US2051457A - Electrical discharge device - Google Patents

Description

1936- J. ca. w. MULDER ET AL 2,051,457

ELECTRICAL DISCHARGE DEVICE Filed NOV. 28, 1952 Patented Aug. 18, 1936 ELECTRICAL DISCHARGE DEVICE Johannes Gijsbertus Wilhelm Mulder, Johannes Bruijnes, and Johannes Hendrikus Josephus 'Maartens, Eindhoven, Netherlands, assignors to N. V. Philips hoven, Netherlands Gloeilampenfabriken, Eind- Application Novemben28, 1932, Serial No. 644,724

In Germany D ecember 9, 1931 6 Claims. (Cl. 250-275) The present invention relates to electrical discharge devices and more particularb to a novel anode construction for discharge tubes.

In certain types of discharge devices, for instance in heavy duty gas-filled rectifying tubes with thermionic cathodes, the anode assumes during operation a high temperature, which for instance, in gas-filled rectifier tubes is primarily due to its bombardment by the ions. Such overheating of the anode is objectionable as it adversely affects the operating characteristics and life of the tube. To prevent such overheating of the anode various means have been suggested in the past, none of which however has been quite successful.

One way of reducing the anode temperature is by increasing the size of the anode, but this correspondingly increases the weight of the anode. A heavier anode not only. requires heavier supports but is specially objectionable in case of glass containers as it increases the load to be carried by the seal and the vitreous envelope of the tube. For instance an otherwise very advantageous seal and support construction, consisting of a chrome-iron disc sealed to one end of the vitreous container and supporting the anode by means of an intermediate rod is unsuitable for heavy anodes as the seal is liable to crack under the weight and momentum of the anode.

It has also been proposed to increase the cooling surface of the anode by means of corrugations provided thereon. However, this gives rise to undesired electron emission from the anode especially at the sharp edges of the corrugations.

It has also been suggested to lighten the anode by means of open cavities provided, for instance, on its side turned away from the cathode. Such construction, however, gives rise to a glow discharge in the cavity, with consequent back discharge between the anode and the cathode.

The present invention provides a novel and simple construction which permits the anode to be provided with a large cooling area without producing the disadvantages of large weight, undesired electron emission, back discharge, etc.

According to the invention the anode is provided with a large and preferably smooth outside area and the anode is lightened by providing it with one or more interior cavities which are fully enclosed and thus are not in communication with the discharge space or with parts outside the tube.

The thickness of the walls of such a hollow anode may be reduced to such extent as is safe for mechanical considerations, and thus a very light, large area anode can be obtained. As the cavity is closed, the electrical conditions prevailing therein have no disturbing influences on the discharge of the tube.

The invention can'bc applied to anodesconsisting of non-metallic materials, for instance, graphite and carbon, which are specially adapted for gas-filled rectifier tubes, as well as to metal anodes.

The invention will be more fully described in connection with the accompanying drawing forming part of this specification which shows as examples specific embodiments of my invention and in which:

Figure 1 is a longitudinal section of a rectifying tube embodying an anode construction according to our invention.

Fig. 2 is a sectional elevation of a modified anode construction according to our invention.

Figure 3 is a side view, partly in section, of a three electrode discharge tube, comprising a still further embodiment of an anode according to our invention.

Referring to Figure 1 there is shown a rectifying tube comprising a vitreous envelope 1 having a reentrant portion carrying a stem 2 on which is supported a filamentary cathode 3, the two ends of which are connected to lead-in wires 8 and 9. The anode is supported by a chrome-iron disc 4 sealed in the opposite end of the envelope I and is carried. by a suitable metal rod it which may be integral with the disc 4 or may be welded, soldered or otherwise secured thereto. The stem It] carries a cylindrical carbon or 5 which is provided with internal threaded carbon plug 6 is tightly block 5 to engage its threads I completely closes the cavity ll.

It should be well understood that the cavity H can take up the major portion of the block 5, the walls of which can be reduced to such extent that their thickness is merely determined by the requirementof mechanical strength. It is obvious that a very large effective anode-area may be obtained with a comparatively low weight of the anode. 7

Instead of providing a threaded joint between the block 5 and the plug 6, a suitable tight fit may otherwise be obtained, for instance, by pressing the plug 6 into the block 5.

The incandescent cathode is preferably provided with a high electron emitting surface, for instance, an earth oxide layer, and an indirectly heated cathode may be used instead of the dithreads l2. A screwed in the 2 and thereby graphite block rectly heated cathode shown in the drawing. As a rule there is also provided a gas filling, for instance, mercury vapor or a rare gas or a combination of both.

Constructions as shown in Figs. 1 and 2 have been found especially advantageous in gas-filled thermionic rectifier tubes for currents of amps. and more voltsand more. In such tubes the gas is preterably argon of pressure of some microns to several mm. The anode is preferably of carbon or graphite or of a refractory metal as zirconium carbonized at itssurface. An anode as shown in' these figures'm'ay have for instance a height of 5 cm. and 'a diameter "of 3cm; in this case the 'cavity has a depth of about 2 cm. and a diameter of about :2 cm.

Figure 2 shows a modification-0f the anodeconstruction in which the plug 6 is provided with a fiange 1 which when the plug is screwed in the block 5 abuts with its upper face against the free end face-l3 of the block. The two 00- V operatingfaces are preferably machined-to prosame or of different materials.

of proper supports a cathode 2.3,

'vide for a tight fit.

The block and the plug may be made .of the Our invention can be ialsoapplied to tubes j 'hav'ing more than two electrodes. .Forzinstance in Fig. 3 there is shown a 'tubeembodying our invention in which a vitreous container 2| .is .provided with a stem 22 which carries .by means a heater .24 .for the indirect heating-of the cathode andv disposed within the cathode, a .grid 21 surrounding the cathode and an anode: 25 surrounding the .grid. The anode 25 is shown as formed of a hollow metal 'ring preferably of a refractory metal. The ring 25 can beformed, for instance, (byv joining a two part casting or it may be made of sheet metal'formed into proper shape and welded togetherzto form aclosed hollow ring member.

. While cylindrically, shaped anodes, as .shown in Figs. 1 to 3 provide as a rule for themost icompact construction my inventioncan .besapplied-to anodes having other shapes, or instead :of a single cavity a plurality .of cavitiesmay beprovided, each being closed by :a plug or otherwise. Various other modifications may suggest themselves and. :we do not wish to be limited tothe examples shown and described, .but desire'the appended claims to be.:construed as broadly as permissible in .view of theprior In the claims the term carbon shall include also graphite and :other. carbon modifications adapted to serve as anode material.

What we:claim is:

r 1. A rectifier tube for currents of 20 amperes or more, comprising. an envelopezzand a .gaseous filling therein, a thermionic oxide cathode land ..a cooperating anode; a discharge :space being formed between said anode and cathode, said anode having a cylindrical shape'zandi av large surface area and being provided with a bore which substantially reduces the weight of the anode, said bore being void of non-gaseous mat- :ter and being ,closed'by a plug member at its .end opposing the cathode. H

and for voltages up to 100,000 7 *matter, a chrome-iron member sealed at :velope, a gaseous filling 2. A rectifier tube comprising an envelope and a gaseous filling therein, a cathode and a cooperating anode, a discharge space being formed between said anode and cathode, said anode hav- 7 ing a cylindrical shape of large surface area,

' chrome-iron member to carry said anode and to serveas anelectri'cal connector therefor.

3. A discharge tube comprising a vitreous entherein, a cathode and a carbonanode disposed within said envelope and forming a discharge path, said anode having a large activecsurface area and being pro- -vided with a large internal cavity to substantially lessen its weight, said cavity being completely closed from the discharge path and being void of all non-gaseous matter, a metal .support member hermetically sealedto said-envelope, and

means exclusively supporting said. anode from said member. '4. A rectifier tube for currents of=20 -amperes and more, comprising a vitreousenvelope anda gaseous filling therein, athermionic oxide cathode, a cylindrical anode body 'having' a large surface area and being provided with ar-closed internal cavity to lessen its weight, and supporting means for said-anodebody comprising a conductor sealedto the vitreous envelope, said anode body and said supporting means-beingex clusively supported by :the seal between said conductor and said envelope. r

5. A discharge tube comprising a vitreous-envelope an anode and a cathode disposed therein to iormra discharge space, said .anode having :a large surface area and being provided with an internal cavity to substantially lessen-its weight, said cavity-being closed from' the space within the envelope and being void of non-gaseous matter, and means supporting said anode -in'noncontacting spacial relationship with'said -envel ope, said means being sealed to-said vitreous envelope and being *exclusively supported by -the seal.

' 'ope and forming a discharge space, "said "anode havinga large surface area and beingprovided with a large internal cavity to substantially iessen its weight, said cavity being completely closed fromthe .discharge'space andbeing void of non-gaseous matter, a'metal member her-,-

-metically sealed tousaidyitreous envelope, land means supporting said f anode from said ..metal member, said anode, supporting emeansfland metal member being exclusively supported .-by, the seal between said metale-member andsaid: :en-

velope. 7 J JQHANNESGIJSBERTUS JOHANNES BRUIJNES. V JOHANNES HENDRIKUS Y JQSEPHUSMAARTENS,

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