US1873683A - Electric discharge device - Google Patents

Description

Aug. 23, 1932.

c. J. R. H. voN'wx-:DEL 1,873,683

ELECTRIC DISCHARGE DEVICE Filed May 9, 1929 @www Patented Aug. 23, 1932 UNITED STATES PATENT? OFFICE CARL J. R. H. VON WEDEL, OF BERLIN, GERMANY, ASSIGNOR TO ELECTRONS, INC,I A

CORPORATION 0F DELAWARE ELECTRIC DISCHARGE DEVICE Application led May 9, 1929. Serial No. 361,651.

My invention relates to electric discharge devices in general and particularly to gaseous discharge tubes employing electron emlssive cathodes.

The objects of my invention may be particularized by the following discussion of the theoretical consideration of the characteristics important in the construction of rectifier tubes which are to be used in the rectification of high voltage, high amperage alternatlng current.

These characteristics may be enumerated as follows:

The heating potential of a directly heated cathode should not exceed the ionization potential of the gas used in the tube;

The unnecessary heat losses of the energy in the' emitting surface due to radiation and like causes should be reduced to a minimum by being reflected to the emitting surface or otherwise confined within the cathode structure;

The emitting surface of the cathode should be protected from cooling by convection cur-- rents within the gaseous filling of the discharge tube;

N o conductive leads to the heated cathode should be placed so near and parallel that there is any possibility that low potential arcs can develop between points of different potential in the emitting cathode and the conductive leads thereto;

Points of different potential along the emitting cathode should be so positioned relative to each other that low potential arcs between such points cannot occur-and further any electronic discharge between such points is reduced to a minimum; and

All conductive elements within the tube should be maintained at as nearly a constant potential relative to the cathode of the tube as possible.

Further objects of my invention will be apparent as the description of the drawing orming a part hereof. in the figures of which like reference numerals indicate similar parts throughout the several views, is developed and in which Figure 1 is a perspective view, partly in section, of my improved rectifier tube C011- structed to take advantage of the above outlined desirable features;

Figure 2 is a lan view of the cathode of my improved tu e, and

Figure 3 is a plan .view of one of the elements thereof.

Referring to Figure 1, numeral 1 designates a glass envelope filled with a rare gas, for example argon, to a pressure of about one millimeter of mercury. Since I have designed one example of this tube to operate at, 250 volts between the anodes, as a fullwave rectifier, that is with a potential of 125 volts between an anode and the cathode, I have shown two presses 2 and 3, in order that high electrical stress will not be placed on the glass of one press, causing fatigue and breaking down thereof.

The press 2 carries a shield S by means of a support 4. This shield has its edges 5 and 6 bent at right angles to the main section thereof and has its lower edge made rigid by means of a conductive support 7 which is carried by the cathode structure each side of the shield S and within a distance therefrom of about or less than the mean free path of the electrons in the gas ifilling hereinbefore mentioned are positioned two carbon anodes 9 and 10 carried by the press 2 and having the leads 11 and 12 within the tube protected by means of small glass tubes 13 which extend with- 8. Upon 1n recesses in the anodes 9 and 10 and within lips 14on the press 2. This construction prevents disintegration of the frail lead-in support wires 11 and 12 by ionic bombardment.

The cathode structure 8 comprises two sup- .porting members 14 and 15 which are carried by the press 3. These supports carry helixes of the usual types of electron emissive filaments, arranged to form an inverted pyramid or like structure as indicated at 22.

The ends of the filaments forming the base of this structure are welded to the upper end of the cylinder 18. The ends of the filaments forming the apex of the structure are welded together and to a support 23 carried by the press 3 and under such tension as to maintain the filaments in a rigid condition when hot. Exterior connection is made to the support 23 by meansvof a plurality of lead-in wires 24 through the press 3.v

Upon the lower end of the shield S I have provided a supplemental shield 25, the area of which is preferably such that a direct discharge by gaseous ionization between the anodes 9 and 10 at the operating voltage will be suppressed. Upon the section 5 of the shield S I have provided a contact member 26 which extends to and makes contact with the film of getter on the interior of the envelope 1. Thereby the potential of all conductive elements within the tube which are not positive elements in the current carrying function of the tube are maintained at the potential of the cathode 8, the detailed function of lsuch structure being fully set forth in application Serial No. 214,192, filed August 19, 1927, by F. Meyer and H. J. Spanner.

By this structure I have developed a rectifier tube in which the heated element of the cathode is partially relieved from direct ionic bombardment and by placing the strips of getter G upon the exterior of the cylinder 18, I can maintain vaporized getter vapor within the tube during the process of manufacture and also continuously during the aging process of operation of the tube as a completed product.

The considerations upon which this feature of my improved rectifier tube is based are as follows. After the envelope 1 has been evacuated and the rare gas has been introduced then the tube is energized to an overload capacity to degas the electrodes by ionic bombardment. Since the shield 25 is of such size that there is no direct line discharge between the anodes and the filaments 22, a large percentage of the ions bombard the exterior of the cylinder 18. This cylinder is thereby heated to a relatively high temperature and the getter G thereon is volatized by ionic bombardment so that any occluded gases which are released from the eletIQdQS Valso during operation of the tube the ionic are instantaneously bound up by the getter. In this manner I have protected the filaments 22k from the heavy ionic bombardment not only during the manufacture of the'tube so that the same will have longer life, but

bombardment is in part upon the exterior of the cylinder 18 which always maintains a vtrace of vaporized getter so that any occluded gases are fixed even though released a relatively long time after the tube has been placed in operation.

From the foregoing description it will be seen that I have developed a rectifier tube in which the potential across the emissive element, being about 2.5 volts at 6 amperes current is less than the ionizing potential of the 'gas within the tube which is about 12 volts,

and which is less than 30.% of the drop in potential along a similar length in the space current path of the tube. rlhe electron emissive surface is very large compared with those surfaces used in tubes of standard construction. Heat loss from the emitting surface is minimized by the reflection back to the filaments of heat radiation intercepted by the cylinder 18. Reduction in temperature of the emissive element by convection currents is substantially reduced since the emissive element is enclosed in a cup of such size that once the temperature of the emissive surface is raised and the gas within the cup is raised to a lcorresponding temperature there is substantially no free circulation of gas within the cup.

Further the' high potential difference through glass between the anodes and the cathode is across the full length of the envelope 1 and the leads 11 and 12 are isolated to the full extremity of the press 2. And 05 also the high current leads to the emissive cathode are split to prevent heating of the v same and spaced a maximum distance apart within the press 3.

It w`ill be further noted in the cathode 11@ structure that the temperature, and there- Y fore the emission, of the flamentary structure increases toward the apex thereof. In this manner I provide a tendency towards maintaining the current flow from the anode 115 to points along the emissive surface more uniformly distributed.

While I have described my improved tube with particularity in order to convey a clear understanding of my invention I do not wish 12o to be limited to the specific structure shown and described since detail changes in the arrangement of elements and materials used therefor may be made within the scope of my invention as defined in the claims ap- 125 pended hereto.

Having thus described my invention what I claim is:

1. A cathode structure for gaseous discharge tubes comprising a metallic cup and 130 velope, a stem extending within said envelope, a press carried by said stem, a metallic cup supported upon said press, a plu- -rality of electron emissive filaments within said cup arranged in the form of a pyramid the base of which coincides withthe. opening of said cup, and an anode adjacent to the opening of said cup.

3. A thermionic tube, comprising an en velope, .a stem extending within said envelope, a press carried by said stem, a metallic cup supported upon said press, -a heatable element within said cup constituting an electron emissive cathode, a cooperating anode adjacent to the opening of said cup, a shield between said anode and said cathode and an electrical connection between said shield and said cathode whereby a large portion of the ionic bombardment is directed against the exterior of said cup.

4. A thermionic tube, comprising an envelope, a stem extending within said envelope, a press carried by said stem, a metallic cup supported upon said press, an electron emissive cathode within said cup, and in conductive relation thereto, an anode adjacent to the opening of said cup, getter material upon the exterior of said cup, and a shield between said anode and the opening of said cup whereby ionic bombardment is directed to the exterior surface of said cup and said getter material is maintained in a vapor state.

5. A thermionic tube, comprising an envelope, a gas within said envelope, a stein eX- tending within said envelope, a metallic cup supported by said stem, an electron emissive element within said cup and electrically connected thereto, a plurality of anodes adjacent to the opening of sa1d cup and spaced Iapart a distance approximately equal to twice the mean free path of electrons within said gas, a shield symmetrically disposed between said anodes, a shield between said anodes and the opening of said cup, and means electrically connecting said shields with said cup whereby ionic bombardment is directed upon the exterior of said cup.

6. A cathode for discharge tubes comprising a cup and an electron emissive element within said cup, said emissive element comprising a plurality of electron emissive filaments arranged in a pyramidal configuration, the apex of which is disposed toward ,tlxe bottom of the cup, and the ends of the `ilaments forming the base of said configuration being connected to the rim of said cup.

7. In a cathode structure for thermionic discharge tubes, a press, a cup mounted upon said press, an electron emissive filament within said cup and means supported above the opening in said cup for directing a lar portion of the ionic discharge against t e exterior of vsaid cup for heating the cup.

8. A cathode structure for gaseous discharge tube comprising a press having leadin wires passing therethrough, a metallic cup mounted above said press and connected to certain of said lead-in wires, a plurality of coated filamentary elements constituting an emissive cathode, each of said elements being conductively connected at one end to the rim of said cup, and a common terminal connected to the other end of each of said elements, said terminal being disposed Within and adj acent the bottom of said cup.

CARL J. R. H. voN WEDEL.

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