US2941109A - Tube having planar electrodes - Google Patents

Description

June 14, 1960 w. H. SENIOR I'AL 2,94l,109

TUBE HAVING PLANAR ELECTRODES Filed Oct. 25, 1957 6 W59 Mw4 l i l 7 m a 5 %W 4 w INVENTORS William H. Senior Morraine E Sfang/ ATTORNEY 2,94l,l09 Paiented June 14,' 1 960 TUBE HAVING PLANAR ELECTRODES William H. Senior, San Mateo, and Morraine E. Stangl, Los Altos, Calif., assignors to Eitel-McCullough, Inc., San Bruno, Calif., a corporation of California Filed Oct. 25, 1957, Ser. No. 692,406

2 Claims. (Cl. 313-450) This invention relates to electron tubes and more particularly to electron tubes of the type having planar electrodes.

The purpose of the invention is to provide a planar electrode tube which will be operable with good efiiciency at anode voltages comparable to screen voltage and at the same time one which will have low output capacitance. Fur-ther, the purpose of the invention is to provide a planar electrode tube having a very eflicient heatercathode structure, and in addition, a planar tube which can be operated at unusually high ambient temperatures.

In addition, the purpose of the invention is to provide a miniaturized, ruggedized tube capable of assembly by automation equipment.

The required electrical capabilities have been achieved by using in their normal arrangement a cathode, control grid and screen grid, and adding a ring-shaped electrode between the screen grid and the anode. The ring electrode can be operated at cathode potential so that secondary electrons released at the anode will be prevented from traveling to the screen grid even if the voltage on the screen is as high as the anode voltage. Thus, the ring electrode serves a purpose similar to that oi the conventional suppressor grid. However, the ring electrode of the invention is devoid of grid bars and thus minimizes the output capacitance.

The required ability tooperate in -a high temperature environment presents a consider-:able problem in maintaining the proper spacings between the electrodes and, of course, the insulating material used in the tube envelope must be capable of withstanding high temperatures. The means which the invention teaches for permitting high temperature operation comprises in combination with a ceramic envelope an arrangement preventing detrimental movement of the electrodestoward and away from each other due to the difierent coefiicients of expansion of the ceramic in the envelope and of the metal elements which support the electrodes on the envelope.

The manner in which all of the required features have been obtained in a planar tube will now be described in detail with reference to the single figure of the drawing, which figure shows the tube in cross section.

Referring to the drawing it will be seen that the tube embodying the invention comprises a generally cylindrical envelope made up of alternate ceramic and metal rings joined' together'. There are six ceramic rings, pref erably of the high alumina type, designated by the reference numerals 2-7 consecutively. There are seven metal rings designated by the numerals 18-16 .consecutively. All of the metal rings are of Kovar except for ring 16 which is preferably copper. The ends of the ceramic rings are metallized by any suitable procedure as, for example, the moly-manganese powder sintering process. The metallized ends of the ceramic rings are then brazed directly to the metal rings except in the case of metal ring 13. A final sealing is provided in the area of metal ring 13 by means of two sealing rings 18 and 19, the

inner portions of which are brazed respectively to the ceramic rings 4 'and 5 and the outer portions of which are joined by a final weld or braze 20. A terminal ring 19' is attached to the sealing ring 19 and carries one or more radially extending terminal tabs (not shown). Metal ring 13 is spot welded to sealing ring 19 to fix its position in the tube, as will be more fully described hereinafter.

The tube comprises a plurality of planar electrodes consisting of a cathode 22, a control grid 23, a screen grid 24, a suppressor electrode 25, and an anode 26. The electrode 25 instead of being a grid-like structure such as grids 23 and 24 is a ring-shaped'member provoiding an unobstructed central aperture; it will be noted from the drawing :that this aperture is of larger area than the area of the cathode and does not perform any beam forming function.

The metal envelope rings 10-16 form lead-ins for the various electrodes and are extended inwardly of the envelope to provide supports and electrical leads for the electrodes. For example, the metal ring 10 is extended inwardly at 23 to form a closure' for the bottom of the tube and a support `for a two-piece heater pin 29 which is brazed within a central aperture in the end closure. Metal ring 11 is extended inwardly at 30 to form a second lead. for the heater, the heater itself being a flat coil 32 of wire coated with an insulating material such as an aluminum oxide. The heater 32 has its ends 33 and 34 attached respectively to the leads 29 and 30 by means of spot welds.

Metal ring 12 is extended inwardly at 36 to provide a support for the cathode 22. -It will be noted that the spacng between cathode 22 and grid 23 isextremely small so that even a very slight change in this spacing i will have a substantial detrimental efiect. Again stating that the tube is designed for operation at extremely high ambient temperatures, for example, 500 degrees centigrade, it will be understood that problems are encountered in avoiding change in grid to cathode spacng due to the different coefiicient of expansion of the various materials employed in the tube. which .has heretofore plagued the industry in this regard is that the radially extending metal electrode supports, such as cathode ring 36,

are held against radial movement. Thus, as metal ring 36 tends to expand more than ceram'c rings 3 and 4 the cathode support. tends to accommodate its radial expansion by the detrimer'tal action known in the art as "oil canning." In other words, when a disk or flat ring is heated and thus tn'es to expand,vt will, if this expansion is prevented, tend to bow up or down at its center. According to the invention this detrimental oil canning action has been avoided by placing a V-shaped corrugation 33 in support ring 36. Thus radial movement of t support 36 due to temperature change is accommodated surface of the cathode disk is, of course,

by opening and closing of 'the V-shaped corrugaton, thereby avoiding the oil canning action.

The cathode heater structure is supported on four legs ita which are spot-welded at their lower ends to support ring 36 and integrally connected at their upper ends to a centrally -apertured support disk 41. The cathode per se comprses a rimmed disk 42 which is spot-welded` to the legs 4@ so as to clamp the heater coil 32 between the support disk 41 and the cathode disk 42. The upper preferably coated with an oxide type emissive material. Three metal heat shields 43 in the form of centrally apertured disks `are spot-welded to the support legs 40.

The metal envelope ring 13 is extended inwardly of `the tube to forma cylindrical support 45 for the control grid 23, the grid itself comprising a number of tungsten The main' problem have a different coelficient of' expansion than the ceramic rings between which they arlial o ces..

c Li wires 46 brazed to a tungsten Washer 47 which is in turn brazed to the cylndrical Kovar support 45. The wires 46 and the Washer could also be molybdenum, one of the essential things being that both the Wires and the Washer, b e of material having the same coeflicient of expansion. If the coefficients of expansion are not the same and the Washer' expands moreit vill Stretch the wires i upon heating, and 'the wires will then sag 'When cooled. If the Washer, expands less than the wires, then the wires will bow or'sag When heated. The grjd-` support 45 is of; KQYELI', which hasi a difierent coetficiertrof expansion than the tungsten or molybdenum Washer. Accordingly, itisnecessarytht support 45 he weakened in the radial direction so as not to overpower the Washer 47, This weakeninghas been accomplished.. bytnaking support 45 cylindial instead oi conical'. andbynking'. itof sub stanfial length, ThejQQf bends 'a't the ends.of cylinder 45, are easily .flexed to. accomtnodate movement due to The bendsgin a concalsupportare greater thn QO and thus, would. offer more, resistanceto move- *ment caused by radial forces. SupportAS'wllnot be subject to detrimental oil cannr'g tactionbecause the 9Q bendsat the upperand lower endst ofthel support i accpn modate the deformation caused by the fact thagring 13 is','hel d 'by the ceramicenvelope. It.will be. realld thatring 13; is spot weldedto scaling ring 19, and it will be undertood thattwhen the tube is evacuated `a 'cold wel d will very? likely occurbetween rings 13 purpose of tpreventing loilanning (as explained in con nection cathode support 36) and also preventingf,

withcontr l grid support'45). It 'Will' be seenfrom the, drayyjng that thescreen grid wij 51Vare algned directly abovethe control grid wiresfl and -it should be under:

r stod thatthesewires are parallel to eah othersol that thevco ntrol wires tend toshield the screen g'd, wires y enyelope ring 15 is ,extend d invar'dly, at Sito su poss ble; to say. fyhere onestarts andgthe Other ends,

tthfe' Koyar support 50 from overpowering thefmngsten orLmolybdenum asher 52-(as explained in; connection cerarnic and metal envelope rings. The subassemblies of: the electrodes and their supports are of course fabricated prior to loading the jigs. For example, heater pin 29 is attached to support 28 by a very high temperature braze, and cathode legs 49 are spot Welded to support 36. The cathode-heater structure is of course first made as a unit consitin g of'cathode disk 42, heater coil 32, support disk 41 and heat shields 43. It should he noted that since the cathode 'is supported on legs rather( than on theusualcylinder of -metal foilit is-possible to spotweld heaterends 33; and 3;4 0'h6 -heater leads 29 and* 34 after the metal rings 10,11, 12 and 18 have beenbrazed to the cer-amic rings 2 3 and 4. After the lower and upper sections of'the 'tube have been brazed as previously described the cathode disk 42 is coated with electron em'ssive material, and metal ring 13 is spot welded to sealingvring 19, after first aligm'ng the control grid wires46 with the screen grd wires sl V Lastlythe upper and-'lower' sections' areioned together and afinalseal 'is made at 20;

Having th s described the invention, what is clain ed' as new .anddescribed to be securedby Letters? Patent is 1. An electron tube comprising an envelope having ;alternat'e ceramic and metalrings joined together, planar electrodes in said envelpe, said electrodes comprising a cathocle, a control gridga screen gri d, an anodeand a suppressor electrode interposdbetween said :screen grid and saidanbde, said cathode comprisng a disk having anelectron ernissive surface and supported on lega ex terding longitudinally ofthe tube, one of said 'metal rings being extended inwardly of' theenvelope to form a support ring for said cathode, sad cathode legs being attached to said support ring; an annular v-shap'ed-cor ing a fiat .rugat'on in ?said support ring; a heater compr i coilof insulatedwire abuttin'g the cathode' disk a, cenr trally apertured support plateattached to said' legs and;

holding 'said heater coil against said cathode disk, accutrallyi apertur'ed heat shielddskattached to said' legs,

separate heaterleads connected to two of saidmetal enveloperin'ggsaid heater coil having two endwires passing, 'through the aperturesin the support plate and'heat shield; i andl spot welds attaching said `'end wires-to s'aid'heater a flatheaterflcoil for saidcathode starting at one end of sadtubethe first said netalring *forms an end closure 2. An 'electronrtube comprising anenv elope having alternate cerarnc' and 'metal rings joinedtogether, a pluralityi'of planar electrode's including' a c'thode; a control i grid. and "a screen grid; an anode,- ahda suppressor elec trode interposed between said screen grid; and 'said anode,

for .the tube and also forms'a lead-in for. said heater the Tlespacing between electrode ;sene the adjaent elec thelsixth metal ring forrnsLboth the suppressor 'electrode second 'metal ring -torms a. second lead-in for said heater, thehird metal ring tormsadead-infor said cathode'the fourthmetalring forms a' lead in forsaid control grid, the fifth'rrietal ring fornisalead-in'forsadscreen gridg and the lead-in therefor, and the last metal ring forms a The ,anode plug has a central exhaustpassage in,whchv i anjexhaust tube 58 is brazed. A cooler 60 ,is attached. tothe anode by a screw;61 Metal ring icarres a' u terminal tab 62, 'As amatterof fact each of the metal rings 10, 11, 12, 1415;and 19' car'y terminal tabs.

The tabs are spaced around the periphery of the tube so that Only themes; for the anode and a tab 63 for i the c-athode. arejvisible in the drawing. i 1 t i 'Thefdesig n of thetuhe issuh that it is particularly -adpted to be nadet with automation equipment; For example, the ceranic 2, -and 4 and the lmetalf' rin'gs 10,;11, 12 and l can allfbelciaded into a simple cylir jdri'al jig by automatic equipment( Similarly; the

simplecylindrical jig., The loaded jigs can be passed ceianfic rings; 5, 6 and 7' and the metal rings 414 15, 16 p and 19 can be loaded by automatic equipment into a closur for the other end of the tube and a lead-inter said. anode sidicathode lead-in ring being exterded internally of the' envelop e mrom a supportring for said cathode, a plurality .of suppo'rit legs mounting said'ca'thodefon said support .ring-a M-shaped annular corrugation in saidlsupport'ring between said legsand the inside of the envelope wallg'rneans' including spot -welds attaching ,the ends ofsaid hater -coil t'o saidheater lead-ins, a

cylindrical supprt f orsaid control grid joinedlat one end i u to ;the control grid and at'the other end of saidfcontrol grid lead-in ring, 'saidcylindricalsupport being' positioned around-thecathode' end of said support legs, said screen grd lead-inring'being exterded 'internzlly of theenvelope to form a support ring for said screen-grid, and a V-shapedtannular corrugation in said screen grid support rn'gg r (Reference on follorving page) References Cited in the file of this patent 2,640,946 UNITED STATES PATENTS Heintz Aug. 31, 1937 2:75( :535

Bondley Ian. 16, 1945 5 2,782,338 Howes Oct. -19, 1948 Halstead Jan. 18, 1949 Knight Jan, 25, 1949 Koch June 6, 1950 Bell une 2, 1955 Dreschman July 7, 1953 Sorg Sept. 27, 1955 Doolttle June 12, 1956 Rhyne Feb. 19, 1957 OTHER REFERENCES Kohl: "Materials Technology for Electron Tubes," Reinhold Pub. Co., 1951, PP. 417-420.

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