US3048740A

US3048740A - Electron beam convergence apparatus

Info

Publication number: US3048740A
Application number: US452954A
Authority: US
Inventors: Morris D Nelson
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1954-08-30
Filing date: 1954-08-30
Publication date: 1962-08-07
Anticipated expiration: 1979-08-07

Description

Aug. 7, 1962 M. D. NELSON ELECTRON BEAM CONVERGENCE APPARATUS 4 Sheets-Sheet 1 Filed Aug. 30, 1954 INVENTOR.

ME @QEMQ Aug. 7, 1962 M. D. NELSON ELECTRON BEAM CONVERGENCE APPARATUS 4 Sheets-Sheet 2 Filed Aug. 50, 1954 wmwmkuwk vi E Aug. 7, 1962 M. D. NELSON ELECTRON BEAM CONVERGENCE APPARATUS 4 Sheets-Sheet 5 Filed Aug. 30, 1954 Aug. 7, 1962 M. D. NELSON ELECTRON BEAM CONVERGENCE APPARATUS 4 Sheets-Sheet 4 Filed Aug. 30, 1954 ttes atet 3,048,740 Patented Aug. 7, 1962 ice 3,048,740 ELECTRON BEAM CONVERGENCE APPARATUS Morris D. Nelson, New York, N.Y., assignor to Radio Corporation of America, a corporation of Delaware Filed Aug. 30, 1954, Ser. No. 452,954 26 Claims. (Cl. 31522) This invention relates to systems for controlling the electron beams of cathode ray tubes and particularly to systems in which a plurality of beams is deflected by a common deflection apparatus.

One type of cathode ray tube with which the present invention may be successfully employed is a color kinescope of the general type described in an article titled A Three-Gun Shadow-Mask Color Kinescope, by H. B. Law published in the Proceedings of the I.R.E., vol 39, No. 10, October 1951 at page 1186. Such a tube has a luminescent screen as part of a target electrode structure and in which different phosphor areas produce differently colored light when excited by electron beams impinging upon it from different angles, the angle of impingement determining the particular color of the light produced by the phosphor areas.

It is necessary for the satisfactory operation of such kinescopes to effect substantial convergence of the diiierent electron beams at all points of the raster scanned thereby at the target electrode structure. In general, this beam convergence problem is treated in an article titled Deflection and Convergence in Color Kinescopes by A. W. Friend, published in the Proceedings of the I.R.E., vol. 39, No. 10, October 1951 at page 1249. One type of apparatus for controlling the convergence of a plurality of electron beams at a target electrode structure and with which the present invention is particularly concerned comprises, in general, individual electromagnetic means located respectively adjacent to the predeflection paths of the respective beams and of such a character as tobe energizable from the beam deflection circuits in a manner to efllect the desired beam convergence.

The particular beam convergence electromagnetic means to which this invention pertains includes for each beam a pair of pole pieces located internally of the kinescope envelope. The internally located pole pieces are energized by magnetic apparatus located externally of the kinescope envelope and associated respectively with the different pairs of pole pieces. The magnetic apparatus may be entirely electromagnetic or it may include some permanent magnetic structure inasmuch as the convergence pole pieces in general require cnergization both statically and dynamically, the latter being in accordance with a iunction of the angles through which the electron beams are deflected. Since the energization of the magnetic convergence apparatus requires additional circuit components, it is generally desirable to provide such energization with a minimum of such additional components.

It, therefore, is an object of the present invention to provide improved apparatus for effecting convergence of a plurality of electron beams in a multiple beam kinescope.

Another object of the invention is to provide improved apparatus by which to energize the individual magnetic structures under the control of which a plurality of electron beams respectively are converged substantially at the target electrode structure of a tri-color kinescope.

In accordance with the invention, the individual convergence magnets of a tri-color kinescope are energized by employing waves which are readily available in both the vertical and horizontal deflection circuits. These waves are suitably shaped and impressed upon respective circuits of a suitable character so as to present the proper impedances to the sources from which the waves are derived, thereby to minimize the additional loading of the deflection circuits and, to avoid undesirable interaction between the two deflection circuits. These results are attained by a novel arrangement of the respective circuit components including resistors, capacitors, and inductors, thereby obviating the need for additional amplification of the energizing waves. The energizing waves are generally symmetrical and non-linear, having substantially parabolic or sinusoidal forms or some intermediate shape.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a view showing the general arrangement of image-reproducing apparatus embodying one form of an electron beam convergence system in accordanw with this invention;

FIGURE 2 is a transverse cross-sectional view taken generally on the line 2-2 of FIGURE 1 and showing the arrangement of the beam convergenc electromagnets;

FIGURE 3 is a schematic circuit diagram of one embodiment of the novel apparatus in accordance with the invention for energizing the beam convergence magnetic apparatus;

FIGURE 4 is a transverse cross-sectional view similar to that of FIGURE 2 and showing a form of permanent magnetic apparatus for effecting the static convergence of the electron beams;

FIGURE 5 is a schematic circuit diagram of another embodiment of the novel apparatus in accordance with the invention for energizing the beam convergence magnetic apparatus; and,

FIGURE 6 is a schematic circuit diagram of another embodiment of the novel apparatus in accordance with the invention for dynamically energizing the beam convergence electromagnetic apparatus, especially where permanent magnet means is employed to effect initial beam convergence.

Reference first will be made to FIGURE 1 for a general description of an illustrative embodiment of electron beam convergence system in accordance with the present invention. The system includes a tri-color kinescope 11 which may be of the same general type -as that disclosed in the H. B. Law paper previously referred to. The kinescope preferably has a luminescent screen 12 provided with a multiplicity of small phosphor areas arranged in groups and capable respectively of producing light of the different component colors in which the image is to be reproduced when excited by an electron beam. In back of and spaced from the screen 12 there i an apertured masking electrode 13 having an aperture for and in substantial alignment with each group of phosphor areas of the screen 12. It will be noted that both the luminescent screen and the masking electrode have partial spherical surfaces which are substantially concentric, whereas th corresponding components of the kinescope shown in the Law paper are substantially planar. It is to be understood, however, that the present invention is equally applicable to either form of target electrode configuration.

In the particular case illustrated, the kinescope also has a plurality of electron guns, equal in number to the number of component colors in which the image is to be reproduced. Each of these guns may be conventional, consisting of a cathode, a control grid and a focussing electrode. Since the three guns are identical, the different parts thereof Will be referred to collectively as the cathodes 14, the control grids 1S, and the focussing electrodes 16. The three electron guns produce schematically represented

electron beams

17, 18 and 19 by which to energize, respectively, the blue, red and green phosphor'areas of the screen 12. When these electron beams are properly converged at the target electrode structure including the screen 12 and the masking electrode 13, they pass through the apertures of the masking electrode from different directions and impinge upon different phosphor areas of the various groups so as to produce blue, red and green light. It is to be noted that the size of the phosphor areas, the angles between the beams and the spacing of the mask 13 from the screen 12 as compared with the length of the tube are exaggerated for better illustration of this aspect of the kinescope.

The electron optical apparatus of the kinescope 11 also includes a beam-accelerating electrode consisting, in'the present instance, of a conductive wall coating 20 formed on the inner surface of the tubular glass neck 21 and conical section 22 of the kinescope extending from the region adjacent to the outer end of the focussing electrodes 16 to the target electrode region. Preferably, the target electrode structure, including the masking electrode 13 and the luminescent screen 12, which for this purpose may be metallized, is electrically connected to the wall coating 20 by suitable conventional means (not shown). Metallization of a luminescent screen of the character described may be efiected in the manner disclosed in a paper by D. W. Epstein and L. Pensak titled Improved Cathode Ray Tubes with Metal-Backed Luminescent Screens published in the RCA Review, vol. VII, March 1946 at pages -10.

The described electrode structure of the kinescope may be energized in a conventional manner such as that illustrated. The source of energy is represented by abattery 23 across the terminals of which there is connected a voltage divider 24. The cathodes 14 are connected to the grounded point of the voltage divider and the control grids are connected to a point which is somewhat negative relative to ground. Similarly, the focussing electrodes 16 are connected to a point on the voltage divider which may conventionally be at a potential of approximately 4,000 volts positive relative to the grounded cathodes. Also, the beam-accelerating anode, including the wall coating 20, is connected to the voltage divider 24 at a point which may conventionally be approximately 27,000 volts positive relative to the grounded cathodes.

The

electron beams

17, 18 and 19 are modulated suitably in intensity under the control of color-representative video signals derived from a source 25. It will be understood that the video signal source is represented herein entirely diagrammatically since it does not form an essential part of the present invention. The signal source 25 usually will be part of a signal receiver and may be understood to include a signal detector, or equivalent device, together with one or more stages of video signal amplification. Alternatively, the video signal source may be a color television camera in the event that the kinescope 11 is employed as a monitor, for example. Also, it will be understood that the illustrated connection of the video signal source 25 to the electron guns of the kinescope 11 is merely diagrammatic and accordingly these connections may or may not be made directly to the cathodes 14. Instead, it will be understood, that they may be made to the grids 15 or, in accordance with other modes of operation of color image-reproducing apparatus, the video sig nal source may be connected both to the cathodes and to the control grids of the electron guns.

Also associated with the color kinescope 11 is a deflection yoke 26 which may be entirely conventional including two pairs of suitably placed coils electrically connected together in such a manner that, when properly energized, electromagnetic fields are produced, whereby to effect both horizontal and vertical angular deflections of the electron beams so as to scan the usual rectangular raster at the target electrode structure. Energization of the deflection coils comprising the yoke 26 may be effected by conventional vertical and horizontal deflection wave generators 27 and 28, respectively. Such apparatus will be understood to function suitably toproduce substantially sawtooth wave energy at both horizontal and vertical deflection frequencies so that the fields produced by the yoke 26 are varied in a substantially sawtooth manner.

The beam convergence system, in accordance with the present invention, also includes a plurality of electromagnetic field-producing elements such an the magnets 29', 30 and 31 (see also FIGURE 2) mounted around the neck 21 of the color kinescope adjacent to the predeflection paths of the electron beams. It is to be understood that the precise location of these magnets is not necessarily indicated in FIGURE 1. Instead, as will appear in greater detail from a subsequent portion of the specification, it is to be understood that each of these magnets is located relative to one of the electron beams so as to influence its associated beam to the virtual exclusion of the others. Furthermore, it is to be understood that these magnets are of a character which, when suitably energized, produce respective fields which are transverse to the associated beam paths and in directions to move the associated beams radially relative to the longitudinal axis of the kinescope 11.

Each of these convergence electromagnets includes a pair of spaced pole pieces and at least one energizing winding. Preferably two windings are provided for each of the electromagnets for separate energization. These features will be described subsequently in greater detail with reference to FIGURE 2.

Before describing the details of the particular beam convergence system in accordance with the present invention, a brief description will be given of the general manner in which the apparatus functions to produce the desired results. The

convergence magnets

29, 30 and 31 are energized, in one embodiment, by substantially unidirectional energy so as to eifect an initial convergence of the electron beams substantially at the target electrode structure including the screen 12 and the apertured masking electrode 13. In order to do this, the unidirectional energization of these magnets is effected in such a way that the magnets may be individually energized in different magnitudes. In effecting this initial beam convergence, it is to be understood that the beams may be in any desired one of their different deflected positions. For example, they may be initially converged at the center of the raster to be scanned. Alternatively, they may be initially converged at one corner of the raster.

The convergence magnets 29, 30' and '31 also are dynamically energized by the control wave energy derived from a suitable generator (shown in, and described subsequently with reference to, FIGURE 3) so as to effect a variation in the magnitude of the transverse fields produced respectively thereby. These field strength variations are in accordance with a predetermined function (usually approximately parabolic) of the angular beam deflection. Variations in the strength of the fields produced by the convergence magnets effect corresponding variations in the paths of the electron beam components relative to the longitudinal axis of the tube. Hence, suitable variations are made in the convergence angles between the various beam components so as to produce the desired convergence of the beam components substantially at the target electrode structure including the screen 12 and the masking electrode 13.

For a further description of this type of beam convergence apparatus, reference now will be made to FIG- URE 2 of the drawings. This figure shows more clearly the positions of the

convergence magnets

29, 30 and 31 relative to one another and to the electron beams with which they are respectively associated. Inasmuch as all of these magnets are substantially the same, only one of ace-e740 them will be described in detail. The convergence magnet 29, which is associated with the blue electron beam 17, is provided with a core 32 having two external pole pieces 33 and 34. These pole pieces are mounted so as to be in close association with the tube neck 21. The magnet also is provided with an energizing structure including coils '35 and 36 shown primarily for convenience of illustration as mounted respectively on the two core legs which terminate in the pole pieces 33 and 34. Alternatively, and perhaps preferably, the coils may be wound as a unitary structure and mounted on the body portion of the core 32.

In FIGURE 2, it also is illustrated that for each of the convergence magnets there are provided on the inside of the tube neck 21 internal pole pieces so as to increase the etfectiveness of these magnets. The magnet 29, for example, is providedwith a pair of inwardly extending internal pole pieces 37 and 38, associated respectively with the external pole pieces 33 and '34. By such means, it is seen that the reluctance of the magnetic circuit is considerably decreased, and also the flux distribution of the field produced between the internal pole pieces 37 and 38 is considerably improved.

Thus, the convergence magnet 29 effectively produces a field which, in the vicinity of the electron beam 17, is substantially transverse to the axis of the kinescope. By means of such a field, the electron beam 17 may be moved radially toward or away from the longitudinal tube axis. The direction and magnitude of such a beam movement is controlled by the energization of the magnet by means including the

coils

35 and 36. The convergence magnets and 31 respectively control the electron beams 18 and 19' in a substantially similar manner.

The convergence magnets may be energized by means of the circuit shown in FIGURE 3, to which reference now will be made. The convergence magnets 29, 3t) and 31 are substantially identical and are energized by substantially identical circuits. Therefore, the description will be limited to the particular circuits by which the coils and 36 of the convergence magnet 29 are energized, it being understood that the same description applies equally well to the circuits illustrated for the energization of the

other convergence magnets

30 and 31. Also, the

magnets

29, 30 and 31, together with the individual energizing and controlling circuits therefore, will be referred to as the blue, red and green convergence apparatus. As used in the particular circuit to be described, the

coils

35 and 36 of the blue convergence magnet 29 have 800 and 1200 turns, respectively. These coils also are connected in a series aiding relationship in the energizing circuits therefor.

A substantially parabolic voltage wave at the vertical deflection frequency is derived from the cathode of the vertical deflection output tube 4%} This wave is impressed upon the energizing circuits of the blue convergence apparatus 41 including the series connection of a potentiometer 42 and a capacitor 43 connected between the cathode of the vertical output tube and a point of reference potential such as ground, for example. The movable contact of the potentiometer 42 is connected to an adjustable resistor 44 and thence through a blocking capacitor 45 and a choke coil 46 to the series arrangement of the convergence magnet coils 36 and 35 in the order named. The value of the blocking capacitor 45 is chosen so as to have, at the vertical deflection frequency, a capacitive reactance which is equal to the inductive reactance of the series combination of the convergence magnet coils 35 and 36 and the series choke coil 46. Hence, in the circuit including the adjustable resistor 44, the blocking capacitor 45, the choke coil 46 and the

convergence magnet windings

35 and 36, the adjustable resistor 44 constitutes the dominant impedance offered to the substantially parabolic voltage wave derived from the output tube and, thus, the current which flows in the described series circuit is caused to be substantially parabolic in Wave shape. The adjustable resistor 44 serves as an amplitude control for the vertical dynamic convergence Wave.

The substantially parabolic voltage wave derived from the vertical output tube 46 is developed across the potentiometer 42 into a voltage Wave having a substantially sawtooth form. By suitably adjusting the movable contact of the potentiometer 42, a controllable amount of this developed sawtooth voltage Wave component is combined with the substantially parabolic voltage wave impressed upon the described series energizing circuit for the convergence magnet coils 35 and 36 which also includes a capacitor 47 connected to the end of the series circuit opposite to that which includes the choke coil 46. The combination of the sawtooth wave with the parabolic Wave is for the purpose of tilting the parabolic wave so as to effectively shift the minimum amplitude point of the parabolic wave either toward the beginning or end of the Wave. Thus, the potentiometer 42 is effectively a vertical tilt or phasing control.

A fixed sawtooth wave component, which is developed across a resistor 48 connected in series with a resistor 49 and a choke coil 51 to the cathode of the horizontal deflection output tube 52, is impressed upon the series energizing circuit for the convergence magnet 29 and effectively tilts the vertical frequency parabolic voltage wave impressed upon the energizing circuit initially in the reverse direction from that produced by the sawtooth wave component derived from the potentiometer 42 Thus, by an adjustment of the potentiometer 42, the vertical frequency parabolic wave may be tilted in either direction. In order to allow the vertical output tube 4% to operate normally despite the derivation from its cathode of the energizing waves for the convergence apparatus, the sawtooth deflection wave capacitor 53 and the associated peaking resistor 54 are connected to the cathode of the output tube 40 instead of to ground, as in the usual case.

A substantially parabolic voltage wave at horizontal deflection frequency is developed at the cathode of the horizontal output tube 52 across the capacitor 55. This parabolic voltage wave is impressed by means including a coupling capacitor 56 upon the convergence apparatus. With respect to the blue convergence apparatus 4-1, an adjustable amplitude of this convergence Wave is impressed by means of a potentiometer 57 and a capacitor 58 upon the 800 turn coil 35 of the blue convergence magnet 29. The capacitor 58, the 800 turn magnet coil 35, the 1200 turn magnet coil 36, the choke coil 46 and a horizontal phasing capacitor 59 connected in parallel with the magnet coils 35 and 36 form a series parallel circuit which is resonant substantially at the horizontal deflection frequency. It is to be noted that the inductance of the magnet coils 35 and 36 is eifectively in shunt with the choke coil 46 for the horizontal frequency convergence wave component, whereas this inductance is in series with the choke coil for the vertical frequency convergence wave component. The horizontal phasing capacitor '59 preferably is adjustable over a range such as that indicated so as to assist in resonating the parallel circuit. The voltage impressed upon the junction of the two convergence magnet coils 35 and 36 is increased by the auto-transformer action in the convergence magnet core at the junction point of the coil 36 and the choke coil 46. The capacitor 58 is series resonant with the net inductive reactance of the described circuit, as seen at the junction point between the two magnet coils 35 and 36, thereby producing a substantially sinusoidal current wave at the horizontal deflection frequency which is required for energization of the convergence apparatus and which is in phase with the substantially parabolic voltage wave derived from the horizontal output tube 52. The phasing of the horizontal frequency substantially sinusoidal convergence current may be shifted by an adjustment of the phasing capacitor 59. The general eifect is similar to that described in connection with the phase control of the vertical frequency parabolic convergence wave by the adjustment of the tilt controlling potentiometer 42. The phase control of the horizontal frequency convergence wave effectively moves the minimum current point toward the left or right hand side of the raster scanned at the kinescope screen.

In order to effect initial convergence of the electron beams at the desired point, the convergence apparatus in this embodiment of the invention is also energized by unidirectional current. Such beam convergence is commonly referred to as the static convergence in contradistinction to the dynamic beam convergence effected by means such as the apparatus described up to this point and varying as a function of the beam deflection angle. In this form of the invention, the static convergence is eifected by electromagnetic means. The D.-C. voltage developed across resistors 48 and 49 by the current flowing in the horizontal output tube 52 is filtered by means of the series choke coil 51 and a capacitor 61 shunting the resistors 48 and 49. The filtered D.-C. voltage is impressed upon a potentiometer 62 which may be adjusted to control the amplitude of the D.-C. energization of the convergence apparatus. The desired amplitude of D.-C. voltage derived from the potentiometer 62 is impressed upon the convergence magnet coils 35 and 36 by means including a series resistor 63. This resistor serves to isolate the circuit in which the D.-C. static convergence voltage is developed from the vertical frequency dynamic convergence wave which is present at the junction point between the choke coil 46 and the resistor 63.

Some simplification of the convergence apparatus may be effected by eliminating the electromagnetic apparatus by which to produce static beam convergence. This may be achieved by providing permanent magnet facilities for effecting static beam convergence. One such facility of this character which may be employed is shown in FIG- URE 4, to which reference now will be made. The

beam convergence magnets

29, 30 and 31' for controlling the blue, red and

green electron beams

17, 18 and 19, respectively, are generally similar to the corresponding beam convergence magnets shown in FIGURE 2. In the present case, however, the core of the magnet 29, for example, is effectively split into two

sections

64 and 65. Mounted between the

core sections

64 and 65 in suitable recesses formed therein is a substantially cylindrical permanent magnet 66. This magnet is polarized substantially diametrically so as to present north and south poles N and S, respectively, in the two halves thereof substantially as indicated. The magnet may be provided with suitable adjusting facilities, such as a screw driver slot 67, formed in one or both ends thereof. The rotation of the permanent magnet 66 between the

core sections

64 and 65 enables the strength of the permanent magnetic field produced between the internal pole pieces 37 and 38 to be adjusted both in magnitude and in polarity. Similar permanent magnets are provided with each of the other convergence magnets 30' and 31' and each is adjustable independently of the others.

It may be seen from the description of the embodiment of the invention shown in FIGURE 4 by which permanent magnetic static convergence is efifected that a somewhat simpler convergence apparatus may be provided with an accompanying lower cost and without any substantial reduction in the flexibility of the apparatus. It is to be further understood that a combination of permanent and electromagnetic static beam convergence apparatus may be employed in practicing this invention by combining the facilities shown in FIGURE 4 with those shown in, described with reference to, FIGURES 2 and 3.

The convergence apparatus embodying the present invention is susceptible of further simplification at the cost of somewhat less flexibility. Two or all three sets of the convergence magnet coils may be connected in parallel and the individual adjustment controls, such as the vertical frequency amplitude controlling resistor 44, the vertical frequency tilt controlling potentiometer 42, the horizontal frequency amplitude controlling potentiometer 57, the horizontal frequency phase controlling capacitor 8 59 and the D.-C. voltage controlling potentiometer 62, may be eliminated for one or two of the convergence magnets. In such a case, it is seen that individual adjustment of the different convergence apparatus is not possible.

Before describing in detail another embodiment of the invention in which some simplification is effected in the apparatus employed without substantial reduction in control flexibility, it is to be noted that the anode of the horizontal output tube 52 is connected in a somewhat conventional manner to an intermediate point on the Winding of an output transformer 68. One terminal of this winding is connected as indicated to a source of positive voltage which preferably is the so-called boosted B supply derived by the usual combination of the low voltage power supply and the damper circuit. Another intermediate transformer tap is coupled by means including a capacitor 69 to the horizontal deflection coils 71. A unidirectional centering current is supplied to the horizontal deflection coils 71 from a centering potentiometer arrangement 72 connected as indicated to a suitable unidirectional voltage source having a grounded terminal. The centering current is applied to the deflection coils through a choke coil 73 and a resistor 74. The A.-C. circuit through the deflection coils 71 is completed by means including a capacitor 75. The capacitors 69 and 75 serve as blocking capacitors for the unidirectional centering current.

It will be understood that the detailed apparatus shown and described with reference to the blue convergence apparatus 41 is substantially the same as that employed for the red and

green convergence apparatus

76 and 77, respectively.

A somewhat different embodiment of the present invention wherein some of the described simplification of control apparatus is incorporated is shown in FIGURE 5, to which reference now will be made. In general, this embodiment of the invention is similar to that shown in, and described with reference to, FIGURE 3. Accordingly, those components which are essentially the same in the two figures are identified by the same reference characters. In this case, a single vertical frequency tilt control is provided. It includes a potentiometer 78 which is connected in series with a capactior 79 from the cathode of the vertical deflection output tube 40 to ground. The adjustable contact of the potentiometer 78 is connected to the convergence magnet coils 35 and 36 by means including a series connection of a resistor 80, the capacitor 45, the vertical frequency convergence amplitude controlling resistor 44 and the choke coil 46.

The connections to the horizontal deflection output circuit also are somewhat different. The terminal of the transformer 68 which is remote from the anode of the horizontal output tube is connected by means including a capacitor 81 to the horizontal convergence amplitude control apparatus including the potentiometer 57' for the blue convergence apparatus. By such means, a substantially parabolic voltage wave at the horizontal deflection frequency is impressed upon the convergence apparatus to control its operation substantially in the manner described. Such an arrangement thereby eliminates the need for such apparatus as that shown in FIGURE 3 including the choke coil 51 and the by-pass capacitor 61 in the cathode circuit of the horizontal output tube 52. The cathode circuit of the horizontal output tube is connected to ground through a resistor 82 which is effectively by-passed 'by the capacitor 55 so as to produce a substantially unidirectional voltage at the cathode of the tube.

The operation of the apparatus shown in, and described with reference to, FIGURE 5 is substantially the same as that shown in, and described with reference to, FIGURE 3. It will be noted, however, that principally because of the somewhat different circuit arrangements in the respective embodiments that the values of certain of the components are indicated as being somewhat different.

9 These components are designated in FIGURE by primed reference characters corresponding to those used in FIG- URE 3.

Still another form of the invention which may be ad vantageously employed with beam convergence apparatus in which the initial beam convergence is eifected entirely by permanent magnetic means, in the general manner described with reference particularly to FIGURE 4-, is shown in FIGURE 6, to which reference now will be made. Apparatus which is similar to that of the other embodiments of the invention shown respectively in FIGURES 3 and 5 is designated by the same reference characters except that, where values of the components are specifical- 1y different in the respective figures, the reference characters are primed. The substantially parabolic voltage wave derived from the cathode of the vertical deflection output tube 40 is impressed by means including a capacitor 83 upon a series circuit including a resistor 84 and a capacitor 85. The terminals of the resistor 84 are connected to the terminals of a potentiometer 86 which serves the general function of a vertical frequency tilt control. As in the embodiment of FIGURE 3, the positioning of the movable contact of the potentiometer 44 determines the amplitude of the substantially sawtooth voltage wave component developed across the resistor 84 which is combined with the substantially parabolic voltage wave developed at the cathode of the tube 4th. The composite voltage Wave which is derived from the movable contact of the potentiometer 86 is impressed upon the beam convergence magnet 29 in a manner similar to that shown in, and described with reference to, FIGURES 3 and 5.

In the case of the energization of the convergence app-aratus at the horizontal deflection frequency, the horizontal deflection output transformer 68 is provided with an auxiliary winding 87 in which there is developed a voltage pulse during flyback or retrace intervals of the horizontal deflection cycle. The voltage pulse developed in the winding 87 is converted by a series connection of a variable inductance coil 38 and a capacitor 89 into a substantially parabolic voltage wave at the junction point between the coil and capacitor. The coil 88 is provided with a movable core 91 by means of which the amplitude of the developed horizontal para-bolic voltage wave may be adjusted. As in the form of the invention shown in FIGURE 5, the horizontal frequency parabolic voltage wave is impressed upon a potentiometer 57, the movable contact of which may be adjusted so as to vary the amplitude of the horizontal convergence energy impressed upon the blue convergence apparatus 41 independently of the red and

green convergence apparatus

76 and 77, respectively. The movable contact of the potentiometer 57' is connected by a series arrangement of a capacitor 58' and a resistor 92 to the junction joint between the serially connected coils 35 and 36 of the blue convergence electromagnet 29.

The apparatus shown in FIGURE 6 operates substantially in the same manner as that shown in, and described with reference to, FIGURES 3 and 5. In the case of the embodiment of the invention shown in FIGURE 6, the parabolic voltage wave at horizontal deflection frequency is produced by integrating a voltage pulse derived from the horizontal output transformer. It has been found that such an arrangement has the advantage of requiring no special precautions to isolate the convergence apparatus from the beam deflection circuits, such as is necessary when the sawtooth voltage wave is derived from the circuits such as those connected to the cathode of the horizontal deflection output tube 52 as in FIGURE 3. It also is apparent that a material simplification in the apparatus is effected by not having to energize the convergence magnets with unidirectional current.

It is seen that the described circuits for energizing the convergence magnet apparatus is of such a character as to present a high impedance to the sources from which the energizing voltages are obtained. Consequently, by reason of the resultant low power drain from these sources, there is no perceptible loading effect on either the vertical or horizontal output tubes 46 and 52, respectively. By reason of the series connection of the convergence magnet coils 35 and 36, the magnetic fields produced respectively thereby aid one another. Consequently, minimum currents are required from the vertical frequency voltage source, including the vertical output tube 40, and also from the source of the D.C. voltage in the cathode circuit of the horizontal output tube 52. Similarly, by reason of the described connections of the

coils

35 and 36 with the auxiliary apparatus by means of which series parallel resonance of the coils is obtained at the horizontal deflection frequency, power is dissipated only in the resistance elements of the coils, thereby minimizing the magnitude of the voltage input required. By reason of the employment of apparatus of the character described, it is seen that the need for amplifiers in the convergence magnet energizing circuits is obviated with a consequent material saving in other circuit components.

What is claimed is:

1. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse pie-deflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflcction beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths; means coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave; and wave conversion means including said beam convergence electromagnet windings and responsive to said parabolic voltage Wave for causing substantially nonlinear current waves to traverse said windings.

2. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse pro-deflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pie-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths, each of said electromagnets having a pair of pole pieces located internaly of said tube and respectively extending into the region of said associated beam component; means coupled to said beam deflection apparatus for developing a plurality of substantially parabolic voltage waves; and wave conversion means including said beam convergence electromagnet windings and responsive to said parabolic voltage waves for causing substantially symmetrical nonlinear-current waves to trav erse said windings.

3. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse pro-deflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pro-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths; means coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave; and wave conversion means responsive to said para- 1 1 bolic voltage wave and including a series connection of said beam convergence electromagnet windings, a resistive component and a capacitive reactance component, said resistive component being the dominant impedance offered to said parabolic voltage wave, thereby causing substantially parabolic current waves to traverse said windings.

4. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a tanget electrode structure, the combination including: a plurality or beam convergence electromagnets respectively mounted adjacent to said pre-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths; means coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave; and wave conversion means responsive to said parabolic voltage wave and including a series connection of said beam convergence electromagnet windings constituting an inductive reactance component, a resistive component and a capacitive reactance component, said capacitive reactance component being substantially equal to said inductive reactance component so that said resistive component conestitutes the dominant impedance ofi'ered to said parabolic voltage wave, thereby causing substantially parabolic current waves to traverse said windings.

5. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse pre-deflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths; means coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave; means coupled to said deflection apparatus for developing a substantially sawtooth voltage wave; means for combining said parabolic and sawtooth voltabe waves to form a composite voltage wave having a tilted parabolic form; and wave conversion means responsive to said composite voltage wave and including a series connection of said beam convengence electromagnet windings, a resistive component and a capacitive reactance component, said resistive component being the dominant impedance offered to said composite voltage wave, thereby causing tilted parabolic current waves to traverse said windings.

6. In a cathode ray tube image reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths; means coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave; means including a potentiometer coupled to said deflection apparatus for developing a substantially sawtooth voltage wave; means for combining said parabolic and sawtooth voltage waves to form a composite voltage wave having a tilted parabolic form; and wave conversion means responsive to said composite voltage wave and including a series connection of said beam convergence electromagnet windings, a variable resistor and a capacitive reactance component, said resistor being the i2 dominant impedance offered to said composite voltage wave, thereby causing tilted parabolic current waves to traverse said windings, the amplitude of said current waves being controllable by said variable resistor and the tilt of said current Waves being controllable by said potentiometer.

7. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pro-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths; means coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave; means coupled to said deflection apparatus for developing a substantially sawtooth voltage wave; means for combining said parabolic and sawtooth voltage waves to form a composite voltage wave having a tilted parabolic form; and wave conversion means responsive to said composite voltage wave and including a series connection of each of said beam convengence electromagnet windings, a variable resistor for each of said windings and a capacitor, said resistors being the dominant impedance oflered to said composite voltage wave, thereby causing tilted parabolic current waves to traverse said windings, the amplitude of the current waves traversing the different windings being individually controllable by the diiferent variable resistors associated respectively with said windings.

8. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse pre-deflection paths that are spaced respectively about the lonigtudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths; means coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave; means coupled to said deflection apparatus for developing a substantially sawtooth voltage wave; means including a potentiometer for each of said windings for combining said parabolic and sawtooth voltage waves to form a composite voltage wave having a tilted parabolic form for each of said windings; and a plurality of wave conversion means responsive to said respective composite voltage waves and each including a series connection of one of said beam convergence electromagnet windings, a variable resistor and a capacitor, said resistors being the dominant impedance offered to said composite voltage waves, thereby causing tilted parabolic current waves to traverse said windings, the amplitude of the current waves traversing the difierent windings being individually controllable by the different variable resistors associated respectively with said windings and the tilt of said current waves being individually controllable by said respective otentiometers.

9. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths; means coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave; means coupled to said deflection apparatus for developing a substantially sawtooth voltage wave; means including a potentiometer for combining said parabolic and sawtooth voltage waves to form a composite voltage wave having a tilted parabolic form; and a plurality of wave conversion means responsive to said composite voltage wave and each including a series connection of one of said beam convergence electromagnet windings, a variable resistor and a capacitor, said resistors being the dominant impedance offered tosaid composite voltage Wave, thereby causing tilted parabolic current waves to traverse said windings, the amplitude of the current waves traversing the different windings being individually controllable by the different variable resistors associated respectively with said windings and the tilt of said current waves being commonly controllable by said potentiometer.

10. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths; means coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave; means coupled to said deflection apparatus for developing two substantially sawtooth voltage waves; means including a potentiometer for combining said parabolic voltage wave with a fixed amplitude of one of said sawtooth voltage waves and with a variable amplitude of the other of said sawtooth voltage waves, to form a composite voltage wave having a generally parabolic form, said two sawtooth voltage waves tending to oppositely tilt said composite voltage wave; and a plurality of wave conversion means responsive to said composite voltage wave and each including a series connection of one of said beam convergence electromagnet windings, a variable resistor and a capacitor, said resistors being the dominant impedance offered to said composite voltage wave, thereby causing generally parabolic current waves to traverse said windings, the amplitude of the current waves traversing the different windings being individually controllable by the different variable resistors associated respectively with said windings and the direction and amount of any tilt of said current waves being controllable by said potentiometer.

11. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths; means coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave; and wave conversion means responsive to said parabolic voltage wave and including said beam convergence electromagnet windings, a first capacitor connected in parallel with each of said windings, a second capacitor connected in series with each of said windings, and a choke coil effectively connected in shunt with each of said windings to form a series parallel resonant circuit at the frequency of said parabolic voltage wave, thereby causing substan- 14 tially sinusoidal current waves to traverse said windings.

12. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angular-1y deflected bot-h horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths, each of said windings comprising two coils connected in a series aiding relationship; means coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave; and wave conversion means responsive to said parabolic voltage wave and including said beam convergence electromagnet windings, a choke coil eiiectively connected in parallel with each of said windings at the frequency of said parabolic voltage wave, a first capacitor connected in parallel with each of said windings and vforming with each winding and its associated choke coil a parallel circuit resonant at the frequency of said parabolic voltage wave, and a second capacitor connected in series from said parabolic voltage wave developing means to the junction of the coils of each of said windings and forming with the net inductive reactance eflective at said coil junction a series circuit resonant at the frequency of said parabolic voltage wave, said wave conversion means thereby causing substantially sinusoidal current waves to traverse said windings.

13. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflcction beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths, each of said windings comprising two coils connected in a series aiding relationship; means including a plurality of potentiometers coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave for each of said electromagnets; and wave conversion means responsive to said parabolic voltage waves and including said beam convergence electromagnet windings, a choke coil effectively connected in parallel with each of said windings at the frequency of said parabolic voltage wave, a variable capacitor connected in parallel with each of said windings and forming with each winding and its associated choke coil a parallel circuit resonant at the frequency of said parabolic voltage wave, and a capacitor connected in series from each of said potentiometers to the junction of the coils of each of said windings and forming with the net inductive reactance effective at said coil junction a series circuit resonant at the frequency of said parabolic voltage wave, said wave conversion means thereby causing substantially sinusoidal current waves to traverse said windings, the amplitude of the current waves traversing the diflerent windings being individually controllable by the different potentiometers associated respectively with said windings and the phasing of said current waves being individually controllable by the different variable capacitors associated respectively with said windings.

14. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical bearn deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths, each of said windings comprising two coils connected in a series aiding relationship; means coupled to said beam deflection apparatus for developing substantially parabolic voltage waves respectively at horizontal and vertical deflection frequencies; horizontal frequency wave conversion means responsive to said horizontal frequency parabolic voltage wave and including said beam convergence electromagnet windings, a choke coil effectively connected in parallel with each of said windings at horizontal deflection frequency, a first capacitor connected in parallel with each of said windings and forming with each winding and choke coil a parallel circuit resonant at horizontal deflection frequency, and a second capacitor connected in series from said beam deflection apparatus to the junction of the coils of each of said windings and forming with the net inductive reactance eflfective at said coil junction a series circuit resonant at horizontal deflection frequency, said horizontal frequency wave conversion means thereby causing substantially sinusoidal current waves at horizontal deflection frequency to traverse said windings; and vertical frequency wave conversion means responsive to said vertical frequency parabolic voltage wave and including a series connection of said beam convergence electromagnet windings, said choke coil, a resistor and a third capacitor, said resistor being the dominant impedance oflered to said vertical frequency parabolic voltage wave, thereby causing substantially parabolic current waves at vertical deflection frequency to traverse said windings.

15. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths, each of said windings comprising two coils connected in a series aiding relationship; means coupled to said beam deflection apparatus for developing substantially parabolic voltage waves respectively at horizontal and vertical deflection frequencies; horizontal frequency wave conversion means responsive to said horizontal frequency parabolic voltage wave and including said beam convergence electromagnet windings, a choke coil effectively connected in parallel with each of said windings at horizontal deflection frequency, a first capacitor connected in parallel with each of said windings and forming with each winding and choke coil a parallel circuit resonant at horizontal deflection frequency, and a second capacitor connected in series from said beam deflection apparatus to the junction of the coils of each of said windings and forming with the net inductive reactance effective at said coil junction a series circuit resonant at horizontal deflection frequency, said horizontal frequency wave conversion means thereby causing substantially sinusoidal current waves at horizontal deflection frequency to traverse said windings; vertical frequency wave conversion means responsive to said vertical frequency parabolic voltage wave and including a series connection of said beam convergence electromagnet windings, said choke coil, a resistor and a third capacitor, said resistor being the dominant impedance offered to said vertical frequency parabolic voltage wave, thereby causing substantially parabolic current waves at vertical deflection frequency to traverse said windings; a source of unidirectional current; and means including a series isolating resistor effectively coupling said unidirectional current 16 source to each of said convergence electromagnet Windings, thereby causing substantially unidirectional current to traverse said windings.

16. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical electromagnetic beam deflection apparatus to scan a raster at a target electrode structure, and having electron beam convergence apparatus mounted adjacent to said pre-deflection beam paths and dynamically and statically energizable to produce a beam convergence field, the combination including: a circuit supplying a substantially sawtooth current wave to said beam deflection apparatus; a capacitor included in said circuit in a manner to be traversed by the A.-C. component of said sawtooth current wave to develop a substantially parabolic voltage wave for controlling the dynamic energization of said beam convergence apparatus; and a resistor included in said circuit in a manner to be traversed by the D.-C. component of said sawtooth current wave to develop a substantially unidirectional voltage for controlling the static energization of said beam convergence apparatus.

17. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical electromagnetic beam deflection apparatus to scan a raster at a target electrode structure, and having electron beam convergence apparatus mounted adjacent to said pre-deflection beam paths and dynamically and statically energizable to produce a beam convergence field, the combination including: a circuit supplying a substantially sawtooth current wave to said beam deflection apparatus; an electron tube having a cathode and anode serially connected in said circuit, said anode being coupled to said beam deflection apparatus; a capacitor included in said circuit and coupled to said cathode in a manner to be traversed principally by the A.-C. component of said sawtooth current wave to develop a substantially parabolic voltage wave for controlling the dynamic energization of said beam convergence apparatus; and a resistor included in said circuit and coupled to said cathode in a manner to be traversed principally by the D.-C. component of said sawtooth current wave to develop a substantially unidirectional voltage for controlling the static energization of said beam convergence apparatus.

18. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse pre-deflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical electromagnetic beam deflection apparatus to scan a raster at a target electrode structure, and having electron beam convergence apparatus mounted adjacent to said pre-deflection beam paths and dynamically and statically energizable to produce a beam convergence field, the combination including: a circuit supplying a substantially sawtooth current wave to said beam deflection apparatus; an electron tube having a cathode and an anode connected in said circuit; means including a capacitor coupling said anode to said deflection apparatus, said coupling being such that said capacitor is traversed principally by the A.-C. component of said sawtooth current wave so as to develop a substantially parabolic voltage wave for controlling the dynamic energization of said beam convergence apparatus; and a resistor included in said circuit and coupled to said cathode in a manner to be traversed principally by the D.-C. component of said sawtooth current wave to develop a substantially unidirectional voltage for controlling the static energization of said beam convergence apparatus.

19. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths; means coupled to said beam deflection apparatus for developing a substantially impulsive voltage wave; and Wave convergence means responsive to said impulsive voltage wave and including said beam convergence electromagnet windings, a first capacitive element connected in parallel with each of said windings, a second capacitive element connected in series with each of said windings, an inductive element effectively connected in shunt with each of said windings to form a series parallel resonant circuit at the frequency of said impulsive voltage wave, thereby causing substantially sinusoidal current waves to traverse said windings, and means to vary one of said elements to control the phasing of said current waves.

20. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse predefiection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode structure, the combination including: a plurality of beam convergence electromagnets respectively mounted adjacent to said pre-deflection beam paths and having respective windings individually energizable to produce respective beam convergence fields transverse to said beam paths; means coupled to said beam deflection apparatus for developing a substantially parabolic voltage wave; and wave convergence means responsive to said parabolic voltage wave and including said beam convergence electromagnet windings, a first capacitive element connected in parallel with each of said windings, a second capacitive element connected in series With each of said windings, an inductive element effectively connected in shunt With each of said windings to form a series parallel resonant circuit at the frequency of said parabolic voltage wave, thereby causing substantially sinusoidal current waves to traverse said windings, and means to vary one of said capacitive elements to control the phasing of said current waves.

21. Dynamic convergence apparatus for a color television tube operable by multiple electron beams converging to a common point, said apparatus comprising, a plurality of circuits respectively corresponding to said beams and each forming a primarily resistive load, a plurality of electromagnets respectively in said circuits to deflect the corresponding ones of said electron beams, said electromagnets being responsive to like currents in their respective circuits to conjointly shift said convergence point in the tube axis direction, a plurality of capacitances respectively coupled in series in said circuits with said electromagnets and in tuned relation with the respective inductances of said circuits to render each circuit oscillatory at horizontal scanning frequency, and a source of fly back pulses separately connected with each coupled electromagnet and capacitance in series and coupled across each primarily resistive load respectively formed by said circuits for shock exciting said circuits into generating synchronous oscillations in the form of respective cosine currents through said electromagnets during horizontal scanning periods.

22. Dynamic convergence apparatus as in claim 21 further characterized by tuning means in at least one of said circuits for tuning said circuit at horizontal scanning frequency to produce a selective phase shift between the cosine current of said one circuit and the cosine current of another of said circuits.

23. Dynamic convergence apparatus as in claim 21 further characterized by respective cosine current gain controls for said electromagnet-capacitance circuits, each gain control being interposed between its respective circuit and the fly back pulse source to vary individually the amplitude of the fly back pulses shock exciting the respective circuit.

24. Dynamic convergence apparatus for a color television receiver having a color tube operable by multiple electron beams converging to a common point, respective dynamic convergence electromagnets for said beams and a fly back pulse source, said apparatus comprising, a plurality of circuits each forming a primarily resistive load and each including one of said electromagnets, a plurality of capacitances respectively coupled in series in said circuits with said electromagnets, each capacitance being tuned with the inductance of its circuit to render the circuit oscillatory at horizontal scanning frequency, and distributory circuit means connected between said source and said electromagnet-capacitance circuits to separately couple said fly back pulses with each associated electromagnet and capacitance in series network relation and to couple said source across each of the primarily resistive loads respectively formed by said circuits, said fly back pulses shock exciting the respective electromagnet-capacitance circuits into generating oscillations in the form of cosine currents through said electromagnets during horizontal scanning periods.

25. Dynamic convergence apparatus as in claim 24 further characterized by a plurality of tuning means respectively connected in said electromagnet-capacitance circuits for varying the tuning thereof at horizontal scanning frequency to produce selected phase shifts between the respective cosine currents of said circuits.

26. Dynamic convergence apparatus as in claim 24 further characterized by respective variable resistors for said electromagnet-capacitance circuits, each resistor being interposed between its respective circuit and said source for individually varying the amplitude of fly back pulses shock exciting the respective circuit to accordingly vary the cosine current amplitude of the respective circuit.

References Cited in the file of this patent UNITED STATES PATENTS 2,574,229 Schlesinger Nov. 6, 1951 2,672,574 Evans Mar. 16, 1954 2,677,779 Goodrich May 4, 1954 2,707,248 Goodrich Apr. 26, 1955