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Publication numberUS3267321 A
Publication typeGrant
Publication dateAug 16, 1966
Filing dateMar 28, 1962
Priority dateMar 28, 1962
Publication numberUS 3267321 A, US 3267321A, US-A-3267321, US3267321 A, US3267321A
InventorsGessford Sr Ross K
Original AssigneeSylvania Electric Prod
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electron discharge device having cathode protective means within the envelope
US 3267321 A
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Description  (OCR text may contain errors)

g- 1966 R. K. GESSFORD, SR 3,

ELECTRON DISCHARGE DEVICE HAVING CATHODE PROTECTIVE MEANS WITHIN THE ENVELOPE Filed March 28, 1962 INVENTOR Ross K. G255 ford, 5

ATTORNEY United States Patent 3,267,321 ELECTRON DISCHARGE DEVICE HAVING CATH- ODE PROTECTIVE MEANS WITHIN THE EN- VELOPE Ross Gessford, Six, Seneca Falls, N.Y., assignor to Sylvania Electric Products Inc., a corporation of Delaare Filed Mar. 28, 1962, Ser. No. 183,246 6 Claims. (Cl. 315--3) axially aligned, closely spaced electrodes normally designated as G1, G2, G3, G4, and G5 formed to provide the modulation, focussing, and acceleration of the electron beam.

The spacing between adjacent ones of these electrodes can be considered inherently to define a given sparking potential in the evacuated tube which is higher than the normal operating potential gradient between these electrodes. However, it is not uncommon that transient high voltage surges originating with the high potential electrodes be imparted to the lower potential adjacent electrodes through disruptive discharges or arc-overs. This discharge often originates between the G3 and G2 electrodes because of the high potential difference normally existing therebetween. Once the discharge occurs, it will then progress to the G1 and then to the cathode, which is insulatingly mounted inside the G1. This disruptive discharge, when applied to the cathode, is often sufficient to destroy at least part of the emissive coating and thereby immediately cause or accelerate failure oi the tube.

Heretoifiore, efforts have been made to protect the tube filament during arcing. The protecting devices used for this purpose consisted of spark gaps or shorting straps interconnecting a grounded heater filament lead and the cathode or control grid. Although some protection was afforded the filament, these arrangements have proven unsatisfactory since they do not provide any protection for the cathode.

There has also been suggested the provision of a high voltage surge suppression circuit generally employing a condenser grounded at one side and connected at the other side to a tube electrode which may be subjected to high voltage surges. Although some suppression occurs in these devices, the tube operation is disrupted [for an undesirable period of time rfrom its normal tfunctioning. lFurther, the suppression circuit does not prevent internal arcing between many electrodes and does not protect the tube cathode.

It is, theretore, an object of this invention to protect the emissive coating of a cathode [from high voltage surge damage.

It is another object of this invention to afford voltage surge protection for the tube and the operating circuit while minimizing the time period of disruption [from normal tube operation.

In accordance with the \foregoing objects there is provided by this invention a transient high voltage surge bypass device incorporated within a cathode ray tube. This device is fabricated, according to one aspect 01f the invention, from an electrically conductive material and has one terminal portion connected to ground potential, while the other terminal portion is connected to the G2 electrode and provides a sparking potential lower than the sparking potential existing between the G1 and G2 electrodes.

Accordingly, when a disruptive discharge occurs between the G2 and G3 electrodes, instead of progressing to the G1 and the cathode closely associated therewith, it will be conducted to ground by way out the by-pass device. By preventing these disruptive discharges from reaching the cathode, .a substantial increase in the life of the emissive coating is achieved, thereby increasing the life of the tube. Also, because the discharge ctr-om the G2 to the by-pass device is in the form of an immediate arc, the time period of disruption from normal tube operation, caused by th abnormally high G2 potential, is minimized.

For purposes of this invention, the spark-ing potential between a given pair of electrodes in a gas is considered to depend upon the length of the spark gap and the pressure of the gas in such a way that it is directly proportional to the mass 0t gas between the two electrodes. Also, the work function of a given metal is referred to as the work per unit charge, expressed as a voltage, which is required to free an electron from the influence ot the charges in the metal and thus to provide escapement from it.

Since the spaced electrodes described herein form an electron gun having prescribed parameters and since the low gas or air content and pressure within the evacuated tube are common to all electrodes, the sparking potential or work function potential can appropriately be referred to as being dependentupon the spacing between electrodes (for comparison purposes.

For a better understanding of the present invention, together with other and turther objects, advantages, and capabilities thereof, reference is made to the iollowing disclosure and appended claims in connection with the accompanying drawings in which:

FIG. 1 is a partial diagrammatic view of a cathode ray tube employing one aspect of the invention;

FIG. 2 illustrates two spaced electrodes embodying an alternate form of the invention; and

FIGS. 3 and 4 show additional embodiments of the invention.

In FIG. 1 there is shown generally a cathode ray tube '10 comprising an evacuated, hermetically sealed envelope 12 with an electron gun 14 mounted therein. Gun 14 employs a cathode assembly 16 having a sleeve '18 with emissive coating 20 on the end thereozE and a heater 22 partially mounted within the sleeve.

Positioned forward of emissive material 20 are a plurality of axially aligned, spaced electrodes designated as G1, G2, G3, G4, and G5. The G1 or control grid has the cathode assembly 16 insulatingly mounted within it by means of ceramic wafer 24. For a grid driven tube, G1 may have a video drive range of about 45 volts relative to the cathode. The G2 serves as the screen grid and G4 is utilized as a focussing ring for the electron beam. These electrodes may be operated at about 450 and 300 volts respectively while the G3 and G5 electrodes,

-which serve as the accelerating electrodes and cooperate with G4 for focussing purposes, are maintained at a relatively high potential which may reach 20 kv. or higher. In order to maintain the proper alignment and spacing necessary for operation, these electrodes are provided with pins 26 for attachment to a plurality of insulating support rods 28, only one of which is shown in the draw-. mg.

While the spacing between any two adjacent electrodes ingun 14 determines the sparking potential therebetween as pointed out above, of primary interest here is the sparking potential across gap 30 which is defined as the spacing between the first electrode G1 and the second electrode G2. Gap 30 is of interest since it is the closest electrical isolating medium to the cathode to G1 sparking potential gap. It will be appreciated that under normal conditions,

if an arc occurs between the high voltage electrode G3 and low voltage electrode G2, there exists momentarily a potential difference between electrodes G1 and G2 which may be in the order of.20,000 volts. Since this voltage far exceeds the normal G1 to G2 sparking potential, an arc will occur therebetween, thus imparting the high voltage surge to G1. Almost instantly then the high volt-age Surge is transferred to cathode 18 because of its close proximity to G1. Of course, the surge voltage difference between the cathode and G1 vastly exceeds the normal sparking potential therebetween. Since electron emissive material 20 is on the surface of cathode 18 closest to G1, this material is inherently in the discharge zone and thereby becomes deleteriously disrupted and contaminated by the discharge.

In order to protect cathode 18, an transient high voltage surge by-pass device 32 is contained within envelope 12 and is mounted, as by welding, to interconnect the second electrode G2 and a ground potential lead 34. The by-pass device 32 is fabricated from an electrically conductive material preferably of ribbon stock or wire, and it is formed to provide a sparking potential across space" 36 which is lower than the sparking potential across gap 30. Accordingly, any are to G2 will pass over space 36 to ground rather than to cathode 18.

The material from which by-pass device 32 is fabricated may be the same as that used for electrodes G1 and G2, for instance a nickel alloy, or it may be chosen from one of the materials known as cold emitters. These include materials as for example titanium, magnesium, and barium-nickel alloy, which have -in common a relatively low work function. When one of the above-mentioned materials is used, it should be chosen so that its work function potential is lower than the sparking potential across space 30.

Referring now to FIG. 2, there is shown an alternate ems bodiment of the bypass device. This transient high voltage surge by-pass device 38 comprises an encapsulating, hermetically sealed envelope 40 of insulating material surrounding a gaseous atmosphere, and a pair of electrically conductive members 42 and 44 fixedly mounted in the wall of encapsulating envelope 40. Members 42 and 44 are afiixed, as by welding, to electrode G2 and ground potential lead 34 respectively and project inwardly of encapsulating envelope 40 to terminate in spaced plates 46, 48. The nature of the gas content, together with the pressure and spacing, provide a predetermined sparking potential across gap 36 which is lower than the sparking potential across space 30. Such a device has the advantage of isolating the discharge and ionization from the evacuated tube atmosphere.

In another embodiment shown in FIG. 3, members 42 and 44 of the by-pass device 50 are fixedly mounted in the upstanding Walls 52 of a substantially U-shaped insulating block 54. The sparking potential of this device is determined by space 36 and it is less than the sparking potential across space 30. Device 50 may be separately constructed in an accurate manner prior to assembly with the gun electrode G2.

FIG. 4 illustrates another embodiment wherein a bypass device 56 comprises a cylindrical block 58 of insulating material having a longitudinal bore 60 and opposed electrically conductive plates 62 and 64, having spherical protuberances 66 and 68 bonded to block 58. Plates 62 and 64 are affixed, as by welding, to conductive members 42 and 44 respectively. The protuberances 66 and 68 are formed to project into bore 60 to provide a space 36 therebetween which determines a sparking potential lower than the sparking potential across space 30. Here again, this device may be separately constructed and it has the additional capability of confining the discharge and resulting ionization therewithin.

, It will be apparent that a by-pass device electrode, preferably conductive member 44, in any of the embodiments, may also be formed from a material having a low work function potential as above described.

While the preferred determinant for the appropriate 1 sparking potential has been illustrated in conjunction with space or gap 30 between the G2 and G3 electrodes, it will be appreciated that other interelectrode gaps may serve as an appropriate determinant in the illustrated electron gun or in other types of guns so long as the cathode is properly protected.

The invention described herein provides a simple economical, rugged, device that will effectively protect the emissive coating on a cathode from transient high voltage surges, thereby enhancing the life characteristics of the tube in which it is employed.

While there has been shown and dscribed what are at present considered the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. A cathode ray tube comprising an evacuated, hermetically sealed envelope, an electron gun positioned within said envelope, said electron gun having a cathode and at least first and second sequentially spaced low voltage electrodes, said second electrode being subject to transient high voltage surges, the spacing between said first and second electrodes defining a given sparking potential, at least one lead terminating interiorly of said evacuated envelope and projecting exteriorly for connection to ground potential, and a voltage surge by-pass device mounted within said envelope interconnecting said second electrode and said ground potential lead, said bypass device being formed to provide a predetermined sparking potential lower than said given sparking potential.

2. A cathode ray tube comprising an evacuated, hermetically sealed envelope, an electron gun positioned within said envelope, said electron gun having a cathode and at least first and second sequentially spaced low 7 voltage electrodes, said second electrode being subject to transient high voltage surges, the spacing between said first and second electrodes defining a given sparking potential, at least one lead terminating interiorly of said evacuated envelope and projecting exteriorly for connection to ground potential, and a voltage surge by-pass device mounted within said evacuated envelope comprising an encapsulating, hermetically sealed envelope of insulating material surrounding a gaseous atmosphere, a pair of electrically conductive members fixedly mounted in the wall of said encapsulating envelope and interconnecting said second electrodes and said ground potential lead, said pair of members being formed to project inwardly of said encapsulating envelope and terminating in a spaced relationship to provide a predetermined sparking potential therebetween lower than said given sparking potential.

3. -A cathode ray tube comprising an evacuated, hermetically sealed envelope, an electron gun positioned within said envelope, said electron gun having a cathode and at least first and second sequentially spaced low voltage electrodes, said second electrode being subject to transient high voltage surges, the spacing between said first and second electrodes defining a given sparking potential, at least one lead terminating interiorly of said evacuated envelope and projecting exteriorly for connection to ground potential, and a voltage surge by-pass device mounted within said evacuated envelope comprising a substantially U-shaped block of insulating material having a base portion and a pair of upstanding walls projecting therefrom, a pair of electrically conductive members fixedly mounted in said upstanding walls and interconnecting said second electrode and said ground potential lead, said pair of members being formed to project inwardly toward the center of said block and terminating in a spaced relationship to provide a predetermined sparking potential therebetween lower than said given sparking potential.

4. A cathode ray tube comprising an evacuated, hermetically sealed envelope, an electron gun positioned within said envelope, said electron gun having a cathode and at least first and second sequentially spaced low voltage electrodes, said second electrode being subject to transient high voltage surges, the spacing between said first and second electrodes defining a given sparking potential, at least one lead terminating exteriorly of said evacuated envelope and projecting exteriorly for connection to ground potential, and a voltage surge by-pass device employing a cold emitter mounted Within said evacuated envelope and interconnecting said ground potential lead and said second electrode, said cold emitter having a work'function potential lower than said given sparking potential.

5. A cathode ray tube comprisinga-n evacuated, hermetically sealed envelope, an electron gun positioned within said envelope, said electron gun having a cathode and at least first and second sequentially spaced low voltage electrodes, said second electrode being subject to transient highvoltage surges, the spacing between said first and second electrodes defining a given sparking potential, at least one lead terminating interiorly of said evacuated envelope and projecting exteriorly for connection to ground potential, and a voltage surge by-pass device mounted within said envelope interconnecting said ground potential lead and said second electrode comprising a cylindrical block of insulating material having a longitudinal bore therethrough, opposed electrically conductive plates having spherical protuberances thereon bonded to said block, said proturberances projecting into said bore to provide a space therebetwee-n, said space defining a sparking potential lower than said given sparking potential.

6. A cathode ray tube comprising an evacuated, hermetically sealed envelope, an electron gun positioned Within said envelope, said electron gun having a cathode and a plurality of intermediate spaced low voltage electrodes axially aligned with and sequentially arrayed from said cathode, at least one of said intermediate electrodes being subject to transient high voltage surges, the spacing between said one of said intermediate electrodes and an adjacent electrode defining a given sparking potential, at least one lead terminating in-teriorly of said evacuated envelope and projecting exteriorly for connection to ground potential, and a voltage surge by-pass device mounted within said envelope interconnecting said one of said intermediate electrodes and said ground potential lead, said by-pass device being formed to provide a predetermined sparking potential lower than said given sparking potential.

Y References Cited by the Examiner UNITED STATES PATENTS HERMAN KARL SAALBACH, Primary Examiner.

ARTHUR GAUSS, Examiner.

S. OHATMO'N, JR., Assistant Examiner.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2083205 *Oct 5, 1934Jun 8, 1937Kurt SchlesingerSafety means for television tubes
US2295379 *Feb 29, 1940Sep 8, 1942Westinghouse Electric & Mfg CoLow voltage protective device
US3045143 *Jul 3, 1959Jul 17, 1962Gen ElectricSpark gap protector
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3546536 *Mar 28, 1968Dec 8, 1970Umin StanleyMeans to indicate,control and cut off excessive x-radiation from television sets
US3810025 *Apr 18, 1972May 7, 1974Jeol LtdField emission type electron gun
US3917981 *Jun 4, 1974Nov 4, 1975Colt Ind Operating CorpScale lightning protection system
US3921078 *Oct 26, 1973Nov 18, 1975Jeol LtdBreakdown protection for field emission electron gun
US3965393 *Apr 21, 1971Jun 22, 1976Admiral CorporationTelevision X-radiation protection device and circuit
US4041357 *May 21, 1976Aug 9, 1977Rca CorporationHigh voltage protection circuit
US4161673 *Jun 30, 1977Jul 17, 1979Zenith Radio CorporationArc suppression and static elimination system for a television CRT
US4326762 *Oct 15, 1980Apr 27, 1982Zenith Radio CorporationApparatus and method for spot-knocking television picture tube electron guns
US6259216Jul 29, 1998Jul 10, 2001Siemens AgCathode ray tube
WO1999007008A1 *Jul 29, 1998Feb 11, 1999Burkhardt KlausCathode ray tube
Classifications
U.S. Classification315/3, 313/441, 361/118, 361/120, 313/325
International ClassificationH01J29/48, H01J29/82
Cooperative ClassificationH01J29/484, H01J29/82
European ClassificationH01J29/48F, H01J29/82
Legal Events
DateCodeEventDescription
Aug 24, 1981ASAssignment
Owner name: NORTH AMERICAN PHILIPS CONSUMER ELECTRONICS CORP.
Free format text: ASSIGNS ITS ENTIRE RIGHT TITLE AND INTEREST, UNDER SAID PATENTS AND APPLICATIONS, SUBJECT TO CONDITIONS AND LICENSES EXISTING AS OF JANUARY 21, 1981.;ASSIGNOR:GTE PRODUCTS CORPORATION A DE CORP.;REEL/FRAME:003992/0284
Effective date: 19810708
Owner name: NORTH AMERICAN PHILIPS CONSUMER ELECTRONICS CORP.,