US1628987A - Thermionic device and method of evacuating the same - Google Patents

Description

. I I 2 May 17, 1927. R. w. N 6 8,987

THERNIONIC nsvxcm m METHOD or Evwunma wan sm:

Filed Sept. 24. 1920 Pat nted May 17, 1927.

1 UNITED STATES 1,628,987 PATENT OFFICE.

ROBERT W. KING, OF NEW YORK, N. Y.) LSSI GN'OB T WESTERN ELECTRIC COMPANY,

mconrom'run, or NEW Yonx, N.

2., A conrona'rroiw on NEW You 'rnnnmomc mm aunnnrnon or nvncua'rnire THE slum.

Application filed September 84, 1920. -Serial,No. 412,587. g

electron discharge devices, and pertains more especially to the evacuation of the containing vessels of-suchdevices,

The object of this invention is to obtain quickly and expeditiously a high degree of vacuum within the containing vessels ofelectron discharge devices. This object is attained by removing the occluded gases from the electrodes by electron bombardment and then cleaning up the gases within the vessel by vapzlfzing calcium within the vessel to absorb t e gases. The calcium is preferably suppor d by one of the electrodes and is heated to its vaporiza-f tion temperature by electron bombardment.

In the accompanying drawings Fig. 1 shows a two electrode tube embodying one form of anode pocket, Fig. 2 shows a three electrode tube embod ing a different form of anode pocket, and .ig. 3 shows part of an anode similar to that of F i 1 except that a third form of anode poc et is shown in '2 n Fig. 1 the tube 4 comprises envelope 5 of glass-or the like having the usual inwardly projecting stem 6'from which rises arbor 7 of glass or the like. The arbor 7 carries a support8 on which a cathode 9 is mounted. The arbor also carries supports (not shown) on which anode plate 10 is mounted. Anodeplate 10 carries conductors 11, which support anode plate 12. Le ding in wires for the cathode are shown at 3 and 14. A leadin in wire for the anode is-shown at 15.

ihe cathode which in the form shown is filamentary, is preferably of the type having a coating of oxldes'of-alkaline earth metals, since that type has special advanta s in connection with this invention as will pointed out in detail hereinafter. An example'of; such a cathode is disclosed in United States Patent to Nicolson and Hull'No. 1,209,324, December 19, 1916, electron emitting cathode and the process of manufacturing the same.

On the anode plate 12 is a pocket 16 for holding a small piece of calcium 17; The side of the pocket is formed by metallic strip .18 in the form" of a vertical trough, the edges '19 and 20 of the trough being welded to anode plate 12.. The bottom of the pocket is "formed by a metallic piece 21, which has a ortion 22 welded to the anode'plate 12 and as a portion 23 bent to form a right angle with the portion 22 and cut to the proper shape -to close the bottom end of the trough. In Fig. 2 the tube 24 comprises an envelope ,25 or glass or the like having a stem 26. The stem carries a metallic collar 27 from which rise anode lates 28 and 29. At their tops the anode p ates carry a metallic box 30 con- I taining a blockof lavite 31"from which are supported a double surface grid 32 and a cathode filament (not shown), the filament being located between the two grid surfaces. Leading in wires for the filament are shown at 33' and 34. A leading in wire for the anode is shown at 35 and one for the grid is shown at 36. The filament preferably. has a coating such as that referred to in the description of Fi 1.

On the ano eplate 29 is 'a pocket 37 for holding a piece of calcium .17 like that referred to in the description of Fig. 1. The

pocket 37 is formed by bowing a square 38 of sheet metal into a shallow dish form and welding the corners of the square tothe plate 29, with one of the upper edges of the dished square bowed away from the plate 29 sufli- 'ciently to permit inserting the calcium in the pocket;

Fig. 3 shows an anode-plate 39 which is like plate 12 of Fig. 1, except that the plate 3.9 has a pocket 40- formed on it by stamping the pocket from the plate 39, the pocket opening toward the cathode and having a suitable closure 41 placed over the opening. The closure 41 is a metallic square-held in place by tongues 42 and 43, which being stamped from the pocket, afi'ords communication between the. pocket and the vessel. The closure 41 is slid between the tongues and the pocket and preferably the edges of the closure are welded to the plate 39 at the edges of the pocket. v

In the preferred method of evacuating tubes such, for example, as those described, the tube is sealed on a suitable pumping apparatus, for instance, a rotary mechanical pump anda mercury 'aspirator, pumped for 11..)

each; (6)- electrically connected for about a 1 minute. This bombardment is not sufficiently vigorous to vaporize the calcium, but is designed to liberate gas from the plate and the grid. Following this bombardment, the plate and the grid are electricallyoonnected and the plate bombarded by electrons from the cathode vigorously enough to heat the plate so that the calcium will be vaporized. The pumping of the tube is preferably continued during all of the foregoing steps. The pressure in the tube should be low enough before the vigorous bombardment of the anode is started, to insure that the plate -can be heated to the vaporization temperature of, the calcium by the electron bombardmcnt of the plate without undue injury to the cathode by bombardment due to positive gas ions. With the alkaline earth oxide coated filament referred to above, it is only necessary that the pressure he as low as about .008 millimeters of mercury. The use of this type of filament presents a great 1 advantage in this respect, for, in a poor vacuum the coated filament is much more active than a tungsten filament, for example, and therefore, less time is required in the case of the coated filaments than in the case of the tungsten filament to pump the tube to the degree of vacuum necessary before the bombardment for vaporizing the calcium can be begun. It requires about 3 or 4 minutes of the vigorous bombardment to heat the calcium hot enough to vaporize it. During this time there-is haze in the tube and the pressure in the tube increases. After the calcium is hot enough to be vaporized, only5 or 6 seconds time is required to clean up the gases,the haze in the tube disappearing as the gases are absorbed. If the bombardment is continued after this stage has been reached, calcium vapor will com I denr-m on the tube walls as a black deposit,

but will not affect the operation of the tube materially as the vapor pressure of the calcium as well as that (if-the compounds of calcium with the gases cleaned up is negligibly low.

. Although it has been stated above that in the preferred method ofevacuating tubes the tubes are baked for about 15 minutes after pumping-has progressed for 3 or 4 minutes, in some instances the evacuation has been satisfactorily carried out without baking, and in other instances of successful evacuation the baking has been done before any preliminary pumping. in any case in which the tube-4 are baked, the durationof the baking may vary considerably from the 15 minute period referred to above, depending upon the tube.

In general, the duration of the baking should be longer the greater the amount of energy the tube will be called upon to dissipate during normal operation.

If instead of using calcium vapor to clean up the gases in the tube, pumping is resorted to, as formerly, for securing the final stage of evacuation, then instead of requiring but a few minutes of bombardment to finish the evacuation, about 20 minutes will ordinarily be required. Thus, the use of the calcium effects a great saving in time.

W'hile calcium is the preferred material for use in the anode pocket, other vaporizable material, for example, magnesium, barium. 01' strontium, having low vapor pressure and 'capable of combining with the gases to be removed from the tube to form compounds having negligibly low vapor pressure at the operating temperature, may

e used in the pocket without departing from the invention.

Although the preferred method of supporting the calcium adjacent the anode is by means of a pocket on the anode, the invention may assume other aspects. For instance, the anode plates may be made of a nickel-calcium alloy containing a small percentage of calcium, or the plates-may be coated with the calcium, without departing from this invention.

The tubes shown in Figs. 1 and 2 embody details of construction which are no part of this invention, the tube of Fig. 1 being claimed in the patent to H. J. Van DerBijl, U. S. Patent No. 1,479,778, issued January 1, 1924, entitled Vacuum tube devices, assigned to the assignee of this application, and the tube of Fig. 2 being claimed in an application of William F. Hendry, Serial No. 217,565, filed Feb. 16, 1918, entitled Electron discharge devices, assigned to the assignee of this application.

What is claimed is: p

In a vacuum tube, a plate electrode, said plate having a portion struck out to form a pocket, 0. cover for said pocket, tabs cut out from said plate toengage said cover to' hold it in posltion, and vaporizable mate-' rial contained within said pocket.

In witness whereof, I hereunto subscribe my name this 20th day of September, A. D.

ROBERT W. KING.

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