US2507979A

US2507979A - Anchoring cathode

Info

Publication number: US2507979A
Application number: US14745A
Authority: US
Inventors: Kelar Joseph
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1948-03-13
Filing date: 1948-03-13
Publication date: 1950-05-16
Anticipated expiration: 1967-05-16

Description

May 16, 1950 J. KELAR 2,507,979

ANCHORING CATHODE Filed March 15, 1948 Inventor 4 49 4 J1: SEPI-I KELAR Patented May 16, 1 950 ANCHORING CATHODE Joseph Kelar, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Dela.-

ware

Application March 13, 1948, Serial-N0. 14,745

2 Claims.

My invention relates to electron discharge devices and in particular to an electron gun structure comprising an improved cathode for use in a cathode ray tube or the like, and is a continuation-in-part of my copending application Serial Number 757,633, filed June 27, 1947, now Patent Number 2,443,916.

A conventional type of cathode ray tube has an electron gun structure comprising in part a tubular cathode enclosing a heater filament and spaced critically from a control grid. Axially spaced along the gun from the control grid is a focusing grid plate, a first anode cylinder and a second anode cylinder. These structures when maintained at appropriate electrostatic potentials form a series of bipotential electron lenses which tend to form the electron emission from the cathode into a beam and accelerate and focus the beam on a fluorescent screen or at the end of the tube.

The construction of the cathode-grid structure of a conventional type of electron gun has previously involved the difiicult process of assembling, by hand operation, many small parts in the proper relationships. The process also involves the fiXing of several sub-assemblies in a predetermined spaced relationship involving critical distances conforming to small tolerances.

In practice, the cathode structure for a cathode ray tube or for some types of high frequency tubes having an indirectly heated cathode, comprises a cylindrical cathode tube mounted through an annular ceramic disc. The cathode tube is fixed to the ceramic by flanged rings slipped over each end of the cathode and welded to the cathode sleeve in abutment to the ceramic. Ordinarily, the emitting surface of the cathode is axially spaced from the control grid by a predetermined critical distance within very close tolerances. This cathode-to-control grid spacing is determined by the axial dimension of a spacer element positioned between the top surface of the cathode support ceramic and the control grid plate, as well as, the axial distance between the emitting surface of the cathode and the top surface of the cathode support ceramic. It has been diflicult in the past to fix the cathode tube to its supporting ceramic with the required distance between the emitting surface of the cathode and the upper surface of the ceramic support.

It is therefor anobject of my invention to provide an electron gun structure of improved design.

It is also an object of my invention to provide an electron gun structure comprising a cathode assembly having few parts.

It is a further object of my invention to provide an electron gun structure having a cathode assembly designed for rapid and accurate construction.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing, in which:

Figure 1 is an elevational view partially in section of a portion of an electron gun structure incorporating the cathode assembly according to my invention;

Figure 2 is a sectional view of a cathode assembly according to my invention;

Figure 3 is a sectional view in elevation of an apparatus for the assembling of the cathode structure according to my invention;

Figure 4 is a sectional view in elevation oi a modification of a cathode assembly and a device used in its construction according to my invention; and

Figure 5 is a sectional view in elevation of modification of a cathode assembly.

Referring to Figure 1 there is shown an electron discharge device having a glass envelope l0 closed at one end by a glass stem l2. This end of the discharge tube It! is enclosed by a conventional base structure I l having base pins l6 fixed thereto. Through the glass stem 12 of the tube are sealed lead pins l5 to support the electrode structure within the tube and for forming conductive paths thereto. Fixed to two of the stem leads I 5 are two ceramic support side rods l8. Mounted on the side rods I 8 immediately above the stem portion [2 is a control grid cylinder 20 coaxial with the tubular envelope 10 of the discharge device. The upper end of cylinder 20 is closed by a grid plate 22 having at its center an aperture 24. Also, mounted on the support ceramic side rods 18 and axially spaced along the tubular envelope 10 from the cylinder 20 is a tubular first anode electrode 26 partially shown in Figure l. v

Mounted within the control grid cylinder 20 is a cathode tube 28 to provide a source of electrons within the tube. The tubular cathode electrode 28 is closed at its top by a cap 29 closelyspaced from the grid aperture 24 and coaxial therewith. Upon the top of cathode cap 29 is deposited preferably a mixture of alkaline earth metal oxides to provide a source of electrons when heated to an appropriate temperature.

For maintaining the electron emitting surface of the cathode cap 29 at the desired temperature, a heater filament 25 is enclosed within the cathode tube 28. Passage of current through the filament 25 maintains the emitting surface of cathode cap 29 at a temperature sufficient to provide an emission of electrons for tube operation. With proper potentials applied to

electrodes

22 and 26 an electrostatic field is established which will form an electron beam. The electron beam may be further focused and accelerated by other electrodes, not shown, to perform any desired function. Such an electrode assembly structure as shown in Figure 1 may be utilized in a cathode ray tube or in any other type of electron beam tube. Furthermore, the type of cathode structure to be described below may be used in other types of discharge devices and should not be considered as confined, by its operation and design, to a tube having a structure similar to that of Figure 1.

Figure 2 shows a preferred form of a cathode assembly similar to that described in Figure l. The cathode assembly of Figure 2 comprises a tubular cathode sleeve 28 having one end closed by cap 29 fixed thereto. The tubular cathode is supported by an annular insulating ceramic disc 36, having an opening or aperture 3! at its center. The tubular cathode sleeve 28 is mounted within the apertured portion 3|, so that the insulating support member 38 fits the tubular walls of the cathode 28 at a portion between the ends of the cathode tube. Cathode tube 28 is also preferably mounted coaxial to the ceramic disc 30. Means are provided for locking tubular cathode 28 to the insulating support 38 in order to prevent any relative movement axially between tube 28 and disc 38. These locking means preferably comprise peripheral ribs or embossments 38 and 40 which are pressed outwardly from the sur- 1 ace of the tube 28, respectively below and above the ceramic support 38. The ribs or

embossments

38 and 48 are forced outwardly until they abut against the ceramic 88 to tightly loci: cathode tube 28 within the aperture 3|.

The outwardly projecting

ribs

38 and 48 on the cathode sleeve 28 may be formed in various ways. Also, it is not felt that the structure of Figure 2 need necessarily be limited to the particular type of embossment or ribs shown. It is conceivable that any type of projection from the surface of the cathode tube 28 may be substituted for the ribs 38 and 40. For example, the outwardly extending

projections

38 and 48 may take the form of flaps cut in the wall of the cathode 28 and bent sharply outward both above and below the ceramic 30 to tightly hold the ceramic to the cathode tube 28.

In Figure 3 there is disclosed a device and method for expanding the walls of the tubular cathode to form the projecting ribs 38 and 40. In Figure 3, is a cathode sleeve 42 similar to cathode 28, of Figures 1 and 2. Sleeve 42 may be formed by using a single piece of metal and with the proper handling the metal may be drawn into a one piece cup having an enclosed end 49. The cup is threaded through the apertured center of the ceramic support disc 38. A spacer block 48 is used having

apertures

45 and 41 therethrough. The opening 47 in the upper side of the spacer block 46 is shown in Figure 3 to be circular and of a size that the ceramic disc 38 may be fitted coaxially therein. The opening 45 is also a circular opening coaxial with aperture 41, and is of a size to freely receive the closed end of the cathode tube 42. Since the two openings 45 and 4! are of different radii, a shoulder is formed therebetween. The cathode sleeve 42 and ceramic support 30 fitted thereto are placed within the apertured portion of block 46 with the closed end 49 of cathode sleeve 42 enclosed within the apertured space 45 and the ceramic spacer 30 upon the shoulder portion 5|. A tool used for forming the ribs 4| and 43 comprises a sleeve 48 fastened in the ram of an arbor press or a drill press 62.

Floatingly mounted within sleeve 48 is a pin 50 having at its lower end a nailhead shaped part 54-. A washer 52 fixed to the upper end of pin 50 prevents the pin from escaping through the sleeve 48. Mounted around the pin 58 and below the nailhead 54 and sleeve 48 are three washers or rings 58, 58 and 80. Washers 56 and 58 are of gum, rubber, and appropriate plastic or of any material having sufficient resiliency that the washers may be deformed by the application of pressure between sleeve 48 and the nailhead 54. Washer 65 may be of a material having relatively no resiliency such as steel but preferably is formed of a hard material having some slight resiliency or give.

The spacer block 45 together with the cathode assembly 8842 fitted therein is placed upon a smooth metal base plate 44 directly under the arbor press Sleeve 43' is then inserted into the tubular cathode 42 by the downward motion of the arbor press 52. Pin 58 and the washers 58 and 558 ride downwardly within the sleeve until the nailhead contacts the inner surface of the closed end 48 of the cathode tube. With the ceramic spacer 38 resting upon the shoulder portion 5! of the spacer 45, further movement of the sleeve 48 forces the cathode cup tightly against the smooth surface 44. When the downward motion of nailheaded pin 58 is stopped, further downward movement of sleeve 48 compresses the washers 58 and 58 and forces washers 5'5 and 58 out at the sides against the wall of the cathode tube 42. Tubular cathode 42 is sufficiently thin to be deformed by the pressure of the washers and 58, when they are compressed between the sleeve 48 and the nailhead 54. The wall of the tubular cathode 42 is pressed outwardly by this action into abutment with the edges of the aperture 3| of the ceramic 3D and is formed into the two peripheral locking rib portions GI and 43. Thus, the ceramic 38 is firmly gripped and tightly held between the expanded portions ll and 43 of the cathode sleeve.

The axial dimension of nailhead 54, as well as,

; that of the hard washer 88 is so chosen that ribs 4! and 43 are pressed outwardly at the proper points to firmly grip the ceramic 38 therebetween. Washer may be made of steel but I have found that improved results are obtained when a hard rubber washer is substituted. The hard rubber washer 58 is slightly compressed, when pressure is applied to the washers 56 and 58, to cause a radial expansion thereof. This slight expansion of the hard washer 50 causes it to fit tightly within the tubular cathode 42, while the rib portions 4| and 43 are being formed. This has an advantage, in that, during rib forming operation, there is no free space existing between the washer 68 and the inside of the cathode tube 42. This prevents the softer rubber of washers 58 and 58 from being forced between washer G0 and the tube wall, and thus reduces excessive wear on washers 5B and 58.

In Figure 1, it is seen that the cathode cap 29 is spaced from the grid plate '22. This cathodeto-grid spacing is rather critical and should very closely conform to a predetermined distance. Cathode 28 is spaced from the grid plate 22 by a spacer ring or eyelet 32. The cathode-to-grid spacing is determined by the axial dimension of the annular spacer ring 32 as well as the distance between the upper surface of the support ceramic 38 and the electron emissive surface 29. It can be seen from Figure 1 that the critical cathodeto-grid spacing depends upon the accuracy with which the annular spacer 32 is made, as well as, the accuracy with which the cathode tube 28 is positioned relative to the ceramic disc 32.

In Figure 3, the spacer block 46 is chosen with an axial depth of aperture 115 which will provide the required distance that the end 49 of the cathode is to be positioned from the surface of the support ceramic 3c. The use of the arbor press 92 forces the cathode sleeve 42 tightly against the smooth surface 44 and when the ceramic disc 39 is suported by the shoulder portion 5|, the proper distance between the closed end 49 and the ceramic 30 is maintained while locking ribs 4| and d3 are formed.

Figure 3 thus discloses a method as well as a means for accurately positioning the cathode tube 42 relative to its supporting ceramic 30 and for locking the cathode assembly together. This method of assembling the cathode sleeve 42 and its ceramic support 39 eliminates the use of other elements and parts, similar to the flange ring 58 of Figure 4, for example, which have been used in the past to lock the supporting ceramic to a cathode sleeve. Furthermore, the positioning of cathode G2 at the predetermined relationship to its supporting ceramic 30 and the locking of cathode 415;. to its supporting ceramic 30 may be accurately and simply accomplished by one operation.

The design of the cathode disclosed in Figures 1, 2 and 3 should not necessarily be limiting, as it is possible to use this method of locking a cathode sleeve to a ceramic, with cathode structures of different design. For example, in Figure 4 there is disclosed a cathode sleeve 64 closed at one end by a cap 55. A flanged washer 68 is slipped over the open end of the cathode and welded at a predetermined position to the outer surface of the tubular cathode 54. The position at which the flanged ring 98 is fixed to the cathode sleeve determines the spacing between the ceramic 39 and the activated surface on top of the cathode cap 56. The ceramic disc support member 30 is slipped over the open end of the cathode sleeve E i until it abuts against the flanged ring 38 and is locked, in this position, by forming a rib or embossed portion or portions 10, projecting outwardly to firmly press ceramic disc 30 tightly against the flanged ring 88 and also prevent any axial movement between the ceramic 30 and the cathode sleeve 65. The embossment l9 placed in the cathode wall may be formed by a tool similar to that shown in Figure 3. For example, the tool may comprise of a stationary sleeve 12 surrounding a pin 74 having a nailhead 76 at one end. Between the nailhead l6 and the adjacent end of sleeve 12 is positioned a resilient washer 18, preferably of deformable rubber. The sleeve 12 together with the pin 14 and the washer I8 therebetween is inserted into the open end of cathode sleeve 64 at an appropriate distance. The inner pin is then forced downwardly while the sleeve 12 is held stationary. The downward motion of the nailhead 16 tends to compress the resilient washer 18 between it and sleeve 12. The thin wall of the cathode sleeve 64 will bulge outwardly and form the ribbed or embossed portion 10.

Figure 5 shows a modification of the cathode assembly shown in Figures 1-4. This cathode sleeve 80 may consist of a metal tube open at both ends, one end of which is closed by a cap 82. However, as shown in Figure 3 the cathode tube of Figure 5 may also be drawn from a single metal piece, so that a cathode cup is formed closed at one end. Such a drawing operation would eliminate additional structure, such as cap 82 and assembly operations to fasten it to the cathode tube. The drawing may be done with proper handling in a single operation. A ceramic support disc 54 is used in the modification of Figure 5. The support 34 has an open center and is coaxially mounted on the tube 89 by slipping the ceramic over the open end of the cathode tube.

A groove 85 is channeled in the surface of the central aperture of the ceramic support 86. When the ceramic o l is properly positioned on the cathode sleeve 80 an embossment or rib 88 is formed in the tubular cathode wall in a manner that the rib 38' will bulge outwardly and project into the channeled groove 86. Rib 38 may be formed in any desired manner such as that suggested in the method disclosed relative to Figure 4. However, the wall of the metal is bulged outwardly to such an extent that the metal of the wall is made to tightly fit into the channeled groove 86. If desired, rib portions may be formed above and below the ceramic disc 84 similar to embossments 33 and iii of Figure 2. However, the rib 85, if properly formed, is sufiicient to firmly lock the ceramic 8A to the cathode tube 80.

While certain specific embodiments have been illustrated and described, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What I claim as new is:

l. A cathode electrode assembly for an electron discharge device, said cathode assembly comprising a cathode tube, an insulating support having an aperture, said aperture having a channel formed in the inner surface thereof, said cathode tube coaxially mounted within said aperture, and means locking said cathode tube to said insulating support, said locking means including a portion of the wall of said cathode tube pressed outwardly into engagement with said channel.

2. A cathode electrode assembly for an electron discharge device, said cathode assembly comprising a cathode tube, an annular insulating support disc coaxially mounted between the ends of said cathode tube, said annular disc having an aperture therethrough and a peripheral groove in the surface of said aperture, and means locking said support disc to said cathode tube, said locking means including a portion of the wall of said cathode tube pressed outwardly as a rib into engagement with said peripheral groove.

JOSEPH KELAR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS- Number Name Date 2,067,967 Kniepen Jan. 19, 1937 2,244,358 Ewald June 3, 1941 2,306,018 Fentress Dec. 22, 1942 2,393,057 OLarte et al Jan. 15, 1946 2,405,399 Bugg et al Aug. 6, 1946 2,417,202 Hull et al Mar. 11, 1947 2,460,580 Huber Feb. 1, 1949