US2875361A

US2875361A - Auxiliary heaters to aid in activation of cathode ray type guns

Info

Publication number: US2875361A
Application number: US511886A
Authority: US
Inventors: Robert P Stone
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1955-05-31
Filing date: 1955-05-31
Publication date: 1959-02-24
Anticipated expiration: 1976-02-24

Description

Feb. 24, 1959 R. P. STONE 2,875,361

AUXILIARY HEATERS TO AID IN ACTIVATION C ODE RAY TYPE GUNS F" d May 31, 1955 a filament adjacent to the cathode surface.

United States Patent 2,875,361 AUXILIARY HEATERS T0 AID IN ACTIVATION 0F CATHODE RAY TYPE GUNS Robert P. Stone, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application May 31, 1955, Serial No. 511,886 Claims. (Cl. 31385) This invention relates to. electron guns and particularly to an improved method of and means for constructing electron guns for cathode ray tubes.

During the conventional construction of electron guns for cathode ray tubes, the cathode is sprayed with a layer of material that includes barium carbonate and/ or strontium carbonate. After the gun assembly has been placed within the neck portion of an evacuated envelope, the barium carbonate and/or strontium carbonate. is converted to the oxide form of the material, as this is the active form, and produces an emission of electrons when heated to a sufiiciently high temperature during tube operation. The barium and strontium oxides are unstable and tend to rapidly combine with moisture and carbon dioxide when exposed to the atmosphere. Thus, the cathode is activated after tube evacuation and before it is sealed off.

The normal method of activating the barium carbonate and/or strontium carbonate on the cathode of an electron gun is to heat the cathode by applying potentials to When heating the cathode, the control grid electrode, which is spaced closely adjacent to the cathode, is also heated in order to prevent it from collecting various breakdown products from the cathode. The reason for this is that these breakdown products would re-evaporate back to the cathode when the control electrode is heated during subsequent tubeoperation and would then cause a decrease in electron emission.

In tubes constructed prior to this invention, the usual method of heating the control grid electrode is by use of a radio frequency coil that is placed around a neck portion of the envelope. This method is highly satisfactory for certain types of tubes. However, in other types of tubes the electron gun is inaccessible to the radio frequency field.

Examples of such tubes are: 1) when the electron gunis supported within a large diameter envelope that does not have a neck; (2) when the electron gun is.

arranged in such a position that heat from the radio frequency coil would harm other tube parts before the control grid is sufliciently heated; (3) when the envelope is metal; and (4) in demountable systems.

It is therefore'an object of this invention to provide a new and novel method of and means for heating the control electrode during activation of an electron gun.

comprises a filament, a cathode and a control grid electrode. The heater element, is arranged in heat transfer relationship with respect to the control grid electrode.

During tube processing, the cathode of the electron gun is heated, at least partially, by conventional means in that current is passed through the filament to provide heat .to the cathode to decompose the carbonate coating.

Simultaneously, the grid electrode is heated by passing current through the heater element. Thus, electron guns lc Patented Feb. 24, 195-9 manufactured in accordance with this invention may be arranged in any desired position within an envelope since it is not necessary that they be .accessible to radio frequency heating.

Other features and advantages of this invention will become more clear from reading the following specification in conjunction with the accompanying single sheet of drawings, wherein:

Figure 1 is a transverse sectional view of a storage tube in which this invention is particularly applicable;

Figure 2 is an enlarged sectional view of parts of a gun structure utilizing an embodiment of this invention;

Figure 3 is an enlarged fragmentary sectional view of another embodiment of this invention.

Referring now to Figure 1 there is shown a transverse sectional view of a storage tube 10 utilizing this invenare inaccessible to conventional electron gun activating means. Thus, the particular storage tube 10 in Figure 1 is shown merely to illustrate one of many useful applications of the present invention.

The storage tube 10 generally comprises, within an evacuated envelope 11, an electron gun 113 which is normallyreferred to as a writing gun. The electron gun 13 provides an electron beam 15 which is scanned over an apertured insulating storage target 17 to deposit charges on the storage target 17. A viewing gun 19 is provided which sprays the storage target 17 with electrons. During operation, the electrons from the viewing gun 19 are repelled from the areas of target 17 which are not charged, or written on, by beam 15. In the areas that have information written thereon, the electrons of the viewing gun 19 pass through apertures in target 17 to strike a fluorescent screen 21.

As shown more clearly in Figure 2, the cathode is supported within the control grid electrode 27 by means of an insulating spacer 29. The control grid electrode, or cylinder, 27 has one end closed by means of an apertured disk member 31. Surrounding the control grid cylinder 27, but insulated therefrom, is a heater 33. Spaced from the closed end of the control grid cylinder 27 is a second grid electrode 34.

During the manufacturing of the electron gun 19 the 7 cathode 23 is coated with a mixture of material that contaminants with respect to the other electrodes, such as oxygen, carbon monoxide, and carbon dioxide are driven from the hot cathode. The contaminants are preferably taken either out of the envelope by the evacuating pump (not shown), or absorbed by a getter 36, so that they will not subsequently return to the cathode and decrease electron emission. However, if the control grid cylinder 27 remains cool during this activation process, these contaminants will be deposited upon the control grid cylinder since it is a surface near to the cathode. If the contaminants are deposited on the control grid cylinder, the first time the control grid is; heated duringnormal tube operation, .the contaminants on the control grid will be driven back to the cathode and will react with the materials, i. e. the barium oxide 3 and strontium oxide, so that electron emission from cathode 23 slumps rapidly and thus the tube life is short due to loss of electron emission. It is for this reason that the control grid cylinder is heated during the cathode activation and degassingprocess.

As can be seen from Figure 1 the writing gun 13 is arranged in an off axis location in the envelope 11 and adjacent to one side thereof. Also, the viewing gun 19 is substantially on the axis of envelope 11 and is spaced from. the walls of envelope 11 a substantial distance. Both of. the electron guns 13 and 19 are thus in such a position within the envelope 1-1 that it is extremely diflicult to heat the control grid electrode of the electron guns by the conventional means of a radio frequency coil. Specifically, if a radio frequency coil were utilized to heat the control grid electrodes in the electron guns 13 and 19, other tube elements might be overheated due to conduction paths which exists in the tubes geometry.

For example, since it is generally necessary to heat a control grid electrode to a temperature of approximately 700 C. to prevent contaminants from the cathode from settling thereon, an extremely large amount of power must be utilized inorder to heat the control grid 27 to such a temperature. This large amount of power is likely to damage other electrodes within the tube, such as those portions of the writing gun 13 that are near the envelope Wall, long before the control grid 27 has attained such a temperature by conventional radio frequency heating means.

In accordance with this embodiment of this invention, the control grid cylinder 27 is heated by current flow through the'heater 33' that surrounds the control grid cylinder. in the exampie'presently under consideration, the heater 33 is made of mil tungsten wire with approximately four, ormore, turns of the wire around the control grid cylinder 27. A heater similar to heater 33 shown in Figure 2 has also'been made of 12 /2 mil thoriated tungsten wire.

During the activation process of manufacturing gun 19, the filament 25 is heated-to a temperature of approximately 1300 C. to 1400 C. which-heats the cathode, by meansof radiation and conduction, to a temperature of approximately 1000 C. to 1200- C. Simultaneously the heater 33 is heated to approximately 2200 C. This temperature for heater 33 generatessuflicient heat to'raise the temperature of the control grid cylinder 27 to a temperature of approximately 700 C. to 800 C. by radiation. These temperatures may be obtained by passing approximately 6 amperes through the heater 33 at a potential'of' approximately 16 volts. The cathode temperature is obtained by passing approXimately 8/10 amperes through the filament 25 at a potential of approximately 10 /2 volts. In the method just described, the potentials for the heater 33 are applied acrossinput terminals 38 and the control grid cylinder 27 is heated solely by heat radiated fromthe heater 33, neglecting the small amount oflheat radiated to the grid cylinder by the cathode.

Another method of operating the device shown in Figure 2 is to raise the temperature of heater 33 until it becomes electron-ernissive. When using this method, the control grid cylinder 27 is made electrically positivewith respect to the heater 33 by means of direct current source 40. When this method is utilized the control gridcylinder 27 is heated byboth electron bombardment and by heat radiation, andthus the heater 33 should be at a' temperature that is highly electron-emissive. For example, the heater 33 iselectron emissive when raised to atemperature of approximately 2200 C. for a tungste'n heater, and approximately 1800 C. for a-thoriated ment of this invention wherein a heater coil 42 is enclosed'within the control grid cylinder 27' and is-insulated therefrom by an insulating coating 44 on the heater, or

auxiliary filament, wires 42. When using this embodiment, a tungsten or thoriated tungsten wire may be utilized, as was previously described, and may be connected to a potential of approximately 6 volts with a current of approximately 4 amperes which is sufficient to raise the temperature of the heater to approximately 1100 C. The particular example given above as illustrative of this invention causes the control grid cylinder 27 to be heated to a temperature of approximately 700 C. to 800 C.

In the embodiment shown in Figure 3, the heat generated by the heater 42 is transferred to the control grid cylinder 27' both by radiation and by conduction. Furthermore, some heat will also be transferred to the cathode by radiation, and therefore it is not necessary to apply as much power to filament 25' for heating cathode 23' to the same temperatures as previously described.

Although the invention was decribed with particular reference to the viewing electron gun, it should be understood that it is also applicable to the writing gun 13. Also, the invention was described with particular reference to a storage tube 10 and it should be understood that this type of tube was shown merely as an example of a particular type of tubewherein this invention is particularly useful.

What is claimed is:

1. An electron gun assembly including a filament, a hollow tubular cathode electrode enclosing said cathode, said hollow tubular grid electrode having an apertured member spanning one end thereof, and means including a heater element arranged adjacent to said grid electrode and in heat exchange relationship with respect to said grid electrode for heating said grid electrode during cathode activation.

2. An electron gun as in claim 1 wherein said heater is between said cathode and said grid electrode.

3. An electron gun as in claim 1 wherein said heater surrounds said grid electrode.

4. An electron gun assembly comprising a filament, a

cylindrical cathode enclosing said'filament and having one end closed, an electrically insulated heater element around said cathode, a control grid cylinder enclosing said cathode and said heater, said heater being adjacent to sai control grid cylinder whereby said control grid is heated by passing currentthrough said heater element.

5. An electron gun assembly comprising a filament a cylindrical cathode enclosing said filament and havingone end closed, a coating of barium carbonate and strontium carbonate on said cathode, a control grid cylinder enclosing said cathode and spaced. therefrom, an auxiliary heater spaced around said control grid cylinder, said filament being in heat exchange relationship with said cathode whereby said barium carbonate and strontium carbonate may be heated bypassing current through said filament, said control grid being in heat exchange relationship with respect to said auxiliary heater whereby said control grid'cylinder may be heated by passing current through said auxiliary heater, and means for applying potentials between said auxiliary heater and said control grid cylinder whereby said control grid cylinder may also be heated by electron bombardment by electrons from said auxiliary heater.

References Cited in the file of this patent UNITED STATES PATENTS 1,927,812 Thomson Sept. 19, 1933 2,073,804 Pratt Mar. 16, 1937 2,189,993 Schenk Feb. 13, 1940 2,401,734 James June 11, 1946 2,413,731 Samuel Jan. 7, 1947 2,458,223 Thomas Jan. 4, 1949 2,570,165 Shekels Oct. 2, 1951 2,671,873 Meier Mar. 9, 1954 2,758,240 ,Szegho Aug. 7, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noi 2,875,361 February 24, 1959 Robert P. Stone I It is hereby certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 28, after enclosing said" insert filament, a hollow tubular grid electrode enclosing said line 44, for sai read said Signed and sealed this 7th day of July 1959.,

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Ofliccr Commissioner of Patents