US2040530A - Electron discharge device - Google Patents

Description

May 12, 1936. A. L. PIPPER I ELECTRON DISCHARGE DEVICE File d Nov. 4,

W RNEY Patented May 12, 1936 UNITED STATES PATENT" OFFICE ELECTRON DISCHARGE DEVICE Delaware Application November 4, 1933, Serial No. 696,606

6 Claims.

This invention relates to electron discharge tubes, and more particularly to tube parts or elements made of ductile iron. Some of the metals commonly used today for elements in electron discharge tubes, such as radio tubes, are nickel, tungsten, and molybdenum which, in general, are satisfactory, but are undesirably expensive as compared with commercial iron.

Attempts to use commercial iron for radio tube 10 elements, such as electrodes and electrode support wires, havenot been commercially satisfactory. It was found that tubes with elements of plain or uncoated iron were exceedingly diificult to exhaust to a high vacuum under mass production conditions, and that tubes with elements of galvanized iron contained, when hot, an objectionable amount of. vapor.

' One of the objects of my invention is to provide commercially satisfactory electron discharge tube elements made of commercial iron. To this end I make radio tube parts or elements, such as electrode support wires, grids, andplates,oi tinned iron of the kind which is known commercially as ingot iron or mild steel and contains so little carbon that it cannot be tempered. Tubes having tube elements of such tinned iron or mild steel can be exhausted by usual factory exhaust methods as easily as tubes having elements of nickel, and do not have an objectionable amount of vapor, probably because tin, as compared with zinc, has a high vaporization point, approximately 800 C. under ordinary radio tube exhaust conditions. High heating of the tinned iron electrodes during exhaust may drive off some of the tin, but the tin vaporized during the high temperature exhaust has no appreciable deleterious effeet and the tube element of tinned iron, even though it loses some tin during exhaust of the tube, is commercially satisfactory.

Radio tube elements made, in accordance with my invention, of iron or mild steel coated with tin, are much cheaper than the elements heretofore used commercially, can be handled in the same way and without special precautions, and a 4,5 tube in which they are used can be exhausted easily by the conventional procedure. Tubes with oxide coated cathodes are definitely limited in their power output by grid emission, particu larly from the grid next the cathode, as in such a tube of high power output, with the first grid close to the cathode, some of the oxide coating of the cathode may be driven off and deposited on the grid. During operation of the tube this grid becomes heated and emits electrons resulting in a change in the grid bias of the tube with a consequent lowering of the power output. The closer the grid is to the cathode the greater this grid emission and its effects.

By my invention the grid emission in a tube with an oxide coated cathode may be made some- 5 what less than is found with uncoated iron wire grids in such tubes.

For a better understanding of this invention, reference may be had to the following description taken in connection with the accompanying 10 drawing in which:

Figure l is a front view of a radio tube made in accordance with this invention, parts being broken away to show the internal structure;

Figure 2 is a perspective view of a tin coated 15 wire of ingot iron or mild steel suitable for use in making grids in accordance with my invention.

In the drawing 'Figure 1 shows a radio tube of the pentode type and of usual construction, with the usual base I secured to the dome type bulb 2 20 which encloses the five electrodes of the tube. The electrode assembly mounted in the usual way on the stem or press 3 comprises an indirectly heated oxide coated cathode 4, a control grid 5,

a screen grid 6, a suppressor grid 1, and a plate 8, 5 all coaxial with and surrounding the cathode 4. Mica spacers 9 and I0 secured to the plate 8 by straps I I space the electrodes and prevent lateral displacement of the electrode assembly in the bulb 2. 30

The electrodes are supported on the press by the usual inner leads, such as the plate leads I2, the grid leads I3 and I4, and the cathode heater leads I5. The control grid 5 is mounted between the mica spacers 9 and I0 and its lead I6 extends 35 through the cap on the upper end of. the bulb. The cathode may be connected to the suppressor grid by connecting the suppressor grid lead to the cathode sleeve by a jumper or connector inside the bulb. A getter tab I1 is supported from one 40 of the plate leads I2.

In accordance with my invention any or all of the cold elements of the tube, such as the inner leads, the grids 5, 6, and I, and the plate 8, as well as the getter tab II, may be made of tinned ingot iron or mild steel instead of the more expensive nickel, molybdenum, or similar metals commonly used for such elements. One kind of iron or mild steel which has been found to be 50 suitable for use in accordance with my invention is ingot iron containing about 0.10% of carbon and made by the basic Bessemer process. A common and widely used type of paper clip is made of such iron coated with tin, and grid wire 55 may be made from tinned iron paper clip wire about 25 mils in diameter, with a coating of tin constituting about'0.5% by weight of the tinned wire. This tinned iron wire is drawn down in the usual way for drawing iron wire to a size, such as 3 to 5 mils in diameter, suitable for grid wire.

Some of'the tin coating may be lost in the drawing, but I have found that if the coating of tin constitutes at least:0.l0% by weight of the wire at grid wire size, a grid made with the tinned wire will give good results. Good results were obtained in tubes in which the tinned iron grid wire inthe exhausted and finished tube showed by chemical analysis about 0.10% of tin. A greater amount of tin seems to do no. harm, and for inner leads, electrode supports and like parts the 25 mil paper clip wire with 0.5% of tin may be used with good results. 7

The problem of grid emission arisesparticularly in connection with the control grid 5, which is usually close to the oxide coated cathode 4. During operation some of the oxide coating l8 on 'the cathode 4 is driven off and deposits on the grid wire of the control. grid 5.. When. this grid 5 with oxide on it is heated by radiation from the cathode 4, the grid wire will emit electrons. The temperature at which the grid emits electrons depends to some extent on the kind of metal of which the grid is formed, and the emission from the tin. coated iron wire of' my invention seems to be somewhat less than from grids which are made of uncoated iron wire.

The plate 8, usually made of nickel or molybdenum, may, in accordance with my invention, be made of tinned iron or mild steel such as is used for grids. The coating of tin may be so thin that even if practically all of the tinis vaporized from the plate during exhaust, the bulb is not appreciably discolored.

Figure 2 is a perspective view of a tinned iron wire with a core IQ of ingot iron or mild steel containing about 0.10% of carbon, and anouter coating 20 of tin which completely covers the iron core and constitutes at least 0.50% by weight of the tinned wire. This wire may be used for inner leads, or plate support rods, or it may be drawn down to a suitable size. Plates or getter tabs or straps, such asthose illustrated in Figure 1 are more conveniently made of sheet iron or mild steel tinned by the usual methods of makin tin plate.

It is to be understood that the specific embodiments described will admit of various changes and modifications the scope of which is limited only by the appended claims.

What is claimed as new is:

1. An electron discharge tube comprising, an oxide coated cathode, ananode, and a plurality of grid. electrodes interposed between. said cathode and said anode, the wire of the grid nearest said cathode consisting of an iron core and a. tin coating on said core.

2. An electron discharge tube comprising, an oxide coated cathode, a grid, and a plate, said grid being concentric with and surrounding said cathode and consisting of iron wire coated with tin, said anode being concentric with and surrounding said grid and consisting of an iron sheet coated with tin.

3. Ari-electron discharge tube consisting'of an electron emitting oxide coated cathode, an anode, and an iron. wire grid electrode, interposed between said cathode and said anode and sufilciently close to said cathode to receive a substantial amount of the oxide coating vaporized therefrom during operation of the tube, and a coating of tin on the iron wire of said grid capable of substantially reducing. the electron emission therefrom, normally caused by said deposited electron emitting oxide coating.

4. Anelectron discharge tube comprising a highly evacuated envelope enclosing .an oxide coated thermionic cathode, and a cold electrode consisting of an iron base and a coating of tin on said iron, said coating being less than 1% by weight of said electrode.

5. An electron discharge device comprising a cathode having an electron emitting oxide surface, an anode, and an interposed control electrode spaced from said cathode and composed of an iron core having a coating containing tin.

6. An electron discharge device comprising an evacuated envelope enclosing an oxide coated thermionic cathode, an anode, and a grid electrode interposed between. said cathode and. anode and having a core of a metal of the iron class with a surface containing tin.

' ARNOLD L. PIPPER.

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