US2768321A - Indirectly heated electron emitter for power tubes and the like - Google Patents

Description

Oct. 23, 1956 PETERSON TED ELECTRON EMITTER UBES AND THE LIKE FRED Wj g mv BY. 724M 7%Q F. W. INDIRECTLY HEA FOR POWER T Filedflay 2', 1955 nited States Patent I rmA'rEn ELECTRGNEEBHTTER FOR POWER TUBES AND THE LIKE Fred W. Peterson, Lancaster, Pat, a'ssignor to Radio Corporation of America, a corporationof Delaware Application May 2, 195 5, Serial N 6. 505,37? 9 Claims. (Cl.- 313'-337) 2,768,321 INDiRECTLY A principal object of the invention is to provide a novel and simplified heater-cathode device for electron tubes, which device is especially usefulin tubes of the power kind, for example such as are used in radio and television transmitters and the like.

A feature of the invention resides in a heater-cathode device which is rugged in construction and can be manufact'ured from a minimum of prefabricated parts and with a minimum of welded joints.

Another feature relates to a heater-cathode unit wherein the heater element is substantially completely enclosed within a closed annular chamber, the inner wall of which chamber constitutes a support for the heater element in the form of a coiled wire, and the outer but closely spaced wall of the said annular chamber carries externally the electron emissive material.

Another feature relates to .an improved heater-cathode unit for power tubes wherein the cathode is formed with two sections, one of which is a thin Walled section of single wall thickness to act as a heat isolating and support element, and another section is a double walled section to house a coiled heater. element, the external surface of the double walled section constituting the electron .emitter.

A further feature relates to the novel configuration, construction and location and interconnection or elements which together constitute a rugged and efiicient heater type cathode for electron tubes and the like.

Other. features will appear from the ensuing descriptions, the appended clairns, and the attached drawing.

In the drawing, which shows one typical and preferred embodiment,

Figure l is an elevational view in section of a heatercathode deviceaccording to the invention; I

Figure 2 is a sectional view of Figure 1, taken'alo'ng the line 2-2 thereof and viewed in the direction of the arrows.

Referring to the drawing, there is shown a typical embodiment of a heater-cathodeunit according to the invention, which can be used as the electron emitter for any well known construction ofthe-electron tube. Since the invention is concerned primarily with such aunt, the remaining parts of the tube with which the cathode unit cooperates-are omitted; It will be understood, of course, that the cathode unit is mounted within any well known evacuated bulb or envelope and is surrounded by one or more electrodes, one of which is an anode, and at least one intervening grid between the cathode and anode. For an illustrative construction of an electron tube in which the device may be used, reference may be had to the application of Nekut and Shrader entitled, Power Tubes For Operation at High Frequencies, Serial No. 505,388 and filed concurrently herewith on May 5, 1955.

2,768,321 Patented Oct. 23,

The'heater-cathode unit, according to the invention, comprises acylindrical tubular member or sleeve 10 of any suitable alloy or metal. Member 10 has its upper section 11 and its lower section 12 formed with different cross sectional wall thickness. The lower section 12' is preferably formed as. an integral part with the section 11', for example by rolling down to the required thinness'consistent with the desired rigidity of the member 10 as a whole, and consistent with the desired heat isolating. properties for section 12. In other words, the section 12 acts to cut down as much as possible, heat conduction between the section 11 and the base of the cathode, while at the same-timeproviding a rigid support for the cathode as a whole. The base portion of the cathode member 10 may be in the form of another relatively thick cross section portion 13, Which is bent at right angles to form a substantially flatannular fiange '14 and an integral downwardly depending cylindrical skirt 15. It will be understood, of. course, that the sections 11, 12, 13, 14 and 15 are preferably formed from a one-piece metal blank. The upper end of member 10 provided with a flat annular rim 16, having a central circular opening 17 for purposes to be described.

Welded to the. lower end of section 11 is another cylindrical metal member 18 having the right angled flange portion 19 which is spot welded to the lower end of section 11. The straight cylindrical Wall of member 18 preferably extends upwardly into contact with the flat rim 16; and the saidupper end is provided with a window 31 through which the end-29 of aninsulated heating coil. 21 emerges. Thus, the section 11 and the member 18 define a cylindrically annular substantially closed chamber within which is housed the heater element 21; The element 21 is in the form of a coiled refractory heater wire 22 carrying a suitable refractory insulator coating 23. The lower end of the wire of coil is spot welded to the horizontal portion of the flange The opposite end of the coil which extends through the window 31 is spot welded to the upper end ofarigid metal rod 24 which passes centrally through the member ltl. It is for this reason that the opening 17 is provided in the. cap 16 to facilitate the insertion of a. suitable spot welding tool. I g V v The rod 24 has welded thereto a metal disc 25 which is arranged to be sealed in a vacuumtight manner, 'for example by brazing, as indicated by the numeral 26, to the lower face of an annular insulator member 27 preferably of ceramic. The rod 24 passes centrally through the opening 28 inceramic 27. The ceramic member 27 seats fiat against the flange 14, to which it can be vacuum-tight sealed, for example by brazing, as indicated by the numeral 29. The sectionll is provided on its external periphery with a coating 30 of any well known electron emissive material such as conventionally used in electron tubes, especially those of the power kind.

The finished unit can then be mounted within a suitable. enclosing envelope in the proper concentric relation to the remaining electrodes, after which the enclosing bulb or envelopecan be evacuated and processedi'n theeonvention'al ways. The foregoing describedcathode he'ate'r unit employs a minimum of prefabricated parts. Furthermore, the part 18, in addition to constituting one wall of the enclosed annular heating chamber, can also be used as a winding spool upon which the heater element 21 can be wound. If desired, of course, the coil 21 can be previously wound to the desired internal diameter so as to be closely telescoped over the member 18. In any event, the cost of manufacture is greatly reduced since only three spot welding operations are required, namely the spot welding between the section 11 and the flange 19, and the spot welding of one end of the coil with the flange 19 and the spot welding of the opposite end of the coil with the rod 24. It is believed that the manner of assembly of the parts will be clear from the foregoing description.

In general, the pre-wound heater coil 21 is assembled over the member 18 and the lower end of the coil is spot welded to flange 19. This assembly of member 18 and coil 21 can be placed over a suitable mandrel and inserted into the member and spot welding is eflected between the member 10 and the flange 19. The mandrel may then be removed and the assembly, consisting of the elements 24, 25 and 27 can be inserted into the member 10, whereupon the end of the heater wire 22 can be spot welded to rod 24. The necessary brazing at the regions 26 and 29 can be effected thus constituting a rigid and efiicient heater-cathode unit.

The invention is not limited to any particular materials, providing the arrangement, configuration and interconnection of parts described above is employed in the final unit.

Various changes and modifications may, therefore, be made in the disclosed embodiment Without departing from the spirit and scope of the invention.

What is claimed is:

1. An electron emitter device for electric discharge tubes, comprising a first tubular metal member and a second tubular member forming at one end of said first member an annular and substantially closed chamber, a heater element supported within said chamber, a rigid metal rod passing through said members in spaced relation to the inner Wall of said chamber, one end of said heater being electrically connected to said rod, the other end of said heater being electrically connected to a wall of said chamber, and electron emissive material on the external peripheral wall of said chamber.

2. An electron emitter device for electric discharge tubes, comprising a tubular metal member having relatively thick walled ends with an intermediate thin walled portion joining said end portions to act as a heat isolator, one of said ends having on its outer surface an electron emissive material, another tubular metal mem ber fastened interiorly of said end but of smaller radius to define with said end an annular substantially closed chamber, a heating element supported within said chamber having one end electrically connected to said housing, a metal rod passing centrally through said member, means insulatingly supporting said rod from the opposite end of said member, means electrically connecting one end of the heating element to said member, and means electrically connecting the opposite end of said heating element to said rod.

3. An electron emitter device for electric discharge tubes, comprising a tubular metal sleeve having a double walled section at its upper end defining a substantially closed heater housing at said upper end, a heater element supported within said housing, one end of said heater element being electrically connected to said sleeve, and a metal member insulatingly supported adjacent the lower end of said sleeve and electrically connected to the opposite end of said heater element.

4. An electron emitter device for electric discharge tubes, comprising a tubular metal sleeve having a double walled section at its upper end defining a substantially closed annular chamber at said upper end, a heater element supported within said chamber, an insulator member vacuum-tight sealed to the lower end of said sleeve, 21 metal rod passing through said insulator, means vacuum-tight sealing said rod adjacent its lower end to said insulator, means electrically connecting one end of said heater to said rod, and means electrically connecting the opposite end of said heater to said sleeve.

5. An electron emitter device for electric discharge tubes, comprising a tubular metal sleeve having a double walled section at its upper end defining a heater housing, a heater element surrounding and supported by the inner wall of said double walled housing, said sleeve having intermediate its upper and lower ends an intervening tubular thin walled heat isolating section, an insulator member vacuum-tight sealed to the lower end of said sleeve, and a connector member vacuum-tight sealed through said insulator member and connected to one end of said heater element.

6. An electron emitter for electric discharge tubes, comprising a cylindrical metal sleeve, a cylindrical metal member Within one end of said sleeve and fastened to the interior wall of said sleeve to define therewith an annular heater housing within said sleeve at its upper end, a coiled heater wire Within said housing surrounding said cylindrical member and supported thereby, means for vacum-tight sealing the opposite end of said sleeve, means vacuum-tight sealed through said sealing means and extending interiorly of said sleeve but insulator therefrom for making electrical contact with one end of said heater element, and electron emissive material on the external surface of said sleeve at its upper end.

7. An electron emitter according to claim 6 in which said vacum-tight sealing means includes an annular ceramic member and said metal sleeve is rigidly supported from said ceramic member by a thin walled heat insulating continuation of said sleeve.

8. A unitary heater-cathode assembly for power tubes, comprising a tubular metal sleeve having a relatively thick walled section at its upper end, a relatively thick walled section at its lower end, an intervening thin Walled heat isolating section between said end sections, a flat annular flange formed with said lower end section, a ceramic member vacuum-tight sealed to said flat flange, a tubular metal member attached to the upper end of said sleeve and spaced therefrom to form an annular heater housing localized at said upper end of the sleeve, a coiled insulated heater wire surrounding said tubular metal member and supported thereby, and means vacuum-tight sealed through said ceramic for making electrical connection to one end of said heater wire.

9. A unitary heater-cathode assembly according to claim 8 in which said upper end section, said lower end section, and said intervening section are formed from a single metal blank, and said tubular metal member is telescoped interiorly of the upper end of said sleeve and is provided with an ofitset flange portion which is welded to said upper end to constitute said heater housing.

References Cited in the file of this patent UNITED STATES PATENTS 2,314,097 Litton Mar. 16, 1943 2,418,390 Atlee Apr. 1, 1947 2,446,270 Eitel et al. Aug. 3, 1948 2,723,363 De Santis et a1. "a Nov. 8, 1955

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