US2853640A - Electron tube - Google Patents

Description

Sept. 23, 1958 f M, v, HOOVER 2,853,640

ELECTRON TUBE Filed Sept. 19, 1955 2 Sheets-Sheet 1 INVENTOR. Man: 1 Heavy? Sept. 23, 1958 M. v. HOOVER ELECTRON TUBE 2- Sheets-Sheet 2 Filed Sept. 19. 1,955

INVENTOR. Mirfl' MA 001m? BY Why 4 ,4 Tam/5r ELECTRON Merle V. Hoover, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application September 19, 1955, Serial No. 535,029

2 Claims. (Cl. 313-447) This invention relates to high frequency, high power electron tubes having improved electrical and thermal characteristics and to improved structures for such tubes. In particular, this invention relates to electron tubes having improved control grid structures which are adapted for more eflicient cooling thereof and which exhibit improved operational characteristics.

In the design of space charge controlled electron tubes (e. g. conventional triodes) for operation at high frequencies, it is desirable to use the smallest possible spacing between the control grid and cathode. Such small spacing reduces the driving power necessary to control the tube as well as the transit time of electrons from cathode to control grid.

The interception of electrons by the control grid may beminimized through the use of very finegrid wires. Such fine grid wires will present less area to the electron stream for electron bombardment. Theireduction in electron interception will reduce both the powerless of the tube as represented by the removal of electrons from the stream proceeding from cathode to anode, and the heating of the control grid produced by such absorption of electrons.

However, it-is diflicult. to reduce the heating of the control grid to a negligible value, particularly wherethe tube is operated at high power output. .In fact, heating of the control grid in high power operation is always sufficient to make it necessary to provide some means of dissipating such. heat in order toprevent the destruction of the control grid. Furthermore, even the provision of an efficient cooling system for the control grid will not eliminate the necessity of considering-the expansion characteristics of the- .control grid under the influence of heat and the possibility ofthe warping or shifting of theucontrol grid due to such expansion.

Thus, an object of this invention is to provide an. elecnited State's Fatent tron tube having improved electrical and thermalcharacteristics.

Still another object of this invention is to provide .an improved control grid structure for anelectron tube.

Another object of this invention is to providean electron tube having a control grid close spaced from the cathode and which comprises very fine wires, but is so supported and cooled that deleterious warping or shifting cannot occur.

A further object ofthe-invention'is to provide an improved means of cooling the control grid structure ofan electron tube.

T he operation of an electrontube at high frequencies creates problems of design relating to the provision of wave spaces and conduction paths for the high frequency energy within the tube. The design of a control grid for the eflicient conduction and utilization of high frequency energy is dllfiCUilZ, due to the inherently poor conduction characteristics thereof. The large number of grid elements or wires and the spacing therebetween is "ice 2 not' conducive to the efficient transmission of high frequency energy.

Furthermore, when the length of the electron active portion of the control grid (as well as the lengths of the electron active portions of the remaining electrodes) becomes a substantial fraction of the wavelength at the operating frequency it is found that voltage and current gradients exist along the length thereofcorresponding to a standing wave of the applied frequency. It is desirable to position the terminals for the control grid as well as the terminals for the remainder of the electrodes of an electron tube in such a way as to take advantage of such standing wave of voltage and current. This can best be accomplished by providing terminals at each end of the control grid and otherwise adapting the tube for double ended operation. Thus, the electron active portion of the electron tube may be effectively located at a voltage maximum of the applied frequency to utilize the standing wave of current and voltage to the best advantage.

Thus, yet another object of this invention is the provision of a control grid'structure adapted to utilize high frequency driving power to the best advantage.

Yet a further object of this invention is to provide an electron tube particularly adapted for double-ended operation.

Briefly, an electron tube accordingto this invention comprises an annular envelope and a plurality of electrodes having generally cylindrical electron active surfaces located within such envelope. Theelectrodes include an anode, cathode and control grid. Theano-de and the. control grid comprise cylindrical membersat least one of which is hollow and the other of which is mounted co-axially therewithin, whereby a side surface of the control grid member faces a side surface of the anode mem ber. The side surface of the control grid member facing the anode is provided with a plurality of parallel longitudinally extending channels and a multiplicity of closespaced turns of fine wire are wound on such surface such that each turn extends across all of such channels. The cathode comprises a plurality of elongated'filaments in cylindrical array at least one of the filaments extending within and along each of the channels in thecontrol grid cylinder closely adjacent to the grid wire turns, whereby the turns are interposed between the cathode filaments and the anode. Means may be provided for additionally cooling the control grid cylinder to reduce deleterious heating of the turns of fine wire thereon (e. g. by making the control grid cylinder a portion of the envelope of the electron tube and directing cooling fiuids against its back surface).

The control grid and the cathode may be insulatingly connected at the ends thereof and supported from a commonsupport to insure accurate spacing therebetween. Electrode terminal members may be provided at each end of the tube to adapt the tube for double-ended operation.

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

Figure 1 is a view partially in elevation and partially in axial section of an electron tube according to this invention;

Figure 2 is a perspective view of a portion of a control grid and cathode assembly according to this invention broken away to show the interconnection between the cathode and the control grid.

Figure 3 is a fragmentary detail view in cross section taken along line 3-3 in Figure 1.

Referring to Figure 1, an electron tube 10, according to this invention, comprises an annular envelope containing a plurality of generally cylindrical hollow elec- I this invention is equally applicable to other tube types such as tetrodes, pentodes, etc. Thus, the electron tube 10, according to this embodiment of this invention, comprises an anode 12 surrounding a cathode 14 and a control grid 16. The control grid 16 comprises a hollow metallic cylinder or grid block 18 coaxial with the anode 12. The outer surface of the cylindrical grid block 18 is provided with a plurality of parallel longitudinally extending channels or grooves 20. A plurality of turns 22 of fine wire are Wound about such outer surface of the grid block 18 such that each turn 22 extends across all 7 of the channels 20. a

The cathode 14 comprises a plurality of elongated filaments 14' in cylindrical array, at least one of such filaments 14' extending within and along each of the channels 20 in the grid block 18. The filaments may be composed of a thermionic emissive material such as thoriated tungsten, for example, and preferably are of ribbon shape to present flat surfaces closely adjacent to the grid turns 22, as shown best in Fig. 3.

Referring to Figure 3, the electron tube 10 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 channel'20 are extremely close spaced from the filamentary cathodes 14'. Such close spacing between the control grid wires 22 and the filamentary cathodes 14' 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 the higher frequencies due to the fact that it is adapted for double-ended operation. Referring to Figure 1, it will be seen that the electrodes 12, 14 and 16 are symmetrical on each side of a transverse plane passing through the longitudinal center lines of such'electrodes. In addition, the cathode 14 and control grid 16 are provided with terminals 24a, 24b, 26a and 26b at each end thereof and the anode 12 is provided with terminal 28 disposed centrally of the length of the tube 10. Thus, input and output circuits may be connected to the tube 10 from either end thereof. For example, in operation an input circuit may be 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 may be connected between the cathode and grid terminals 24b and 26b at the other end of the tube 10. Similarly, an output circuit may be connected between the grid and anode terminals 26b and 28 at one end of the tube 10 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 when the tube is operated in the high frequency ranges- 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 electrical terminal members 24a, 24b, 26a, 26b and 28 and annular insulating (e. g. ceramic) members 30a, 30b, 31a and 31b in stacked and alternated array. A gas tight seal exists be-;

sion. The compressive force necessary to produce the seals is provided by a center bolt 32 extending axially inwardly of the inner wall of the annular envelope and acting on header members 34 and 36 at each end of such envelope.

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 38 on the terminal member 24a which engage the lower ends of the cathode filaments 14'. The other heating voltage terminal is provided by the lower header member 34 which passes axially through the lower cathode terminal member 24a and is sealed thereto in water tight relation by means of a mica gasket 40 and a metallic ring 42 under compression. The lower header member 34 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 44, a contraction joint 46, a massive filament support block 48 and a filament tensioning system 50.

A parallel path for the filament heating voltage from the lower header member 34 to the upper ends of the filaments 14' exists through the center bolt 32 to the upper header member 36 and from there to the upper cathode terminal member 2412 through a metallic spacer ring 52. The upper cathode terminal member 24b is electrically connected to the filament support block 48 through a sliding contact means 54 comprising a helical spring compressed between the terminal member 24b and the support block 48.

The annular envelope of the electron tube 10 is evacuated through an exhaust tabulation 56 which passes through the upper header member 36 and a thin metal envelope closure disc 58. After the envelope is evacuated, the exhaust tnbulation 56 is closed by means of a cold weld pinch-off and covered by a protection cap 60. A similar protection cap 61 covers an extending end of a tubular getter structure (not shown).

The anode terminal 28 of the electron tube 10 is provided with coolant passageways 62 and 64 which provide for the introduction of a cooling fluid into the anode structure 12. Means 66 including. channels and a baffle plate are provided at the outer surface of anode opposite the electron active face thereof for intensely cooling such face.

According to a feature of this invention the grid block 18 forms a major portion of the inner wall of the annular envelope of the electron tube 10. Thus, the grid structure maybe intensely cooled by circulating a cooling fluid in direct contact with the inner surface of the grid block 18. A study of Figure 1 will reveal that the inner surface of the grid block 18 and the thin metal sleeve 44, contraction joint 46, and filament support block 48 from an annular cooling chamber 68. The cooling fluid flows into such chamber 68 through a passageway 70 in the lower header member 34 and passes out of such chamber 68 through a passageway 72 in the filament support block 48. The cooling fluid then proceeds down along the center bolt 32 and flows out of the electron tube 10 through a passageway 74 (shown in dotted lines) in the lower header member 34.

The cooling fluid must have insulating properties in order to avoid shorting out the heating voltage applied to the cathode 14 through the lower cathode terminal 24a and the lower header member 34 or the driving voltage applied to the grid 16. For example, distilled water may be used as the cooling fluid.

Referring to Figure 2, the cathode and control grid assembly is shown in greater detail. The turns 22 of fine wire are indicated generally at several locations along the grid block 18. It should be understood that the grid wires actually cover the entire outer surface of the channeled portion of the grid block 18. Further, it should be understood that the representation of the turns of ag regate wire 21hr Boar Figured and Figur'e 2' is exa gerated-1m size-for'the purpose ofillustration. Actually, the turns 2201? who are very fine and much more closely spaced than would be amenable to illustration in scale. For example, according to one embodiment of this invention, the wire has a diameter of 0.003 inch and there are seventy-two turns thereof per inch. Since the turns 22 of wire are so fine, they must be intensely cooled in order to prevent them from warping or actually melting due to heating thereof during the operation of the tube 10.

The channels 20'of the'grid block 18 are separated by land portions 78 which provide efficient heat conduction from the turns 22 of wire to the grid block" 18 where it is dissipated into the cooling fiuid. In order toinsure the best possible heat transfer, the turns 22 of wire may be embedded in the lands 78 of the grid block 18 as by peening them into transversely extending grooves corresponding generally to the wire in size. In Figure 3, thedotted lines extending across the lands 78 indicate the embedded or peened-in portions of'the turns'22 of grid wire.

The turns 22 of wire onthe grid block are extremely close spaced from the cathode filaments 14', as mentioned above, in order to reduce the driving power necessary to control the tube. Any deviation in the spacing between the cathode and control grid will affect the operational characteristics of the tube, a small deviation in such spacing resulting in a substantial change in operational characteristics of the tube. Therefore, it is necessary that the filaments 14' and-the grid wires 22 be accurately positioned with respect to each other.

According to this invention, anv improved cathodecontrolgrid assembly is provided inwhich the spacing between the control grid and the cathode is independent of other structural features of the electron tube in which it isused. Referring to Figures 1 and 2, it will be seen that the cylindrical control grid structure 16 and the coaxial. cylindrical array of cathode filaments 14' are rigidly interconnected at' each of their ends by insulating mechanical means. This mutually aligned cathodecontrol grid assembly is supported from the lower cathode terminal member 24a. Thus, the cylindrical array of cathode filaments 14' and the control grid structure 16 are interconnected at both ends by elements 24a, 80, 82, 84, 86, 88, 90 and 48 (Fig. 2) thus making the spacing therebetween independent of the remaining tube structure including the electrical connections thereto.

Referring to Figure 2, the interconnection between the lower end of the cylindrical array of cathode filaments 14' and the lower end of the cylindrical control grid structure 16 coaxial therewith comprise a first metallic collar 80 butt-welded at one end thereof to the lower cathode terminal member 24a, an insulating ring 82 (e. g. of ceramic) one surface of which is butt-sealed by a brazed joint to the other end of the first metallic collar 80, and a second metallic collar 84 butt-sealed at one end to an opposite surface of the insulating ring 82 and buttwelded to the grid block 18. The interconnection between the cathode filaments 14' and control grid structure 16 at the upper end comprises a third metallic collar 86 butt-welded at one end thereof to the grid block 18, a second insulating ring 88 (e. g. ceramic) one surface of which is butt-sealed by a brazed joint to the other end of the third metallic collar 86, and a fourth metallic collar 90 butt-sealed by a brazed joint at one end thereof to an opposite surface of the insulating ring 88 and butt-welded at the other end thereof to the massive filament support block 48. The cathode filaments 14' are mechanically and electrically connected between the lower cathode terminal member 24a and the massive filament support block 48.

The filaments 14 are provided with lateral extensions forming T-shaped heads 92 at the ends thereof. Each of the heads 92 at the lower ends of the filaments 14 engages two hook-like projections" 38 '(in Figure 1) on the lower cathode terminal'member 24a. The heads 92 on the upper ends of the filaments 14' engage the upper edges of slots 94 in the ends of conductive fingers 96 which'along with cooperating spring fingers 98 comprise the filament tensioning system 50. The spacing between the filament tensioning system 50 and such hook-like projections38 is such that'filaments of the proper length will be' subjected to tension by' the filament tensioning system 50 when such filaments are cold. The tension thus produced in the cathode'filaments 14' when cold will be partially relieved when the filaments expand upon being'heated to provide thermionic emission. Thus, the expansion of the filaments will not result in the warping or buckling thereof but will be dissipated in the relief of the tension therein. The tension in the cathode filaments 14 also insures eificient electrical contact between the hook-like projections 38and the conductive fingers 96 by providing compressiveconta'cttherewith.

The electron tube 10, according'to this invention, is particularly adapted for high frequency operation through the provision of short wave paths into the input space between the cathode filaments 14 and the unitary con trol grids 16', andout of the output space formed between the control grid structure and the anode 12. As shown in Figure2, the grid block 18 is provided with an integral radially extending flange or grid foot 100" at each end thereof and apertures 102 extending axially through such flange 100 and communicating with chan nels 20 in the grid block'18. The filaments 14 extend within and along each channel 20 and through the apertures 102 and are connected to-the hook-like projections 38 at one end and thefilament tensioning system 50 at the other. Each flange 100 'also .has an axially extending portion which insures adequate shielding between the anode 12 and cathode 14 and which provides a surface to which the grid terminals26a and 26bm'ay be connected by means of a slidingcontact 54. p

The high frequency input'waves enter the tubebetween the cathode and control grid terminals 24a and 26a and follow a very short path into the space between the cathode filaments 14' and the unitary grids 16'. The output waves are conducted out of the cavity formed between the anode 12 and control structure 16 through, a similarly short path, the lands 74 on the grid block 18 providing a broad area surface which aids in the con-- duction of the high frequency output wave. Further-- more, the shielding between the input and output cir-- cuits which is necessary to prevent oscillation or spurious: responses is completely insured due to the interposition of the control grid terminals 26a and 26b, the grid flangesv 100 and the grid structure 16 between the anode 12 including its terminal 28 and cathode 14 including itsterminals 24a and 24b.

A study of Figure 1 will reveal that an electron tube It according to this invention is particularly suited for high frequency, high power operation in conjunction. with wave guide or cavity resonator types of circuits. The electrodes 12, 14, and 16 are cylindrical in form and are coaxially and coextensively arranged. The anode terminal 28 is located, and electrically connected to the anode 12, in a central plane transverse to the longitudinal center line 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 terminalsv 24a and 24b are equidistantly spaced from the anode ter minal 28 and are located at and electrically connected to opposite ends of the cathode 14. As stated above the control grid terminals 26a and 26b are interposed in the envelope wall between the anode terminal and the cathode terminals 24a and 24b.

If the wave guide circuit used is properly designed, the electron tube 10 will operate as if it is the central portion of a half-wave line closed at both ends. In other words, an attempt has been made to enable the simulation of a closed 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 cooperate with external linesto form a closed half-Wave line. For example, the input circuit comprises two external coaxial transmission lines connected one at each end of the tube between the terminals 26:2,2612, 24a, and 24b of the control grid 16 and cathode 14. The line at one end of the tube 10 is connected to the input' source and the line at the other end of the tube maybe thought of as a dummy (or slave) input line, the primary purpose of which is to balance the input circuit such that the electron active portion of the electron tube 10 will be positioned at the center thereof. Similarly, an output line and a dummy output line may be connected between the anode terminal 28 and control grid terminals 26a and 26b to produce closed output half-wave 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 with a maximum of ef ficiency. In addition, the unitary construction of the electron tube 10 according to this invention makes extremely high-power output possible in the operation thereof. In a successful experiment, an electron tube constructed in accordance withthis invention gave an output of 110 kilowatts at 540 megacycles with a power gain of about 25 and under bandwidth conditions suitable for col-or TV 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. An electron discharge device comprising an annular envelope including concentric inner and outer walls,

lel longitudinally extending channels, said grid also cornprising a multiplicity of spaced turns of wire on said other surface of said member with each turn extending across all of said channels, and said cathode comprising a plurality of elongated filaments, at least one of said filaments extendingwithin and along each of said channels in spaced'relation to the sides thereof and closely adjacent to said wire turns, whereby said turns of wire are interposedbetween said cathode filaments and said anode. i I V 2. An electron tube comprising an annular envelope including concentric inner and outer walls, a plurality of annular electrodes at least the electron active surfaces of which are within said envelope, said electrodes including an anode and a cathode and a control grid, said control grid comprising a tubular member which forms a portion of said inner wall of said annular envelope, a plurality of annular electrode terminal members and annular insulating members forming portions of said outer wall of said annular envelope, there being at least one terminal member for and connected to each of said electrodes.

References Cited in the file of this patent UNITED STATES PATENTS "2,496,003 'Eaves Jan. 31, 1950 2,512,858 Hegbar June 27, 1950 2,517,334 Murdock Aug. 1, 1950 2,520,016 Ronci et al. Aug. 22, 1950 2,683,237 Scullin L July 6, 1954 2,707,757 Agule May 3, 1955.

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