US2901665A

US2901665A - Cathode ray tube deflection yoke

Info

Publication number: US2901665A
Application number: US564897A
Authority: US
Inventors: Barkow William Henry; Clifford C Matthews
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1956-02-13
Filing date: 1956-02-13
Publication date: 1959-08-25
Anticipated expiration: 1976-08-25

Description

Aug. 25, 1959 w. H. BARKow ET Al- 2,901,665

CATHODE RAY TUBE DEFLECTIONvYOKE Filed Feb. 13, 195e 4 sheets-sheet 1 Ji B @af/ae@ 5? www 23% mwz/ irme/ffy w. H. BARKow ETAL 2,901,665 cATHoDE RAY TUBE: DEFLECTIGN YoKE Aug. 25, 1959 4 Sheets-Sheet 2 Filed Feb. l5, 1956 Aug. 25, 1959 Filed Feb. l5, 1956 w. H. BARKOW ET AL CATHODE RAY TUBE DEFLECTION YOKE 4 Sheets-Sheet 3 INVENToR. Mu/MH .5in/aw Aug; 25, 1959 w. H. BARKOW ETAL. 2,901,665

CATHODE RAY TUBE DEFLECTIONfYOKE Filed Feb. 13, 1956 4 Sheets-Sheet 4 B @www United States Patent O l 2,901,665 p CATHODE RAY TUBE DEFLECTION YOKE William Henry Barkow, Pennsauken, and Clifford C.

Matthews, Merchantville, NJ., assignors to Radio Corporation of America, a corporation of Delaware Application February 13, 1956, Serial No. 564,897 18 Claims. (Cl. 315-27) become more acute than in the case of narrow angles l of deflection. This fact is apparent `from a consideration of the geometry of cathode ray tubes such as those employed as television image reproducing devices, in that the electron beam is caused to scan from what may be termed its center of deflection through a wide angle so that it covers a generally rectangular area on the face plate of the tube. These problems are accompanied by practical considerations which require that the deflection apparatus be maintained within reasonable physical limits and that the cost be kept as low as possible.

AIt is, therefore, a primary object of the present invention to provide a new and improved deflection system capable of producing wide angle deflection of electrons in a cathode ray tube.

As is generally known, an electron-beam which is acted upon by a uniform transverse magnetic deflection field is caused to travel along a path which is a sector of a circle. Such theoretical conditions as a uniform eld do not, however, exist in the case of practical beam deflection systems. One reason is that a conventional electromagnetic dellection yoke is of finite length and produces a field which is not symmetrical. Thus, it has been found that the path of an electron in the case of a practical deflection eld is more nearly represented by a parabola rather than by an arc of a circle. Since one of the requirements of a deflection yoke is sensitivity (i.e., amount of deflection per unit of yoke energization), it has been found to be desirable to design cathode ray tube deflection yokes such that the conductors of the coils comprising the yoke follow closely the path of the beam in its extremities of deflection.

In U.S. Patent No. 2,570,425, granted October 9, 1951, to C. V. Bocciarelli, it is stated, for example, that the desired relationship between the configuration of a de- Vflection yoke an-d the path of a beam electron traversing the magnetic field thereof will be substantially satisfied as the displacement of the turns of the yoke from the longitudinal axis of the cathode ray tube is related to the displacement along such axis measured from the point of entry of the beam into the yoke in accordance with a hyperbolic function. In contradistinction to the foregoing statement in the patent, the present applicants have found, as mentioned briefly above, that the beam path from a point within the `deflection yoke to the target screen of the cathode ray tube follows closely and may be defined by the equation for a parabola. Euch a beam path was measured in a cathode ray tube kinescope whose beam was deflected through a total angle of approximately 110. It is, therefore, a feature of the present invention that the deflection yoke associated with a cathode ray tube Aof. a portion of the yoke casingof Figures: l and 9;,and

f ice be shaped in such manner as to conform to the path of an electron beam within such tube, namely, in such manner that the inner surface of the deflection yoke windings are shaped to `define a surface of Vrevolution which, upon intersecting a plane passed through the longitudinal axis of the yoke, defines, at least in part, a parabolic curve. In order that full advantage maybe had of the known beam deflection path, it is a further feature of the present invention that the bulb portion of a cathode ray tube be formed to conform to a surface of revolution produced by revolving a portion of' a parabola about the longitudinal axis of the tube. By such means, highly efficient deflection through a wide angle ofthe order of is achieved.

In accordance with the present invention, the bulb portion of a cathode ray tube kinescope is formed, at least in part, so that it constitutes the surface of a paraboloid of revolution whose axis coincides with the longitudinal axis of the tube. An electro magnetic `dellection yoke associated with such tube comprises first and second pairs of coils located around the tube such that the coils of the lsecond pair lie around the coils of the rst pair, the bundles of conductors forming the coils being shaped at their inner surfaces to conform to the parabolic curvature of the tube. Thus, substantial efliciency is afforded, since the conductors of the coils forming the yoke lie in close proximity to the path of the beam during maximum deflection, while not undesirably lying within the beam path at any point.

In accordance with another feature of the invention, the efllciency of the yoke is optimized by allocating conductor material to the first and second pairs of coils (i.e., conventionally termed the horizontal and vertical coils) in such manner as to exploit the fact that the two pairs of coils are energized with current of rather widely different frequencies. Further, the cross-sectional vshapes of the bundles of the conductors of the coils arel controlled according to the invention in such manner as to produce minimum astigmatism of the beamwithout undesirably degrading the shape o-f the raster scanned by the beam. Magnetic means are lfurther provided in accordance with the present invention to aid in controlling the raster shape.

According to another feature of the invention, the elliciency of the yoke is increased by reason of a novel yoke casing and terminal board assembly which permits full utilization of the axial length of the yoke coils between the end conductors for a ferro magnetic core, the presence of which increases the efficiency of the yoke.

Additional objects and advantages -of the present invention will become apparent Yto those skilled in the art from a study of the following detailed description of the accompanying drawing, in which:

Figure l is an elevational View of a cathode ray tube kinescope and deflection yoke in accordance with a specific form of the present invention;

Figure 2 illustrates certain beam path and deection yoke and tube contours to be described;

Figures 3a and 3b are illustrative of the horizontal coils of a yoke in accordance with the invention;

Figures 4a and 4b are similar views of a verticalV deilection coil;

Figure 5 illustrates the contours ofthe tube and dellection yoke of the preceding figures;

Figure 6 is a vertical sectional View o-f the yoke of Figure l; v

Figure 7 is an enlarged Vertical sectional vie'w of a portion of the tube of Figure 1; Y

Figure 8 illustrates one portion of the core forming means associated with the yoke of the present invention;

Figures 9 and l0 are, respectively, side and end views of a novel form of yoke casing; v

Figures 1l and l2 are, respectively, side and end views Figures 13 and 14 are, respectively, end and side views of a yoke insulating member according to the invention.

Referring to the drawing and, particularly, Figure l thereof, there is shown an electromagnetic deilection system in accordance with the present invention. The system comprises a cathode ray tube kinescope having a generally cylindrical neck portion 12 and a ared bulb portion 14, to be described more fully hereinafter. Associated with the kinescope 10 is an electromagnetic deection yoke indicated in its entirety by reference numeral 16, which yoke comprises a rst pair of deflection coils 18 (i.e., the horizontal dellection coils), a second pair of deection coils 20 (i.e., the vertical deflection coils), a multi-part ferromagnetic core 22 and a yoke casing 24. The assembled parts of the yoke 16 are secured together by means of a steel strap 26 passed around the yoke and secured at its end by means of a bolt 28. Mounted at the rear end of the yoke casing 24 in a manner to be described more fully are two permanently magnetized rings 30 and 32 which serve as centering means for the yoke.

Before describing the tube and yoke in greater detail, reference will be made to Figure 2 which illustrates diagrammatically certain of the considerations involved in the design of the present yoke and tube. Specifically, the curve 34 illustrates the forward portion of the path of an electron beam such as is produced within the tube 10 of Figure l in its extreme deflected position when the total angle of deilection is of the order of 110. By forward beam path is meant that portion of the trajectory of the electrons from the beam from a point Within the deection yoke 16 to the screen (not shown) of the tube. It will be seen that the beam path 34 is approxi mately parabolic in curvature. This curvature, as measured in practice, departs substantially from the theoretical arcuate path of an electron beam which is assumed for a uniform transverse deflection eld. The degree of cleparture is readily apparent from a comparison of the curve 34 with the curve`36 which represents an arc of the circle whose radius is chosen such that the arc most nearly approximates the curve 34. Also shown in Figure 2 by the curve 38 is a selected contour of the portion of the bulb portion 14 of the tube of Figure l. It is apparent from the relation of the curves 36 and 38, both of which are drawn in the same relation to the curve 34, that in the region of the deflection yoke `16 there exists a rather wide departure of the circular contour 36 from the beam path 34 as compared to the departure of the parabolic contour 38 from the path 34. This departure, in the region in question, is of importance insofar as the eliiciency of a deflection yoke is concerned, since, as mentioned, it is desirable that a deflection yoke be in close proximity to the desired beam path at all points along the yoke longitudinally of the axis of the tube.

Assuming for the present that the inner and outer surfaces of the bulb portion 14 of the tube 10 are parallel (which is not completely true in the case of practical tubes) it may be assumed that the curve 38 represents the contours of the inner and outer surfaces of the bulb portion 14 of the tube of Figure l. Moreover, and as will be treated in greater detail, the parabolic curve 38 is also illustrative of the contour of the inner surface of the coils forming the deection yoke 16. Despite certain minor differences in curvature between the inner and outer surfaces of the tube bulb and the surface of the coils of the deflection yoke which will be described below, it Will be appreciated that the parabolic contour of these surfaces quite closely approximates the parabolic path 34 of the beam electrons. Further, this degree of approximation is seen to be much greater than that afforded by the circular contour 36, as indicated by the shaded area 40 between the curves in the region of the yoke. It may also be noted, in this connection, that the beam path 34 is more truly defined as a parabola than as a hyperbola, since the latter curve is one which,

by definition, is asymptotic at both extremities to a pair of intersecting axes.

In order that the various curvatures mentioned briey thus far and shown in detail in Figure 5 may be better appreciated, the structure of the coils themselves is illustrated in Figures 3 and 4. Figures 3a and b are, rcspectively, planned and front elevational views of one of the horizontal deflection coils 18 of Figure 1. As shown in Figure 3a, each of the horizontal coils 18 is made up of side or longitudinal conductors 42 and end conductors 44; in general accordance with conventional practice. That is to say, each coil 18 is made up of a plurality of turns of wire of suitable size (e.g., No. 30-B and S gage), such that the longitudinal conductors and end conductors actually comprise a bundle of turns. The longitudinal conductors 42 may, if desired, be shaped, for a portion of their length d, to conform to a cylindrical shape. The remaining portion of the length of the longitudinal conductors 42 is flared outwardly from the axis of the yoke in such manner that the inner surface of the latter portion of the longitudinal conductor bundles is of parabolic configuration. The end conductors 44 are turned generally radially outwardly from the axis of the yoke in order to remove the fringe ilux linking the end conductors from the region of the tube. Such turning-up of the end conductors of a deflection coil is well known in the art and need not be described further.

Figures 4a and b are views similar to those of Figures 3a and b but are illustrative of one of the vertical deflection coils 20 of the yoke 16. Each coil 20 is made up of a plurality of turns of wire (e.g., No. 26-B and S gage) and comprises longitudinal conductor bundles 46 and end conductor bundles 48. The longitudinal conductors 46 of the vertical dellection coils 20 are flared outwardly from the axis of the yoke along parabolic curves so that the coils 2t) may be placed around the coils 18 with a close iit. When the vertical deflection coils 20 are thus located around the coils 18, the longitudinal conductors 46 partly overlap the longitudinal conductors 42 of the horizontal deilection coils and lie, in part, within the Window openings defined by the longitudinal and end conductors of the coils 18. The end conductors 48 of the vertical deliection coils are curved to iit snugly behind the up-turned end turns of the horizontal coils, both at the front and rear of the yoke.

Referring now to Figure 5 of the drawing, there is shown, in section, a portion of the yoke and tube assembly of Figure l, from which showing the several curvatures described thus far are more readily apparent. More specifically, Figure 5 illustrates certain speciiic contours of a tube and yoke in accordance with a speciiic, operative embodiment of the present invention. The outer surface of the bulb 14 of the kinescope 10 is represented by reference numeral 50 and constitutes a surface of revolution of a parabolic curve having the equation which takes into `account the fact that the bulb portion 14 is blended into the cylindrical neck 12 of the tube. That is to say, the joint of the neck and bulb is made with a gradual liare, as shown. The horizontal deilection coil 18 is so shaped that its inner surface is a surface of revolution of a parabola delined by the equation In a similar manner the inner surface of the vertical dellection coils 20 is a surface of revolution of a parabola of approximately the same shape as that of the outer surface of the coils 18. in the interest of completeness of description, it may be noted that the horizontal and

vertical coils

18 and 20 are separated from each other by insulating means 52, to be described in greater detail hereinafter.

The 'outer surface 3of 'the vertical "deflection k:coils 20, 2in 'the region of their longitudinal conductors, -is a suriface 'of revolution of aparabola having the yequation The relationship of the up-turned end turns V44 and 48 of the horizontal and vertical coils, respectively, is also .illustrated in Figure 5, showing their -parallel relation.

The co're 22 -is also shown in Figure 5 so that its relation yto Athe coils 'of the yoke may be -better appreciated. The core 22 may, for example, be made up of four longitudinal sections vof `high permeability material, 'such as ferrite, `"fthe sections being disposed around the coils so that they form a continuous sleeve. The finner surface of v the core :sleeve is a surface of revolution of a parabola which may fbe `defined by theequation which is seen to beonly slightly 'larger than the outer surface of ythe vertical dellection coils 20. The core 22 will further be seen -to have an outer surface shaped somewhat in conformity with its inner surface, that is, convexly toward the axis ofthe yoke. The curvature of the outer surface ofthe core y2.2 is not particularly critical but is curved, according lto the .present inventi'om-in order .to economize'on the use of the core material over the -amount required if the outer surface of the core vwere to be cylindrical. The only other requirement on the core 22 is that -it have sutllcient thickness to provide the desired low reluctance return path for the yoke flux, except as -to its length which aids in increasing the sensitivity of -the yoke. This last mentioned matter will be explained more fully below.

As has been mentioned, the inner and outer surfaces of the bulb portion of the kinescope need not be parallel to each other and, in fact, the requirements of manufacture-may militate against such parallelism. Thus, for example, as shown in Figure 7, the inner surface 58 of the bulb 14 has a curvature dened by the relationy=.'5x2+.42'0 (s) which results in a gradual thickening 'of the bulb from fthe 'neck toward the screen of the tube, for ypurposes of 'mechanical strength. The `diilerence in curvature between the inner `and outer surfaces of .the bulb, Vhowever, isltoo slight to yhave any appreciable affect upon the sensitivity of the yoke. That is to say, the parabolic 'contour 'of the outer surface of the tube bulb and thesubstantially v'equal contour of the inner surface of the dellection yoke coils insures that the activeconductor's of the coils are as close -as possible to the maximum deilected beam path.

Figure 6 is a vertical sectional View of a portion of the yoke 16 showing the cross sectional shape of fone'of the vertical coil longitudinal conductor bundles 46 and 'one of the horizontal coil vconductor 'bundles '42. The turns distribution ofthe coil 42 is, as shown, selected 'to provide a slightly pin cushioned magnetic field such as has been found in practice to be necessary for minimizing beam focus distortion or astigmatism. The turns distribuvtion of the longitudinal conductors of the horizontal coils is constant throughout the length of the coils, allthough the thickness of the bundles'of conductors gradu- -ally changes from one end of the coil to the other, in accordance with known practice. It willfurthe'r benoticed 4that the horizontal coils are spaced from each other (ile, in the region of their longitudinal conductors 4Z) by a-dis'tance equal to 2.5', the dimension s being yshown in 'Figurei as the distance of'one of the vconductor bundles -42 from the horizontal axis. It `will be understood ythat "'the adjacent longitudinal conductor bundle =of the other, horizontal 'deilection coil is similarly `spaced a distance s from the axis. This spacing serves "to `reduce .materially the pin cushioning of the lield produced by the coils in -this region, so Ithat optimurnspot focusmay be .maintained =throughout horizontal delvlection of the beam. e;

The vertical dellection coils on the other .-hand, have their Vturns distributed -in such manner as to .provide a more greatly pin cushioned magnetic .-eld than 'that which is :provided by the horizontal deflection coils. That is to say, the coils of the present yoke take advantage of -the fact that, where a scanned raster has an aspect ratioother than unity (e.g., the conventional 4:3 aspect ratio ,-of `television practice), the -beam defocusing effect v of the field which produces the smaller angle of deflection is less than in a case of the field which produces the wider angle of deflection. More specifically, the vertical deflection angle in the present case is vless than the horizontal deflection angle, so that the vertical deflection coils are wound in such manner as to vproduce a pin cushion deilection lleld 'which results in optimum scanning raster rectangularity. The small amount of defocusing of the beam in the vertical direction which thus results has been found to be so slight ast'o be unobjectionable. The shape ofthe vertical deflection eld is further controlled in the present case by reason vof the fact that the adjacent longitudinal conductor bundles of the vertical deilection coils are in close proximity to each other, rather than being vseparated yby the rather wide spacing described in connection with the vhorizontal deflection-coils. As the case of the horizontal deflection coils, 4the turns distribution of the vertical deflection coils -is constant'throughout their length, despite the gradual change in width and Ithickness of the coils.

Figure 6 also -illustrates the manner in which the present invention exploits the difference in operation of the horizontal and vertical coils Aof the deflection yoke, linsofar as the respective eicencies of the two pairs of coils are concerned. The efficiency of the vertical deflection 4coils which operate at 60 c.p.s. dependsupon the resistance 'of the coils, the figure of merit o-f the vertical coils being proportional to the 12R of the coils. On the other hand,

vthe figure of `merit of the horizontal deflection coils .is

proportional to the stored energy, so that it is proportional to the product L12, where Lis the inductance of the horizontal deflection coils. Stated otherwise, the vreactive impedance plays a greater part in determining the current which ilows through the horizontal coils than Ydoes vthe resistance of the coils, as opposed -to the case-of the 'vertical deflection coils. Thus, as illustrated in Figure 6, the vertical delleotion coils are made up of a sulicient amount of conductor material (e.g., copper wire) to present a rather small resistance to the energy source, such as a total resistance for the two vertical deflection coils of 11 ohms. The amount of copper allocated v'to the horizontal dellection coils, however, is appreciably less than that contained in the vertical coils, .thereby economizing on the use of copper while not affecting undesirably the eiliciency of the horizontal deflection coils. Since, `in -the case of both 'the horizontal and vertical 'deflection coils, the amplitude of deflection is proportional to the product of the number of turns of the coil Nand the current flowing through the coil, the optimum -dellection -eflciency -is -realized thro-ugh the selective Aallocation of conductor material to the two pairs of coils, respectively. It Will )thus be appreciated that thevsize andturns distri- 'bution of the two pairs of coils are selected, in accordance with rthepresent invention, in such .manner as to take full advantage of -t'he dillerent deflection angles horizontally and vertically, both with vrespect to :economical use of conductor material lwithout attendant decrease yin ileilec- -tion sensitivity and with respect to beam focus and raster kpatternshape. `In this connection, it may be noted that, in designing the horizontal deilection coils for optimum beam focusl throughout the horizontal deflection `angle, la certain amount-of horizontal .pin cushioning of the deilection raster may result. This raster distortion is readily corrected by locating a small .permanent magnet (one of which is shown at -60 in Figure l) on each side *of the deflection yoke, each of the twopenmanent magnets ybeing polarized so that lits :flux aids the flux produced by the horizontal deflection coils of the yoke, thereby-increasing the amplitude of `deflection between the top and bottom edges of the raster in a manner to pull out the sides of the raster. In addition to improving raster shape, the permanent magnets will also be understood asaiding generally in effecting a wider angle of deflection in the horizontal plane.

As has been set forth briefly above, the magnetic core 22 associated with the deflection coils 18 and 20 has its inner surface shaped as a surface of revolution of a parabola whose equation is substantially equal to the parabola of which the outer surface of the vertical deflection coils is a surface of revolution. The core 22 actual- Vly comprises, in the specific embodiment described, four vlongitudinal sections of a cylinder7 one of which is shown separately in Figure 8. The longitudinal surfaces of the core sections may be ground so that a close t between the sections without undesirable air gaps is achieved. The axial length W of the core 22 is substantially equal to the distance between the inner surfaces of the upaturned front and rear end turns 46 of the vertical deflection coils. In this connection, it may be noted that conventional delllection yokes require a. terminal board or member to which the start and finish leads of the deflection coils are brought out and connected for electrical connection to the deflection wave generating circuits. Typically, .the terminal board is located directly behind the core member which surrounds the coils, so that the thickness of the terminal board requires shortening of the axial ldimension of the core itself. Such shortening, although of the order of one-eighth inch, for example, undesirably decreases the sensitivity of the yoke coils, since the low reluctance core does not extend throughout the length of the coils. In accordance with the present invention, as mentioned above, a novel yoke casing and terminal board arrangement permit full utilization of the axial distance between the end turns of the vertical deflection coils for core material.

The yoke casing of the present invention is illustrated in Figures 9 and 10.

Figure 9 shows one of the :two parts of `the yoke casing per se. The casing is formed of suitable insulating material such as a plastic material. Each half of the casing is generally a longitudinal half section of a cylinder having a portion 64 of reduced diameter which fits snugly around the outer surface of the core 22. The remainder of the length of the yoke casing is of suflicienlt diameter to clear the up-turned rear end turns of the coils l and which, therefore, are accommodated within the annular space defined by the Wall 66 and the rib 68. A second rib 70, extending radially inwardly from the yoke casing 24 as does the rib 68, is spaced from the latter rib by approximately one-eighth inch, so that the ribs 68 and 70 serve in a manner to be described, to support a terminal board directly behind the yoke coils. A further annular, inwardly extending rib 72 is located rearwardly of the rib 70 and cooperates with a pair of radially inwardly extending tabs 74, one of which is shown in its entirety in Figure 10. Each of the tabs 74 may, for example, subtend an angle of approximately 80 of the circle defined by the two sections of the casing 24.

The yoke casing is assembled on the yoke in the following manner: a disk-like terminal board of suitable insulating material and of outer diameter generally equal to the inner diameter of the chamber defined by the ribs 68 and 70 is placed edgewise between the ribs 68 and 70 of one of the casing halves which is then placed around the assembled coils and core of the yoke such that the reduced pontion 64 fits around the core 22 while the rear end turns of the coils fit within the chamber defined by the wall 66 and the rib 63. The other half of the casing is then placed around the core, facing the first half so as to complete the cylindrical form of the casing. The clamp or strap 26 is then placed around the two halves of the casing 24 in the region 68 and tightened by the bolt28, thereby rigidly securing the two halves of vthe casing around the yoke. The strap 26 may, if desired, be permanently lmagneltized across its diameter for the purpose of imparting a fixed amount and direction of centering field for the beam which passes through the yoke field. It will be appreciated from the foregoing that the terminal board is conventionally located behind the yoke coils and does not require any space around the coils themselves. Moreover, the novel yoke casing, by reason of the manner in which it is secured to the yoke, requires no space between the core and coils of the yoke, as is the case with certain prior art arrangements.

In accordance with conventional practice, the yoke 16 may further be provided with a pair of permanent magnet rings for effecting initial centering of the beam. Such rings and their operation are well known in the art and need not be described. The yoke casing 24 of the present invention, however, affords ready means for mounting such magnets in operative position with respect to the yoke. Specifically, a magnet supporting member 78 such as that shown in Figures ll and l2 is provided. The member 78 is in the form of a disk having a pair of radial, outwardly extending tabs 8f) which are narrow enough to t within the openings defined by the tabs 74 which extend inwardly at the rear end of the casing 24. An axial 'tubular extension 82 of sufficient diameter to accommodate the neck 12 of the cathode ray tube extends rearwardly from the member 78 so that the ring magnets 3f) and 3-2 may be slid onto the tubular extension 82. The rear end of the extension 82 may then be turned outwardly to prevent removal of the ring magnets. The tabs 8f) of the magnet supporting member 78 may further be provided with bent portions 84, so that when the member 78 is placed between the rib 72 and tabs 74 and rotated so that the tabs 30 are between the rib 72 and tabs 7 4, a tight fit results.

The final arrangement of the yoke is the insulating member 52 mentioned earlier in connection with Figure 5. A specific form of insulator for this purpose is shown in Figures 13 and 14. The insulator 52 has front and rear radial flanges S8 and 90, respectively, which are designed to fit between the horizontal and vertical deflection coils in the regions of their front and rear end turns. The body portion 92 of the insulator 52 is generally in the form of a paraboloid so that it conforms to the total outer surface of the horizontal coils and the inner surface of the vertical deflection coils. The insulator, which may be formed of vulcanized rubber or other resilient insulating material may further be provided with a pocket 94 on each side of its horizontal axis for supporting one of the magnets 60, described above. The insulator 52 may be split longitudinally as at 96 to facilitate the placing of the insulator around the assembled horizontal deflection coils. A pair of radially, inwardly extending ribs 98 at opposite sides of the inner surface of the body portion 92 of the insulator serve to space the adjacent conductor bundles of the coils 18 from each other by the required amount 2s described earlier.

By way of rsum, it will be appreciated that the yoke of the present invention, while low cost, affords a high degree of sensitivity and is capable of producing a wide angle deflection of the order of By virtue of the parabolic contour of the tube bulb and the yoke coils, this sensitivity is maximized. In comparing the present yoke with one which was designed so that its inner surface was the surface of revolution of an arc of a circle and adapted to produce the same order of deflection, it has been found that the present yoke used 37% less copper in the horizontal deflection coils `and 17% less copper in the vertical deflection coils than was used in the circular yoke. Moreover, by virtue of the concavity of the outer surface of the core, a saving in core material of approximately three times was effected.

In the interest of completeness of description, it may be noted that a practical, operative, tube with which the yoke of "the present invention may Ebe associated 'is "one having a 'neck whose-outer'diameter is reduced :from the conventional ldimensions of 1.5 Ainches fto I`l (125 inches.

lHavingthus `described out invention, what We claimals new and desire to secure by Letters Patent is: v I l. An electromagnetic vdeflection yoke lfor a cathode ray ytube having .al generally cylindrical neckand a flared bulb lwhose contour is generally parabolic, `saidyokecoinprisingz a ypair of vdeflection fcoils, said coils being ar- 'ranged in opposing Irelation and shaped, foratleast 1a `portion -of their flength, with Va generally parabolic con- Lfour so that said coils mayiconform to the flared con-tour f such tube, the paraboliccontour of said bulb and the -parabolic contour-of said coils .being defined by the equation y=ux2+ C, where x-and y are the loci of points 4defining aparabolic curve in a Vsystem of rectangular coordinates and'lC is aconstant.

`2. electromagneticjdeection yoke fora cathode frayI tubelhav'in'g a :generallyacylindrical neckand `a flared bulb whose contourlis generally parabolic, said yoke comprising; .a Afirst pair of .deflection coils, Asaid coils ibeing farranged -in kopposing frelation and shaped, for at least alportionof their length, with a. generally parabolic con- ;tour so that said coils may conform to the flared contour `of such tube; and a second =pair of coils arranged around said first .pair of-coils, the parabolic contour of said bulb and the :parabolic contour of said first pair of Icoils .being defined bythe equation y=ax2|-C, where x and y are the loci of points ydefininga parabolic curve in 1a system of rectangular coordinates and C is a constant.

3. VAn electromagnetic deflection yoke for a cathode ray tube having a generally cylindrical neck andV a fiared bulb Whose contour is generally parabolic, said yoke comprising: a vrst pair -of deflection coils, said coils being arranged in opposing relation and shaped, for at least a portion-of their length, with a generally parabolic contour so that said coils may conform to the flared contour of such tube;landa second pair of coils arranged around said first vpair `of coils, said second pair of coils being shaped -to conform tothe contour of said first pair of coils, the Yparabolic-contour of said bulb and the parabolic contour of said first Ipair of coils being defined by the equation y=ax2+C, Where x and y are ythe loci of points defining a parabolic curve in a system of rectangularcoordinates and C is a constant.

4. An electromagnetic defiection yoke for a cathode 4ray tube having a generally cylindrical neck andafiared bulb whose vcontour is generally parabolic, said yoke comprising: a first ,pair of defiection coils, said coils being arranged in opposing relation and shaped, for vat 'least 'a portion lof their length, with a generally parabolic contour so that said coils may conform to the fiared contour of such tube; and a second pair of coils arranged around said first pair of coils, said second pair of coils Vlacing shaped to conform to the contour 'of said first 'pair of coils; and a core of magnetic material surrounding said first and second pairs of coils, said core beingforrned with an inner surface of v,generally parabolic contour to conform to said coils, each of said parabolic contours being defined by -the Vequation y=ax2|-C, where x and y .are the loci of .points Vdefining a parabolic curve in a system o'f rectangular coordinates and C -is a constant.

5. electromagnetic defiection yoke for a cathode vray tube having a generally cylindrical neck and a flared bulb Whose contour is generally parabolic, said yoke cornprising: a first pair of deflection coils, said coils being arranged yin opposing relation and shaped, for atleast a portion of their length, with a generally parabolic contour so that said coils may conform to the flared contour of such tube; and a second pair of coils arranged around said first pair of coils, said second pair of coils being shaped to conform to the contour of said first pair of coils; and a core of magnetic material surrounding said first and second pairs of coils, said core being formed with an inner surface of generally parabolic contour to conform to Asaid coils and with an outer surface which is shaped concave 4inwardly toward Vthe yneck `of such tube, YLthe inner dimensions of said lfirst pair ofcoils being of minimum `value'so thatlthe inner surface of said first :pair 'of coils is spaced afminirnurn distance from such tube.

V6. A cathode ray tube 'having a generally cylindrical 'neck portion and a bulb vportion extending therefrom, said bulb -portion'having outer and inner surfaces of gen- 'crally parabolic contour, each parabolic contour being defined by the equation y=ax2-IC, where x and y are -the loci of points defining a parabolic curve in a system -iof yrectangular coordinates and C Ais a constant.

7. `In combination with a cathode ray tube having a generally cylindrical neck Aportion and a bulb portion extending therefrom, said bulb portion having an outer surface which is a surface of revolution of a parabola, an electromagnetic deflection yoke which comprises `a first pair of deflection coils arranged in opposing relation around a portion of 'the length of "said tube including a fportion of said 'bulb portion, said coils having an inner surface which conforms to the outer surface of said tube; fandfa second pair-of coils arranged around said first pair of coils,- said parabola being defined by the equation 'y=ax2+'C, lWhere x and 'y are 'the loci of points defining Ia'parabolic curve in 'a sys-tem 'of rectangular coordinates and C is a constant.

8. In combination with a Vcathode 'ray tube having a generally cylindrical neck portion and a bulb portion exltending therefrom, said bulb portion having an outer surface which is 'a surface of revolution of a parabola, an electromagnetic deflection yoke which comprises a first pair `of defiection coils `'arranged in opposing relation around a Vportion of the length of said tube including a portion of said bulb portion, said coils having an inner surface which conforms to thefouter surface of lsaid tube; and a second pair of coils arranged :aroundsaid first pair of coils; said parabola vbeing 'defined by the equation 'y=.62'x2|.'570 and said linner surface of said 4firstipairof `coils being a surfaceoffrevolutioncf a parabola defined by the equation 'y-'-.74x2i.625, where x and .y are the iloci of points on said Iparabola lin a system of rectangular coordinates.

V9. .An electromagnetic deflection yoke for ,defiecting an electron v-beam in a cathode ray tube, which yoke comprises la first pair of deflection coils, each coil being made up of a plurality-0f turns of a conductor 'such that :it has longitudinal and end 'bundlesvof turns, said coils being arranged yto face each other, the inner'surfaces of said coils being a surface of revolution of a parabolagja lsecond ,pair of coils arranged around said first coilsfin such manner that amagnetic field produced by the longitudinal conductor turns of said first coils -is substantially normal *to -a 4field -produced by the corresponding conductor turns'of said `secondpair of coils, thecoils of said second pair being shaped in substantial conformity with-the coils of said first pair, Athe inner dimensions of said first -pair -of v-coils being of Aminimum value so that the inner surface of said first pair of coilsis spaced in a :minimum distance from the beam of such tube in its maximum :deflected position. l

l10. An telectromagentic deflection yoke for a cathode ray tube, which yoke comprises a first pair of defiection coils, each coil being made up of a plurality of turns of a conductor such that it has longitudinal and end bundles of turns, said coilsfbeing arranged to 'face each other, the inner surfaces of said coils being a surface of revolution of aparabola; a second pair of coils arranged around said 'first coils in such rnanner that vamagnetic field pros duced by the longitudinal `conductor 'turns A'of said ifirs-t coils is substantially normal to a field produced by the corresponding conductor turns of said second pair of coils, the coils of said second pair being shaped in substantial conformity with the coils of said first pair, said second pair of coils having a lower total electrical resistance than that of said first pair of coils.

ll. An electromagnetic deflection yoke for a cathode ray tube, which yoke comprises a first pair of deiiection lll coils, each coil being made up of a plurality of turns of a conductor such that it has longitudinal and end bundles of turns, said coils being arranged to face each other, the inner surfaces of said coils being a surface of revolution of a parabola; a second pair of coils arranged around said first coils in such manner that a magnetic field produced by the longitudinal conductor turns of said first coils is substantially normal to a field produced by the corresponding conductor turns of said second pair of coils, the coils of said second pair being shaped in substantial conformity with the coils of said first pair, said coils of said first pair having a substantially constant turns distribution throughout the length of such longitudinal bundles of conductor turns, said parabola being defined by the equation y=ax2-l -C, where x and y are the loci of points on said parabola in a system of rectangular coordinates and C is a constant.

12. An electromagnetic deflection yoke for a cathode ray tube, which yoke comprises a first pair of deflection coils, each coil being made up of a plurality of turns of a conductor such that it has longitudinal and end bundlesl of turns, said coils being arranged to face each other, the inner surfaces of said coils being a surface of revolution of a parabola; a second pair of coils arranged around said first coils in such manner that a magnetic field produced by the longitudinal conductor turns of said rst coils is substantially normal to a field produced by the corresponding conductor turns of said second pair of coils, the coils of said second pair being shaped in substantial conformity with the coils of said first pair, said first and second pairs of coils each having substantially uniform turns distributions throughout their lengths, said parabola being defined by the equation y--ax2-l-C, where x and y are the loci of points on said parabola in a system of rectangular coordinates and C is a constant.

13. An electromagnetic deflection yoke for a cathode ray tube, which yoke comprises a first pair of deflection coils, each coil being made up of a plurality of turns of a conductor such that it has longitudinal and end bundles of turns, said coils being arranged to face each other, the inner surfaces of said coils being a surface of revolution of a parabola; a second pair of coils arranged around said first coils in such manner that a magnetic field produced by the longitudinal conductor turns of said first coils is substantially normal to a field produced by the corresponding conductor turns of said second pair of coils, the coils of said second pair being shaped in substantial conformity with the coils of said first pair, said coils of said first pair being so wound as to produce a magnetic field of such shape as to effect substantially uniform focus of an electron beam passing therethrough and said coils of said second pair being wound so as to produce a magnetic field whose shape is more greatly pincushioned than the field of said first pair of coils.

14. An electromagnetic deflection yoke for a cathode ray tube, which yoke comprises a first pair of deflection coils, each coil being made up of a plurality of turns of a conductor such that it has longitudinal and end bundles of turns, said coils being arranged to face each other, the inner surfaces of said coils being a surface of revolution of a parabola defined by the equation y=ax2,}-C, where x and y are the loci of points on said parabola in a system of rectangular coordinates and C is a constant; a second pair of coils arranged around said lirst coils in such manner that a magnetic field produced by the longitudinal conductor turns of said first coils is substantially normal to a field produced by the corresponding conductor turns l2 of said second pair of coils, the coils of said second pair being shaped in substantial conformity with the coils of said first pair; and core forming means of magnetic material surrounding the longitudinal conductor turns of said first and second coil pairs. 15. An electromagnetic deflection yoke for a cathod ray tube, which yoke comprises a first pair of deflection coils, each coil being made up of a pluralityr of turns of a conductor such that it has longitudinal and end bundles of turns, said coils being arranged to face each other, the inner surfaces of said coils being a surface of revolution of a parabola; a second pair of coils arranged around said first coils in such manner that a magnetic iield produced by the longitudinal conductor turns of said first coils is substantially normal to a eld produced by the corresponding conductor turns of said second pair of coils, the coils of said second pair being shaped in substantial conformity with the coils of said first pair, said coils of said first pair being so wound as to produce a magnetic field of such shape as to effect substantially uniform focus of an electron beam passing therethrough and said coils of said second pair being Wound so as to produce a magnetic field Whose shape is more greatly pincushioned than the field of said first pair of coils; and a permanent magnet mounted on each side of said firstV pair of coils in such manner that the flux of each magnet aids the flux produced by said first pair of coils.

16. An electromagnetic deflection yoke casing for use with a yoke of the type comprising two pairs of normally arranged coils surrounded by a core of magnetic material which fits between the end turns of said coils, which casing comprises: a shell of insulating material, said shell being made up of a plurality of sections of a generally cylindrical member; means for securing said shell around such core near one end of said shell; and means for supporting a terminal board Within said shell at a location beyond one end of said yoke.

17. An electromagnetic deflection yoke casing for use with a yoke of the type comprising two pairs of normally arranged coils surrounded by a core of magnetic material which fits between the end turns of said coils, which casing comprises: a shell of insulating material, said shell being made up of a plurality of sections of a generally cylindrical member; means for securing said shell around such core near one end of said shell; and means for supporting a terminal board within said shell at a location beyond one end of said yoke; a pair of permanent ring magnets; and means for supporting said magnets at the end of said shell remote from its first-named end.

18. A cathode ray tube having a generally cylindrical neck portion and a bulb portion extending therefrom along a single axis, said bulb portion having an outer surface which is a surface of revolution of a parabola whose equation is y=.62x2i.570, where x and y are the loci of points on said parabola in a system of rectangular coordinates.

References Cited in the file of this patent UNITED STATES PATENTS 2,186,595 Ruska Jan. 9, 1940 2,266,773 Law Dec. 23, 1941 2,553,792 Smith May 22, 1951 2,565,331 Torsch Aug. 21, 1951 2,570,425 Bocciarelli Oct. 9, 1951 2,785,329 Tirico Mar. 12, 1957 2,793,311 Thomas May 21, 1957