US2014787A - Thermionic cathode - Google Patents

Thermionic cathode Download PDF

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Publication number
US2014787A
US2014787A US728062A US72806234A US2014787A US 2014787 A US2014787 A US 2014787A US 728062 A US728062 A US 728062A US 72806234 A US72806234 A US 72806234A US 2014787 A US2014787 A US 2014787A
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United States
Prior art keywords
cathode
wire
layer
helix
insulating material
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Expired - Lifetime
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US728062A
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English (en)
Inventor
Smithells Colin James
Treloar Leslie Ronald George
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
MO Valve Co Ltd
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MO Valve Co Ltd
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Publication date
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/20—Cathodes heated indirectly by an electric current; Cathodes heated by electron or ion bombardment

Definitions

  • This invention relates to indirectly heated cathodes for thermionic tubes and, more particularly, to those suitable for receiving valves.
  • the heating wire usually a tungsten filament
  • insulating refractory material such. as alumina
  • metal usually nickel
  • alkaline earths which coating forms the cathode surface.
  • the heating wire cannot be pushed into the casing, except possibly by elaborate and therefore inconvenient methods. Consequently it is impossible to manufacture long lengths of cathode which can subsequently be cut up in order to provide the cathodes of individual valves.
  • the object of this invention is to overcome this difficulty and to provide a method of manufacturing indirectly heated cathodes, suitable for mass production, in which cathodes for many valves are made at the same time.
  • the limitation on length can be removed by depositing the casing on the insulated heater rather than placing the insulated heater within a preformed casing.
  • the problem can be solved, at least in part, by making the cathode first in the form of a helical wire wound on a single straight heating element of continuous indefinite length and then cutting off the desired length for the cathode and doubling it on itself so that successive limbs are adjacent and substantially parallel.
  • the magnetic fields of the 5 parts of the heating elements within the successive limbs compensate each other, not perhaps as completely as when they are within the same cathode surface, but sufiiciently for many purposes. 10
  • the turns of the spiral must be in contact at least when the cathode is very long; for if they were separated, so that current flowing through the wire has to pass along 18 its length, the wire would be heated unequally by the thermionic current drawn from it; consequently the wire would be much hotter at one end than at other. But we have found that this expectation is not fulfilled, probably because 20. the wire is in good thermal contact with the insulating layer on the heater and the alkaline earth layer deposited on it (which enters into thermal contact with the insulating layer), so that the temperature of the wire cannot rise appreciably above that of the insulating layer.
  • the function of the wire spiral is, of course, to convey current to the oathode proper which (according to the theory accepted at present) is a monomolecular layer of alkaline earth metal on the surface of the 0xides. It appears that the conductivity of the cathode surface in the direction parallel to its surface is so great that an appreciable distance between points on its surface and the nearest part of the wire spiral does not introduce unde- 4O sirable large differences of potential over neigh' bouring parts of the cathode surface.
  • the insulating layer between the heater and the spiral must be of a suitable character in order that it may not crack off when the cathode is bent.
  • a suitable layer can be provided by depositing on the heater finely divided insulating material, such as alumina, from a suspension.
  • FIG. 1 and 2 of the accompanying drawing show successive stages of manufacture.
  • I is the heater consisting of a. tungsten wire 0.1 mm. in diameter.
  • a layer 2 of alumina between 0.1 and 0.2 mm. thick, either by spraying or drawing the wire of indefinite length continuously through a coating bath.
  • On this layer 2 is wound a spiral 3 of nickel wire 0.1 mm. in diameter, the average pitch of the spiral being about 0.11 mm.
  • the whole is then sprayed with a suspension of barium and strontium carbonates, forming a coating 4 which is afterwards converted into oxides in the usual manner.
  • the structure so formed and shown as a broken away section in Figure 1 after being formed in a continuous indefinite length is cut into appropriate lengths and each length is doubled on it self, as shown in Figure 2, so that successive branches are adjacent.
  • a plurality of leads 5 connected to each other and to earth are joined to the spiral 3 at its two ends and at one or more intermediate points.
  • the branches of the oathode may be supported in the usual or any preferred manner.
  • an indirectly heated cathode comprising a continuous metal core adapted to serve as the heating element, a continuous layer of refractory insulating material covering said core, a continuous wire helix on said insulating material, a continuous thermionically emitting layer on the wire and on the insulating material not covered by said wire, said continuous cathode being doubled on itself so that successive limbs are adjacent and substantially parallel and conductors connecting said helix at least at one end and at least at one point intermediate between its ends to an external conductor for earthing the same.
  • an indirectly heated cathode comprising a continuous metal core doubled upon itself so that successive limbs thereof are adjacent and approximately parallel, said core serving as the heating element, a continuous layer of refractory insulating material covering and adhering to said core throughout its length, a continuous wire helix wound with successive turns in spaced relation on said insulating material, the helix windings being continuous over the bends to successive limbs and a layer of electron emitting material adhering to and continuously coating the wire of the helix and the insulating material between successive turns so as to be in conducting engagement therewith and leads connected with said helix.
  • thermionic tubes having an indirectly heated cathode bent upon itself so that adjacent lengths are substantially parallel
  • the process which includes coating a metal core with a layer of finely divided insulating material deposited thereon from suspension, winding upon the insulating material a continuous wire helix having successive turns slightly separated, then coating the helix and the insulating material between successive turns thereof with a layer of electron emitting material, the respective coatings being so constituted that with the spacing of the turns of the helix the core may be bent to bring portions of the cathode into parallel relation without rupturing the coatings at the bends, and connecting conductors to at least one end and to at least one intermediate point between the ends of said helix.

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  • Solid Thermionic Cathode (AREA)
  • Coating By Spraying Or Casting (AREA)
  • Water Treatment By Electricity Or Magnetism (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
US728062A 1933-06-24 1934-05-29 Thermionic cathode Expired - Lifetime US2014787A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB18051/33A GB419096A (en) 1933-06-24 1933-06-24 Improvements in thermionic cathodes

Publications (1)

Publication Number Publication Date
US2014787A true US2014787A (en) 1935-09-17

Family

ID=10105780

Family Applications (1)

Application Number Title Priority Date Filing Date
US728062A Expired - Lifetime US2014787A (en) 1933-06-24 1934-05-29 Thermionic cathode

Country Status (5)

Country Link
US (1) US2014787A (de)
BE (1) BE403333A (de)
FR (1) FR772609A (de)
GB (1) GB419096A (de)
NL (1) NL38569C (de)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2489367A (en) * 1946-11-13 1949-11-29 Hartford Nat Bank & Trust Co Cathode assembly for electric discharge tubes
US2589522A (en) * 1952-03-18 Cathode heater structure
US2589521A (en) * 1952-03-18 Heater
US2653268A (en) * 1950-05-01 1953-09-22 Beverly D Kumpfer Directly heated cathode structure
US2749470A (en) * 1952-06-11 1956-06-05 Int Standard Electric Corp Indirectly heated cathodes
US2872611A (en) * 1953-11-16 1959-02-03 Sylvania Electric Prod Cathode
US3195004A (en) * 1960-08-19 1965-07-13 Rca Corp Cathode heater for electron discharge devices
US3226806A (en) * 1960-03-18 1966-01-04 Eitel Mccullough Inc Method of making a cathode heater assembly
EP1983546A1 (de) * 2007-04-20 2008-10-22 PANalytical B.V. Röntgenstrahlkathode und -röhre

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2589522A (en) * 1952-03-18 Cathode heater structure
US2589521A (en) * 1952-03-18 Heater
US2489367A (en) * 1946-11-13 1949-11-29 Hartford Nat Bank & Trust Co Cathode assembly for electric discharge tubes
US2653268A (en) * 1950-05-01 1953-09-22 Beverly D Kumpfer Directly heated cathode structure
US2749470A (en) * 1952-06-11 1956-06-05 Int Standard Electric Corp Indirectly heated cathodes
US2872611A (en) * 1953-11-16 1959-02-03 Sylvania Electric Prod Cathode
US3226806A (en) * 1960-03-18 1966-01-04 Eitel Mccullough Inc Method of making a cathode heater assembly
US3195004A (en) * 1960-08-19 1965-07-13 Rca Corp Cathode heater for electron discharge devices
EP1983546A1 (de) * 2007-04-20 2008-10-22 PANalytical B.V. Röntgenstrahlkathode und -röhre
EP1983547A1 (de) 2007-04-20 2008-10-22 PANalytical B.V. Röntgenquelle
WO2008129006A1 (en) * 2007-04-20 2008-10-30 Panalytical B.V. X-ray source
US20100150315A1 (en) * 2007-04-20 2010-06-17 Bart Filmer X-ray source
JP2010525506A (ja) * 2007-04-20 2010-07-22 パナリティカル ビー ヴィ Ｘ線源
CN101720491B (zh) * 2007-04-20 2012-07-04 帕纳科有限公司 X射线源
US8223923B2 (en) 2007-04-20 2012-07-17 Panaltyical B.V. X-ray source with metal wire cathode

Also Published As

Publication number Publication date
NL38569C (de)
FR772609A (fr) 1934-11-02
BE403333A (de)
GB419096A (en) 1934-11-06

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