US1674520A - Electric tube device having coiled filaments - Google Patents

Description

June 19, 1928.

E. Y. ROBINSON ELECTRIC TUBE DEVICE HAVING COILED FILAMENTS Filed May 24, 1924 2 SheetsSheet 1 June 19, 1928; 1,674,520

E. Y. ROBINSON ELECTRIC TUBE DEVICE HAVING COILED FILAMENTS Filed May 24, 1924 2 Sheets-Sheet 2 Patented June 19, 1928.-

UNITED S'lATES PATENTQOFFICE.

ERNEST YEOMAN ROBINSON, OF WITHINGTON, MANCHESTER, ENGLAND, ASSIGNOB TO METROPOLITAN-VICKERS ELECTRICAL COMPANY LIMITED, LONDON, ENG- LAND, A. BRITISH JOINT STOCK COMPANY.

ELECTRIC TUBE DEVICE HAVING COILED FILAMENTS.

Application filed May 24, 1924, Serial No. 715,655, and in Great Britain June 12, 1923.

. This invention relates to electric tube devices of the kind having coiled filaments or coiled wire cathodes such as electric incandescent lamps, electron discharge tubes, and like devices. The object of the invention is an improved method of supporting such coiled members.

A common method of supporting a helical filament or cathode consists in bending the filament wire at the end convolution substantially at right angles thereto so that the Wire lies in an extension of a generating line of the cylinder containing the helix and the end portion of the wire thus conformed is secured to a rigid support such as leadingin Wires. Another method commonly adopted is to reduce progressively the diameter of several of the end turns of the helix so as to form a conical spiral and to bend the.

end of the filament wire so that it is co-axial with the helix. In the first case the end turns of the helix tend to pull out, that is to say, the. pitch of the helix is not uniform and further the. helix can rotate about the point of support since the latter is not coaxial with the helix. In either case the filament is not rigidly supported and it is found that the axis of the whole helix is shifted out of its normal position when the filament is heated this being probably due to unequal heating of the bent end portions of the filament which are attached to the supports or lead-in wires.

Furthermore when a filament cathode is employed in a vacuum electric tube in which the gap between the cathode and another electrode such as the anode, is small, as described in the specification of my copending application Serial No. 603,715, filed 27t N ovember1922, it is important that the filament should not move over and touch the other electrode. It is also important that the cathode should be rigid in itself, that is, the cathode should not be capable of being pulled over to the anode by electrostatic strain existing'in the vacuum electric tube. Moreover, it is important in the construction of short gap valves that the. cathode should be accurately registered with respect to the support or supporting stem in order that the electrodes may be easily assembled by the use of jigs.

According to the present invention the end convolution of a helical filament or cathode is supported at a plurality ofpoints around said convolution so that a. rigid mounting of the filament is obtained and a convolution other than the end conv0lu-- tion. The end convolution of the filament may be. supported continuously over a relatively large portion of its length, for example, over a portion which is at least equal in length to half of the perimeter of the convolution. Several of the end convolutions may be supported continuously in this manner.

To enable the invention to be clearly understood it will now be described with reference to the accompanying drawings in which Fig. 1 is a perspective view of part of a coil filament supported in accordance with the invention, Fig. 2 a view of modified form of supporting member and Fig. 3 a perspective view of another form of the supporting member. Fig. dis a sectional view of part of a coil filament supported by means of a still further form of supporting member. Fig. 5 is an elevation partly in section of the electrodes of a vacuum electric rectifier having a coiled filament supported in accordance with the invention, Fig. 6 is a side view of the arrangement illustrated in Fig. 5 and Figs. 7 and 8 are views of details. Fig. 9 is an elevation of modified electrodes of a vacuum electric rectifier. Fig. 10 is a sectional elevation of a still further construction of the electrodes of a vacuum electric tube, and Figs. 11 to 15 inclusive are plan views of certain members of the structure shown in F ig. 10.

Referring to Fig. 1 of the drawings, the end portion of a helically coiled filament constituting an electrode of an electric tube device is indicated at 1, and a supporting member for such end of the-coiled member is indicated at 2, the member 2 being attachedto a supporting stem 3 which may constitute a lead-in wire for the electrode. The member 2 is provided with a plurality of radial arms 4, for example three arms as illustrated, said arms having a symmetrical angular displacement. The ends of the arms 4 are severally bent round the end convolution of the coil filament 1 as indicated at 5 so as firmly to clamp the latter. The supporting member 2 may be made of sheet metal of sufficient thickness to provide the three-armed support 2 may be riveted,

welded or otherwise secured to the stem or lead-in wire..- By the use. of an additional washer of moldbdenum, for example riveted to the stem, thinner material may be employed for constructing the three-armed support owing to the further support provided by the washer and also the bending of the arms of the support around the convolutions of the filament. wire is facilitated. As illustrated in Fig. 2, the three-armed support may be in the form of a triangular plate the corners of which may be bent around the end convolution of the filament wire. The triangular plate may be of relatively thin sheet metal su ported by a washer 2* attached for example y riveting or welding to the end of the stem 3.

A modified form of en port illustrated in Fig. 3, comprises a plura ity of strips 6, say three, of nickel or molybdenum which are attached to a supporting stem 3 and are conically splayed, their free ends being bent as at 5 around the end convolution of the wire is previously described with reference to 3 further 'form of support as shown in Fig. 4 comprises a short tube of diameter which is equal to'or slightly larger than the internal diameter of the filament helix 1 and said tube is provided with a flange or flare Sand one or more of the end convolutions of the helix are disposed on the supporting tube and retained thereon by means of the flare or flange a 'ortion of the circumference of which may e interrupted to permit a turn of the helix to pass through it. The flange is preferably provided with projecting tongues which may be bent over one or more turns of the helix to grip the same. The

end convolutions thus supported may be ar-' ranged as shown to have a smaller pitch than the main portion of the helix or may even be arranged so that they are substantially in contact with one another. The tube 7 is attached to the stem 3 in any desired manner.

Referring to Figs. 5 to 8 inclusive, the electrodes therein illustrated are as set forth in the splfcification above referred to, that is to say, t e cathode 1 is of such a form as to provide a concentrated source of electrons, the anode 9 is closely spaced from thecathode 1 so that in combination with the concentrated electron \source the inter-electrode space is small and the thermionic discharge between the cathode and anode is confined to such small inter-electrode space and thus the paths available for the discharge areal short. The cathode 1 consists of a helix of suitable material such as tungsten, or it may for example be of molybdenum coated with a mixture of barium and strontium oxides to facilitate the emission of electrons therefrom. The convolutions of the helix are closely spaced from one .another in order to provide the concentrated source of electrons.

The cathode helix is supported at its ends by the molybdenum or nickel stems 3 to which are attached molybdenum or nickel washers 10 which in turn support relatively thin molybdenum or nickel supporting members 2 having arms which are bent around one or more of the end convolutions of the helix. Such construction will be clear from Fig. 8 which is drawn to a larger scale than Figs. 5 and 6. The stems 3 are supported in the tubes in the manner hereinafter described.

The anode 9 is constructed of two similar sheet metal plates bent to the shape shown in Fig. 7 and superimposed to one another so as to constitute a tube within which the cathode 1 is disposed. In addition two relatively small tubes 11 are provided in the flan e portion 12 of the anode thus constituted, and the supporting wires 13 of nickel or molybdenum for the anode pass into the tubes 11. The two portions of the anode 9 are welded, stapled or otherwise fixed together and to the supports 13. The lower ends of the supports 13 are fused into the glass pinch 14 at the end of the re-entrant tube 15 of the device. The supports 13 may be constructed of two materials, the portions in the neighbourhood of the anode bein of molybdenum and the portions whic pass into the pinch 14 being of nickel. One of the supports 13 passes through the seal 14 to an external lead-in conductor 16.

The lower of the filament supports 3 is welded to a filament lead-in wire 17 which passes through the pinch 14 to an external conductor 18 whilst the upper filament support 3 is welded between a pair of tongues 19 at the end of a nickel bracket 20 which is fused as indicated at 21 into the pinch 14. The cross section of the nickel bracket 20 may be angular or channel to provide stiffness. The bracket 20 is connected through the seal 14 to an external conductor 22.

Referring to Fig. 9 the construction therein illustrated only difi'ers from that illustrated in Figs. 5 and 6 in that the Supporting stems 13 for the anode 9 extend beyond the upper end of the latter and are connected together at both ends by means of cross members 23 of pyrex glass inlZOWlllCll the stems 13 are fused. The latter may cenveniently be of n'iolybdenum Wl1l('l1 material has a coefficient of expansion of the same order as that of pyrex glass. The members l3and 23 constitute a rectangular fral'nework which enables the electrodes to be permanently fixed and registered-with respect to one another in an easy manner similar to that described and claimed in the specification of my copending application Serial No. 722,811 filed June 27, 1924. The filament .supporting stems 3, preferably of molybdenum, are also pinched into the cross members 23. In assembling the electrodes they are held and registered with respect to one another in a jig whilst the cross members 23 are being pinched on to the stems and supports. The upper filament support 3 is connected with a member 24 which is connected with an external filament lead.

Referring now to Figs. 10 to 15, the cathode 25 is a molybdenum tube which is coated on its outer surface with a mixture of barium and strontium oxides. The coating may be effected in the manner described in the specification of copending application Serial No. 715,653 filed May 24, 1924. The cathode tube 25 is heated to a temperature at which it emits electrons readily by means of a heating coil 26 axially disposed within the tube 25 and supported from the stems 3 in the manner hereinbefore described with reference to the helical cathode 1. The anode 9 is coaxial with the cathode tube 25 and closely surrounds the latter so that the inter-electrode space is small. The discharge is confined to this small interelectrode gap by reason of the fact that the ends of the cathode tube 25 do not become sufiiciently heated to emit electrons freely. To this end the cathode tube 25 is longer than both the heating coil 26 and the anode 9 in order that its ends may remain cool and constitute effective shielding means for confining the discharge.

The electrodes are supported on the framework in a manner similar to that set forth and claimed in the specification of my copending application Serial No. 722,811 above referred to. The framework comprises a pair of parallel nickel wires 27 and a pair .of end members 28 attached thereto, and the electrodes are mounted upon this framework by a plurality of cross members such as illustrated in Figs. 11 to 14 inclusive similar to those described and claimed in the specification of my copending application Serial No. 722,811 above referred to. One of the members 28 is shown in plan in Fig. 11. The

anode 9 may assume the form shown in secof further tion in Fig. 15, comprising four sheet metal plates bent to the shape illustrated so asto constitute when assembled a tube having radial flanges 29. The anode 9 thus constituted is supported by means of a pair of cross pieces 30 one of which is illustrated in plan view in Fig. 12. ach cross piece 30 comprises a diamond shaped plate having a central perforation 31 with four radial extensions 32 corresponding to the shape of and adapted to receive the anode 9. The plate 30 is provided at its ends with perforations 33 through which the side members 27 of the rectangular framework pass. The plates 30 are fixed in position upon the side members 27 of the framework by welding or by means of members34 clamped or welded around the members 27 or fixed thereon.

The cathode tube 25 is supported by cross pieces 35 one of which is separately illustrated in plan in Fig. 13. ach member 35 comprises a metal plate having a central perforation 36 adapted to receive the cathode tube 25 and end perforations 37 through which insulation tubes or bushes 38 of steatite or glass are passed, the bushes 38 being disposed upon the upper and lower ends of the side members 27 of the supporting framework. They may be maintained in position by means of members such as 34 as clearly shown in Fig. 10. The cathode tube 25 may be supported in the two crossmembers 35 by means of outwardly bent tongues as shown provided on the ends of the tube. The supporting stems 3 of the auxiliary heating coil 26 are supported from cross pieces 39 one of which is illustrated in plan in Fig. 14. It comprises a metal plate having a central perforation 40 through which the stem 3 passes. and two end perforations 41 through which the insulating bushes 38 pass. The stems 3 are secured in the supporting cross pieces 39 in any convenient manner such as by welding metal on either side of the cross pieces as indicated at 42, whilst the cross pieces 39 are themselves secured to the insulating bushes 38 by binding wires as indicated at 43. In addition the supporting stems 3 of the auxiliary heating coil 26 are guided or registered by means cross pieces 44 which are similar in construction to the cross pieces 39 (see Fig. 14). and are similarly fixed to the insulating bushings 38.

The whole framework carrying the elec trodes mounted thereon as described is supported from the re-entrant tube 15 of the vacuum device by means of a'clamp 45 which surrounds the re-entra-nt tube and carries two arms 46 to the upper ends of Which are welded nickel clips 47 which are in turn connected by means of binding wires as indicated at 48, to the lower pair of insulating bushings 38. The upper and lower stems 3 are otherwise 1: at at least one of its ends,

' at a plurality of the heating coil 26 are connected respectively t llead-in conductors 49 and 50 passing throu h the pinch of the re-entrant tube 15. The ead-in wire 51 for the cathode is connected with a conductor 52 which in turn is connected with one or other or both of the cross pieces which support the cathode.

I claim as my invention 1. The method of imparting rigidity to a helically coiled filamentary member of an electric tube device without short-circuiting the convolutions thereof, which consists in connecting a filament support both mechanically and electrically at a plurality of points distributed around at least one of the end convolutions of the helically coiled member at at least one end thereof.

2. An electrode structure for an electric tube device comprising a helically coiled filamentary member, a supporting member for supporting said filamentary member at at least one of its ends, said supporting member being secured to at least one of the end convolutions of the filamentary member of points distributed around its periphery, and a lead-in member rigidly connected to said supporting member and extending axially from an end of said filamentary member. a 3. For an electric tube device having a helically coiled filamentary member supported only at its ends, a supporting member for supporting said filamentary member said supporting member comprising a plurality of radiating electrical conducting arms which are connected both mechanically and electrically at a corresponding number of points distributed around at least one of the end convolutions of the filamentary member.

4:. In an electric tube device having a helically coiled filamentary member supported only at its ends and a cooperating electrode supported in closely spaced relation to its peripher a supporting member for supporting sai filamentary member at at least one of its ends, sai supporting member comprising an element having a plurality of radiating arms which are secured at a corresponding number of points distributed around at least one of the end convolutions of the filamentary member.

5. In an electric tube device having a helically coiled filamentary member supported only at its ends and a cooperating electrode supported in closely spaced relation thereto. a supporting member. for supporting said filamentary member at at least one end, said supporting member comprising a thin sheet metal member having a plurality of radiating arms which are secured at a corresponding number of points distributed around at least one of the end convolutions of the filamentary member, said arms being bent around said convolution, and a lead-in member for said filamentary member connected to said supporting member.

6. For a helically coiled filamentary member of an electric tube device, a support for at least one of the end convolutions thereof comprising a metal rod constituting a leadin Wire, a sheet-metal triangular member attached to the end of said rod, and a disk also attached to the end of said rod adjacent to the triangular member so as to stiffen the same, the relative dimensions of the disk and triangular member being such that the apices of the latter project beyond the disk and can be bent around an end convolution of the filamentary member.

In testimony whereof I have hereunto subscribed my name this ninth day of May, 1924:.

ERNEST YEOMAN ROBINSON.

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