US2879430A

US2879430A - Electron discharge devices

Info

Publication number: US2879430A
Application number: US603661A
Authority: US
Inventors: Behram H Wadia
Original assignee: Machlett Laboratories Inc
Current assignee: Machlett Laboratories Inc
Priority date: 1956-08-13
Filing date: 1956-08-13
Publication date: 1959-03-24
Anticipated expiration: 1976-03-24

Description

March 24, 1959 Filed Aug. 13, 1956 B. H. WADIA ELECTRON DISCHARGE DEVICES 2 Sheets-Sheet 1 INVENTOR.

BEHRAM H. WADIA March 24, 1959 B, H, WADIA 2,879,430

ELECTRON DISCHARGE. DEVICES F'iledAug. 13, 1956' 2 sheets sheet 2 6 "Q FIG.4 T b a l L Q INVEN TOR. BEHRAM H. WADIA United States Patent ELECTRON DISCHARGE DEVICES Behram H. Wadia, Darien, Conn., assignor to Machlett Laboratories, Incorporated, Springdale, Conn., a corporation of Connecticut Application August 13, 1956, Serial No. 603,661

6 Claims. (Cl. 313-293) This invention relates to improvements in electron discharge devices and has particular reference to novel means and method of providing electron tubes with a relatively low amplification factor.

In the manufacture of electron tubes of the triode type embodying an anode which is spaced from a cathodewith a grid structure disposed between the cathode and anode, it has long been a problem to provide the tube with a low amplification factor without arranging the electrodes in a manner which will provide the tubes with poor operating characteristics. The present invention is directed primarily to the provision of an electron tube of this type wherein a low amplification factor is achieved by widely spacing the respective wires of the grid structure so as to produce an effective mu across the cathode which is variable, and by providing the cathode with effective electron emitting areas restricted to the areas thereof where the mu is relatively low and constant.

One known means and method of reducing the amplification factor of an electron tube is by decreasing the spacing between the anode and the grid. The reduction in grid-anode spacing, however, may only be carried out to a certain limit below which the voltage rating of the tube begins to deteriorate. Another method of reducing the amplification factor is by increasing the spacing between the respective grid wires to a limited extent. With this method the grid wires may be spaced apart only to an. extent where the min across the cathode is maintained substantially constant since further spacing of the grid wires results in a variable mu which is relatively low in the areas between grid wires and is relatively high adjacent each grid wire. cutolf, a condition which is conducive to excessive distortion of the waveshape imposed on the tube.

One of the primary objects of this invention is to overcome the above and other objections by the provision of novel means and method of providing an electron tube with a relatively low amplification factor and with acceptable operating characteristics.

Another object is to provide an electron tube of the above character wherein the amplification factor is maintained at not more than approximately 10.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawings, in which- Fig. l is an axial sectional view of an electron tube embodying one form of the invention;

Fig. 2 is an enlarged sectional view taken on line 2-2 of Fig. 1;

Fig. 3 is a sectional view similar to Fig. 2 showing conventional electrode spacings;

Figs. 4 and 5 are diagrams illustrating the invention; and

Fig. 6 is a sectional view similar to Fig. 2 showing a modification of the invention.

Referring to the drawings, the electron tube shown in Fig. 1 includes an anode 10 formed as a deep cylindrical This variation leads to remote cup of highly conductive metal such as copper. Mounted tion with the circle of grid wires.

2,879,430 Patented Mar. 24,

- around the anode 10 near the open end thereof is a ring nal 15.

Grid terminal 15 also carries a tubular grid support 16 which extends inwardly of the structure toward the anode 10, the grid support 16 having a supporting ring 17 screwed or otherwise secured in coaxial relation to its inner end. The ends of a plurality of spaced grid wires 18 are secured to the inner surface of ring 17 and extend into the anode to form a cagelike structure of parallel Wires, which structure, in cross-section, defines a circle. The inner ends of the wires are secured to a disc 19 which maintains the wires in desired spaced relation.

A second vitreous ring 20, of smaller diameter than ring 13, is sealed at one end by a Kovar member 21 to the grid terminal, and at its other end by a Kovar member 22 to a cathode terminal ring 23. A first cup-shaped cathode support 24 extends inwardly from terminal ring 23. One end of a plurality of filament supporting posts 25 are mounted in the end of the support and extend into the grid structure. A second group of posts 26 are arranged alternately with posts 25 so as to define, in crosssection, a circle of posts within the grid wires 18. Posts 26 extend through clearance openings 27 in the bottom of the cup-shaped support 24 and their ends are mounted in the bottom of a second cup-shaped support 28 which is located within and spaced from support 24. The open end of the support 28 is sealed to a second cathode terminal ring 29 which is sealed, by a pair of Kovar

rings

30 and 31 having a vitreous ring 32 therebetween, to the terminal ring 23. The inner ends of the

filament supporting posts

25 and 26 extend slightly into the grid structure and each carries a respective filament wire 33.

The wires 33 are mounted on the posts 2526 by means of clips or clamps 34 and extend substantially parallel with grid wires 18. In cross-section, wires 33 define a circle of wires within and in predetermined spaced rela- The inner ends of wires 33 are joined at 35 to complete the cathode structure. An exhaust tubulation 28a is sealed in the open end of support 28.

In the manufacture of electron tubes of the triode type, it is necessary to accurately position the grid wires with respect to both the anode and the cathode, and various spacings of the electrodes relative to one another may be used to provide tubes having difierent amplification factors.

One common arrangement is shown in Fig. 3 wherein the anode 10a and cathode 33a are spaced apart a predetermined distance. Between the anode and cathode is a gird 18a, the respective wires in the grid being spaced apart a distance which is substantially the same as the distance between the grid and the cathode. With electrodes arranged in this manner, the mu across the cathode is substantially constant. To increase the amplification factor of the tube, the anode may be moved away from the grid or the spacings between the grid wires may be decreased, or both.

Also, the amplification factor of the tube may be decreased by decreasing the space between grid and anode or increasing the spacings between grid wires. -It has been found, however, in producing tubes with very low mu, that when the spacings between grid wires begin to get larger than the grid-cathode spacing, the effective mu becomes variable across the cathode. Under these circumstances the parts of the cathode situated centrally between the grid wires have a much lower mu than peaks in curve c the cathode is cylindrical in shape.

spaced a known distance a from grid wires 37 and the spacing between grid Wires is indicated by b. It will be noted b is several times larger than a. This produces a variable mu across the face of the cathode which is illustrated by curve in Fig. 5. The high indicate the relatively high mu adjacent each grid wire 37, and the dip in the curve indicates that the mu is lower between grid Wires.

1 have discovered that the lower portion of the curve is relatively level throughout a restricted length, as indicated at d. Throughout this restricted area the mu is substantially constant, that is, the variation is small and is not sufiicient to cause distortion in the waveshape imposed on the tube. Therefore, I have spaced grid 'wires 18 (Fig. 2) apart a distance which is considerably larger than the grid-cathode spacing and which produces such a variable mu across the cathode, and have located the filament wires 33 of the cathode between the grid wires at the locations where the mu is relatively low, preferably not more than about 10. Since the filament wires extend parallel with the grid Wires, there is no emissive portion of the cathode in the relatively high mu areas adjacent the grid wires, all emission being restricted to the low mu areas.

In the example shown in Figs. 4 and 5 a mu of about 5 is obtainable. However, if a higher or lower mu is desired it is merely necessary, in accordance with this invention, to appropriately space the wires 37 so as to produce a curve wherein the relatively level area d is located at the desired mu, and the cathode emission is restricted to that portion of the cathode which is within that area.

It is possible to apply this invention to tubes wherein This is shown in Fig. 6 wherein a cylindrical cathode 38 is positioned coaxially within an anode 39 and a grid structure embodying wires 4-0 is closely spaced about the cathode. In this structure the distance between grid wires is considerably larger than the grid-cathode spacing, which produces the variable mu across the face of the cathode as desired in accordance with this invention.

The cathode 38 is provided on its outer surface with elongated strips 41 of electron emitting material, such as an oxide coating. Strips 41 extend parallel with the grid wires 40 and are of controlled width so that no portions thereof extend transversely into the relatively high mu areas, the emission thus being restricted to the low mu areas.

In electron tubes of this type the cathode takes advantage of the so-called beaming effect to reduce currents intercepted by the grid. This low interception not only reduces distortion of the input waveshape but also reduces heating of the grid wires. Furthermore, this latter property aids in reducing deformation of the grid due to uneven heating.

It is to be understood that this invention may also v be applied to electron tubes having electrodes of planar,

shown and described and are pointed out in the annexed claims, it is to be understood that various omissions, fisubstitutions and changes may be made bythose skilled .in the art without departing from the spirit of the invention. Therefore, it is to be understood that all matter -shown or described is to be interpreted as illustrative and not in a limiting sense.

This

I claim:

1. An electron tube having a low amplification factor for producing an output waveshape substantially undistorted with respect to the waveshape imposed on the tube, said tube comprising an envelope containing an anode, a cathode, and a control grid, the grid having a plurality of parallel wires positioned substantially parallel with and at predetermined distances from and between the anode and cathode and spaced apart a distance which is greater than the grid-to-cathode spacing for producing a variable mu across the cathode which is defined by a curve having relatively high peaks in areas adjacent each grid Wire which blend gradually into relatively low and constant levels in areas between the grid wires, and the cathode having efifective electron emitting portions positioned only in the areas thereof where the mu is relatively low and constant.

2. An electron tube having an amplification factor of not more than about 10 and producing a waveshape substantially undistorted with respect to the waveshape imposed on the tube, the tube comprising an envelope containing an anode, a cathode, and a grid, the control grid having a plurality of parallel wires positioned substantially parallel with and at predetermined distances from and between the anode and cathode and spaced apart a distance which is greater than the grid-to-cathode spacing for producing a mu across the cathode which is relatively high adjacent each grid wire and which blends gradually into levels of not more than about 10 in areas between the grid wires, and the cathode having elfective electron emitting portions positioned only in the areas thereof where the mu is not more than about 10.

3. An electron tube having an amplification factor of not more than about 10 and producing a waveshape substantially undistorted with respect to the waveshape imposed on the tube, the tube comprising an envelope containing an anode, a cathode, and a control grid, the grid having a plurality of parallel wires positioned substantially parallel with and at predetermined distances from and between the anode and cathode and spaced apart a distance which is greater than the grid-to-cathode spacing for producing a mu across the cathode which is relatively high adjacent each grid wire and which blends gradually into relatively constant levels of not more than about 10 in areas between the grid wires, and the cathode having effective electron emitting portions positioned only in the areas thereof where the mu is relatively low and constant.

4. An electron tube having a low amplification factor comprising an envelope containing a hollow anode, a cathode embodying a plurality of electron emitting wires extending longitudinally of and parallel with the anode and defining a cylinder within the anode, and a control grid located between the anode and cathode and embodying a plurality of grid wires extending substantially parallel with the cathode and positioned with respect to one another so as to define a cylinder encircling the cathode in predetermined spaced relation therewith, the grid wires being spaced apart a distance which is greater than the grid-to-cathode spacing for producing across the cylinder defined by the cathode wires a mu which is relatively high adjacent the grid wires and which blends gradually into relatively low and'constant levels between the grid wires, the electron emitting wires of thecathode being positioned only in the areas where the mu is relatively low and constant.

5. An electron tube having a low amplification factor comprising an envelope containing a hollow anode, a cylindrical cathode within and extending axially of the anode, and a control grid located between the anode and cathode and embodying a plurality'of grid wires extending substantially parallel with the cathode and encircling the cathode in predetermined spaced relation therewith, the grid wires being spaced apart a distance which is greater than the grid-to-cathode spacing for producing 5 across the cathode a mu which is relatively high adjacent the grid wires and which blends gradually into relatively low and constant levels betwxen the grid wires, the cathode having deposits of electron emitting material which deposits are positioned only in areas on the cathode where the mu is relatively low and constant.

6. An electron tube having a low amplification factor comprising an envelope containing an anode and a cathode in predetermined spaced relation, and a control electrode having efiective portions positioned between the cathode and anode and spaced apart a distance which is greater than the cathode-to-control electrode spacing References Cited in the file of this patent UNITED STATES PATENTS 2,358,542 Thompson Sept. 19, 1944 2,459,792 Chenigry Jan. 25, 1949 2,485,668 Smyth Oct. 25, 1949