US2535307A - Grid-controlled electron tube - Google Patents

Description

Dec. 26, 1950 A. H. MANKIN EI'AL GRID-CONTROLLED ELECTRON TUBE 2 Sheets-Sheet 1 Filed April 5, 1946 ARTHUR ff lfA/v/d/v 0/1 via 5. Ju/vJTE/N INVENTOR S B A, ATTOZfEY Dec. 26, 1950 Q A. H. MANKIN ETAL 2,535,307

GRID-CONTROLLED ELECTRON TUBE Filed April 5, 1946 2 Sheets-Sheet 2 ARTHu'R HMANKIN DAVID E. Jz/NJrE/N' INVENTORS ATTO R N EY Patented Dec. 26, 1950 UNITED STATES PATENT OFFICE GRID-CONTROLLED ELECTRON TUBE Application April 5, 1946, Serial No. 659,684

17 Claims. (01. 250--27.5)

This invention relates to electron discharge tubes, and more especially to tubes of the gridcontrolled type.

A principal object of the invention is to provide an improved grid structure for electron discharge tubes, whereby improved tube characteristics are obtained. Amongst these improved characteristics are sharper plate current cutoff, higher power output with comparatively lower plate voltage than heretofore required, and extension of the utility of the tube into the higher frequency ranges.

Another principal object of the invention is to provide a novel grid structure whereby the potential gradient throughout the grid openings or windows is rendered more uniform.

Another object is to provide a grid structure which is so designed that the greater part of the electrons from an associated cathode, arrive at the grid plane all in substantially the same phase. As a result, it is possible to design tubes for very high frequency use wherein the tube functions by reason of the electron transit time between a cathode (either actual or virtual) and a succeeding foraminous grid.

A. feature of the invention relates to an improved grid structure for electron tubes wherein each major grid opening or window is provided with special field-forming means for insuring that the potential gradient is substantially uniform throughout the plane of the window.

Another feature relates to a novel grid structure having spaced grid wires between which an electron stream is arranged to pass, each of said wires having supplemental and substantially coplanar wires for controlling the potential fields in the plane of said grid wires.

A further feature relates to a grid structure for electron tubes having a plurality of spaced control wires, ordinarily referred to as gridlaterals, which are arranged in groups, with the spacing between groups very much greater than the spacing between individual wires of each group.

A further feature relates to a grid structure for electron tubes wherein each main grid lateral is provided with a pair of spaced auxiliary laterals. In accordance with this feature, the main laterals and the associated auxiliary laterals can be statically biased with relation to each other so .that the potential field between the main laterals is rendered substantially uniform.

Another feature relates to an electron discharge tube having at least one grid, such for example as the signal control grid, constituted of grid laterals arranged in spaced groups of three 2 or more per group. Each group has certain of its laterals biased or energized to a different extent from the remaining groups so as to maintain the potential field within the grid windows substantiaily uniform.

A still further feature relates to the novel organization, arrangement and relative interconnection of parts which cooperate to provide an improved grid-controlled electron tube.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

In the drawing which illustrates certain preferred embodiments by way of an example:

Fig. 1 is ageneralized view of two conventional spaced grid laterals used in explaining the principles of the invention.

2 i sa composite structural and graph diagram to explain the usual potential field distribution with the conventional grid laterals.

Fig. 3 is a modification of the grid laterals according to the invention.

Fig. 4 is a composite structural and graph diagram to explain the functioning of a grid according to theinvention.

Fig. 5 is an elevational view of a simple flat grid embodying the invention.

Fig. 6 is a modification of Fig. 5.

Fig. 7 is a view of an electron tube mount having the novel grid structure according to the invention.

Fig. 8 is aplan view of part of Fig. 7 to explain a preferred manner of assembling the composite grid laterals to coplanar form.

Fig. 9 is an enlarged view of part of Fig. 7.

Fig. 1G is a schematic circuit diagram showing a typical amplifier tube embodying the invention.

Fig. 11 is a view, partly sectional, of a cathoderay tube embodying certain features of the invention.

'Heretofore, in the design of grid-controlled electron tubes employing control grids of the conventional parallel grid wire type, it has been known when a steady direct current potential is appliedto or assumed by the grid, the potential distribution in the planar space between, adjacent laterals is notuniform. We have found that this non-uniformity of inter-lateral potential gradient is the cause of certain drawbacks in gridcontrolled tubes. One of these drawbacks is the lower ratio of mutual transconductance to plate current that is obtained because of the rounded or gradual cutoff characteristic of ordinary grid structures, as distinguished from the ideal or either side of this central region.

, laterals ca.

sharp cutoif of the current tending to traverse the grid plane. These drawbacks become of increasing importance when the tube is used as a power amplifier or in the higher frequency circuits, particularly those wherein electron transit times between certain electrodes are of importance. However, in certain of its aspects, the in vention is applicable to any grid-controlled tube where uniformity of potential in the plane of the grid is a desired characteristic.

Referring to Fig. 1, there is indicated a pair of spaced parallel wires 19 Whose spacing is D and whose length is E. These wires may represent therefore a pair of spaced grid laterals such as are employed in any usual form of wire wound grid or planar grid. When such a grid is interposed in the path of an electron stream which for example is perpendicular to the plane of the laterals, and the grid is subjected to a direct current or other energizing potential which is different from the free potential existing in the plane of the grid due to the potentials on various electrodes adjacent to the grid (which potential the grid tends to assume when floating), the potential field between the conductors is far from uniform. Thus, as shown in Fig. 2, the potential or the space in the region between the wires 29 is represented by the curve it. The solid curve of Fig. 2 is the potential which obtains with grid wires of finite radius or thickness, whereas the dotted curve is that theoretically obtained with grid wires of zero radius or thickness. From this curve, it will be seen that electrons arriving at the plane of the grid, will be subjected to dilferent retarding or accelerating actions dependent upon the portion of the cathode from which they were emitted. In other words, considering the central region between the grid wires b (Fig. 1) arriving electrons will be subjected to a smaller retarding force, than the force acting on the electrons on If the tube operates on the electron transit time principle, this inequality of actual inter-wire potential seriously limits the high frequency range at which the tube can be used, since the transit time for a given electron will be dependent upon the position of that electron within the grid aperture. Furthermore, this inequality militates against a very sharp plate current cutofi characteristic.

We have found that by supplementing the main grid conductors or wires 1) with auxiliary or closely adjacent conductors in substantially the same plane, and by suitably energizing the wires in groups, it is possible to modify the interwire field characteristic so that it becomes substantially flat. One arrangement for accomplishing this is diagrammatically shown in Fig. 3, wherein each grid lateral may be considered as being tri-part and composed of three strands of wires 11, b, a. The wires in may be considered as auxiliary field controlling wires for the main grid Preferably, wires a are equally and closely spaced on opposite sides of the cooperating wire b, the spacing being sufficient to prevent short-circuiting when the wires are in the same plane. The wires 17 of all the sets may be connected to a suitable negative biasing direct current source indicated as battery H, while the wires a are, together, connected to a negative direct current biasing source l2 which may be lower in negative potential than the source ii. For example, if, in a conventional tube, the usual grid wires are biased negatively nine volts for linear operation, then, in the grid according to Fig. 3, wires b may be biased to more than 9 'IPI all

4 volts (e. g., '15 volts), while the wires a may be biased to substantially less than -9 volts (e. g., -1 volt).

With such an arrangement, the potential field in each grid window, is substantially uniform as indic ted by the curve l3 (Fig. i). The equation for the potential 12 at any given point in the region bounded by succeeding sets of the tri-part grid wires is approximately,

:L. 1 a )l" wherein m is the potential applied to wires 1); m is the potential applied to wires a; D is the distance between the wires b; h is the distance between wire I) and the adjacent wire a; and the exponent n is the ratio of oz to w (distances are measured between wire centers).

It will be noted that, even though grid wires 0. may be positive, the presence of negative potential on wires 2) causes a deflecting field which tends to reduce the current drawn by wires a to an extent which may maintain the current drawn thereby substantially zero even though the wires a be several volts positive. Thus a screen grid built according to this coplanar array principle may be designed to draw no current, yet provide the desired accelerating and shielding function of an ordinary screen grid. In this application of the invention, the plate should be maintained more positive than the grid wires a, or other means should be provided to reduce secondary emission from the anode in order to maintain the screen current substantially zero.

It will be understood that the invention is not limited to any particular manner of mounting each set of three grid wires a, b, a, nor to the use of exactly three wires, since the approximately fiat field configuration may be obtained by arrays of 2, 3, 4, 5, or more wires in groups, each wire being suitably energized. In fact the more wires used in each group, the closer is it possible to obtain a perfectly flat field in the window between the groups.

In Fig. 5 there is shown, by way of example, a simple iiat planar grid comprising a pair of side rods or uprights it, it, across which are transversely fastened the sets of tri-part grid wires 16, each set consisting of three wires a, b, a, as above described. In order that different potentials can be applied to the a and b wires of each set, the side rods it, i5, can be composed of an insulating material, the :1 wires being connected to a common conductor i7, while the 1) wires are connected to a common conductor iii. If desired, the side rod it may be undercut to receive the a wires, and the other side rod it can be undercut to receive the respective 12 wires as indicated in the magnified View of Fig. 6.

Referring to Figs. 7 and 8, there is shown one typical form of electron tube mount which embodies ccplanar tri part grid laterals according to the invention. in Fig. '7, there is indicated an electron-emitting cathode it which is preferably in the form of a flattened tubular metal sleeve having its opposite flattened sides coated with electron-emissive material in the usual manner. Surrounding the cathode i9 is a heli ally wound grid 29 consisting of a fine wire helically wound around, and with the turns fastened to the respective side rods 2 i, 22. Preferably, the grid 29 is formed on a winding mandrel so as to have a substantially flattened tubular contour as indicated in Fig. 8. Also surrounding cathode I9 is another grid 23 consisting of two fine wires hell--v cally woundaroundcorrespondingside rods 24,

25; The grid 23likegrid 2% is of elongated fiat- ,tened tubular peripheral shape and with the minor axis substantially equal to the minor axis of the grid 28. The two grids 2t and 23 are assembled between the upper and lower mica spacers 26, 2i, so as to preserve the concentricity of the grids with respect to the cathode. As shown more clearly in Fig. '7, the grids are so mounted that each turn of grid 2%! is located between two adjacent turns of grid 23. It will also be observed that in winding the grids 23, the

turns 23a and 2319 (Fig. 9) are preferably wound with a minor spacing 25: which corresponds to the spacing between a wires (Fig. 4). Likewise, the turns of grid 23 and 2e are wound with a turn spacing D. Consequently, when the grids are properly assembled between the discs 2% and 21, the successive individual turns of grid 28 are located equally between each cooperating pair or closelyspaced turns of the grid 23. Since the cathode i9 is of flattened tubular form, the greater part of the emission takes place through the coplanar sides of grids 2i and 23, as shown by the dotted lines in Fig. 8. If desired, the end sections of cathode is may be left uncoated.

One or more additional grid electrodes such as shield grids, suppressor grids and the like, may surround the coplanar grid unit 26-23, and a suitable plate or anode 28 may be provided for the mount.

Referring to Fig. 10, there is shown a typical circuit arrangement in which the tube of Fig. '7 may be employed. The tube-may have an enclosing envelope 29 for the electron assembly or mount such as that shown in Fig. 7, and the parts of Fig. corresponding to those of Fig. '7, bear the same designation numerals. Merely for simplicity in the schematic showing of Fig. 10, the grids 2B and 23 are shown as laterally displaced, but it will be understood that this is intended to represent any coplanar arrangement such as shown in Figs. 5, 6 and '7 or 8. The signal input circuit comprising for example the input coupling transformer 35, has one of its secondary terminals connected through the negative biasing battery 3| to the grid 29, that is, to the 12 wires described in connection with Figs. 3 and l. The opposite terminal of the secondary of the input transformer is returned to the grounded cathode I s in series with an additional negative biasing battery 32. A suitable tap from the secondary of the input transformer is connected to the grid 23 which therefore corresponds to the a wires (Fig. 3). With this arrangement, it will be seen that the a wires (grid 23) are fed with a smaller signal and are supplied with a smaller negative bias than are the b wires (grid 2%). Consequently, the potential field in the space D (Fig. 9) between successive coplanar grid arrays or windows is substantially uniform.

While Fig. 10 shows a tube or" the pentode type comprising a shield grid 33 and a suppressor grid 34, it will be understood that this tube may be either of the triode, tetrode or other multi-grid kind.

While in the foregoing description, reference has been made to a grid structure wherein the grid wires are arranged in spaced groups of three wires per group, it will be understood that each group may consist of a greater number than three so as to render even more uniform the potential distribution between adjacent groups.

Fig. 11 shows the inventive concept embodied in a cathode-ray tube 35 of any well-known con struction including for example the usual electron gun 36, and a beam deflector system 31 comprising one or more sets of deflecting elements. Suitably mounted between the fluorescent electron gun 3t and the deflecting system 3'! is an annular electrode array comprising three concentric and substantially coplanar rings 39, 40 and 1. The ring corresponds functionally to the grid wires b in the embodiments of Figs. 1-10, while the rings ie and ii correspond respectively to the associated auxiliary grid wires a, a. The rings id and :3! are connected together and thence to a common lead-in conductor 62, as is the ring $9 with its individual lead-in conductor 43. The conductors s2 and 43 are connected respectively to suitable potentials as described above so that the potential field within the plane bounded by the ring il is substantially uniform.

The embodiments of the invention described herein are designed to operate with electrons, however the principles of our invention may be applied to any system intended to be operated with suitable charged particles.

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

What is claimed is:

1. A grid system for electron tubes and the like, comprising main grid wires defining a main grid opening through which a stream of charged particles is to pass, and means to maintain the potential field in the plane of said opening substantially uniform throughout, the last-mentioned means consisting of a group of auxiliary grid wires mounted on each side of the main grid wires and insulated therefrom.

2. A grid system for electron tubes and the like comprising means defining a main grid opening through which an electron stream is to pass without obstruction, said means including main conductive members having closely adjacent thereto and on each side thereof and spaced and insulated the "chem auxiliary conducting members.

3. A grid structure for electron tubes and the like comprising a plurality of groups of grid wires with the groups spaced relatively far apart to define main grid openings, each group comprising a plurality of closely spaced and substantially coplanar individual wires, the spacing of said wires in each group being much smaller than the spacing between the groups, for the purpose of maintaining a uniform potential held throughout substantiall the entire region between the groups.

4. A grid structure for electron tubes and the like comprising a plurality of groups of grid wires with the groups spaced relatively far apart to define main grid openings, each group comprising a set of three closely spaced sub stantially coplanar wires, the spacing between the wires of each group being smailer than the spacing between the groups for the purpose of maintaining a uniform potential field throughout substantially the entire region between said groups.

5. A grid structure according to claim 4 in which the central wire of each group is provided with a separate lead-in conductor and the adjacent two wires of each group are connected together and provided with a common lead-in conductor for applying respective and difierent direct current biasing potentials to the central wire of each group as compared with the adjacent two Wires of each group for the purpose of maintaining said uniform potential field.

6. A grid structure for controlling an electron stream and the like, comprising a plurality of spaced groups of grid laterals, each group com: prising a central lateral and a pair of adjacent auxiliary laterals on opposite sides thereof, all the laterals of each group being substantially coplanar in a direction transverse to the arriving electron stream to be controlled, the wires of each group being closely spaced as compared with the spacing between groups for the purpose of maintaining a uniform potential field throughout substantially the entire region between the groups.

7. A grid structure comprising a pair of spaced parallel uprights, groups of laterals extending across said uprights, said groups being spaced apart along the length of said upri hts to define a series of grid openings through which electrons pass for control purposes, each group comprising a central wire and a pair of wires on opposite sides thereof, means connecting the central wires or" the groups to a common lead-in conductor, and means connecting said pairs of wires to a common lead-in conductor, the wires of each group being closely spaced with respect to the spacing between groups for the purpose of maintaining a uniform potential field througln out substantially the entire region of each or" said grid openings.

8. A grid system for electron tubes comprising a helically-wound grid section, another helicallywound grid section, means to support said sections around a common center and with the wires of one section substantially coplanar with corresponding wires of the other section throughout a substantial part of their lengths, one grid section having its turns arranged in spaced groups with each group comprising at least two closely spaced turns, and with a turn of the other grid section located between each of said two closel spaced turns, to form a series of spaced tri-part grid laterals with the spacing between the three wires in each tri-part lateral being much less than the spacing between successive tri-part laterals for the purpose of maintaining a uniform potential field throughout substantially the entire region between each set of tripart laterals.

9. A grid system for electron tubes comprising a first helically-wound grid section with the helical. turns arranged in relatively widely spaced groups to define main grid openings, each group comprising a least two closely spaced turns, a second helically-wound section surrounding the first grid section and ha -ing single turns spaced apart approximately the width or" said grid openings, and means to support said grid sections so that each turn of the second section is located between the two closely spaced turns of the first section and subs antially coplanar therewith for a substantial part of the length of each turn, to form a series of relatively widely spaced tri-part grid laterals for the purpose of maintaining a uniform potential field throughout substantially the entire region between successive tri-part laterals.

10. A discharge device, comprising, a source of charged particles, 0. pair of grid wire groups forming a window extending substantially transverse to the direction of travel of said particles, each wire group consisting of a main grid conductor and a pair of adjacent and substantially coplanar auxiliary conductors on opposite sides of the main conductor, a lead-in conductor connected in common to all the main grid conductors for applying one electrical bias thereto, and another lead-in conductor connected in common to all the auxiliary conductors to apply a diiferent electrical bias thereto.

11. An electron discharge device comprising an electron-emitting cathode, a grid having a series of grid windows extending transversely to the electron trajectories of said cathode, said grid comprising a series of conductor groups with the groups spaced apart to define said windows, each group comprising a main grid conductor and a pair of closely adjacent and substantially coplanar auxiliary conductors, and a source of biasing potential connected to said main and auxilary conductors to energize said main and auxiliary conductor with diiferent direct current potentials proportioned with respect to each other for the purpose of maintaining the potential field within each window substantially uniform throughout.

12. An electron dischage device according to claim 11 in which each of said groups of conductors comprises a central conductor and at least one pair of closely adjacent conductors on opposite sides thereof.

13. An electron discharge device comprising an electron emitting cathode, a grid having a series of substantially coplanar grid windows extending transversely to the electron stream from said cathode, each window being defined by two relatively widely spaced groups of grid wires, each of said groups having a main wire and at least two closel adjacent auxiliary wires for maintaining the potential field in each grid window substantiall uniform throughout.

14. An electron discharge device, comprising, an electron-emitting cathode, a grid having a series of substantially coplanar grid windows extending transversely to the electron streams from said cathode, each window being bounded on opposite edges by a set of three grid laterals with the spacings between the three laterals of each set being very much smaller than the width of said windows, means connecting all the central laterals of each set to a common lead-in conductor for applying an electrical bias thereto, means connecting the remaining laterals of all sets to another common lead-in conductor to apply a different electrical bias thereto for the purpose of maintaining the potential field in each grid window substantially u1..form throughout.

15. Electric signal apparatus, comprising, an elecJron discharge device having an electronemitting an output anode, a control grid system for the electrons flowing between cathode and anode, said grid system comprising main grid wires defining a main grid opening through which the electrons pass, each main grid wire having auxiliary grid wires on opposite sides thereof and spaced from the main grid wire a distance very much less than the spacing between successive main grid wires, means to apply a predetermined electrical bias to the main grid wires, and means to apply a different electrical bias to the auxiliary grid wires for the purpose of maintai 1mg an electrical potential field in the main grid opening which is substantially uniform throughout.

15. Electric signal apparatus according to claim 15, in which said main and auxiliary grid wires are substantially coplanar, and the auxiliary grid wires are biased negatively to the cathode to a lesser extent than the negative biasing of the main grid wires with respect to the cathode.

17. Electric signal apparatus according to claim 16, in which a source of input signals is connected across said control grid system and the cathode.

ARTHUR H. MANKIN. DAVID E. SUNSTEIN.

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

Number 10 UNITED STATES PATENTS Name Date Trimble Aug. 21, 1923 Pidgeon Aug. 22, 1933 Heising Mar. 22, 1938 Toulon Sept. 12, 1939 Hansen Jan. 8, 1946 Mouromtseff et a1. Feb. 5, 1946

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