US2783412A - High voltage supply - Google Patents

Description

Feb. 26, 1957 B. v. voNDERscHMl-rT 2,783,412

HIGH VOLTAGE SUPPLY Filed March 15, 1954 INI/ENTOR.

BY v ATTORNEY nited States Patent 1V 2,783,412 HIGH VOLTAGE SUPPLY Bernard V. Vonderschmitt, Merchantville, N. J., assigner vto Radio Corporation of America, a corporation of Delaware Application March 15, 1954, Serial No. 416,186 Claims. (Cl. 315-15) This invention relates generally to voltage supplies and more particularly to voltage supplies of the type suitable for use to satisfy the high voltage requirements of a cathode ray tube.

t It has been more or less conventional in the monochrome television art to obtain the high voltages required by a receivers kinescope from a pulse type supply, developing the high voltages via rectification of the transient iyback pulses appearing across the receivers horizontal output transformer during retrace periods of the line scanning cycle. Direct adaptation of such supplies to use in color television has usually been found not to be feasible, for with color kinescopes of the types presently known, the high voltage requirements are generally of greater magnitude, more critical as to regulation, and over all present a significantly more complex problem than the monochrome kinescope supplies. As an example, a presently contemplated tri-color kinescope, of the shadowmask type and incorporating the use of electromagnetic beam convergence apparatus, requires a well regulated voltage of approximately 27,000 volts for its ultor electrode (i. e. its final accelerating electrode), and a similarly well regulated voltage adjustable in the range of approximately 7000 volts to 9000 volts for the individual focusing electrodes of the tubes three electron guns.

While step-up of the flyback pulse potential in the horizontal output transformer to the voltage level required for the, nal anode of a back-and-white kinescope is readily attained, llyback pulse step-up to a potential of 27 kv. via transformer action is a burden imposing limitations on output transformer design that renderA such a manner of achieving the necessary step-up impractical.

'Consequently, the practice of using so-called voltage doubles in the high voltage supply has been contemplated as a solution to this problem. However, the usual voltage Vdouble requires a minimum of three tubes, two serving as rectifers of the peak amplitude ilyback pulses and the third serving as a D. C. coupler between the rectiiers to permit the doubling action. A fourth tube is also required to obtain the focus voltage, and the sensitivity of the-kinescopes color image reproduction operation to variations in the ultor and focus voltages dictates the presence of a fifth tube serving as a regulator. It will be appreciated that a tive-tube high voltage supply, with the attendant filament supply and insulation problems, represents a considerable amount of expensive components and production time in a receiver which is to be used on a commercial basis.

In a co-pending application of Leonard Dietch, Ser. No. 407,921, led February 3, 1954, now U. S. Patent No. 2,729,764, issued January 3, 1956, and entitled High VoltageA Supply, there is disclosed a markedly simple high voltagesupply suitable for a color kinescope, which has a reduced tube complement as contrasted with the supplies above discussed. Rather than employing conventional voltage doubling, the disclosed supply involves what may be termed as a one and a half voltage multiplying action, permitting a combination of focus and ultor voltage rectification which effects a saving of at least onev tube. There is also disclosed in the aforesaid Dietch patent novel means for effecting sampling controlof the supplys voltage regulator whereby power losses involved in the sampling apparatus are minimized. p

In accordance with the present invention a novel high voltage supply of the aforementioned one and a half 2,783,412 Patented Feb. ze, 1957 the present invention a further saving in tube complementA over that shown in the aforementioned Dietch patent is eected by eliminating the need for a coupler tube. Also in accordance with an embodiment of the present invention a saving in power losses of the supply is achieved through the derivation of the desired adjustable focus voltage and the derivation of the sampling or reference voltage for control of the regulator tube from a common means.

Accordingly it is a primary object of the present invention to provide a novel and improved high voltage supply suitable for use with cathode ray tubes.

It is a further object of the present invention to provide a novel and improved high voltage supply for a color television receiver with simplified circuitry, minimized tube requirements, and improved eiciency.

Other objects and advantages of the present invention will become readily apparent to those skilled in the art upon a reading of the following detailed description and an inspection of the accompanying drawings in which:

Figure 1 illustrates in block and schematic form a color television receiver including a high voltage supply in accordance with an embodiment of the present invention.

Figure 2 illustrates a modification of the high voltage supply of Figure l in accordance with another embodiment of the present invention.

Referring to Figure 1 in greater detail, a high voltage supply in accordance with an embodiment of the invention is illustrated in the setting of a color television receiver. The illustrated receiver is generally representative of presently contemplated color receivers for a simultaneous subcarrier type color television system in accordance with the revised FCC color standards, and is in general accord with the principles and apparatus discussed in the article entitled Principles and Development of Color Television Systems, by G. H. Brown and D. G. C. Luck appearing in the June 1953 issue of the RCA Review. Carrier waves modulated by a composite color picture signal are illustrated as being received by conventional signal receiving apparatus 11, which may include the usual R. F. tuner, converting apparatus, I. F. amplifier, signal detector, etc. The video frequency signals recovered from the modulated carrier in the receiving apparatus 11 are amplified in the video amplifier 13. Synchronizing information is derived from the recovered signals in the sync separator 15 and utilized to synchronously control the receivers subcarrier drive apparatus 17, to control the generation of scanning waves in the vertical deflection circuits 19, and control the generation of horizontal frequency sawtooth voltage waves in the horizontal sawtooth wave generator 21.

Respective color mixture signals (e. g. narrow band EQ signals and wider band E1 signals, discussed in detail in the aforementioned article) are recovered from thel video signal output of amplifier 13 in respective color demodulator channels which include bandpass lters 25 and 27 of respectively appropriate passbands, synchronous demodulators 31 and 33 receiving respectively appropriate phases of the output of the subcarrier drive apparatus 17, and low pass filters 35 and 37 having the respectively appropriate narrow and wider responses. The receiver is also provided with a brightness channel, including a low pass filter 36 having the desired wide band response,

through which the broad band monochrome portion ofV the composite picture signal may pass. The outputs of the brightness channel and two color channels are suitably combined in the matrixing circuits 39 of the receiver to obtain the simultaneous color signals which may be applied to appropriate beam control elements of a color image reproducer 40.

The color image reproducer 40 is illustrated schematievenals callyras being of the three-gun, shadow-mask kinescope type. Color image reproducers of this general type are discussed in some detail in an article by H. B. Law entitled A Three-Gun-ShadoW-Mask ColoriKinescope, and appearing in the October l951-issue of the Proceedings of the I. R. E. In a color image reproducer or"this type, three electron beams are used, one foreach primary color. The beams strike a phosphor screen composed of -a regular array of red, green-, and blue-emitting phosphor dots. Between the electron gun position and the phosphor screen, there is placed a thin perforated metal sheet -for the purpose of partially masking the electron beams. The phosphor dot array on the screen comprises a plurality of closely spaced phosphor dot trios, -each trio consisting of a red-, green, and blue-emitting phosphor dot with the centers of the dots lying at the corners of an equilateral triangle. The trios themselves lie at the corners of an equilateral triangle of larger size. Assoc-iated with each of the phosphor trios is a hole in the video mask, these holes also being located at the corners of an equilateral triangle. The three beams, disposed 120 apart about the tube axis, are converged to a point on the mask by suitable static and dynamic beam con verging means. The electron beam which is to contribute the red portion of the picture is prevented, by the mask, from striking those areas on the screen containing blue and 'green emitting phosphors. Likewise the green and blue beams can strike only the green and blue emitting phosphor dots, respectively. The target structure 51 of `the illustrative kinescope 40 may be considered to be of the general shadow-mask type above described.

`As schematically illustrated, the three electron beams are developed and shaped in respective electron gun structures, each including a thermionic cathode 41, a control grid 43, a rst anode or accelerating electrode 45, and a focusing electrode 47. The electron gun structures may be of the general type disclosed in the co-pending application of Hannah C. Moodey, Ser. No. 295,225, filed June 24, 1952, and disposed symmetrically about the tube axis Such as toprod-uce three substantially parallel beams as in said Moodey application, or may be inclined at respective angles to the tube axis so as to provide three beams substantially converging at a common point on the target, as in the co-pending application of Albert M. Morrell, Ser. No. 364,041, led on June 25, 1953, now U. S.Patent No. 2,752,520, issued June 26, 1956. A common convergence cup 49 may beprovided for receiving the three focused beams, and which may serve as the convergence electrode where electrostatic convergence is employed, or which may merely serve to provide a confnedre'gion in which electromagnetic convergence is employed. Inthe illustrative embodiment of the present invention, the color`kinescope 40 is shown as employing a'convergence yoke S5 to provide the electromagnetic form of convergence control. The electromagnetic convergence apparatus'may be entirely external of the tube 40, but where individual control of the three beams is desired, the apparatus may incorporate internal pole pieces. The individual control of the three beams by electromagnetic convergence apparatus is disclosed inthe co-pending application of Hunter C. Goodrich, entitled Electromagnetic Beam Convergence Systems for Tricolor Kinescopes, Ser. No. 322,653, tiled November 26, 1952, now U. S. Patent No. 2,707,248, issued April 26, 1955. Electromagnetic convergence apparatusof the individual beam control type and involving the employment of internal pole pieces is disclosed in the aforesaid Goodrich and vMorrell patents.

In an article entitled Deection and Convergence in Color KinescopesVA by AlbertW. Friend appearing in the October 1951 issue ol the Proceedings of the I. R. E., tne use of the beam alignment magnets to correct beam trajectories individually is discussed. While `three such beam alignment magnets yhaveV often been.V employedin shadow-mask type kinescopes for correction purposes, it`

is indicated in the aforementioned Goodrich patentthat where individual adjustment of the beam positions in a radial direction relative to the tube axis is provided by the electromagnetic convergence apparatus, a single beam alignment magnet associated with one of the three beams and effective in adjusting such beam in a direction perpendicular to the radial convergence adjustment for ,that beam provides suicient control. In the aforesaidv Morrell patent, the single beam alignment magnet thus `required is illustrated as cooperating with another set of internal pole pieces to provide the individual beam alignment control desired. In a co-pending application of Albert M. Morrell, Ser. No. 383,340, led September 30, 1953, and entitled Tri-color Kinescope, an improved form of such internal pole pieces for the beam alignment magnet is shown. En the co-pending application of M. Obert, entitled Electron Beam Control Means, filed January 21, 1954, Ser. No. 405,445, a single beam alignment magnet of the permanent magnet type and utilizing such improved internal pole pieces is shown.

In the drawing herein, the electromagnetic convergence apparatus has been illustrated by the schematic representation of a yoke 55, and the details of the internal pole pieces and individual yokes which may specifically be employed in accordance with the aforesaid applications have not been illustrated for the sake of simplicity in the drawing. Similarly the beam alignment magnet 57 has been illustrated only schematically, but may for example take a permanent magnet form as illustrated in the aforementioned co-pending Obert application.

Beam convergence circuits for appropriately energizing the convergence yoke 5S have been indicated in the drawing by the block 56, which is illustrated as deriving sawtooth wave energy of iield and line frequency from the vertical deection circuits 19 and horizontal output transformer 63, respectively. The convergence circuits 56 may be, for example, of the general type described in the aforementioned A. W. Friend article, and thus involve derivation .of essentially parabolic current waves from the respective sawtooths, and combination of these parabolic (dynamic convergence) waves with the requisite (static convergence) D.C. component.

In addition to the beam controlling apparatus already described, the illustrated colorkinescope 40 is also provided, as is generally customary, with a color purity yokel 54, applyingauniform transverse magnetic eld to allthe electron beams to-orient the system of beams as desired. VThe yoke maycomprise either'a-rotatable single pair of.coils, or two fixed pairs of coils atright angles, fed from an adjustable source of D.C. (as indicated on the drawing). The -use of such a purity coil to deilect theithree beams equally so that they may be adjusted to pass through their respective color-centers is explained in greater detail in the aforesaid Friendarticle, and inthe co-pending application of Friend,-Ser.fNo. 202,185,r tiled December 22, 1950, Vand entitled Beam AlignmentDevice, now U.v S. Patent 2,719,249, issued September 27, 1955.

The kinescope is provided, as is conventional, with a nal accelerating electrode, the ultor '50, which may take the usual form of a conductive coating on Ythe inner surface of the kinescope 40 vextending from the vicinity.A of the convergence .cup 49 to the beam target structureY 52. Where ,the flared portion ofthe kinescope envelopeis. of metal, the conductive coating need only extendy forward suciently to makeelectrical contact with the metal ared portion. l

To achieveV commondeflection of vthe three beams to trace a scanning raster` on the target .structure 51a. deflection yoke 53 is provided zwith appropriately'disposedhorizontaland vertical ,deflection windings. Theyokefjs illustrated as--having vertical yoke terminalsV-V,;. to which. field-frequency ,scanning wavesdevelopedinnhe vertical defiectioncirlcuits 1,9 are applied. 'Ihqho'rizpntal yoke terminals H--H derive line,l frequencypsanning efz'ssgiia waves from the horizontal output transformer 63 (illustrated as an autotransformer) of the horizontal output system, which conventionally includes a horizontal output tube 61, energized by sawtooth voltage waves from generator 21 and developing a current which provides the desired scanning sawtooth in the horizontal yoke. To prevent the transient iiyback pulses generated during retrace periods from setting up a series of oscillations, and in accordance with well-known reaction scanning principles, a damper tube 65 is provided.

The details of the yoke and damper connections and associated circuitry, including the provision of a B-boost capacitor, linearity control inductance 67, D.C. blocking capacitors 91, 93, combination series-shunt inductance type raster width control 95, 97, etc. are illustrative only, and various modifications, augmentations or revisions thereof may be achieved without departing from the scope of the present invention. Thus, for example, modifications of the illustrated connections to additionally provide circuits for eecting a horizontal centering adjustment, to additionally provide circuits for discouraging ringing in the yoke, to provide a different type of raster width control, etc. are readily compatible with the operation of the high voltage supply associated with the horizontal output transformer 63, the supply embodying the particularly novel subject matter of the present invention and now to be described.

In accordance with the invention, the high voltage supply is illustrated as including a first rectifier, diode 69 with its plate tapping the output transformer 63 at an intermediate point Y between the connection point X for the output tube plate and the high potential terminal Z. Transient iiyback pulses appearing periodically across the horizontal yoke are stepped-up at point Y by the autotransformer action. As these stepped-up pulses are rectified by diode 69, a D.C. potential is built up on capacitor 71, which is connected between the cathode of diode 69 and a point of reference potential (i. e. ground in the illustrative embodiment). A second rectifier, diode 73, is connected with its plate tapping the transformer 63 at the high potential terminal 2, coupling to the terminal Z, being effected via the capacitor 75. The plate of diode 73 is also connected to the cathode and diode 69 by means of a D.C. coupling path including a resistance 81 and a choke 80. The choke 80, presenting a relatively low impedance to the ow of direct current, possesses a relatively high A.C. impedance, and is preferably wound such as to minimize its distributed capacity.

It will be appreciated that the coupling path 80, 81 readily permits the impression of the D.C. voltage at diode 69s cathode across the capacitor 75, but appears effectively open-circuited to the tiyback pulses passed by capacitor 75. It may thus be appreciated that the D.C. voltage developed by the first rectifier 69 is effectively added to the high amplitude iiyback pulses appearing at terminal Z, and that the rectified output of the second rectifier 73, developed across capacitor 77 connected between diode 73s cathode and ground, is substantially equivalent to the sum of these potentials.

The ultor voltage desired for operation of the color kinescope 40 is obtained from the described supply by coupling the ultor terminal U to the cathode of diode 73. The adjustable focusing voltage desired for the electron gun structure of kinescope 40 is obtained from the described supply by coupling the focus terminal F to an adjustable tap on the resistance 81 in the aforesaid D.C. coupling path. Regulation of the supply voltages is effected by the shunting of a voltage regulator tube 8S across the output of the second rectifier 73. Control of the voltage regulator tube in accordance with supply voltage variations is obtained by connecting the control grid of regulator 85 to a sampling point on the resistive voltage divider 87, illustrated as being connected' between the cathode of the first rectifier 69 and ground. An alternative connection for the sampling voltage divider 87,

asrindicated in the aforesaid Dietch patent,` is betwee the end of resistance 81 remote from diode 69s cathde and ground, such alternative connection providing the advantage of increased range of focus adjustment where focus voltage is derived by adjustably Atapping resistance 81, since the current drawn by divider 87 passes through resistance 81 in addition to the regulated ultor current.

ItA may be noted that the supply embodiment of the present invention, as just described, is of the general one and a half type disclosed in the aforesaid Dietch patent. As in the aforesaid Dietch patent, a focus voltage is derived from an impedance in the D.C. coupling path of the voltage multiplier. Also, as in the aforesaid Dietch patent sampling control of the shunt regulator is obtained with referencek to a potential of the lower order ofthe focus voltage as developed by the first rectifier. A distinguishing feature of the Figure l embodiment of the present invention over the aforesaid Dietch patent is, however, the absence of a D.C. coupling diode. Rather than use of a diode, with the attendant problems of filament supply, etc., the present invention proposes the use of inductive choke, which satisfactorily performs the desired functions of providing a low D.C. impedance and a high A.C. impedance. The advantages of a supply in accordance with the Dietch application, e. g. the provision of a combined focus-ultor supply with a saving in tube complement, the provision of a low impedance focus supply without the accompanying power losses thatrcomparable prior art supplies would involve, the sampling control of the voltage regulator with a minimum of wasted power, etc., are realized in the illustrative embodimentrof the present invention, with the further advantage of a further saving in :component expense, circuit complexity, and wiring time through the elimination of the necessity for a coupling diode. The illustrative embodiment of the present invention therefore provides a novel, well-regulated, ecient high voltage supply of a type suitable for satisfying the rigid requirements of a color kinescope, such a supply requiring only three tubes including the voltage regulator tube.

In Figure 2 a modification of the high voltage supply of Figure l is illustrated in accordance with a further embodiment of the present invention. Reference to the drawing will reveal that the modified supply is again of the one and a half voltage multiplying type, the inductive choke S0 again serving in the D.C. coupling path between rectifiers 69 and 73 as a high impedance to A.C. and a low impedance to D.C. The operation of regulator tube 85 in Figure 2 is similar to the operation described with respect to Figure l, the sampling voltage for the con trol grid of regulator 35 being obtained from a resistive voltage divider 87 connected between the cathode of diode 69 and ground. However, it will be noted that in the modifiedl supply of Figure 2, the focus voltage is not derived from a resistance in the D.C. coupling path, but rather from the same resistive voltage divider 37 which provides the regulators reference voltage. The saving in power losses obtained by using the same voltage divider for focus and regulator sampling is readily apparent. While Figure 2 illustrates the use of both the D.C. coupling choke and combined focus-sampling potentiometer features of the present invention, it will be appreciated that the latter feature may also prove of advantage in a supply of the type utilizing a diode in the D.C. coupling path. Y

While embodiments in the present invention have been particularly described with relation to satisfying the voltage requirements of particular types of color kinescopes, it will be appreciated that advantage may be taken of the various features of the present invention in voltage supplies utilized for satisfying the high voltage require. ments of other types of color kinescopes, such as'those utilizing electrostatic type beam converging apparatus, or in voltage supplies for other purposes apart from television apparatus.

. Having thus described my invention, what is claimed is:

`1. In a cathode ray tube system, a high voltage vpower supply comprising in combination a periodically pulsed transformer, a first rectifying means having an input terminal and an output terminal, said first rectifying means input terminal being coupled to an intermediate point on said transformer, a second rectifying means having an input terminal and an output terminal, a capacitor, said capacitor coupling said second rectifying means input terminal to a point on said transformer of higher pulse potential than said intermediate point, and an inductive choke coupled between said first rectifying means output terminal and second rectifying means input terminal, a first output circuit coupled to said first rectifying means output terminal, and a second output circuit coupled to said second rectifying means output terminal, each of said first and second output circuits providing a respectively different cathode ray tube electrode operating potential.

2. In a cathode ray tube system, said cathode ray tube including a focus electrode and an ultor electrode, a high voltage power supply comprising in combination a trans former having a plurality of points of different potential, a first rectifying means having input and output circuits, said first rectifying means input circuit coupled to an intermediate point on said transformer, a second rectifying means having input and output circuits, a capacitor, said capacitor coupling said second rectifying means input circuit to a point on said transformer of higher potential than said intermediate point, D.C. coupling means connected between said first rectifying means output circuit and second rectifying means input circuit, voltage regulating means shunting the output of said second rectifying means, a voltage divider shunting the output of said first rectifying means, means for supplying the output of said second rectifying means to said ultor electrode, means for adjustably coupling said focus electrode to a point on said voltage divider, and means for coupling said voltage regulating means to another point on said voltage divider.

3. In a 'color television receiver including a color kinescope requiring a focusing voltage of a first order and an ultor voltage of a second higher order, said receiver also 4including a defiectiori wave output transformer in which fiyback pulses periodically appear, a high voltage supply comprising in combination first rectifying means coupled to said transformer forvdeveloping a D.C. poten'- ltial of said first order from said periodic flyback pulses, means for adding the developed D.C. potential of said first order to flyback pulses additionally derived from said transformer, and second rectifying means coupled to said adding means for developing a second unidirectional potential of said second order from the sum of said first D.C. potential and said latter derived flyback pulses, said.

adding means comprising an inductan'ce having a relatively low D.C. impedance and a relatively high A.C. impedance, said inductance being coupled between said first and second rectifying means.

4. A high voltage supply in accordance with claim 3 including voltage regulating means shunting the output of said second rectifying means, and means for controlling said voltage regulating means in accordance with variations in the developed D.C. potential of said first order, said controlling means comprising a voltage divider to which the developed D.C. potential of said first order is applied, and means for deriving said focusing voltage from said voltage divider.

5. In a color television receiver including a color kinescope and a deflection wave transformer subject to the periodic appearance of fiyback pulses, a high voltage supply for supplying a final beam accelerating voltage to said color kinescope, said high voltage supply comprising in combination a first rectifier having an input electrode and anoutput electrode, said first rectifier input electrode being coupled to an intermediate point on said transformer, a second rectifier having an input electrode and an output electrode, a capacitor, said capacitor coupling said second rectifier input electrode to a point on said transformer of higher flyback pulse potential than said intermediate'point, and inductive means coupled between said first rectifier output electrode and said second rectifier input electrode, said inductive means having a relatively high A.C. impedance and a relatively low D.C. impedance, said final beam accelerating voltage being derived from said second rectifier output electrode.

6. A high voltage supply in accordance with claim 5 for additionally supplying a focusing voltage to said color kinescope, said supply also including a voltage divider connected between said rst rectifier output electrode and `a point of reference potential, said focusing voltage being derived from said voltage divider.

7. in a color television receiver including a color kinescope and a deflection wave output transformer subject to the periodic appearance of flyback pulses, a high voltage power Vsupply for supplying ultor and focusing voltages for said color kinescope, said high voltage supply comprising in combination a first rectifier having an anode and a cathode, means for coupling said first rectifier anode to an intermediate point on said transformer, a second rectifier having an anode and a cathode, a capacitor, said capacitor coupling said second rectifier anode to a point on said transformer of higher flyback pulse potential than said intermediate point, an inductive v choke coupling said first rectifier cathode to said second rectifier anode, a bleeder resistance connected between said first rectifier cathode and a point of reference potential, means for adjustably tapping said bleeder resistance to derive the desired focusing voltage, and means for deriving said ultor voltage from said second rectifier cathode.

8. A high voltage supply in accordance with claim 7 also including a voltage regulator tube having a space discharge path effectively coupled between said second rectifier cathode and said point of reference potential, said voltage regulator tube including a control electrode, and means for connecting said control electrode to said bleeder resistance.

9. In a color television receiver including a color kinescope and a deflection wave output transformer subiect to the periodic appearance of iiyback pulses, a high voltage power supply for supplying ultor and focusing voltages for said color kinescope, said high voltage supply comprising iri combination a rst rectifier having an anode and a cathode, means for coupling said first rectifier anode to an intermediate point on said transformer, 1 second rectifier having an anode anda cathode, a capacitor, said capacitor coupling said second rectifier anode to a point on said transformer of higher flyback pulse potential than said intermediate point, a D.C. coupling means connected between said first rectifier cathode and said second rectifier anode, sai/dk D.C. coupling means presenting a relatively high impedance to the yback pulses appearing at said second rectifier anode, said ultor voltage being derived from said second rectifier cathode, a focus bleeder Vconnected vbetween said first rectifier cathode and a point of reference potential, means for adjustably tapping said focus bleeder to derive said focus voltage.

10,'A high voltage powersupply in accordance with claim 9 also including a control tube having a space disharge path effectively coupled between said second rectifier cathode and said point of reference potential ,and means for controlling th'ecurrent fiow in said Vspace discharge path in accordance with variations in the voltage :.ppearing yacross said focus bleeder. e i

References Cited in thefle of this patent UNITED STATESVVPATENTS 2,226,996 Schlesinger Dec. 31, 1940 2,601,153 Knight June 17, 1952 2,621,305y Lime Dec. 9, 1952

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