US2075122A - Indirectly heated cathode - Google Patents

Indirectly heated cathode Download PDF

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Publication number
US2075122A
US2075122A US540185A US54018531A US2075122A US 2075122 A US2075122 A US 2075122A US 540185 A US540185 A US 540185A US 54018531 A US54018531 A US 54018531A US 2075122 A US2075122 A US 2075122A
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United States
Prior art keywords
cathode
nickel
jacket
barium
indirectly heated
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Expired - Lifetime
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US540185A
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English (en)
Inventor
Loewe Siegmund
Wienecke Bruno
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Individual
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Individual
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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

  • the invention relates to indirectly heated cathodes, the highly emissive surface of which consists of barium or a similar highly emissive metal.
  • Cathodes of this type should possess the following characteristics which, until now, could not all be secured in one device.
  • the emissive layer must adhere to the surface of the cathode in such a manner that it does not split away during the operation of the tube.
  • the cathode must possess a perfect equipotential area of good conductivity.
  • the equipotential area must be sufficiently insulated from the points of the filament which have difierent potentials.
  • the cathode must possess suificient heat inertia so that the inavoidable small fluctuations in temperature of the filament will not cause audible fluctuations of the emission current.
  • the time required for heating the cathode should not be excessive.
  • the remnant gases should be bound during the step of vaporizing the metallic barium on to the cathode surface.
  • the object of the invention is an indirectly heated cathode which is constructed in such a way as to fulfil simultaneously all of the stated conditions.
  • the insulating tube which may consist for example of porcelain, or fired mixtures of magnesia, silicates and the like is furnished, prior to the application of the barium, with a so tightly fitting metallic jacket that no portion of the barium, or at least no essential proportion thereof, impinges the insulating material when the barium is vaporized on to the cathode.
  • Said jacket may consist of a massive cylinder or a piece of sheet metal disposed round the tube, or also a closely wound wire spiral. In those cases in which the jackets possess small gaps through which parts of the insulator are exposed, these gaps, slits or the like are preferably so disposed that the main quantity of the barium vaporized on to the oathode is withheld therefrom. If a reaction mixture is employed forproducing the barium, and a slotted sheet metal jacket is employed, the side of the jacket remote from the slot is disposed opposite the reaction mixture.
  • the metal jacket is then coated with that 5 particular metal on which the barium efficiently adheres and provides good emission for example tungsten.
  • Said tungsten may be applied in the form of a tungsten wire wound upon the metal jacket. It may also be applied by means of 10 spraying or by reduction of tungsten hexachloride.
  • the metallic base for the tungsten is made of a material which possesses a greater coefiicient of expansion than 5 tungsten or the particular metal which is applied to the metallic jacket.
  • tungsten wire as a carrier for the barium, there is preferably chosen a metallic cylinder composed of nickel. This, upon heatingyexpands 20 to a greater extent than tungsten; the greater, therefore, the extent of heating, the more the tungsten wire presses against the nickel jacket. Thus shaky contacts or disturbing humming noises cannot occur.
  • the tungsten wire may 25 under certain circumstances fit so tightly against the nickel jacket that the same later, even after cooling, constitutes a unitary whole. In any case, however, the hitherto existing difficulty is overcome.
  • insulating tubes are employediwhich, in propor-' tion to their diameter, possess only a relatively 40 small thickness (for example, .3 mm. thickness of wall with tubes .8 mm. thick).
  • the use of insulating tubes of this kind having a comparatively great inner diameter allows of using a spiralized filament instead of the straight filament 45 which otherwise must be employed. Since the emissive layer requires to be raised merely to a low temperature, the heating period, in accordance with requirement 5, is small, particularly as the heat capacity of the porcelain tube is consid- 50 erably less owing to the reduced thickness. On the other hand, due to the low emission temperature, the cooling of the cathode is considerably less than in the case of higher temperatures.
  • FIG. 1 shows an electrondischarge-device .conv taining the indirectly heated cathode according to the invention
  • Fig. 2 shows a longitudinal 'sect'ion
  • Fig. 3 a cross-section of the cathode'of the;
  • tungsten wire which, must beraised to a temperature-'of more than 1000" 01100-1400
  • the porcelain tube is surrounded by a nickel jacket 3 which, in the-manner'shownsectionally in Fig. 3, may be produced from a folded piece of sheet metal.
  • a layer'of tungsten wire for example wound. in the form ofa helix 4?.
  • the nickel base of this tungs sten wire possesses at5: the tapping contact which establishes an efficient.
  • conductive connection with the single wire windings .or other tungsten sections, and over the latter with the layer of barium 5 which is produced on the tungsten wire.
  • barium.- is vaporized on to the cathode in the manner illustrateddiagrammatically by arrows in. Fig. 1, not only the tungsten wire; is furnished with a 'thin coating ofi the metal, which later acts as emissivelayer-,but also the nickel is coveredthereby.
  • This barium deposited on the nickel serves as..a. gas binding. agent: during the operationof theftube. 1 7
  • This efiect maybe amplified. by the, counter-pressure exert-ed'by a. material havinga smaller ccefiicient of. expansion. such as tungsten.
  • a favourable; di tribution of pressure is capable of being attained with the assistance, of
  • Bar oumrlydesirawe is an: embodiment acc rdin to- (crosse tion), in which the two ed es of; the'she t nicke overlap; 1
  • the additional advantage that very good. contact is produced between the equipotential cathode and the cathode tapping.
  • the layer of nickel is created by separation from a gaseous nickel compound, for example from a 'nickel-tetracarbonyl atmosphere. This is particularly suitable in systems. with very weak heating power, which in consequence have only a very small thickness of porcelain tube and may therefore be very easily strained mechanically by the spraying process.
  • Anindirectly heated electron emitting cathode for an electron discharge device comprising a heater filament, an insulating tube surrounding said heater filament, a metal layer surrounding said insulating tube, a further metal layer the coefficient of expansion of which is lower than that of the first metal layer surroundi ing the first metal layer and consisting of a spiral wire, and a highly emissive layer surrounding the r spiral wire.
  • An indirectly heated electron emittingcathode for an electron discharge device comprising a heater filament, an insulating tube surrounding said heater filament, a metal layer surrounding said insulating tube, a further metal layer the coeflicient of expansion of which is lower than that of the first metal layer surrounding the'first metal layer and consisting of'a helix of tungsten wire, and a highly emissive layer surrounding said helix of tungstenwire.
  • An indirectly heated electron emitting cathode for an. electron discharge device comprising a heater filament, an insulating tube surrounding said heater filament, a metal layer surrounding said insulating tube, afurther metal layer the coefiicient of expiansion 0,1 which is lower than that of the first metal layer surrounding the first a highly emissive layer 01' barium surroundingv the spi al wire 4.

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  • Microwave Tubes (AREA)
  • Solid Thermionic Cathode (AREA)
US540185A 1930-05-28 1931-05-26 Indirectly heated cathode Expired - Lifetime US2075122A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE379334X 1930-05-28

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US2075122A true US2075122A (en) 1937-03-30

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US540185A Expired - Lifetime US2075122A (en) 1930-05-28 1931-05-26 Indirectly heated cathode

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US (1) US2075122A (enrdf_load_stackoverflow)
BE (1) BE380140A (enrdf_load_stackoverflow)
FR (1) FR731971A (enrdf_load_stackoverflow)
GB (1) GB379334A (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2447038A (en) * 1945-10-31 1948-08-17 Raytheon Mfg Co Cathode structure
US2817784A (en) * 1951-01-31 1957-12-24 Siemens Ag Cathode for use in electrical discharge devices
US4925741A (en) * 1989-06-08 1990-05-15 Composite Materials Technology, Inc. Getter wire
US5066885A (en) * 1988-04-30 1991-11-19 Futaba Denshi Kogyo Kabushiki Kaisha Indirectly heated filamentary cathode

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE760248C (de) * 1933-11-08 1953-10-19 Georg Seibt Nachf Dr Indirekt geheizte Kathode fuer Kathodenstrahlroehren

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2447038A (en) * 1945-10-31 1948-08-17 Raytheon Mfg Co Cathode structure
US2817784A (en) * 1951-01-31 1957-12-24 Siemens Ag Cathode for use in electrical discharge devices
US5066885A (en) * 1988-04-30 1991-11-19 Futaba Denshi Kogyo Kabushiki Kaisha Indirectly heated filamentary cathode
US4925741A (en) * 1989-06-08 1990-05-15 Composite Materials Technology, Inc. Getter wire

Also Published As

Publication number Publication date
FR731971A (fr) 1932-09-10
GB379334A (en) 1932-08-26
BE380140A (enrdf_load_stackoverflow)

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