US2942128A

US2942128A - Electrodes for electron gun unit

Info

Publication number: US2942128A
Application number: US738389A
Authority: US
Inventors: Jay H Johnson
Original assignee: JOHNSON AND HOFFMAN Manufacturing CORP
Current assignee: JOHNSON AND HOFFMAN Manufacturing CORP
Priority date: 1958-05-28
Filing date: 1958-05-28
Publication date: 1960-06-21
Anticipated expiration: 1977-06-21
Also published as: GB870190A; FR1216116A

Description

June 21, 1960 J. H. JOHNSON 2,942,128

ELECTRODES FOR ELECTRON GUN UNIT Filed May 28, 195B Y Y)Afl/f? JAY H. JoHNsoN and 5 M ATTORNEY nited States Fatent ELECTRODES FOR ELEC'IRON GUN UNIT Jay H. Johnson, East Williston, N.Y., assignor to Johnson and Holman Manufacturing Corporation, Mineola, N.Y., a corporation of New York Filed May 28, 1958, Ser. No. 738,389

11 Claims. (Cl 313--82) This invention relates to electron discharge devices and particularly to cathode ray tubes including television picture tubes.

`In cathode ray tubes, a'beam of electrons is produced, focused and directed toward the viewing screen end of the tube by an arrangement of electrodes, known as the gun Heretofore, the gun electrodes, which are thin walled metal tubes and certain of which are closed at one end except for a small aperture, have usually had welded to them mounting studs, pins, wires or straps whose free ends were embedded in glass rods or posts while the electrodes were temporarily held in position in -an aligning jrg.

" 'This prior type of gun construction has many dis- .l

advantages including those now specified. The localized pressures and temperatures to which the electrodes werey subjected during welding thereto of the mounting elements often distorted the electrodes so that it was diicult or impossible to etfect their precise alignment in the assembly jig. Consequently, the electrodes as permanently aiiixed to the glass supporting rods or posts `did not provide a gun having satisfactory beam forming and directing characteristics. Moreover, the welding of the studs was often accompanied by weld-splash, pitting and other irregularities whose sharp points or whiskers resulted in corona discharge between gun electrodes operated at diierent potentials. Furthermore, in etorts to obtain resistance to displacement under conditions of shock and vibration, individual electrodes were often pro- Y vided with axially spaced pins with the result that the length of the leakage path through or along the surface of the support posts between the mounting pins of dilerent electrodes enforced wider electrode spacing or lower operating voltages than desired.

such that the spacing between the ends of the adjacent electrodes would be uniform when they were axially positioned or moved in the aligning jig in preparation for their permanent attachment to the support posts.

The foregoing disadvantages of the prior constructions.

are overcome, in accordance with the presentrinvention,

by making individual electrodes in the form of a ref entrant tube whose shorter outer portion has a radial ange providing an integral mounting element intermedi-V ate the ends of the electrodes. ly spaced regions, the flange may be notched to `provide lIn some cases, in eiortsl Ato'reduce interelectrode leakage, additional supporting integral ilange mount and reverse bend of the individual electrodes provides a rigid mounting, insuring maintenance of proper alignment and by elements whosej greatly enhanced spacing along the supporting posts pre* cludes leakage without need for special glasses or extra posts between certain electrodes. Furthermore, the electrodes are shaped and drawn by dies providing precise dimensioning, including parallelism of the opposite ends of individual electrodes; thus, the electrodes may be assembled with their adjacent faces or ends closely unil. a compound focusing electrode in the gun array, to elli formly spaced and with their axes in precise alignment by engagement of their undistorted perimeters with the4 aligning jig.

One of the features of the invention is the provision of ciently collimate the beam of electrons in its axial travel cup form of electrode is provided with a reverse turned j wall-portion coaxial with the main side wall of the elec,-V trode so that the end of said latter wall terminates about p the central length of the electrode. This wall ilows into a radial ange portion which forms the support of the cornpound electrode. superimposed on the closed end of the primary cup `electrode is an auxiliary frontlens electrode having a reduced neck portion projecting: away from the.. closed end ofy the focus electrode. The two superimposed electrodes are spot-welded to form an integraL collimating lens for focusing the intense beam of electron Speciiically,l at peripheral generated in the axis of the gun structure.

Another feature relates to the consolidation of all the.

vthe central aperture in the electrode and electrodes in the gun unit into an integral `assembly in which the highest degree of insulation resistance is at-l tained without'affecting the relatively close spacial relation of the various electrodes in the gun structure.

Another advantage of the ruggedized construction of the invention is concerned with the reinforced double-4 Wall feature of the electrode so that the concentricity of the inner wall of the electrode is insured with respect to distortion is substantially eliminated.

out-of-roundV The new construction also permits reduction in length i,

of the gun stack of electrodes which materially facilitates the achievement of close tolerances in the new type television tubes. These limits may be attained by further4 reduction in dimensions of the electrodes, since smaller electrodes could easily be fabricated by the proposed` double-walled construction without any deleterious effectsV 1n the formation of the electrodes. Another advantage of the reduction in length of the gun unit is the physical effect of increasing the eiciency of the structure and at the same time attaining approximately twice the beatri-` current at the same modulating voltage as employed in;

the same prototype structure.

The rigid flange construction also provides a shielding? effect of the gun unit stack of electrodes, particularly in respect to the shielding ofl the lirst grid against'pre-v; ignition effects, due to excessive heating caused by the,

enclosed heater and cathode and the combined effect of;

i getter dust dispersion when the getter is ilashed during ears or lugs for sealing into the supporting postsof the f piusand thereA isA absentthe distortion of thecross-secthe final processing of the Atube `during manufacture.

TheY unique construction also contributes to the anti-Q emission characteristics of the tube by. the novel radia-- `tion features of the electrodes, since the increased metal farea in each electrode materially radiates heat, both Y 3 physical and electrical, in the normal functions of the gun unit in operation.

Another feature relates to the removal of excess flange material, to reducethe radial dimension .of the .unit in one'. diameter, whereby the lead wires to the Various control electrodes may be suitably located without 1ncreasing the dimensions of the neck of the tube to pro' vide clearance of the Wires along the sides of the unit.

-A further lfeature of the invention along the same lines as the preceding idea is the fact that the attenuation of the flange construction provides a self-indexing characteristic 4to the structure of the electrodes, since the electrodes mayk be easily stacked in jigs without regard to the location of spaced projections on the anges which are used in anchoring the electrodes in a unitary assembly.

A still further feature of the ruggedized construction of the electrodes is that when the stack is assembled in the jig unit, the whole assembly may be hydraulically compressed, to insure stable localization of the electrodes when theV side posts are fused to embed the liange projections of the electrodes therein.

Another feature of the heat 'radiating characteristics of the electrodes of this invention relates to the `freedom from burning effects at the aperture in the first grid or control electrode where the emission fromthe cathode is substantially in excess `of the required emission provided in therbeam of electrons projected from the cathode through the grid aperture. The complete. and effective heat radiationv characteristics of the proposed construction insures .the maintenance of stable operation in the controlof the beam, so that burning of the aperture rim is substantially eliminated.

' The ruggedized construction also materially improves the operating life of the tube by the elimination of weak supports, fragile lateral connectors and auxiliary str-aps which tend to reduce the strength of the assembly. The structure also provides accurate alignment so that greater efficiency is obtained in the manufacture and service of the`tube.

A further feature of the ruggedized assembly of the gun unit is that greater salvage value may be attained with the present design in view of the fact that when the tube is disabled because of effects in the tube other than the gun structure, it is very easy to reclaim the gun after the tube is opened, and then replace the cathode and .heater in the rst grid and thereby reuse the structure which constitutes a large potential value in the tube reclamation field.

A still further feature relates to eicient production whereby increased benets and lower costs may be realized. This is accomplished by reason of the fact that the majority of the electrodes in the gun structure may be fabricated by the same set of dies, since all but` the shield 'element surrounding the focus anodes andthe reduced neck components maybe produced by the samedie sets. An auxiliary'feature of this same aspect of the invention is the fact that the production process of formation of the cup portion of the electrode from flat strip metal the waste is cut off the bottom'of the cup. In the present environment, the reverse bend portion, and the flange are formed from the-scrap portion and the Iexcess metal which is lost is considerably reduced, thereby materially increasing the value of the raw material in the industrial processes of electronics manufacture.

VThese and many other features and advantages may be realized ymore fully by reference -to the following detailed description when considered in connection with the accompanying drawings, in which;

Fig. 1 is a view in elevation, partly in cross-section, showing, on a greatly enlarged scale, the neck portion ofa typical television tube with -the gun mount supported therein and embodying the electrode structure' of this invention; Y

"agendas t Fig. 2 is a side elevation view of the array or stack of electrodes in the gun mou-nt, taken on the `line 2-2 of Fi 1; j

iig. 3 is a plan view of the electrode assembly of this invention, to show the flange construction and the cutout ears formed at diametrically opposite points across the ange thereof;

Fig. 4,is a view in cross-section, taken on the line 4-4 of Fig. 3, of one vform of cup electrode, to show the reverse bend in the wall of the electrode whereby the electrode is physically extended without increasing the elective length of the electrode, so far as its -elect on the electron beam is concerned;

Fig. 5 is a plan view, taken on the line 5 5 of Fig. l, showing the relationship of the electrode support postsA and the bent ears of the electrodes embedded in the posts; and,

Fig. 6 shows a partial perspective view of the` configuration of the electrode of --this invention andthe relation of the bent ear on the flange portion.

Referring to the drawings, and particularly to Fig.- l,"

the invention is embodied in a partial view of a television tube having a neck portion 10, provided with a stem 11, which supports a gun unit or electrode mount, for

projecting a beam of electrons along the axis of the tube.

The gun unit involves a series of reentrant tubular' electrodes, of which the primary electrode is an inverted cup electrode or first grid 12, shown in cross-section in Fig. 4, having a central aperture 13, in the closed end,

to form the initial control electrode of the gun array. The cylindrical wall of this electrode is extended and reversely bent or turned at y14, to extend substantially one half the distance back from the lower open end of lthe electrode. The reverse bend portion 14 terminates in a radial ange portion 15, which forms the support of the control grid. The electrode 12 is formed ofnonmagnetic stainless steel or similar highly refractory material, of light gauge, about ..010 inchthickness and is thoroughly degreased `and freed from injurious` contanrinants prior to' assembly in the gun unit. Mounted within the first grid 12 is a small tubular cathode and heater, no shown, which serve as the electron source for projecting an electron beam through the array of electrodes constitutingthe gun unit. The outer wall 14 and the ange 15 enhance the heart radiating surface of the grid and so minimize its temperature changes, despite its proximity to the heater, with consequent improved stability of the close spacing between this grid `and the adjacent grid 16.

The second grid 16 is a short cup-shaped electrode having its closed end facing toward the closed end ofthe i ii'rst grid and provided with a central aperture 13A, which is coaxially aligned with the aperture 13 in the iirst grid 12. The spacing between the adjacent faces of grids 12 `and 16 is only a few thousands of an inch, of the order of .020 to .O40 inch. The cup grid 16 has a` reverse bend wall portion 17, concentric with the cup wall 16 and turned downwardly from the open end to be joined to a flange portion 18, which forms the support extension of the second grid electrode. As indicated in Figs. l vand 2, the closed ends of the rst and

second grids

12 and 16, respectively, are relatively `close together while their support lianges 15 and 18 are widely spaced apart, thereby materially increasing the leakage resistance betweenthese control electrodes.

Beyond the second or #2 grid electrode is a focusing anode assembly composed of a group of cooperating electrodes which influence the beam just in advance of' its passage through electrostatic or electromagneticl elds which control its deflection across the area of the luores- I! cent screen on the viewing end of the tube. rIhis group of focusing electrodes include a lower lens 19, an upper lens 20, in contraposed relation .to lens 19, and a cylindrical shield anode 21, encompassing the reduced ends of the cooperating

lens electrodes

19 and 20.

The focus lens electrodes V19 and 20 are identical in construction so that a description of lens 19 will sutiice for both; The electrode 19 is formed of a cup portion 22, similar to the rst grid 12, and having a small central aperture 23, in the closed end. A reversely turned wall extension 24, continues from the open end and projects back from the open end to about one half the length of the cup portion 22. The extension wall 24 is coaxial with the cup walls 22 and is of larger diameter. The rim of the extension 24 terminates in a flange 25, which extends radially in the same relation as

grids

12 and 16. The inverted cup portion 22 Iabove the reverse bend portion 24 and the flange 25 is enveloped by an auxiliary shell portion 26, slightly larger in diameter thanthe cup portion 22, so that it fits in telescopic relation and is affixed thereto.

The shell 26 is provided with a reduced neck portion 27, having a recessed closed endY 28, with a central large aperture 29, coaxial with aperture 23 in the shell portion 22. A shoulder 30, couples the neck portion 27 to the shell 26 and is spaced in parallel relation to the closed end of the cup portion 22, to form an axial passageway between the apertures'23 and '29, so that these compound electrodes 212 and 26 form an electron focus lens for concentrating the beam of electrons projected through the gun mount or assembly.

The complementary focus lens assembly 20 is mounted in opposed relation to lens electrode 19. In this relation the reduced neck portions of both lens assemblies varemounted in coaxial relation and the intervening focus area is surrounded by a shield anode electrode 21, formed of a cylindrical metallic portion 31, having a curled rim 32, surrounding the neck portion 27a of lens assembly 20. The opposite end of the cylinder portion 31 has a reversely turned Wall portion 33 surrounding and extending approximately lto the central portion of the cylinder where it is flared outwardly to form a radial flange 34. The shield anode establishes a magnetizing field in the vicinity of the focus lens area so that the electrons are 'concentrated in the axial beam through -this portion of the gun assembly. The energizing high potential of the shield anode precludes straying of electrons from the beam in its progress toward the screen.

The multiple focus assembly, which includes the composite individual lens electrodes, is thus comprised of a series of reentrant tubular electrodes whichl are widely spaced in relation to their support points but are closely spaced in their functional relation with respect to the beam of electrons which passes through them. Furthermore, the high potential anode 21 is widely spaced in relation to the

flange portions

25 and 25a, of the lens assembly respectively, so that the leakage paths between the various electrodes is materially lengthened and the danger of high potential breakdown is essentially eliminated.

The anged reverse bend portions on all the electrodes have an extremely beneficial effect on the physical and electrical characteristics of the gun assembly. The reverse bend stilfens the open end of the electrode so that despite the thin wall, the inner cylinder retains its original cross-sectional shape. This is important both in assembling of the electrodes in precise alignment and in production of proper fields from `an electrical standpoint during operation of the tube. The flange mount extending radially of the reverse bend in a plane substantially remote from both ends of the individual electrodes provides for their attachment to the supporting posts with wide spacing between the support points o=f adjacent electrodes. The reverse bend and flange construction thus provides both a rigid mount and long non-conductive trons is directly axially through the aligned apertures in the various electrodes and combined into an integral unit or mount in the gun assembly. To achieve this result, each electrode is provided, as above described, with a radial flange portion which forms the support junction with a pair of glass or

ceramic posts

35 and 36, which are Ymounted in parallel vertical relation from stem 11 in the lower end of the neck portion 10 of the vessel by stub wires or rods 37.

As shown in Fig. 4, each flange portion is provided with diametrically opposed cut-out portions which form a central ear or tab38, which is twisted, at 39, in Fig. 6, transversely of the plane of the flange, so that ear may be sealed into the posts, as shown in cross-section in Fig. 1. VThe relation of the electrodes mounted betweennthe posts 35 and 36 is shown clearly in plan view in Fig. 5, in which the twisted ears are perpendicular to the plane of the flange and are sealed into the inner surfaces of the posts in linear alignment, as shown in Fig. 2.

Thesealing of the ears of the electrodes into the glass support posts is effected while the electrodes are held temporarily in'a jig in axial alignment and with properinterelectrode spacing. Since the electrodes-have :not been distorted by welding pressures and temperatures, they properly cooperate with the locating surfaces of the jig in attainment of precise alignment of the beam aper-.z tures of the gun electrodes. In production,the shrinkage loss, due to rejection of guns and tubes for faulty alignment or for poor cathode ray spot formation, is practically eliminated.

The manufacture of the individual electrodes from a disc blank involves drawing and extrusion operations, all performed by precision dies, vthereby insuring accuratedimensioning of the electrodes, including parallelism of their opposite faces withinA a tolerance easily held to less than two thousandths of an inch. Thus, in the assembly jig, in readiness for their attachment to the support posts, the electrodes may be precisely positioned for predeten, mined control in the formation of the cathode beam and with very close spacing of the adjacent faces of the

grids

12 and 16, without danger of internal short-circuits or other malfunction. t

The connection of the electrodes 16 and 21to the terminals or pins inthe stem 11 may be effected by

lead wires

40 and 41, welded to the marginal flange area of the electrodes, as indicated in Fig. 2. The first grid 12.'

may be connected to a pin in the stem by a short wire 42,l welded to the outer tubular section 14 of electrode 12. The two focusing `

anode electrodes

19 and 20, may be connected to each other by wire 43, welded to their mar-v ginal flanges, Fig. 2, and to an interior conductive coating ofthe tube by spring contacts, not shown, so that the high energizing potential may be applied to the focusing` anode assembly. As indicated by dotted lines in Figs. 4 and 5, the mounting ange may be cut awayY at 44 between the cut-out ears, to provide more clearance Abetween the gun electrodes and theneck portion of the tube for dressing the lead wires in the gun unit. The attenu.

ated electrodes are, therefore, more easily stacked in a jig assembly by the self-indexing parallel edges of the flange portions and provide a biased assembly whichmaterially enhances the production processes of manufacture 'of the gun unit.

' While the invention has been set forth specifically in aparticular embodiment, it is, of course, understood, that various modiiications may be made in the detailed structure of the electrodes and their assembly without departingfrom the scope of the invention as defined vin the appended claims.

-What is claimed is:

1. An electrode, `comprising a double walled metallic member having the outer wall concentric with the inner wall and extending approximately half the distance beyond one end of said member, said outer wall being spaced away from said inner wall, an integral annular junction connecting said walls together at said one end to form a reverse bend between vsaid inner and outer walls, and an lintegral outwardly extending ange projecting from the free end of said outer Wall and having integral mounting lugs angularly spaced about its periphery and -each defined by notches extending inwardly from said periphery,

2. In an electron gun assembly, an electrode comprising a double walled metallic member having the outer wall concentric with the inner wall and extending approximately half the distance beyond one end of said member, said outer wall being spaced away from said inner wall, an integral annular junction connecting said walls together at said one end `to form a reverse bend between said inner and outer walls, and an integral outwardly extending flange projecting from the free end of said outer wall, said flange having integral cut-out mounting lugs at dimetrically opposed points on the edge thereof, the outer ends of said mounting 'lugs being within the outer boundary of said tiange.

3. In an electron gun assembly having support posts, an electrode comprising a double walled metallic member having the outer wall concentric with ythe inner wall and extending approximately half the distance beyond one end ofV said member, said outer wall being spaced away from said inner wall, an integral annular junction connecting said walls together at said one end to form a reverseA bend between said inner and outer walls, and an integral outwardly extending flange projecting from the free end of said outer wall, said flange having cut-out ear portions at diametrically opposed points on the edge thereof, said ear portions being twisted perpendicularly to the plane of said ange for sealing into said support posts.

Y 4i In an electron gun :assembly having support posts, an electrode comprising a double walled metallic member having the outer wall concentric with the inner wall and extending approximately half the distance beyond one end of said member, said outer wall being spaced away from said inner wall, an integral annular junction connecting said walls together at said one end to form a reverse bend between said inner and outer walls, and an integral outwardly extending flange projecting from the free end of said outer Wall, said flange having cutout ear portions at diametrically disposed points on the edge thereof, said ear portions being twisted perpendicularly to the plane of said flange for sealing into said support posts, said ear portions being formed within the boundary of the periphery of said iiange.

5. An electron gun assembly comprising a series of reentrant tubular electrodes `each having an integral ange extending radially outwardly from the outer tu-f bular section of the electrode in a plane parallel to and spaced substantially midway from the opposite ends of the inner reentrant tubular section of the electrode, each of said iianges having integral mounting elements angularly spaced about its periphery, and support posts respectively directly attached to said angularly spaced mounting elements of `each electrode flange with each PQSt attached at predetermined points along its length to the corresponding integral mounting elements of the successive tianges rigidly to maintain the. electrodes in spacedY i axialaligninent and to provide increased leakage resistance between the successive electrodes of the series.

6. An electron gun assembly as in claim 5 in which said angularly spaced mounting elements of the electrode flanges are ears defined by peripheral notches and each twisted perpendicularly to the plane of the associated flange.

7. An electron gun assembly including a tube stern, support posts attached at one end to said stern and extending `therefrom parallel to each other, and a stack of reentrant tubular electrodes each having an integral flange extending radially from ythe outer tubular section of the electrode in a plane parallel to and spaced substantially equally from the opposite ends of the inner reentrant tubular section of the electrode, the periphery of said flanges having integral angularly spaced mounting elements directly attached to said support posts rigidly to maintain the alignment and axial spacing of theV electrodes of the stack.

8. An electron gun assembly including two reentrant tubular grid electrodes each having an integral mounting ange extending radially outwardly from the outer tubular section of the electrode in a plane parallel to and spaced substantially equally from the open reentrant end of the inner tubular section of the electrode and from the closed apertured end of said inner tubular section, said iianges each having integral mounting elements angularly spaced about its periphery, said reentrant grid electrodes being in mutually inverted relation with their closed apertured ends in close proximity, and support posts respectively `directly attached to said angularly spaced mounting elements of each of said iianges and individually attached at axially spaced regions to the corresponding mounting elements of the flanges of the two grid electrodes rigidly to maintain the aperture alignment and spacing of the closed ends of said grid electrodes and by a mounting arrangement providing increased leakage resistance between said grid electrodes.

9. An electron gun assembly including two lens electrodes and an intervening shield electrode, each of said three electrodes being reentrant tubular electrodes each having an integr-al mounting ange extending radially outwardly from the outer tubular section of the electrode in a plane parallel to and substantially equally spaced from the opposite ends of the inner reentrant tubular section of the electrode, the three flanges each having integral mounting elements angularly spaced about its periphery, said reentrant lens electrodes being in mutually inverted relation with their closed aperture-d ends faced toward one another and each having a tubular shell fitting over its inner reentrant tubular section, said shells of the lens electrode extending into the space dened'by the inner reentrant tubular section of the shield electrode.

with their closed apertured ends in spaced relation, and support posts respectively directly attached to the angularly spaced mounting elements of each of said three anges and individually attached at axially spaced regions to the corresponding mounting elements of the lens electrodes and the intervening shield electrode rigidly to maintain the `aperture alignment and spacing of. said electrodes and by a mounting arrangement providing increased leakage resistance between said shield electrode and each of said lens electrodes.

10. An electron gun assembly including in sequence a first grid electrode, a second grid electrode, a focusing electrode, a shield electrode and a second focusing electrode, each of said electrodes comprising a reentrant tubular structure having an integral flange extending radially `outwardly from its outer tubular section in a plane parallel to and spaced substantially equally from the opposite ends of the inner reentrant tubular section, said tianges of all electrodes having the same radius and having'similarly angularly spaced mounting ears defined .by peripheral notches, and support posts in each of WhlCh are? @imbedded .the corresponding axially aligned ears ofv Y said electrodes to provide a mounting arrangement rigidly maintaining said electrodes in spacedv axial alignment and having increased leakage resistance between the successive electrodes.

ll. An electron gun assembly including a tube stem, support posts attached at one end to said stem and extending therefrom parallel to each other, and a series of electrodes including in spaced axial sequence a rst grid electrode, a second grid elect-rode, a focusing electrode, a shield electrode and a second focusing electrode, each of said electrodes comprising a reentrant tubular structure having an integral ange extending radially from the outer tubular section of the electrode in a plan parallel to and spaced substantially from the opposite ends of the inner reentrant tubular section of the electrode, each of said iianges having angularly 10 spaced integral peripheral ears embedded. in said support posts rigidly to maintain the alignment and axial spacing of said electrodes and by a mounting arrangement providing increased leakage resistance between said electrodes.

References Cited in the le of this patent UNITED STATES PATENTS 2,233,795 Pensak Mar. 4, 1941 2,567,893 Poble et al. Sept. 11, 1951 2,627,585 Van Ornurn Feb. 3, 1953 2,690,517 Nicoll et al. Sept. 28, 1954 2,732,511 Dichter Ian. 24, 1956 2,792,515 Broderick et al. May 14, 1957 2,847,599 Kaseman Aug. 12, 1958 2,853,639 Knochel et al. Sept. 23, 1958 UNITED STATES PATENT oEEICE CERTIFICATION OF CORRECTION Patent No 2,942,128 June 21 1960 Jay H Johnson It s hereby oertifedthat error appears in the above numbered patent requiring correction and that the Said Letters Patent should read as corrected below.

Column 4v line 47, for "no" read -m not mw; column 5Y line 14, for "walls" read mwall Q-g column 9,1 line 14i for "plan" read plane Signed and sealed-this 18th day of July 1961a (SEAL) lttest:

ERNETVWSVHDEB. DAI)L.LADD

Attesting Officer Commissioner of Patents