US3914638A - Cathode structure for cathode ray tube - Google Patents

Cathode structure for cathode ray tube Download PDF

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Publication number
US3914638A
US3914638A US393970A US39397073A US3914638A US 3914638 A US3914638 A US 3914638A US 393970 A US393970 A US 393970A US 39397073 A US39397073 A US 39397073A US 3914638 A US3914638 A US 3914638A
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United States
Prior art keywords
cathode
sleeve
closure member
ledge
planar
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Expired - Lifetime
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US393970A
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English (en)
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Floyd K Collins
John J Miller
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GTE Sylvania Inc
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GTE Sylvania Inc
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Priority to US393970A priority Critical patent/US3914638A/en
Publication of USB393970I5 publication Critical patent/USB393970I5/en
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Publication of US3914638A publication Critical patent/US3914638A/en
Assigned to NORTH AMERICAN PHILIPS CONSUMER ELECTRONICS CORP. reassignment NORTH AMERICAN PHILIPS CONSUMER ELECTRONICS CORP. ASSIGNS ITS ENTIRE RIGHT TITLE AND INTEREST, UNDER SAID PATENTS AND APPLICATIONS, SUBJECT TO CONDITIONS AND LICENSES EXISTING AS OF JANUARY 21, 1981. (SEE DOCUMENT FOR DETAILS). Assignors: GTE PRODUCTS CORPORATION A DE CORP.
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
    • H01J29/04—Cathodes

Definitions

  • This invention relates to cathode ray tubes and more particularly to improved indirectly heated cathodes for use in the electron gun structures thereof.
  • Cathode ray tubes conventionally employ one or more electron guns having indirectly heated thermionic cathode structures therein.
  • Such cathodes are usually end-emissive structures utilizing heat responsive electron emissive materials as sources of electron beam energy.
  • a common type of cathode assembly is in the form of a metallic sleeve whereof one end is closed by a metallic cap on which an area of electron emitting material is exteriorly disposed. Heat is supplied to the cathode by a discretely formed heater positioned within the sleeve in a manner to promote efficient use of the heat generated.
  • the internal dimension of the cap is of necessity greater than the exterior dimension of the sleeve to facilitate a sliding fit relationship. Manufacturing tolerances respectively inherent in the fabrication of caps and sleeves further aggravate the dimensional deviation therebetween.
  • To affix the cap to the sleeve it is con ventional practice to dispose several spaced apart pressure welds between the skirt of the cap and the sleeve. In so doing, portions of the skirt are substantially forced in against the wall of the sleeve, a condition that slightly deforms areas of the skirt thereby aggravating and fostering the establishment of additional residual stresses in the formed cap; stresses which sometimes tend to promote a slight doming effect ofthe emissive surface. This tendency for doming or oil-canning of the end surface of the cap is an undesirable condition as it disturbs the uniformity of the emitted electron beam.
  • the overlapping areal contact between the skirt of the cap and the end portion of the sleeve makes up a conductive heat sink which aggravatively influences the warm-up efficiency of the cathode structure.
  • This mass of material contiguous to the end-emissive area tends to slow the rise in temperature of the emissive area, thereby hindering rapid operational heating of the cathode.
  • the diameter of the aperture in the control grid electrode approaches the diameter of the endemissive surface of the cathode cap.
  • a control grid aperture in a low power gun may have a diameter in the order of 0.035 of an inch, while the diameter of the cap of the cathode spatially associated therewith may be of a value in the neighborhood of 0.042 of an inch.
  • Another object is to provide an improved rapidheating indirectly heated end-emissive cathode structure for use in a cathode ray tube electron gun wherein there is limited contact between the end-emissive portion and the contiguous supporting sleeve structure.
  • a further object is to provide a cathode ray tube indirectly heated end-emissive cathode having an improved planar emitting surface.
  • an improved indirectly heated thermionic cathode structure as utilized in a cathode ray tube electron gun, wherein a cathode sleeve of substantially passive cathode material is formed to have top and bottom open ends. At the top open end thereof, a terminal ledge is extremitally formed in a manner substantially normal to the sidewall of the sleeve.
  • a planar closure member of a substantially active cathode material having a perimetric shape similar to the cross-sectional shape of the sleeve, is seated on and affixed to the terminal ledge on the sleeve. There is thus provided a flat substrate upon which electron emissive material is subsequently disposed.
  • FIG. 1 is an enlarged prior art cross-sectional view of the control grid portion of a cathode ray tube electron gun showing an indirectly heated cathode assembly positioned therein;
  • FIGS. 2 and 3 are enlarged sectional views illustrating two embodiments of the improved cathode structure of the invention.
  • FIG. 1 is a prior art view illustrating an indirectly heated cathode assembly 11 positioned within the control grid electrode 13 of an electron gun of the type conventionally employed, either singly or plurally, in cathode ray tubes.
  • the cathode assembly comprises a cathode sleeve 15 having a sidewall portion 17 with open top and bottom ends 19 and 21 respectively.
  • the cathode sleeve is fabricated of a passive cathode material, i.e., a metal or alloy that does not readily sublime or emit electrons upon heating.
  • the top open end 19 of the sleeve is closed by a cathode cap 23 affixed thereto and made of an active cathode material, i.e., one that promotes the emission of electrons when heated.
  • the exterior end surface of the cap 23 has disposed thereon a coating of an electron emissive material 25, such as a combination of carbonates of barium and strontium, and sometimes calcium.
  • a formed insulatively coated heater 27 Positioned within the sleeve is a formed insulatively coated heater 27 which provides the operational temperature level necessary to produce electron emission from the emissive material 25.
  • the cathode assembly 11 is suitably supported as, for example, by cathode shielding means 29 which is formed for attachment to the lower portion of the sleeve by several spaced apart welds 31.
  • the control grid electrode 13 and the cathode assembly support means 29 a're affixed to a plurality of electron gun support beads, not shown, by attachment means 33 and 35 respectively.
  • the cathode is mounted in a manner that the electron emissive material 25 is in spaced relationship with the aperture 37 provided in the end wall 39 of the control grid electrode 13.
  • the electrons emitted by the emissive material 25 pass through-the grid aperture 37 as an electron beam and thence sequentially traverse the associated electron gun electrodes, not shown, to be directed to the screen of the tube.
  • the skirt 22 of the cathode cap 23 telescopes over the top end of the sleeve 15 making extensive contact with the upper sidewall portion of the sleeve thereby effecting a comprehensive heat sink relationship.
  • the heater 27 warms up, during the initiation of tube operation, the heat thereof radiates to both the sleeve 15 and the mass of the skirted cap 23 thereby retarding the temperature rise of the emissive portion and lengthening the initial time-lag of tube activation.
  • Attachment of the cap to the sleeve is normally accomplished by a plurality of bondings, such as by welds 41.
  • Such bonding is usually effected by pressuring the skirt 22 of the cap against the sidewall 17 of the sleeve.
  • This procedure sometimes causes a slight doming ofthe flat end surface 24, as exaggeratively shown in FIG. 1, or may set up residual stresses in the cap which tends to produce doming or oil-canning of the end region during operational heating.
  • any doming of the emissive surface relative to the adjacent electrode aperture 37 is detrimental to the uniformity of the subsequential electron beam and thus affects the desired operational efficiency of the tube.
  • the cap 23 has an external diametrical dimension a" which is greater than the external sleeve diameter b. Due to the rolled periphery 45 of the cap, and the feathered periphery 47 of the emissive coating 25, the substantially uniform emission area evidences a lateral dimension c which substantially approximates the diameter d of the aperture 37.
  • the close relationship of these dimensions which are particularly common in low-power applications, emphasizes the criticality of alignment of the cathode and electrode aperture in such instances.
  • the cathode sleeves of the invention are denoted as being cylindrical, but such is not to be considered limiting as the cross-sectional shaping thereof may also be substantially elliptical or rectangular.
  • the indirectly heated end-emissive cathode structure 49 is oriented within the control grid 13 in a manner similar to that described for the prior art, but the upper portion of the cathode structure 49, per se, is markedly different.
  • the substantially cylindrical cathode sleeve 51 is formed of substantially passive cathode material having open top and bottom ends, of which the top end 53 is shown. Dimensionally, the sleeve has inner and outer diameters designated as e amd f respectively.
  • a terminal ledge 55 is extremitally formed to be circumferentially outstanding from the top end of the sleeve; such ledge 55 being formed in a'manner substantially normal to the exterior surface of the sleeve 51.
  • a substantially disc-shaped planar closure member 57 formed of a substantially active cathode material, as for example, known nickel alloys, is of a perimetric shape similar to that of the sleeve.
  • the closure approaches the diametrical dimension g of the terminal ledge.
  • This planar closure member is seatedon and affixed to, the outstanding ledge in one of two manners; either by a plurality of at least three spaced bonds or welds 58, or by a substantially continuous perimetric bonding therearound.
  • the peripheral bonding between the ledge 55 and the peripheral portion of the closure member 57 is consummated in a substantially flat surface-to-surface compression relationship wherein, longitudinally directed bonding pressure fosters maintenance of the flatness of the planar member. There are no stress vectors set up of the type evidenced in the prior art cap-to-sleeve attachment.
  • the closure member provides a flat substrate having a planar area upon which a uniform electron emissive coating 59 is disposed.
  • the substrate area is greater than the cross-sectional area of the sleeve,.i.e., diametrically g exceeds f.
  • the cathode coating 59 while exhibiting a feathered periphery 61, has a uniform area of the diameter h which exceeds the diameter i of the elctr ode aperture 63.
  • the required operational temperature is provided by the insulatively coated heater 27 positioned within the cathode structure as shown.
  • a second embodiment of the invention is referenced in FIG. 3, wherein the indirectly heated end-emissive cathode structure is positioned within the control electrode 13.
  • the upper portion of the cathode structure of this embodiment 65 differs from the described first embodiment 49, in that the top of the cathode 67 is extremitally formed to have an instanding terminal ledge 69 circumferentially thereabout.
  • Such ledge being formed in a manner substantially normal to the interior surface of the sleeve 67.
  • a substantially discshaped planar closure member 71 having a diametrical dimension m which does not exceed the external cross-sectional dimension fof the sleeve, is seated on and affixed to the instanding ledge 69.
  • This affixation is in the form of at least three spaced apart bonds or welds 73 or by the application of a continuous perimetric bonding. Whichever procedure is utilized, the union is effected by a substantially even surface-to-surface compression relationship wherein the jointure pressure maintains flatness of the planar closure member 71.
  • the flat substrate thus provided has disposed thereon a uniform area of an electron emissive coating 75 having a diameter 0" which exceeds the diamter p of the adjacent electrode aperture 77.
  • An improved two-piece indirectly heated endemissive cathode structure having a jointure region of minimum mass for use in a cathode ray tube, said cathode structure comprising:
  • tubular cathode sleeve formed of a substantially passive cathode material having top and bottom open ends and a sidewall portion therebetween and dimensioned to accommodate associated thermionic heater means therein, said bottom end of said tubular cathode being formed for affixation to cathode support means;
  • a substantially planar disc-shaped closure member formed of a substantially active cathode material having a perimetric shape similar to that of said cathode sleeve and a transverse diametrical dimension not exceeding the external cross-sectional dimentioning of said sleeve, said closure member being seated directly upon said narrow ledge to facilitate contiguous affixation thereto;
  • bonding means to effect a limited area transverse terminal jointure between the active material closure member and the ledge oriented passive material of said cathode tubular member, said transverse jointure being peripherally oriented and of minimum mass prevents doming of the planar closure member and promotes rapid heating of the cathode while minimizing the heatsink characteristics of the cathode structure, said active material closure portion providing a flat substrate having an area approximating the crosssectional area of said sleeve whereupon a coated area of electron emissive material is subsequently disposed.
  • planar disc-shaped closure member is affixed directly to said narrow terminal ledge by substantially continuous perimetric bonding therearound.
  • planar disc-shaped closure member is affixed directly to said narrow terminal ledge at a plurality of at least three spaced-apart discrete areas of peripherally related bonding means.
  • an improved two-piece indirectly heated end-emissive cathode assembly having a jointure region of minimum mass, the emission area of said assembly being oriented in spaced relationship to a control grid electrode having an aperture therein smaller than the diameter of said cathode, said cathode assembly comprising:
  • a tubular cathode sleeve formed of a substantially passive cathode material having top and bottom open ends and a sidewall portion therebetween with internal dimensions to enclose a thermionic heater means therein, the bottom end of said cathode being formed in a manner to facilitate affixation of said cathode sleeve to compatible support means;
  • a planar disc-shaped closure member of a substantially active cathode material having a perimetric shape similar to that of said sleeve and not exceeding the cross-sectional dimension thereof, said closure member being seated directly on said narrow ledge to facilitate contiguous affixation thereto;
  • cathode assembly support means affixed to the bottom of said sleeve to provide positioning of said cathode sleeve whereof said planar closure with said electron emissive material disposed thereon is spacedly related to the aperture of said control grid

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  • Electrodes For Cathode-Ray Tubes (AREA)
US393970A 1972-05-24 1973-09-04 Cathode structure for cathode ray tube Expired - Lifetime US3914638A (en)

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US393970A US3914638A (en) 1972-05-24 1973-09-04 Cathode structure for cathode ray tube

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Application Number Priority Date Filing Date Title
US25643172A 1972-05-24 1972-05-24
US393970A US3914638A (en) 1972-05-24 1973-09-04 Cathode structure for cathode ray tube

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4401919A (en) * 1980-08-07 1983-08-30 Itt Industries, Inc. Indirectly heated Wehnelt cathode
US4554479A (en) * 1983-12-08 1985-11-19 Rca Corporation Cathode-ray tube having a low power cathode assembly
DE4131660A1 (de) * 1990-09-22 1992-04-02 Samsung Electronic Devices Verfahren zur herstellung einer vorratskathode
FR2895144A1 (fr) * 2005-12-16 2007-06-22 Thomson Licensing Sas Oeillet de cathode pour canon a electrons

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4782263A (en) * 1984-05-21 1988-11-01 Rca Licensing Corporation Inline electron gun having at least one modified cathode assembly

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2413689A (en) * 1942-02-12 1947-01-07 Bell Telephone Labor Inc Electron discharge device
US2445993A (en) * 1944-02-12 1948-07-27 Gen Electric Cathode structure
US3293476A (en) * 1963-01-04 1966-12-20 Varian Associates Electrode assembly for an electron discharge device made from a material having a low carbon content

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2413689A (en) * 1942-02-12 1947-01-07 Bell Telephone Labor Inc Electron discharge device
US2445993A (en) * 1944-02-12 1948-07-27 Gen Electric Cathode structure
US3293476A (en) * 1963-01-04 1966-12-20 Varian Associates Electrode assembly for an electron discharge device made from a material having a low carbon content

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4401919A (en) * 1980-08-07 1983-08-30 Itt Industries, Inc. Indirectly heated Wehnelt cathode
US4554479A (en) * 1983-12-08 1985-11-19 Rca Corporation Cathode-ray tube having a low power cathode assembly
DE4131660A1 (de) * 1990-09-22 1992-04-02 Samsung Electronic Devices Verfahren zur herstellung einer vorratskathode
US5131878A (en) * 1990-09-22 1992-07-21 Samsung Electron Devices Co., Ltd. Process for manufacturing dispenser cathode
FR2895144A1 (fr) * 2005-12-16 2007-06-22 Thomson Licensing Sas Oeillet de cathode pour canon a electrons

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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.,

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