US1685326A - Thermionic vacuum tube - Google Patents

Description

Sept. 25, 1928.

,v J. D. JYOYRDAN THERMIONIC VACUUM TUBE Fiied Jan. 16, 1926 WMM n 6M o@ vT n m w w Tl. 3 ev m o J byf wr Y msgs @if Patented- Sept. 25, 19278.

UNITED STATES PATENTl OFFICE.

.TAKES DENNEY JORDAN, OF OWNSBOBO, KENTUCKY, ASSIGNOB. TO THE KEN-RAD CORPORATION, OF OWENSBOBO, KENTUCKY, A CORPORATION OF KENTUCKY.

THEBIIONIC VACUUI TUBE.

Application med January 16,1928. Serial No. 81,684.

My invention relates to a construction of elements in a thermionic vacuum tube which nres the degree of vacuum obtained control- It is a known fact that the degree of vacuum obtained in any vessel can never be better' than that permitted by the vapor pressure of the various elements contained in that vessel. It is also a known fact that in obtainin a high 1o degree of vacuum the application o? heat is necessary in order to liberate all volatile matter.

I have discovered a construction of elements which may be used in a vacuum tube'iwhich permits the heating of the various elements involved, even to their`m`elting point, without vaporizing the material used as al getter.

The use of the word getter at this point, and

throughout this specification, refers to any material which is very active chemically and combines with residual vapors and gases in a vacuum tube producing a solid at the temperature and pressure used. It is readily seen that if elements are used with a relatively low vapor pressure in the construction of the tube, the ultimate pressure obtained will be that of the vapor pressure of the particular getter used. As an example, a thermionic vacuum tube may beconstructed with low vapor pressure elements throughout and any convenient getter used. In this case the best vacuum obtainable will be represented by the vapor pressure of the getter or 'of the compounds formed by its actlon on the residual vapor not removed by the pump.

If a construction is used such as described in this specifica-tion, the elements of the tube may maintainedv at any desired temperature below the melting point of the elements 40 for as long a period as desired While the tube is connected to a vacuum pump. This heating process may consist of bombardment of the elements with electrons from the cathode or exposure to a high frequency electric eld which induces electric currents in the various elements producing the desired temperature. After the various elements have beendenuded of volatile material in this manner the getter may be vaporized either by bombardment or byl exposure to a hi h frequency electric field. In case the high requency method is used with the construction I have discovered the electric field must bein a direction preferably at right angles to the field used in the denuding process of the various elements.

By virtue of the roperties of myconstruction of elements I y ave discovered that if a high frequency electric field is placed about the elements of the tube in a direction parallel to its axis the elements of the tube become hot, while if this field is approximately perpendicular to the axis of the tube, and to the plane of thc support to which the get-ter is attached, the getter will be vaporized without generatinga high temperature in the elements themselves. l

My invention may bc better understood by referring to the drawings which are annexed hereto and form a part of this specification, and which diagrammatically illustrate two of the man possible applications of the principles involved. S

Fi ure 1 represents a construction which may used on tubes having elements lying in a parallel plane, or in parallel planes; while Figure 2 represents a possible construction for tubes whose elements are cylindrical in shape and concentric.

Referring to Figure 1,

A represents the etter mounting, which may be in the form o a wire as shown in the drawing or in the form of a sheet of material i whosepplane is parallel to the axis of the other elements of the tube;

B2 represents the cathode;

C represents the anode;

D represents the auxiliary third electrode, hereinafter referred to as the grid;

E represents the support wire for the cathode;

F represents the support for E;

G represents that part of the glassstructure through which the lead wires make entrance to the vacuum chamber. Throughout this specification this structure will be known as the press;

H represents the flared glass tubing used in the manufacture of the stem;

I represents the tube through which the device is evacuated; and

J represents the glass bulb which forms the outer walls.

The small letters on Figure 2 refer respectively to the same elements as the large letters do in Figure 1. v

Referring to Figure 1, the exhausting process may be carried out in accordance with the following schedule- I should be connected to a suitable vacuum pump capable of exhausting to an absolill.

` cury or less.

current should be placed over the bulb in such a lnanner that its axis coincides with that of the bulb. IVit-h a suitable frequency and current in this coil the anode and grid may be heated to the desired ten'iperature which is just below the melting point of th'e material used in its construction. It will be noted that this last process does not generate heat in A, the getter mounting. The getter mounting A may be heated by conduction from the anode to a temperature just below that at which the getter vaporizes.

At this stage of the process, if the absolute pressure inside the bulb is less than .001l of mercury, the exhaust tube may be melted off near the flare, thereby hermetically sealing the structure inside the bulb. In this state the high frequency coil may be held in such a position that its axis is perpendicular to the plane of A, the getter mounting, and with a suitable frequency and current heat will be generated in said mounting which raises the temperature of the getter to a point where vaporization occurs. The getter in its vapor state being highly active chemically combines with the vapors which were not removed by the vacuum pump and forms solid compounds.

After this operation it is obvious that the pressure on the inside of the vacuum chamber is equal to the Vapor pressure of the con struction material having the highest vapor pressure.

The foregoing process applies to a structure made in accordance with Figure 2 or any other structure whereby the vaporization of the getter takes place subsequent to the heating of the elements.

The structure adapts itself readily to variations in the exhausting process. As an example, after the elements have been thoroughly denuded of foreign material the getter may be vaporized before the vessel is sealed from the vacuum pump. In this case the vapor acts as a fiush forcing any other vapor which might be present out of the bulb. If this is done, however, sealing from the vacuum pump should take place immediately in order to 'eliminate oil and other vapors from finding their Way back into the tube.

My discovery permits the activation of the cathode by means of Various activating materials which, if placed on the gettermounting represented by A Figure 1, may be vaporized at any convenient time during the manufacturing process by heating the. getter mounting in the same manner 4as that described for vaporizing the getter itself. For example., a suitable filament may be used as a cathode and a very high degree of vacuum obtained in the pumping process. A cutting length of this filament may be selected whereby the finished tube will be very deficient and the cathode an exceedingly poor emitter of electrons. If this same f' tube had a small piece of activating material mounted on the getter mounting A, and if same should be subsequently vaporized by any of the above mentioned heating processes, the vapor of the activating material would deposit on the cathode and make a combination which would develop the cathode into an excellent electron emitter. In other words, the cathode can thusly be made a more efficient emitter of electrons by using the activating material, and same would consequently operate in service at a temperature considerable below that necessary, if no activating material had been used.

IVhat I claim as new and desire to secure by Letters Patent of the United States is:

1. A thermionic vacuum tube comprising an evacuated vessel, grid, filament and plate electrodes within said vessel and aligned with the vertical axis of said vessel, and a mounting for activating material Within said vessel, said activating material mounting extending laterally across said electrodes in a. substantially horizontal direction with respect to the vertical axis of said vessel and connecting with opposite sides of said plate electrode.

2. A thermionic vacuum tube comprising an evacuated vessel, a plurality of electrodes supported 4in axial alignment within said vessel, and a bridge member forming a support for activating material extending across one end of said electrodes and connected to opposite sides of said plate electrode.

3. A thermionic vacuum. tube comprising anevacuated Vessel, grid, filament and plate electrodes supported within said vessel in axial alignment, and an arch member supported from opposite sides of said plate electrode and extending across one end of said grid and filament electrodes, said arch member providing aI supportfor activating Inaterial within said tube in a position substantially coincident with the central 'axis of said electrodes. v

In witness whereof, I have hereto setmy hand this the 12th day of January, 19:26.

JAMES DENNEY JORDAN.

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