US2699518A - Grid for electron tubes - Google Patents

Description

Jan. 11, 1955 E. COHN 2,699,518

GRID FOR ELECTRON TUBES Filed March 19, 1952 GRID PLATINUM RUTHENIUM ALLOY IIIIIIIIIIIIIIIIII,

INVENTOR Eugene 0072 BY WWW United States Patent GRID FOR ELECTRON TUBES Eugene Cohn, White Plains, N. Y. Application March 19, 1952, Serial No. 277,402 3 Claims. (Cl. 313-300) This invention relates to electron tubes, and more particularly to miniature and subminiature electron tubes having one or more grids therein. By a miniature electron tube is meant an electron tube, the envelope of which has a height not exceeding approximately 1 /2 inches and an outside diameter not exceeding about /51 inch, and by a subminiature electron tube is means an electron tube the envelope of not exceeding about 1 /2 inches and not exceeding about inch.

In the manufacture of miniature and subminiature electron tubes successive convolutions of the grids employed therein are usually spaced apart minute distances. Also the distance between the grids or between the innermost grid and the cathode is very small. Such c ose spacing, in operation of the tube, to meet commercial specifications must be maintained within a tolerance of the order of only .0005 inch. The grid wire must have adequate tensile strength to permit winding under the necessary tension to maintain such spacing within the tolerances above noted during cleaning, sizing and other handling to which the grids are subiected in the manufacture of the tube. Also the grid wire must have the necessary physical character istics to remain in the desired spaced relationship relative to successive convolutions of the grid and to the other parts of the tube during operation of the tube at the elevated temperatures which then occur due, for example, to heating of the cathode. The grid wire must also have the property of not developing harmful oxides when the grid is made and also during subsequent heat treatment employed in making the tube; for example, to etfect its exhausting. In use, the grid shou d not emit electrons in sutficient quantities to deleteriously affect the operation of the electron tube; this phenomenon is commonly known as and will be hereinafter referred to as secondary emission.

In the manufacture of electron tubes, and particularly the miniature and subminiature electron tubes, it is now conventional practice to produce the grid from tungsten Wire coated with a precious metal, such as gold, palladium, rhodium or platinum, usually gold. The precious metal coating is employed to minimize the formation of harmful oxides and to reduce secondary emission; the tungsten base is employed to obtain the necessary tensile strength. Such grids have been found objectionable for a number of reasons among which may be mentioned it is frequently necessary to operate the cathode at such high temperatures that vaporization of the plated gold takes place with consequent impairment of the operation of the tube. Furthermore, the tungsten grid wire of necessity must be made by a powder metallurgy technique. This results in a wire that is not uniform throughout its length, i. e., the wire has brittle or weak spots along its length. Such variations in the wire cause difiiculties when the wire is wound to form a grid; for example, brittle spots in the wire may deleteriously affect the aforesaid spacing or result in the wire breaking as it is wound to form the grid.

It is an object of this invention to provide an electron tube having one or more grids therein, which in use show no harmful secondary emission, conform with existing tolerances, can be operated without harmful effects at materially higher temperatures than heretofore known grids including the commonly used gold plated which has a height an outside diameter tungsten grid, and do not develop harmful oxides during fabrication of the electron tube or in use thereof.

Other objects and advantages of this invention will be apparent from the following detailed description thereof.

In accordance with this invention the grid or grids of the electron tubes are made by winding a wire consisting of an alloy containing from 5% to 10% ruthenium and from to platnium, the wire having a diameter of from .0015.0004 inch under tension about the grid supports to produce the grid winding. The alloy is produced by melting the platinum and ruthenium constituents in the proportions within the range above noted, producing an ingot from the melt, then wire drawing and annealing between successive Wire drawing operations to produce a grid wire of the desired diameter within the range above noted. As the production of the wire may be in accordance with any well known procedure for producing fine wire of maximum tensile strength, it is believed further description thereof would serve no useful purpose.

The platinum constituent of the alloy may be pure platinum or any commercial grade of platinum, preferably Grade 4 Platinum, containing a minimum of 99% platinum, the rest being impurities, such as ruthenium, palladium or other impurities found in platinum. The ruthenium used may be pure ruthenium or a commercial grade of ruthenium containing small amounts of impurities. Preferred alloys contain 90% to 92.5% platinum and 7%% to 10% ruthenium, although, as above noted, the proportions may be varied within the range of from 90% to 95% platinum and 5% to 10% ruthenium. Melting of the platinum and ruthenium to produce an alloy ingot which is wire drawn to a diameter size of from .0015 to .0004 inch and annealing between successive wire drawing operations results in a wire having a surprisingly high tensile strength, e. g., over 300,000 pounds per square inch and usually about 360,000 pounds per square inch in the case of a wire having a diameter of .001 inch.

The accompanying drawing shows, for purposes of illustration only, an electron tube of the pentode type. In this drawing Figure 1 is a perspective view on an enlarged scale showing a conventional type of electron tube in which the invention may be embodied, the glass envelope being broken away to show the interior structure of the tube;

Figure 2 is a fragmentary perspective view on a still larger scale showing the relative arrangement of the grids, cathode and plate; and

Figure 3 is a horizontal section taken ing through line 3-3 of Figure 2.

Referring to the drawing, 10 indicates a glass bulb or envelope which encloses the five electrodes of the tube. The electrode assembly is mounted in the usual way on the base 11 which carries a heated cathode 12, a control grid 13, a screen grid 14, a suppresser grid 15 and a plate 16 all surrounding the cathode 12. Suitable spacers 17 and 18 space the electrodes from each other and prevent lateral displacement of the assembly in the tube.

Spaced rods 19 and 20 are suitably supported at their ends in the spacers 17 and 18 and provide supports for the successive convolutions of the grid wire wound thereabout to form the control grid 13. This wire is wound under tension sufiicient to maintain successive convolutions of the wire in desired spaced relation and also to maintain the desired spacing between the control grid 13 and the cathode 12 and between the control and screen grids. Similarly, spaced rods 21 and 22 provide supports for the convolutions of the grid wire forming the screen grid and supports 23 and 24 provide supports for the convolutions of the grid wire forming the suppresser grid. Some or all of these supporting rods may be provided with spaced niches or serrations for receiving and holding the wire wound thereabout, as is well known in this art.

Leads 25 extend from the plate, grids and cathode as is conventional. Since the construction of the electron tube apart from the composition of the grid wire may be of any well known type, it is believed further description thereof is unnecessary.

in a plane passscreen grids and, if' desired; alsothe In accordance with the invention the control and are made by winding the ruthenium platinum alloy hereinabove described about the grid supports under tension suflicient to maintain; the: grid.- wire in place." on the: grid supports;v The tension used Willi depend. on the structure ofithe-grichsupports, thezdesignzof the. tube,

suppresser "gridetc.. In:v-iew'of.the hightcnsile strengthzof thezplatinurnruthenium alloys, the grid wire can readily be: wound about: itssupports. under; tension as high; as: 300,000 pounds. per square inch; without. danger of: the' wire breaking and the wound'wire'will remain in the desired spaced relationship on. the :grid'. supports.

In. use: it: has been found that grids. made of the ruthenium-platinum alloys do: notxdevelopt harmfult sec ondary emission oroxides- Further, the gridwire; has the: necessary tensile strength and other physical: propertiesto maintain-the aforesaid spacing'within the tolerance above' noted. during the handling of the grids necessary in orderrto mount the grids withinthevacuum tubes and also; inuse of the tubes evenat the relatively high. temperatures at which the cathode may beeperated; Since: the grid wire is. produced from an alloy melt: and not by a metallurgical technique, it" is 11111 form initsphysical properties. and chemical composition throughout its length; Because. of: this greater uniformity it can be wound with less danger of. breaking and will maintain the aforesaid spacing within the toleranceabove. noted muchmore effectively than the gold.

plated tungsten wire heretofore used.

WhileI have: described myimprovement iIll connection with the grid of a miniature or subminiature electron tube, it' will be understood the invention is applicable tothe production. of. grids. of other electron.

tubes.

Ordinary commercial platinum and ruthenium often contain: traces of other. metals, such as gold or: silver. Hence, the presence of trace quantities; of such. other 4.. metals in the alloy is not to be construed as a departure from the -scopeand' spiritoftheinvention;

Since different embodiments of the invention could be made without departing from the scope of this invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A grid electrode suitable for use in an electron tube consisting of an alloy wire having a diameter from .0015 to. .0004 inch, the. alloy consisting of from 5% to 10% ruthenium and from to platinum.

2. A grid electrode: suitable for: use in an electron tube consisting ofan alloy wire having a diameter from .0015 to .0004 inch, the alloy consisting of from 7.5% to 10% ruthenium and from 90% to 92.5% platinum.

3. Anelectron tube having a. cathode; a'COHtIOI. grid, a screen grid, a suppresser grid. andia-plate surrounding the cathode, the control grid and screen grid. being composed. of an. alloy wire. having a diameter from .0015to..0.004 inch,,the a11oy consisting of from7.5% to 10%. ruthenium and from.90%. to 92.5% platinum OTHER REFERENCES Metal Industry, Platinum Metals, April 2, 1948, pages 267, 268.. Copy in. Scientific Library.

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