CA1117175A

CA1117175A - Projection television tube and process for forming same

Info

Publication number: CA1117175A
Application number: CA000316119A
Authority: CA
Inventors: Henry E. Kloss
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-02-06
Filing date: 1978-11-10
Publication date: 1982-01-26
Also published as: NL175118B; BR7900494A; SE438574B; JPS6233243Y2; IT7967111A0; DE2855390C2; JPS5910528B2; FR2416548B1; DK152466B; NL7811618A; IT1118307B; GB2013974A; DK152466C; AU522177B2; GB2013974B; JPS54107621A; NL175118C; AU4110478A; DE2855390A1; SE7811268L

Abstract

ABSTRACT OF THE DISCLOSURE

A projection television tube envelope and projection television tube constructed of components, the configuration and manner of assembly of which are used as the sole means to position the optical elements of the envelope and the tube.
This is accomplished by forming one component, a cylindrical member, with one accurate dimension and providing it with an annular sealing surface having a predetermined spherical configuration.

Description

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This invention relates to ~rojection television and more particularly to an improved envelope for a projection tele-vision tube, to a projection television tube incorporating the envelope and to a process for forming the envelope.
Projection television is a well established teehniaue.
Ho~ever, because of the high cost involved in manufaeturing the projection televisicn tubes used, projection television has ge-nerally been limited to expensive, complieated, large screen units which are both diffieult to install and expensive to main-tain in satisfaetory alignment. Thus the eomplexity and eost ofthe presently available projection television tubes have eritieal-ly eurtailed the development and aeeeptanee of projeetion tele-vision systems for home entertainment, a use which could represent a very high-volume market.
Projection television systems for color projection commonly include three tubes each having a different color (eon-veniently referred to as red, green and blue) projecting pictures whieh are superimposed in registry on a common view sereen. Typ-ically, the most efficient of sueh tubes incorporate the optics of a Schmidt-t~pe projection system and comprise a target illu-n,inatea in a single color by a suitahle specific phosphor as an electron beam raster, a s~herical reflector directinq the light around the peri~hery of the target and a eorrection lens for any spherical aberration.
Wi~hin these tubes, certain dimensions are critieal, a fact which has heretofore given rise to the high cost of con-structing the pro~ection tube envelol~es to achieve a high level of reliability and reproducibility of optical characteristics.
In partieular, it is essential to locate and maintain the spacing

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be-tween the mirror surface and the target surface at a predeter-mined value within about +0.001 to 0.002 inch (about 0.025 to 0.050 mm) Projection tubes of the prior art have therefore been constructed to incorporate expensive and compllcated means both to position the target during envelope and tube manufacture and to adjust its location both during manufacture and instal-lation. A reLatively early approach to achieving a partial solution to this problem w~s to incorporate the mirror within the tube envelope by forming it on that internal en~elope surface opposing the target sur~ace. This, however, still necessitated maintaining the critical dimensions of more than one envelope component as well as the precise relative positioning of the components, (See for example U,S. Patents 2,467,462, R. D.
Brown, Jr., issued April 19, 1949 and 2,637,829, V. Trad, issued May 5, 1953.) As this art has progressed in its development, more and more complex mechanisms have been incorporated into the tubing envelope and associated with it to achieve and maintain the required mirror/target aIignment and critical distance.
Thus, it is obvious that it would be highly desirable to provide an envelope for a projection television tube which is relatively simple in construction but which is capable of achiev-ing during construction and maintaining during use the required precise spatial distance between mirror and target surfaces.
It is, therefore, a primary object of this invention to provide an improved envelope for a projection television tube which is relatively simple to construct and which, therefore, offers the possibility of providing less expensive components for a projection television system. It is another object of this invention to provide an envelope for a projection television tube of the character described which uses the envelope components as the sole means to position the target relative to the mirror and which requires that only a single component of the tube envelope be made with one very accurate dimension. It is still another object of ~his invention to provide an envelope for a projection television tube and the television tube incorpo-rating it which is free of any need for means to adjust the position of the target surface either during tube assembly or installation of the tubes in a projection television system. Yet a further object is to provide an envelope for a projection tele-vision tube and a projection television tube incorporating the 10 envelope which allows minor variations in the location of the target relative to the mirror surface to compensate for the re-quired positioning of each of the three projection tubes in a set relative to the projection screen used.
It is another primary object of this invention to provide an improved process for the manufacture of projection television tubes. An additional object is to provide a process of the char-acter described which requires forming only one dimension of one tube envelope component, aside from optical components, with great accuracy. It is another object to provide such a process 20 which materially re~uces the cost of the resulting ~rojection television tube through reduction in cost of the component parts of the envelope used and in cost of the envelope assembly. Other objects of the invention ~Jill, in part, be obvious and will, in part, bc apparent hcreinafter.
According to one aspect of this invention there is provided an envelope for a projection television tube com-prising an end ~late, the internal surface of which defines a spherically configured mirror; a cylindrical member affixed to the end plate and terminating in an annular face plate sealing 30 end configurea and positioned such that a sphere in stable po-:

'7 ~, sition resting on thc sealing end will have its center of curvature essentially coincident with the center of curvature of the sphere defining the surface of the mirror; target suppoxt means engaging the seal;.ny end and supportiny a target defining a spherical surface having a center o~ curvature essentially coincident with the center of curvature of the sphere determin-ing the configuration of the face plate sealing end; and a face plate sealed to said cylindrical member.
In a preferred embodime~t the sphere determining the surface of the target and the sphere determining the configura-tion of the sealing end of the cylindrical member have essential-ly the same radi.i; and in a further preferred embodiment the face plate serves as the target support member.
According to another aspect of this invention there i.s provided a projection television tube comprising an end plate, the internal surface of ~hich defines a spheri.cally configured mirror; a neck sealed to the end plate; a cylindrical member affixed tc t.he end plate and terminating in an annular face plate sealing end configured and positioned such that a sphere in sta-ble position resting on the sealiny end will have its centerof curvature e~sentially coincident with the center of curvature oi the sphere defining the surface of the mirror; target support means engaying the sealing end and supporting a target defining a spherical surface having a center of curvature essentially coincident with the center of curvature of the sphere determin-ing the cor.figuration of the face plate sealing end; a face ~late sealed to the cylindrical member; connecting means to electric-ally connect the target and the mirror and to provide an external annode terminal; electron ~un means sealed within the neck ar-ranged to produce an electron beam to print a raster on the target;

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and electron beam focusin~ means.
According to a further aspect of this invention there is provided a process for forming an envelope for a projection television tube, comprising the steps of forming an end plate to have a sph~rically configured mirror on its internal surface;
affixing to the end plate a cylindrical member which ter~.inates in an annular face plate sealing end configured and positioned such that a sphere in stable position resting on the sealing end will have its center of curvature essentially coincident with the center of curvature of the sphere defininy the surface of the mirror; positioning on the face plate sealing end of the cylindrical member a target support means configured to engage the face plate sealing end and supporting a target defining a spherical surface having a center of curvature when so positioned which is essentially coincident with the center of curvature of the sphere determinin~ the configuration of the face plate sealing end, the positioning of the target support means in conjunction with the height of the cylindrical me~er sexving to attain a predetermined location of the target with respect to the mirror;
2~ and sealing a face plate to the cylindrical member thereby to permanently affix the target in the predetermined location.
According to yet another aspect of thls invention there is provided a process for forming a projection television tube comprising the steps of forming an end plate to have a spherically configured mirror n its internal surface; sealing a neck to the end plate; providin~ a cylindrical ~ember which terminates in an annular face plate sealing end configured and positioned such that a sphere in stable position resting on the sealiny end will have its center of curvature essentially coinci-dent with the center of curvature of the sphere definlng the sur-: -6-.

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face of the mirror; applying an electrically conductive coating to the internal wall of the cylindrical member; sealing an annode terminal through the wall of the cylindrical member; positioning on th~ face plate sealing end of the cylindrical me~ber a ~arget support means configured to engage the face plate sealing end and supporting a target defining a spherical surface having a center of curvature when so positioned which is essentially co-incident with the center of curvature of the sphere determining the confiquration of the face plate sealing end, the positioning of the target support means in conjunction with the height of the cylindrical member serving to attain a predetermined location of said target with respect to said mirror; providing a face plate: affixing the end plate to the cylindrical member; pro-viding an electrical connection between the mirror and the target;
sealing the face plate to the cylindrical member thereby to permanently affix the target in its predetermined location;
providing an electron gun assembly arranged to direct an electron beam onto the target, and sealing the electron gun into the neck; sealing off the neck in a manner to create a vacuum within the tube volume; and affixing electron beam focusing means to the neck.
The invention accordingly comprises the several steps and the relation of one or more o such steps with respect to each of the others, and the articles possessing the features, properties/ and the relation of elements, which are exemplified in the following detailed disclosure, and the scope of the in-vention will be indicated in the claims.
For a fuller understanding of the nature and objects of the invention, reference should be had to the following de-tailed descrlption taken in connection with the accompanying IL7.5 drawinqs in which E~ig. 1 is a longitudinal cross section through theenvelope portion of one embodiment of a projection television tube constructed in accordance with this invention;
Fig. 2 is plan view of the internal surface of the face plate of the tube envelope of Fig. l;
Fig. 3 is an expanded, perspective view illustrating the assembly of the projection television tube envelope of Fig. l;
Fi~s. 4-9 illustrate in cross sectional detail dif-ferent techniques for sealing the face plate and cylindrical sections of the projection television tube envelope;
Figs, 10 and 11 illustrate the incorporation of heat transfer means arranged to cool the target surface;
Figs. 12-14 are longitudinal cross sections through two additional embGdiments of the projection television tube envelope constructed in accordance ~ith this invention in which the target support member comprises a target substrate affixed to the face plate;
Pigs. 15 and 16 are longitudinal cross sections through another embodiment of a projection television tube envelope con-structed in accordance with this invention incorporating a sepa-rate target support means;
Fig. 17 is a ~lan view of the target support means used in the envelope embodiment of Figs. 15 and 16;
Fig~ 18 is a longitudina] cross section of a projection television tube constructed in accordance with this invention and incorporating the tube envelope of Fig. l;
Fig. 19 is a simplified diagram of a projection tele-vision system; and 7~
Fig. 20 illu~trates diagrammatically the ef~ect of a small lateral shift in the center of the fiphere defining the target surface, relative to the mirror ~urface, to compensate for the optics of a projection television system.
Figs. 1 and 2 illustrate a preferred embodiment of the projection television tube envelope of this invention; and Fig. 3 is an expanded view of the three components forming the envelope. A complete projection television tube incorporating the envelope of Figs. 1-3 is shown in ~ig. 18 and described below.
The projection television tube envelope of this in-vention, generally designated by the reference numeral 10, is shown in Fig. 1 to be formed of three principal components which comprise an optically transparent face plate 11, a cylinder-like wall member 12 which may be slightly flared, and an end plate 13 to ~hich is joined a central neck section 14. In keeping with known practice, the annular internal surface 15 (Fig. 3) of end plate 13 facing the internal wall of face plate 11 is configured with the sphericity of a sphere having a center 16 and a radius ~ep That annular portion of surface 15 within en-velope volume 17 is coated~ e.o., aluminized, to provide a mir-ror 18. Thus, mirror 18 can be said to be a spherical segment or, more conveniently, to he of spherical configuration, a term used hereinafter to denote a portion of a spherical surface.
~t will, of course, be appreciated that mirror 18 is not as thick as shown in Yig. 1. However, mirror and target surfaces are exaggerated in the drawings for ease of identificationO
The internal surface 19 of neck 14 is coated with a suitable electrically conductive coating, such as a colloidal graphite coating sold under the tradename of Dag. This coating ~,.
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extendq up to and in contact with the erlge of mirror 18.
In the Schmidt ~ystem a beam of electrons is directed against a phosphor tar~et 20 within a sp~cified target ~urface area referred to as the raster 21 (Fig. 2). The target surface, generally rectangular in shape, must be of a spherical configura-tion, i.e., configured with the sphericity of a sphere of radius Rt which has a center essentially coincident with center 16 of the sphere defining the configuration of the surface of mirror 18.
In this manner the radial distance D~ between mirror 18 and target 20 remains essentially constant. The attaining and maintaining of this distance Dc is critical to the manufacturing of pro-jection television tube envelopes and the tubes incorporating them.
In accordance with the practice of this invention the positioning of target 20 to achieve the desired relationship with mirror 18 is accomplished by providing the cylinder-like member, thereinafter, for convenience, referred to as the cylindrical member) with an annular face plate sealing end 22 configured and positioned relative to mirror 18 such that a sphere in stable position resting on sealing end 22 will have its center of cur-vature essentially coincident with the center of curvature of the sphere defining the surface of mirror 18. Thus, as diagram-med in Fig. 1, sealing end 22 is configured with the sphericity of a sphere of radius P.Se with a center essentially coinciding with center 16 of the sphere of radius P~ep defining the surface of mirror 18. Alternatively, sealing end 22 may be configured to present a surface to position and support a s-phere of radius Rse as detailed be1ow in conjunction with the description of Figs. 6 and 8.
By affixing target 20 to a target support member which 7~
engages the sealing end 22 of cylinder-like member 12, the target support member and the target affixed thereto may experience small lateral motion along the sealing line without causing any effective shifting of the target surface relative to the mirror, Thus, a lateral motion of the target support member of up to as much as from about 0.050 to about 0.070 inch (about 1 2S to about 1.75 mm) from true sealing surface alignment during as-sembl~ and sealing will not adversely affect the optical char-acteristics of the projection tube incorporating the envelope so constructed, since the critical distance Dc will be maintained.
Thus the role of the cylindrical member, in addition to that of forming a portion of the envelope wall, is that of accurately positioning the target surface relative to the mirror surface to attain the desired, predetermined spacing Dc. This means that the height of the cylindrical member is the one critical dimension in the tube envelope construction7 Because the cylindrical member can take various cross sectional configurations, a cylindrical member of predetermined height may be defined as that cylinder-like member which, when inter-posed between the end plate mirror and the spherical surfaceof the target holding means results in the essential coinci-dence of the centers of curvatures of the mirror and target.
The cylindrical member thereby becomes the envelope component serving as the sole means for positioning the target relative to the mirror.
~ s will be apparent from the following detailed de-scription, the target support member may take any of a n~er of forms, so long as it has a sealing edge configured to engage the sealing end of the cylindrical member, the sealing edqe being de-fined. by the surface of that sphere which, in its stable posi-tion, rests on the sea].ing end 22 of cyli.ndrical member 12 and has its center essentially coincid~nt with center 16 of mirror 1~. In the tube envelope embodiment of Figs. 1-3, face plate 11 serves in the dual role of target support member and face plate, the target being deposited directly on the internal surface 23 of face plate 11. Typically, target 20 will be formed by vacuum depositing an aluminum fi:Lm on surface 23 and then deposit-ing the desired phosphor over the aluminum. ~s will be seen in Pig~ 2, the actual target area 20 is made somewhat larger in both dimensions than the raster 21-to be printed on it, For example, it will generally be desirable to form the target ahout 0.060 to about 0.06~ inch (about 1.5 to about 1.75 m~,) larger than raster 21 on each of the four sides to compensate for any of the allo~-able lateral mov~ment o~ the target support mem~er in asse~bling and sealing the envelope.
~ .lthouyh target 20 is illustrated ~or convenience ir the drawiny to have a considerable thickness, it should be under-stood that fcr all practical purposes it may be considered to have a surface coincident with internal surface 23 of face plate 11, or of any other substrate on which it is deposited. This, in turn, reans that the internal surface 23 of face plate 11 an~
the surface of target 20, in order to meet the requirements for target alignment, are also confi~ured with the sphericit~
Gf a sphere essentially identical to that sphere of radius RSe.
~ence, the spherical surfaces defining face pl.ate 11 and taraet :~ 20 can be seen to have radii Rfp and Rt which are esser.tiall~
e~ual to Rse. ~hus, in the preferred envelope embodiment shown in Pigs. 1~3 the spherically configured face plate is affixed to sealing end 22 in any suitable manner such as illustrated in Figs. 4-6 and 8 to achieve the desired radial-distance Dc between ~ .'3mirror and t~rgct.
The ~nvelope embodiment of Figs. 1-3 is constructed of three separ~te components as shown in the expanded view of Fig. 3. In such a case, race plate 11, cylindrical member 12 and end plate 13 with neck 14 are molded of an appropriate glass and machined to define the desired configuration of the mirror and sealing surfaces. In those ènvelope embodiments in which the cylindrical me~ber 12 is to he affixed to the end plate, it is also necessary to shape the end plate sealing end 25 of cylin-drical member 12 to essentially conform or to present a surfacewhich essentially conforms in sphericity to that of mirror 18, i.e., to the internal surface 15 o~ the end plate. Thus it may be seen that the end plate sealing end of cylindrical member 12 presents a surface which is configured with the sphericity of a sphere of radius Rep.
Plthough it is ~enerally preferable to form cylindrical member 12 with G slight flare, it is also, of course, within the scope of this invention to form it with any other suitable con-figuration. It will, however, be appreciated that the critical dimension, Dc, is determined by the distance maintained between the target support member and mirror and that this distance is determined solely by the height dimension of cylindrical member, takina into account, if necessary, the thickness of any frit layer or layers interposed between the components~
Before discussing the various techniques ~hich may be used to seal together the components of the envelop-e, it will be convenient to complete the description of the remaining ele-ments of the envelope. In accordance with known techniques in ; constructing the envelope, the internal surface 26 of cylindrical member 12 is coated with an electrically conductive coating, e.g., 7 ~
a suitable colloidal graphite coating, and an electrical con-nection is provided between mirror 18 and targek 20. This elec-trical connection comprises a film strip 27 of an electrically conductincJ material, ~.g., aluminum, coated on face plate sur-face 23 contacting target 20 (Fig. 2) and terminating in an en-larged contact area 28, e.g., one coated with colloidal graphite;
and an electrically conductive wire 29, e.g., of stainless steel, shaped to force its dimpled ends into contact with area 28 and mirror surface 18. An external anode terminal 30 is inserted through and sealed to the wall of cylindrical member 12, by frit 31, to contact wire 29 through spring clip 32 thus providing one of the necessary electrical contacts for the projection tele-vision tube incorporating the envelope. Alternatively, this an-node terminal ma~ be inserted through and sealed in the end plate.
A correcting lens 33 is held in spaced relationship to face plate 11 by a lens supporting ring 34 which when seated on face plate 11 results in automatically aligning lens 33 with re-spect to the other optical components of the tube. Supporting ring 34 is affixed to the envelope through a plurality of spaced an~led arms 35 held to cylindrical member 12 by an adustable band 36. Lens 33 not only serves to correct the spherical aber-rations inherent in the optics of the system, but also, with support ring 34, protects face plate 11. The actual design and positioning of lens 34 is within thc capabilities of an artisan of ordinary skill in the optical arts; and it will be apparent that the proper seIection of correction lens with slightly dif-ferent effective powers can he used to correct for any small dimensional inaccuracies of the envelope.
Figs. 4-9 illustrate in cross sectional detail several 30 ways in which~face plate 11, cylindrical member 12 and end plate 13 of the envelope embodiment of Yigs. 1-3 may be sealed together.
In the sealing modifi~ation of Figs. 4 and 5, the face plate sealing end 22 of cylindrical member 12 is ground to hav~ the required s~hericity and the end plate sealing end 25 i5 ground to the same sphericity as mirror 18. Sealing is accomplished through the use of two layers o~ frit 39 and 40 (typicall~ a commercially available lead oxide frit) between the face plate and cylindrical-member and between the cylindrical member and end plate, respectively. It will be appreciated that in this sealing embodiment it is necessary to accurately control the thickness of frit layers 39 and 40 and to subtract the combined thicknesses of these frit layers in calculating the height dimension of cylindrical member 12 which controls the distance, Dc, between the target and mirror.
The actual thickness of frit layers 39 and 40 may be controlled by the use of shim means shown in the modification of Fig. 5 to be accurately graded beads 41 formed of a glass having a melting point sufficiently higher than the activation temperature of the frit material so that they will retain their origir.al shape during sealing. It is also, of course, desirable t~.at the glass from which the beads 41 are formed has a coeffi-cient of thermal expansion essentially the same as that from which the components of the envelope are made. Other suitable shim means such as shcrt glass rods or tetrahedrons of appropriate dimensiGns may be used. In general, it will be preferable to use frit thicknesses ranging between about 0.005 and about 0.015 inch (about 0.1 and about 0.4 mm). Thus, 0.010 inch (0.25 mm) diameter glass beads may be cited as exemplary shim means.
Figs. 6-9 illustrate several sealing modifications which do not require the making of allowances for frit thick-ness in determirlin~ and achieving the desired accurate heiyht dimension of the cylindrical member. In the modlfication of Fig. 6, surface 22 of cylindrical member 12 is ground to have the desired sphericity and then a frit groove 42 is cut out to contain frit A3, taking care to maintain the integrity of internal line contact 44 so that it and the remaining portion of surface 22 present a sealing surface with the desired spher-icity~ In similar manner, surface 15 of end plate 13 has a frit groove 45, containing frit 46, cut in it to provide a con-tact line 47 which, with the remaining portion o surface 15,provides the required sealing surface. Alternatively, as shown in Fig. 7, a frit groove 48 may be cut in sealing end 25 of the cylindrical-member, retaining a portion of spherically confi~ured end surface 25 and creating a co~tact line 4g on the spherical surface with radius Rep.
Fig. 8 illustrates a sealing modification in which two parallel circular contact lines 50 and 51 in face plate sealing end 22 of cylindrical member 12 are provided for seat-ing face plate 11 serving as the target support member. Between these contact lines a frit space 52 is provided. It will, of course, be appreciated that both contact lines 50 and 51 must lie on the required spherical surface of the sphere with radius RSe, corresponding to surface 22 of the face plate sealing end of cylindrical member 12. Thus, these two parallel contact lines 50 and 51 meet the requirement of presenting a surface which conforms in sphericity to the prescribed sphere of radius P~se and center 16. E~arallel contact lines 53 and 54, defining frit space 55 between them, may also be cut in the peripheral surface of end plate 13 to seal cylindrical member 12 thereto.
Finally, as ~hown in Pig. 9, the peripheral surface of end :

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plate 13 may be Pormed to have an essentially flat ~urface 56 so that the end plate sealing end 25 of cylindrical member 12 form a contact line 57 with the end plate and leaves a frit space 58 for sealing.
It will be apparent that a number of combinations of sealing surfaces may bc used in constructing the projection television tube envelope and tube of this invention so long as the face plate sealing end surface of the cylindrical memher is configured as previously defined.
The face plate configuration of the projection tube of this invention permits the incorporation of external cooling means for the target, thus offering the possibility of attain-ing a higher light level and a longer tube life. As shown in Fig. 10, a ccntoured plate 60 formed of a material-having rela-tively hish heat conductivity, e.g., copper, is bonded to ma~e thermal contact with the external surface 61 of face plate 11 and positioned to correspond with the position of target 20.
Extending upward from plate 60 and in heat transfer contact therewith is a post 62 having one or more heat dissipating fins 63 affixed thereto.
Fig. 11 illustrates a modification of the external cooling means of Fig. 10 in that the plate 60 is set in a well ; ~4 cut in face plate surface 61. Inasmuch as the thickness of the face plate wall through which target heat is transferred ~ by conduction to plate 60 is less than in the arrangement of :~: rig. lo, the cooling of targct 20 is somewhat more efficient ;~ in tbe arrangement of Fig. 11. .
The projectlon television tube envelope embodiments shown in Figs. 12-14 use the face plate as a part of the target support means while providing flexlbility in the tube optlCs.

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In the envelope embodiment of Figs. 12 and 13, in which the same reference numbers are used to identlfy like elen,ents of Fig. 1, the face plate 11, cylindrical member 12 and end plate 13 are configured as described in connection with Figs. 1 and 3 and sealed by any suitable technique such as one of those de-scribed in conjunction with Figs. 4-9. However, the target 20, deposited as previously described, is on the surface of a substrate 70 preferably formed of the same glass as the en-~elope or of a glass having essentially the same coefficient of thermal-expansion as the envelope glass. Target substrate 70 preferably has two or more feet 71, the surfaces 72 of which are ground to have the same sphericity as internal wall 23 of face plate 11 to accurately locate target 20 on face plate 11 when affixed thereto with frit 73 which is applied in a quantity to-fill a pGrtiOn of the sp~ce between substrate 70 and s~rface 23. Thus, the t~rget support means in this embodiment is comprised of f~ce plate 11 and ta~get substrate 70 affixed thereto.
In the e~bodiment of Fig. 12, the target substrate provides a target 20 having a surface configure~ Wi th the sphericity of a sphere of radius ~t and a center which essen-tially coincides with center 16 of the mirror-defining spherical surface. Thus, although Rt is somewhat greater than Rse, the conditions set forth for the support of the target relati~e to the mirror are met since small lateral excursions of face plate 11 with target substrate 70 affixed thereto will have vir-tually no effect on the radial distance, ~c' between target and mirror.
In order to provide the electrical connection between target 20 and mirror 18, a narrow film of aluminum 74, or other 7~
electrically conductive material, (Fig. 13) may be deposited beginning at the target edge and running along the side and substrate surface opposite the target surface to make contact thxough a conductive clip 75 with a conductive film 27 deposited on surface 23 of face plate 11 and terminating in a contact area 28 as shown in Fig. 2. The remaining connection through a wire 29 is identical to that shown in Fig. 1. It is, of course, within the scope of this invention to provide any other suit able electrical connection between the target, anr.od~ terminal and mirror.
The optics of the embodiment of Fig. 12 are such that a correction lens need not be used since face ~late 11 may serve that purpose. This is made possible because there is some freedom in this arrangement to locate the face plate with respect tG the mirxor; and, if required, the surfaces of the face plate may be configured with reference to the mirror sur-face to enhance its optical corrective characteristics. It is also, of course, possikle and ~7ithin the scope of this invention to add to the embodiment of ~ig. 12 an appropriately configured corrective l~ns in the manner shown in FigO 1 to provide a tele-vision projection tube of the highest performance capabilities.
The projection television tube envelope of Fig. 14 employs a target substrate 80 affixed by frit 81 to a flat face plate 82 as the target support means engaging the cylin-drical member sealing end surface 22. In this embodiment the peripheral enga(~ing surface 83 of face plate 82 is ground to have the sphcrlcity of a sphere of radius P~Se and the target substrate 80 to have the sphericity of a sphere of radius Rt, both having centers of curvature essentially coincident with that of the sphere of radius ~ep defining the mirror surface.

It will be apparent that this embodiment also meets the require-ments for the envelope components.
The use of an essentially flat face plate necessitates, for qood performance, the incorporation of ~ correction lens 85 supported on a lens support B6 which is sealed to the outer rim of face plate 82. The configuration of lens 85 is known in the art and it is positioned so that its optical center es-sentially coincides with spherical center 16; and in the as-sembly of the envelope components, lens 85 is located by well-known optically observed self-imaging techniques.
In the tube envelope embodiment shown in Figs. 15-17 the end ~late 90 and cylindrical member 91 are formed as an in-tegral piece 92 prior to the sealiny of the face plate to the cylindrical member. Thus, cylindrical member 91 may be flame sealed to end plate 90 or these two components may be initially moldec as an intesral piece. This arrangement is, of course, applicable to an~ of the tube envelope embodiments of this in-vention. Alternatively,the envelope of Fig. 15 may be constructed of a separate end plate and cylindrical member as previously described. The embodiment of Figs. 15-17 also incorporates a target holding means which is separate and distinct from the face plate. In this arrangement the inner surface95 of the face plate sealing end of cylindrical member 91 is ground to have the required sphericity, i.e., that of a sphere of radius Rse; and the outer surface 96 is ground flat to support and have sealed thereto, through frit 97, a flat, circular face plate 98 (see Fig. 16).
The tarqet support means 100, shown in a top plan view in Fig. 17, comprises a circular positioning and seating ring 101 from which narrow supportinq spokes 102 extend inwardly .

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to hold target substrate 103 on which target 20, defining raster 21, i5 deposited. It will be appreciated from Figs. 15-17 that target support means 100 is shaped to have the configuration of a segment of a sphere with radius Rt (essentially equal to Rse) to provide the required surface configuration for target 20 and the enga~ement of targct positioning and seating ring 101 with spherically configured sealing surface 95 of the cylindrical member. Thus through the use of this spherically configured target support means and the spherically configured surface 95 (or one which conforms to a spherical surface such as shown in Fig. 8) the desired positioning of the entire target surface 20 with respect to mirror 18 is assured. The target support means 100 are preferably formed from stainless steel using well-known etching techniques.
In order to maintain continuous engagement of target support ring 101 with surface 95, a plurality of spring clips 104 is located around the target support between the internal wall 105 of face plate 98 and ring 101. If target support means 100 is formed of an electrically conducting metal it may serve as an electrical connection between the target and wire 2g.
Alternatively, as shown in Figs. 16 and 17, the electrical con-nection between the target and mirror may be through a thin conductive strip 106 terminating in an enlarged conductive area 107 and wire 29 contacting area 107 in the ~anner descri~ed for the envelope of Fig. 1.
It will be apparent from the above detailed descrip-tions of the embodi~ents of the projection television tube en-velope which are illustrated as exemplary of the inventlon, that many combinations of target support means, envelope con-figurations,,sealing techniques and electrical connections L7;~

within the tube are possible.
Fig. 18 is a longitudinal cross section of a pro-jection television tube constructed in accordance with this in-vention, that is one includiny the tube envelope of this inven-tion~ The tubc envelope illustrated in the tube of ~ig. 18 is that of Fig. 1-3. The tube may, however, use any of the envelope embodiments shown or described. In kee~ing with well-accepted projection television tube design, neck 14 is sealed off to provide fluid-tight evacuated envelope volume 17. An electron gun 110 of well-known design is sealed in neck 14 and is shown to comprise a cathode 111 with associated heater 112, grids 113 and 114 and anode 11~ which is electrically connected to annode terminal 30 through the electrical conducting coating 19 which extends down through the internal wall of neck 14 to make con-tact with annode 115, mirror 18, and wire 29. The projection tele~-ision tube has a magnetic focusing lens assembly 116, a convergence controllir.g means 117 and deflection controlling means 118, all of ~hich are standard components.
In the precedlng detailed descriptions of the television projection tube envelope~end of the tube incorporating the en-velope in accordance with this invention, the centers of curva-tures of the spheres defining the contours of the mirror, the target surface and the face plate sealing end surface of the cylindrical men~er have been defined as being essentially coinci-dent. This term as used herein is meant to include any combina-tiGn oi the locii of these centers which satisfies the require-ment that the radial distance, Dc, from any poi~t on the target surface to the mirror surface is a constant value within a Fre-determined tolerance range which permits the achievement of the deslred optical characteristics and performance of the tube.
:

.

'7~
As will be apparent to tho~e skilled in the ar~, the real centers of curvatures of the optical element~ may be slightly displaced to achieve the optimum optical design which compensates for work-ing at a finite distance.
Thus, for example, in a televisi.on projection tube of what might be termed a "standard size" having a radial distance, Dc, from target to mlrror of about four inches (about 10 cm) the tolerance r~r,ge for Dc is from about ~.002 to about 0.00 inch (fro~ about 0.050 to about 0.10 mm) greater or less than the predetermined radial distance. This, in turr" means that for such a "standard-size" tube, a slight shifting of the locus of the center of curvature of the s~here corresponding to the target surface either up or down on the tube a~is and/or laterally a~ay from the axis ~hich results in a lateral motion of the target support ~eans of no greater than about one-sixteenth of ar. inch ~about 0.06 to about 0.07 inch or about 1.~ to abcut 1.75 mm) fror perfect ali~nment can be tolerated during assembly and sealing.
In fact, a slight lateral shifting of the locus of the center of curvature defining the target surface configura-tion fro~, the tube axis is required in a tele~ision projection system which uses three separate projection tubes, one each for projecting red, blue and green images. It is not, of course, ph~sically possible to position three tubes to have their ax~s coincident and the a~es cannot be parallel since the images rom : : the three tubes must meet and be precisely superimposed on the screen. Moreover, as will be seen diagrammed in Fig. 19, in order to provide a direct line of sight from the screen 125 to the viewer 126, it: is necessary to-direct the images from the three tubes housed in projecti.on system 127, at an angle, e.g., :~ ~ ~23-7;~
from about S to 10. Thus, it is highly desirable if the pro-jection television tube is built to Gompen.sate for these factors.
This compensation is readily accomplished in the practice of this invention by a slight lateral shift of the target center of curvature within the limits previously defined.
This may be seen in Fig. 20 wherein the magnitude of this lateral shift is exaggeratered better to illustrate the effect. It ~7ill be seen that when the center 16 of the target suface 20 is shifted to 16a, the target surface 20a also shifts which results in a slight but effective shift of the beam emitted by the tube, thus making it possible to use three projection tubes to pre-cisely superimpose their images on a screen~ Generally, such a slight lateral shift of the target center oE curvature will range from about 0.005 to about n.OlQ inch (from about 0.13 to about 0.25 mm). Such a latexal shift, while accomplishing the desired focusing of the beam, ~ill not violate the prescribed tolerance range for Dc. Moreover, any consequent departure, ~ithin the establishecl set limits, from the ideal position will not cause any observable degradation ~ithin the color television require-mer.ts.

~ he components comprising the envelope, (face platecylindrical mem~er, end plate an~ tubulation for the neck) are pre erably formed from an electronic glass, the glass in each component havincJ a coefficient of thermal expansion as nearly as possible the same as that of the other components in any one envelope. It is also possible to form the cylindrical mem-ber of a ceramic material or metal so long as it also has a coefficient of thermal expansion approximating that of the glass in thc other components.

-2~-'7~
The process of this invention may be il~ustrated using the formation of the projection television tube of Fig. 18 as an example. The three components of the envelope and a section of tubing to be used as the neck tube are molded and the optical surfaces of the face plate and end plate as well as the seal-ing surfaces of the cylindrical member are ground and polished to the desired configurations. The optical surfaces of th~
components are then completed. The target, conductive strip and terminating conductive area are deposited on the internal surface of the face plate. The location of the target within the required area on the face plate surface may be accomplished, for example, by the use of a photosensitive binder in the manner employed in the manufacture of direct-view television tubes.
The internal surface of the cylindrical member is coated ~ith an opaque conductive coating, the annode terminal is sealed in the ~!all and the conductive ~Jire is attached. The mirror is deposited on the end plate surface and the electrically conduc-tive coating is applied to the internal neck joint surface of the face plate and the internal surface of the neck tubulation to a predetermined line. The open neck tubulation is then flame sealed to the end plate. ~t this point, the required amcunt of frit is applied to the two sealing ends of the cylindrical member and the face plate and end plate are positioned on the cylindri-cal member for sealing of the envelope assembly by bakina in an oven. This positioning is accomplished by aligning the outer edges of the face plate and cylindrlcal member and seating the cylindrical member on the end plate to ensure complete continuous contact therewith.
In a typical bakir.g and sealing cycle, 45 minutes are taken to bring the envelope assembly up to the frit activation temperature of about 44SC. This activation temperature level is maintained for about 30 minutes and then about one and one-half hours are used for cooldown. It has been found preferable during the later part of the warmup and early part of the frit activation heating portions of the cycle to raise the temper-ature o~ the cylindri.cal member near the face plate to some-what above, e.g., about 30~C above, the temperature of the face plate. This may be done by directing infrared radiation locally on the appropriate area of the cylindrical mem~er surface.
This additional localized heating is believed to control the direction of induced strains and thus to form a st~onger tube envelope.
In accordance ~ith known practice, the components of the electron gun are then flame sealed into the tube neck, the temperature of the tube is raisea to between 3~0C and ~00C, the cathode is electrical].y activated, and finally the en~ of the nec~ is sealed off. Finally, the correcting lens is attached in the r.,ar,r.er previGusly described and the external focusing means affixed to the neck.
lt is apparent from the above detailed description of the prG jection television tube envelope, of the completed tube and of the process for forming the envelope and the tube, that this invention provides a true advancement in the projection television art by providing a relatively simFle, inexpensive, optically acceptable television projecti.on tube~ This advance-ment is achieved through the configuration of the components formins the tube envelope and by the use of these envelope com-ponents as the sole means to position the target relative to the mirror. Moreover, only one component, the cylindrical mem-ber, need be formed with one very accurate dimension.

: -26-L7~
It will thus be seen that the ob~ects set forth above, among those made apparent from the preceding description, are e~ficiently attained and, since certain changes may be made in carrying out the above process and in the articles set forth without departing from the scope of the invention, it is in-tended that all matter contained in the above desciption or shown in the accom~,anying drawings shall be interpreted as il-lustrative and not in a limitinc sense.

Claims

The embodiments of the invention in which an ex-clusive property or privilege is claimed are defined as follows:

1. An envelope for a projection television tube comprising, in combination (a) an end plate, the internal surface of which de-fines a spherically configured mirror;
(b) a cylindrical member affixed to said end plate and terminating in an annular face plate sealing end configured and positioned such that a sphere in stable position resting on said sealing end will have its center of curvature essentially coincident with the center of curvature of the sphere defining the surface of said mirror;
(c) target support means engaging said sealing end and supporting a target defining a spherical surface having a center of curvature essentially coincident with said center of curvature of said sphere determining the configuration of said face plate sealing end; and (d) a face plate sealed to said cylindrical member.

2. An envelope for a projection television tube in accordance with claim 1 wherein the surface of said face plate sealing end is configured as a spherical surface.

3. An envelope for a projection television tube in accordance with claim 2 wherein said face plate is sealed to said cylindrical member through a frit layer of a predetermined thickness.

4. An envelope for a projection television tube in accordance with claim 3 wherein said frit layer includes shim means determining said thickness.

5. An envelope for a projection television tube in accordance with claim 4 wherein said shim means comprise glass beads.

6. An envelope for a projection television tube in accordance with claim 1 wherein said face plate sealing end comprises a spherical surface in combination with a frit groove cut to provide a contact line.

7. An envelope for a projection television tube in accordance with claim 1 wherein said face plate sealing end comprises parallel contact lines having a frit groove defined therebetween.

8. An envelope for a projection television tube in accordance with claim 1 wherein said cylindrical member is integral with said end plate.

9. An envelope for a projection television tube in accordance with claim 1 wherein said cylindrical member is separate from said end plate and sealed thereto through an end plate sealing end.

10. An envelope for a projection television tube in accordance with claim 9 wherein said end plate sealing end of said cylindrical member comprises parallel contact lines having a frit groove defined therebetween.

11. An envelope for a projection television tube in accordance with claim 9 wherein said end plate sealing end of said cylindrical member has a spherical configuration essential-ly identical to that of said sphere defining said surface of said mirror.

12. An envelope for a projection television tube in accordance with claim 11 wherein said end plate is sealed to said cylindrical member through a frit layer of a predetermined thickness.

13. An envelope for a projection television tube in accordance with claim 12 wherein said frit layer includes shim means determining said thickness.

14. An envelope for a projection television tube in accordance with claim 11 wherein said end plate has a peripheral sealing edge comprising a spherical surface in combination with a frit groove cut to provide a contact line.

15. An envelope for a projection television tube in accordance with claim 11 wherein said end plate has a periph-eral sealing edge comprising parallel contact lines having a frit groove defined therebetween.

16. An envelope for a projection television tube in accordance with claim 11 wherein said end plate has a flat peripheral edge the inner boundary of which is adapated to form a contact line with the inner wall of said cylindrical member, said flat peripheral edge defining a frit space between its sur-face and said end plate sealing end of said cylindrical member.

17. An envelope for a projection television tube in accordance with claim 1 wherein said sphere determining the configuration of said face plate sealing end of said cylin-drical member and the sphere determining said spherical-surface of said target are essentially identical.

18. An envelope for a projection television tube in accordance with claim 16 wherein said face plate is said target support means and said target surface is affixed directly to the internal surface of said face plate.

19. An envelope for a projection television tube in accordance with claim 17 wherein said target support means com-prises a target support member separate and distinct from said face plate.

20. An envelope for a projection television tube in accordance with claim 19 wherein said target support member has an overall spherical configuration essentially identical to said sphere determining the configuration of said face plate sealing end of said cylindrical member and comprises a circular positioning and seating ring having inwardly extending spokes supporting a target substrate.

21. An envelope for a projection television tube in accordance with claim 20 wherein said face plate sealing end of said cylindrical member comprises an inner spherically configured surface arranged to engage said positioning and seating ring and an outer flat surface for sealing said face plate thereto.

22. An envelope for a projection television tube in accordance with claim 21 wherein said face plate is flat and including means between said positioning and seating ring and said face plate to urge said ring into engagement with said inner spherically configured surface.

23. An envelope for a projection television tube in accordance with claim 1 wherein said target support means com-prises in combination said face plate and a target substrate affixed to said face plate.

24. An envelope for a projection television tube in accordance with claim 23 wherein said face plate is of a spher-ical configuration essentially identical to said sphere de-termining the configuration of said face plate sealing end of said cylindrical member and said target substrate is affixed by frit in a spaced relationship to said face plate accurately controlled by spacer feet the surfaces of which are ground with the same sphericity as the internal surface of said face plate.

25. An envelope for a projection television tube in accordance with claim 23 wherein said face plate is essentially flat and has a peripheral sealing edge of a spherical configura-tion essentially identical to said sphere determining the con-figuration of said face plate sealing end of said cylindrical member.

26. An envelope for a projection television tube in accordance with claim 1 wherein the dimensions of the surface of said target are slightly greater than the dimensions of the raster to be printed thereon.

27. An envelope for a projection television tube in accordance with claim 1 including correcting lens affixed to said face plate to correct for spherical aberrations.

28. An envelope for a projection television tube in accordance with claim 27 wherein said face plate is of a spher-ical configuration essentially identical to said sphere de-termining the configuration of said face plate sealing end of said cylindrical member and said correcting lens is held in spaced relation to said face plate by support means seated on said face plate such that said correcting lens is aligned with respect to said mirror and said target.

29. An envelope for a projection television tube in accordance with claim 27 wherein said face plate is essentially flat and said correction lens is affixed through lens support means to said face plate.

30. An envelope for a projection television tube in accordance with claim 1 including heat dissipation means as-sociated with said target.

31. An envelope for a projection television tube in accordance with claim 30 wherein said face plate is of a spher-ical-configuration essentially identical to said sphere de-termining the configuration of said face plate sealing end of said cylindrical member with said target deposited directly on the internal surface of said face plate and wherein said heat dissipation means comprises heat conducting plate means affixed on the external surface of said face plate correspon-ding in location to said target and heat exchange surface means arranged to conduct heat from said target through said face plate wall to the surrounding atmosphere.

32. An envelope for a projection television tube in accordance with claim 31 wherein said plate means is placed in a wall in said face plate whereby the thickness of said face plate through which said heat from said target is conducted is reduced.

33. An envelope for a projection television tube in accordance with claim 1 including connecting means to electri-cally connect said target and said mirror.

34. An envelope for a projection television tube in accordance with claim 33 wherein said connecting means comprise, in combination, an electrically conductive film, in contact with said target and deposited on said target support means, a con-ductive wire electrically connecting said film and said mirror, and an anode terminal extending through the wall of said en-velope.

35. An envelope for a projection television tube, comprising in combination (a) an end plate, the internal surface of which de-fines a spherically configured mirror;

(b) a face plate the internal surface of which is configured with the sphericity of a sphere having a center of curvature essentially coincident with the center of curvature of the sphere defining the surface of said mirror;
(c) a target deposited on said internal surface of said face plate whereby said target is of spherical configura-tion;
(d) a cylindrical member affixed to said end plate and terminating in an annular face plate sealing end configured and positioned such that said face plate in stable position resting on said face plate sealing end and sealed thereto will have its center of curvature essentially coincident with the center of curvature of said sphere defining the surface of said mirror, the height of said cylindrical member serving as the sole means for affixing said target a predetermined radial distance from said mirror.

36. An envelope for a projection television tube in accordance with claim 35 wherein the surface of said face plate sealing end is configured as a spherical-surface.

37. An envelope for a projection television tube in accordance with claim 36 wherein said face plate is sealed to said cylindrical member through a frit layer of a predetermined thickness.

38. An envelope for a projection television tube in accordance with claim 37 wherein said frit layer includes glass beads serving as shim means determining said thickness.

39. An envelope for a projection television tube in accordance with claim 35 wherein said cylindrical member is separate from said end plate and sealed thereto through an end plate sealing end.

40. An envelope for a projection television tube in accordance with claim 39 wherein said end plate sealing end of said cylindrical member has a spherical configuration essential-ly identical to that of said sphere defining said surface of said mirror and is sealed to said end plate through a frit layer of a predetermined thickness.

41. An envelope for a projection television tube in accordance with claim 40 wherein said frit layer includes glass beads serving as shim means determining said thickness.

42. An envelope for a projection television tube in accordance with claim 35 wherein the dimensions of the surface of said target are slightly greater than the dimensions of the raster to be printed thereon.

43. An envelope for a projection television tube in accordance with claim 35 including correcting lens held in spaced relation to said face plate by support means seated on said face plate such that said correcting lens is aligned with respect to said mirror and said target.

44. An envelope for a projection television tube in accordance with claim 35 including heat dissipation means as-sociated with said target and comprising heat conducting plate means affixed on the external surface of said face plate cor-responding in location to said target and heat exchange sur-face means arranged to conduct heat from said target through said face plate wall to the surrounding atmosphere.

45. An envelope for a projection television tube in accordance with claim 35 including connecting means to electrical-ly connect said target and said mirror.

46. An envelope for a projection television tube in accordance with claim 45 wherein said connecting means comprise, in combination, an electrically conductive film in contact with said target and deposited on said internal surface of said face plate, a conductive wire electrically connecting said film and said mirror, and an anode terminal extending through the wall of said envelope.

47. An envelope for a projection television tube in accordance with claim 46 wherein the internal wall of said cylindrical member is coated with an opaque, electrically con-ductive coating.

48. A projection television tube comprising, in com-bination (a) an end plate, the internal surface of which defines a spherically configured mirror;
(b) a neck sealed to said end plate;
(c) a cylindrical member affixed to said end plate and terminating in an annular face plate sealing end configured and positioned such that a sphere in stable position resting on said sealing end will have its center of curvature essentially coincident with the center of curvature of the sphere defining the surface of said mirror;
(d) target support means engagng said sealing end and supporting a target defining a spherical surface having a center of curvature essentially coincident with said center of curvature of said sphere determining the configuration of said face plate sealing end;
(e) a face plate sealed to said cylindrical member;
(f) connecting means to electrically connect said target and said mirror and to provide an external anode ter-minal;
(g) electron gun means sealed within said neck ar-ranged to produce an electron beam to print a raster on said target; and (h) electron beam focusing means.

49. A projection television tube in accordance with claim 48 wherein the surface of said face plate sealing end is configured as a spherical surface and said cylindrical member is separate from said end plate and sealed thereto through an end plate sealing end having a spherical configuration essentially identical to that of said sphere defining said surface of said mirror.

50. A projection television tube in accordance with claim 49 wherein said face plate and said end plate are sealed to said cylindrical-member through frit layers of predetermined thickness.

51. A projection television tube in accordance with claim 50 wherein said frit layers include glass beads serving as shim means determining said thickness.

52. A projection television tube in accordance with claim 51 wherein said sphere determining the configuration of said face plate sealing end of said cylindrical member and the sphere determining said spherical surface of said target are essentially identical.

53. A projection television tube in accordance with claim 48 wherein said face plate is said target support means and said target surface is affixed directly to the internal surface of said face plate.

54. A projection television tube in accordance with claim 48 wherein said target support means comprises a target support member separate and distinct from said face plate.

55. A projection television tube in accordance with claim 48 wherein said target support means comprises in com-bination said face plate and a target substrate affixed to said face plate.

56. A projection television tube in accordance with claim 55 wherein said face plate is of a spherical configura-tion essentially identical-to said sphere determining the con-figuration of said face plate sealing end of said cylindrical member and said target substrate is affixed by frit in a spaced relationship to said face plate accurately controlled by spacer feet the surfaces of which are ground with the same sphericity as the internal surface of said face plate.

57. A projection television tube in accordance with claim 48 wherein the dimensions of the surface of said target are slightly greater than the dimensions of said raster.

58. A projection television tube in accordance with claim 48 wherein the internal surface of said cylindrical member is coated with an opaque, electrically conductive coating and said connecting means comprise, in combination, an electrical-ly conductive film in contact with said target and deposited on said target support means and a conductive wire electrically connecting said film and said mirror.

59. A projection television tube, comprising in com-bination (a) an end plate, the internal surface of which de-fines a spherically configured mirror;
(b) a neck sealed to said end plate, (c) a face plate the internal surface of which is configured with the sphericity of a sphere having a center of curvature essentially coincident with the center of curvature of the sphere defining the surface of said mirror;
(d) a target deposited on said internal surface of said face plate whereby said target is of spherical config-uration;

(e) a cylindrical member affixed to said end plate and terminating in an annular face plate sealing end configured and positioned such that said face plate in stable position resting on said face plate sealing end and sealed thereto will have its center of curvature essentially coincident with the center of curvature of said sphere defining the surface of said mirror, the height of said cylindrical member serving as the sole means for affixing said target a predetermined radial-distance from said mirror;
(f) connecting means to electrically connect said target and said mirror comprising an electrically conductive film in contact with said target and deposited on said internal sur-face of said face plate, a conductive wire electrically con-necting said film and said mirror, and an anode terminal-ex-tending through the wall of said cylindrical-member connected to said wire;
(g) electron gun means sealed within said neck ar-ranged to produce an electron beam to print a raster on said target; and (h) electron beam focusing means.

60. An envelope for a projection television tube in accordance with claim 59 wherein the dimensions of the surface of said target are slightly greater than the dimensions of said raster.

61. An envelope for a projection television tube in accordance with claim 59 including correcting lens held in spaced relation to said face plate by support means seated on said face plate such that said correcting lens is aligned with respect to said mirror and said target.

62. A process for forming an envelope for a projection television tube, comprising the steps of (a) forming an end plate to have a spherically con-figured mirror on its internal surface;
(b) affixing to said end plate a cylindrical member which terminates in an annular face plate sealing end configured and positioned such that a sphere in stable position resting on said sealing end will have its center of curvature essentially coincident with the center of curvature of the sphere defining the surface of said mirror;
(c) positioning on said face plate sealing end of said cylindrical member a target support means configured to "
engage said face plate sealing end and supporting a target de-fining a spherical surface having a center of curvature when so positioned which is essentially coincident with said center of curvature of said-sphere determining the configuration of said face plate sealing end, said positioning of said target support means in conjunction with the height of said cylindrical member serving to attain a predetermined location of said target with respect to said mirror; and (d) sealing a face plate to said cylindrical member thereby to permanently affix said target in said predetermined location.

63. A process in accordance with claim 62 wherein said step of affixing said cylindrical member to said end plate com-prises flame sealing said cylindrical member to said end plate or molding said cylindrical member integrally with said end plate.

64. A process in accordance with claim 62 wherein said step of affixing said cylindrical member to said end plate com-prises sealing said cylindrical member through an end plate sealing end to said end plate, said end plate sealing end be-ing configured to present a surface having the sphericity of a sphere the radius and center of curvature of which are es-sentially identical to the radius and center of curvature of said sphere defining the surface of said mirror.

65. A process in accordance with claim 64 wherein said steps of sealing said face plate to said cylindrical mem-ber and sealing said cylindrical member to said end plate are accomplished simultaneously through the use of frit deposited between the surfaces to be sealed and comprise forming an assembly of said face plate, cylindrical member and end plate with said frit and exposing said assembly to a heating cycle comprising warmup, frit-activation and cooldown periods.

66. A process in accordance with claim 65 wherein said frit is deposited as layers of predetermined thicknesses between said face plate and said face plate sealing end and between said end plate and said end plate sealing end.

67. A process in accordance with claim 66 including the step of incorporating shim means in said layers of frit thereby to achieve said predetermined thicknesses.

68. A process in accordance with claim 67 wherein said shim means are glass beads.

69. A process in accordance with claim 65 in-cluding the step of maintaining the temperature of said cylin-drical member near said face plate sealing and at a temperature above that at which said face plate is maintained during the last part of said warmup and first part of said frit-activation periods of said heating cycle.

70. A process in accordance with claim 62 wherein said face plate is either said target support means or has said tar get support means affixed thereto and said positioning of said target support means comprises positioning said face plate on said cylindrical member.

71. A process in accordance with claim 62 wherein said target support means is separate and distinct from said face plate and said sealing of said face plate to said cylin-drical member serves to retain said target in said predetermined location subsequent to said positioning of said target support means.

72. A process for forming a projection television tube, comprising the steps of (a) forming an end plate to have a spherically con-figured mirror on its internal surface;
(b) sealing a neck to said end plate;
(c) providing a cylindrical-member which terminates in an annular face plate sealing end configured and positioned such that a sphere in stable position resting on said sealing end will have its center of curvature essentially coincident with the center of curvature of the sphere defining the surface of said mirror when said end plate is affixed to said cylin-drical member;
(d) affixing said end plate to said cylindrical member;
(e) applying an electrically conductive coating to the internal wall of said cylindrical member;
and (f) affixing an anode terminal;
(g) positioning on said face plate sealing end of said cylindrical member a target support means configured to engage said face plate sealing end and supporting a target de-fining a spherical surface having a center of curvature when so positioned which is essentially coincident with said center of curvature of said sphere determining the configuration of said face plate sealing end, said positioning of said target support means in conjunction with the height of said cylindrical mem-ber serving to attain a predetermined location of said target with respect to said mirror;
(h) providing a face plate;
(i) providing an electrical connection between said mirror and said target;
(j) sealing said face plate to said cylindrical mem-ber thereby to permanently affix said target in said predeter-mined location;
(k) providing an electron gun assembly arranged to direct an electron beam onto said target, and sealing said electron gun into said neck;
(1) sealing off said neck in a manner to create a vacuum within the tube volume; and (m) affixing electron beam focusing means to said neck.

73. A process in accordance with claim 72 wherein said step of affixing said cylindrical member to said end plate comprises sealing said cylindrical member through an end plate sealing end to said end plate, said end plate sealing end be-ing configured to present a surface having the sphericity of a sphere the radius and center of curvature of which are es-sentially identical to the radius and center of curvature of said sphere defining the surface of said mirror.

74. A process in accordance with claim 73 wherein said steps of sealing said face plate to said cylindrical mem-ber and sealing said cylindrical member to said end plate are accomplished simultaneously through the use of frit deposited between the surfaces to be sealed and comprise forming an as-sembly of said face plate, cylindrical member and end plate with said frit and exposing said assembly to a heating cycle comprising warmup, frit-activation and cooldown periods.

75. A process in accordance with claim 74 including the step of maintaining the temperature of said cylindrical member near said face plate sealing end at a temperature above that at which said face plate is maintained during the last part of said warmup and first part of said frit-activation pe-riods of said heating cycle.

76. A process in accordance with claim 75 wherein said temperature of said cylindrical member near said face plate sealing end is maintained about 30°C above the temperature of said face plate.

77. A process in accordance with claim 74 wherein said frit is deposited as layers of predetermined thicknesses between said face plate and said face plate sealing end and between said end plate and said end plate sealing end.

78. A process in accordance with claim 76 including the step of incorporating shim means in said layers of frit thereby to achieve said predetermined thicknesses.

79. A process in accordance with claim 78 wherein said shim means are glass beads.

80. A process in accordance with claim 72 wherein said face plate is either said target support means or has said tar-get support means affixed thereto and said positioning of said target support means comprises positioning said face plate on said cylindrical member.

81. A process in accordance with claim 72 wherein said target support means is separate and distinct from said face plate and said sealing of said face plate to said cylin-drical member serves to retain said target in said predetermined location subsequent to said positioning of said target support means.

82. A process in accordance with claim 72 including the step of mounting a correction lens on said face plate.

83. A process in accordance with claim 82 wherein said face plate is configured with the sphericity of a sphere the center of curvature of which is essentially coincident with the center of curvature of said sphere defining said surface of said mirror and the step of mounting said correction lens on said face plate comprises mounting said lens in a cylindrically-configured lens support, seating said lens support in a stable position on said face plate whereby said lens is automatically optically aligned with respect to said target and said mirror, and affixing said lens support in said stable lens position to said cylindrical member.

84. A process in accordance with claim 82 wherein said face plate is configured as an essentially flat disk and the step of mounting said correction lens comprises mounting said lens in a cylindrically-configured lens support and sealing said lens support to said face plate.