 8 and the screen grid 6. These conductors are insulatingly taken through the header by means of improved seals, an example oi which is shown in Fig. 4 and was described in connection with that ligure. It will be understood that any other suitable form of seal may be employed for this purpose. The leading-in conductor I3 at the top of the envelope preferably employs a seal having a long extended glass portion 48 provided with a groove between the glass and the conductor, also between the glass and the eyelet 28 so as to offer increased leakage paths between the conductor and the eyelet. As in the case of the seal shown in Fig. 4, the seal shown at the upper end of Fig. 6 is also disclosed and claimed in my patent application Serial No. 744,165.

As stated in the application, Serial No. 744,165, the improved seal not only insulatingly carries the leading-in conductor I3 through the metal closure member but also serves as a support member for the mica disk 36. I! desired, a seal similar to the one shown in Fig. 4 may be employed for this purpose and a spacer substituted for the portion d8 between the upper surface of the disk 36 and the lower surface of the attened end portion of the envelope tI. It is apparent that in view of the support provided by the glass extension member I8 and the ledge 35, the mica member 36 is very rigidly held in position at the upper end of the envelope.

In addition to the seals 28 and the support members 2l, the header member 3 carries a metal seal-olf tube 38 which is hermetically sealed to the header as was explained in connection with Figs. i and 2. The end of the seal-off tube remote from the envelope is hermetically closed, preferably by welding, after the exhaust and gettering treatments have been completed. In order 4 aoeasos to getter a tube of this type, there may be provided a gettering material indicated by reference character Il, which may consist of a piece of magnesium pressed tightly between the wall I2 and the upper end of the envelope ll, the getter being in such a positionthat it may be vaporized readily by torching the upper end of the metal envelope adjacent the getter. In order to prevent the getter vapor from migrating to undesired positions within the tube, it may be desirable to provide a metal bame l0 provided with openings 6l for evacuation land gettering purposes. 'I'he baille is of such a diameter as to nt snugly within the envelope 3| and has an opening at the center which mayfit tightly about the uprights 38 of the suppressor grid. l

It is apparent in Figs. 5 and 6 that the cathode and suppressor grid are connected together and are maintained at the same potential as the envelope. On the other hand, the screen grid l is insulated from the envelope and a leading-in. conductor 41 is brought out from this grid so v that various potentials may be applied thereto with respect to the cathode. It is obvious that these potentials may be predetermined in order to permit the screen grid to intercept and neutralize the effect of the electrostatic lines of force which normally pass between the control grid and the anode. Inasmuch as the envelope Il is at the same potential as the cathode, it also will serve as a part of the screening system and will intercept the electrostatic lines of forcey which tend to move between the control grid and the exterior surface of the anode. 'Ihe configuration of the upper end of the envelope 3| is such thatthe electrostatic lines of force between the grid leading-in conductor i3 and the exterior surface of the anode are eifectively intercepted by the metal closure. It is apparent that this end of the 4o envelope performs the function of not only serving as a closure for the envelope but also takes on the role of a screen member which is similar in function to the cap member 24 shown in Figs. 1 and 2. Accordingly, the improved form of envelope eliminates the necessity for the cap member and to that extent represents a more simple construction.

The tube shown in Figs. 5 and 6 oii'ers the advantage that no leading-in conductor is necessary for the cathode or suppressor grid, since these members are maintained at the same potential as the envelope to which a connection may be readily made in order to connect with the respective elements. Inasmuch as the anode is physically independent of the remaining electrodes and is n'ot supported by a dielectric member in common with the other electrodes, greater screening edects may be realized in a tube of the character shown in Fig. 6 than in the tube construction shown in Fig. 2. However, it will also be understood in this connection that if desired, the internal elements of the tube shown in Fig. 2 may be supported in such a manner as to employ less dielectric material than is illustrated and thus realize enhanced screening effects.

'I'ubes improved in accordance with my invention in which the metal container serves as part of the screening or shielding system are readily adapted to external shielding, since the container or envelope may constitute an integral part of the shielding apparatus which is provided in connection with the radio receiver set of which the improved tube may constitute one amplincation or detection stage. An example of the enhanced 15 external shielding onered by the metal container,

is when the tubes are clamped through a shield partition mounted approximately midway of the length of the envelope in such a manner that the plate lead is in one compartment provided by the partition ncf the grid lead is in another 5 compartment provided by the same partition. Obviously, since the partition and the metal envelope are effectively grounded or at least connected to cathode potential, no electrostatic lines of force, regardless of their curvature or length, lo can possibly extend between the grid and plate leads.

In view of the foregoing,` it is apparent that I have disclosed a screen gridtube which 'is readily adapted to be manufactured on a quantityl 15 production basis and which lends itself to any number of grid electrodes by simply changing .the number of openings and distance between openings in the respective mica disks 36 and 39, with proper provision in the header member I 20 for insulatingly taking out leading-in conductors from the various electrodes. The metal container Il in connection with the upper closure member oii'ers the most effective shielding for the contained electrodes so that in a tube of this 25 character, there is no tendency for the production of undesired high frequency oscillations by reason of interelectrode capacity. As stated hereinbefore, considerable saving is offered by a metal tube of this type in providing enhanced 30 screening effect without necessitating additional electrodes and leading-in conductors, since the metal container serves the dual function of an envelope as well as a screen electrode.

Some of the screening features shown herein 36 are disclosed and broadly claimed in the Livingston application Serial No. 704,503, filed December 29, 1933, entitled E'lectrostatically con-l trolled arc discharge devices, assigned tothe same assignee as the present invention. This 40 application has matured into Patent 2,044,618.

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

1. An electric discharge device comprising a metal envelope containing a cathode, an anode, 45 I and a control grid, said envelope being provided with a metal end portion formed integrally withA the envelope where the control grid leading-in conductor passes through the envelope, and means including said envelope and the metal end 50 portion for intercepting substantially all of the electrostatic lines of force extending between the exterior surface of the anode and said leading-in conductor.

2. An electric discharge device comprising a 55 metal envelope and containing a cathode, an anode, a control grid, and a screening grid, leading-in conductors for the anode, control grid and screening grid. said envelope being connected to the cathode and provided with a metal end por- 60 tion formed integrally with the envelope where the control grid leading-in conductor passes through the envelope, said envelope end portion enectively'intercepting substantially all electro# static lines of force extending from the anode 55 toward the control grid leading-in conductor.

3. An electric discharge device comprising a metal envelope containing a cathode, an anode. and a control grid, said envelope being provided with a metal end portion formed integrally with 70 the envelope where the control grid leading-in conductor passes through the envelope. means for intercepting substantially all of the electrostatic lines of force extending between the anode and the control grid, said intercepting means consisting in part of said envelope and the metal end portion, and in part of a screening element interposed between the anode and the control grid.

4. An electric discharge device comprising a hollow metal cylinder closed at one end by a metal header hermetically secured thereto'and at the other end by an integral reentrant portion.

at the other end by an integral reentrant portion which terminates in a chamber extending rec- 20 tilinearly with respect to said cylinder, a plurality oi' electrodes in said cylinder, means for insulatingly mounting the electrode structure, at one end from said header and at the other end from the wall portion which forms said chamber, 25 leading-in conductors for the electrodes hermetically sealed in said header and insulated therefrom.

6. An electric discharge device comprising a hollow metal cylinder closed at one end by a. 30 metal header hermetically secured thereto and at the other end by an integral reentrant portion which terminates in a chamber extending rectilinearly with respect to said cylinder, a getter material in said chamber, a plurality of electrodes 35 in said cylinder, means for insulatingly mounts ing the electrode structure, at one end from said header and at the other end from the wall portion which forms said chamber, leading-in conductors for the electrodes hermetically sealed in said header and insulated therefrom.

7. An electric discharge device comprising a hollow metal cylinder closed at one end bya metal header hermetically sealed thereto and at the other end by an integral reentrant portion which terminates in a chamber extending rectilinearly with respect to said cylinder, a getter material in said chamber, a plurality of electrodes in said cylinder, means for preventing the vapor of said getter material when ashed from striking said electrodes, and means for insulatingly mounting the electrode structure, at one end from said header and at the other end from the wall portion which forms said chamber, leadingin conductors for the electrodes hermetically sealed in said header and insulated therefrom.

8. An electric discharge device comprising a hollow metal cylinder closed at one end by a metal header hermetically sealed thereto and at the other end by an integral reentrant portion which terminates in a chamber extending rectilinearly with respect to said cylinder, a getter material in said chamber, a plurality of electrodes in said cylinder, means including a shield member interposed between the getter material and the electrodes for preventing the vapor of said getter material when ashed from striking said electrodes, and means for insulatingly mounting the electrode structure, at one end from said header and at the other end from the wall portion which forms said chamber, leading-in conductors for the electrodes hermetically sealed in said header and insulated therefrom.

JAMES E. BEGGS.

Images