US2844752A - Electron discharge device - Google Patents

Description

July 22, 1958 M. v. mom 2,844,752

ELECTRON DISCHARGE DEVICE Filed March 9, 1956 3 Sheets-Sheet 1 INVENTOR,

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July 22, 1958 I HOOVER 2,844,752

ELECTRON DISCHARGE DEVICE Filed March 9, 195a s Sheets -Sheet 2 25 Q a/ H INVENTOR.

4 1; Marie IlHoover j I:

l I I l ATTORNEY "July 22, 1958 M. v. HO0VE R 2,844,752

ELECTRON DISCHARGE DEVICE Filed March 9, 1956 ,I 3 Sheets-Sheet 3 I NVE NTOR.

Merle IZHoover ,ywwd W TOR NE 1 .diation from the directly heated cathodes.

United States Patent ELECTRON DISCHARGE DEVICE Merle V. Hoover, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application March 9, 1956, Serial No. 570,532

14 Claims. (Cl. 313-307) This invention relates to electron discharge devicesand particularly to improvements in so. called. super-power devices capable of an output of the order of half a million watts or more. This application is a continuation-in-part of my copending application, Serial No. 318,245, filed November 1, 1952.

There are two basic types of super-power tubes. One of these types, the'first type of super-power tube to be developed, comprises a cylindrical beam-former having a plurality of longitudinally arranged slots therein, with an elongated cathode or filament disposed within each cross bar of each T serves to shield a grid element on each side of the vertical portion of the T from the parts of the anode which are radially opposite said grid elements. This type of super-power tube is. described by L. P. Garner in U. S. Patent No. 2,636,142.

One of the factors which limits the performance of the super-power tubes, of both the unshielded and shielded types, is the grid dissipation capabilities, bothv electrical and thermal. The grids of super-power tubes, like the grids of low power tubes, are heated by thermal ra- Because of the mechanical, electrical, and electron optical problems associated with the proper positioning of the grids in super-power tubes, the grid supporting structure used provides only a one or two line contact at each end of the elongated grids, affording only a limited path for conducting heat from the grids. While this grid supporting arrangement has proven to' be the most satisfactory one available, it does not represent an ideal arrangement for conducting heat away from the grid elements.

Another problem which has arisen in connection with the. shielded triode version of the super power tube is that, because of the arrangement of the T-shaped shield, the number of unit triodes which can be placed around a beam former of given diameter has been reduced from, for example, forty-eight to twenty-four. This has necessarily reduced the power output. Increased power output could be obtained by enlarging the diameter of the beam former and consequently the diameter of the anode, but it would also increase the total interelectrode capacitance. This would seriously limit the upper frequency operation of the tube. Since one of the principal reasons for making the shielded triode version of the tube was to provide a substantial decrease in. grid-plate. capacitance, and thus raise the maximum operating frequency of the tube without resorting to grounded grid circuit out- 2,344,752 Patented July 22, 1%58 "ice put, achieving more power at the expense of greater grid-plate capacitance would be undesirable.

In addition, if a tube has a high power output, and especially if the tube has an output of a million watts or more, it is highly desirable that the amount of power necessary to drive the tube be as small aspossible. Reducing the required driving power may be achieved by placing the grid elements closer together to exert a greater influenceupon the flow of electrons between cathode and anode, but in the past such arrangements have resulted in higher grid currents. I

Also, since super power tubes are relatively expensive, anything which can be done to increase the life of the tube would considerably enhance its desirability so far as the purchaser of the tube is concerned.

A principal object of the present invention is to provide an improved power tube capable of large power output and a long useful life.

Another object of the present invention is to provide an improved electrode structure for a power tube which will decrease grid power absorption in the tube.

A further object of the present invention is to provide an improved electrode structure for a power electron tube which more effectively shields the grids from direct thermal radiation by the cathode.

Yet another object of the present invention is to provide an electron tube which makes possible greater power output with a beam former having a given peripheral surface than has been heretofore practicable.'

A still further object of the present invention is'to reduce interelectrode capacitances in an electron tube.

Still another object of the present invention is to provide an electron tube capable of high power output and in which small excitation power will drive the tubeto its full output capabilities.

An ancillary object of the present invention is to provide a shielded triode having improved electron-optical characteristics.

Briefly, an electron tube made in accordance with one feature of the present invention comprises a beam former electrode which has at least one undercut recess or channel. in a surface thereof, and a cathode extending along and within said channel and having a width approximately equal to the width of the aperture of said channel. In accordance with another feature of this invention, a pair of grid elements are mounted adjacent the bea'm former, one on each side of said channel to form a unit triode structure with the tube anode.

In actual practice, however, more than one unit triode is usually used, the beam former electrode being either planar or cylindrical inform, and having a plurality of spaced apart undercut channels, with a cathode extending along and within each of the channelsand grid elements extending along the sides of the channels.

In providing the beam former with undercut channels rather than rectangular channels as described in U. S. Patents 2,544,664 and 2,636,142, important mechanical and electrical advantages are achieved.

Increased power output in a tube of given beam former diameter may be achieved if undercut channels or slots are used. For example, each of 'the channels shown in Garner et al., 2,544,664, may be undercut to accommodate larger cathode elements. With all other structural features unchanged, the use of larger cathode elements will ,result inrnore space current and, thus, increased power output. Alternatively, and in some ways preferably, undercut slots of the same size and accommodating the same size cathode elements as those shown in Garner et al. may be used, in which case the grid elements on eachside of the channels may be moved closer together. Accordingly, a larger number of the unit triodes may be spaced about the circumference of the beam former.

The above described structures will enable an increase in power output over a tube constructed according to Garner et al. of up to 75%.

The use of an undercut channel in a unit triode which is otherwise substantially identical to those disclosed in Garner et al., 2,544,664, will also result in a substantial improvement in the amplification factor or mu of such unit triode. The reason for such improvement in amplitication factor is not fully understood. However, it is believed to be due in part to the better shielding of the cathode from the anode by the undercut channel, and in part to the relatively closer spacing of the grid elements from each other made possible by the undercut channel.

The use of an undercut channel in a unit shielded triode of the type disclosed in Garner, 2,636,142, produces the advantages above described and in addition results in -a substantial improvement in the ratio of anode current to grid current. The reason for such improvement in the ratio ofanode current to grid current is not fully understood. However, it is believed to be due to a co-operation between the lips or projection of the undercut channels the transverse portions of the shields to produce improved electron optics resulting in a more concentrated beam. Stated in a different way, it is believed that the lips or projections of the under-cut channels and the transverse portions of the shields cooperate to produce fields which maintain a better defined electron beam, at least adjacent the grid elements.

Referring to the accompanying drawings:

Fig. 1 is an elevation view of a shielded triode electron discharge device constructed in accordance with the present invention;

Fig. 2 is an enlarged partial axial sectional view of the device in Fig. 1;

Fig. 3 is a transverse fragmentary sectional view of a portion of the active electron region of an unshielded triode device constructed in accordance with the teaching of U. S. Patent 2,544,664;

Figs. 4 and 5 are transverse fragmentary sectional views of the active electron regions of unshielded triode devices constructed in accordance with this invention;

Fig. 6 is an enlarged transverse fragmentary sectional view of the shielded triode device of Figs. 1 and 2 taken along line 66 of Fig. 2;

Fig. 7 is a transverse fragmentary sectional view similar to Fig. 6, but showing a different embodiment of the present invention; and

Figs. 8 and 9 are transverse fragmentary sectional views similar to Figs. 4 through 7 but showing the present invention incorporated in tetrode type tubes.

For the purpose of illustration, the present invention will be principally described in connection with shieldedand unshielded triode types of super power electron discharge devices. However, it should be understood that it is not limited to the particular devices shown. As will be apparent, certain features of the illustrated device and the modifications thereof are described and claimed in U. S. Patent Nos. 2,544,664, or 2,636,142. Constructional features which are common to said patents will not be described in detail here in the interest of brevity and clarity except Where necessary for a complete understanding of the present invention.

Referring now to the drawings and to Figures 1 and 2 in particular, an electron discharge device 20 is shown which is an internally water cooled, super-power, beam triode having a demountable evacuated envelope as shown.

A plurality of elongated cathode elements 21 constitute a source of electrons. Each cathode element 21 is supported adjacent its upper end by a flexible support means indicated generally at 22 which, in turn, is supported from a central supporting conductor 23. The supporting conductor 23 is electrically connected to a terminal ring 24.

The lower or other end of each cathode element 21 is mounted in a ring 25 which is brazed to a supporting conductor 26. The supporting conductor 26 surrounds and is coaxial and concentric with the supporting conductor 23. The supporting conductor 26 is connected to a terminal ring 27 and below the ring forms part of the exterior or envelope of the tube. A beam former portion 26a (Fig. 6) is provided on the conductor 26 above the ring 25 by a plurality of spaced apart channels, slots or recesses '28, one of the cathode elements 21 being disposed along and within each of the slots 28.

A partition 29 extending between the supporting conductors 23 and 26 forms two cooling channels for a fluid coolant such as water.

It should be noted that the supporting conductors 23 and 26 are rigidly connected by a mechanically strong and hermetic seal adjacent their upper or inner ends as indicated generally at 30.

Insulated from and supported on the supporting conductor 23 is a hat-shaped support member 31 having a peripheral flange at its lower extremity with slots and centering or locating if-notches formed therein. There is one slot for each of a plurality of elongated control electrode or grid elements 32. The grid elements 32 each hook into the slots in the support member 31 and are accurately positioned by means of the V-notches. Adjacent their lower ends each of the grid elements 32 is hooked into a separate flexible support means 33 which, in turn, is supported from a grid terminal ring 34. The flexible support means '22 and 33 are laminated as described in detail and claimed in U. S. Patent 2,570,120, issued to W. E. Harbaugh, and assigned to the same assignee as the instant case. The support 22 is highly flexible while the supports 33 are each both flexible and resilient.

As is apparent from Figures 1 and 2, an output or anode electrode 35 is provided which is reentrant and coaxial with the cathode and grid electrodes. The anode 35 has a plurality of coolant channels 36 formed therein closed along one side thereof by a loosely fitting sleevelike partition 37. The inner or upper end'of the anode 35 is closed 'by a wall 38 while the other end of the anode vice of U. S. Patent No. 2,544,664. Figure 3 is a fragmentary sectional view of a portion of the electron active region of a tube constructed in accordance with U. S. Patent 2,544,664, having rectangular slots or recesses 41 in the beam former 26b.

One way of increasing the power output capabilities of the unshielded triode tube represented by Fig. 3 is shown in Fig. 4. The width of the opening or aperture 42 of the slots or recesses and the location of the grid elements 32 with respect thereto are unchanged, but the slots or recesses 28' are undercut so that the inner portion 43 of the slots 28 is substantially wider than the aperture or throat 42 thereof. The wider inner portion 43 of slots 28' permits wider cathode elements 21' to be used without necessitating an increase in the diameter of beam former 26b. The increased cathode area results in greater space current being produced in the electron stream between cathode elements 21 and anode 35. The throat portion 42 of the slots 28 seems to constrict the electron stream from the wider cathode elements 21' into a more concentrated stream than the electron stream in tubes where the slots 41 are not undercut. Thus greater power output is possible because of ,the increased space current from the wider cathode elements 21 and yet the grid current does not rise with the increased space current as would be expected.

Conversely, if long useful tube life is more important than increased power output, the larger cathode elements 21' may be run at a lower operating temperature which will extend the life of the cathode elements.

Fig. 5 illustrates the use of undercut beam former slots 28 with the same width cathode elements 21 as previously used in super power tubes constructed in accordance with U. S. Patent 2,544,664 not having undercut beam former slots and shown in Fig. 3. The arrangement of Fig. 5 is more compact than that of Fig. 3 because although the inner part 43 of the slots 28 have the same width as the non-undercut slot 41, the width of the aperture 42 is less, which permits the grid elements 32 to be more closely spaced and thus allows more unit triodes to be disposed within a given peripheral portion of the beam former 2611. Increasing the number of unit triodes will, of course, increase the power output capabilities of a given tube and is often preferable to increasing thev power output by increasing the width of the cathode elements 21 as is the case in Fig. 4 because the space current in the cathode-anode region may become great enough, in the arrangement of Fig. 4, that the existing grid structure will not efficiently control the flow of electrons between cathode and anode.

emission of the portions of the cathode filament which are overhung will be inhibited. If the amount of undercutting is reduced, less than the optimum results will be obtained.

Since super-power tubes of the types described herein consist of a plurality of unit discharge devices contained within a common envelope, developmental experiments are customarily conducted by fabricating atube consisting of a single one of the unit devices and subjecting it to experimental tests. The results of such tests may then be extrapolated to give performance data for a tube consisting of a given number of unit devices. For example, a tube fabricated for experiment and test may comprise an elongated bar of copper having a slot or channel cut. longitudinally along one surface thereof to act as a beam former. An elongated cathode filament may be suspended within and along such channel by appropriate mounting and electrical terminal means. Two elongated grid elements may be suspended, one along each side of the channel, by appropriate mounting and electrical terminal means. A massive anode member may be mounted opposite the opening of the channel and the entire array may be enclosed in a gas-tight container which may be evacuated and sealed or continuously pumped.

In an unshielded-triode' unit tube constructed according to this invention for the purpose of experiment and test, a beam former bar having an electronically active length of 8 inches and being 0.50 inch square was provided with an undercut channel having a depth of 0.10 inch. The width of the throat or aperture of the channel was 0.058 inch. The threat surfaces of the channel tapered at an angle of approximately 45 downwardly with respect to the surface of the beam former bar until a channel width of 0.10 inch was reached, the remainder of the channel being rectangular. A cathode filament having an electronically active length of 8 inches, a width of 0.057 inch and a thickness of 0.023 inch was suspended within and along the channel at a depth of 0.0l7inch. Two elongated grid rods of trapezoidal cross section were arranged one along each side of the channel with their broad dimension facing and parallel to the beam former. The grid rods were 0.062 inch thick with a broad dimension of 0.122 inch and a narrow dimension of 0.065 inch and had an electronically active length of 8 inches. A massive anode electrode having an electronically active length of 8 inches and a width substantially larger than the width of the channel was positioned opposite the channel. were spaced approximately 0.034 inch from the beam former and approximately 0.061 inch from each other, and the anode was spaced approximately 0.322 inch from the beam former.

By way of comparison, a unit electron tube constructed according to the teaching of U. S. Patent 2,544,664, utilized a rectangular channel 0.10 inch wide and 0.10 inch deep in place of the undercut channel of this invention. All other physical dimensions were substantially the same as in the unit tube above described. The cathode filament was set to a depth of 0.025 inch in the channel; the grid rods were spaced 0.037 inch from the beam former and 0.103 inch from each other; and the anode was spaced 0.325 inch from the beam former. By comparing the spacing of the grid rods from each other in each of the above described unit tubes, it will be seen that the grid rods of a unit tube constructed according to the teaching of this invention are 0.041 inch closer together.

With a heating voltage of 6.0 volts and a heating current of 48 amperes applied to the filament of the above unit tube, a cathode voltage of zero volts, and the anode and grid elements electrically connected together and raised to a potential of 1500 volts, it was found that the unit tube constructed according to the teaching of this invention produced an anode current of 7.3 amperes and a grid current of 0.40 ampere. By contrast, the unit tube constructed according to the teaching of U. S. Patent 2,544,664 produced an anode current of 6.50 amperes and a grid current of 0.37 ampere. Thus, it will be seen by comparison that a unit tube constructed according to this invention will produce as great or even greater anode current with substantially the same grid current and for a smaller transverse space consumed than a unit tube constructed according to U. S. Patent 2,544,664. Extrapolation of the above results to provide operational data for electron tubes of given beam former circumference has revealed that an improvement in power output of 38% is possible through the use of the subject invention.

In addition to the power output advantage of the subiect invention, it has been found that the amplification factor (or mu) will be more than doubled. For example, in the above described unit tube, constructed according to this invention, the amplification factor at the 0.1 ampere point was 112, Whereas the amplification factor of the unit tube constructed according to U. S. Patent 2,544,664, was 44.8. The explanation of such improvement is not fully understood. However, two features of the subject invention would necessarily have a direct relation thereto. Since the amplification factor or rnu of a tube utilizing electron optics, as in the case of super-power tubes, may be considered to be a measure of the degree of shielding between the anode and the cathode, it may be postulated that the undercut channels provide better shielding of the cathode from the anode, thus increasing the mu. Furthermore, since the spacing between the grid rods may be reduced, according to this invention, it may be postulated that the grid would have greater control over the electron stream, which also would increase the amplification factor or mu. Regardless of the explanation of the improvement in the amplification factor, it seems apparent that the undercut channels operate in a substantially different manner from non-undercut channels, at least insofar as electron optics are concerned.

Referring to Figures 1, 2, and 6, the electron tube shown is in fact a shielded triode type of superpower tube such as is described in U. S. Patent 2,636,142. The shielded triode differs from the unshielded triode, shown in Figures 3-5 and hereinabove described, in that a plural- The grid rods ity of shield members 44 are provided which are attached directly to the beam former and which extend between the grid rods and the anode. Referring to Figure 6, which is a cross sectional view of a portion of the shielded triode tube shown in Figures 1 and 2, it will be seen that the shields 44 may be formed by T-shaped members protruding from the beam former 26a, the transverse portions or cross bars 44a of which extend parallel to the beam former surface and the anode surface and between the anode 35 and the grid elements 32.

The cross bar portion 44a of the shields 44 may be provided with axial extensions or tabs 44a, as shown in Figure 2, which are electrically connected to a cathode terminal ring 45 positioned between the anode terminal ring 40 and the grid terminal ring 34. Because of this intermediate positioning of the cathode terminal ring 45, complete shielding between the input and output circuits may be obtained outside the tube 20 in addition to the electrostatic shielding provided between the grid elements 32 and anode 35 by the shields 44 within the tube 20.

Although shielded triodes have certain electric advantages over unshielded triodes, the power output of a shielded triode is necessarily less thah the power output of an unshielded triode of comparable size. The decrease in power output results from the fact that each shield 44 takes the place of at least one unit discharge device thus reducing the total number of unit discharge devices which may be positioned about a beam former 26a of given circumference.

The use of the undercut beam former channels 28 and 28' with the shielded triode type of super-power tube 20 makes possible an increase in power output of the same magnitude and for the same reason as described above with respect to unshielded types of super-power tubes. Similarly, the improvement in amplification factor or mu also results from the use of undercut channels 28 and 28' with the shielded type of super-power tubes as with the unshielded types. However, an additional advantage in the form of a substantial improvement in the ratio of plate current to grid current results from the use of undercut channels 28 and 28' in a shielded triode. The explanation of such improvement is not fully understood but seems to result from the co-operation of the edges of the undercut channels 28 and 28 and the edges of the cross bars 44:: of the shield members 44 to produce electron optics which are conducive to the high ratio of plate current to grid current.

The best results were obtained through the use of undercut channels with a shielded type tube of the construction shown in Figure 7. It will be noted that the structure shown in Figure 7 includes features in addition to the undercut channel 28 which are diflFerent from the prior art. For example, the grid elements 32 are square as compared to the trapezoidal grid elements 32 heretofore used. Other modifications of similar nature are used to conserve space; and thus, the structure shown in Figure 7 has been called the fine grain structure. For this reason, direct comparison of the structure shown in Figure 7 to prior art structure in terms of the effect of the various features embodied therein on the operation thereof is diflicult. However, a unit tube constructed for the purpose of experiment and test having a structure similar to that shown in Figure 7 produced a maximum current division ratio of anode current to grid current of about 275 as compared to a maximum of about 85 for shieldedtriode unit tubes constructed according to U. S. Patent 2,636,142.

In a unit triode having a structure similar to that shown in Figure 7, the beam former channel 28 was 0.100 inch deep and had an aperture 0.058 inch wide. The inner portion of the channel was 0.100 inch wide and the throat surfaces were inclined approximately 45 with respect to the surface of the beam former. The cathode element 21" was 0.057 inch wide and 0.023 inch thick and was set to a depth of 0.017 inch in the channel. The grid 8 elements 32 were 0.038 inch square and were spaced 0.0625 inch from each other and 0.030 inch from the beam former. The shield members 44 were spaced 0.110 inch from each other and 0.028 inch from the grid elements and had 0.030 inch thick transverse portions 44a. And the anode 35 was spaced 0.322 inch from the beam former. With a filament heating voltage of 6 volts and a current of 48 amperes, a cathode voltage of 0 or ground, and the anode and grid electrically connected together and raised to 1500 volts, a grid current of 0.020 ampere and an anode current of 5.50 amperes were measured.

Undercut beam former slots 28 and 28' may also be used to good advantage in tetrodes. Fig. 8 illustrates a tetrode arrangement in which both control grid elements 32 and screen grid elements 46 are shieled from the anode by the shield member 44.

In Fig. 9 there is illustrated a shielded tetrode in which a double T shielding member 47 having two transverse portions 47a and 47b is used, the second of the transverse portions 47b extending between the screen grid elements 46 and control grid elements 32.

However, if it is desired to provide some other degree of decoupling betweenthe control grid elements 32 and screen grid elements 46 without afiecting the electron optics of the tube, the second transverse portion or arm 47b of the shield member 47 may extend between the two grid elements for a distance less than indicated in the drawing. The exact length of the decoupling arms 4711 would have to be determined empirically.

()ne of the advantageous features of the shielded tetrode of Figs. 8 and 9 is the fact that the output circuit displacement currents will not flow on the screen elements 46 and give rise to screen coupled circuit instabilities of various types. The double T shielding member 47 of Fig. 9 further reduces the anode to control grid interelectrode capacitance, which is one of the prerequisites for stable grounded cathode operation at the higher frequencies. In addition, because of the nearness of the screen grid elements 46 to the shield member 47 and especially to the shield member 47a in the electrode configuration of Fig. 8, the screen grid is continuously bypassed. The shield members 47a and 47b are also of value in absorbing and conducting away heat radiated from the hot screen grid elements 46.

One additional advantage of the use of the undercut beam former is that it shields the grid elements from the corners of the cathode elements 21. While it cannot be stated positively that high grid current is due to emission beamed from the corners of the cathode elements 21, examination of tubes drawing excessive grid current has shown that usually some of the cathode elements have had damaged corners which resulted either from arcing within the tube during operation or from chipping during manufacture of the filamentary cathode elements of the tube.

From the foregoing it is apparent that electron discharge devices constructed in accordance with the present invention are capable of operation with greater efficiency at higher power output than devices heretofore used.

What is claimed is:

1. An electron tube comprising an anode, a beam former spaced from said anode and having an elongated recessed portion, said recessed portion having a throat substantially narrower than the inner part thereof, and an elongated cathode extending along and within the inner part of said recessed portion, the width of said cathode being approximately equal to the width of said throat. I

'2. An electron tube comprising an anode, a beam former spaced from said anode and having a plurality of spaced apart elongated recessed portions, each of said recessed portions having a throat substantially narrower than the inner part thereof, and a cathode comprising an elongated cathode element disposed along and within 't heinner part of each of said recessed'portions, the width of each: of said elements being approximately equal to the width. of each of said throats.

3.- An electron tube comprising a beam former havingan elongated recess, said recess having a throat substantially narrower than the inner part thereof, an elongated cathode element extending along and within the inner part of said recess, the width of said cathode element being approximately equal to the width of said throat; a grid and an anode spaced from said beam former, said grid comprising an elongated element extending along each side of the throat of said recess and between said beam former and said anode.

4. An electron tube comprising an anode, a beam former spaced from said anode and having a plurality of spaced apart elongated recesses therein, each of said recesses having a throat substantially narrower than the inner portion thereof, a cathode comprising an elongated element disposed along and within the inner part of each recess, the width of said cathode elements being approximately equal to the width of said throats, and a grid comprising an elongated element extending along each side of the throat of each of said recesses and between said anode and said beam former.

5. An electron tube comprising an anode, a beam former spaced from said anode and having an elongated recess, said recess having a throat substantially narrower than the inner part thereof, an elongated cathode element extending within and along said inner part of said recess, the width of said cathode element being approximately equal to the width of said throat, a grid comprising an elongated element extending along each side of said throat of said recess between said beam former and said anode, and a shield electrode comprising an elongated element extending along each of said grid elements between said grid elements and said anode and closely electrically coupled to said beam former.

6. An electron tube comprising an anode, a beam former spaced from said anode and having a plurality of elongated recesses therein, each of said recesses having a throat substantially narrower than the inner portion thereof, a cathode comprising an elongated element disposed along and within the inner part of each recess, the width of said cathode elements being approximately equal to the width of said throats, a grid comprising 'an elongated element extending along each side of each of said recesses and between said beam former and said anode, and a shield electrode comprising an elongated element extending along each of said grid elements between said grid elements and said anode and closely electrically coupled to said beam former.

7. In an electron discharge device, a cathode comprising a circular array of discrete and separate elements, and a generally cylindrical beam forming member having a plurality of undercut channels in its surface, each of said cathode elements extending within and along one of said channels, the width of said cathode elements being approximately equal to the width of the aperture of said channels.

8. An electron discharge device comprising concentric and coaxially arranged cathode, beam former, grid and anode structures forming cylindrical arrays, said cathode and said grid structures each including a plurality of spaced elements, said beam former having a pluralityv of spaced elongated undercut beam forming recesses, each of said grid elements extending along one side of one of said recesses, each of said cathode elements extending through one of said recesses, the width of said cathode elements being approximately equal to the width of the apertures of said recesses, the diameter of said beam former being intermediate that of said cathode array and that of said grid array, and the diameter of said grid array being intermediate that of said beam former and that of said anode.

9. An electron tube comprising a cathode, a beam a. surface thereof, said cathode extending through said channel, one of said grid elements being onv each side of said. channel, the width of said cathodebeing approximately equal to the width of said channel. at the surface of said beam former and approximately equal to the distance between said grid elements, said. anode being spaced from said grid'elements. I

10. An electron tube comprising an electrode having a plurality of longitudinal undercut slots. in a surface thereof and a pluralityof elongated members of substantially T-shaped cross section extending from said surface, the transverse portions of said elongated members being remote from said electrode, there being one of said elongated members between each pair of said slots, an array of cathode elements, each of said cathode elements extending along and within one of said slots, the width of said cathode elements being approximately equal to the width of the aperture of said slots,- and a first and a second array of grid elements, said grid arrays being positioned between said electrode and the transverse portion of said elongated member, the elements of each of said grid arrays being substantially in register one with another, a grid element of each of said grid arrays being located on each side of each of said slots, the spacing between transverse portions of adjacent elongated members being at least as great as the width of the slot which lies therebetween.

11. An electron tube comprising a cylindrical beam former having a plurality of longitudinal undercut slots in the outer surface thereof and a circular array of elongated metallic members of, substantially T-shaped cross section extending from said outer surface, the

transverse portion of said members being remote from mediate that of said beam former and that of said array of said metallic members of T-shaped cross section at the transverse portions thereof, one of said grid elements being located on each side of each of said slots and adjacent to the surface of said beam former, and a hollow cylindrical anode surrounding and spaced from said array of T-shaped members.

12. An electron tube comprising an electrode having a plurality of undercut .slots in a surface thereof and a plurality of elongated members extending from said surface, there being one of said elongated members between each pair of said slots, a cathode element disposed along and within each of said slots, the width of said cathode elements being approximately equal to the width of the apertures at said slots, first and second arrays of grid elements, a grid element of each of said arrays being located adjacent to each side of each of said elongated members, and an anode spaced from said grid elements, each of said elongated members having a pair of crossbar portions, one crossbar of each elongated member extending between the elements of said first and second grid array which are adjacent thereto, and the other crossbar of each of said elongated members extending between said anode and the elements of the grid array which lies adjacent thereto, the spacing between crossbars of adjacent elongated members being at least as great as the width of the-slot between said adjacent elongated members.

13. An electron tube comprising a hollow cylindrical beam former having a plurality of spaced apart undercut longitudinal channels in the outer surface thereof, a circular array of cathode elements, each of said cathode elements extending along and within one of said channelsythe width of said cathode elements being approximately'equal to the width of the apertures of said channels, a circulararray of grid elements, said'array of grid elements being of larger diameter than said beam former, a grid element being positioned adjacent to each side of each of said channels, and an anode surrounding and spaced from said grid elements.

14. An electron tube comprising a beam former having a plurality of spaced apart undercut channels therein, an elongated cathode element extending along and within each of said channels, an elongated grid element extending along each side of each of said channels, and

an anode spaced from said grid elements, the width of each cathode element being approximately equal to the width of each of said channels at the surface of said beam former and approximately equal to the spacing between the grid elements at each side of said channels. r

' "References Cited in the file of this patent UNITED STATES PATENTS Garner'et a1 Mar. 13, 1951 2,636,141 Parker Apr. 21, 1953 2,636,142

Garner Apr. 21, 1953

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