US2957999A - High perveance electron tube - Google Patents

Description

Oct. 25, 1960 J. w. GAYLORD HIGH PERVEANCE ELECTRON TUBE Filed June 10, 195'? 2 Sheets-Sheet l @l f f lllllllll u INVENToR.

T :n1-mW. E HY I DRD 0ct. 25, 1960 J. w. GAYLORD 2,957,999

HIGH PERVEANCE ELECTRON TUBE Filed June 10. 1957 2 Sheets-Sheet 2 INVENTOR. TCJHN W EHYLURD mm gw meds/v HIGH PERVEAN'CE ELECTRON TUBE .lohn W. Gaylord, Leacock, 'Pa., assignor to Radio Corporation of America, a corporation of Delaware 'Filed :Tune 10, 1957, Ser. No. 664,694

3 Claims. (Cl. 313-260) This invention relates to small power transmitting electron tubes and provides such a tube particularly suitable for use in small broadcast stations or amateur equipment. Thevtube of lthis invention is especially applicable to single side band operation and to those applications Where a high perveance tube having rugged, shock resistive qualities iis called for.

In transmitting equipment designed to operate with a power Voutput in the vicinity of 300 to 400 Watts, it has been found that tubes available according to prior art design require `high, `gridsignal driving power and potentials and 4high anode operating voltages. The latter requirement of rhigh anode voltage in turn requires .expensivepower `supply circuitry. A tube with operating characteristics which would overcome these `objections by operating at a `relatively low anode voltage and require relatively low drivingsignal power and which would still be commercially feasible to produce and market by the manufacturer, has never been obtainable according to prior art design.

, From the standpoint ofthe manufacturer itis desirable in making such a tube to use fabrication methods which lend themselves to assembly line procedures. fI-Iowever, prior art design of low power transmitting tubes .usually requires jigging during sealing schedules and often during some phases of mounting assemblage. Moreover, prior art design "has necessitated the welding of carbom'zed metallic parts which has proved to be a difficult procedure resulting in unreliable fabrication. Both jigging `and welding operations serve to increase manufacturing costs and may result in a lower quality, less reliable product.

It is therefore an object of my invention to provide a tube having a rugged electrode mount resistive to physical shock.

Another object is to provide a novel anode vdesign which will improve heat radiation therefrom.

Still vanother object is to provide high resistance .electrical leakage paths between electrodes.

Still another object is the provision of a rugged cageto-stem mount with a minimum of parts which is adapted to production line methods of assembly.

Yet another object is to provide improved means of electrostatic shielding between input and `output circuits.

According to my invention the above objects are attained through the provision of a tetrode tube having certain novel features in which a unitary electrode cage is assembled between a pair of ceramic spacers. The cage is fastened to a dish-like metal shield by a number of long tubular eyelets which also receive a corresponding number of stern leads to index `the cage relative to the stem. The anode, fabricated from sheet metal, comprises a plurality of heat radiating fins with such relative disposition that theyeach receive and dissipate approximately equal portions of the generated heat. Mounting wings on the anode are cut away at their ends and butt mounted against ceramic sleeves which are shadowed j, 2,957,999 Patented Oct. 25, 1960 from conductive cathode -spray -by the anode itself to provide leakage discontinuity. The entire cage is anchored to the envelope atthe opposite end from the stem by -a ductile copper -braze joint connecting a pair of crossed anode connector rods to a beaded anode stem lead.

Referring to the drawings, in which like numerals refer to like parts throughout:

Figure 1 shows a side elevation with parts cut away of a tube incorporating the features of my invention.

Figure 2 is an exploded perspective view of the electrode cage of the tube of Figure 1.

VFigure 3 is a plan view of the tube vanode according Vto my invention.

Figure V4 -is a detail in cross-section of the ceramic sleeve-anode mounting construction according to my invention taken along lines 4-4 of Figure 1.

Figure 5 is a plan view showing my novel cage-to-stem mount taken lalong lines 5-5 of Figure l.

Figure 6 is a Vdetail of a portion of my novel cage-tostem mount taken along lines 6 6 of Figure 1.

Referring to Figures l and 2, an electron tube 10 according to my invention includes an envelope 12, preferably of glass, sealed to a stem structure 14 which has a plurality of rigid lead-in conductors 16 sealed therethrough in a circular array. A unitary electrode cage 18, mounted within the envelope 12 upon the stem leads 16 comprises an indirectly'heated cathode 20 surrounded by a w-ire wound control grid 22, a wire wound screen grid 24 aligned therewith, and a sheet metal anode 26, all mounted between `two planar cross-shaped kceramic spacersZ'S and 3,0. The cage 18 is `held rtogether by four :anode side rods 3-2 which pass through apertures 34 in the ceramic spacers and 'through ceramic sleeves 36 and anode mounting wings 38 and 40. The two spacers 28 and 30 are held firmly against the ceramic sleeves 36 by metallic sleeve washers 42 which are disposed around the anode side rods and in abutment with the outer surfaces of the spacers. The washers are spot Welded to the side rods to iix the assembly. The four anode side rods 32 comprise Athe legs of a pair of U-shaped members whose transverse elements 44 serve as anode connectors. The connectors 44 are brazed togetherand to an anode lead 46 sealed through the Vend of the envelope 12 opposite the stem 14 to provide an anchorage for the cage 18 and an electrical connection externally of the envelope 12. A metal dish-shaped electrostatic shield 48 is attached to the spacer 30 adjacent the stern 1-4 of the tube and serves to shield the output circuit (anode and the elements electrically connected thereto) yfrom the input circuit elements (cathode and grid lead-ins of the stem). A small trough-like shield 50 is attached to the outer surface of the other spacer 28 and electrostatically shields the cathode 20 and the side rods Y52 and 54 of two grids 22 and 24 respectively, exposed above the spacer 28, from the anode connectors y44 and the anode lead 46. This shield 5,0 also serves to prevent heater coating material, heater base material, and cathode vsleeve material, which is evaporated from the heater and cathode respectively, from being deposited onto the envelope wall around the anode lead `,46. Such a deposit, `if permitted to collect on the envelope wall, vcan give yrise to eddy current losses, dielectric losses, electrical -leakage, and the shifting of the interelectrode capacities of the tube. Also included within the envelope 12 are .one or more conventional getters vbars 56 capable -of being activated by RF energy Yto provide -degasiication of the sealed tube. y

The anode 26, as shown in IFigure 3, is fabricated from four separate pieces Acomprising two pair of identical pieces. Eachlpiece 58 ofthe rst ypair includes an integral, externally folded radiator n 60 and two right angled flanges 62 and 64, one at either end of a section thereof. The two flanges are somewhat similar except that the one flange 62 is slightly longer than the other flange 64. Similarly, each piece 66 of thesecond pair includes an integral externally folded n 60 and two right angle flanges 68 and 70, one at either end thereof. The sections of the anode 26 are iixedly assembled by folding, crimping, and staking operations. The longer flange 62 of a section 58 is flatly abutted with the longer flange 68 of a section 66 and crimped by folding back over the latter anges end. Stakes 72 (Figure 2) are then stamped through the abutting anges and also crimped. In like manner the shorter flange 64 of a section 58 is joined to the shorter flange 70 of a section 66. In the assembled anode 26 a ange 62 of one section co-operates with a flange 68 of another section to form a mounting wing 38 and as such also serves as a heat radiator and conductor for anode cooling purposes.

Since the, cathode is flat, and because of the relative geometry-of the cathode, control grid and anode, electron bombardment occurs over only a fractional part 74 of the anode circumference, falling centrally of the flat surface portions thereof. The disposition of the integral tins 60 relative to the mounting wing iin 38 are such that optimum anode cooling is obtained. On either side of the anode the pair of integral tins 60 and the intermediate mounting wing lin 38 join the anode at closely spaced positions along the bombarded area 74 of the anode. As a result, approximately equal thirds of the heat generated in the anode by electron bombardment is conducted to and disposed of by each of these three elements-by the integral iins by radiation and by the mounting wing fin by both radiation and by conduction to the anode side rods 32 and the anode connectors 44. The two integral fins 60 are folded out at approximately 45 so that radiation from one of these ns to the mounting wing n is minimized.

The fact that radiator fins are provided by integral folds without resorting to the welding on of separate pieces results in a weldless anode. Non-welded, integral ns are highly desirable because of the better thermal conductivity obtained between the bombarded heated area and the radiating fin than exists between parts joined by welds.

Figure 4 shows a novel manner of shadowing the anode supports from the deposit of conductive materials evaporated from the cathode. It is a known fact that in operation of cathodes, especially oxide coated cathodes, cathode base material and cathode coating material is evaporated therefrom in a line-of-sight path. These materials, which are of a conductive nature, collect upon and cover insulating spacer members used to support the various electrodes and result in a lower resistance electrical leakage path between electrodes than would exist with a clean insulator surface. One way of combating this is to shadow portions of the insulator surfaces from this conductive spray and to thereby provide discontinuities in the leakage path which would otherwise exist. To this end, and as shown in Figure 2, the ceramic spacer members 2S and 30 themselves are provided with suflciently deep channels 76 cut across straight line surface paths between the electrode mount apertures so that bottom portions of the channels are effectively shadowed from the spray thus providing electrical discontinuity between electrode mount apertures. In addition to channeling of the spacer, ceramic insulating sleeves 36 are disposed around the anode side rods 32 in abutment with the spacers 28 and 30 to further isolate the anode 25 from conductive deposits on the spacer. In this case electrical discontinuity by shadowing is provided by making the anode mounting wings 38 and 40 shorter than the anode itself, and filling those portions between the spacer and the mounting wing where the side rod supports areV exposed with the ceramic sleeves 36. As such,

the anode proper shadows a portion 78 of each sleeve where it abuts its corresponding mounting wing.

Figures l, 2, 5, and 6 best illustrate my unique method of mounting `the cage 18 upon the stern leads 16 which at the same time provides electrical connections therebetween. In assembling the present tube, a glass stem 14 having a plurality of rigid lead-in conductors 16 sealed therethrough in a circular array is provided. To mount the electrode cage 18 to this stem, a dish-like shield member 48 is attached to the bottom of one of the ceramic spacers 3@ by two elongated metal tubular eyelets 80. In so doing, an electrical connection is rnade between the shield 48 and the eyelets 80. The shield 48 has three ribbon tabs 82 stamped therefrom, two of which when bent at right angles fall adjacent the ends of the two screen grid side rods 54 which pass through apertures in the spacer 30. The screen grid 24 may be adjusted longitudinally of the cathode 20 until its wires are in alignment with those of the control grid 22 and then the screen grid side rods 54 are spot welded to their adjacent shield tabs 82 to fix the position of the screen grid and make electrical connection thereto. The cage 18 with attached shield 4S can then be mounted upon the stem leads 16 and indexed relative thereto by inserting two of the stem leads 16 into the two eyelets 80 which clamp the shield 48 to the spacer 30. Spot welds can then be made to iix the assembly. The two stem leads received by the eyelets as well as a third stern lead 16 are made slightly longer than the others. The increased length of the received leads serve to give a firmer mount with less wobble, while the third lead 16 is permitted to butt against the spacer 30 thus indexing the vertical spac- -ing between the cage 18 and the stem 14. This is shown most clearly in Figure 6. This lead is spot welded to the third ribbon tab stamped from the shield and provides for a third external screen connection-the other two being those two leads which are seated in the clamping eyelets.

A cage-to-stem mount provided in accordance with the above description is highly desirable in that a minimum of parts serve a number of functions and at the same time provide an extremely rugged mount. The eyelets serve to: (a) mechanically attach the screen grid to the cage by eyeleting it to the spacer; (b) form an electrical connection between the screen shield and the screen stem leads; and (c) support the cage assembly on the stem and index it relative thereto. The shield serves to: (a) provide necessary shielding between the input and output circuits; (b) provide a low inductance electrical connection between the screen and the screen leads through three integral tabs; (c) provide high thermal conductivity between the screen and the screen shield, which serves as a heat radiator; and (d) mechanically support the screen grid and at the same time permit alignment of the screen grid with the control grid after the mount is completed by providing a weld tab.

Referring again to Figure 2, the ceramic spacers 28 and 30 have been designed to provide low thermal conductivity from the cathode to the spacers. To achieve this, the spacer apertures 84 in which the cathode 20 is seated is counterbored so that the contact area between cathode and spacer is lessened. This prevents the ends of the cathode from losing excessive heat by conduction to the spacer, and consequently enables the ends to operate at a higher temperature than they otherwise would. Moreover, a more uniform temperature is maintained over the length of the cathode. As a result, electron emission is increased at the ends of the cathode and a more uniform emission obtained. Since plate voltage is not changed, increased emission means increased tube current and consequently increased perveance.

Figures l and 2 also illustrate the novel cage anchorage and anode lead connection of the present tube. An external connection to the anode and a top anchorage for the cage is simultaneously made via the anode lead 46 sealed through the tube envelope 12 and connected to the two crossed anode connectors 44. Here the anode lead 46 is butted against one of the connectors 44 at the intersection 86 of the connectors and copper brazed thereto. Due to the relative disposition of the tube connectors and the abutting lead, the braze can be made by inserting a thin copper sheet between the parts to be joined and then heating by RF induction in a reducing atmosphere until copper flows. Total heating time is but three to four seconds. This prevents molybdenum embrittlement which might otherwise result if the connectors are, according to the preferred embodiment, made of molybdenum. Oxidation is rapidly removed by the reducing atmosphere as soon as heat is applied making cleaning unnecessary. Moreover, the heat may be localized to the extent that brazing can be within 9i@ of an inch of the anode lead bead 88 without cracking or softening it. Such a brazed joint is advantageous in that a connection suitable for anchoring the cage is provided which is mechanically strong, highly conductive, devoid of molybdenum embrittlement, economical, and especially in that its slightly ductile or supple thereby capable of withstanding shock or relative movement of parts. In addition, an anode connection having four connectors 44 and four side rods 32 is thus provided, resulting in a lower inductance external lead-in connection.

I claim:

1. An electron tube comprising an electrode cage including a pair of spaced parallel planar insulating members, and a cathode and an anode mounted in spaced relationship in the space between said insulating members, at least one electrically conductive anode support rod extending between said members, said support rod being connected to an exteriorly available terminal said anode having at least one electron receiving portion and at least one mounting wing extending in a direction away from said cathode and mounted on said anode support rod, said mounting wing being cut away at each end to provide a rod engaging portion shorter than said anode, a pair of insulating sleeves disposed on said support rod, each abutting one of said members and one end of said rod engaging portion of said mounting wing, whereby a portion of said sleeve is shadowed from said cathode by an end portion of said anode.

2. An electron tube comprising: a stem structure including a plurality of leads sealed through an insulator base; a unitary electrode cage including two parallel planar insulating spacers, and a cathode, a grid having side rods, and an anode, mounted in spaced relationship between said spacers; a conductive shield member disposed between said cage and said stem; a plurality of elongated tubular eyelets fastening said shield to one of said spacers and fitting over some of said leads and Welded thereto, thereby indexing and supporting said cage upon said leads; said shield having at least one ribbon tab stamped therein; said tab disposed adjacent a grid side rod and iixed thereto to x said grid in position.

3. An electron tube comprising: an envelope and a stem sealed thereto having a plurality of conductors sealed therethrough in a circular array; said envelope containing a unitary electrode cage including a pair of spaced parallel insulating spacers, and a cathode, a grid having side rods extending through one of said spacers, and an anode, all mounted between said spacers; a dishshaped conductive shield disposed between said cage and said stem and attached to said one of said spacers by a pair of elongated tubular eyelets, said eyelets being so disposed that they receive a pair of said conductors thereby mounting said cage upon said stem; one of said conductors being more extensive internal of said envelope than other of said conductors and having its end internal of said envelope in abutment with said one of said spacers thereby longitudinally indexing said cage relative to said stem; said shield having a plurality of ribbon tabs stamped therefrom and bent toward said stern, a diierent one of said tabs lying adjacent and welded to each of said screen grid side rods, another of said tabs lying adjacent and Welded to said one of said conductors.

References Cited in the tile of this patent UNITED STATES PATENTS 1,675,073 Weeks June 26, 1928 1,791,275 Jones Feb. 3, 1931 1,934,378 Ronci Nov. 7, 1933 2,356,035 Downing Aug. 15, 1944 2,760,100 Klopping Aug. 21, 1956

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