US2897395A

US2897395A - Grid electrodes for electric discharge devices

Info

Publication number: US2897395A
Application number: US529302A
Authority: US
Inventors: Carl F Miller
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1955-08-18
Filing date: 1955-08-18
Publication date: 1959-07-28
Anticipated expiration: 1976-07-28

Description

c. F. MILLER 2,897,395

GRID ELECTRODES FOR ELECTRIC DISCHARGE DEVICES July 28, 1959 Filed Aug. 18, 1955 INVENTOR Carl E Miller ATTORNEY GRID ELECTRODES FOR ELECTRIC DISCHARGE DEVICES Application August 18, 1955, Serial No. 529,302

3 Claims. (Cl. 313-350) This invention relates to electron discharge devices and, more particularly, to a method of fabricating grid electrodes for such electron discharge devices.

In electron discharge devices suitable for use at ultrahigh frequencies one of the major problems is keeping the lateral grid wires taut over the complete range of temperatures encountered during manufacture and operation. Because of the very close spacing required in such devices, if the lateral grid wires are loose, troublesome vibrations occur leading to large variations in the characteristic output of the devices. To obtain the necessary very accurate spacings of the cathode, grid and anode assemblies required in ultra-high frequency electron discharge devices, planar grids are frequently used. In fabricating a typical grid electrode of this type, lateral grid wires may be joined to a grid frame member by brazing. If the lateral grid Wires and the grid frame member are of different materials, so that the grid frame member has a large coeflicient of thermal expansion as compared with that of the lateral grid wires, their different rates of expansion or, in this case, contraction will cause the tautness of the lateral gn'd wires, which may have been satisfactory at the time of brazing, to be markedly reduced upon cooling. Therefore, at temperatures lower than those encountered during the brazing operation, the lateral grid wires are under less tension and become loose and slack which results in harmful Vibrations.

Accordingly, it is an object of this invention to provide an improved method of making grid electrodes for electron discharge devices.

It is another object to provide improved grid electrodes for electron discharge devices in which the lateral grid wires are under tension both during and after the operation of joining the lateral grid wires to the grid frame member.

It is a further object to provide an improved method of joining grid lateral wires to a grid frame member.

These and other objects of the invention will be apparent from the following description taken in accordance with the accompanying drawings which form a part of this application in which:

Figure 1 shows a top sectional view of an electron discharge device embodying a grid electrode made according to my invention;

Fig. 2 shows a top-sectional view of two grid electrodes similar to the grid electrode shown in Fig. 1 after the lateral grid wires have been wound but before the grid electrodes are removed from the mandrel upon which they are mounted during the winding operation;

Fig. 3 shows a front view of a grid electrode during the lateral grid Wire brazing operation;

Fig. 4 shows a side View of two grid electrodes in position for the lateral grid wire brazing operation; and

Fig. 5 shows a front view of a grid electrode made according to my invention.

In Fig. 1 there is shown an electron discharge device embodying a grid electrode made according to my invention including a cathode member 11, an anode member States Patent 0 Patented July 28, 1959 ICC 13 and a grid electrode member 15 positioned between said cathode member 11 and said anode member 13. An electron-emissive coating 21 is placed on the portion of the cathode member 11 closest to the anode member 13. The cathode member 11 is heated by a heater member 12 including insulation covered heater wire members 14. The grid electrode member 15 includes a grid frame member 19 and lateral grid wires 17. The elements of this electron discharge device are enclosed in a suitable glass or metal envelope 23.

In Fig. 2 there is shown a top sectional view of two grid electrode members 15 positioned on a mandrel member 25 after the lateral grid wire winding operation. The lateral grid wires 17 have been wound around the mandrel member 25 and the gn'd frame member 19.

In Fig. 3 there is shown a front view of a grid electrode member 15 during the lateral grid Wire 17 brazing operation. Cooling members 29 hold the grid frame cross bar members 31 in position so that heating members 27 may heat the grid frame side members 33 in such a manner as to braze the lateral grid wires 17 to the grid frame member 19. Screw members 35 adjust the tightness of the cooling members 29 upon the grid frame cross bar members 31. The heating members 27 may be radiant burners or electrical heat elements or other suitable heating means. The grid electrode members 15 need not be removed from the mandrel member 25 until after the brazing operation is completed.

In Fig. 4 there is shown a side view of Fig. 3 including cooling members 29, screw members 35, mandrel member 25, and grid electrode members 15. The grid electrode members include grid frame members 19 and lateral grid wires 17. Support members 37 support the cooling members 29.

In Fig. 5 there is shown a front view of a grid electrode member 15 made according to my invention. Lateral grid wires 17 have been joined to a grid frame member 19. The grid frame member 19 includes grid frame cross-bar members 31 and grid frame side members 33.

In accordance with my invention the grid frame member is prevented from expanding laterally during the brazing operation which joins the lateral grid wires 17 to the grid frame member 10. Cool-ing is a means of preventing the lateral expansion of the grid frame member, and such cooling may be done by the method shown in Figs. 3 and 4 in which the cooling members 29 conduct heat away from the grid frame cross-bar members 31, thereby cooling them. For good cooling, the cooling members 29 should be made of a material having good heat conduction properties, such as copper. The cooling members 29 may be water cooled if necessary. The mandrel member 25 which may be made of molybdenum may also aid in cooling by conduction during the brazing operation.

The brazing operation may be done in a hydrogen furnace to prevent oxidation of the materials involved. The heating members 27 should be positioned close to the grid frame side members 33 and the brazing should be done as quickly [as possible. If tungsten lateral grid wires are brazed to nickel plated steel (8. suitable steel being SAE 1010 which contains approximately 0.08% carbon, 0.31% manganese and small amounts of phosphorus, sulfur, silicon, nickel, chromium, molybdenum, aluminum and arsenic), a brazing powder composed of 15% silver, copper and 5% phosphorus may be used. The brazing should be done at a temperature of 700 for not more than three minutes. There should be a minimumof live minutes cooling in hydrogen to prevent oxidation When the brazed grid electrode is taken from the furnace. If desired, additional cooling may be obtained by playing a blast of cool hydrogen on parts of the grid frame cross-bar members 31 during the brazing and cooling operations.

grid frame side members 3 3, to be heated to brazing temperature for a short time, while the central portions, namely; the grid framec'rossehar members 31, are: kept ata lower temperature. Therefore, even though thexgrid frame.member 19 is. made of a material withta' com- .paratively. .hi'gh coefl'icient. of thermal expansion, the l ateralygridwires' 17,.though made ofamaterial'with a comparatively flow coefiicie'nt of'thermal expansion, are not stretched-beyond their limit. of elasticity because of the smalllateral expansion -o'f' the gridxframe crossbar members. 31 due to their. comparatively low temperature during the brazing operation.

If the grid frame cross-bar members31 were" not 'coolled during the brazing operation and if the grid frame crossbar members 31 were 'made of a material having a high coefiicient ofthermal expansion as compared to that of the lateral grid wires 17,. thelateral grid wires 17 very probably would be stretched beyond their limit of elasticityand aper'rnanentse't in the. lateral grid wires 17 would be introduced or. the lateral grid wires 17 might break. Asa result the. lateral grid wires 17 wouldbe loose and slack at any temperatures below the brazing temperatures. As temperatures which grid framecrossbar members 3 1' reach during theoperatio'n of a typical electron discharge device of this type areusually 6onsiderably below .the brazing temperatures, the loose and slack lateral gridwires 17 would cause the troublesome vibrations and large variations in characteristic output mentioned above. I V V The use of a material for the 'g'ridframe member 19 of high wander: of thermal expansion as comparedwith that'of the lateral grid Wires 17, has thedesirable ether of keeping the lateral grid wires 1'1 urlder tension at temperatures reached during op'eration H Suitable materials for the grid fram'e'members 19 having a comparatively high coefiicient of thermal ex ansion include aluminumfcoeflicient of linear thermal expansion 23.9 l'0 per degree cehtig'rade'); and its alloys, copper (16.5 X10 p'er degree Centigrade) and its alloys, nickel 13.3 X10 per degree centigra'cle) or particularly nickel plated steel (SAE 1010 steel'-"-l2'.2 l0- er degree Centigrade). Suitable materials for the lateral grid wires. 17' havinga com arativ ly low coefficient or thermal expansiba include mol bdenum (eoefllcient of linear thermal eXpafision;4l9X10 per de ee centig'rade) and, particularly tungsten (43 1x1 er degree eentigran). 'It'is seen'that the mat rials suitable for the grid frame members 19' have a coe'fiicient of linear thermal expanses gre ter than 10x10- per degree centigrade-and the materials suitable ferrhe lateral'g'rid wires 17 have aeoefii lem or linear thel'nial ex ansive less than IOXlO-f er degree 4 Centigrade,- but suitable materials not restricted to these limits;

It is also seen that the materials suitable for the grid fr-amemen'ibers 19-"have' a coefficient of linear ex anslqn atleast twice that of the lateral grid wires, but suitable materials are'liltewise not restricted to these limits.

While the present invention been 's'howri in a few forr'ns, it will be obvious to those skilled in the art that it is not so limited, butis sns'cptibleof various other changes and modifications withoiit departing from the s irit a d scopethereef;

I claim as my invention:

1. Iii the art at marluraelaring electron discharge devices; the metliod'of fabricating a gi'id electrode including the 's'teps offorniing a griclfr'an'ie memberhaving grid frame side memheis warmed by grid name cross-bar members-pr a material having a linear c'oeflicient of al ernate-man led greater than; 10X 10- per de ee centigrade, winding wire-of a2- mareriarhaviag 'a'liii'ar coefficient of thermal ea assiba less stal ions-9 isle degree ceatigrade to ferm-gridlateral placifig a co'olingmember having a mass substantially greater than that of said grid flame member in heat conductive contact with said grid frame cross-bar members, circulating a cooling fluid over portions of said cooling memben attaching said grid lateral wires to said grid frame side members by the application of heat to a substantial portion of said grid frame side members such that heat energy flb'ws into saideressbar members, and simultaneously conducting said heat energy from said cross-bar members at a rate su'ch' that the temperature differential between said crbss-bar members and said grid lateral Wires is such that the grid wire laterals are not stretched beyond -l mit f.. l .ty-,

2. In the artofmanufacturing electron discharge devices, the method of fabricating a grid electrode including the steps of forming a grid frame member having grid frame side members connected by grid frame crossbar members of a material having a first thermal coefliciefit or expansion; winding wire materials having a second thermal cdificient or erpanslorl less than said first coe'fiicierit of thermal expansion upon said grid frame memberfo ferm grid lateral wires, placing a cooling memberhaving amass substantially greater than that'of said *gi'itl 'frairiem'emb'er-inheat conductive contact with said gfid frame cros's ha'r ar'embers, aaah1ng said-grid lateral to 'said' grid frz'iniememher by the application of heat to substantial por ions of said grid frame side members that a portion at the heat energy flows into said cross-bar members, and simultaneously conducting 'saiil'he at energy frdm said cross-bar members at a rate such that the reaper diifeieritial between said crossbar members and sal wires exceeds the temperature diaeresrial between grid frame Side members and said wiiesslich that' grid wires are not stretched beyond their limitbfelasticity. v I 3Q- th e' art of manufacturing electron dischar gedevices, the'ii'l'ethod "of fabricatinga 'g'rid electrode, includfforming 'a grid frame member having grid x connected by grid framecross-har members of material having a linear coeificierit of eater l0 perdegree centiars material having a linear coefij- 9.1110 X 1 P r degree centigrade members form grid lateral wires, I I p a V I p rim heatconductive Contact with said grid frame' cross-bar member's, heating said grid frameside members to a temperature of about 700 degrees centig'rade for aperiod of notmor'e than three minutes'sueh a" portion of the heat energy flows into 51 1 cras -bar rambejrsyaha simultaneously conducting li'e at'energy from said crossbar members by means or said cooling member to. maintain the cross-ba'rs at a iib'stahtially lo wer than 700 degrees centifree the lateral expan'si'tin (if 'said grid providing necessary heat to a sub- V p grld frairi e sidemeiiihers to attach said lateral "grid to grid frame member.

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