US2707757A - Electron discharge device - Google Patents

Description

G. J. AGULE ELECTRON DISCHARGE DEVICE May 3,' 1955 3 Sheets-Sheet 1 Filed Sept. 19. 1950 ATTORNEYS X g I INVENTOR GEORGE [A6045 CM w I l iiiiit a i E s n I a y 1955 G. J. AGULE 2,707,757

ELECTRON DISCHARGE DEVICE Filed Sept. 19. 1950 s Sheets-Sheet 2 INVIENTOR 550/?65 J 66015 y 3, 1955 G. J. AGULE 2,707,757

ELECTRON DISCHARGE DEVEECE Filed Sept. 19, 1950 '3 Sheets-Sheet 3 INVENTOR GA-ORGEJAQ/LE ATTO R N EYS United States Patent ELECTRON DISCHARGE DEVICE George J. Agule, Stamford, Conn., assignor to Machlett Laboratories Incorporated, Springdale, C0nn., a corporation of Connecticut Application September 19, 1950, Serial No. 185,645

13 Claims. (Cl. 313-247) This invention relates to electron discharge tubes adapted for use at high frequencies. More particularly, the invention relates to a novel electrode supporting structure and envelope construction in a tube of the coaxial type.

Tubes adapted for high-frequency use require relatively close spacing between electrodes in orderv to obtain a sufiiciently short transit time for the passage of electrons from cathode to anode. Also lead inductance and capacitance must be reduced to a minimum. Furthermore it is highly desirable that the structure and terminal arrangement be adapted for use with coaxial tuning cavities as well as other tuning arrangements. At the same time, for high power applications the areas of the electrodes must be large in order for the cathode to provide sutficient eiectron emission and for the anode to dissipate large amounts of heat.

The tube of the present invention is of the concentric cylindrical type having coaxially arranged terminals. By virtue of the concentric cylindrical arrangement the radial distance between electrode surfaces may be made relatively small, and the length of the cylindrical surfaces provides the necessary large areas for high-power use. In the specific embodiment described, a directlyheated filament cage is employed composed of a number of axially-extending filament wires in a cylindrical configuration. Encircling the filament cage, and closely adjacent thereto, is a grid cage likewise of cylindrical form and coaxial with the filament cage. A coaxial cylindrical anode encircles the grid cage.

In tubes of this type a very important problemis the precise spacing and alignment of the cylindrically arranged electrodes.

Close spacing and accurate alignment is a common problem in the design and manufacture of high-frequency tubes. Most of the methods and techniques developed up to the present time, however, are in the field of lowpower tubes. The development of tubular structures using coaxial, ring-seal construction has been possible because low-power tubes require only small light parts which may be drawn to intricate shapes with high uniformity, and which may be accurately handled by suitable jigging techniques. The use of planar electrodes is common in low-power tubes so that the problem of spacing is more a matter of axial spacing than axial alignment. Even when cylindrical elements are employed, the interelectrode spacing is not as small relative to the axiallength of the electrodes as it is in-large power tubes. Thus by the use of a few accurate die-drawn pieces to support the electrodes, and by providing sliding adjustments, it is possible at the present time to get extremely close electrode spacing in low-power tubes. Y

In high-power tubes the much larger size of the electrodes makes it far more diificult to form the filament and grid electrode structures with the necessary accuracy, and toobtain precise alignment with small interelectrode spacing. In order to obtain adequate ruggedness, the electrodes must be strong and the electrode supports ice relatively massive. Due to the required increased thickness of the metal parts, the intricate shapes possible in small tubes become very ditficult to form with the necessary accuracy.

Heretofore the assembling of high-power tubes has been largely performed by skilled persons relying to a great extent upon visual accuracy. lthough some jigging equipment has been employed, the manner of mounting the electrodes has been such as to still require the workers skilled eye for accurate positioning.

In high-power tubes of the coaxial cylindrical type mentioned above, considerable difficulty is encountered in accurately forming the filament cage so that it is absolutely symmetrical about its axis. In accordance with the present invention, a construction is provided which enables the filament assembly to be produced with a high degree of precision. To this end, a so-called freehung self-supporting filament cage is employed with mounting means at one end adapted to hold the filament strands in precision alignment.

After the filament structure has been formed with the necessary accuracy, 21 further problem exists in assembling it with the surrounding grid structure so as to maintain precise alignment and close spacing within the necessary close tolerances. The present invention pro- I vides a structure which can be assembled readily with the necessary precision by the aid of relatively simple jigging equipment. To this end, sturdy mounting means are provided for both filament and grid assemblies and designed and constructed to enable them to be sealed together with great accuracy. Similar considerations are involved in assembling the anode structure with the grid and filament structure, and similar construction is provided.

Prior art tubes operating at high power, and hence at high voltages, have commonly been relatively fragile, because a large area of their envelopes were constructed of glass, or have been heavy and cumbersome due to the use of heavy glass parts. The tube of the present invention utilizes a metal concentric construction with ring seals made of a minimum amount of glass so as to yield a relatively light tube of great mechanical strength, yet with adequate insulation to withstand high voltages. The use of re-entrant sections has been avoided, since the glass in such sections is often difiicult to cool adequately. Furthermore, the tube is designed so that heat radiated from the filament does not reach the glass seals, the tubular elements themselves acting as heat shields.

Further features and advantages of the tube of the invention will in part be pointed out hereinafter in connection with the description of a specific embodiment thereof, and will in part be obvious to those skilled in the art.

The invention will be more fully understood by reference to the following description of a specific embodiment thereof, taken in conjunction with the drawings in which:

Fig. 1 is a cross section taken along the axis of the tube, with portions of the filament and grid assemblies shown in elevation;

Fig. 2 is a cross section taken along the line 2-2 of Fig. 1 showing the arrangement of filaments and grid cage;

Fig. 3 is a cross section taken along the line 33 of Fig. 1 showing the filament supporting rod structure;

Fig. 4 is a cross section taken along the line 4-4 of Fig. 1 showing the end mounting structure for the grid;

Fig. 5 is a cross section taken along the line 5-5 of Fig. 1;

Fig. 6 is a cross section taken along the line 6-6 of Fig. 1 showing the lower spacing plate of the grid cage; and

Fig. 7 is a cross section taken along the line 77 of Fig. 1 showing the manner of joining the filament wires at the free end of the filament cage.

The tube illustrated in the drawings is capable of generating many kilowatts at frequencies extending up to the region of 150 megacycles. In order that a general idea of the size of the tube may be obtained, in a specific embodiment which has been operated with success the overall height of the tube is approximately eighteen inches. It will, of course, be understood that the size of the tube and the proportions thereof may be altered depending upon the use contemplated. In particular, by shortening the tube still higher frequency operation may be obtained while still obtaining large power outputs.

In the drawings anode 10 is a deep cylindrical cup of highly conductive metal such as copper. An exhaust tubulation 11 is sealed in the end wall of the cup and is sealed otf by a glass seal 12 after processing and evacuation. The seal-off 12 may be protected by a cap 13.

A water cooling system is employed in order to prevent overheating the anode in use. Water is fed into the tube at 14 in the space between neck 19 and the exhaust tubulation, and passes upwards between anode 10 and a cylindrical baflle 15. At the upper end of the anode the water passes around the end of baffle 15 and down between the bafi le and the outer coaxial cylindrical anode support 16. Support 16 is soldered to the upper end of the anode at 17. An end cap 18 is soldered to the lower end of cylinder 16 and has an inwardly-extending flange 18 which is soldered to the neck 19. A number of holes 21 are provided in flange 18' to permit water to flow out of the jacket. The outer cylinder 16 may be formed in two pieces soldered together at joint 22, if desired for convenience in assembly.

It will be observed that the annular flow of water in close contact with the anode assures very eflicient cooling thereof.

A heavy annular metal disk 23 is soldered to the outside of cylinder 16 and is provided with a metallic cylindrical section 24 soldered thereto. Cylinder 24 is advantageously of kovar so as to permit a strong seal to be made between it and the vitreous ring seal 25.

A heavy grid support ring 26, with an olfset flange 26, has a short metal cylindrical section 27 soldered thereto. A cooperating metal cylindrical section 28 is sealed to the vitreous ring 25, and is hence advantageously of kovar. Rings 27 and 28 are formed and sealed together at 30 in the manner described in my co-pending application Ser. No. 118,878, filed September 30, 1949, now Patent No. 2,654,822. As explained in that application, the joining of members 27 and 28 forms the final seal in the assembling of the tube. The cylindrical portions of sections 24, 27 and 28 are advantageously of the same diameter to facilitate accurate alignment during assembly.

It is advantageous to form vitreous ring 25 with a bowed out section as illustrated in order to provide strength. This will be discussed more fully hereinafter.

The grid cage is formed with a number of support rods 31 axially aligned and arranged in the form of a cylinder. At one end the grid support rods are attached to grid mounting ring 32 (Fig. 4). At the other end they are attached to a metal dish 33 (Fig. 6) which may be scalloped as illustrated. The grid wire 34 is helically wound around support rods 31. It will be readily appreciated that the grid cage as described can be readily assembled as a unit with great precision. The grid mounting ring 32 is mounted in position on the heavy grid support ring 26 by means of the metal collar 35 and bolts 36. Metal collar 35 has a triangular cross section except for the recesses provided for bolts 36. It is advantageously split as shown in Fig. 5 so as to permit ready assembly. It will be appreciated that the heavy ring 26 may be readily machined with great accuracy so as to precisely locate the grid cage in the assembled structure. Collar 35 also serves as a shield between the end portion of the grid and the adjacent anode.

The filament cage is formed of a number of wires 37, advantageously of tungsten, extending in an axial direction with cylindrical configuration. Advantageously an even number of wires are employed, and sixteen are used in the specific embodiment shown. The filament cage is of the so-called free-hung self-supporting type, being supported at one end only in a manner to be described. The lower ends of the filament wires 37 are bent inwards and then spaced around a central spool 38 (Fig. 7). A fine wire 39 is then wound around the ends of the wires. The wound portion may then be soldered or welded so as to form a joint of good conductivity between the ends of all the filament wires.

Filament wires 37 are attached to filament support rods 41 by radially-extending clips 42. These are advantageously formed of two pieces of metal (Fig. 5), riveted together, and cupped at the ends to receive the filament wires and support rods. The use of clips 42 permit the rods 41 to have a sufficiently srn-all radius of configuration 'to pass through ring 26 during assembly while permitting a larger radius of configuration for the filament wires 37 for close spacing with the grid. The clips permit attaching the filament wire cage to the rods after the filament supporting structure has been assembled, thus avoiding possibility of damage to the relatively fragile wire cage. If desired, however, other means for attaching the filament wires to the supporting structure may be employed.

A pair of heavy coaxial cylinders 43, 44 are provided for supporting the filament structure. Alternate support rods 41 are attached to an inwardly-extending flange on cylinder 43. The intermediate support rods 41 extend through holes 45 provided in the flange (see Fig. 3) and are attached to cylinder 44. Instead of employing holes 45, the flange of cylinder 43 may be scalloped to allow alternate rods 41 to pass thereby in non-contacting relationship. Respective rods 41 are inserted into corresponding holes in cylinders 43 and 44, and the holes are drilled in respective circular patterns having the same radius. Cylinder 44 is closed by an end cap 46, soldered thereto. A short metallic cylindrical section 47 is soldered to end cap 46, and a section 48 of the same diameter is soldered to ring 49 which in turn is soldered to cylinder 43. Sections 47 and 48 are joined together by ring seal 51 of vitreous material.

This design of the filament structure enables the filament wires to be assembled and maintained in alignment with great precision. Cylinders 43 and 44 may be held in a fixture in a glass lathe in accurate alignment while vitreous ring seal 51 is formed. This insures the correct alignment of filament support rods 41 inasmuch as the corresponding holes in cylinder 44 and the flange of cylinder 43 were initially drilled in circular patterns of the same radius. This assures, in turn, that filaments 37, affixed to support rods 41 by clips 42 will be precisely aligned axially, and that the cylindrical configuration of the filament wires will be in precise axial alignment with the terminal cylinders 43, 44.

Annular ring 49 is provided with a short metal cylindrical section 52 and heavy ring 26 is provided with a cooperating section 53 of like diameter. Sections 52 and 53 are then joined together by ring seal 54 of viterous material. Here again, it is readily apparent that by holding the cathode assembly and the heavy ring 26 in a fixture during the formation of ring seal 54, the ring 26 may be precisely aligned with the filament terminal cylinders 43, 44 and the remainder of the filament structure. Then, when the grid cage is afl'rxed to heavy ring 26, as previously described, the grid and filament structures are mounted and maintained in correct alignment with great precision.

The anode structure previously described, including ring 23, vitreous ring 25 and the short metal ring 28 may likewise be assembled in a glass lathe wit-h precision so that ring 28 is correctly aligned with the anode. When both assemblies have been completed, they may be joined together at 30 as previously described.

any advantageous features of the tube of the present invention will now be apparent. Since the filament terminal and support cylinders 43, 44 are solid and heavy, holes may be precision bored therein at the same radius and parallel to the axis thereof to assure perfect parallelism of the heavy filament support rods 41. Cylinders 43 and 44 may be readily held in alignment during the formation of ring seal 51, and short cylinders 47, 48 may be advanced toward each other a precise amount in a glass lathe during the formation of the ring seal so that the resulting terminal structure is correctly aligned and accurately spaced in the axial direction. When the filament wires 37 are attached to support rods 41 by means of clips 42,- the resulting filament structure is extremely rugged and of proper dimensions and symmetry.

The grid support ring 26 is likewise heavy and massive so that it may be machined with great accuracy and tapped bores precisely located therein for receiving bolts 36. Ring 26 may be accurately aligned and axially spaced with respect to the filament structure during the formation of glass seal 54 in the same manner as just explained for the two filament terminals. The grid cage may be separately assembled with precision and then secured to terminal ring 26.

Similarly the anode structure may be assembled with precision and then joined to the grid ring 26 in the manner above described so as to secure and maintain accurate alignment.

While glass seals are employed, the amount of glass used is kept to a minimum and this factor, together with the use of heavy metal supports for the electrodes insures a rugged tube.

The bowing of the largest glass section further assures adequate ruggedness. It will be understood that when the tube is evacuated the atmospheric pressure tends to press the ends of the tube toward each other in an axial direction, thus placing all the glass seals 25, 51 and 54 under compression. This is advantageous in that glass is much stronger under compression than under tension. At the glass seal 25, there is also a radially inwards pressure produced by the atmosphere, and the bowing provides strength against this pressure.

The tube also has highly desirable electrical characteristics. The precision of the mechanical assembly permits employing closely spaced cylindrical configurations to reduce transit time and insures uniformity of characteristics from tube to tube. The support members for each electrode are separated from those of each other electrode so as to reduce capacitance therebetween. Lead inductance is minimized by the concentric configuration and the straight paths involved. The elimination of all intricate parts not only simplifies the construction of the tube but greatly reduces the grid-'to-filament capacitance. The use of heavy filament terminal cylinders assures a low resistance path to the filament wires, and the heavy grid ring 26 provides a low-loss path to the grid cage.

It will be understood that many of the details of construction may be changed within the spirit and scope of the invention and that some of the features thereof may be employed in a given case while omitting others.

I claim:

1. An electron discharge tube which comprises a pair ment with the other support, a filament cage structure having axially-extending cylindrically-arranged filament wires with respective axially-extending cylindrically-ararranged mounting sections, a plurality of alternate 6 mounting sections being attached to the mounting poitions of said flange in a circular configuration of selected diameter and the intermediate mounting sections passing through the open portions of said flange and being attached to said other support in a concentric circular configuration of the same diameter, a pair of coaxial metal cylindrical sections of like diameter joined to respective cylindrical supports and sealed together by an insulating ring seal, said sections and seal extending between the outer support and the outer end of the inner support to form a non-reentrant seal, a coaxial heavy annular metal grid supporting ring extending generally laterally of the tube and positioned axially between said filament supports and said filament wires, one side of said ring being insulatedly joined to the outer filament support by'a pair of coaxial metal cylindrical sections and an interposed insulating ring seal, the inner diameter of said supporting ring being less than that of the last-mentioned ring seal and less than that of the cylindricallyarranged filament wires, the other side of said supporting ring having an accurately formed annular surface, a cylindrical grid structure having a mounting ring at one end thereof, said mounting ring being secured to said annular surface to position said grid structure in coaxial encircling relationship with said filament wires, and a coaxial cylindrical anode encircling said grid.

2. An electron discharge tube which comprises a pair of concentric cylindrical metal filament supports, the inner of said supports extending axially beyond the outer support, a flange on one of said supports having alternate mounting portions and open portions in axial alignment with the other support, a filament cage structure having axially-extending cylindrically-arranged filament wires with respective axially-extending cylindricallyarranged mounting sections, a plurality of alternate mounting sections being attached tovthe mounting portions of said flange in a circular configuration of selected diameter and the intermediate mounting sections passing through the open portions of said flange and being attached to said other support in a concentric circular configuration of the same diameter, a pair of coaxial metal cylindrical sections of like diameter joined to respective cylindrical supports and sealed together by an insulating ring seal, said sections and seal extending be tween the outer support and the outer end of the inner support to form a nou-reentrant'seal, a coaxial heavy annular metal grid supporting ring extending generally laterally of the tube and positioned axially between said filament supports and said filament wires, a pair of coaxial metal cylindrical sections of like diameter joined to one side of said ring and to said outer filament support respectively and sealed together by an insulating ring seal, the inner diameter of said supporting ring being less than that of the last-mentioned ring seal and less than thatof the cylindrically-arranged filament Wires, a cylindrical grid structure secured to the other side of said supporting ring in coaxial encircling relationship with said filament wires, and a coaxial cylindrical anode encircling said grid.

3. An electron discharge tube which comprises a pair of concentric cylindrical metal filament supports, the inner of said supports extending axially beyond the outer support, a flange on one of said supports having alternate mounting portions and open portions in axial alignment with the other support, a filament cage structure having axially-extending cylindrically-arranged filament wires with respective axially-extending inwardly-offset cylindrically-arranged mounting sections, a plurality of alternate mounting sections being attached to the mounting portions of said flange in a circular configuration of selected diameter and the intermediate mounting sections passing through the open portions of said flange and being attached to said other support in a concentric circular configuration of the same diameter, a pair of coaxial metal cylindrical sections of like diameter respectively joined at one end thereof to respective cylindrical supports, the opposite ends of said cylindrical sections being sealed together by a vitreous ring seal, said sections and seal extending between the outer support and the outer end of the inner support to form a non-rccntrant seal, a coaxial heavy annular metal grid supporting ring extending generally laterally of the tube and positioned axially between said filament supports and said filament wires, a pair of coaxial metal cylindrical sections of like diameter respectively joined at one end thereof to one side of said ring and to said outer filament support, the opposite ends of the last-mentioned cylindrical sections being sealed together by a vitreous ring seal, the inner diameter of said supporting ring being greater than said cylindrically-arranged mounting sections but less than that of the last-mentioned ring seal and less than that of the cylindrically-arranged filament wires, a cylindrical grid structure having a mounting ring at one end thereof, said mounting ring being secured to the other side of said grid supporting ring to position said grid structure in coaxial encircling relationship with said filament wires, and a coaxial cylindrical anode encircling said grid.

4. An electron discharge tube which comprises a pair of concentric cylindrical metal filament supports, the inner of said supports extending axially beyond the outer support, a flange on one of said supports having alternate mounting portions and open portions in axial alignment with the other support, a filament cage structure having axially-extending cylindrically-arranged filament wires with respective axially-extending eylindrically-arranged mounting sections, a plurality of alternate mounting sections being attached to the mounting portions of said flange in a circular configuration of selected diameter and the intermediate mounting sections passing through the open portions of said flange and being attached to said other support in a concentric circular configuration of the same diameter, a pair of coaxial metal cylindrical sections of like diameter joined to respective cylindrical supports and sealed together by an insulating ring seal, said sections and seal extending between the outer support and the outer end of the inner support to form a non-reentrant seal, a coaxial heavy annular metal grid supporting ring extending generally laterally of the tube and positioned axially between said filament supports and said filament wires, a pair of coaxial metal cylindrical sections of like diameter joined to one side of said ring and to said outer filament support respectively and sealed together by an insulating ring seal, the inner diameter of said supporting ring being less than that of the last-mentioned ring seal and less than that of the cylindricallyarranged filament wires, a cylindrical grid structure secured to the other side of said supporting ring in coaxial encircling relationship with said filament wires, a coaxial cylindrical anode encircling said grid, and a pair of coaxial metal cylindrical sections of like diameter joined to said grid supporting ring and to said anode respectively and sealed together by an insulating ring seal, the metal section joined to said supporting ring extending axially beyond the adjacent end of the anode whereby the respective ring seal is shielded from the filament Wires.

5. An electron discharge tube which comprises a pair of concentric cylindrical metal filament supports, the inner of said supports extending axially beyond the outer support, a flange on one of said supports having alternate mounting portions and open portions in axial alignment with the other support, a filament cage structure having axially-extending cylindrically-arranged filament Wires with respective axially-extending cylindrically-arranged mounting sections, a plurality of alternate mounting sections being attached to the mounting portions of said flange in a circular configuration of selected diameter and the intermediate mounting sections passing through the open portions of said flange and being attached to said other support in a concentric circular configuration of the same diameter, a pair of coaxial metal cylindrical sections of like diameter respectively joined at one end thereof to respective cylindrical supports, the opposite ends of said cylindrical sections being sealed together by a vitreous ring seal, said sections and seal extending between the outer support and the outer end of the inner support to form a non-reentrant seal, a coaxial heavy annular metal grid supporting ring extending generally laterally of the tube and positioned axially between said filament supports and said filament wires, a pair of coaxial metal cylindrical sections of like diameter respectively joined at one end thereof to one side of said ring and to said outer filament support, the opposite ends of the second-mentioned cylindrical sections being sealed together by a vitreous ring seal, the inner diameter of said supporting ring being less than that of the last-mentioned ring seal and less than that of the cylindrically-arranged filament wires,- a cylindrical grid structure secured to the other side of said supporting ring in coaxial encircling relationship with said filament wires, a coaxial cylindrical anode encircling said grid, and a pair of coaxial metal cylindrical sections of like diameter respectively joined at one end thereof to said grid supporting ring and to said anode, the opposite ends of the last-mentioned cylindrical sections being sealed together by a vitreous ring seal and the metal section joined to said supporting ring extending axially beyond the adjacent end of the anode whereby the respective ring seal is shielded from the filament wires.

6. A high-power electron discharge tube for high-frequency use which comprises a pair of concentric cylindrical metal filament supports, the inner of said supports extending axially beyond the outer support, a flange on one of said supports having alternate mounting portions and open portions in axial alignment with the other support, a plurality of axially-extending mounting rods attached to the mounting portions of said flange in a cylindrical configuration of selected diameter, a like plurality of axially-extending mounting rods passing through the open portions of said flange and attached to said other support in a cylindrical configuration of said selected diameter, a free-hung self-supporting filament cage having axially-extending wires arranged in a cylindrical configuration of larger diameter than said mounting rods and connected together at the free end thereof, alternate wires being connected to the first mentioned mounting rods and intermediate wires being connected to the second-mentioned mounting rods, a pair of coaxial metal cylindrical sections of like diameter respectively joined at one end thereof to respective cylindrical supports, the opposite ends of said cylindrical sections being sealed together by a vitreous ring seal, said sections and seal extending between the outer support and the outer end of the inner support to form a non-reentrant seal, a coaxial heavy annular metal grid supporting ring extending generally laterally of the tube and positioned axially between said filament supports and said filament wires, a pair of coaxial metal cylindrical sections of like diameter respectively joined at one end thereof to one side of said ring and to said outer filament support, the opposite ends of the second-mentioned cylindrical sections being sealed together by a vitreous ring seal to form a non-reentrant seal, the inner diameter of said supporting ring being greater than said cylindrically-arranged mounting rods but less than that of the last-mentioned ring seal and less than that of the cylindrically-arranged filament wires, a cylindrical grid structure having a mounting ring at one end thereof,

said mounting ring being secured to the other side of said grid supporting ring to position said grid structure in coaxial encircling relationship with said filament Wires, a coaxial cylindrical anode encircling said grid, and a pair of coaxial metal cylindrical sections of like diameter respectively joined at one end thereof to said grid supporting ring and to said anode, the opposite ends of the last-mentioned cylindrical sections being sealed together by a vitreous ring seal and the metal section joined to said supporting ring extending axially beyond the adjacent end of the anode whereby the respective ring seal is shielded from the filament wires.

7. A high-power electron discharge tube for highfrequency use which comprises a first metal cylinder having a plurality of axially-extending cylindrically-arranged mounting rods mounted in equally-spaced holes in one end thereof, a second coaxial metal cylinder encircling said first cylinder and having a flange overlapping said one end and provided with holes through which said rods pass in non-contacting relationship, the other end of said first cylinder extending axially beyond said second cylinder, a like plurality of axially-extending mounting rods mounted in equally-spaced holes in said flange in a cylindrical configuration of the same diameter as the first-mentioned rods and alternating therewith, a freehung self-supporting filament cage having axially-extending cylindrically-arranged wires connected together at the free end thereof, the cylindrical diameter of said wires being larger than that of said mounting rods, alternate wires being connected to the first-mentioned mounting rods and intermediate wires being connected to the second-mentioned mounting rods, a pair of coaxial metal cylindrical sections of like diameter respectively joined at one end thereof to respective metal cylinders, the opposite ends of said cylindrical sections being sealed together by a vitreous ring seal, said sections and seal extending between the second cylinder and the outer end of the first cylinder to form a non-reentrant seal, a coaxial heavy annular metal grid supporting ring extending generally laterally of the tube and positioned axially between said filament supports and said filament wires, a pair of coaxial metal cylindrical sections of like diameter respectively joined at one end thereof to one side of said ring and to said second cylinder, the opposite ends of the second-mentioned cylindrical sections being sealed together by a vitreous ring seal to form a non-reentrant seal, the inner diameter of said supporting ring being greater than said cylindrically-arranged mounting rods but less than that of the last-mentioned ring seal and less than that of the cylindrically-arranged filament wires, a cylindrical grid structure having a mounting ring at one end thereof, said mounting ring being secured to the other side of said grid supporting ring to position said grid structure in coaxial encircling relationship with said filament wires, a coaxial cylindrical anode encircling said grid, and a pair of coaxial metal cylindrical sections of like diameter respectively joined at one end thereof to said grid supporting ring and to said anode, the opposite ends of the last-mentioned cylindrical sections being sealed together by a vitreous ring seal of outwardly-bowed axial cross section and the metal section joined to said supporting ring extending axially beyond the adjacent end of the anode whereby the respective ring seal is shielded from the filament wires.

8. An electron discharge tube which comprises an envelope, a pair of concentric cylindrical metal filament supports arranged one within the other to extend into the envelope, the inner of said supports extending axially beyond the outer support at the end terminated at the envelope, a flange on the inner end of one of said supports having alternate mounting portions and open portions in axial alignment with the other support, a filament cage structure having axially-extending cylindrically-arranged filament wires with respective axially extending filament mounting sections, a plurality of cylindrically-arranged alternate filament mounting sections being attached to the mounting portions of said flange in a circular configuration of selected diameter and intermediate filament mounting sections passing through the open portions of said flange and being attached to said other support in a concentric circular configuration of the same diameter, a pair of coaxial circular heavy metallic envelope portions at which the respective filament supports terminate, a pair of coaxial metal sections of right circular cylindrical shape and of like diameter joined to the respective heavy envelope portions, an insulating ring seal joining said pair of metal sections, said metal sections and ring seal, in order to form a non-reentrant seal, providing a direct connection in the form of a cylindrical column extending between and terminating respectively at the heavy envelope portion which terminates the outer filament support and the heavy metallic envelope portion which is affixed to the inner filament support, a coaxial cylindrical grid encircling said filament wires and a coaxial cylindrical anode encircling said grid.

9. An electron discharge tube which comprises an envelope, a pair of concentric cylindrical metal filament supports arranged one within the other to extend into the envelope, the inner of said supports extending axially beyond the outer support at the end terminated at the envelope, a flange on the inner end of one of said supports having alternate mounting portions and open portions in axial alignment with the other support, a filament cage structure having axially-extending cylindrically arranged filament wires with respective axially-extending cylindrically-arranged filament mounting sections, a plurality of alternate filament mounting sections being attached to the mounting portions of said flange in a circular configuration of selected diameter and intermediate filament mounting sections passing through the open portions of said flange and being attached to said other support in a concentric circular configuration of the same diameter, a pair of coaxial circular heavy metallic envelope portions at which the respective filament supports terminate, a pair of coaxial metal cylindrical sections of right circular cylindrical shape and of like diameter respectively joined at one end thereof to the respective heavy envelope portions, an insulating ring seal joining said pair of metal sections, said metal sections and ring seal, in order to form a non-reentrant seal providing a direct connection in the form of a cylindrical column extending between and terminating respectively at the heavy envelope portion which terminates at the outer filament support and an outward extending part of the heavy envelope portion which is affixed to the inner filament support, a coaxial cylindrical grid encircling said filament wires, and a coaxial cylindrical anode encircling said grid.

10, A coaxial electron tube having an envelope providing support for elements within the tube envelope, said envelope comprising at least three heavy highly-conductive terminal members of circular shape coaxially arranged to avoid reentrant sections, each of which terminals has an aperture at its center, except the terminal which forms an end cap, right circular cylindrical columns directly joining adjacent pairs of terminal members, at which members the columns terminate, each of which columns consists of a pair of relatively light gauge coaxial metal cylindrical sections of like diameter joined by an insulating ring seal, and support members for rigidly supporting electrodes on each of the terminal members whereby close spaced electrodes are prevented from shorting from one to the other.

11. A coaxial electron tube having an envelope providing support for elements, including the filament, within the tube envelope, said envelope comprising at least three heavy highly-conductive terminal members of circular shape coaxially arranged to avoid reentrant sections, each of which terminals is a metallic ring, except the terminal which forms an end cap, right circular cylindrical columns directly joining adjacent pairs of terminal members, at which members the columns terminate, each of which columns consists of a pair of relatively light gauge coaxial metal cylindrical sections of like diameter joined by an insulating ring seal, heavy coaxial cylindrical support members extending into the envelope from each of said terminal members, and electrodes rigidly supported on each of the terminal members whereby said electrodes may be close spaced without danger of shorting from one to the other.

12. A coaxial electron tube having an envelope providing support for the grid and two sides of the filament, respectively, within the tube envelope, said envelope comprising three heavy highly-conductive terminal members of circular shape coaxially arranged to avoid reentrant sections, at least two of which terminals are metallic rings, right circular cylindrical columns directly joining adjacent pairs of terminal members, at which members the columns terminate, each of which columns consists of a pair of relatively light gauge coaxial metal cylindrical sections of like diameter joined by an insulating ring seal, heavy coaxial cylindrical support members extending into the envelope from each of said terminal members, and electrodes rigidly mounted on the support members in such a manner that they may be close spaced to one another without shorting from one to the other.

13. A coaxial electron tube having an envelope providing a filament support structure within the tube envelope, said envelope comprising a pair of heavy highlyconductive terminal members of circular shape and of different size coaxially arranged to avoid reentrant sections, the larger of which terminals is a metallic ring, a right circular cylindrical column directly joining said terminal members, at which members the column terminates, which column consists of a pair of relatively light gauge coaxial metal cylindrical. sections of like diameter joined by an insulating ring seal, heavy coaxial cylindrical support members extending into the envelope from each of said terminal members, and a filament structure rigidly supported upon the heavy coaxial support members in such a manner that alternate strands of the filament extend to one support member and intermediate strands extend to the other support member.

References Cited in the file of this patent UNITED STATES PATENTS 2,489,872 Elder et al. Nov. 29, 1949 2,489,873 Thorson Nov. 29, 1949 2,542,639 De Walt Feb. 20, 1951

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