US2144249A - Cathode for electron discharge devices - Google Patents

Cathode for electron discharge devices Download PDF

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Publication number
US2144249A
US2144249A US7853A US785335A US2144249A US 2144249 A US2144249 A US 2144249A US 7853 A US7853 A US 7853A US 785335 A US785335 A US 785335A US 2144249 A US2144249 A US 2144249A
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cathode
tungsten
thoria
electron discharge
filament
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US7853A
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Victor O Allen
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RCA Corp
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RCA Corp
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Priority to NL48128D priority Critical patent/NL48128C/xx
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Priority to US7853A priority patent/US2144249A/en
Priority to FR801936D priority patent/FR801936A/en
Priority to GB4808/36A priority patent/GB462706A/en
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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
    • H01J1/14—Solid thermionic cathodes characterised by the material
    • H01J1/146—Solid thermionic cathodes characterised by the material with metals or alloys as an emissive material
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S428/00—Stock material or miscellaneous articles
    • Y10S428/922—Static electricity metal bleed-off metallic stock
    • Y10S428/9335—Product by special process
    • Y10S428/934—Electrical process
    • Y10S428/935—Electroplating
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
    • Y10T428/12611—Oxide-containing component
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
    • Y10T428/12611—Oxide-containing component
    • Y10T428/12618—Plural oxides
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/1266—O, S, or organic compound in metal component
    • Y10T428/12667—Oxide of transition metal or Al
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12771—Transition metal-base component
    • Y10T428/12806—Refractory [Group IVB, VB, or VIB] metal-base component
    • Y10T428/12812—Diverse refractory group metal-base components: alternative to or next to each other

Definitions

  • My invention relates to electron discharge devices, more particularly to improvements in thermionic electron emitting cathodes for such devices.
  • the pure tungsten filament cathode is a very stable emitter and is eflicient but must be operated at very high-temperatures to obtain ample emission.
  • the activated thoriated tungsten cathode such as described in U. S. patent to Langmuir 1,244,216,
  • the activated thoriated filament is apt to be brittle, and if operated at too high a temperature quickly deactivates and loses its ability to emit a suflicient numberof electrons to be useful.
  • the oxide coated niokelcathode operates at a much lower temperature than either kind of tungsten cathode and is efiicient, but cannot be satisfactorily operated in tubes in which very high plate voltages, such as 1000 volts, are used, and requires considerable processing and seasoning.
  • An object of my invention is to provide a duo-' tile thermionic cathode which is a stable, efficient and long lived emitter, at desirable operating temperatures.
  • a further object is to provide an eflicient thermionic cathode which can be satisfactorily used at high frequencies and high voltages and requires little seasoning or'processing.
  • Another object of my invention is to provide'an indirectly heated cathode for high voltage gas or vacuum tubes.
  • a refractory metal having a high melting point preferably 2400 C, or higher combined with thoria and chromium or their equivalents.
  • a refractory metal having a high melting point preferably 2400 C, or higher combined with thoria and chromium or their equivalents.
  • tungsten, molybdenum or tantalum are refractory metals that are used.
  • the thoria may be incorporated in the tungsten metal to form a base, and the chromium plated on the thoriated tungsten base, or the pure tungsten, molybdenum or tantalum base may be chromium plated and the thoria applied as a coating on the plated base.
  • the thoriated tungsten base may be prepared as a ductile metal in accordance with U. S. Patent I 1,082,933 to W. D. Coolidge, or. by squirting the finely divided material admixedwith a binder.
  • a binder for example, if tungsten is used I may add powdered nitrate of thoria. to the powdered oxide of tungsten before the reduction of the oxide of tungsten, or I may add thoria to the oxide of tungsten after reduction but before consolidation of the metal powder by sintering and mechanical working to the solid state as described in the said Coolidge patent.
  • the amount of thoria may vary from about /2 of 1% by weight of the metal to about 3%0f the metal.
  • Tungsten-containing more than 2% or 3% of thoria is eX- tremely brittle and hard to work, but in general I have found it desirable for best results to add as much thoria as may be tolerated in the refractory metal without interfering with the subsequent swaging and drawing of the metal. This has been found in practice to be up to 1 for tungsten. A filament of this thoriated metal may be used. In general thelarger the percentages of thoria the better the emitter. While thoria is preferred, equivalents of thoria, for eX-.
  • yttrium and lanthanum may be used with tungsten to form a base and the base then chromium plated in a conventional chromium plating bath,
  • the essential constituents of which are chromic base may vary between wide limits, for example,
  • the resulting chromium plated thoriated wire' may be used for a thermionic electron emitting cathode without further treatment, but for best results in the case of the thoriated tungsten base I prefer to flash theplated filament in vacuum at'over voltage; for example, to heat the filament to a temperature of approximately 2600 K. for about thirty seconds, and thereby facilitate the activation of the filament. It is also desirable, though not necessary, to insure stability of emission to season the filament by operating the electron discharge device containing the filament with normal voltages applied for approximately fifteen minutes in an oscillating circuit.
  • a cathode made in accordance with my invention has a normal operating temperature several hundred degrees K. below the normal operating temperature of the conventional activated thoriated tungsten cathode, and in the conventional type of tube operated at the customary plate voltage the same plate current can be obtained from my improved cathode at its normal operating temperature with only about one-half the energy per unit area that must be used to obtain the same plate current from the conventional activated thoriated tungsten cathode at its normal operating temperature.
  • the chromium acts as a catalyst to facilitate the rapid diffusion of the electron emitting metal, such as thorium, to the surface of the filament. for producing copious emission.
  • a pure tungsten, molybdenum, or tantalum filament may be chromium plated as above described and then brushedwith thoria powder suspended in acetone and of a particle size which will pass thru a 200 mesh screen or smaller. This will also provide a very efiicient emitter.
  • the thickness of the coating should come within the limits described above. Treatment to insure stability of emission as described above is desirable but not necessary.
  • any of the cathodes above described may be coated with the usual electron emitting coating of alkaline earth metal oxides, such as barium oxide and strontium oxide, which may be applied in a conventional manner by applying barium and strontium carbonates and converting them into the oxides.
  • alkaline earth metal oxides such as barium oxide and strontium oxide
  • a cathode made in accordance with my invention is a very eflicient emitter. It will operate at a comparatively low temperature (1200 K.) and very high voltages can be used on the plate of a tube using my cathode up to approximately 3000 volts without the cathode suffering any ill efiects due to ion bombardment. These last two characteristics make my invention particularly suitable for indirectly heated cathodes in high voltage gas or vacuum tubes.
  • Cathodes made according to my invention are very satisfactory in tubes used for generating very high frequencies at high voltages and while seasoning improves the initial stability and operating characteristics it is not essential in order to provide a cathode which is a good emitter and operates satisfactorily.
  • the resulting cathode is a Very stable emitter and is not easily poisoned by as.
  • the cathode readily recovers its emitting characteristics even if accidentally operated temporarily at too high temperatures. ionization will not destroy the tube due to ion bombardment, and the cathode will recover its emission if temporarily impaired by being subjected to high voltages.
  • a thermionic cathode adapted for use as an electron emitter in electron discharge devices comprising a refractory metal body consisting predominantly of tungsten, and the remainder containing thoria and electrolytically applied chromium.
  • titanium, vanadium, yttrium and lanthanum titanium, vanadium, yttrium and lanthanum.
  • a thermionic cathode for use in an electron discharge device and consisting essentially of tungsten and containing thoria and a coating of electrolytically applied chromium on the thoriated tungsten.
  • a thermionic cathode for use in an electron discharge device consisting essentially of one of the group of metals, tantalum, tungsten or molybdenum and a coating of thoria and elec trolytically applied chromium on said metal.
  • a thermionic cathode for use in an electron discharge device and. comprising a metal of high melting point, a chromium plating on said metal and a coating of thoria on said chromium plating.
  • a thermionic cathode for use in an electron discharge device and comprising molybdenum, a chromium plating on said molybdenum and a coating of thoria on said chromium plating.
  • a thermionic cathode for use in an electron discharge device and comprising tungsten, a chromium plating on said tungsten and a coating of thoria on said chromium plating.

Landscapes

  • Discharge Lamp (AREA)
  • Solid Thermionic Cathode (AREA)

Description

Patented Jan. 17, 1939 PATENT OFFICE 2,144,249 CATHODE FOR ELECTRON DISCHARGE DEVICES Victor 0. Allen, Madison, N. J., assignor, by mesne I assignments, to Radio Corporation of America,
. New York, N. Y., a corporation of Delaware No Drawing. Application February 23, 1935,
Serial No. 7,853
'7 Claims.
My inventionrelates to electron discharge devices, more particularly to improvements in thermionic electron emitting cathodes for such devices.
The present application relates to modifications of the invention described and claimed in copending United States patent application, Serial No. 43,714, filed October 5, 1935, by Victor 0. Allen and Joseph Johnson as joint inventors, and assigned to the same assignee as thepresent invention.
In conventional electron discharge devices with the filament type of thermionic cathode commercial use has been made of pure tungsten filaments,
activated thoriated' tungsten filaments, and oxide coated nickel filaments. The pure tungsten filament cathode is a very stable emitter and is eflicient but must be operated at very high-temperatures to obtain ample emission. The activated thoriated tungsten cathode, such as described in U. S. patent to Langmuir 1,244,216,
may be operated at lower temperatures than a pure tungsten filament and is more efficient, but is easily poisoned by oxygen and other gases which adversely affect the emission, is not very stable when operated "at high voltages, and requires special processing and seasoning. It has also been found that when operated at ultra' high frequencies, for example above 15 or 16 megacycles, that emission becomes erratic and that there is sometimes a total loss-of emission. In addition, the activated thoriated filament is apt to be brittle, and if operated at too high a temperature quickly deactivates and loses its ability to emit a suflicient numberof electrons to be useful. The oxide coated niokelcathode operates at a much lower temperature than either kind of tungsten cathode and is efiicient, but cannot be satisfactorily operated in tubes in which very high plate voltages, such as 1000 volts, are used, and requires considerable processing and seasoning.
Thoriated molybdenum has also been thoroughly investigated as a filament cathode emitter, but has proved to be rather unstable, quite sen .sitive to poisoning by gas within the tube, and
must be operated at fairlyhigh temperatures, between 1400 and 1600 C. to provide satisfactory emission. For these and other reasons thoriated molybdenum has not come into commercial use as a cathode filament material.
In the conventional high vacuum or gas tube operating at high voltages, only filamentary type cathodes have heretofore been used because the oxide coatings of the indirectly heated cathodes quickly disintegrate at high voltages, and without these coatings no material was available which had sufiicient emission unless raised to very high temperatures which cannot be practically generated with the conventional indirectly heated cathode construction,
An object of my invention is to provide a duo-' tile thermionic cathode which is a stable, efficient and long lived emitter, at desirable operating temperatures. A further object is to provide an eflicient thermionic cathode which can be satisfactorily used at high frequencies and high voltages and requires little seasoning or'processing. Another object of my invention is to provide'an indirectly heated cathode for high voltage gas or vacuum tubes.
In accordance with my invention I use a refractory metal having a high melting point, preferably 2400 C, or higher combined with thoria and chromium or their equivalents. Of these refractory metals I prefer to use tungsten, molybdenum or tantalum. The thoria may be incorporated in the tungsten metal to form a base, and the chromium plated on the thoriated tungsten base, or the pure tungsten, molybdenum or tantalum base may be chromium plated and the thoria applied as a coating on the plated base.
The thoriated tungsten base may be prepared as a ductile metal in accordance with U. S. Patent I 1,082,933 to W. D. Coolidge, or. by squirting the finely divided material admixedwith a binder. For example, if tungsten is used I may add powdered nitrate of thoria. to the powdered oxide of tungsten before the reduction of the oxide of tungsten, or I may add thoria to the oxide of tungsten after reduction but before consolidation of the metal powder by sintering and mechanical working to the solid state as described in the said Coolidge patent. The amount of thoria may vary from about /2 of 1% by weight of the metal to about 3%0f the metal. Tungsten-containing more than 2% or 3% of thoria is eX- tremely brittle and hard to work, but in general I have found it desirable for best results to add as much thoria as may be tolerated in the refractory metal without interfering with the subsequent swaging and drawing of the metal. This has been found in practice to be up to 1 for tungsten. A filament of this thoriated metal may be used. In general thelarger the percentages of thoria the better the emitter. While thoria is preferred, equivalents of thoria, for eX-.
yttrium and lanthanum may be used with tungsten to form a base and the base then chromium plated in a conventional chromium plating bath,
. the essential constituents of which are chromic base may vary between wide limits, for example,
from a few hundreths of an ampere to over 1 ampere per square centimeter, for best results a current density of about 1 ampere per square centimeter for a period of one minute seems to produce the most satisfactory results. The resulting chromium plated thoriated wire'may be used for a thermionic electron emitting cathode without further treatment, but for best results in the case of the thoriated tungsten base I prefer to flash theplated filament in vacuum at'over voltage; for example, to heat the filament to a temperature of approximately 2600 K. for about thirty seconds, and thereby facilitate the activation of the filament. It is also desirable, though not necessary, to insure stability of emission to season the filament by operating the electron discharge device containing the filament with normal voltages applied for approximately fifteen minutes in an oscillating circuit.
A cathode made in accordance with my invention has a normal operating temperature several hundred degrees K. below the normal operating temperature of the conventional activated thoriated tungsten cathode, and in the conventional type of tube operated at the customary plate voltage the same plate current can be obtained from my improved cathode at its normal operating temperature with only about one-half the energy per unit area that must be used to obtain the same plate current from the conventional activated thoriated tungsten cathode at its normal operating temperature.
.While I do not wish to be limited to any particular theory it is believed that the chromium acts as a catalyst to facilitate the rapid diffusion of the electron emitting metal, such as thorium, to the surface of the filament. for producing copious emission.
A pure tungsten, molybdenum, or tantalum filament may be chromium plated as above described and then brushedwith thoria powder suspended in acetone and of a particle size which will pass thru a 200 mesh screen or smaller. This will also provide a very efiicient emitter. The thickness of the coating should come within the limits described above. Treatment to insure stability of emission as described above is desirable but not necessary.
When the cathodes are to be used in low voltage tubes, for example under 1000 volts, to increase the electron emissivity any of the cathodes above described may be coated with the usual electron emitting coating of alkaline earth metal oxides, such as barium oxide and strontium oxide, which may be applied in a conventional manner by applying barium and strontium carbonates and converting them into the oxides.
A cathode made in accordance with my invention is a very eflicient emitter. It will operate at a comparatively low temperature (1200 K.) and very high voltages can be used on the plate of a tube using my cathode up to approximately 3000 volts without the cathode suffering any ill efiects due to ion bombardment. These last two characteristics make my invention particularly suitable for indirectly heated cathodes in high voltage gas or vacuum tubes.
Cathodes made according to my invention are very satisfactory in tubes used for generating very high frequencies at high voltages and while seasoning improves the initial stability and operating characteristics it is not essential in order to provide a cathode which is a good emitter and operates satisfactorily. The resulting cathode is a Very stable emitter and is not easily poisoned by as. The cathode readily recovers its emitting characteristics even if accidentally operated temporarily at too high temperatures. ionization will not destroy the tube due to ion bombardment, and the cathode will recover its emission if temporarily impaired by being subjected to high voltages.
While I have indicated the preferred embodiment of my inventionof which I am now aware and have also indicated only certain specific application for which my invention may be employed, it will be apparent thatmy invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.
What I claim as new is:
1. A thermionic cathode adapted for use as an electron emitter in electron discharge devices comprising a refractory metal body consisting predominantly of tungsten, and the remainder containing thoria and electrolytically applied chromium.
2. A thermionic cathode for use in an electron discharge device and consisting essentialy of one of the group of metals tungsten and tantalum, in
combination with electrolytically applied chromium and at least one of the group of substances consisting of thoria, zirconium, uranium, cerium,
titanium, vanadium, yttrium and lanthanum.
3. A thermionic cathode for use in an electron discharge device and consisting essentially of tungsten and containing thoria and a coating of electrolytically applied chromium on the thoriated tungsten.
, 4. A thermionic cathode for use in an electron discharge device and consisting essentially of one of the group of metals, tantalum, tungsten or molybdenum and a coating of thoria and elec trolytically applied chromium on said metal.
5. A thermionic cathode for use in an electron discharge device and. comprising a metal of high melting point, a chromium plating on said metal and a coating of thoria on said chromium plating.
6. A thermionic cathode for use in an electron discharge device and comprising molybdenum, a chromium plating on said molybdenum and a coating of thoria on said chromium plating.
7. A thermionic cathode for use in an electron discharge device and comprising tungsten, a chromium plating on said tungsten and a coating of thoria on said chromium plating.
- VICTOR O. ALLEN.
High voltage CERTIFICATE OF CORRECTION. Patent No. 2,1hl 2u9.
January 17, 1959. VICTOR o. ALLEN.
It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, sec- 0nd column, line 2, for (1200 IL) read (1200 0.); and, that the said Letters Patent should be read with this correction therein that the same may conform to the record of the ca se in the Patent Office. Signed and sealed this 18th day of July,- A. D. 1.959.
Henry Van Arsdale, Acting Commissioner of Patents.
(Seal) I
US7853A 1935-02-23 1935-02-23 Cathode for electron discharge devices Expired - Lifetime US2144249A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
NL48128D NL48128C (en) 1935-02-23
US7853A US2144249A (en) 1935-02-23 1935-02-23 Cathode for electron discharge devices
FR801936D FR801936A (en) 1935-02-23 1936-02-17 Cathode enhancements for electronic discharge devices
GB4808/36A GB462706A (en) 1935-02-23 1936-02-17 Improvements in or relating to cathodes for electron discharge devices

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2497111A (en) * 1947-07-25 1950-02-14 Eitel Mccullough Inc Electron tube having carburized thoriated cathode
US2509702A (en) * 1947-01-14 1950-05-30 Eureka Television And Tube Cor Cathode for thermionic valves
US2512617A (en) * 1947-02-04 1950-06-27 Electrons Inc Electron discharge device
US2726178A (en) * 1950-11-17 1955-12-06 Rca Corp Thermionic cathode with thoria coating
US2848390A (en) * 1953-11-10 1958-08-19 Owens Corning Fiberglass Corp Method and apparatus for applying metal to glass
US2996795A (en) * 1955-06-28 1961-08-22 Gen Electric Thermionic cathodes and methods of making
US3041209A (en) * 1955-06-28 1962-06-26 Gen Electric Method of making a thermionic cathode
US3240150A (en) * 1963-12-20 1966-03-15 Max J Doppelt Base member for duplicating device
US3272603A (en) * 1964-01-23 1966-09-13 Mallory & Co Inc P R Refractory metal composite

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH582951A5 (en) * 1973-07-09 1976-12-15 Bbc Brown Boveri & Cie

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2509702A (en) * 1947-01-14 1950-05-30 Eureka Television And Tube Cor Cathode for thermionic valves
US2512617A (en) * 1947-02-04 1950-06-27 Electrons Inc Electron discharge device
US2497111A (en) * 1947-07-25 1950-02-14 Eitel Mccullough Inc Electron tube having carburized thoriated cathode
US2726178A (en) * 1950-11-17 1955-12-06 Rca Corp Thermionic cathode with thoria coating
US2848390A (en) * 1953-11-10 1958-08-19 Owens Corning Fiberglass Corp Method and apparatus for applying metal to glass
US2996795A (en) * 1955-06-28 1961-08-22 Gen Electric Thermionic cathodes and methods of making
US3041209A (en) * 1955-06-28 1962-06-26 Gen Electric Method of making a thermionic cathode
US3240150A (en) * 1963-12-20 1966-03-15 Max J Doppelt Base member for duplicating device
US3272603A (en) * 1964-01-23 1966-09-13 Mallory & Co Inc P R Refractory metal composite

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FR801936A (en) 1936-08-21
GB462706A (en) 1937-03-15

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