GB2034108A - Convergence adjustment arrangement using magnetic tabs with differential motion - Google Patents

Abstract

If the self-converging deflection yoke assembly in an in-line colour television tube is displaced vertically to achieve minimum raster distortion, the resulting small convergence error may be eliminated by the provision of diametrically opposed first and second magnetically permeable tabs 440a, b fixedly mounted with respect to one another for joint vertical adjustment e.g. by the engagement of the insertable gear 470 with the rack 456 formed on the tab support plate which is slidably mounted on the yoke support 426. A similar horizontally displaceable pair of tabs may additionally be employed. <IMAGE>

Description

SPECIFICATION Kinescope convergence adjustment This invention relates to convergence adjustment for a color TV kinescope display arrangement.

Color television kinescopes or picture tubes create images having portions of different colors by causing electrons to impinge upon or illuminate phosphors having different colored emissions.

Normally, phosphors having red, green and blue light emission are used, grouped into myriad trios or triads of phosphor areas, with each triad containing one phosphor area of each of the three colors.

In the kinescope, the phosphors of each of the three colors are illuminated by an electron beam which is intended to impinge upon phosphors of only one color. Each electron beam has a relatively large cross-section compared with a phosphor triad, and each beam iiluminates several triads.

The three electron beams are generated by three electron guns located in a neck portion of the kinescope opposite the viewing screen formed by the phosphors. The electron guns are oriented so that the beams as generated leave the guns in parallel or somewhat converging paths directed towards the viewing screen. In order to allow the display of a gamut of colors, the phosphor array in a given area must be illuminated by the three electron beams with an intensity dependent upon the color to be displayed. The three electron beams leaving the electron guns in separate parallel paths will, if unconverged, illuminate the viewing screen in three different locations, forming separated dots of different colors. In order to enable a single illuminated area to display a color gamut, the electron beams are caused to converge at or near the viewing screen.At the center of the screen, this may be accomplished by the use of a permanent magnet assembly mounted in the neck region of the kinescope, for producing a static magnetic field which causes the three beams to converge or register at the center of the viewing screen. This adjustment is known as "static convergence".

With the three electron beams illuminating the same area of the viewing screen, some means must be provided for causing each of the red, green and blue beams to illuminate only its respective phosphor. This is accomplished by the shadow mask. The shadow mask is a conductive screen or grill having a large number of perforations through which portions of the electron beams may pass. Each perforation is in a fixed position relative to each triad of color phosphor areas. Portions of the converged electron beams pass through one or more of the perforations and the portions begin to diverge and separate as they approach the viewing screen. At the viewing screen the portions are separated and fall upon the appropriate phosphor color based upon the direction of electron beam incidence.

That is, each electron beam of the three beams approaches a perforation from a slightly different 'direction. The beams diverge slightly after passing through the perforation and before falling upon the appropriate individual color phosphor areas. The method depends upon a high order of accuracy in the placement of the phosphor triads relative to the perforations and the apparent source of the electron beams. In order to insure that the apparent source of the electron beams is correct, a "purity" adjustment is made by which each beam is caused to illuminate only a particular one of the phosphor areas of each triad.

In order to form a two-dimensional image, the lighted dot on the viewing screen caused by the three statically converged electron beams must be moved both horizontally and vertically over the viewing screen to form a lighted raster area. This is accomplished by means of magnetic fields produced by a deflection yoke mounted upon the neck of the kinescope. The deflection yoke usually deflects the electron beam with substantially independent horizontal and vertical deflection systems. Horizontal deflection of the electron beam is provided by pairs of conductor arrays of the yoke which produce a magnetic field having vertically extending field lines. The amplitude of the magnetic field is varied with time at a relatively high rate.Vertical deflection of the electon beams is accomplished by pairs of conductor arrays producing a horizontally extending magnetic field which varies with time at a relatively low rate.

A permeable magnetic core is associated with the yoke conductors. The conductors are formed into continuous windings or coils by return conductors which may enclose the core within the coil to form a toroidal deflection winding, or which form a saddle coil winding if the coil does not enclose the core.

The viewing screen is relatively flat. The electron beam, which traverses a given distance from the point or center of deflection to the center of the viewing screen, will traverse a greater distance when deflected towards the edge of the viewing screen. From geometrical consideration, it would be expected that the electron beams will converge at a point on the surface of a sphere centered at the point of deflection since the screen surface is not spherical, but relatively flat, this alone would result in a separation of the landing points of the three electron beams near the edge of the screen. In addition, unavoidable longitudinal components of the deflecting magnetic fields cause the electron beams to be more strongly converged, whereby the surface at which the beams converge is further distorted.These effects combine to cause the light spots generated by the three beams at points away from the center of the viewing screen to be separated, even though each of the beams illuminates only its appropriate color phosphor. This is known as misconvergence, and results in color fringes about the displayed images.

A certain amount of misconvergence is tolerable, but complete separation of the three illuminated spots is generally too apparent to be acceptable.

Misconvergence may be measured as the amount of separation of the ideally superimposed red, green and blue lines of a crosshatch pattern of lines appearing on the raster as an appropriate test signal is applied to the receiver.

Formerly, kinescopes had the electron guns in a triangular or delta configuration. Convergence df the electron beams to form a coalesced light spot at points away from the center of the viewing screen was accomplished in delta-gun systems by dynamic convergence arrangements including additional convergence coils mounted about the neck of the kinescope and driven at the deflection rates by dynamic convergence circuits, as described in U.S. Patent 3,942,067 issued March 2, 1 976 to Cawood.

As described in U.$. Patent 3,789,258 issued January 1974 to Barbin, and in U.S. Patent 3,800,176 issued March 26, 1974 to Gross, et al.

current television display arrangements utilize an in-line electron gun assembly together with a selfconverging deflection yoke arrangement including deflection windings for producing negative horizontal isotropic astigmatism and positive vertical isotropic astigmatism for balancing the convergence conditions of the beams on the deflection axes and in the corners such that the beams are substantially converged at all points on the raster. This eliminates the need for dynamic convergence coils and circuits. With the increased deflection angles necessitated by commercially desirable short kinescopes, the deflection yoke is required to correct for pincushion and other raster distortions as well as providing satisfactory selfconvergence.The magnetic field nonuniformity providing the istropic astigmatism necessary for self-convergence makes the convergence dependent upon the position of the longitudinal axis of the yoke relative to the longitudinal axis of the kinescope. This sensitivity together with normal manufacturing tolerances makes it necessary to adjust the yoke transversely relative to the kinescope to achieve the best compromise convergence, but may affect the raster distortion.

If a position is selected for the yoke in which the raster distortion is satisfactory, there may be a residual convergence error. It is known that placing a permeable tab adjacent the yoke can correct the residual convergence error, but finding the correct side of the kinescope on which to apply the tab, locating the proper position and affixing the tab to the yoke with glue is timeconsuming, because the alignment operator is -normally in front of the kinescope while performing other alignments, and must be behind the kinscope to add the tabs. It is desirable to have an arrangement by which an alignment operator may conveniently correct residual convergence error.

In accordance with a preferred embodiment of the invention, a convergence correction arrangement for a deflection yoke adapted to be disposed about and substantially coaxial with a multi-color kinescope having an in-line electron gun assembly, comprises first and second magnetic field influencing means located contiguous with the yoke, and on diametrically opposite sides of the axis. A mounting means maintains a fixed separation between the influencing means and provides for differential adjustment of the influencing means relative to the axis.

In the Drawings: FIGURE 1 is a perspective view of a kinescope and yoke assembly according to the prior art; FIGURE 2 represents a displayed residual convergence error which may require correction; FIGURE 3 represents magnetic field patterns useful in expiaining the operation of the invention; FIGURES 4 and 5 are rear and perspective views, respectively, of portions of a kinescope and yoke assembly embodying the invention; FIGURE 6 illustrates another form of displayed convergence error which may be correct by an arrangement according to the invention; FIGURE 7 represents horizontal deflection magnetic field patterns useful in explaining the invention; FIGURE 8 illustrates in side and rear views an arrangement according to the invention by which two forms of converged error may be independently corrected;; FIGURE 9 is a perspective view of a convergence adjustment arrangement embodying a further embodiment of the invention, which may be mounted upon a kinescope and deflection yoke assembly; and FIGURES 10 and 13 represent individual portions or components of the arrangement of FIGURE 9 FIGURE 1 illustrates a prior art kinescope and yoke arrangement. In FIGURE 1, a kinescope designated generally as 10 includes a neck portion 1 2 containing the electron guns and a flared portion 14 through which the deflection electron beams pass to strike a phosphor screen. A yoke assembly designated generally as 20 includes a yoke mount 22 adapted to be fastened to kinescope 10 for supporting the various parts of the yoke and holding the yoke substantially coaxial with the kinescope.Mount 22 includes a front or forward portion 24 and rear portion 26 between which are placed two halves of a core 30 held together by a fastener 32. Each half of core 30 is associated with a toroidally wound vertical deflection winding 34. Pincushion correction magnets 36 are fastened at the top and at the bottom of front portion 24 of yoke mount 22. The various terminals of windings 34 and of the horizontal deflection windings, not shown, are fastened to terminals on a terminal board 38. As so far described, the deflection yoke is similar to that described in U.S. Patent Application Serial No. 938,243 filed August 1978 (British Application 7,929,336).

As known, it may be necessary to move yoke assembly 20 transversely in order to achieve optimum raster distortion. For example, the yoke described in the aforementioned Barkow application may desirably be moved transversely during factory alignment in order to obtain optimum pincushion distortion.

Vertical translation of the yoke relative to the kinescope may result in a small amount of convergence error of the form illustrated in FIGURE 2. In FIGURE 2, the red and blue vertical lines through the center of the raster are illustrated as separated. The separation, of course, may have blue on the left and red at the right at the top of the raster for the opposite direction of yoke translation. This is normally corrected in known fashion by placing a permeable tab illustrated as 40 in FIGURE 1 near the rear portion 26 of yoke mount 22, either above or below neck portion 1 2 of the kinescope. When the correct side of the neck to which the tab should be affixed is determined, the tab is temporarily affixed in an approximate position and the resulting convergence is viewed at the front of the kinescope.If the position is correct, the operator then affixes the permeable tab permanently in position. If adjustment of the position of the tab is required, a further approximate position is selected, and the result is again viewed at the front of the kinescope, and the procedure is continued until a satisfactory result is obtained.

This method is time-consuming because the operator must repeatedly move from front to back of the kinescope and yoke being aligned.

FIGURE 3a illustrates the ideal barrelled field produced by the vertical deflection windings in the vicinity of neck 12. The presence of a magnetically permeable tab 40 perturbs the horizontal magnetic field lines and tends to increase the bowing of the field lines such as lines 300 in the vicinity of the tabs, as illustrated in FIGURE 3b.

The straight field lines such as.302 which previously defined the center of the yoke field also become bowed, and previously curved lines such as 304 become straight and define the new center of the field. The presence of a tab can be thought of as tending to move the effective center of the field away from the tab. Thus, the effective center of the deflection field near the entrance end of the yoke can by use of a permeable tab be repositioned slightly relative to the mechanical center.

FIGURE 3c illustrates the result of using two tabs equidistant from the center of the yoke field.

The center of the field remains unchanged.

However, when a pair of tabs are used in an asymmetrical configuration, such as illustrated by tabs 40a and 40b in FIGURE 3d, the influence of tab 40b is exceeded by that of 40a and the center of the field is changed.

FIGURES 4 and 5 illustrate portions of a kinescope and yoke assembly embodying the invention. In FIGURE 4, the rear portion of a yoke mount is designated 426 and forms channel portions 45a and 450b. A plate 452 is arranged to slide in channel 450 formed by portions 450a and 450b. Plate 452 has en elongated central aperture 454 wider than the neck 1 2 of kinescope 10 to allow motion of plate 452 in the vertical direction without interference by the neck (12). First and second magnetic field influencing means in the form of a pair of permable tabs 440a and 440b are affixed within suitable recesses in plate 452.

The tabs are maintained on opposite sides of an axis 16 of kinescope 10 by plate 452 and are contiguous with the yoke assembly.

Both plate 452 and rear portion 426 of the yoke mounting are formed of a resilient thermoplastic material. Plate 452 is slightly thicker in the central region near the permeable tabs than at the edges riding in the channel. The taper of the thickness of plate 452 is dimensioned relative to the size of channels 450a and 450b to provide a friction fit to prevent undesired motion of plate 452 during and after adjustment.

Adjustment of plate 452 is effected by means of a gear rack 456 molded into the side of plate 452 which rides in channel portion 450a. A hole 458 formed in an enlarged portion 460 of yoke mount 426 is dimensioned to expose a part of channel portion 450a to provide a location for gear drive of rack 456. A gear illustrated as 470 of FIGURE 5b has a diameter adapted to fit into hole 458 and mates with the teeth of rack 456. Gear 470 is connected to a flexible drive shaft 472.

In operation, the kinescope with the yoke assembly aligned is placed in a yoke adjustment machine (YAM) (not shown) by which the position of the yoke relative to the kinescope can be adjusted from the screen side of the kinescope.

The operator, located in front of and viewing the screen of the kinescope, adjusts the position of the yoke for least raster distortion. In order to correct residual convergence error, the operator turns gear 470 by means of flexible drive shaft 472, thereby moving plate 452 up or down relative to the yoke and kinescope as required.

Vertical motion of plate 452 causes a differential motion of tabs 440a and 440b toward and away from axis 16; i.e., when tab 440a moves towards neck portion 12 and axis 16, tab 440b moves away. This results in a shift of the center of the deflection field, as described in conjunction with FIGURE 3, and may be used to correct residual convergence error. Gear 270 is then removed from hole 458, and the kinescope-yoke assembly is ready for use. If desired, glue may be used to hold plate 452 and thereby prevent inadvertent misadjustment.

The same principle can be applied in the horizontal direction. A form of convergence error involving raster size is illustrated in FIGURE 6. The horizontal size or width of the red raster is greater than that of the blue raster. The green or centerbeam raster (not shown) lies midway between.

This distortion may be corrected by an arrangement similar to that illustrated in FIGURES 4 and 5 providing differential motion of the tabs in a horizontal plane.

FIGURE 7a illustrates an unmodified pincushion-shaped magnetic field (or a field having negative isotropic astigmatism).

Field line 602 is straight, representing as in the case of FIGURE 3 the center of the magnetic field.

The presence of a single tab horizontally displaced to the right from the axis of the kinescope as in FIGURE 7b results in a curvature to field line 602 and straightens field line 600, while line 604 remains curved. The tab may be viewed as isolating or shielding the axis region of the kinescope from the region of greatest magnetic field strength on the right, whereby the field from the left becomes more influential. The straightening of field line 600 moves the effective center of the magnetic field to the right.

The use of a pair of tabs symmetrically located with respect to the axis results in a symmetrical field configuration similar to the unmodified field in FIGURE 7a. Offsetting the pair of tabs to the left as illustrated in FIGURE 7d straightens field line 600 and moves the effective center of the magnetic field to the right, thereby providing the same result as the single tab of FIGURE 7b. The tabs are adjusted so as to cause the red and blue rasters to coincide.

Both horizontal and vertical motion of the tabs may be provided by mounting the four tabs on a wobble plate providing vertical and horizontal motion. However, this may result in undesirable interdependence of the adjustments. Independent motion in each of two orthogonal directions may be provided by a pair of independent sliding supports as illustrated in FIGURE 8. In FIGURE 8, elements corresponding to those of FIGURE 4 are provided with the same reference numbers. In FIGURE 8, a horizontal slider plate 852 bears tabs 840a and 840b located adjacent a central aperture 854 which is larger than the neck of the kinescope. Plate 852 is positioned in a pair of channels 850a and 850b which allow motion of plate 852 in the horizontal direction. A drive mechanism for plate 852, not shown, may be coupled to a YAM machine for remote positioning of plate 852 for raster size adjustment.

Other embodiments of the invention will be apparent to those skilled in the art. A friction drive may be used instead of rack 456 and gear 470, slots and screws may be used to retain plate 452 rather than using channels 450, and the longitudinal position at which permeable tabs 440 are located may be selected at other than the rear of the yoke. The gear drive may be integral with and remain a part of the yoke assembly. Also, the gear drive may, if desired, be at right angles to that shown.

The above convergence correction arrangement has the disadvantage that at the extremes of the positioning of the magnetic tabs the sliding plate 452 or 482 upon which the tabs are mounted may project beyond the edge of the main portion of the yoke body. Thus, the plate 452 or 482 or both may interfere with a YAM mechanism in any but its center position. It may be desirable to have a convergence correction arrangement by which magnetic tabs at the rear of the yoke may be moved vertically with a differential motion by a mechanism which does not project beyond the rear of the yoke or farther than the extreme position taken by the tab.

In FIGURE 9, a circular baseplate designated generally as 110 includes a central aperture 114 dimensioned to clear the neck of a kinescope, not shown. Baseplate 110 also includes locking arms 120 and 122 by which the baseplate can be affixed to the rear or beam entrance end of a deflection yoke, not shown. Baseplate 110 includes a vertically-extending channel 11 2 and vertically extending slots 11 6 and 118 centered in channel 112.

Baseplate 110 is molded from a relatively flexible plastic material. Locking arms 1 24 and 126 are molded integrally with the other portions of baseplate 110. Arm 124 includes a flexure point or hinge 130 which allows arm 124 to be moved relative to baseplate 110. In one extreme of its position, the major portion of arm 124 is within a cutout 136, the outermost portions of arm 124 then lie within the radius of the principal portion of baseplate 110. Locking arm 126 includes a flexure point or hinge 1 28 for similar purpose. Locking arms 124 and 126 include locking teeth 134 and 132, respectively.

The convergence adjustment arrangement also includes a tab carrier designated generally as 1 50.

Tab carrier 1 50 has a flat body 1 51 defining a central aperture 1 52. Body 151 of carrier 1 50 is dimensioned to fit within and slide along channel 11 2. The smaller dimension of central aperture 1 52 clears the neck of the kinescope. Tabs 1 54 and 1 56 of magnetically permeable material are positioned in the top and bottom of body 1 51. A set of pins 1 58 and 1 60 projects from the top and bottom of body 151. That portion of pin 1 58 extending towards baseplate 110 is intended to index with slot 11 6. Similarly, that portion of pin 1 60 projecting towards baseplate 110 is intended to index with slot 118.The indexing of pins 1 58 and 160 with slots 11 6 and 118, together with the mating of the sides of body 151 with the sides of channel 112 constrain body 1 50 from any rotational motion relative to baseplate 110 and together act as a track allowing only vertical motion of carrier 1 50.

The convergence adjustment arrangement further includes a rotary drive plate designated generally as 1 70. As illustrated, drive plate 1 70 includes a central aperture 172 through which the neck of the kinescope can project. The outer diameter of drive plate 1 70 is somewhat larger than the outer diameter of baseplate 110 and is approximately equal to the diameter of the rear of the yoke to which baseplate 110 is affixed. A drive gear illustrated as 1 74 forms at least a portion of the outer periphery of drive plate 170. Gear 174 is adapted to be engaged by a drive gear of the YAM.

A second track formed by a pair of channels 180 and 1 82 is formed in the side of drive plate 1 70 facing tab carrier 1 50. Channels 1 80 and 1 82 are intended to index with pins 1 58 and 1 60, respectively. The distance between tracks 1 80 and 182 along any diameter of drive plate 1 70 equals the distance between pins 1 58 and 1 60.

Channels 1 80 and 1 82 extend in directions including both radial and tangential components relative to the central axis of the baseplate. When assembled, tab carrier 1 50 fits within channel 112 to form a substantially flush surface against which the principal portion of drive plate 170 can bear.

The outer periphery of drive plate 1 70, however, overlaps the outer diameter of baseplate 11 0. An internal tooth structure 184 (FIGURE 11) is formed in the periphery of drive plate 170 in this overlap region to allow the plates to be locked together after adjustment. A pair of slots 176,178 are formed at a fixed radius from the center of drive plate 1 70. Slots 1 76 and 178 overlap a portion of locking arms 124 and 126 to provide access for forcing locking arms 124 and 1 26 outward and thereby engage toothed portions 132 and 1 34 against the internal tooth structure 184 of drive plate 1 70 in order to lock the entire assembly together after adjustment.

In operation, baseplate 110 is affixed to the rear of the deflection yoke and kinescope assembly by slipping central aperture 11 4 of baseplate 110 over the neck of the kinescope and engaging the yoke with locking arms 120 and 122. Baseplate 110 is thereby oriented in a position in which channel 112 and slots 116, 118 extend vertically. Central aperture 152 of tab carrier 1 50 is slipped over the neck, and body 1 51 is pushed into channel 112.Central aperture 1 72 of drive plate 170 is then placed over the neck of the kinescope, and rotated so as to index pins 1 58 and 1 60 with tracks 1 80 and 1 82. Locking arms 124 and 126 are then depressed so as to pivot them at hinge points 128 and 130 and thereby depress toothed portions 132, 134 below the radius of the principal portion of baseplate 110.

Drive plate 170 is then pushed into engagement with pins 1 58, 160 and locking arms 124, 126.

The complete assemblage of kinescope, yoke and convergence adjustment arrangement can then be mounted into a YAM for adjustment.

During the adjustment, a drive gear of the YAM engages drive gear 174 of drive plate 170 and turns it relative to baseplate 110. This causes index pins 1 58 and 1 60 to ride to a different position along channels 180 and 1 82. However, the rotational motion imparted to drive plate 1 70 cannot cause a rotational motion of carrier 1 50 because of the indexing of pins 158 and 160 with slots 116 and 118 of baseplate 110, and also because the sides of channel 112 bear upon the sides of body 151.

After completion of the convergence adjustment by rotation of drive plate 1 70, the alignment operator inserts a screwdriver through slot 1 76 and engages it between the end of locking arm 124 and cutout 136 to force the end of the locking arm out of bottom portion 138 of cutout 136, whereby the end of arm 124 will snap into engagement with portion 1 40 of cutout 136.

This forces the teeth 1 34 of locking arm 1 24 against the internal tooth structure 184 of drive plate 170. Similarly, a screwdriver inserted through slot 1 78 is used to force teeth 132 of locking arm 1 26 against the internal tooth structure 184 of the drive plate 170. Thus, drive plate 170 is fixed in position with respect to baseplate 110, and the tabs on carrier 1 50 are also held in a fixed position relative to baseplate 110 and the rear of the yoke.

It will be apparent to those skilled in the art that either slots 116,118 or channel 112, alone, would be sufficient to restrain tab carrier 1 50 against rotary motion and thus either alone may serve as the first track. Thus, slots 11 6, 11 8 when used in conjunction with channel 112 may be a loose fit so as to merely provide stop limits to the vertical motion of carrier 1 50 in channel 112.

Other arrangements may be used for locking drive plate 1 70 to baseplate 110 upon the completion of adjustment, as for example by the use of screws or adhesive rather than by the use of locking arms, It is also apparent that body 1 51 of tab carrier 1 50 establishes a fixed separation between tabs 1 54 and 1 56, and thus motion of either tab will cause the other to move in a tracking relation.

Consequently, only one of channels 180 or 182 and the pins with which they index is necessary.

It is also possible to eliminate body 1 51 of carrier 1 50 altogether, so long as the tabs 1 54, 1 56 are fitted with suitable projecting pins. With this arrangement, the fixed separation between the tabs is determined by the radial separation of tracks 1 80 and 1 82. Such a configuration if used without a channel might allow the tabs to rotate about the pins, if single pins 1 58, 1 60 were to be used as illustrated. Such a rotation could be prevented by the use of multiple pins engaging the track.

It is apparent that the assembly may be positioned at 900 to the position shown in FIGURE 9, so that tabs 1 54 and 1 56 move in a horizontal direction.

It is also possible to make the tracks from ridges projecting from the surface of the drive plate and/or baseplate. With such an arrangement, the ridges would engage matching slots or depressions in the tabs or in the tab carrier.

Finally, it will be apparent that baseplate 110 can be formed as an integral portion of the rear of the deflection yoke itself for savings in both material and in assembly labor.

Claims (15)

1. A convergence correction arrangement for a deflection yoke adapted to be disposed about and substantially coaxial with a multi-color kinescope, having an in-line electron gun assembly, said arrangement having first and second magnetic field influencing means disposed contiguous with the yoke, said first and second influencing means are located on diametrically opposite sides of the axis; and mounting means are provided for maintaining a fixed separation between said first and second field influencing means and for providing for differential adjustment of said first and second means towards said axis.

2. An arrangement according to Claim 1 wherein said first and second magnetic field influencing means comprise magnetically permeable tabs.

3. An arrangement according to either of Claims 1 or 2 wherein said first and second field influencing means are disposed near the entrance end of said yoke.

4.An arrangement according to Claims 1 to 3 wherein said mounting means comprises a member which maintains said fixed separation between said first and second field influencing means, for simultaneous linear translation of said member, and said first and second field influencing means, along a path perpendicular to said axis.

5. An arrangement according to Claim 4 wherein said member defines an aperture larger than the neck portion of the kinescope.

6. An arrangement according to Claim 4 further comprising a guide channel associated with said yoke for restraining said member against motion except along said path perpendicular to said axis.

7. An arrangement according to Claims 5 or 6 wherein said path is substantially vertical.

8. An arrangement according to Claims 5 or 6 wherein said path is substantially horizontal.

9. An arrangement according to Claim 6 wherein said member includes a rack by which its position relative to said channel may be adjusted.

10. An arrangement according to Claim 2 wherein first channel means coupled to the body of said yoke and to said tabs for restraining said tabs against tangential motion about said axis while allowing radial motion; and rotational drive means rotatably coupled to said body of said yoke and including second channel means coupled to said tabs, said second channel means having radially and tangentially-extending components, said second channel means being coupled to said tabs for converting a rotational force on said rotational drive means to a radial force on said tabs.

11. An arrangement according to Claim 10 wherein said first channel means comprises first and second radially-extending slots.

12. An arrangement according to Claim 11 wherein said first and second tabs include projections for engaging said first and second slots.

13. An arrangement according to Claim 12 wherein said second channel means comprises at least third and fourth slots formed in said mounting means, and wherein said tabs further comprise projections coupled to said third and fourth slots.

14. An arrangement according to any previous Claim further comprising fixed means coupled to said yoke and to said mounting means for fixing the relative position of said yoke and said mounting means when convergence correction is completed.

15. An arrangement according to any previous Claim wherein said mounting means comprises engagement means adapted for coupling to a YAM.

1 6. A method for aligning a deflection yoke in conjunction with a kinescope, comprising in order the steps of: mounting the deflection yoke on the kinescope; adjusting said yoke relative to said kinescope for minimum raster distortion; differentially adjusting first and second field influencing means located on opposite sides of the kinescope axis for best convergence.

1 7. Convergence correction arrangement or method substantially as hereinbefore described with reference to Figures 4 and 5 or Figure 8 or Figure 9 or Figures 9-13.