US1626858A - Vacuum tube - Google Patents

Description

7 1,626,858 May 1927- H. E. METCALF VACUUM 'I UBE Filed Feb. 28. 1924 ,[170 entor Patented May 3, 1927.

UNITED STATES PATENT OFFICE.

HERBERT'E. ME'I'CALF, OF SAN LEANDRO, CALIFORNIA, ASSIGNOR TO THE MAGNAVOX COMPANY, OF OAKLAND, CALIFORNIA, A CORPORATION OF ARIZONA.

? vacuum TUBE.

, Application filed February 28, 1924. Serial No. 695,681.

This invention relates to vacuum tubes of the three-electrode type, for use as rectifiers, amplifiers and electric-wave generators.

The object of the invention is to improve the construction and operation of such a device, whereby it is made more sensitive to weak oscillations andwhereby the internal capacity of the device is kept to a minimum. especially the capacity between the grid anil plate.

n the construction of three electrodc tubes, the practice has become quite general toemploy a-gridbetween the plate and filament.' which offers mechanical obstruction and interferes with the sensitivity of the devices In' the present invention I place the grid out of'the electron-stream, yet in such a position and of such construction that its minutest voltage changes fully effect the emission of electrons from the filament, whereby extreme sensitiveness is obtained.

In the accompanying drawings I show a variety of difierent forms which my invention may assume.

In the drawings,

Fig. 1 shows aside view in perspective of a tube embodying my invention;

Fig. 2 shows an end view of the same;

Fig. 3 shows a side elevation of a tube using a slightly difi'erent form of grid;

Fig. 4 shows a cross-section of the form of device illustrated in Fig. 3;

Fig. 5 shows a side elevation of a further modification of the invention; I

Fig. 6 shows a similar view of another form of the invention;

Fig. 7 shows a cross-section of the form of device illustrated in Fig. 6;

Fig. 8 shows a diagram illustrating the current and phantom circuits of the tube;

\ Fig. 9 shows a dia ram illustrating the action of electro-static fields within the tu e.

Fig. 10 is a view in diagram showing a' modificationof the present invention when a plurality of grid members are utilized with a single plate. i Fig. 11 is a view in diagram showing the modification of the invention when a plurality of grid members and a plurality of plate members are used in connection with a single filament.

follows exactly the course of the filament and is disposed with its edge towards the fila.ment..so that the maximum action of the grid voltage is obtained without mechanical obstruction of the electron flow. In Fig. 1 the grid consists simply of a straight strip of metal, whereas in Fig. 3 the grid is made in the form of a V-shaped strip of metal, to conform with a filament of a similar configuration. Various other shapes and designs of grids may be employed, depending on the shape of the filament. In Fig. 5 I show the grid as consisting of a wire which follows substantially the course of the filament, and so positioned as to concentrate the grid voltage on the filament by narrowing down the electro-static field of the grid and focusing the same on to the filament. As illustrated in Fig. 6. the grid may be molded so as to present a rib or projection C close to the filament and so as to concentrate its field on the filament.

Inasmuch as the usual vacuum tube circuit consists of two separate circuits. both bound together, there is a phantom capacity between the grid and filament as indicated at D in Fi 8. between the grid and plate as indicate at E, and between the filament and plate as indicated at F. I find that the sensitivity of the tube will be increased by the arrangement herein shown. inasmuch as the electro-static field between the plate and grid converges or focuses on the thin edge of the grid. This field is illustrated in diagram in Fig. 9. The filament being just inside this focus and in longitudinal alignment therewith,is fully acted upon by slight changes in such electro-static field. In addidisposed as to place the filament justwithin the focus of the electro-static field between the grid and plate, and with the said grid concentrating the elcctro-static filament-grid field on the filament, affords every desired objectin a three-electrode tube construction without obstruction of the passage of electrons between .the filament and the plate.

It is preferred to cover the plate with a thin film of volatile metal such as mercury, sodium, potassium, etc. It is well known that metallic vapors tend to increase the sensitiveness of the tubes and also increase the vacuum, due to their occlusive properties. By covering the plate with a thin film of these metals I find that great sensitivity is obtained. This may be done by placing the volatile metal on the filament and heating the latter. or by placing it upon the grid and heatingby cathode rays, whereby it is thrown off from the grid and is deposited upon the plate, leaving the grid clean. There are other ways well known in the art for depositing a volatile metal upon the plate. Other forms of construction than those here illustrated and described will be appar- -entto those skilled in the art, and may be employed without departing from the spirit of my invention as disclosed in the appended claims.

\Vhat I claim and desire to secure by Letters Patent is:

l. A three-electrode tube having a plate on one side of the filament and a linear grid on the. opposite side, in the form of a thin strip with its edge close to and following substantially the course of the filament and disposed towards the plate.

2. A tln-ee-electrode tube having a plate, a lilan'ient. and a grid, the latter in the form of a strip having an edge surface following substantially the course of the filament, said grid being located outside of the electron path between the plate and filament and being so arranged with respect to the plate and filament as to concentrate the electrostatic field between the grid and plate upon the filament.

3. A three-electrode tube having a curved plate, a filament and a grid, the latter composed of a plurality of narrow strips, each following substantially the course of the filament, all of said grid members being located outside of the electron path between the plate and filament and disposed radially with respect to the plate.

4. A three-electrode tube comprising an anode ('Oll'lPOSd of a plurality of curved plates and a grid also composed of a plurality of narrow strips, each following substantially the course of the filament, all of sa d grid members being located outside of the electron path between the anode and filament and disposed radially with respect to the anode plates. 7

HERBERT E. METCALF.

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