US2872610A - Thermionic tubes - Google Patents

Description

W. H. HUNTER THERMIONIC TUBES Filed Sept. 30, 1954 Feb. 3, 1959 lNl ENTOR WINDSOR H. HUN TEI? THERMIONIC TUBES Windsor H. Hunter, Anbumdale, Mass., asslgnor to Raytheon Manufacturing Company, Waltham, Mass., a corporation of Delaware Application September 30, 1954, Serial No. 459,359

1 Claim. (Cl. 313-260) This invention relates to thermionic tubes and more specifically to such tubes constructed so as to resist vibration and reduce the microphonics in their output.

Therrnionic tubes, when subjected to vibrations as in aircraft, produce a type of noise called microphonics due to movement of tube elements with respect to each other. The movement of a grid, particularly the control grid with reference to the other tube electrodes, particularly the cathode, is most likely to cause such microphonic noise as it is well known that the distance between the grid and cathode is an important factor in determining the characteristics of the tube, particularly its transconductance. The problem is to provide stiffening for a grid without affecting the operation of the tube adversely and in as inexpensive a way as possible.

In the present invention this is accomplished by mounting stakes in both the upper and lower mica spacers on either side of the grid supports and welding a metal strip between each stake and its associated grid support. A strip of metal is also attached to the outside of each grid support. Great improvement in the operation of tubes constructed in this way is obtained over tubes of the same type not having this construction. This improvement is obtained with only a small increase in the cost of production.

Other and further advantages, objects, and features of the invention will be better understood from the following description taken in conjunction with the accompanying drawing, wherein:

Fig. 1 is an enlarged longitudinal sectional view partly broken away of a tube made according to the invention;

Fig. 2 is a further enlargement of a portion of the tube shown in Fig. 1; and

Fig. 3 is a section taken along the line 3-3 of Fig. 2.

In the drawing the reference numeral designates the envelope of the tube sealed with a button type seal 11. Although a button type seal is shown it is to be understood that the invention may be used with any type of seal. An indirectly heated cathode 12 is inserted in openings in two spacers 13 and 14 which are usually made of mica. The cathode 12 is connected through a conductor 15 that passes through the seal 11 to the external circuit. A heater (not shown) is mounted within the cathode 12 and connected to the external circuit through conductor 16. An anode 17 is mounted about the cathode 12 between the spacers 13 and 14 on two supports 18 and 20. A grid 21 is formed with a wire 22 wound about two support rods 23 and 24. The wire 22 is swaged into notches formed in the support rods 23 and 24. Four stakes 25, 26, 27, and 28 are mounted one near each end of the grid support rods 23 and 24. Two of these stakes 27 and 28 are mounted in the spacer 14 from below and two such stakes 25 and 26 are mounted in the upper spacer 13 from above. A short metal strap 30 is welded or otherwise attached to the support rod 23 and the stake 25. A second such strap 31 is welded to the support rod 24 and to the stake 26. A similar short metal strap 32 is welded to the support rod 23 and the stake 27 which also acts as the connector to the outside circuit through the seal 11. A similar short strap 33 is welded to the support rod 24 and the stake 28 which also acts as the connector to the outside circuit through the seal 11. The bottom stakes need not necessarily form a part of the electrical circuit; they may be used solely as additional mechanical support as are the top stakes 25 and 26 as shown in Figs. 1 and 2. The added stakes 25, 26, 27, and 28 and the connecting straps 30, 31, 32, and 33 serve to give additional support to the grid 21 in the plane of thesupport rods 23 and 24. In addition a metallic ribbon 34 or 35 is attached to each of the support rods 23 and 24 on their outer surfaces. These ribbons 34 and 35 are shown as being formed with an inward curve. This inward curve is desirable but not necessary. These ribbons serve to reduce the movement of the grid 21 from one side to the other of the original plane of the support rods 23 and 24. The mount structure of the tube is completed by a getter 36 of any of the well-known types supported on and electrically connected to the anode 17.

The structure resulting from this construction resists distortion due to vibration because the addition of the ribbons to the support rods increases the resonant frequency of the rods by increasing the stiffness to mass ratio and so greatly reduces the production of microphonics in the output of a tube made in this way. In a representative tube type the construction of this invention reduced the microphonic output under white noise vibration by a factor of 56 and the microphonic output with 40 cycles per second vibration at an intensity of 15 Gs was reduced by a factor of 44. This considerable improvement was obtained at a small additional production cost.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurates with the scope of the invention within the art,

What is claimed is:

Support means for a grid in a thermionic device comprising a pair of rods, a pair of dielectric spacers into which the rods are inserted and a strip of metal attached to the outside of each rod between the spacers and extending to either side beyond the rod.

References Cited in the file of this patent UNITED STATES PATENTS Walsh Apr. 17, 1951

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