US3007075A

US3007075A - Cathode

Info

Publication number: US3007075A
Application number: US25601A
Authority: US
Inventors: Leonard D Schwender
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1960-04-29
Filing date: 1960-04-29
Publication date: 1961-10-31
Anticipated expiration: 1978-10-31

Description

Oct. 31, 1961 Filed April 29, 1960 L. D. SCHWENDER 3,007,075

CATHODE 2 Sheets-Sheet 1 NV ENTO R Leona/d Z2 Sc/lavender Oct. 31, 19 D. SCHWENDER CATHODE 2 Sheets-Shet 2 Filed April 29, 1960 Uillllfi ware Filed Apr. 29, 1960, Ser. No. 25,601 7 Claims. (Cl. 313-346) This invention relates generally to electron tubes and more specifically to electron tube cathode electrodes.

It is now recognized that the prior art practice of spraying cathode sleeves with a coating ultimately suitable for electron emission tends to produce a coating texture which lacks the surface uniformity desirable in many tube ap plications. It is also recognized that a major improvement has been achieved by using a wrap-around coating prepared in the form of a film which is suitable for cutting into small rectangular pieces and attachment to the cathode sleeve through the use of any one of a number of labelling techniques such as the technique taught in United States patent application Serial Number 453,235, filed in the name of Kerstetter et al. on August 31, 1954 and assigned to the same assignee as this application. Other labelling techniques may also be used. For example, an adhesive may be applied to either the cathode sleeve or the coating wrap and the cathode sleeve rotated while in contact with the wrap. Also by wetting either the cathode sleeve or the coating wrap with a suitable solvent, it is possible to bring the wrap close to the cathode sleeve and use a puff of air to attach the wrap in position.

Regardless of the labelling technique used, wrapped cathodes at present involve the use of a rectangular shaped piece of coating film which when wrapped around the cathode sleeve tends to form a vertical seam or undesirable discontinuity in coating uniformity. Tolerances are usually established which will not allow the seam discontinuity in the form of an overlap seam. Though under optimum conditions it is best to abut opposite edges of the wrap so as to provide a gapless seam and an absolute minimum discontinuity, manufacturing tolerances must allow for some size variation and thus it has been found desirable to set the tolerance range so as to accept a small gap at the seam of the coating wrap.

In many tube applications it is possible to orient the tes Patent seam of the coating wrap so as to place it immediately opposite a grid side rod or at a position where electron emission density is at a minimum. When so placed, the seam even though of a gap type causes little if any difficulty. Unfortunately, where automatic machines are used for assembling the tube mount it is sometimes difficult to rotationally pre-orient a cylindrical cathode relative to the grid. Thus it would be desirable to provide a wrap coated cathode having a seam contour which minimizes the need for cathode rotational orientation relative to the grid during tube assembly. It would be desirable further to provide a cathode wrap having a seam contour which minimizes differences in possible electron emission between separate vertical portions of the cathode coating.

Thus it is an object of this invention to minimize orientation problems between the cathode and other electron tube electrodes using a wrap-coated cathode.

It is a still further object of this invention to distribute the possible loss in cathode emission arising from a gap seam in a wrapped cathode over the surface area of the cathode so as to minimize emission variations.

Basically, my invention, in at least one aspect, comprises a cathode base covered with a rhomboidal shaped cathode coating wrap which is applied to the cathode base material so as to form a spiral seam of no more than a single turn.

For a better understanding of the present invention, to-

gether with other and further objects and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the accompanying drawings in which:

FIG. 1 shows a prior art wrapped cathode with vertical seam; and

FIG. 2 shows a top view of a vertical seam wrapped cathode relative to a grid; and

FIG. 3 shows a rhomboidal shaped coating strip about to be applied to a cathode base sleeve; and

FIG. 4 shows a spiral wrapped cathode; and

FIG. 5 shows a spiral wrapped cathode positioned within a grid helix.

In FIG. 1 there is shown a prior art cylindrical cathode sleeve 11 coated with a vertical seamed electron emissive wrap 15. Basically, the emissive coating wrap 15 may comprise a cast film made from the triple carbonates, calcium, barium and strontium, in a cellulose binder. The film may be cast on a large smooth casting wheel of the type used in film fabrication and then stripped when hardened and cut intoindividual 'wraps, each wrap being suitable for enclosing one cathode sleeve. For a more detailed teaching, reference is made to the above-mentioned United States patent application Kerstetter et al.

As shown in FIG. 1, wrap 15, as contemplated by the prior art, is made from a rectangularly cut piece of film which when wrapped may form a gap 17 between adjacent edges 19. When the cathode sleeve 11 is assembled with a grid 21, as shown in FIG. 2, gap 17 in the emissive wrap '15 may appear at a position which affects desirable tube characteristics. For example, gap 17 is shown in FIG. 2 closely adjacent the lateral wires of grid 21 at a point of desirably high emission density. On the other hand if the cathode sleeve were rotated during fabrication so that gap 17 were positioned adjacent the side rods, it seems obvious that the loss of emission area would be minimized because gap 17 then would be oriented relative to the grid so as to be in a position from which few if any electrons are taken. Unfortunately, considerable difficulty and expense is involved in attempting to orient a cylindrical cathode relative to the grid where machine assembly is used. Especially is this true where the assembly machines in question assemble some tube types using prior art sprayed cathodes which do not require pre-orientation.

.In FIG. 3, in accordance with the invention, there is shown a cathode sleeve 11 and a fiat rhomboidal shaped wrap 25 prior to labelling. Wrap 25 is similar to Wrap 15 in FIG. 1 in that both may be made from the same material and both may be applied by similar labelling processes. However, wrap 25 in FIG. 3 differs from wrap 15 in FIG. 1 in that wrap 25 is of rhomboidal shape, i.e., it is cut to include two acute corner angles 27 and two obtuse corner angles 29, while rectangular wrap 15 in FIG. 1 includes four corner angles.

FIG. 4 shows rhomboidal shaped wrap 25 of FIG. 3 after it has been attached to cathode sleeve 11 by any one of the previously mentioned labelling processes. It will be noted that wrap seam 31, in FIG. 4, is spiral in form and that the spiral seam 31 makes approximately one complete turn around the cathode from top to bottom. The rhomboidal shaped wrap of FIG. 4 with its one-turn spiral seam is the optimum shape for minimizing possible loss in electron emission due to orientation of the surface discontinuity of seam 31 relative to the grid.

Referring now to FIG. 5, the cathode of FIG. 4 is shown in mounted position Within a grid 33 comprising grid laterals 35 and a pair of side rods 37. In the particular cathode-grid arrangement shown in FIG. 5 the major areas of high emission density on coating 25 are those areas most closely adjacent grid laterals 35, and it is in these areas that the vertical seam 17 of a FIG. 1 type cathode causes the greatest difficulty. When rhomboidal shaped wrap 25 with its spiral seam 31 is used, however, it can be seen that the coating areas most closely adjacent grid laterals 35 contain only a small portion of the wrapped seam 31 and that the major portion of wrap seam 31 is positioned in less critical areas in which lower emission densities are normally realized. Also in the structure of FIG. 5, rotational orientation of cathode 11 relative to grid 33 makes little if any difference as far as emission characteristics are concerned. In other words, cathode 11 with its spiral seam wrap, as shown in FIG. 5, may be assembled on a tube mount by a machine incapable of orienting the cathode relative to the grid, without concern as to the final position of wrap seam 31 relative to the grid laterals 35. Regardless of the rotational position of cathode 11 there is always a given length of wrap seam 31 in the critical emission areas and this length of wrap seam 31 changes little from tube to tube. Though it is true that in one tube the wrap seam 31 may appear at the top and the bottom of the critical areas and in the next tube the wrap seam 31 may appear more closely centered in the electron window, in most tube types the vertical position of the spiral seam 31 relative to the critical cathode emission area has been found to be relatively unimportant.

While the structure of FIG. has been shown with a spiral seam 31 of one complete turn, it is to be noted that a spiral seam 31 of less than one turn also provides substantial advantages over the vertical seam prior art structure as shown in FIG. 1. Thus, in some tube types it may be desirable to provide a rhomboidal shaped wrap with a seam of approximately a half turn or some other portion of a whole turn. Though the cathode rotational orientation problems would not be completely minimized with a cathode seam of less than a full turn, the shortened spiral seam, if by chance it became positioned in a critical emission area upon assembly, would provide a critical area emission considerably improved over a cathode of the prior art vertical seam type where the vertical seam was positioned in a critical area.

The exact rhomboidal shape ultimately used in any given tube type may prove to be a compromise between a solution to the critical area emission problem and the problem of attaching the wrap to the cathode by a given labelling process. The cut cathode wrap, he it of a prior art rectangular shape or a rhomboidal shape, as taught herein, is of a fragile nature, and it has been found that in some films it is difiicult to wrap a sharp cornered rhomboidal shape without excessive shrinkage or loss arising from either film breakage at a relatively sharp corner or poor bonding between the sharp corners and the cathode sleeve. Thus, in tube types where such fragile films are necessary, it may be desirable to cut a rhomboidal wrap which makes only a partial spiral seam and accept the variation which arise in emission characteristics from tube to tube in order to realize a wrap shape more easily attached to the cathode sleeve by usable labelling techniques.

Though the invention has been described in connection with a cylindrical type cathode it is to be noted that cathode sleeves or bases of a shape other than cylindrical may be wrapped as taught herein. For example, though sleeves of rectangular cross section are more easily preoriented than cylindrical sleeves, it may be desirable when using a rectangular cross sectioned cathode sleeve to dispense with the orientation problem and use a spiral wrap as taught herein.

Cathode wraps cut to provide a spiral seam of more than one turn are unsatisfactory both from the labelling technique viewpoint and the emission viewpoint. As the spiral seam is lengthened over one turn, the length of wrap seam in the critical area increases with a resulting loss of possible emission over the critical area. Further, even without considering emission characteristics it would be extremely diflicult to attach a wrap of more than one turn without extremely high shrinkage or rate of loss.

The use of a rhomboidal shaped wrap of one turn or less distributes the possible loss in cathode emission from a gap seam over the surface area of the cathode so as to minimize emission variations while at the same time minimizing rotational orientation problems between the cathode and the grid.

While there has been shown and described what is at present considered the preferred embodiment of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the appended claims.

Having thus described my invention, I claim:

1. "In an electron tube cathode of the wrap-around coated type the combination comprising a cathode base sleeve and an attached rhomboidal shaped coating sheet having opposite edges forming a spiral seam, said spiral seam being no longer than one turn around the cathode base sleeve.

2. In an electron tube cathode of the wrap-around coating type the combination comprising a cylindrical metal cathode base and an attached rhomboidal shaped coating sheet having opposite edges forming a spiral seam, said spiral seam being no longer than one turn around the cathode base.

3. In an electron tube cathode the combination comprising a cylindrical cathode base and a spiral wrapped rhomboidal shaped film of cathode coating material, said spiral being no more than one turn.

4. In an electron tube cathode the combination comprising a metal cathode base supporting an attached spiral wrapped rhomboidal shaped film of cathode coating material, said spiral being no more than one turn.

5. In an electron tube cathode the combination comprising a metal cathode base and an attached spiralseamed film of cathode coating material, said spiral seam being no longer than one turn around said base.

6. In an electron tube cathode the combination comprising a metal cathode base suitable for wrapping with a sheet of coating material, and an attached rhomboidal shaped sheet of coating material having opposed edges forming a spiral seam of less than one turn around the cathode base.

7. In an electron tube cathode the combination comprising a cathode coating support base suitable for wrapping with a sheet of coating material, and an attached rhomboidal shaped sheet of coating material having opposed edges forming a spiral seam of less than one turn around the cathode base.

No references cited.