CA1065961A - Spark gap and discharge path arrangement for a television picture tube or like device - Google Patents

Abstract

Abstract of the Disclosure A spark gap arrangement is provided ior a television image reproducing system including a television picture tube having a relatively high voltage focus electrode and relatively low voltage cathode, screen grid and control grid electrodes.
Spark gaps are respectively coupled between the electrodes and a reference potential to discharge energy deveoped at thc electrodes when undesirable arcing occurs between the electrodes which might otherwise cause damage to respective portlons of the signal processing system coupled to the electrodes. Separate relatively low impedance paths for conducting discharge currents produced in the spark gaps are coupled to the spark ?ap associated with the relatively high voltage focus electrode and the spark gaps associated with the relatively low voltage cathode, screen grid and control grid electrodes to substantlally prevent arc discharge currents associated with the focus electrode from being coupled to the cathode, screen grid and control grid electrodes through the spark gaps associated with the relatively low voltage elec-trodes themselves. In addition, the spark gaps are designed to inhibit excessively high voltages developed at the focus electrode from discharglng to adJacent electrodes, thereby circumventing the purpose of the separate discharge path arrangement, rather than through the associated spark gap.

Description

~Q65~6~ RCA 68,5gl 1 This application relates to apparatus for control-ling the effects of arcing between electrodes of a cathode ray tube or like device and in particular relates to appara-tus for controlling the effects of arcing between electrodes of a television picture tube.
Cathode ray tubes include a plurality of electrodes' for developing, controlling and accelerating an electron beam. For example, most color television picture tubes include relatively high voltage focus and ultor electrodes and relatively low voltage screen grid, control grid and cathode electrodes. When excessively high voltage gradients develop between the electrodes of a cathode ray tube, there is a tendency for a relatively high transient energy flash-over current or arc to flow from a relatively higher voltage electrode to a relatively lower voltage electrode through the space separating the electrodes. This arc may seriously damage signal processing circuits coupled to the electrode receiving the f]ashover current. Signal proces~ing circuits of color television receivers are particularly susceptible to arcing since the ultor and focus electrodes are operated at especially high voltages with respect to the low voltage electrodes and the focus electrode is spaced at relatively close distance from the low voltage electrodes.

Apparatus is known for inhibiting arcing due to the development of excessively high voltage gradients at the electrodes of a cathode ray tube. Of particular interest are spark gap devices. In general, a spark gap device includes two electrodes spaced apart by a suitable distance to cause a discharge current to ~low between the electrodes when a voltage in excess of a predetermined breakdown voltage .~

1~596~ RCA 68,591 I is developed across the spark gap electrodes. Typically, one of the spark gap electrodes is connected externally to an electrode of the cathode ray tube while the other electrode of the spark gap is connected through a relatively low impedance path to a point for absorbing the discharge current. Thus, when arcing occurs between the electrodes of the cathode ray tube, energy developed at the electrode receiving an arc is discharged through the spark gap and the' discharge path rather than through the cathode ray tube.

Spark gap arrangements useful for inhibiting destructive coupling of arcing in a television signal pro-cessing system are described in an article entitled "Flashover in Picture Tubes and Methods of Protection,"
by A. Ciuciura, appearing in the March 1969 edition of The Journal of the Institution of Electronic and Radio Engineers.
Although prior spark gap arrangements tend to inhibit damage to signal processing circuits, potentially destructive high transient energy produced when one spark gap fires may be coupled to spark gaps associated with other electrodes and then to respective signal processing circuits through the spark gaps themselves. For example, it is common in television receivers to employ a single common return path for all of the spark gap devices coupled to the electrodes of a picture tube. As a result, discharge cur-rents and associated high voltages from one spark gap devicemay be undesirably coupled back through the common return to affect the operation of other spark gaps. Therefore, prior spark gap arrangements are not as effective as is desired and, in certain instances, may cause damage to signal ~06596~ RCA 68,59l 1 processing systems which they are intended to protect.
In accordance with the present invention, an apparatus for protecting signal processing circuits coupled to the electrodes of a cathode ray tube, having at least one electrode operated at a relatively high voltage and another electrode operated at a relatively low voltage, is provided. A plurality of spark gap means are each coupled to respective ones of the electrodes for inhibiting the development of potentially destructive energies at the electrodes. First relatively low impedance means are coupled between a first of the spark gap means associated with the high voltage electrode and a point of reference potential.
A second low impedance means, separate from the first im-pedance means~ is coupled between at least a second of the spark gap means associated with the low voltage electrode, exclusive of the first spark gap means, and the point of reference potential. Thus, the operation of the second spark gap means is substantially isolated from the operatlon of the flrst spark gap means.
In accordance wlth another aspect ol the present invention, the cathode ray tube forms a television picture tube or like device including, for instance, a relatively high voltage focus electrode and relatively low voltage screen grid, control grid and cathode electrodes. The spark gap means associated with the relatively high voltage focus electrode is coupled to the first impedance means, while the spark gap means associated with the relatively low voltage cathode, screen grid and control grid electrodes are coupled to the second impedance means.
3 In accordance with still another aspect of the RCA 68,59l ~06596~

1 present invention, means are provided for substantially preventing a relatively high voltage electrode, such as, for example, a focus electrode, from arcing to an adjacent cathode ray tube electrode thereby circumventing the purpose of the separate impedance means arrangement. These means include means for isolating the spark gap associated with the relatively high voltage electrode from changes in environmental conditions such as changes in atmospheric pressure.
These and other aspects of the present inventioh will become clear from the following description in conjunc-tion with the drawing, in which:
FIGURE l shows the general arrangement of a color television signal processing system including a spark gap and discharge path arrangement formed in accordance with the present invention for protecting the signal processing sys-tem against the effects of arcing;
FIGURE 2 shows a prior art spark gap arrangement useful in understanding the advantages of the present spark gap and discharge path arrangement shown in FIGURE l;

FIGURE 3 shows an apparatus for maintaining the operation of a spark gap device substantially independent of environmental variations useful in the present spark gap and discharge path arrangement shown in FIGURE l;
FIGURE 4 shows a cross-sectional plan view of a first picture tube socket having a spark gap and discharge path arrangement formed in accordance with the present invention; and FIGURE 5 shows a cross-sectional plan view of a second picture tube socket and associated printed circuit ~o6596~ RCA 68,591 1 board having a spark gap and discharge path arrangement formed in accordance with the present invention.
Referring now to FIGURE 1, the general arrangement of a color television receiver employing the present in-vention includes a signal processing unit 12 responsive toradio frequency (RF) television signals for generating by means of suitable intermediate frequency (IF) circuits (not shown) and detection circuits (not shown) a composite video signal comprising chrominance, luminance, sound and syn-chronizing signal portions. Outputs of signal processingunit 12 are coupled to a chrominance channel 14, a luminance channel 16, a channe] 18 ~or processing synchronizing sig-nals and a channel (not shown) for processing sound signals.
Chrominance channel 14 includes a chrominance processing unit 20 which serves to derive chrominance signals and color phase signals, e.g., in-phase (I) and quadrature (Q) signals, from the composite video signals. The chromi-nance signals and the color phase signals are coupled to a synchronous detector 22 which serves to derlve color dif-ference signals, e.g., R-Y, B-Y and G-Y signals, from the chrominance and color phase signals.
The color difference signals are coupled to a picture tube or kinescope driver circuit 24, where they are matrixed with the output signal, Y, of luminance channel 16 to produce color signals, e.g., R, B~ and G signals. The color signals are coupled to picture tube or kinescope 42 Luminance channel 16 includes signal processing units 26 and 28 which serve to amplify and otherwise process luminance signal portions of the composite video signals.
Contrast control unit 30 and brightness control unit 32 are ` ` 106S96~ RCA 68,591 I coupled to luminance processing unit 28 to control the contrast brightness properties o~ the images produced by kinescope 42.
Channel 18 includes synchronization signal separa-tor (sync separator) 34 which serves to separate horizontaland vertical synchronization pulses from the composite video signal. The synchronization pulses are coupled ~rom sync separator 34 to horizontal deilection circuit 36 and vertical deflection circuit 38 which serve to control the deflection o~ the electron beam gençrated by kinescope 42 in a conven-tional manner. Deflection circuits 36 and 38 also produce a blanking signal which is coupled to luminance processing unit 28 to inhibit its operation during vertical and horizon-tal beam retrace periods. Horizontal de~lection circuit 36 IS is coupled to high voltage supply 40 which serves to generate the high voltages required to operate kinescope 42.
The circuit arrangement oi' a television receiver oi the type shown in FIGURE 1 i9 shown in detail in RCA(Trademark) Color Television Service Data, 1973, No. C-8 (a CTC-68 type ` 20 receiver), publlshed by-RCA Corporation, Indlanapoli~, Indiana.
Kinescope 42 may be any suitable type oi aathode ray tube or like device i'or producing images in response to electrical signals. For example, kinescope 42 may be a mu]ti-gun kinescope, such as a delta gun or precision in-line gun shadow or slotted mask kinescope or the like. ~s shown, kinescope 42 comprises asealed bottle-shaped body 44 ~ormed oi' a dielectric material such as glass. The neck end 46 oi' the hody 44 houses an electron gun structure ~or deve~oping an electron beam in response to e]ectrical signals coupled to RCA 6~,591 ~6596~

I the appropriate ones o~ the electrodes. A translucent face-plate or screen 48 is located at the broad end remote from neck 46. Phosphors are deposited on the inside of the face-plate for developing an image when impinged by the electron . . .
beam. The body of the kinescope, between the neck and the faceplate, has an inner conductive coating 50 and an outer conductive coating 52 across which is coupled a high voltage ' supply 40. The high voltage supply produced by high voltage supply 40 accelerates the electron beam developed by the gun structure. The outer conductive ~oating is composed, ~or example, of Aquadag~Trademark~material.
The neck 46 of kinescope 42 contains an electron gun structure for each of the different phosphGrs, e.g., red, green and blue, deposited on the inner side of the faceplate. Each gun comprises relatively low voltage elec-trodes, including cathode electrodes (generally indicated as 54), control grid electrodes (generally indicated as 56) and screen grid electrodes (generally indicated as 58). A

relatively high voltage focus electrode 60 is also provided.

2~ Relative]y lQw volta~e color sigt~als (typically less than 150 vo1ts peak to pea~, supplied by a kinescope driver 2~ are coupled to respective cathodes 54. Relatively low bias control voltages (typically less than 100 volts DC) are coupled to control grids 56 ~rom control grid bias unit 6~, while somewhat higher ~ias voltages (typically in the order oi' 600-800 volts DC) are coupled to screen grids 58 from screen grid bia~ unit 66 to ad~ust the cuto~f point and gain o~ each gun. A multiplicity o~ bia~
control voltages, as illustrated in FIGURE 1, are generally

3 utilized since the operating characteristics of thé ~everal 106S9~1 RCA 68,59l 1 guns may be expected to vary with respect to each other. It should be appreciated that the number of bias control voltages may be modified depending on the particular gun configuration of kinescope 42.
A relatively high voltage (typically greater than 5 kilovolts DC) is coupled to focus electrode 60 from high voltage supply 40. A beam accelerating voltage (typically of the order of 20-30 kilovolts DC) produced by high voltage supply 40 is coupled to inner coating 50 through connection 62, sometimes called the ultor connection, located near the center of the kinescope bulb and thence, via the inner coating 50, to the ultor electrode 62a of the electron gun.
Thus, relatively high voltages may exist between ultor electrode 62a and focus electrode 60, between ultor electrode 62a and cathode 54, control grid 56 and screen grid 58 and between focus electrode 60 and cathode 54, control grid 56 and screen grid 58. Since the electro~des are spaced closely with respect to one another, an arc may be expected to flow between a pair of electrodes if a sufficiently large voltage gradient to cause an arc in relation to the spacing between the electrodes is developed between the electrodes. Focus electrode 60 is particularly susceptible to arcs from ultor electrode 62a because of the close spacing and high voltage difference between the ultor and focus electrodes. In turn, lower voltage electrodes are susceptible to arcs from focus electrode 60. Arcs can also occur between the external pins at the base of the kinescope which serve to couple the electrodes to signal processing portions of the receiver. In either case, since arcs are high in transient energy, the signal processing _g_ RCA 68,591 ~06596~

1 circuits may be over-stressed, thereby changing their operating characteristics and increasing the likelihood of their catastrophic failure. In the case of extremely high energy arcs, signal processing circuits may undergo immediate catastrophic ~ailure.
Typically, spark gap devices are coupled to the electrodes of a kinescope or like device for preventing the occurrence of excessively large voltage gradients between the electrodes which can result in the generation of un-desirable arcs. These spark gap devices include two elec-trodes spaced apart by a gap of a predetermined length so that when voltage in excess of a predetermined breakdown voltage occurs, a discharge current will flow from one electrode to the other through the gap, thereby dissipating the energy associated with the arc. The receiving or referenoe potential electrode of the gap is coupled through a relatively low impedance path to a point for absorbing the discharge current such as the Aquadag outer coating of the kinescope or chassis ground of the receiver. Care must be taken in providing a suitable discharge arrangement for spark gap devices coupled to each of the electrodes in view of the manner in which the kinescope is coupled to receiver ground potential. The selection of an inappropriate ground return arrangement will, in general, reduce the effectiveness of the spark gap arc protection arrangement and may, in certain circumstances, increase the likelihood of damage to the receiver due to arcing.
Before describing a spark gap and discharge path arrangement according to the present invention for suppres-sing the effect of arcing between electrodes of a kinescope RCA 68,591 ~065961 as shown in FIGURE 1, a description of a prior spark gap and discharge path arrangement shown schematically in FIGURE 2 is presented. In FIGURE 2, a high voltage supply 212 has a high voltage output coupled to the ultor electrode 216 of a kinescope (not shown) through a conductor 218.
Supply 212 also has a conductor 214 coupled to chassis ground of a television receiver in which the kinescope and high voltage supply are included. Ultor electrode 216 is coupled to the inner conductive coating 224 of the kinescope as represented schematically by a conductor 222. The inner conductive coating 224 of the kinescope and the outer con-ductive coating 226 of the kinescope, separated by the dielectric body of the kinescope, form a capacitor 228.
Outer conductive coating 226 is coupled to chassis ground through conductors 230 and 232. Typically, conductor 230 is a relatively low impedance braided or ribbon strap well known in the art, while conductor 232 is an ordinary wire. Capacitor 228 is charged from high voltage supply 212 through the path comprising conductors 218,222, 230 and 232.
It should be noted that the kinescope is held ln place in the receiver by mounting hardware typically includ-ing a wire loop placed around the broad end of the kinescope near its i'aceplate and associated hardware to firmly hold the kinescope between the loop and the cabinet of the receiver. Since outer coating 226 of the kinescope comes in contact with the wire loop, outer coating 226 is coupled to ground through the mounting hardware as is indicated by con-ductor 260 in FIGURE 2. This mounting hardware typi~llyinch~Ps spring components which exhibit some inductance as well as resistance and capacitance. Furthermore, a conductor may be RCA 68,591 ~065961 lntentionally provided between the mounting hardware and chassis ground.
A focus voltage output of high voltage supply 212 is coupled to a focus electrode 217 of the kinescope through conductor 220.
A signal processing circuit 234 has an output coupled to another electrode 236 of the kinescope through a conductor 238 and a return coupled to chassis ground through a conductor 240. Signal processing circuit 234 represents one of the various relatively low voltage signal processing circuits, such as the kinescope driver, typically coupled to one of the low voltage electrodes of the kinescope, such as a cathode electrode.

A spark gap device 242, comprising two electrodes 244 and 246 spaced apart by a predetermined distance, is coupled between focus electrode 217 and a bus 248. A spark gap device 250, comprising two electrodes 252 and 254 spaced apart by a predetermined distance is coupled between low voltage electrode 236 and bus 248. Similarly, spark gap ~ devices (not shown) are coupled between other low voltage electrodes of the kinescope and the common bus 248. Common bus 248 is returned via strap 230 to outer coating 226 to provide a path for discharge currents which may flow between the electrodes of spark gaps 250.
The common bus such as bus 248 is often included in a socket mounted on the neck end of the kinescope. The socket is formed of a nonconductive or insulating body and includes terminals suitably adapted to receive pins of the kinescope. The terminals of the socket are connected to conductors coupled to various portions of the receiver. The RCA 68,591 ~065~61 I pins of the kinescope are connected to the electrodes of the kinescope. The terminals are spaced ~part ~rom the conducting~ ring to form an arrangement of spark gaps for the associated kinescope electrodes.. SUCtl sockets are described, for example, in U.S. Patents 3,327,910, entitled "Kinescope Socket", issued to R. B. Pittman on January 4, 1966; 3,377,612, entitled "El~ctron ~Ibe Arc-Over Ring", issued to L. Klier et al., on April 9, 1968; 3,423,720, entitled "Co].or Kinescope Socket", issued to R. B. Pittman on January 21, 1969; 3,502,933, entitled "Kinescope Socket with Spark Gap", is~ued to B. J. Leimontas et al., on March 24, 1970; 3,543,098, entitled "Electron Tube Socket Assembly", issued to S. S. Simovits et al., on November 24, 1970; and 3,733,522, entitled "Arc-Over Protective Device", issued to S. S. Simovits et al. J on May 15, 1973.
; In the operatlon o~ the system o~ FIGURE a, capacitor 228 is charged irom high voltage supply 212 through the path provided by conductors -~18, 222, 230, 232 and 260.
Roughness o~ the rOcus or ultor electrodes or ~ragments oP ~oreign matter may cause an arc (indicated hy 25ff) to develop betwffen ultor electr~de 216 and ~ocu~ electrode 217, thereby in~tantaneously coupling an excessively high voltage, in the order o~ the high voltage developed across capacitor 228 and in excess Or the breakdown voltage o~ spark gap 242, to ~ocus electrode 217. Since bus 248 is coupl.ed through strap 230 to the energy source Or the arc, i.e., capacitor 228, a discharge current flows ~rom electrode 244 to elec-trode 246, through bus 248 and strap 230 to capacitor 228. The energy associated with the arc wlll therefore rapidly be dissipated in the low impeda~ce path ~'''' .

~06S961 RCA 68,591 1 and arcing from the focus electrode 217 to a low voltage electrode such as 236 will be prevented.
One would expect that some amount of current from spark gap 242 would flow to chassis ground through conductor 232 or through conductor 220 and high voltage supply 212.
However, this is not the case, since, as noted above, the energy source of the arc is capacitor 228. Furthermore, currents from spark gap 232 cannot readily reach capacitor 228 through conductor 220 and high voltage supply 212 and then through conductors 232 and 260 because of the relatively high impedance of this path.
As the arc current flows to capacitor 22~ through strap 230, a voltage Vs, determined by the impedance of strap 230 and the arc current, is developed across the strap with the polarity as indicated in FIGURE 2. Although strap 230 is selected to have a relatively low resistance and inductance, e.g., typically in the order of 0.1 ohms and 0.6 microhenries, because of the relatively large rate of change of the dis-charge current, e.g., typically in the order oi 3~101 amperes per second, Vs may be expected to reach a relatively high level, e.g., in excess of 18 kilovolts. It should be noted that Vs is referenced to chassis ground, since outer conduc-tive coating 226 is coupled to chassis ground through mount-ing hardware 260. Therefore, excessively high voltages may be developed with respect to chassis ground at common bus 248 which are coupled to each spark gap electrode connected to bus 248. Since a relatively low voltage with respect to chassis ground is supplied to low voltage electrode 236 from signal processing circuit 234, a relatively high reverse gap voltage VsG may be developed between electrodes RCA 68,591 1(~6596~
1 254 and 252 of spark gap 250, as is shown in FIGURE 2 If VsG exceeds the predetermlned breakdown voltage of low voltage spark gap 250, an arc (indicated by 262) will occur in the reverse direetion from electrode 254 to 252, causing current to flow through conductor 238 to signal processing clrcuit 234. As a result, signal processing circuit 234 may be damaged. Other circuits coupled to relatively low voltage electrodes of the kine-scope (not shown) may be similarly damaged. It should be noted that conductor 232 exhibits a relatively high im-pedance in the fre~uency range of the arc and therefore is not effective to bypass Vs by shunting it to ground.
Although the impedance o~ conductor 232 in the frequency range of the arc may be somewhat reduced by the appropriate selection of conductor 232, it has been found that the impedance cannot be reduced sufi'iciently to effectively shunt Vs such that reverse arcs to the low voltage elec-trodes do not occur. Thus, the discharge arrangement shown in FIGURE 2 is undesirable, since voltages developed across strap 230 (or equivalent lmpedance to outer coating 226) may cause the spark gaps associated with the relatively low voltage electrodes of the kinescope to iire in the reverse direction causing a potentially destructive current to flow to the circuits coupled to the low voltage electrodes.
Returning now to FIGURE l, there is shown a kinescope spark gap and discharge path arrangement which avoids the disadvantages of the prior art arrangement shown in FIGURE 2. Spark gaps, generally indicated as 68, each have one electrode respectively coupled to a low voltage electrode of kinescope 42 and the other electrode coupled RCA 68,591 ~06~961 1 to a bus 70. Bus 70 is coupled to outer conductive coating 52 through a relatively low impedance conductor 72. Bus 70 and conductor 72 provide a discharge path for the spark gaps associated with the relatively low voltage cathode, control grid and screen grid electrodes.
Spark gap 76 has one electrode coupled to focus electrode 60 and the other electrode coupled to outer coating 52 through a relatively low impedance conductor 78 which serves as a discharge path for spark gap 76. Thus, spark gap 76 associated with relatively high voltage focus electrode 60 has a return path to the coating 52 which is separate from the return path including bus 70 and conductor 72 of spark gaps 68 associated with the relatively low voltage electrodes 54,56 and 58 of kinescope 42.
It is desirable that conductors 72 and 78 comprise conductors such as braided straps or the like having as low inductance as possible, to inhibit the generation of high voltage transients when discharge currents flow through them which might otherwise adversely affect the operation of the receiver.
Mounting hardware 74 is similar to that described above in connection with FIGURE 2 and couples outer coating 52 to chassis ground. Mounting hardware 74 may touch other receiver hardware connected to chassis ground or a conduc-tor may intentionally be provided to connect the mounting hardware to chassis ground.
In operation, the capacitor formed by inner conductive coating 50 and outer conductive coating 52 is charged by high voltage supply 40 through the path comprising the conductor coupling high voltage supply 40 to ultor ~06S961 RCA 68,591 1 electrode 62 and mounting hardware 74. If an excessively high gradient is developed between ultor electrode 62a and focus electrode 60 (for example, because of the presence of foreign particles on or near one of these electrodes) and such gradient results in an arc to focus electrode 60, the voltage at focus electrode 60 rises and spark gap 76 fires, causing current to flow to outer coating 52 through conductor 78. A voltage so developed across conductor 78 will not cause spark gaps 68 to fire in the reverse direc-tion since the return path of current through spark gap 76, comprising conductor 78, is separated from the return path of spark gaps 68, comprising bus 70 and conductor 72.
It is known in the art that the time it takes for a spark gap to fire can be shortened by the application of an over-voltage in excess of the breakdown voltage across the electrodes of the spark gap. This over-voltage is respectively provided for spark gaps 68 and 76 of FIGURE 1 by the resistors generally indicated as 82J coupled between relatively low voltage electrodes 54,56 and 58, and their respective signal sources, and by resistor 84, coupled between focus electrode 60 and the focus output of high voltage supply 40. In the initial stages of arcing, some portion of the arc current will flow through the respective resistor from the electrode receiving the arc to the circuit coupled to the electrode. As a result, the requisite over-voltage to speed up the response of the associated spark gap is developed. Once the spark gap fires, the bulk o~
the arc current will pass through the spark gap.
Resistors 82 and 84 also serve to limit the amount of arc current flowing into the respective portions RCA 68,591 1~16S96~

1 Of the receiver to which they are coupled. Furthermore, resistors 82 and 84, in conjunction with any stray capaci-tance (not shown) of tne respective circuits to whlch they are coupled, form low pass filter arrangements which act to limit harmful transients generated during arcing. It should also be noted that during arcing a spark gap presents a low impedance path for the circuits coupled to the electrode associated with the spark gap, as well as being a discharge path for the electrode, and that resistors 82 and 84 are therefore useful in limiting tne amount of current supplied by the circuits to which they are coupled during arcing.
It is desirable that spark gap 76 fire before an arc is formed between focus electrode 60 and adjacent relatively low voltage electrodes. Such arcing could in essence bypass the separate discharge path arrangement of FIGURE 1 thereby limiting its effectiveness.
The distance between the electrodes of spark gap 76 is made considerably wlder than the distance between the electrodes o~ spark gaps 68 because o~ the respective breakdown voltage selected. Even though the distance between the electrodes of spark gap 76 is in the same order of magnitude as the distance between the pin connected to focus electrode 60 of kinescope 42 and adjacent pins con-nected to respective electrodes, it is desirable that the distance between the electrodes of spark gap 76 be smallerthan the distances between the pin connected to focus electrode 60 and adjacent pins so that spark gap 76 fires before an arc is formed between the pin connected to focus electrode 60 and adjacent pins.

1065961 RCA 68,591 1 Furthermore, spark gaps are susceptible to changes in environmental conditions such as atmospheric pressure. That is, for example, as the atmospheric pressure decreases, a spark gap tends to fire at relatively lower break own voltages and, as the atmospheric pressure increases, a spark gap tends to fire at relatively higher breakdown voltages. Since the operation of spark gap 76 associated with focus electrode 60 is important to the effective opera-tion of the arc suppression arrangement of FIGURE 1, spark gap 76 is desirably arranged to operate substantially independently of changes in environmental conditions. This may be accomplishedJ for example, by mounting spark gap 76 in a hermetically sealed container as is indicated by block 80 in FIGURE 1. Such spark gap units are commercially avail-able as model number KA-6 from the Siemens Corporation.
In FIGURE 3, there is shown another spark gap unit which is arranged to fire at a breakdown voltage sub-stantially independent of changes in atmosplleric pressure wherein a pressure sensing device 312 is coupled to a movably mounted electrode 314 of a spark gap 316 in a manner such that electrode 314 is moved with respect to a fixedly mounted electrode 318 in response to changes in atmospheric pressure. Specifically, pressure sensing device 312 comprises a container 320 sealed by a flexible membrane-like member 322 Membrane-like member 322 may, for example, be formed of a resilient, flexible plastic or rubber material or a corrugated metal, as shown. A
pressure sensing device suitable for use in the spark gap apparatus shown in FIGURE 3 is manufactured by the Sylphon Corporation. Lever-like member 324 is pivotably mounted RCA 68,591 lC~6S961 1 on fulcrum 326. A member 328 is coupled between membrane-like member 322 and one end of lever-like member 324. The other end of lever-like member 324 is connected to movably mounted electrode 314. Guide members serve to guide the motion of electrode 314. Electrical conductors 332 and 334 are respectively connected to electrodes 314 and 318 and serve to couple the spark gap unit of FIGURE 3 to the appro~
priate portion of the receiver such as shown in FIGURE 1. It should be noted that the structural members of the spark gap apparatus of FIGURE 3 may be electrically isolated from the receiver so that electrodes 314 and 318 may be coupled to the receiver as desired without regard to polarity.
In operation, if the pressure outside of pressure sensing device 312 is greater than the pressure within device 312, membrane-like member 322 moves inwardly causing lever-like member 324 to rotate counterclockwise. As a re-sult, the spacing between electrodes 314 and 318 is decreased.
Similarly, the spacing between electrodes 314 and 318 is in-creased if the atmospheric pressure is less than the pressure within pressure sensi~g unit 312. Thus, the spacing between electrodes 314 and 318 is changed in inverse relationship to the atmospheric pressure. Since the breakdown voltage of a spark gap is directly related to the distance between the electrodes o~ the spark gap and directly related to the atmospheric pressure, the spark gap apparatus tends to change the distance between electrodes 314 and 318 in a manner so as to compensate for the changes in breakdown voltage due to changes in atmospheric pressure.
In FIGURE 4 there is shown a plan view partially in cross-section of a kinescope socket which may be used to RCA 68,591 ~S96~
1 couple various signal processing portions of the receiver of FIGURE 1 to the electrodes of kinescope 42,. The socket includes a spark gap and discharge path arrangement for suppressing arcing between the electrodes of kinescope 42 in accordance with the present invention. Body 412 of the socket is formed of a nonconductive material and has a generally cylindrical shape. The cross-sectional view shown in FIGURE 4 is taken just above base 414 of the socket. Base 414 is formed of a nonconductive material and has a keyed opening 416 to receive the stem of the base of a kinescope. Conductive terminals 418 and 420 for receiving the pins of the kinescope connected to the electrodes of the kinescope are inserted in base 414 parallel to the direction of the axis of the socket. It should be noted that although ;j eight pins are shown circumferentially located around opening 416 for purposes of illustration, the number of terminals depends on the particular kinescope employed.
Terminals 418 are associated with the relatively low voltage , electrodes of the kinescope whlle terminal 420 is associated wlth the relatively high voltage ~ocus electrode of the kinescope. Terminal 420 is separated from terminals 418 by upstanding walls 424a and 424b formed of a nonconductive material to inhibit arcing between terminal 420 and adjacent ones of terminals 418. Terminals 418 and 420 are respec-tively connected to conductors 422 which are coupled to respective portions of the receiver.
A conductive ring segment 426 (corresponding to bus 70 of FIGURE 1) is mounted on base 414 concentrically with opening 416. Conductive elements 428 are mounted on base 414 and extend radially from terminals 418 to _21-~06596~ RCA 68,591 1 appropriate distances from segment 426 to form spark gaps (corresponding to spark gaps 68 of FIGURE 1) for the relatively low voltage electrodes of the kinescope. Ring segment 426 may be formed, for example, as a "printed"
conductor on base 414, while conductive elements 428 may be formed as part of the metallic female connectors which receive the pins of the kinescope. It should be noted that terminals 418 may be disposed relative to ring segment 426 in other suitable arrangements such as described in the Pittman, Klier et al., Leimontas et al., and Simovits et al. patents, supra, to form the spark gaps for the relatively low voltage electrodes. A conductor 430 (cor-responding to conductor 72 of FIGURE 1) is suitably connec-ted to ring segment 426 and serves as a path for discharge currents produced through the spark gaps formed by ring segment 426 and conductors 428 associated with the rela-tively low voltage electrodes. Conductor 430, like conductor 72 of FIGURE 1, could be appropriately coupled to chassis ground of the receiver.
A spark gap 432 (corresponding to spark gap 76 of FIGURE 1) for the ~ocus electrode is connected between terminal 420 and a conductor 434 (corresponding to conduc-tor 78 of FIGURE 1) mounted on base 414. It is desirable that spark gap 432 be of the type formed to operate sub-stantially independently of changes in environmental conditions such as changes in atmospheric pressure or the like. For instance, spark gap 432 may be a sealed spark gap or of the type described with reference to FIGURE 3.
Conductor 434 serves as a path for discharge current produced at spark gap 432 separate from the discharge RCA 68,591 1~65961 1 path of the spark gaps associated with the relatively low voltage electrodes. Conductor 434 may, for instance, be coupled to the outer coating of the kinescope in the manner of conductor 78 of FIGURE 1.
In FIGURE 5 there is shown a cross-sectional plan view of another kinescope s~cket 508 mounted on a printed circuit board 510 including a spark gap and discharge path arrangement formed in accordance with the present invention and useful in the receiver arrangement shown in FIGURE 1.
Body 512 of the socket is formed of a nonconductive material and has a generally cylindrical shape. The cross-sectional view of FIGURE 5 is taken just above base 514 of the socket.
Base 514 is affixed to printed circuit board 510 and is formed of a nonconductive material. A keyed opening 516 lS is provided through base 514 and printed circuit board 510 to receive the stem of the base of a kinescope. Conductive terminals 518 and 520 for receiving pins connected to the electrodes of the kinescope are inserted in base 514 parallel to the direction of the axis of the socket. It should be noted that although eight pins are shown circumferentially located around opening 516 for purposes of illustration, the number and orientation of terminals depends on the particular kinescope employed. Terminals 518 are the termi-nals for the relatively low voltage electrodes of the kinescope, while terminal 520 is the terminal for the relatively high voltage focus electrode of the kinescope.
Terminal 520 is separated from terminals 518 by walls 504a and 504b formed of a nonconductive material to inhibit arcing between terminal 520 and adjacent ones of terminals 3 518. Terminals 518 are respectively connect to "printed"
_23-~6S961 RCA 68,591 1 conductors 522 deposited on printed circuit board 510.
Terminal 520 is connected to ~printed" conductor 524 deposited on printed circuit board 510.
Conductors 522 are respectively coupled to eonductors 526 through resistors 528. Conductors 526 serve to couple the relatively low voltage electrodes to respec-tive portions of the receiver. Resistors 528 serve similar purposes as resistors 82 of FIGURE 1 previously described.
Conductor 524 is coupled to conductor 530 through resistor 532. Conductor 530 serves to couple the focus electrode to the focus output of high voltage supply of the receiver. Resistor 532 serves a similar purpose as resistor 84 of FIGURE 1 previously deseribed.
A circular segment oi conductor 534 (corresponding to eonductor 70 of FIGURE 1) is deposited on printed on printed circuit board 510. Conductors 522 extend radially from terminals 518 to an appropriate distance from segment 534 to form spark gaps (corresponding to spark gaps 68 of FIGURE 1) for the relatively low voltage elee-trodes oi' the klnescope. A eonduetor 536 (eorresponding to eonduetor 72 of FIGURE 1) is suitably eonneeted to ring segment 526 by a solder eonneetion or the like, and serves as a path for diseharge eurrents produced at the spark gaps formed by segment 534 and eonductors 522 assoeiated with the relatively low voltageeleetrodes. Conduetor 536 may, for instance, be coupled to chassis ground of the receiver in the manner of conduetor 72 of FIGURE 1.
A spark gap 538 (corresponding to spark gap 76 of FIGURE 1) for the focus electrode is connected between terminal 524 and a conductor 540 (corresponding to eonductor _24-RCA 68,591 ~06SS~l 1 78 of ~IGURE 1) through a solder connection or the like to a conductor deposited on printed circuit board 510.
It is desirable that spark gap 538 be of the type ~ormed to operate substantially independently of changes in environmental conditions such as changes in atmospheric pressure or the like. For instance, spark gap 432 may be a sealed spark gap or of the type described with reference to FIGURE 3. Conductor 540 serves as a separate path from the discharge path of the spark gaps associated with the relatively low voltage electrodes for discharge current produced by spark gap 538. Conductor 540 may, for instance, be coupled to the outer coating oi the kinescope in the manner of conductor 78 of FIGURE 1.

_25-

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An apparatus comprising: cathode ray tube means including a plurality of electrodes for developing and accelerating an electron beam, at least one of said electrodes being operated at a relatively high voltage and another being operated at a relatively low voltage; a plurality of spark gap means each coupled to a respective one of said electrodes for inhibiting the development of excessively high energies at said electrodes; a reference point whose potential does not substantially change during operation of said spark gaps; a first relatively low impedance coupling a terminal of a first of said spark gap means associated with said high voltage electrode to said reference point; and a second relatively low impedance means, separate from said first impedance means, coupling a terminal of a second of said spark gap means associated with said low voltage electrode, to said reference point.

2. The apparatus recited in claim 1 wherein:
said cathode ray tube means is a television picture tube formed of a dielectric material having an inner and an outer coating and including a relatively high voltage focus electrode, a relatively high voltage ultor electrode coupled to said inner coating, and relatively low voltage cathode, control and screen electrodes;
said first impedance means being coupled to the spark gap means associated with said focus electrode and said second impedance means being coupled to at least one of the spark gap means associated with said cathode, control and screen electrodes.

3. The apparatus recited in claim 2 wherein:
said first impedance means is directly coupled to said outer coating.

4. The apparatus recited in claim 3 wherein:
said outer coating is directly coupled to said reference point.

5. The apparatus recited in claim 1 wherein:
said first and second impedance means have minimal amounts of inductance.

6. The apparatus recited in claim 1 wherein:
means are provided to substantially isolate the spark gap means associated with said relatively high voltage electrode from environmental conditions.

7. The apparatus recited in claim 6 wherein:
the spark gap means associated with said relatively high voltage electrode is mounted in a sealed container.

8. The apparatus recited in claim 6 wherein:
the spark gap means associated with said relatively high voltage electrode comprises a fixedly mounted electrode;
a movably mounted electrode, spaced apart from said fixedly mounted electrode; and pressure sensing means coupled to said movably mounted electrode for controlling the spacing between said movably mounted electrode in accordance with the atmospheric pressure.

9. The apparatus recited in claim 8 wherein:
said spacing between said movably mounted electrode and said fixedly mounted electrode is controlled in inverse relationship to the atmospheric pressure.

10. The apparatus recited in claim 1 and further comprising:
means for coupling signals to said electrodes of said cathode ray tube comprising a socket having a non-conductive body and including conductive terminals for receiving respective conductive pins of said cathode ray tube means connected to said electrodes of said cathode ray tube means;
said spark gap means associated with said relatively low voltage electrodes including a conductive ring segment positioned in said socket in a spaced relationship with the terminals coupled to said relatively low voltage electrodes, said ring segment coupled to said second impedance means;
said spark gap means associated with said relatively high voltage electrode including a first electrode connected to the terminal coupled to said relatively high voltage electrode and a second electrode spaced apart from said first electrode, said second electrode coupled to said first impedance means.