US2490786A - Cathode for electron discharge devices - Google Patents

Description

Dec. 13, 1949 R. w. DEUTSCH CATHODE FOR ELECTRON DISCHARGE DEVICES Filed June 26, 1947 ATTO R N EY Patented Dec. 13, 1949 I'CATHODE FORELEGTRON "*DISGHARGEDEVICES 6 Claims. 1

My :invention relates. to electron' discharge deyiceszandsdealsparticularly with cathode: struci-turesrfor; electron discharge devices of the .large :01 power class.

f{iIf-'itheCathOd electrode .of a power tube must dissipate .more 1 than a few kilowatts, it is "usually sfabricated from. a number of parallelstraight .-filamentary cathodes disposed cylindricallyand coaxial with a cylindrical grid and anode. lteis easy-.to support the ifila'ments at the base end of the tube on short stiff lead-in conductors through the stem, butysupportsfor .the'outer ends of the filaments are not so simple. The outer ends cannot be" braced "against the "grid-or anode-partly because of assembly problemsinmanufacture and partly-because :there'jare; norommercial insulators available which have satisfactory. high- ..voltage' high-frequency characteristics"at the .goper ating temperatures.

""One' ofthe'more" common outer-end supports comprises a heavy rod anchored firmly in the stem or base portion of the tube and extending along the center of the cathode to the outer end, each filament wire being attached to the periphery of a transverse metal disc which is centered on the outer end of the support rod. In attempts to prevent bowing and buckling, springs at one end of the cathode assembly have been tried, but degassing and exhausting temperatures usually take the temper out of spring metals, and sticking between parts that are intended to slide cause, rather than prevent, bowing. Unequal expansion and contraction of the filaments further complicate the problem.

One of the objects of my invention, accordingly, is to provide improved cathode assemblies for electron discharge devices.

Another object is to provide a filamentary cathode for power tubes which may be closely held in position and which will not bow or buckle.

The scope of my invention is defined in the appended claims and one embodiment is described in the following specification and shown in the accompanying drawing, in which:

Fig. 1 is a perspective view partly in longitudinal section of my cathode assembly; and

Fig. 2 is a segmental plan view of the outer or depending end of the assembly of Fig. 1.

The particular cathode illustrated comprises a plurality of hair-pin filaments l, the parallel legs of the filaments being symmetrically spaced about the center-line of the cathode structure. One leg of each filament is solidly attached at its base end, as by eyelet type rivets or bushings 2, to the periphery of a round metal plate 3 and the other 2 eleg-li-isysimilarlyattached toa:-second' metal plate v.4. The-rim of 'thewsecond plate d -is serratedtas shown to accommodate, without touchin fithe efilament legs secured to the plated. Thebight 5 aofteachvhairpincomprises a transverse section,

1 with-squareibends,and with a length correspondving-to the desired distancebetween the legs'ofthe .filament. Each :plate 3-and- 4- solidly supported aon'lead-inconductors,6 and l-sealed in-a'conl0 eventional.stempnbase element. Thecenter-support rod 9 is coaxial :with the-cathode structure ;-:and.-may. befixed at its baseend to the tube stem eazoraelsewhere. in the tubeenvelopeiinany desired i zmannel'.

qUpon theouter-end of thecenter rod fiis looscly afittedja .bushing 40 .of quartz, ceramic For other .insulating material, :and: upon the bushing, in a.-turn,--is centered-a thin light-Weight and flexible rmetal disc I. The bushing 'and' disc are loosely 20.;secu-red; together I as. byaa; retainer cup H l 2 which to accurately position and hold the filament.

Radial slots [5 are cut in the disc between the tongues. In assembly, the filament bight is simply laid over the tongue in the notches and the tongue is folded over the bight.

The connection between the filament and the disc permits the filament bight to pivot freely under the tongue so that slight flexing of the disc, by elongation or contraction of the filament, can only bear on the filament along a line lengthwise of the filament and will not tend to bow the filament.

If desired, equipotential mid-points of the filament legs may be joined with brace wires for further stiffening as disclosed in the copending application of Andrew Tierney, filed August 3,

1946, Serial No. 688,326, now abandoned, and assigned to the assignee of this application. While freedom of the bushing on the center rod accommodates large changes in the length of the cathode, as when the temperature of the filaments are increased from room to operating temperature, the pivotal connection of each bight and the flexibility of each segment accommodates inequalities in filament expansion.

The cathode of my invention obviates the complications and expense of spring tensioning means, has no sticking metal-to-metal sliding contacts, and will hold the filaments accurately in place without bowing or buckling. Elimination of springs and many of the metal parts heretofore thought necessary not only lightens the structure but simplifies degassing and exhaust.

I claim:

1. A cathode assembly comprising a cylindrical assembly of parallel filamentary cathodes, a support rod coaxial with said assembly, a flexible disc, an insulating bushing freely slidable on said rod, means on said disc loosely supporting said bushing centrally thereof, each filament being fastened at one end of said cathode assembly to a relatively immovable plate and attached at the other end of said cathode assembly to the periphery of said flexible disc to permit unrestrained longitudinal movement of said filaments parallel to said rod.

2. A cathode assembly comprising a cathode filament, said filament being fixed at one end of said cathode assembly, a rod parallel to and spaced from said filament, and a flexible spacer at the other end of said cathode assembly, said spacer having a bushing retainer and an insulated bushing loosely held by said retainer and freely slidable on said rod whereby unrestrained longitudinal expansion and contraction movements of said filament are permitted while transverse displacement thereof is prevented.

3. A cathode structure comprising a support rod, a fixed plate transverse to said rod, a flexible metal disc, an insulating bushing supporting said disc transverse to said rod, said bushing being freely slidable on said rod, a member on said disc loosely retaining said bushing on said disc, a plurality of parallel filamentary cathodes attached at opposite ends of said cathode structure to said plate and said disc, said flexible disc having a radial slot between each pair of filamentary cathodes.

4. A cathode structure comprising a thin metal disc having symmetrically spaced radial slots, a plurality of hairpin shaped filamentary cathodes, the bights of said cathodes being pivotally attached to the periphery of said disc between said slots, and the legs of said cathodes being parallel and extending substantially normal to said disc.

5. The cathode structure defined in claim 4 further comprising integral tongues on the periphery of said disc between said slots, notches in the periphery of the disc on either side of each tongue, each tongue encircling the bight of one filamentary cathode and holding the legs of the cathode in said notches.

6. A cathode structure comprising a plurality of fixedly supported lead-in conductors, close spaced parallel plates transverse to said conductors and electrically connected to different conductors, a fixedly supported center support rod extending centrally through said plates, an insulating bushing freely slidable on said rod near the outer end of the rod, a flexible metal disc centered and loosely retained on said bushing, said disc having symmetrical radial slots, a plurality of hairpin filamentary cathodes, the ends of the legs of each cathode being connected, respectively, to said plates, and the bight of each cathode being connected to the periphery of said disc between said slots.

ROBERT W. DEUTSCH.

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

UNITED STATES PATENTS Number Name Date 2,385,435 Werner et al Sept. 25, 1945 2,419,124 Dailey Apr. 15, 1947

Images