US2909698A

US2909698A - Electron tube

Info

Publication number: US2909698A
Application number: US534971A
Authority: US
Inventors: Lloyd P Garner
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1955-09-19
Filing date: 1955-09-19
Publication date: 1959-10-20
Anticipated expiration: 1976-10-20

Description

Oct. 20, 1959 Filed Sept. 19', 1955 L. P. GARNER ELECTRON TUBE 2 Sheets-Sheet 1' .INVENTOR. LLOYD E EBRNER BY %%M J Oct. 20, 1959 L. P. GARNER 2,909,698

ELECTRON TUBE Filed Sept. 19, 1955 2 Sheets-Sheet 2 INVENTOR.

LLOYD E EHRNER member is unavoidable.

United States Patent 2,909,698 ELECTRON TUBE Application September 19, 1955, Serial No. 534,971.

11 Claims. (Cl. 313--237) This invention relates to improved structures for electron tubes and to improved means for assembling such structures. In particular, this invention relates to electron tubes utilizing mechanical, high electrical conductivity, gas tight seals and other related structural features, which render the tube particularly suitable for operation at high frequencies. I

Gas tight seals between electrical insulating members and electrical conducting members require a surface to surface relationship between the members of such intimate nature that gas molecules cannot pass therebetween. According to the prior art, such intimate relationship is usually obtained by chemical means. That is, a chemical bond is produced between the surfaces of the members with or without an intermediate bonding medium. The production of such a chemical bond usually requires the use of heat resulting in the melting of a portion of one or both of the members.

An object of this invention is to provide a seal between an electrical insulating member and an electrical conducting member which is substantially free of a chemical bond between the surfaces of such members.

When an electrically conductive material is chemically bonded to or alloyed with any other material, even with another electrically conductive material it has been found that the electrical conductivity thereof will be reduced. Thus, when seals are made by producing a chemical'bond between the surfaces of the members to be sealed areduction in conductivity of the surface of the conducting The decrease in surface conductivity of the electrical conducting member Will be most detrimental when high frequency currents are to be carried by the conducting member since high frequency currents tend to flow along the surface or' in a thin surface layer of the conducting member.

The reduction in conductivity of the surface of such member at the seal area will result in electrical losses and I localized heating at said area. If the amount of high frequency current carried by the conducting member is small the electrical losses produced at the seal area will attenuate such current and may be suflicient to deleteriously effect the Q of a circuit of which the conducting mem- The use of seals according to this invention in the envelope of an electron tube necessitates the use of structural features which will allow axial movement of certain parts of the tube relative to each other during the assembly of such tube, and yet will maintain accurate lateral spacing therebetween.

I Thus, another object of this invention is toprovide an 2,909,698 Patented Oct. 20, 1959 ICC 2 improved electron tube structure particularly adapted to the use of mechanical gas tight seals.

When the length of the electronically active portion of the electrodes of an electron tube is an appreciable fraction of a wavelength of the operating frequency of such tube, it has been found that a standing wave of voltage and current variations will exist along such electrodes corresponding to such fraction of a wavelength of the operating frequency. Thus, it is desirable to provide electrical connections to the electrodes of the electron tube which will utilize such standing wave of voltage and current to the best advantage.

Therefore, a still further object of this invention is to provide an improved electron tube structure particularly adapted for use at frequencies having a wavelength of which the length of the electron active portion of such tube is an appreciable fraction.

A gas tight seal according to this invention comprises an annular ceramic member having a high modulus of rupture, an annular conducting member and a stress concentrating means between such members. Means are provided for maintaining such stress concentrating means under compression between such members. The stress concentrating means may take the form of an annular,

relatively narrow, deformable element of high electrical conductivity and may be either separate from or an integral part of the conducting member.

An electron tube according to this invention comprises an annular envelope having coaxial inner and outer walls and a plurality of electrodes, at least the electron active portions of which are within such envelope. The outer wall of theenvelope comprises at least two annular electrode terminal members and at least one annular hard insulating member intermediate such electrode terminal members and having surfaces in contact therewith. The tube structure includes means for maintaining such surfaces of the insulating members in intimate compressive contact with surfaces of such electrode terminal members resulting in a gas tight seal therebetween. The electron active portions of the electrodes of the electron tube are symmetrical about a longitudinal centerline of the tube and the electrode terminal members are electrically connected to the electrodes such that the electron tube is adapted to form a portion of a waveguide circuit. The electrical connection of certain of the electrode terminal members to certain of the electrodes is designed to allow relative axial motion between such terminals and such electrodes during and after fabrication of the electron tube.

This invention is described in greater detail hereinafter with reference to the appended two sheets of drawing wherein:

Figure l is a view, partially in side elevation and partially in axial section, of an electron tube according to this invention;

Figure 2 is an enlarged detail view in axial section of a portion of the envelope of the electron tube of Figure v.1 showing a set of gas tight seals according to this invention;

Figure 3 is a fragmentary detail View in cross section taken along line 3--3 in Figure 1;

Figure 4 is an exploded view in axial section of an electrode and an electrode terminal member of the electron tube of Figure 1' showing in detail the means for providing electrical contact therebetween.

Referring to Figure 1, an electron tube 10 according to this invention may comprise a triode having an anode 12, cathode 14, and control grid 16, all of cylindrical form and in coaxial array. Although a triode has been chosen for purposes of illustration and explanation, it is to be understood that this invention is not limited to triodcs, but

is equally applicable to other types of tubes (e.g. tetrodes,

iystrons, etc.). The anode 12 of the embodiment shown comprises a ring-shape metallic member which surrounds the control grid 16 and cathode 14. The control grid 16 comprises a cylindrical grid block 18 having a plurality of longitudinally extending channels 20 in the outer surface thereof and a plurality of turns 22 of fine wire wound about such outer surface whereby each turn 22 extends across all of the channels 20. The cathode 14 comprises a plurality of elongated filaments in cylindrical array, at least one of such filaments extending within and along each of the channels 28 in the grid block 18.

Referring to Figure 3, the electron tube comprises a plurality of small unit triodes in cylindrical array, their elemental anodes being integral with each other to form the single cylindrical anode 12 which surrounds elemental control grids 16 and filamentary cathodes 14'. Each filamentary cathode 14' is contained within the control grid structure, being recessed in one of the channels 20 in the grid block 18. It will be seen that the grid wires 22 extending across the channels 20 are extremely close spaced from the filamentary cathodes 14'. Such close spacing between the control grid wires 22 and the filamentary cathodes enables the use of low driving power as compared to the power output of the tube 10.

According to another feature of this invention the electron tube 10 is particularly suited for operation at very high frequencies due to the fact that it is adapted for double-ended operation. Referring to Figure 1, it will be seen that each of the

electrodes

12, 14, 16 is symmetrical on each side of a transverse plane passing through the longitudinal center of such electrodes. In addition, the cathode 14 and control grid 16 are provided with

terminals

24a, 24b, 26a, 26b at each end thereof and the anode 12 which is provided with a terminal 28 disposed centrally of the length of the tube 10. Thus, input and output circuits may be connected to the tube 10 from each end thereof. In operation, an input circuit is connected at one end of the tube between the

terminals

24a and 26a of the cathode 14 and grid 16, and a dummy (or slave) input circuit is connected between the cathode and grid terminals 24b and 2611 at the other end of the tube 10. Similarly, an output circuit may be connected at one end of the tube 10 between the

terminal

26b and 28 of the grid 16 and anode 12, and a dummy (or slave) output circuit may be connected between the grid and

anode terminals

26a and 28 at the other end of the tube 10. As will be explained hereinafter, this arrangement makes possible the best utilization of the standing wave which may be produced along the

electrodes

12, 14 and 16 particularly when the tube is operated in the UHF range or higher.

The envelope of the electron tube 10 is annular and has coaxial inner and outer walls. The outer wall of such envelope is formed by the

electrode terminal members

24a, 24b, 26a, 26b and 28 and annular hard insulating (eg. ceramic)

members

38a, 38b, 31a and 31b in stacked and alternated array. A gas tight seal exists between each of the insulating members and the electrode terminal members in contact therewith. According to this invention, the seals between such hard insulating members and such electrode terminal members are mechanical seals produced by bringing the members into intimate contact under compression as is more completely described hereinafter.

Serrations are formed in the outer surface of the

output insulating members

31a and 31b to provide longer electrical air-interface paths between the anode terminal 28 and the

grid terminals

26a and 26b. Thus the leakage resistance between the anode 12 and control grid 16 is increased and the possibility of corona discharge therebetween is reduced.

The lower cathode terminal member 24a serves also as one lead-in for the filament heating voltage. The cathode filaments 14 are electrically connected to the terminal member 24a by means of hook-like projections 36 on the terminal member 24a which engage lateral extensions forming heads on the lower ends of the cathode filaments 14. The other heating voltage terminal is provided by a lower header member 38 which passes axially through the lower cathode terminal member 24a and is sealed thereto in water tight relation by means of a mica gasket 37 and a metallic ring 39. The lower header member 38 is electrically connected to the other ends of the cathode filaments 14 through metallic structural portions of the tube 10, including a thin-metal sleeve 40, a contraction joint 41, a massive filament support block 42 and a filament tensioning system 44,

A parallel path for the filament heating voltage from the lower header member 38 to the upper ends of the filaments 14 exists through a center bolt 46 to an upper header member 48 and from there to the upper cathode terminal member 24b through a metallic spacer ring 50. The upper cathode terminal member 24b is electrically connected to the filament support block 42 through a sliding contact means 52, which will be described in greater detail hereinafter with reference to Figure 4 showing a similar sliding contact means 54 electrically connecting the upper grid terminal member 26b to the control grid 16.

The annular envelope of the electron tube 10 is evacuated through an exhaust tubulation 56 which passes through the upper header member 48. After the envelope is evacuated, the exhaust tubulation 56 is closed by means of a cold weld pinch-off and covered by a protection cap 58. A similar protection cap 59 covers a getter tube structure, not shown.

Reference to Figure 1 will reveal that the grid block 18 forms a major portion of the inner wall of the annular envelope of the tube 10. According to the embodiment of the invention, the grid block 18 is mechanically supported on the lower cathode terminal 26a, but insulated therefrom by an insulating ring 60. The massive filament support block 42 is in turn supported on the grid block 18, but insulated therefrom by a second insulating ring 62. The rings 60 and 62 are preferably of ceramic material.

The grid block 18 also forms one wall of an annular cooling channel 64 through which an insulating fluid coolant is circulated to cool the control grid 10. For example, distilled water may be used as the cooling fluid. The coolant is introduced into the channel 64 through a passageway 66 in lower header member 38 and passes upwardly through the channel 64 and out through a passageway 68 in the filament support block 42. The coolant then proceeds downwardly around the center bolt 46 and is drawn out through a second passageway 70 (shown in dotted lines) in the lower header member 38.

Coolant passageways

72, 74 are also provided in the anode terminal member, and means 76 for intensely cooling the electron active surface of the anode 12 are provided within the anode structure.

Referring to Figure 2, the mechanical type of gas tight seal used according to this invention may be accomplished by providing a stress concentrating means on the electrode terminal members 24b, 26b in the form of annular ridges or shoulders 32 which contact opposite surfaces of the hard insulating member 30b. When compressive force is applied to the members, each projecting ridge or shoulder 32 is deformed and forced into such intimate contact with the surface of the hard insulating member 30b that gases cannot pass therebetween.

The exact mechanism of the seal produced as described above is not completely understood. It is believed that the metal of the ridges 32 is caused to flow by the pressure exerted thereon and that the flow of metal fills the interstices and irregularities in the surface of the insulating material. Apparently, molecular or near molecular contact is produced between the metal and theinsulating material by such flow which prevents the passage of gas molecules between the metal and the insulating material. However, it is clear that this type of seal is to be distinguished from seals made by the chemical diffusion of materials into each other usually under the influence of heat.

In place of the ridges 32 on the electrode terminal members 24b and 26b, a narrow gasket 34 of relatively soft or deformable metal may be clamped between a flat surface on an electrode terminal member and a flat surface on a hard insulating membenas shown between terminal member 28 and insulating members 31a and 311). However, if the

stress concentrating means

32 or 34 on 'each side of an insulating member are not in substantial alignment a bending moment will be introduced into the insulating member which will tend to cause such insulating member to fracture in tension. Thus, the use of gaskets 34 require accurate fixtures for placing the gaskets prior to the application of compressive forces, whereas the ridges 32 may be accurately formed on the electrode terminal members, eliminating the possibility of misalignment thereof if the electrode terminal members are properly aligned. On the other hand, if ridges 32 are used in making a seal, there is a high probability that the seal could not be demounted and the electrode terminal member involved, used again in a new seal. In other words, once the ridges 32 on an electrode terminal member have been deformed to produce a gas tight seal there is a possibility that the ridges may have been rendered incapable of being used to make a new seal if the original seal is demounted. A gas tight seal made with a gasket 34, however, is demountable and a new seal may be produced between previously sealed member with a new gasket 34 inserted therebetween.

Thus, in the embodiment of this invention shown in Figures 1 and 2, the seals between the anode terminal member 28 and the insulating

members

31a and 31b adjacent thereto are made with gaskets 34. The remaining seals utilize ridges 32 formed on the electrode terminal members. The gasket type of seal is used at the anode terminal 28 for two reasons: First, the anode structure including the anode terminal 28 is preferably made of tool steel in order to provide sufiicient strength for the cooling structure. While it would be possible to form a seal according to this invention through the use of integral ridges on such anode structure, it is preferable to use a separate soft metal gasket to reduce the compression forces necessary to make the seal and the attendant possibility of fracture of the insulating members of 31a and 31b. The tool steel is plated with silver to provide high electrical conductivity at high frequencies and to prevent the corrosion thereof. The second reason is that the anode terminal is intimately attached to the remaining anode structure 12 and, if. it

should be necessary to demount the seals, it is desirable that the anode structure 12 including the anode termi- .'nal 28 be capable of reuse.

Otherwise, the expensive (as compared to the

other terminals

24a, 24b, 26a and 26b) anode structure Would have to be discarded or rebuilt.

In accordance with this invention, both the ridges 32 and the gaskets 34 used in accomplishing gas tight seals are made of metals having high electrical conductivity. For example, the

electrode terminal members

24a, 24b, 26a and 2617 may be made of a metal having high electrical conductivity, such as copper] Thus, ridges 32 formed on such electrode terminal members will also be of high electrical conductivity metal. In the case of the gasket type of seal, the gasket 34 may be composed of copper, for example, which is readily deformable in addition to having high electrical conductivity. Since a :mechanical seal according to this invention does not pro- .duce any substantial chemical bonding or alloying of --materials at the seal area, no reduction in conductivityan electrical conductivity approximating that of the metal of which the

electrode terminal members

24a, 24b, 26a and 26b are composed, or, in the case of the gasket type of seal, the metal of which the gasket 34 is composed.

The hard insulating

members

30a, 30b, 31a and 3117 used in accordance with this invention must be sufliciently strong to withstand the compressive forces necessary to produce the mechanical seal. That is, they must have a surface hardness sufiicient to deform the ridges 32 or gaskets 34 to produce the intimate contact which will prevent the passage of gas molecules, and in addition, they must have a modulus of rupture high enough to prevent fracture thereof due to bending moments which may be induced therein. A suitable hard insulating material that may be used in the production of seals according to this invention is a ceramic containing more than 50.26% of aluminum oxide, as disclosed in Patent No. 2,290,107 granted July 14, 1942, to Daniel W. The ceramic above described may have a modulus of rupture higher than 187,000 pounds per square inch, 21 very high electrical resistance and a fairly high heat conductivity.

The compression between the

electrode terminal members

24a, 24b, 26a, 26b and 28 and the insulating

members

30a, 30b, 31a and 31b necessary to produce the mechanical seal according to this invention is provided by the bolt 46 which extends longitudinallyof the electron tube and is centrally located inwardly of the inner Wall of the annular envelope. The two

header members

38 and 48 are removably attached to opposite ends of the bolt 46 and are brought into engagement with the stacked array of electrode terminal members and insulating members. For example, the

header members

38 and 48 may be in threaded engagement with the ends of the bolt 46. Preferably, one header member (the upper one 48) may be in threaded engagement with one end of the bolt 46 and the other header member 38 may be slidable along the bolt 46. A compressive force may then be produced between the

header members

38, 48 as by tightening a nut 78, in threaded engagement with the other end of the bolt 46, against the slidable header member 38. The compressive force will be transmitted through the stacked array of

electrode terminal members

24a, 24b, 26a, 26b, and 28 and insulating

members

30a, 30b, 31a, and 31b, producing the necessary compressive forces therebetween to cause them to enter into gastight relation.

The exact amount of compressive force necessary to produce the gas tight seals will vary with the materials used and with the dimensions of the seals to be made. However, experience has shown that, when the stress concentrating means are composed of copper and the insulating members are composed of the ceramic material described above having moderately smooth sealing surfaces, a compressive stress of about 100,000 pounds per square inch will produce gas tight seals.

The production of a compressive force of such magnitude by tightening the nut 78 against the lower header member 38 would involve impractically large wrenches and lever arms and associated impractical torques. Thus, the compressive force is obtained, according to one method, by butting a hydraulic ram (not shown) against the lower header member 38 and attaching the piston of the ram to the center bolt 46. The ram may then be caused to subject the header member 38 to compressive force while pulling on the center bolt 46 to produce tensile force therein. The nut 78, previously applied loosely to the center 'bolt 46, may then be tightened against the header member 38 to maintain substantially, the forces created'by the ram. 4

Since the seals are to be used in the construction of electron tubes, the additional complication of temperature cycling must be considered. If the seals are produced at a given temperature and later subjected to a higher temperature during operation of the tube 10, it is possible that the center bolt 46 will exhibit enough thermal expansion to allow the seals to fall apart. This would be true if substantially the total applied compressive force were relieved by the deformation of the

stress concentrating means

32 and 34. However, according to this invention, the center bolt 46 and the two

header members

38 and 48 are used as strain storage means or springs. In other words, the compressive force applied as described above is sufficient not only to deform the

stress concentrating means

32 and 34 to produce the gas tight seals, but also to produce tensile strain in the center bolt 4-6 and to bend the

header members

38 and 48. So long as the elastic limit of the material of which the center bolt 46 and

header members

38 and 48 are composed is not exceeded they will tend to return to their unstrained state and thus will continually exert a compressive force on the stacked array of electrodes

terminal members

24a, 24b, 26a, 26b and 28 and

insulator members

30a, 30b, 31a and 31b. If the tube is then subjected to a temperature above that at which the seals were produced, the thermal expansion of the bolt or other members will result only in the partial relief of the stored strain.

Calculations from empirical work on a specific test indicate that a compressive force as low as 800 pounds per lineal inch will maintain a seal according to this invention, after it has once been produced. In making seals according to this invention the center bolt 46 is subjected to tensile stress and the header member 38 to compressive stress as described above and the resulting elongation of the center bolt 46 measured. When such elongation of the center bolt indicates a tensile stress of 100,000 pounds per square inch, the nut 78 is brought up tight against the header member 38 and the application of force discontinued. Thus, sufilcient strain storage is provided to enable the seals to remain gas tight throughout an appreciable temperature cycle. The amount of strain storage may be varied to make allowance for temperature cycles of different magnitudes, but is, of course, subject to the limitations of the materials used in the construction of the electron tube.

The limitations of the materials used are the compressive strength of the insulating material of which the

insulators

30a, 30b, 31a and 311) are composed and the elastic limit and strain relief characteristics of the metal of which the bolt 46 is composed. The bolt 46 may be made of a tool steel alloy, such as 883 tool steel alloy made by the Carpenter Steel Company, which has been heat treated for red-hard characteristics. One inch diameter bolts of the 88.3 alloy have been strained an amount equivalent to 200,000 pounds per square inch and baked for many hours at 450 C., and have not seriously normalized or strain relieved, but continue to store substantially all of such strain.

An electron tube according to this invention includes several features necessitated by the type of seals used and the adaptation of the tube for double ended operation. The deformation of the ridges 32 and gaskets 34 in accomplishing the seals results in a certain amount of longitudinal motion of the members interposed in the envelope walls, during and after the assembly of the tube. Since there must be two terminals, one at each end, for both the cathode and control grid and since such terminals are interposed in the envelope wall and are thus subject to the above mentioned longitudinal motion, at least one of the terminals associated with the cathode and at least one of the terminals associated with the control grid must be electrically but not mechanically connected thereto. Furthermore, the cathode and control grid must be very precisely positioned with respect to each other during the assembly of the tube 10 and such positioning must not be disturbed by the longitudinal motion of the envelope members resulting from the formation of the seals.

The above requirements are satisfied according to this embodiment of the invention by supporting both the cathode filaments 14 and the control grid structure 16 on the lower cathode terminal member 24a only, as was hereinabove described with respect to Figure l. The lower ends of the filaments 14' are both electrically and mechanically connected to such lower cathode terminal member 24a and the lower end of the control grid structure 16 is mechanically connected thereto but insulated therefrom. The upper ends of the cathode filaments 14 are insulatingly supported by the upper end of the control grid structure 16, thus insuring proper positioning therebetween. The electrical connections between the remaining cathode terminal member 2412 and the cathode filaments 14 and between the two

grid terminal members

26a and 26b and the control grid structure 16 are made by means of sliding contacts, thereby allowing for the longitudinal motion described above.

Referring to Figure 4, an exploded view of the grid terminal 26b and a portion of the grid 16 is shown to better illustrate the nature of the sliding contact 54 therebetween. The sliding contacts 52 and 54 between the other grid terminal 26a and the grid 16 and between the cathode terminal 24b and the cathode 14 are substantially the same as the one shown in Figure 4.

The grid terminal 26b is in the form of an apertured disc or washer. A circuit contacting surface is provided at the outer periphery of the terminal 26b. A groove 82 is formed in the inner periphery of a terminal member 26]). A helical spring 54- is positioned in such groove 82 and has a diameter adapted to allow it to fit loosely in the groove 82 and a length sufiicient to allow it to extend in and along such groove 82 about the entire inner periphery of the terminal member 2617. The grid block 18 of the control grid 16 is provided with an electrical contact surface or extension in the form of a grid flange or foot 86. The outer diameter of such grid foot 86 is slightly less than the diameter of the inner periphery of the terminal member 26b to provide clearance for such grid foot 86 within the inner periphery of the terminal member 26b, if the helical spring 54 were not interposed therebetween. Thus, the insertion of the grid foot 86 into the aperture of the terminal member 26!) will compress the helical spring 54 against the inner periphery of the terminal member 26b causing the helical spring to assume an elliptical shape. The turns of the spring 54 will bear against the sides of the groove, in which it is contained, as well as the contacting surface of the grid foot 86, and will tend to bite, or dig, into the surfaces of the grid foot 86 and the electrode terminal member 2612, to insure positive electrical connection therebetween. Furthermore, such electrical connection will occur over a large area which is particularly desirable when the tube 10 is to be operated at high frequency.

Referring to Figure 1, it will be seen that the anode 12 is supported by a single anode terminal member 28. The anode terminal member 28 is interposed in the outer envelope wall and is located at the longitudinal center thereof. Thus, the anode 12 and the anode terminal member 28 are not subjected to the longitudinal motion resulting from the formation of the seals as described above. The clamping action of the

header members

38 and 48 and the bolt 46 occurs equally from each end of the electron tube 10 causing longitudinal motion of opposite sense on each side of the anode terminal member 28, the anode terminal member being an equilibrium member acted upon equally from opposite sides.

The longitudinal motion occurring in the envelope structure exclusive of the outer wall of the envelope is compensated by the flexure of a thin metal envelope c10- sure member 88. Similarly, thelon'gitudinal motion occurring in the tube structureexclusive of theen'velope structure is compensated by the flexure of the contraction joint 41. Other mechanical features of the'assembly ofan electron tube according to this invention will be apparent tothose skilled in the art after a careful study of the drawings.

A study of Figure 1 will reveal that an electron tube according .to this invention is particularly suited for high frequency,'high power operation in Conjunction with a wave guide or'walve cavity type of circuit. The

electrodes

12, 14 and 16 are cylindrical in form and are coaxially and coextensively arranged. The anode terminal 28 is located at and electrically connected to the anode 12 at the longitudinal center of the

electrodes

12, 14 and 16. The two

grid terminals

26a and 26b are equidistantly spaced from the anode terminal 28, one of such terminals being located at and electrically connected to each end of the control grid 16. Similarly, the two cathode terminals 24a and 24b are equidistantly spaced from the anode terminal 28 and are located at and electrically connected to opposite ends of the cathode 14. It will be noted that the

control grid terminals

26a and 26b are interposed in the envelope wall between the anode terminal and the cathode terminals 24a and 24b thus providing for the shielding of the cathode from the anode.

If the waveguide circuit used is properly designed, the electron tube 10 will operate as if it is the central portion of a half wave line. In other words, an attempt has been made to enable the simulation of a half wave coaxial line, a central portion of which has been made electronically active. Thus, the

electrode terminal members

24a, 24b, 26a, 26b, and 28 as well as the

electrodes

12, 14 and 16 themselves, are designed to form a portion of an external circuit which completes a half-wave line. For example, the input circuit may comprise a coaxial transmission line connected between the

terminals

26a and 24a of the control grid 16 and cathode 14 at one end of the tube 10. This circuit is terminated by a second input coaxial transmission line connected between the terminals 26b and 24b of the control grid 16 and cathode 14 at the other end of the tube 10. The circuit at such other end of the tube may be thought of as a dummy (or slave) input circuit, the primary purpose of which is to balance the half-wave line such that the electron active portion of the electron tube 10 will be positioned at the center of such half-wave line. Similarly, an output circuit and a dummy output circuit may be connected between the anode terminal 28 and the

control grid terminals

26a and 26b to produce an output half-Wa ve line,

having the electron active portion of an electron tube as a.

central portion thereof.

The tube 10 is thus adapted to be operated at frequencies in the UHF range or higher with a maximum of efficiency. In addition, the unitary construction of the electron tube 10 according to this invention makes extremely high-power output possible in the operation thereof. constructed in accordance with this invention gave an output of 110 kilowatts at 540 megacycles with a power gain of about 25 and under bandwidth conditions suitable for color T.V. service. Much higher frequencies and power output are obtainable from electron tubes constructed according to this invention given proper circuitry.

What is claimed is:

1. A high conductivity seal comprising an annular refractory ceramic member, an annular conductive member, stress concentrating means in the form of an annular, relatively narrow, deformable element of high electrical conductivity between and in intimate contact with said members, and means for applying force to said members for maintaining said stress concentrating element under compressive stress sufiicient to maintain a gas tight seal, said ceramic member having a modulus of rupture high In a successful experiment, an electron tube 10 enoughto prevent fracture thereof when subjected to :said force.

f 2; A high conductivity seal according to claim 1, where'- in said conductive member is made of tool steel plated with silver and said deformable element is made of copper.

3. A high conductivity seal comprising an annular refractory ceramic member, an annular conductive member, stress concentrating means on said annular conductive member in the form of an annular, relatively narrow, deformable element of high electrical conductivity in intimate contact with said ceramic member, and means for applying force to said members for maintaining said stress concentrating element under compressive stress sufficient to maintain a gas tight seal, said ceramic memher having a modulus of rupture high enough to prevent fracture thereof when subjected to said force.

4. A high conductivity seal as in claim 3, wherein said conductive member is made of copper and said deformable element is an annular rib integral wih said conductive member.

5. A high conductivity seal according to claim 3, wherein said ceramic member is a ceramic containing more than 50.26% of aluminum oxide and having a modulus of rupture greater than 187,000 pounds per square inch.

6. A high conductivity seal according to claim 3, wherein said compressive stress is about 100,000 pounds per square inch.

7. An electron tube comprising an annular envelope including coaxial inner and outer walls, said outer wall of said envelope comprising at least one annular electrode terminal member and at least one annular refractory ceramic member having a surface adjacent to said terminal member, stress concentrating means in the form of an annular relatively narrow deformable element of high electrical conductivity between and in intimate contact with said members, and means for producing and maintaining a mechanical compression gas-tight seal between said members including a tension bolt coaxially positioned within said inner wall of said envelope, said ceramic member having a modulus of rupture high enough to prevent fracture thereof when subjected to said force.

8. An electron tube according to claim 7, wherein the last named means includes strain storage means engaged between said tension bolt and said outer wall, said strain storage means exerting a compressive force longitudinally through said outer wall by virtue of strain stored therein by said tension bolt.

9. An electron tube according to claim 8, wherein said strain storage means comprises a plate attached to said bolt adjacent one end thereof and contacting said outer wall around the periphery of said plate.

10. An electron tube according to claim 8, wherein said strain storage means comprises a pair of annular strain storage plates, said strain storage plates being positioned one on each end of said tube attached to said bolt and contacting said outer wall around their outer peripheries and being strained toward each other by said center bolt to longitudinally compress said outer wall.

' 11. An electron tube comprising an envelope and a plurality of hollow cylindrical electrodes in concentric array having at least their electron active areas within said envelope; said electrodes including a cathode, a control grid, and a surrounding anode spaced in the order named; a plurality of annular terminal members connected to said electrodes and extending substantially radially with respect to the axis thereof, one peripherally connected to said anode midway between the ends there of, one peripherally connected to each end of said control grid, and one peripherally connected to each end of said cathode; said control grid terminal members and said cathode terminal members being symmetrically axially spaced from said anode terminal member with each of said control Igrid terminal members being intermediate bers each disposed between adjacent ones of said annular terminal members; said annular insulator members and said annular terminal members comprising said envelope. 5

References Cited in the file of this patent UNITED STATES PATENTS Lovekin June 26, 1900 10 Ferrell et al. Dec. 1, 1931 12 Gorny et al. Sept. 6, Hornback Aug. 22, McArthur May 26, Gethmann July 15, Nergaard et a1. July 13, Eaves Jan. 31, Duke Oct. 21,

FOREIGN PATENTS Great Britain July 20, Great Britain Dec. 24,