US2866127A

US2866127A - Cathode ray tube apparatus

Info

Publication number: US2866127A
Application number: US367270A
Authority: US
Inventors: Harrison S Allwine
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1953-07-10
Filing date: 1953-07-10
Publication date: 1958-12-23
Anticipated expiration: 1975-12-23
Also published as: FR1107965A; GB754169A; DE950561C; NL189079B

Description

Dec. 23, 1958 H. s.AL| w1NE CATHODE RAY TUBE kAPPARATUS 3 Sheets-Sheet l Filed July l0, 1953 Dec. 23, 1958 H. s. ALLwlNE 2,856,127

cATHoDE my TUBE APPARATUS Filed July 1o. 195:5 s sheets-sheet 2 Jax/k Juf/a4 Y fawn 5mm L /I TTOR NE Y Dec. Z3, 1958 H. s. ALLwlNE 2,866,127

CATHODE RAY TUBE APPARATUS Filed July 10. 1953 3 Sheets-Sheet 5 ATTORNEY CTHDE RAY TUBE APPARATUS Harrison S. Allwine, Trenton, N. 3., assignor to Radio `Corporation of America, a corporation of Delaware Application .luiy liti, 1953, Serial No. 367,270

The terminai fteen years of the ternrof the patent to be granted has heen disclaimed S Claims. (Ci. 315-14) The present invention relates to cathode ray tube apparatus and, more specifically, to color kinescopes, camera tubes and other cathode ray devices of the type containing a target assembly comprising one or more wire grills or other non-rigid structures through which beam electrons pass in transit to a nearby screen.

In cathode ray tubes of the variety described, there has long existed the problem of vibration of the grill wires which, as persons skilled in the art will appreciate, results in color error and other image defects in the case of color kinescopes, for example. In View of the deleterious effects on images resulting from vibration of the grill wires, there have been several proposals for alleviating the condition. For example, French Patent No. 86.6,065 to W. Flechsig, published 1941, discloses a color line screen unit which includes a grill comprising a series of parallel metal wires whose spacing is maintained by several very tine wires positioned at right angles to the rst wires.7 It will be noted, however, that reinforcing wires, regardless of how thin they may be formed, produce shadows which mar the image on the screen of the tube. Another proposal which has been set forth in the prior art provides for relatively thick reinforcing or damping rods and a plurality of auxiliary electron lens elements for reuniting the electron beam after it has been split by such bars. These and other proposals are subject to the criticism of being complicated and, therefore, quite costly.

it is, therefore, a primary object of the present invention to provide means for eliminating wire vibration in cathode ray tubes of the type described, thereby elimihating or, at least, reducing substantially the effects of color dilution, loss of contrast and the like.

Another object of the invention is the provision of such means in a simple and inexpensive manner.

In the held of color kinescopes, by way of illustration, two important varieties of structure have evolved, namely, post-deection acceleration, such as shown by Flechsig and, more recently, post-deflection deceleration tubes. A post-detiection deceleration (or, simply, post deceleration) kinescope, which is one wherein an electron beam is subjected to an auxiliary decelerating force after rasterscanning deflection and immediately prior to its arrival at the screen is disclosed and claimed in the co-pending U. S. application of E. G. Ramberg, S. N. 277,182, filed March 18, 1952, now U. S. Patent No. 2,728,024. Such a tube may include two wire grills spaced a small fraction of an inch apart and operated with as much as iive kilovolts difference in potential, both being at relatively high potentials in the region of fifteen to twenty kilovolts. As picture content changes, the load on the high voltage supply or supplies will also change, thereby tending to cause the potentials on the grills to change. lf color purity alone is considered, large changes in these potentials are not too objectionable, provided the ratio of the two voltages remains constant. For reasons of maintaining constant deection, however, it is frequently desirable to limit the amount of change permitted in the voltages to minute values such as one-half of one percent,

Patented Dec. 23, 1958 for example, and supplies giving this degree of regulation are currently in use. In post acceleration kinescopes (i. e., post-deflection acceleration), a similar situation exists between the target screen and an auxiliary wire grill through which an electron beam within the tube must pass before striking the target.

It has been found by the present applicant that the variations in supply voltage resulting from the load variations cause the electrostatic force between the electrodes to vary cyclicly with suthcient amplitude to induce mechanical vibrations in the wires, even when reasonably Well regulated supplies are used. At rst glance, therefore, it would seem that, in order for such varying voltage difference to be obviated, it would be necessary to provide for a much closer degree of regulation in the power supplies which, with presently known techniques, would increase the cost of the supply. However, it has further been found by the present applicant that it is possible to overcome the vibration-producing voltage variations between the electrodes of a target assembly without resorting to extremely fine voltage regulation.

In general, the present invention contemplates the coupling on the alternating potential variations from that target electrode which is more subject to load-induced voltage variations (normally the one operated at a higher potential) to the target electrode which is less subject ot such variations. ln other Words, assuming that the vertical blanking signal produces a load variation resulting in alternating components of 60 cycles and its harmonics in the supply voltage of one target assembly grill, the present invention provides means for inducing a similar voltage variation, having substantially the same amplitude and phase, on the adjacent wire grill thereby eliminating or greatly reducing variations in the difference voltage between the electrodes in question, stabilizing the electrostatic force between them.

Thus, it is another object of the invention to provide means for coupling alternating voltage variations from one to another electrode in a target assembly of the type described to prevent vibrations.

A further and more specific object hereof is the provision of means for coupling the alternating current voltage variations from a target assembly electrode operated at a given potential to an adjacent grill type electrode normally operated at a diierent potential.

Still another object is to provide means for causing said electrodes in the target assembly as set forth to have the same load-change-induced alternating current components.

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

Fig. 1 illustrates schematically a tri-color kinescope of the post deceleration type;

Fig. 1(a) is a graph showing the potential gradient within the tube of Fig. 1;

Fig. 2 is a frequency spectrum to be described in connection with the invention;

Fig. 3 shows one embodiment of the invention relating to a post-deceleration tube, such as the one in Fig. l;

Figs. 4, 5 and 6 illustrate, respectively, different additional embodiments of the invention with post-deceleration tubes of the type shown in Fig. l;

Fig. 7 is a schematic showing of a post-acceleration tricolor kinescope;

Fig. 7(a) is a graph showing the potential gradient within the tube of Fig. 7;

Fig. 8 illustrates a form of the invention employed with a tube of the type shown in Fig. 7;

Fig. 9 is a diagram showing another form of the invention;

Fig. illustrates still another embodiment of the invention; and

Figs. 11 and 1l(w) are schematic showings of two additional forms of the invention, relating to still another type of kinescope.

Referring to the drawings and, particularly, to Fig. 1 thereof, reference numeral 10 indicates generally a tri-color kinescope of the post deceleration variety claimed in the above cited Ramberg co-pending application. Since the kinescope is described in great detail in that application, and does not constitute part of the present invention, it is necessary herein to note only its general structure. Within the envelope .12 there are included three electron guns 14 which may, for example, emit beams of electrons adapted to strike, respectively. red, green and blue light-emitting phospho-r lines of subelemental width which comprises the target screen 16. The reference characters R, G and B indicate the sequence which may be employed lfor the screen 16. The electron beams (not shown) produced by guns 14 are or may be given a predetermined degree of acceleration by means of a rst anode which is connected to a suitable source of positive potential (not shown) and are caused to scan a raster by means such as an electromagnetic deflection yoke 22, in a conventional manner. As pointed out in the Ramberg application, the basic idea of a focusing grill disposed in the path of an electron beam traveling from its target screen is shown in the Flechsig French Patent 866,065 and its German counterpart 736,575 (1943). Broadly, the theory of such a focus grill as that shown at 24 in Fig. 1 is to cause the electrons of a beam to converge toward a predetermined target area. Thus, a post-acceleration kinescope effects such convergence by means of an electrostatic eld whose change is in the negative direction (i. e., the focus grill separates a region of less ac celeration from a region of greater acceleration nearer the target). At this juncture, it may be noted that, where a field change is positive (i. e., going from a region of greater electron acceleration to one of less acceleration), the electrons comprising the beam are caused to diverge.

In accordance with the Ramberg invention, an auxiliary wire grill 26 is disposed within the target assembly which further includes the screen 16 and focus grill 24, the wires of the auxiliary grill being perpendicular to those of the focus grill and, therefore, perpendicular to the direction of orientation of the phosphor lines R, G and B. 'In accordanceY with the Ramberg teaching, the kinescope 10 is or may be operated as a post deceleration device with its second anode 23 and auxiliary grill 26 at a given potential of, for example, 20 kilovolts and with its focus grill at the same potential as that'of the screen, namely, 15 kilovolts. One important function of the auxiliary grill in a post-deceleration kinescope is that of preventing color dilutio-n which 'would otherwise be caused by back scattering of secondary electrons produced by impingement of the electron beam on the screen 16.

Fig. l(a) illustrates the potential gradient within the tube 1t) and shows that for a 'substantial distance behind the auxiliary lens 26 (i. e., toward the guns 14) the potential is 20 kilovolts, dropping sharply to l5 kilovolts between the auxiliary grill and the focus grill 16.

As has been stated briefly above,`the load on the high voltage power supplies (indicated diagrammatically by block in a color kinescope such as that shown in Fig. l, changes as a function of changing beam current, and the changing load in turn causes changes in the voltage supplied. That is to say, as is well known in power supply operation generally, a decreasing load will ordinarily result in an increased potential at the output of the power supply. Hence, as the load changes within kinescope 10 (e. g., as the beam is moved from a bright portion of the picture to a darker part, or .as

4 the beam is blanked out during the time for return trace) the voltage at the output of supplies 30, namely, the l5 kv. and 20 kv. terminals, will also change.

Where supplies having voltage regulation of the order of one-half of one percent are used with a post-deceleration tube such as that of Fig. 1, wherein the two

wire grills

24 and 26 may be separated by 0.125 inch or even less, with five kilovolts or more difference in potential, it has been found that the variation in supply voltage resulting from the variation in load (i. e., beam current) which is produced by the vertical blanking and by other low frequencies present in the video signal, causes the voltage difference between the grills 24 and Z6 to have alternating components of vertical -scan frequency and its harmonics, of sufficient amplitude to induce mechanical vibrations in one or both of the grills, since some of the harmonics coincide with the mechanical resonant frequencies of some of the wires comprising the grills.

Fig. 2 illustrates a frequency spectrum ranging from one cycle per second to 4.5 megacycles, illustrating how the energy present in a typical video signal is concentrated mostly at the scan frequencies and their harmonics. Thus, for example, load variations with their attendant voltage supply variations may occur at all of these frequencies. However, the high frequency variations such as those above l0 kc., usually have negligible amplitude because they are by-passed by the inherent capacitance between. the two

grills

24 and 26 and by the capacitance in the power supplies. Furthermore, these high frequencies are ordinarily very much higher than the mechanical resonant frequency of the wires. The variations occurring at the vertical scan rate and its harmonies fall within the range of the resonant frequencies encountered in mo-st grill wires as indicated by the bracket designated FR in Fig. 2, and these harmonics are of sufficient amplitude to produce undesired vibration of the wire grills.

Hence, by way of example, if variations of onehalf of one percent occur in the 20 kv. supply with substantially smaller variations such as 1%0 of one percent occurring in the l5 kv. supply (the latter variation being smaller because the load on the l5 kv. supply is smaller) the difference voltage between the grills will contain, in addition to the desired 5 kv. D. C., an alternating cornponent equal to volts minus 7.5 volts or 92.5 volts. A variation of such magnitude is in excess of that required for causing the objectionable wire vibration. In view of the foregoing, it has been suggested that the only possible solution is that of providing a far greater degree of regulation than the values presently employed, thereby rendering the apparatus more costly, and with conventional components, unwieldy for home instrument use.

The present invention, however, precludes Wire vibration in a far different manner, namely, increasing the voltage variation on the lower potential grill until it is substantially equal to the variations on the higher potential grill, thus effectively reducing to Zero the variations in the difference voltage. Although the present invention is a departure from heretofore orthodox techniques of maintaining a constant ratio between the voltages on the two grills, the small amount of intentional change in the voltage ratio which is introduced in accordance with this invention is insufficient to cause color change, if the two voltage swings are substantially in phase. That is, con ventional operation requires that VTM/12K, to maintain color purity. However, for changes of the order of lOO volts or less, the applicant finds that, in the interests of preventing vibrations, operation according to The simplest form of this invention is illustrated in Fig` V3. wherein there is shown a post deceleration kinescope 1 0,

having a tri-part target assembly comprising a screen 16, focus grill 2d and auxiliary grill 26, the first two electrodes being connected to a terminal of a power supply 3!) from which there is available a potential of l5 kv., while the last-named electrode and the kiuescope final anode 2S are connected to a 20 kv. terminal. Assuming a load change at a 60-cycle rate resulting from vertical blanking of the kinescope lil or from low frequency components of the video signal, as mentioned in the numerical example set forth above, the 2t) kv. terminal will have an alternating voltage component with a peak-to-peak amplitude of 1GO volts, or 92.5 volts greater than that on the l5 kv. terminal. Since a swing of this amplitude would induce vibrations of the grill wires, the present invention provides, according to the form of Fig. 3, a large capacitor 34 connected between the 2O kv. and l5 kv. terminals for coupling the voltageY fluctuationV from grill 26 tof'grillV 2&5.' Assuming, for example, that the capacitor is sufliciently large (e. g., 9.03 mfd.) to couple the vai .tions Without appreciable amplitude or phase change and that its impedance is small compared to that of the supplies, the net effect of the lcoupling capacitor 3d is to reduce substantially to zero the alternating component of the voltage difference between grills 2d and 26, so that that cause of vibration is eliminated. The apparatus of Fig. 3, it should be noted, by reason of its departure from conventional technique, provides a simple yet extremely eective means for eliminating the specified source of vibration stimulus.

Fig. 4 illustrates another form of the invention as applied to a post deceleration tube and includes a screen i6, focus grill 24 and auxiliary grill 26, the last-named grill being supplied with a 20 kv. potential from source 30(11). The kv. power supply for grill 24 and screen 16 is indicated by the circuitry within dotted line box 30(1)) and may include, for example, a source of l5 kv. D. C. indicated diagrammatically, which, in practice, may be in the form of a yback power supply of the type well known in the television art. rl`he direct current at the input of supply 39(1) is filtered as by means of the capacitor-input filter which includes capacitor resistor 40 and output capacitor 42. Normally, the output capacitor 42 of a filter such as that illustrated is chosen of large enough value that A. C. load variations produce negligible voltage variations. According to the present invention, however, capacitor 42 is of such smaller value that it regulates the l5 kv. potential less efficiently for low frequency variations in load, thereby causing the voltage swing on the l5 kv. grill to equal that on the 2O kv. grill in spite of the fact that the load on grill 2d is substantially smaller than that on grill 26. Thus, it will be appreciated by those skilled in the art that the eect of the smaller capacitor d2 on the output side of the filter of power supply 3tl(b) is that of allowing the load variations to cause voltage variations of the l5 kv. supply equal to those of the 2G kv. supply and in phase therewith, since a given transfer of charge (represented by one half cycle of load variation, for instance) will cause a larger voltage change in a small capacitor than in a larger one.

Reducing the value of capacitor 42 effectively increases the internal impedance of supply 39(17) so that the product of its load current and its internal impedance is increased to equal substantially the product of load current and internal impedance of the kv. supply.

In the embodiment of the invention illustrated in Fig. 5 which again includes screen 16, focus grill 2f.- and auxiliary grill 26, the 2O kv. potential for the last-named grill is furnished by supply 3901). The power supply 3(3(b) for the focus grill 24 includes a suitable source of D. C., indicated diagrammatically, and a shunt regulator tube il of a conventional type whose operation is well known. The bleeder resistance 46 of the power supply StMb) rcflects load variations of the grill 24 so that there is available at tap d'7 a sample of the voltage variations resulting therefrom. ln conventional regulators of the type in question, the sample of the varying voltage is applied to the control electrode 44 of a voltage regulator tube by means of a filter which may comprise

shunt capacitors

48 and 49 and a series resistor 50. In conventional practice, the capacitors i8 are made sufficiently small that they will by-pass or attenuate only the frequencies high enough to cause unwanted oscillations. In accordance with the present invention, capacitors 4S and 49 are larger than in ordinary practice so that they result in poor regulation of the l5 kv. supply insofar as low frequency fluctuations are concerned. In this case, as in the case of the apparatus of Fig. 4, the specific values for the capacitors may be determined by calculation, using conventional network theory, once the characteristics of the supplies and of the regulator tube are known.

The apparatus of Fig. 6 includes screen 16, focus grill f-l and auxiliary grill 26 of a post deceleration color kinescope. The auxiliaryV grill is provided with a 20 kv. potential by supply 30m). As will be understood, any load variations of grill 26 will produce corresponding voltage variations across the voltage divider 5l, assuming the irnpedance of the divider is high compared with that of capacitor 51 coupling it to grill 26. Power supply 30(b) includes a bleeder 52 and shunt regulator tube 5d similar in function to its counterpart in the apparatus of Fig. 5. instead of the control tube 54- being supplied only with a sample of the voltage across bleeder 52, the cathode 54 is coupled via filter 56 to a point on voltage divider 5l of the 2O kv. supply. ln this way, the 20 kv. supply variations are coupled to the l5 kv. regulator tube so that, assuming the load on grill 26 decreases, the voltage across voltage divider 5i will increase, thereby increasing the positive cathode bias on the regulator tube S4 and making it conduct less, so that the voltage on grill 24- is increased. More specifically, the values of the various circuit components are chosen so that the changes in voltage on grill 24 are equal to and in phase with the voltage variations on grill 26.

lt should be borne in mind that, in the apparatus of Fig. 6, as well as in the apparatus of Fig. 5, correspending circuit connections may be made to produce the same results where the voltage regulator tubes are of the series or rheostat type. ln other words, if the regulator tube 54 of Fig. 6 were a series type, the voltage sample from voltage divider Sl `would be fed to its control electrode rather than to its cathode. This point is well understood by persons skilled in the art and need not be explained in greater detail here.

The foregoing description has been concerned with illustrative embodiments of the invention in connection with a tri-part target assembly post deceleration tube of the type set forth in the above-cited Ramberg application. The invention is also applicable to post acceleration cathode ray tubes having a bi-part target assembly which includes, for example, a phosphor screen and a focus grill. Such a tube is illustrated in Fig. 7 wherein reference numeral 60 indicates generally a tri-color kinescope having three electron guns 62, a first anode 64E- connected to a source of positive potential (not shown), a final anode 66 in the form of a wall coating, a target screen 68 rnade up of a plurality of phosphor strips adapted to emit light of the primary colors, red, green and blue, and a focus grill '70 made up of wires arranged parallel to the phosphor lines. The post acceleration kinescope is well known in the art, as illustrated by the above-cited Flechsig patents and need not be described in detail here, beyond mentioning the fact that the electron beams traveling from guns 62 toward the target screen 68 are caused to converge by reason of the electrostatic lens effect brought about by the negative changing field in the region of focus grill 76. That is to say, the potential distribution within tube 6?, as shown in Fig. 7(11), is such that the electron beams pass through a substantially constant potential of 5 kilovolts from at least the gun-end of the final anode 66 to the focus grill 70, both of these elements being connected to a 5 kiloeffect on the electrons.

7 volt terminal of a power supply 72. From the focus grill to the screen 68,' the potential gradient rises steeply from kilovolts to 20 kilovolts vso that the electrostatic eld changes from one of less acceleration to one of greater acceleration, thereby producing a converging lens With changes in beam current, the voltage on the kilovolt power supply for the target lscreen 68 will also change correspondingly such that, by

virtue of the imperfect regulation of that supply, the 2G kv. potential will have an alternating component of given amplitude. The focus grill 70, on the other hand, being at a potential of one-fourth the target screen potential, will have a smaller load and, therefore, the potential variations of the 5 kv. power supply will be substantially less than those of the 2O kv. supply. The result vof this discrepancy would normally bring about different alternating components of the'two potentials, with the attendant vibration of the wires of grill 70. if the secondary emission ratiopof the grill wires is greater than one, the current supplied to the grill is negative instead of positive, and the voltage swings then are'of opposite polarity to those on the 20 kv. supply, which causes the alternating component of the difference voltage to be even greater, and the vibration more severe.

ln order to obviate the diierent alternating components of the two electrodes potentials, the apparatus of Fig. 8 which shows diagrammatically the target 68 and focus grill '70 being supplied with potentials of 20 kv. and 5 kv., respectively, from power supplies 72 further includes a large coupling capacitor 74 connected between the two electrodes. As in the case of the apparatus of Fig. El,` the capacitor 74 should be large enough to couple the alternating component of potential from target screen 65 to focus grill 7d without appreciable loss of amplitude or shift in phase. In general, it may be stated that the larger the value of capacitor 74, the more faithfully it will couple the alternating component of the target screen potential to the focus grill, both as to amplitude and phase. It should have a large enough value that its impedance is much smaller than the internal impedance of the supplies. By so coupling the lluctuations from screen 68 to grill 70, the apparatus eliminates the varying potential difference between the two electrodes which otherwise induce vibration of the grill wires.

Still another form of the invention is shown in Fig. 9 in connection with a post acceleration tube having a target screen 68 and focus grill 70. 1n this case, the target screen electrode of the bi-part target assembly is supplied with a nominal potential of 20 kilovolts from a power supply indicated diagrammatically by the block `'72(u). The potential for focus grill 70 is provided by the 5 kv. supply 72(1)).

Included within the supply are a bleeder resistance 76 and a shunt regulator tube '7S whose control electrode is connected to a tap on the bleeder. 1n order to prevent vibration of the grill wires 70 which would otherwise be induced by the substantial amplitude of alternating variations on the power supplies as explained supra, the apparatus of Fig. 9 includes means such as capacitor 80 and voltage divider S2 for coupling to the cathode 7S of regulator tube 7S the alternating current component present on the target screen 6d. Thus, assuming, for example, that the load on target screen 68 varies at a rate corresponding to vertical blanking and low frequency components in the video signal, there will be corresponding variations of the 20 kv. potentiai. Assuming further that at a given time (e. g., blanking interval) the load on target screen 6&5 drops, the potential at the output terminal of supply 72.(a) will rise in value. This voltage rise will be coupled to the cathode 78' to render regulator tube 76 less conductive, thereby reducing the load on the 5 kv. supply, so that the voltage applied to grill 70 will be increased,

- the tap on voltage divider 82 being adjusted until the alternating voltage between grill 70 and target 68 is zero or reaches a minimum.

Fig. 10 illustrates diagrammatically another form of the invention shown, by way of example, in connection with a post deceleration tri-color kinescope 10 having a target screen 16, focus grill 24 and auxiliary grill 26, in addition to the usual nal anode 28, iirst'anode 20 and electron guns 14. The target 16 and focus grill 24 are supplied with a potential of 15 kv. by power sup ply 30, while the auxiliary grill 26 and nal anode 2S are connected to the 20 kv. terminal of the power supply. Since it is a basic concept of the present invention to cause the voltage on each electrode of the multi-part target assembly to fluctuate with load equally with the fluctuations of the voltage on each of the other electrodes, the embodiment of Fig. 10 provides means for detecting load variations directly and coupling them to the 15 kv. terminal which, as will be understood from the preceding description, would otherwise have smaller variations than the 20 kv. supply. More specifically, as shown, the electron guns 14 are connected to a suitable bias source indicated by the resistor connected between ground and a source of positive potential so that the load current of the kinescope willbe present at the junction of the electron g'un cathodes (point 91). The load current will also flow through that portion of the resistance 90 between tap 91 and ground so that a voltage drop varying in accordance with the load will also appear across that portion of the resistor. Although most of the alternating component of this voltage is by-passed by capacitor 96, a small part of the low frequency components remains. This voltage is` applied to amplier 92 whose output is coupled via capacitor 94 to the 15 kv. grill 24. The resistor 97 prevents the supply from short-circuiting the signal obtained through 94. By suitably adjusting the gain of amplifier 92, the amplitude of the voltage swings applied to the l5 kv. grill 24 may be made substantially equal to those occurring on the 20 kv. grill 26 as a result ofk load variations. Thus, as will be appreciated, the voltage variations Aon the two supply terminals may be rendered equal.

While the invention has, to this point, been described by way of its applicability to post-deceleration and postacceleration tubes of the variety set forth, it is also effective in preventing wire vibrations in still another'form of tube, namely, that described and claimed in U. S. Patent 2,446,791 granded Aug. 10, 1948 to A. C. Schroeder for Color Television Tube. Tubes of the kind disclosed in that patent provide multi-color television images, for example, through the agency of a single electron beam and a multicolor line screen target with means for switching the beam alternately to the several color strips of the screen. For purposes of simplicity, the Schroeder tube will be referred to hereinafter as one which switches at the screen. In general, the beam switching is accomplished by electron-deliecting electrode structure, such as a pair of parallel wire grills located in the same plane and disposed in the path of an electron beam directed toward the screen. A switching voltage is applied to the two grills such that, in order for the beam to strike one color strip, both grills are at the same potential, but, where the beam is intended to strike a second color strip, one grill is rendered more positive and the other grill more negative, thereby causing the beam to be deected toward the more positive grill. i

Fig. 11 illustrates the pertinent elements of switching at the screen color tube operated as a post-acceleration device as described above and includes, by way of example, a ruled line screen including a plurality of phosphor strips arranged in the vertical sequence of red (R), green (G), red (R), blue (B), red (R), and so forth. Screen 100 is connected to a source 102 of 20 kv. potentential. The switching grills are indicated at 104 and 106 and may be connected to a source 108 of 5 kv. mean wave switching waveform through transformer 112 whose secondary is or may be center-tapped to A. C. ground. Thus, an electron beam traveling toward screen 100 may be switched between E, G and B phosphor strips by applying diterent potentials to the

grills

104 and 106 in what is new a well-known maner. It should be noted, however, that load changeinduced potential variations of the screen supply 102 will generally be substantially greater than the corresponding swings of the kv. supply. Since it is necessary for the proper operation of such a tube that the two grills be permitted to differ in potential in accordance with the switching waveform from source 110, it is readily apparent that they cannot be coupled together and to the screen 100 as in the case of the nonswitching tubes. To accomplish the vibration-eliminating object of this invention, despite this paradox, one mode being as follows: By reason of the fact that the grills such as those shown at 104 and 106 are switched at source frequency such as 15,000 cycles per second or higher, it is practical to distinguish between the necessary l5 kc. switching voltage and the lower frequency (60 cycles and its lower harmonics) variations which tend to produce the undesired grill vibration. Thus, the

grills

104 and 106 may be connected to the 5 kv. supply 108 through frequency-responsive impedances 114 and 116, which, as illustrated, may take the form of inductances or low-pass filters. The impedance of each of the inductances is directly proportional to frequency (X L=21rfL), so that impedances 114 and 116 are relatively high to the l5 kc. switching voltages, but relatively low to those frequencies in the range capable of producing mechanical vibration of grills. virtue of the impedances 114 and 116, therefore, the high frequency switching Waveforms may be maintained separate on the grills, while permitting coupling of the two grills for purposes of imparting to them load-change-induced voltage variations generally equal in amplitude to and in phase with the corresponding swings of the 2O kv. supply. The lastrecited function is performed by capacitor 118 which, as in the case of Figs. 3 and 8, should be sufficiently large to couple the load-change-induced potential swings from screen 100 to the two grills with little or substantially no change in amplitude or phase.

A simplification of the apparatus of Fig. 1l is shown in Fig. 11(61), wherein like reference numerals indicate like parts. in this latter ligure, the frequency-responsive impedances 114 and 116 are eliminated and the 5 kv. power supply for the grills is connected to the center tap 112m) of the transformer secondary. Since the two halves of the secondary winding are practically pure inductances, their impedances will vary directly as frequency, thereby presenting a relatively high impedance to the l5 kc. switching waveforms and a relatively low impedance to those frequencies within the critical range in question, insofar tendency to produce wire-vibration is concerned. Moreover, the Vgrill charging currents must ilow through the secondary of the transformer in opposite directions so that they eiectively cancel each others transformer core-magnetizing flux. Capacitor 118, therefore, couples the load-change-induced voltage swings of screen 100 to

grills

104 and 106 to reduce the net amplitude of the alternating potential dilerential. Persons skilled in the art will recognize the fact that the embodiments of Figs. ll and 1l(a) allow the two

grills

104 and 106 as a unit to be capacitively coupled to the phosphor screen 100 for frequencies which are capable of causing wire vibration but do not significantly increase the capacitance which the switching circuit 110 must drive, since the frequency-responsive impedances are inserted between the grills and the large capacitor.

From the foregoing description of Figs. 1 through ll(a), it will be understood that the present invention accomplishes the important aim of eliminating wire vibration in a grill-type cathode ray tube and in a manner far different from and much simpler than heretofore proposed methods. In general, this end is realized according to certain forms by coupling load-variation-induced voltage lluctuations from that electrode of a multipart target assembly which is at a higher potential to the grill electrode of the assembly which is at a lower mean potential or by causing the lower potential electrode to have the same fluctuations as the other.

The advantages of the latter aspect of the invention may, therefore, be recognized as follows: Designing a power supply to have improved regulation (i. e., to have a lower internal impedance) necessarily increases its cost, while causing a supply to regulate less eliciently (i. e., to have a higher internal impedance) decreases its cost by reason of the fact that smaller circuit components may be employed. An obvious mode of preventing the load-change-induced, vibration-producing potential variations would be that of providing improved regulation in the supply having the greater swing (i. e., decreasing its internal impedance), which mode of operation would substantially increase the cost of the power supply. The present invention, on the other hand, according to certain of its above-described aspects, causes the power supply which experiences less fluctuation to regulate less efficiently, thereby decreasing the overall power supply cost. Thus, by way of illustration, while it would not be economically feasible to provide l5 kv. and 20 kv. supplies for a home color television receiver of such design that the load-change-induced variations never exceeded 20 volts in either supply, it is (as disclosed herein) not nearly as expensive to provide a 2() kv. supply in which the variations are l0() volts and a 15 kv. supply in which the variations are volts. Such supplies, moreover, would not produce wire-vibrations since the difference between the two variations would not exceed 10 volts, which is insuflcient for causing the vibration.

Hence, it should be understood that, where used in the present specification and claims, the expression rendering the voltage variations substantially equal should be construed as the optimum result but should also include situations wherein the difference in voltage swings is reduced to a value which is too small to effect noticeable wire-vibration through a varying electrostatic force.

Although the invention has been illustrated by way of several specific embodiments, it should be borne in mind that various other changes and modications within its scope will further suggest themselves to persons skilled in the art.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. In combination with a cathode ray tube of the type having a multi-part target assembly which includes a rst target electrode connected to a source of predetermined mean potential and a second target electrode comprising a non-rigid structure whose members have mechanical resonant frequencies of a predetermined range, said second electrode being connected to a source of lower potential than said first-named potential such that the potential of said irst electrode is subject to an alternating variation, due to load changes, of greater amplitude than is said second-named potential; said secondnamed source including a voltage regulator tube and a voltage-divider; lter means including a shunt capacitor connecting a point on said voltage-divider to a conduction-controlling electrode of said regulator tube for transmitting a sample voltage signal from said voltage divider to said regulator tube whereby to vary the conduction of said regulator tube to compensate for changes in the mean load in order to regulate the mean potential of said second-named source; said capacitor being suiciently large as to attenuate the alternating components of said sample signal for Variations occurring at frequencies within said predetermined range, thereby reducing the eiciency of regulation for such variations.

2. In combination with a cathode ray tube of the type having a multi-part target assembly which includes a first target electrode connected to a source of predetervmined mean potential anda second target electrode comprising a non-rigid structure connected to a source of lower mean potential than said first-named potential such that the potential of said first electrode is subject to a substantially greater alternating variation due to load changes than is the potential of said second electrode; said second-named potential having a voltage regulator tube for maintaining its mean output potential generally constant despite changes in mean load; and means for coupling said alternating potential variations from said first-named potential source to said regulator tube in such manner as to cause said second source to vary substantially equally and in phase with said alternating variations of said first-named source.

3. In combination with a cathode ray tube of the type having a multi-part target assembly which includes a first target electrode connected to a source of predeter mined mean potential and a second target electrode cornprising a non-rigid structure whose members have mechanical resonant frequencies of a predetermined range; said second electrode being connected to a source of lower potential than said rst-named potential such that the potential of said first electrode is subject to an alternating variation, due to load changes, of greater amplitude than is said second-named potential; said secondnamed source having vo-ltage regulating means for controlling its output potential; lter means for applying to said regulating means a sample signal of its load-changeinduced potential variations to modify the conduction of said regulator means as a function of the amplitude of such signal, said lter means being such as to attenuate the amplitude of any such signal whose frequency is one of which an integral multiple is in said predetermined frequency range.

4. In combination with a cathode ray tube of the type having a multi-part target assembly which includes a first target electrode connected to a source of mean potential and a second target electrode connected to a source of dilferent means potential, such dierence in mean potential being of such magnitude as to produce an appreciable electrostatic force between said rst and second target electrodes which lis caused to vary cyclically from a mean value by load variations on said first and second-named sources of potential differing in at least one of the factors phase and amplitude, at least one of said target electrodes comprising a non-rigid structure subject to undesirable mechanical vibration from such cyclic electrostatic variations occurring within a predetermined range of frequencies; electrical means for rendering substantially equal as to phase and amplitude such load-change-induced po-tential variations of said rst and second target electrodes within said predetermined frequency range.

5. The invention as set forth in claim 4 wherein said 12% electrical meansv comprises means for coupling such potential variations from saidl target electrode having greater amplitude load-change-induced variations to said other electrode.

6. The invention as set forth in claim 5 wherein said non-rigidtarget electrode comprises a pair of grills of the type adapted to deflect an electron beam in a direction dependent upon a switching voltage applied between them to vary the relative polarity of one grill to the other, thefrequency of such switching being relatively high with respect to said predetermined range of frequencies; land said electrical means further comprising frequency-responsive means coupling said grills to each other for presenting a high impedance to said high frequencylswitching voltage and a relatively low impedance to said load-variation-induced cyclic potential variations. 7. Apparatus comprising a cathode ray tube of the type ,havingV a .multi-part ltarget assembly which includes a first target electrode connected to a source of meanv potential and a second target electrode connected to a source of diferent mean potential, such diiference in mean potential being of such magnitude as to produce an appreciable electrostatic force between said rst and second target electrodes which is caused to Vary cyclically from a mean value by load variations on said first and second-named sources of potential differing in at least `one of the factors phase and amplitude, at least one of lsaid target electrodes comprising a non-rigid structure subject to undesirable mechanical vibration from such cyclic electrostatic variations occurring within a predetermined range of frequencies; each of said first and second potential sources having an internal impedance; and means for rendering said internal impedances of such value that, for load variations within said predetermined frequency range, the product of load current on ysaid first target electrode and the internal impedance of Vits source is substantially equal to the product of the load current on said second target electrode and the internal impedance of its source.

8. The apparatus defined by claim 7 wherein said lastnamedjmeans comprises means for increasing the internal impedance of said potential source having the lower mean potential, whereby to increase the amplitude of its load-change-induced potential variations.

References Cited in the le of this patent UNITED STATES PATENTS 2,265,311 Preisach et al Dec. 9, 1941 2,372,282 Kilgore Mar. 27, 1945 2,558,019 Toulon June 26, 1951 2,669,675 Lawrence Feb. 16, 1954 2,728,025 Weimer Dec. 20, 1955 2,755,410 Schlesinger .llly 17, 1956