US1942080A - Heater for indirectly heated cathodes - Google Patents

Heater for indirectly heated cathodes Download PDF

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Publication number
US1942080A
US1942080A US559753A US55975331A US1942080A US 1942080 A US1942080 A US 1942080A US 559753 A US559753 A US 559753A US 55975331 A US55975331 A US 55975331A US 1942080 A US1942080 A US 1942080A
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US
United States
Prior art keywords
heater
cathode
indirectly heated
wire
rod
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US559753A
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English (en)
Inventor
Andrew H Young
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.)
General Electric Co
Original Assignee
General Electric Co
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Filing date
Publication date
Application filed by General Electric Co filed Critical General Electric Co
Priority to US559753A priority Critical patent/US1942080A/en
Priority to FR42178D priority patent/FR42178E/fr
Priority to GB24002/32A priority patent/GB390405A/en
Application granted granted Critical
Publication of US1942080A publication Critical patent/US1942080A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • H01J1/22—Heaters

Definitions

  • the present invention relates to thermionic apparatus and more particularly to the cathodes thereof.
  • An object of the present invention is to provide a heater which may be energized directly from commercial voltages and which does not have the foregoing disadvantages, but on the contrary, has a long and satisfactory operating life, and is also adapted to quantity production methods.
  • Other objects are to provide an indirectly heated cathode with a readily replaceable heater, also to provide a heater which may be manufactured as a member, complete in itself and separate from the cathode proper. These objects are attained in brief, by coiling the heater wire in a fine helix and winding the latter about an insulator designed to withstand electrolysis.
  • the heater wire is held rigidly in place by the application of one or more coats of an insulating paste containing a material highly resistant to electrolysis at high temperatures and voltages, and which when dry, forms a hard, solid mass.
  • the heater in the finished form is an article complete in itself. self-supporting, and is embedded in an insulating material which effectively precludes arcing between the turns and protects the enclosed metal member from injury.
  • Fig. 1 illustrates an exemplary tube which employs the improved heater to advantage
  • Fig. 2 is an enlarged view showing a preliminary step in the manufacture of the heater
  • Fig. 1 illustrates an exemplary tube which employs the improved heater to advantage
  • Fig. 2 is an enlarged view showing a preliminary step in the manufacture of the heater
  • Fig. 1 illustrates an exemplary tube which employs the improved heater to advantage
  • Fig. 2 is an enlarged view showing a preliminary step in the manufacture of the heater
  • Fig. 1 illustrates an exemplary tube which employs the improved heater to advantage
  • FIG. 3 is a view of the heater infinal form and mounted in place, ready to be inserted into the cathode casing;
  • Fig. 4 is a view partly in section of the heater shown in Fig. 3, while
  • Fig. 5 is a sectional view of an improved cathode taken along the line 5-5 of Fig. 1.
  • numeral 1 designates the envelope of an electrostatically controlled arc discharge device embodying a tipless seal so-called, and containing an indirectly heated cathode 2, an electrostatic control or grid member 3 of mesh material and an inverted dish-shaped anode 4.
  • a device of this sort ordinarily contains an ionizabie medium such as mercury or an inert gas which in operation, reduces the space charge effect to such an extent as to allow large amounts of current to flow, controllable by the charge on the grid.
  • Alternating voltage is usually impressed between the cathode and anode and is rectified within the tube.
  • the cathode structure 2 shown more clearly in Fig. 5, consists of quadrant pieces of sheet metal bent to a shape so that when fitted together, two concentric cylinders 8 are formed, separated by four radially extending vanes 7. These vanes, as well as the two cylinders, are coated with an electronically active substance, such as barium carbonate (311003).
  • an electronically active substance such as barium carbonate (311003).
  • the improved heater which forms the subject of the present invention fits snugly within the inner cylinder 6 and serves to heat the latter, also the outer cylinder and vanes, to an electronemitting temperature in the well understood manner.
  • the heater is constituted preferably of tungsten wire 10 of relatively small gauge, coiled as a fine helix, as shown more clearly in Fig. 2.
  • the coil is wound in a cold state, as a coarse helix 11o aboutaroundrodorcore 11 of highlyfired alumina (AhOa) but which may also comprise zirconia (ZrOz) beryllia (BeO), or other insulating refractory which resists electrolysis to a high degree.
  • a stiff molybdenum wire 12 driven through a central opening in the rod to which wire the upper end of the heater is attached so as to serve as a combined lead and tie wire.
  • the lower end of the heater coil conveniently is bound to the alumina rod by a wire thong 13 which may be extended to constitute the other lead.
  • the combined coil and its rod support are first dipped in water and then in a coating material consisting of a suspended solution of starch paste and fairly coarse, highly fired, pure alumina powder.
  • refractory insulating materials such as beryllia and zirconia, may be employed, provided they are inert with respect to the material of the embedded filament at high temperature and are highly resistant to electrolysis, also are capable of being thoroughly degassed; The slightest trace of gas in the material causes a severe shortening of the heater life.
  • the coating is dried in the open air or in a closed oven operated at about .100 C. or less, and preferably is accomplished in such a manner as to insure uniformity of drying. The dipping process allows a very even coat to be picked up from the solution and as the water evaporates, the particles are drawn together by surface tension and the adhesive effect of the starch to form a relatively hard and compact mass.
  • the heater When the first coating is dry, the heater is again dipped in the suspension and dried in this manner until the proper thickness of material has been built up. A complete coat may be obtained with only two dips by regulating the condition of the suspension. It is desirable to have an extra heavy coat at the top of the heater which ordinarily is the point of maximum voltage between the heater and the cathode, and for this reason the upper portion of the coated member is given one or more extra dips.
  • the next step is to fire the heater, which is carried out at a temperature between 1575 C. and 1600 C. in an atmosphere of moist hydrogen.
  • This firing step serves not only to get rid of the gas and volatile portion of the binder material and to decarbonize the less volatile portion of the binder, but also to sinter the coating.
  • the filament heater is thus encased in a thick layer of pure aluminum oxide A10: which takes on an extremely hard, sintered character.
  • the member as a whole is rugged, self-supporting, and is capable of being handled readily. It is also apparent that the described process of manufacture of the heater is relatively simple, and lends itself to quantity production methods.
  • the heater is now ready to be assembled within the cylinder or casing of the cathode, and in order to obtain a snug fit, it may be necessary to sandpaper the exterior of the coating.
  • the heater is supported in a vertical position by means of a combined cap and collar member 14 which has an opening in the top to receive the heater, and which fits snugly over a piece of glass tubing as a pant leg 15 sealed to the press 16 of the envelope 1.
  • the lower end of the heater member may be tapered slightly.
  • the central wire 12 is passed through the glass tubing and is connected to one of the not only by the proper choice of insulating mabetween the filament and the cathode, so that external base contact 17. from the heater is secured in any nertoarigldconductorlafused and connected to another of the 17.
  • the bottom of the cathode structure is closed by a metal cap (not shown) and the memberasawholesupportedfromthepreabya rigid metal rod 19, in addition to the conductor 18, which on account of being attached tothe cap serves as a lead for the cathode as well as for the heater.
  • the cathode preferably is mounted so as to extend a short distance within the grid member and is spaced concentrically therefrom by means of a surrounding disc of insulation material 20.
  • the press also supports the grid 3 conveniently by means of stay rods 21 secured to a clamp 22.
  • a tube of this sort contains an ionizable medium such as mercury v r, or an inert gas at a pressure sufiicient to su port an arc-like discharge at the impressed voltages. It has been found that notwithstanding the presence of the medium in this condition, also the high voltages employed, any portion of the heater which is accessible to' the arc successfully withstands the positive ion bombardment. This may be due to the hard and dense texture of the fused coating.
  • the heater may be energized directly from a 110 volt alternating current or direct current supply without the use of voltage reducing accessories, as the size and length ofthewirearesuchastolimitthe currentat these voltages to the proper amount.
  • the improved heater is not subject to electrolysis which ordinarily attacks all other heaters at temperatures of this order. This desirable result is brought about terlals in which the wire is embedded and 011' which it is wound, but also by the improved process of manufacture and design of the heater. It is known that the degree with which the phenomenon of electrolysis takes place in a given ma-- terial depends not only upon the electrical stress to which the material is subjected but also on the temperature of the material.
  • the improved heater is so designed as to minimize this temperature, the design being an embodiment in which the heater is wound as a double helix on a rod of suitable insulating material. Moreover.
  • the member 14 which is completely insulated by reason of its glass support and also by virtue of the fact that only the insulating cover of the heater con- 5 tacts with it, serves to prevent arcing between the lower end of the wire 12 and of the helix 10 between which full heater voltage is applied and also precludes positive ion bombardment of the wire which tends to take place in the gas.
  • An indirectly heated cathode for a gasfllled tube and adapted to be energized directly by current of commercial voltages said cathode comprising a heater wire wound on a rod of refractory insulating material and completely embedded in a mass of aluminum oxide, a heater lead extending through the rod, said mass or aluminum oxide resting on a metal cap which is insulatingly supported within the tube. said lead passing through the interior of said cap.
  • An electron discharge device comprising an envelope terminating in a stem, cooperating electrodes in said envelope including an indirectly heated cathode adapted to be energized by current of commercial voltages, said cathode comprising a heater wound on a rod 01' refractory insulating material and completely embedded in a mass of refractory insulating material, a heater lead extending through the rod, a collar or refractory material for supporting said mass of insulating material from said stem, said lead passing through said collar to the exterior of the envelope.
  • An electron discharge device comprising an envelope terminating in a stem provided with a cylindrical projection, cooperating electrodes in said envelope including an indirectly heated cathode adapted to be energized by current of commercial voltages, said cathode comprising a heater wound on a rod of refractory insulating material and completely embedded in a mass of refractory insulating material, a heater lead extending through the rod, a metal collar fitting snugly over said projection and over said mass of insulating material for supporting the latter from said stem, said lead passing through the collar to the exterior of the envelope.

Landscapes

  • Discharge Lamp (AREA)
  • Vessels And Coating Films For Discharge Lamps (AREA)
  • Lasers (AREA)
  • Solid Thermionic Cathode (AREA)
US559753A 1931-08-27 1931-08-27 Heater for indirectly heated cathodes Expired - Lifetime US1942080A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US559753A US1942080A (en) 1931-08-27 1931-08-27 Heater for indirectly heated cathodes
FR42178D FR42178E (fr) 1931-08-27 1932-08-04 Perfectionnements aux valves à décharge électronique
GB24002/32A GB390405A (en) 1931-08-27 1932-08-27 Improvements in and relating to electric discharge devices

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US559753A US1942080A (en) 1931-08-27 1931-08-27 Heater for indirectly heated cathodes

Publications (1)

Publication Number Publication Date
US1942080A true US1942080A (en) 1934-01-02

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Family Applications (1)

Application Number Title Priority Date Filing Date
US559753A Expired - Lifetime US1942080A (en) 1931-08-27 1931-08-27 Heater for indirectly heated cathodes

Country Status (3)

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US (1) US1942080A (fr)
FR (1) FR42178E (fr)
GB (1) GB390405A (fr)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2424293A (en) * 1944-03-09 1947-07-22 Westinghouse Electric Corp Thermionic cathode construction
US2436907A (en) * 1945-06-23 1948-03-02 Nasa Indirectly heated cathode
US2444072A (en) * 1942-10-08 1948-06-29 Raytheon Mfg Co Gaseous electrical space discharge devices and circuits therefor
US2514165A (en) * 1942-11-23 1950-07-04 M O Valve Co Ltd Thermionic gas-filled rectifier
US2653268A (en) * 1950-05-01 1953-09-22 Beverly D Kumpfer Directly heated cathode structure
US3248680A (en) * 1962-12-11 1966-04-26 Ward Leonard Electric Co Resistor
US3265920A (en) * 1964-06-22 1966-08-09 Rauland Corp Electron-discharge device cathode assembly with radiation shield
US3295090A (en) * 1962-02-26 1966-12-27 Dale Electronics Electrical resistor having a core element with high heat dissipating properties

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2444072A (en) * 1942-10-08 1948-06-29 Raytheon Mfg Co Gaseous electrical space discharge devices and circuits therefor
US2514165A (en) * 1942-11-23 1950-07-04 M O Valve Co Ltd Thermionic gas-filled rectifier
US2424293A (en) * 1944-03-09 1947-07-22 Westinghouse Electric Corp Thermionic cathode construction
US2436907A (en) * 1945-06-23 1948-03-02 Nasa Indirectly heated cathode
US2653268A (en) * 1950-05-01 1953-09-22 Beverly D Kumpfer Directly heated cathode structure
US3295090A (en) * 1962-02-26 1966-12-27 Dale Electronics Electrical resistor having a core element with high heat dissipating properties
US3248680A (en) * 1962-12-11 1966-04-26 Ward Leonard Electric Co Resistor
US3265920A (en) * 1964-06-22 1966-08-09 Rauland Corp Electron-discharge device cathode assembly with radiation shield

Also Published As

Publication number Publication date
FR42178E (fr) 1933-05-31
GB390405A (en) 1933-04-06

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