US2417459A - Electron tube and electrode for the same - Google Patents

Description

Mafch 1947- W; w. EITEL ET AL Q 2,417,459.

ELECTRON TUBE AND ELECTRODE FOR THE SAME Filed May 21, 1945 I N VEN TORS William M E/fe/ ELQ.. duck 4 M 'c'ullo /7 ATTORNEY Patented Mar. 1 8, 1947 ELECTRON TUBE AND ELECTRODE FOR THE SAME William W. Eitel, Woods ide, and Jack A.

McCullough, Millbrae, Calif., assignors to Eitel- McCullough. Inc., San liruno, Calif., a corpora- M tion .of California Application May 21, 1945, serial No. 594,847 H '3 Claims. (diam-27.5)

Our invention relates .to electron tube, and

, more particularly. to. an. improved electrode for such a tube.

The broad object of our invention is to provide a grid electrode having improved mechanical and electrical properties.

The invention possesses other objects and features of advantages, some of which, with the foregoing, will be set forth in the following description of our invention. It is to be understood that we do not limit ourselves to this disclosure of species of our invention as we may adopt variant embodiments thereof within the scope of the claims.

Referring to the drawing:

Figure 1 is a side elevational view of a tube embodying the improvements of our invention.

Figure 2 is a cross sectional view of the grid wire; and

Figure 3 is a similar view showing a modified grid wire.

In terms of broad inclusion, our electron tube comprises an envelope enclosing a plurality of electrodes, such as an anode and cathode and grid. The invention particularly relates to an improved material for one of the electrodes, especially adapted for the grid electrode. In one embodiment the grid comprises a core of refractory metal clad with a layer of a different refractory metal, these metals being selected for certain desired properties, such as a core of molybdenum clad with a layer of tantalum. In another modification the composite electrode includes an additional layer of electron emission inhibiting material, such as platinum over the tantalum layer.

In greater detail, and referring to the drawing, our tube is illustrated as a triode having a grid embodying the improvements of our invention, it being understood that this is merely for illustration and that the improvements may be applied to other electrodes and to other types of tubes. The tube illustrated comprises an envelope 2 of glass or the like having a re-entrant stem 3 carrying an exhaust tubulatio-n 4. After evacuating the tube and sealing off the tubulation, a suitable base 6 having prongs l is cemented to the lower portions of the envelope,

A plurality of electrodes including cathode 8, anode 9 and the improved grid H are disposed coaxially within the envelope. Anode or plate 9 has a cap I2 connected by a bracket It to a lead l4 sealed to the top of the envelope. The anode may be of any suitable material such as tantalum,

: and is preferably provided fins l5. l Cathode 8 is .with heat radiating preferably a thor-iated. tungsten filament, comprising a coil welded top and bottom to-a pair of leads I! sealed to stem 3. Flexible conductors l8 connect the cathode leads with a pair of base prongs. It is understood that the cathode or filament may assume other shapes than the type illustrated.

From the structural standpoint, grid l I is preferably of the cage type comprising vertical wire bars terminating at a base ring 2| supported by brackets 22 on a pair of rods 23 sealed to stem 3. One of these rods functions as a lead and is connected to a base prong by conductor 24. The shape of the grid and its mounting means may of course be varied between wide limits.

Our improved grid has its bars made of a composite wire comprising a core 25 of a refractory metal having good mechanical strength and non-warpage properties, such as molybdenum or tungsten. Molybdenum is especially suited as a core material and is preferred. This core is clad with a layer 2! of another refractory metal particularly selected to form a good base for a surface layer 23. Tantalum and columbium provide satisfactory base layers, tantalum being preferred. Figure 2 shows a wire having a core 26 clad with layer El. In fabrication, the wire may be drawn in this state and supplied as a product of manufacture for later application of the surface layer 28.

Surface layer 28 is preferably of a material adapted to inhibit emission of primary electrons from the grid. Platinum is a satisfactory surfacing material and is preferred. Other nonemissive surfacing materials, such as those comprising metallic oxides. may be employed. When platinum is used, which is capable of being worked, the complete composite wire as shown in Figure 3 may be fabricated by ordinary Wire drawing operations.

The intermediate tantalum layer performs several functions. In the case of a platinum surfacing, the tantalum provides a protective layer between the platinum and the molybdenum core material. Tests show that if the platinum is in direct contact with a molybdenum core, the platinum loses its non-emissive properties, probably due to excessive absorption of molybdenum into the platinum. Our improved grid wire retains the advantage of a molybdenum core (for strength purposes), yet maintains the non-emissive properties of the platinum surface layer. A certain amount of tantalum is probably absorbed into the platinum from our intermediate layer 21, but this has not'bfeen found detrimental. It might be asked why the surface layer is not applied directly over a solid tantalum core. This is not desirable because tantalum has very peculiar crystal growth characteristics at elevated temperatures, causing bad warpage of the grid. In'

: an intermediate layer .of tantalum, and a surface layer of an electron emission inhibiting material. 2; An electron tube comprising an envelope,

and a plurality of electrodes in the envelope including a grid comprising a core of molybdenum, an intermediate layer of tantalum, and a surface layer consisting essentially of platinum.

3. A grid material for an electron tube comprising a core of molybdenum, an intermediate layer of tantalum, and a surface layer of an electron emission inhibiting material.

WILLIAM W. EITEL.

JACK A. MCCULLOUGH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,226,720 Hansell Dec. 31, 1940 2,358,200 Atlee Sept. 12, 1944 2,282,097 Taylor May 5, 1942 1,929,661 Von Wedel Oct. 10, 1933 1,180,614 Simpson Apr. 25, 1916 1,829,237

Ruben Oct. 27,1931

Images