US2617056A - Electron discharge device for high frequency - Google Patents

Description

2 H. J. DAlLEY ETAL 2,617,056

ELECTRON DISCHARGE DEVICE FOR HIGH-"FREQUENCY Filed Feb. 10, 1949 J? 5.; 1 a1 a2 W/T/Vffi'jf: INVENTORS Mm]! ATTORNEY W 7 ymc 9K3 Patented Nov. 4, 1952 UNITED STATES PLATE-NT OFFICE ELECTRON FOR-HIGH Hampton J. Dailey, Verona, and- Leo 0. Werner, Bloomfield, N. J., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pin, a corporation of Pennsylvania Application February 10, 1949, Serial No. 75,508

Claims. 1

This invention relates to electron discharge devices for high frequency and particularly to tubes of that classification wherein high frequency is involved.

Vacuum tubes wherein the operating frequency is increased for utilization of the device at high radio frequency, introduce problems not encountered in prior art tubes operating at lower frequencies, and the present invention is directed to the solution of the inadequacies of construction of relatively low frequency tubes to the manufacture and use of high radio frequency electron discharge devices.

As the operating frequency of vacuum tubes is increased, the tube must be made shorter and shorter so that tube elements are not a large fraction of wave length, for otherwise standing waves exist along the elements and decrease the efficiency of the device. As tubes become shorter, the dissipation of heat conducted along the cathode supports to the vacuum-enclosing envelope becomes more difiicult. At lower frequencies the supports may be made sufiiciently long so that the heat may be radiated by the supports; A further object of the invention is to enable use of short supports by provision of cooling means,

and to combine the cooling means as part of the electrical conductive lead-in structure.

It is necessary, in such a tube, to take into consideration the inductance and capacitance of not only the electrode elements but of the leadin and supporting parts as well. As the tube is used for higher frequencies, the capacitance between its said elements and parts must .be brought to as low a value as possible. The invention accordingly contemplates accomplishment of this desideratum. In this connection it must be appreciated that the capacitance between said elements and parts is charged and discharged each cycle and that the radio frequency current effecting that charge is carried by the lead-in parts to the electrode elements.

A further requirement in tubes operating at high radio frequency is that the electrode elements must be closely spaced in order to reduce the time required for an electron to move from the cathode to the collecting plate or anode. The transit time of electrons may be reduced by employing near the cathode a voltage gradient which The voltage gradient, V, may therefore be increased either by increasing the numerator,

or by reducing the denominator, X. Increasing either of the components of the numerator contributes to tube inefficiency, whereas, within practical constructional limits, reduction of distance X has no detrimental effect on the efficiency, but does accomplish the desired increase of voltage gradient, V. The present invention has for an object to provide a construction reducing the cathode-to-grid spacing X to its practical minimum.

Referring to the accompanying drawings in which like numerals of reference indicate similar parts throughout the several views:

Fig. l is a vertical or longitudinal section of an electron discharge device showing the several features of the present invention;

Fig. 2 is a plan looking upwardly toward the bottom of Fig. 1;

Fig. 3 is an elevation of the control grid and its mounting supports;

Fig. 4 is a detail sectional view of a portion of the upper ends of the cathode and control grid; and

Fig. 5 is a plan of the bight-engaging plate for the cathode.

In the specific embodiment of the invention illustrated in said drawing, the reference numeral l0 designates an envelope in general which is here shown as comprising a glass bowl H the rim of which is sealed to a metallic ring l2 in turn sealed to'a dome-like portion l3 which also acts as the anode. The lower end of the anode is at a lower level than the glass-to-metal seal of bowl and ring and protects that junction from high field penetration. A tubulation l 4 protruding from the bottom of the bowl enables the envelope to be evacuated.

Coax'ially within the anode is a metallic or other post It the upper end of which terminates considerably -below the dome end of the anode and the lower end of which is shown approximately at "the level of the lower end of the anode and is there provided with a pedestal 16 having a fiat-under face for fiat-wise engagement and attachment, as by brazing, to the inside bottom surface of a metallic cup I? by which the post is held solidly in fixed and upright position. A similar but inverted metallic cup l8 has its fiat wall in engagement with and secured, as by brazing, to the under fiat face of the first mentioned cup, and the downwardly directed rim of the inverted cup is sealed into the upper edge of a glass ring IS the lower edge of which is similarly sealed to the upper rim of a metallic eyelet 20. The lower part of said eyelet is larger than the upper rim thereof and provides a, downwardly directed rim which is sealed to the glass of the bowl at an upturned annular inner flange 2| thereof defining the circumferential edge of a central opening 22 through the bowl bottom wall. By these several intervening instrumentalities, therefore, the said post is rigidly supported from the bowl and is within the evacuated enclosure.

Arranged in a coaxial annular series around and in parallelism to said post, are a plurality of filament or cathode strands 23 here shown as of hairpin formation with the ends toward the hair-pin formation with the ends toward the bottom and the loops or bight-s at the top opposite an upper end portion of said post. The bights are carried next the edge of a metallic plate 24 the mid portion whereof is in turn carried by an insulating button 25 slidable upon said post. Support for said button is supplied by a sleeve 26 coaxial of and around said post and which extends toward the lower part of the post but at a distance therefrom, admitting inclusion of one or more springs 21 between the bottom of said sleeve and the post pedestal It. An inverted cup 28 and shield disc 29 are interposed between the tops of the springs and the lower end of the sleeve. The lower ends of the strands forming the legs of the hairpins are separately anchored so as to provide for proper electrical connections. One leg of each hairpin filament connects to an inner collar 30 in turn mounted on and soldered or spot welded to the post-supporting cup [1, and the other leg of each connects to an outer much longer collar 3| which depends around the glass sealing ring ill to make connection, through agency of a filler piece 32 spot welded thereto, with the aforementioned eyelet 20. Partially within and soldered or otherwise secured to the lower neck portion of eyelet is a metallic ring 33 the lower end of which protrudes from the eyelet and has a circumferential flange which is drilled parallel to the axis to receive the upper ends of lead-in wires 34 securely attached by soldering, brazing or otherwise in the drilled holes of said metallic ring.

The bottom of the glass bowl is received in an appropriate base cemented, as at 35, thereto and shown comprising a metallic ferrule 36 overlapping the lower peripheral margin of the bowl and having a transverse insulative: disc 31 gripped at its circumferential edge by the lower margin of said ferrule. A central hole is provided through said disc 31 in which is rigidly mounted a length of tubing 38 projecting downwardly therefrom. Coaxially of and in spaced relation thereto around said tubing is an outer tube 39 secured to the insulative disc by a plurality of screws 40. The aforementioned lead-in wires 34 depending from the metallic ring 33 and eyelet 20 are passed through the insulatin disc and soldered or otherwise made fast to the outer circumferential surface of said outer tube 39. Extending through tubing 38 and upwardly to the inverted cup 18 is a pipe 4!, the upper end of which has a cap 42 closing the pipe and providing a plane top surface for brazing or otherwise securing the pipe to said inverted cup. Where said pipe projects from the lower end of tubing 38, a solder or other suitable connection is made. According to the structure attained by the foregoing description, a coaxial filament feed line is provided of which said pipe M is the inner conductor and outer tube 39 constitutes the outer conductor.

Coaxially of and around the cathode is a control grid 43 shown as constructed from an annular series of parallel wires the upper ends of which are welded to the depending flange 60 of the cap 44 and lower portions welded to an annular band 45. Alternate grid wires 66 are longer than intervening wires 41 and project below said band. These alternate longer grid wires are secured, as by welding, to a spider frame 48 the legs of which diverge downwardly and are mounted next their ends between adjusting nuts 59 on posts 50 of which at least one constitutes a leadin connection for the grid from the exterior of the envelope. Extending only alternate grid Wires from the grid band 45 to the spider frame 48 very materially reduces the inter-electrode capacity from that of a grid having all of its wires of full length, and without any material increase in inductance.

The electron discharge device of the present disclosure is provided with a screen grid El, and like the control grid, comprises an annular series of parallel wires with the said screen grid coaxial to the other electrodes and located between the control grid and anode. The upper ends of said wires are welded or otherwise secured to a depending flange of a top cap 52 and the lower ends are similarly attached to the upper end of a flaring sheet metal skirt 53 which has a transverse shoulder 54 for securing between adjusting nuts 55 on posts 56 of which at least one constitutes a lead-in connection for the screen grid from the exterior of the envelope. Said skirt preferably extends substantially to the bottom of the glass bowl so that it forms a shield for the lead-in and metallic supporting parts within the bowl and skirt. The upper end of said skirt projects well within the lower portion of the anode and above the cathode-tensionin springs and control-grid annular band 45 and projects downwardly out of the bottom of the anode and entirely girdles the lead-in connections of the oathode and control grid within the envelope.

Utilization of the bowl II as part of the envelope, and the flaring construction of supports for the grids with consequential wide spacing of the lead-in connections for the several electrodes obtains desirable shortening of the tube length, discouraging to production of standing waves, and obtains a minimizing of the capacitance between supporting and lead-in connections witl in the envelope to the electrodes. The shielding nature of the coaxial outer cathode lead-in support and of the screen grid skirt, however. results in a trapping of heat, dissipation of which constitutes an important feature of the present invention. In furtherance of this objective, the coaxially central lead-in connection for the oathode has been shown as, and above-identified as, a pipe 4|, thereby constituting a conduit for inflow of a forced air blast to the upper end thereof. As the said pipe is closed at its top by cap Q2, the air blast impinges on the under side of said cap and will absorb heat therefrom. The said cap has metallic connection through the metallic cup wall-s thereon with inner collar 30 for the filament which together constitute a heat-conductive path. Lateral holes 57 in the sides of the pipe below its cap 42 and preferably within the glass ring [9, provide for outflow of the air from the pipe and direct the air stream against the lass wall of said ring to carry on heat therefrom. By virtue of the greater inner diameter of eyelet 20 and metallic ring 34 than the outer diameter of pipe 4 l, the outflow air finds adequate exit therebetween and final escape from openings 58 in the base insulative disc 31,

A further and highly important feature of the present invention is the accomplishment of closer spacing between the control grid and cathode than heretofore found possible. It may now be called to attention that the metallic plate 24 supporting the bights of the cathode filament has a diameter no greater than, and preferably less than, the diameter of the annular series of hairpin strands except forthe series of lugs or fingers 5 9 received within and supporting said bights. Said lugs or fingers are bent upward at their ends to keep the filament bights from sliding off, and it is therefore only the thickness of the metal forming the said lugs which is further outward radially than the filament strands. Furthermore, as shown in Fig. 4, the annular flange 60 of the control grid cap has an inside radius greater than the radius of the outer upturned faces of the series of lugs represented by spacing m of relatively small amount. The grid wires 46, 41, are secured on the inside of the said flange 60 and have a passing clearance of less amount than m and represented in the drawin by reference character n with n preferably not exceeding one half of dimension m. It is also preferable that the said grid wires terminate at a level below the plane of the underface of said plate 2 4 a distance at least as great as aforementioned dimension m and the upper edges of lugs 59 terminate below the under face of the cap at least as much as dimension m.

Consequently the nearest approach of the grid and cathode is represented by the spacing as between the filament strands and the grid wires which is a distance slightly less than dimension m. By this construction, the grid-tocathode spacing a: is made very close and commensurate with the electron transit time for cathode to grid and still permits use of high voltage gradient therebetween. Spacing of the nearest part of the screen grid 51 likewise is made to also approximate the aforementioned dimension m.

We claim:

1. An electron discharge device for high fre quency comprising a coaxial assembly of a cathode, anode and grid, a metallic cup coaxial to said assembly with a space intervening between said cup and cathode, a second metallic cup secured to the first mentioned cup and extending toward the cathode in said intervening space and connected with said cathode, and a cooling medium conducting pipe coaxial to said assembly and terminating substantially at the first mentioned said cup for conducting cooling medium thereto for cooling the first mentioned said cup.

2. An electron discharge device comprising an envelope and a coaxial assembly of cathode, anode and grid enclosed by said envelope, 3, glass ring included as part of the enclosing envelope. a metallic cup having a transverse wall and having a cylindrical wall with said cylindrical wall sealed to said ring, and a cooling medium conducting pipe at the exterior of the enclosure and terminating at and secured to the transverse wall of said cup for conducting cooling medium thereto for cooling said cup and seal thereof with said ring.

3. An electron discharge device comprising an envelope and a coaxial assembly of cathode, anode and grid enclosed by said envelope, a glass ring included as part of the enclosin envelope, an inverted metallic cup having a transverse wall and having a cylindrical wall with said cylindrical wall sealed to said ring, and a cooling medium conducting pipe at the exterior of the enclosure and projecting through said glass ring and terminating at and secured to the transverse wall of said cup, said pipe having lateral exit openings therein within and directed toward said glass ring for obtaining flow of the coolin medium in con-tact with said ring.

4. An electron discharge device for high frequency, comprising a coaxial assembly of filamentary cathode, anode and grid, said grid having longitudinally disposed grid wires, a plate having lugs for supporting said filamentary cathode, a cap over the cathode for support of said grid wires and. said grid wires being secured to the inside of said cap toward said filamentary cathode and stopping short of said plate.

5. An electron discharge device for high frequency, comprising a coaxial assembly of filamentary cathode, anode and grid, said grid having longitudinally disposed straight parallel grid wires, a plate having lugs for supporting said filamentary cathode, a cap over the cathod for support of said grid wires and said grid wires being secured to the inside of said cap toward said filamentary cathode and stopping short of said plate, and the clearance between said plate and cap at nearest approach therebetween substantially equalling the spacing of said grid wires from said filamentary cathode.

HAMPTON J. DAILEY. LEO C. WERNER.

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

UNITED STATES PATENTS Number Name Date 1,834,761 Berthold Dec. 1, 1931 2,108,830 Skellett Feb. 22, 1938 2,323,364 Wing July 6, 1943 2,143,327 Snook et a1 June 15, 1945 2,431,767 Murdock et al Dec. 2, 1947 2,441,349 Eitel et 'al May 11, 1948 2,446,270 Eitel et al Aug. 3, 1948 2,463,524 Derby Mar. 8, 1949

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