US2678403A - Grid probe structure - Google Patents

Description

May 11, 1954 K. J. GERMESHAUS'EN GRID PROBE STRUCTURE Filed May 3, 1946 INVENTOR KENNETH J. GERM ESHAUSEN ATTORN EY Patented May 11, 1954 GRID PROBE STRUCTURE Kenneth J. Germeshausen, Newton Center, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application May 3, 1946, Serial No. 666,880

4 Claims.

This invention relates in general to hydrogen thyratrons and more particularly to the prevention of grid emission in hydrogen thyratrons of the inside coated cathode type.

Thyratron tubes have many applications in electronic circuits. Hydrogen thyratrons have been developed having advantages over other thyratrons which make them more desirable in many applications. A hydrogen thyratron is disclosed in patent application entitled Hydrogen Thyratron, Serial Number 576,113, filed February 3, 1945 by Kenneth J. Germeshausen. Grid emission, caused by cathode coating materials being evaporated from the cathode and depositedon the grid has proved troublesome in these tubes.

It is therefore anobject of this invention to prevent grid emission in hydrogen thyratron tubes employing inside coated cathodes.

It a further object of this invention to provide a tube structure which maintains good grid starting characteristics while preventing such grid emission.

These and other objects will be apparent from the following specification when taken with the accompanying drawing in which:

Fig. 1 illustrates the structure of this invention; and

Fig. 2 shows an improved type heater for oxide cathodes of the type used in some thyratron tubes.

The invention will now be described in detail with reference to Fig. 1, which shows the electrode structure of a hydrogen filled thyratron type tube. For simplicity the envelope II has been symbolically shown. An oxide film I is coated on the inside surface and enclosed by a cylindrical conductive structure 12 which has an aperture I4 at the top as shown. The electron discharge from oxide film l0 passes through this orifice toward the grid and anode. A cylindrical grid structure I6 is placed around cylindrical structure l2. This grid has a transverse mesh is between the top of cylindrical structure I2 and anode 20.

' To prevent grid emission, it is necessary to keep evaporated metal, such as barium, from the oxide film l0 away from mesh section I8 of the grid structure. This is accomplished by placing a baflle 22 between the cathode, structure [2 and grid mesh I8. This battle is conductively attached to the cathode structure [2 by a supporting member 24. The bafiie when connected in such a manner shields the grid 18 and prevents substantially all evaporated metal from reaching the grid mesh 18. Bafile 22 connected in this manner shields the cathode so completely that it is difi'icult to start a discharge between grid and cathode to start thyratron conduction. To eliminate this diificulty and increase control sensitivity a small diameter probe 26 is attached to grid mesh 18 and extends axially through a small aperture in the center of baflie 22 a short distance in the direction of cathode structure I2. This probe 26 enables the start of a discharge between grid mesh [8 and cathode [2, which readily reaches the anode. The small area of the probe 26 exposed to the cathode discharge, its location, and small cross-section prevent it from causing grid emission difficulties even through some evaporated metal may be deposited on the end of the probe.

Thus it may be seen that this invention provides means for preventing grid emission trouble in hydrogen thyratrons of inside coated cathode types without interfering with the desirable operating features of such tubes.

Now referring to Fig. 2 there is shown an improved type heater for use with oxide cathodes. A cathode 40 with an electron emissive coating 42 is heated by a heater element 44 inside the cathode sleeve 40. The heater element 44 is constructed of a ribbon shaped metal such as tungsten. The cross section of the ribbon is selected such that adjacent turns of the helically wound ribbon touch each other and completely fill the space inside the cathode sleeve 40. As the heater 44 is operated at low voltage, no special insulation is required. This construction prevents sagging of the heater, and it is thus possible to use ribbon of less refractory metal than tungsten, as for example, molybdenum. In addition to these features, the arrangement shown, wherein adjacent turnsare in contact presents almost a uniform heating surface to provide very uniform heating of the cathode sleeve 40 and coating 42.

It is believed that the construction and operation as well as the advantages of my improved thyratron tube structure will be apparent from the foregoing detailed description thereof. It

will also be apparent that while I have shown and described my invention, in a preferred form, changes may be made in the apparatus disclosed without departing from the spirit of the invention as sought to be defined in the following claims.

What is claimed is:

1. A hydrogen thyratron having an anode, a cylindrical cathode and a cylindrical sleeve mesh and connected electrically to said cathode for preventing grid emission in said tube, and a 7 probe connected to said grid and extending through said baflle plate aperture toward said cathode.

2. A hydrogen thyratron having an anode, a cylindrical cathode and a cylindrical sleeve shaped grid, said cylindrical cathode having an inside coating and an aperture at one end thereof for the emission of electrons toward said anode, said grid substantially enveloping said anode and said cathode and having a transverse wire mesh secured thereto between said anode and said cathode, a transverse bafiie plate between said cathode and said grid having a small central aperture and connected to said cathode for preventing grid emission in said tube, and a short probe connected to said grid and extending axially a short distance through said aperture toward said cathode for providing sensitive conduction control.

3. A hydrogen thyratron having an anode, a cylindrical cathode and a cylindrical sleeve shaped grid, said cylindrical cathode having an inside coating and an aperture'at one end thereof for the emission of electrons toward said anode, said grid substantially enveloping said anode and said cathode and having a transverse wire mesh secured thereto between said anode and said cathode, a baifie having a centrally located aperture between said grid and said cathode for preventing substantially all metallic particles evaporated from said cathode from reaching said grid, and a short probe fastened to said grid and extending axially through said aperture a short distance toward said cathode, said baffle and probe being operative to provide accurate conduction control by said grid with substantially no grid emission.

4. An electron tube having at least a cathode, an anode and a grid, said cathode being substantially a hollow cylinder open at one end and coated on the interior surfaces thereof with electron einissive material, said grid being a hollow cylinder concentric with and substantially surrounding said cathode and said anode, a circular mesh affixed within said grid cylinder transversely thereof and disposed between said cathode and said anode, a. probe extending from said mesh toward said cathode, an annular baffie plate disposed between said cathode and said mesh and conductively connected to said cathode, said annular baflle plate surrounding said probe.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,893,837 Giard Jan. 10, 1933 2,014,539 Stansbury Sept. 17, 1935 2,032,179 Lowry Feb. 25, 1936 2,065,997 Edwards Dec. 29, 1936 2,106,847 Kniepkamp Feb. 1, 1938 2,166,817 Maser July 18, 1939 2,271,938 Etzrodt Feb. 3, 1942 2,273,054 Le Van Feb. 17, 1942 2,392,397 Litton Jan. 8, 1946 2,399,003 Crapuchettes Apr. 23, 1946 2,416,661 Lawton Feb. 25, 1947 2,492,665 Sloan Dec. 27, 1949 2,492,666 Sloan Dec. 27, 1949 2,572,881 Rothstein Oct. 30, 1951

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