US2729763A

US2729763A - Electron tube grids

Info

Publication number: US2729763A
Application number: US277403A
Authority: US
Inventors: Cohn Eugene
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-03-19
Filing date: 1952-03-19
Publication date: 1956-01-03
Anticipated expiration: 1973-01-03

Description

Jan. 3, 1956 E. COHN 2,729,763

ELECTRON TUBE cams Filed March 19, 1952 GRIDS OF RHODIUM NICKEL ALLOY INVENTOR Z'zqgene 00/122 BY I I TTW Patent Office 2,729,763 Patented Jan. 3, 1956 2,729,763 ELECTRON Eugene Cohn, Whitejl'laiiss, N. Application March 19, 1952,Serial'No. 277,403 .1 Claim. (or. 313 311 This invention relates to electron tubes, and more particularly to miniature and subminiature electron tubes 'having one or more grids therein. By a miniature electrons tube is meant an electron tube, theenvelope of which has a height not exceeding approximately 1 /2 inches and an outside diameter not exceeding about 4 inch, and by a subminiature electron tube is meant an electron tube the envelope of which has a height not exceeding about 1% inches and an outside diameter not exceedingab ut in h- 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 verysmall. Such close 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 tensilestrength to permit winding underthe nece ary ension to maintain s ch. p g within. th o e ances above noted dur n cleaning sizing and, oth r h l to hi h. th grids e jecte in the. manufacture of the tube. Also the grid wire must have the necessary physical characteristics 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 effect its exhausting. In use, the grid should not emit electrons in suflicient quantities to deleteriously affect the operation of the electron tube; this phenomena 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 g'oldplated tungsten grid, and do not develop harmful oxides during fabrication of the electron tube or in use thereof. 1

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

In accordance with this invention the grid or grids of theelectron tubes aremade by'windi'n'g a wire-consisting of analloy containing from 30% to 50% rhodium, from 44% to 70% nickel and from 0% to-6% molybdenum ortungsten, the wire having a diameter of from .00l5 .0004 inch under tension about the gridsupports to produce the grid winding. The alloy is produced by melting the rhodium,- nickel and molybdenum ortugnsten, if employed, in the proportions within the ranges above noted, producing an ingot from the melt, then wire drawing and annealing between successive wire drawing operations to produce 'a *giid wire of the desired diameter. 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 nickel constituent of the alloy may be pure nickel or the commercial grade of nickel sold byInternational Nickel Company as Grade A nickel which contains 99.4% nickel and cobalt, the rest being impurities found in commercial nickel. The rhodium, tungsten and molybdenum -may be pure or commercial--grads containing trace amounts of impurities. Preferred alloys are: a

(a) 43% rhodium and 5.7% nickel;

(b) 42.2% rhodium, 53.9% nickel and 3.9% molybdenum;

(c) 42.2% rhodium, 53.9% nickel and 3.9% tungsten.

Melting of the rhodium, nickel and molybdenum or tungsten, if used, 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 in a plane passing 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 sufficient 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 to 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 accordance with this invention the control and screen grids and, if desired, also the suppresser grid are made by winding the rhodium nickel alloy hereinabove described about the grid supports under tension sufficient to maintain the grid wire in place on the grid supports. The tension used will depend on the structure of the grid supports, the design of the tube, etc. In view of the high tensile strength of the rhodium nickel alloys, the grid wire can readily be wound about its supports 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 rhodium nickel alloys herein disclosed do not develop harmful secondary emission or oxides. Further, the grid wire has the necessary strength and other physical properties to maintain the aforesaid spacing within the tolerance above noted during the handling of the grids necessary in order to mount the grids within the vacuum tubes and also in use of the tubes, even at the relatively high temperatures at which the cathode may be operated. Since the grid wire is produced from an alloy melt and not by a metallurgical technique, it is uniform in its physical 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 tolerance above noted much more effectively than the gold plated tungsten wire heretofore used.

While I have described my improvement in connection with the grid of a miniature or subminiature electron tube, it will be understood the invention is applicable to the production of grids of other electron tubes.

Ordinary commercial rhodium and nickel often contain traces of other metals, such as platinum and silver. Hence, the presence of trace quantities of such other metals in the alloy is not to be construed as a departure from the scope and spirit of the invention.

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:

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 30% to'50% rhodium, from 44% to nickel and from 0% to 6% of a metal from the group consisting of tungsten and molybdenum.

References Cited in the file of this patent UNITED STATES PATENTS 1,169,182 Nicolson Jan. 25, 1916 1,779,602 Kingsbury Oct. 28, 1930 1,832,307 Kingsbury Nov. 17, 1931 1,975,140 Eitel et al. Oct. 2, 1934 2,015,327 Wheeler Sept. 24, 1935 2,066,870 Wise et al. Jan. 5, 1937 2,081,125 Carter a- May 18, 1937 2,472,760 Ratchford June 7, 1949 2,533,750 Adler et a1 Dec. 12, 1950 2,567,714 Kaplan Sept. 11, 1951