Patent Publication Number: US-3881126-A

Title: Fast warm-up cathode assembly

Description:
United States Patent 1191 Boots et a1.  
 1 1 Apr. 29, 1975 1 FAST WARM-UP CATHODE ASSEMBLY {75] lnventors: Wendell K. Boots, Seneca Falls.  
 N.Y.; William E. Buescher; Donald R. Kerstetter, both of Emporium, Pa.  
 [73] Assignee: GTE Sylvania Incorporated.  
 Stamford, Conn.  
 [22] Filed: Mar. 6, 1974 [21] Appl. No.1 448,464  
 [52] US. Cl. 313/337; 313/346; 313/270 [51] Int. Cl H01j 1/20; HOlj 19/14 [58] Field of Search 313/337. 341, 346. 270. 313/271 [56] References Cited UNITED STATES PATENTS 2.469.626 5/1949 Bccrs 313/337 X 2.717.975 9/1955 Wihtol 2.720.608 10/1955 Wihtol 313/341 X 2.723363 11/1955 Santis et a]. 313/370 2.808530 10/1957 Katz 313/337 X 3.221.203 ll/1965 Ragland. Jr.... 313/341 X 3,553 521 1/1971 Bakker 313/337 Primary E.\-an1inerSaxfield Chatmon, Jr. Attorney, Agent. or FirmNorman J. OMalley; William H. McNeill; Cyril A. Krenzer [57] ABSTRACT A fast warm-up cathode comprises a solid core body having a heater wrapped thereabout. One end of the core is provided with a widened area of cathode nickel alloy and has on an upper surface thereof an electron emissive material. The opposite end of the core can be provided with a support member which can be fixed into an electrically insulating body. Additionally, electrically conductive legs can be also positioned within the electrically insulating body to provide attachments for the heater.  
 7 Claims, 2 Drawing Figures FAST WARM-UP CATHODE ASSEMBLY BACKGROUND OF THE INVENTION This invention relates to electron discharge device cathodes and particularly to fast warm-up cathodes having particular application in cathode ray tubes. Conventional cathode ray tubes generally employ a cathode which is indirectly heated, that is, they comprise a tubular cathode assembly which is hollow having an insulated filamentary heater contained therewithin to provide the heat necessary to cause an emissive material to emit electrons. The cathodes conventionally employed in current cathode ray tubes normally have a warm-up time of 12 to seconds; that is, it requires that long for a sufficient electron cloud to be present from the cathode and to be drawn to the anode and establish a raster on the face plate of the picture tube. These warm-up times have been considered to be detrimental to the viewing public in that it requires a long wait from turn-on to an acceptable or viewable picture on the face of the tube. In the past this detrimental condition has been obviated by the provision of an instant on feature provided by some television receiver manufacturers. With this feature a raster or viewable picture is obtained on the picture tube almost instantaneously with the turn-on of the set; however, this feature has not in the past been accomplished by a fast warm-up cathode but rather by a bleeder current which constantly maintains the cathode heater at a near normal operating temperature. Thus, in effect, the cathode ray tube is never completely turned off. When the television receiver is either a complete tube version including many receiving tubes or a hybrid version including some receiving tubes and some solid state devices, the bleeder current of the instant on feature is also applied to the heaters of the other receiving tubes within the set. This condition has been alleged to provide a dangerous fire hazard in some receivers. It is also quite wasteful of electrical energy since, as mentioned above, the receiver is never completely turned off and the set is constantly drawing electrical power. It would be a decided advance in the art if a more economical fast warm-up system could be provided. Attempts have been made in the past to provide fast warm-up cathodes; however, many of the proposed types have been extremely difficult to build or have been very expensive.  
 OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, an object of the invention to obviate the disadvantages of the prior art.  
  It is another object of the invention to enhance the warm-up characteristics of cathode ray tubes.  
  It is yet another object of the invention to provide an acceptable and economical fast warm-up cathode for color cathode ray tubes.  
  These objects are accomplished in one aspect of the invention by the provision of a fast warm-up cathode assembly which comprises a solid, heat conductive, elongated core. One end of the core is provided with a widened cathode area affixed thereto. A layer of electron emissive material is positioned on the outermost surface of the widened area. To bring such a cathode to operating temperature a coiled heater is wrapped about the core body. This construction provides intimate heater contact with the cathode core which conducts the heat directly to the widened cathode area which carries the electron emissive material. By keeping the mass of the cathode assembly low extremely fast warm-up times can be provided by this rugged and economical construction.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational sectional view of the cathode assembly of the invention; and  
  FIG. 2 is a sectional plan view taken along the line 22 of FIG. 1.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the present invention together with other and further objects, advantages, and capabilities thereof, reference is made to the following disclosure and appended claims taken in conjunction with the above described drawings.  
  Referring now to the drawings with greater particularity there is shown in FIG. 1 a cathode assembly 10 which comprises a solid, heat conductive, elongated core 12 having a widened cathode area 14 affixed to one end thereof. A layer of electron emissive material 16 is provided on the upper surface of widened area 14. The material of widened area 14 is selected from the group of nickel cathode alloys; that is, alloys comprised primarily of nickel with small amounts of additives. Many useful materials are known in this area, and a partial list can be found in Materials and Techniques for Electron Tubes; Walter H. Kohl; Reinhold Publishing Corporation, New York, N.Y., 1960; pages 560 et seq. The core 12 can be a similar material or can be essentially plain nickel or any other material compatible with electron tube environment and having good heat conductivity characteristics. A coiled heater 17 is wrapped about core 12 to provide heating thereof.  
  The end of core 12 remote from the widened area 14 can be provided with a core support 18. In this instance core support 18 is shown as being a rod-like construction and preferably is constructed of a low heat conductivity material such as one of the glass sealing alloys. A glass sealing alloy such as Rodar, available from the Wilbur B. Driver Company, Newark, N..l., provides excellent results. To further reduce heat conductivity through the core support 18 it is preferably of smaller cross section than core 12. Core support 18 can be attached to core 12 by any suitable method such as buttwelding. The end of core support 18 can be affixed in an electrically insulating material which in this instance is shown as being a glass button 20. The button 20 can be further provided with a first pair of electrically conductive legs 22 and 24 which extend therethrough. The upper ends 26, 28 respectively of the conductive legs 22 and 24 are formed to receive the heater connections.  
  An electrostatic and heat reflective shield 30 can also be provided to surround the cathode assembly 10. In this particular instance electrostatic shield 30 is shown as being a substantially cup shaped device having an apertured top portion 32 and an upstanding circumferential side wall 34 projecting therefrom. The aperture 36 in end 32 is of sufficient size to allow widened area 14 to be positioned therein. When an electrostatic shield 3Q is employed, means 38 can additionally be provided to support shield 30 and these means 38 can be carried by button 20. In the particular embodiment shown means 38 comprise a plurality of rods 40 which have one end thereof positioned and affixed in button 20 and which extend upwardly and outwardly therefrom to a point 42 whereat they can be affixed as by welding to the interior wall surface of shield 30.  
  It will be seen from the above description that a novel fast warm up cathode is provided. The structure is rugged and simple to fabricate and economical to use.  
  While there have been shown what are at present considered to be the preferred embodiments of the invention it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention as defined by the appended claims.  
 What is claimed is:  
  1. A fast warm-up cathode assembly comprising: a solid, heat conductive, elongated core; a widened cathode area affixed to one end of said core; a core support at the other end of said core, said core support extending from said core and being smaller in cross-section than said core; a layer of electron emissive material on said area; and a coiled heater wrapped about said core.  
 2. The assembly of claim 1 wherein the end of said support remote from said core is affixed in an electrically insulating material.  
  3. The assembly of claim 2 wherein said electrically insulating material is glass.  
  4. The assembly of claim 2 wherein said electrically insulating material is further provided with a first pair of electrically conductive legs which extend therethrough.  
  5. The assembly of claim 4 wherein said heater is electrically connected to the uppermost portion of said pair of extending legs.  
  6. The assembly of claim 5 wherein said cathode assembly is surrounded by an electrostatic, heat reflective shield.  
  7. The assembly of claim 6 wherein said shield is supported and positionally maintained by means carried by said electrically insulating material.