US1889106A - Thermionic tube - Google Patents

Description

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Nov. 29, 1932. H.- w. PARKER THERMIONIC TUBE Filed March 15, 1952 INVENTOR Hem-H MK Parker ATTORNEY Patented Nov. 29, 1932 UNH'lE s'rares 1,889,,ltt

PATENT @FFFCE HENRY W. PARKER, OF TORONTO, ONTARIO, CANADA, ASSIGNOR TO, ROGERS RADIO TUBES, LIMITED, OF TORONTO, ONTARIO, CANADA, A CORPORATION OF ONTARIO,

CANADA rnnnrrronrc TUBE Application filed March 15, 1932. Serial No. 598,911.

My invention pertains to thermionic tubes and relates in particular to thermionic tubes employing screening electrodes.

One of the principal objects of my invention comprises producing a thermionic tube of simplified form having screening electrodes.

A further object comprises producing an eflicient screen grid tube of simplified construction.

A still further object comprises producing a construction for screen grid tubes which, while retaining the same desirable electrical characteristics of such tubes now in use, may be fabricated in mass production more easily and cheaply. v I

I accomplish the above desirable features and others which will be hereinafter pointed out and discussed by extending the metallic member which serves as the supporting medium for the active electron emissive substances of an indirectly heated cathode to form a shield for the terminal of the control grid and to function as a screening electrode for cooperation with an inner screen electrode and outer screen electrode which may be attached to the glass envelope of the tube to achieve fully effective screening.

In the drawing accompanying and forming a part of this specification and in which like reference numerals designate corresponding parts throughout; 7

Fig. 1 is an elevation of my improved tube with a portion of the glass envelope broken away;

Fig; 2 is a partially sectioned view of my improved cathode showing the details of the screening extension thereof.

Referring now particularly to the figures, my improved tube comprises the usual glass envelope 1 cemented in the usual base 27. A stem 26 supports the usual anode 21 by means of standards 22 and 23, one of which, 22, may serve as a terminal therefor. The. cathode 9 of the indirect heated type is provided with the usual heating wire 10, the terminals of which are connected as usual to the proper contact prongson" the bas'e '27. The heating wire 10 is maintained within the cathode cylinder 9 and out of electrical contact therewith by means of the cylinder 12 of refractory insulating material. The metallic cylinder 9 of the cathode, preferably composed of nickel, is extended upward beyond the portion used as shown in'liig. 2 to carry the active electron emissive substances and is provided with a bushing 8 of refractory insulating material having a central aperture therethrough, through which the terminal 6 of the control grid, supported by standards 18 and 19, extends. The terminal 6 of the control grid is electrically connected with the usual terminal cap 5 secured to the top of envelope 1 inthe usual manner. The terminal 6 emerges through an aperture in the wall of the cathode tube 9 and is prevented from contact therewith by means of a glass or ceramic bead 7. Electrical contact between the control grid and terminal 6 is made through standard-19 as shown in Fig. l. The control grid is formed preferably of a helix of wire wound on the supports 18 and 19.

The inner screen grid may be in the form of a metallic mesh but is preferably formed of a helix of wire wound on supports 16 and 17. To the lower extremities of the screen grid supports 16 and 17 there is provided a shouldered metallic ferrule 28 which is attached to supports preferably by spot-welding. The shoulder of the ferrule supports a washer 29 of mica or other refractory insulating material provided with apertures through which the standards 18 and 19 of the conrto-l grid pass and also an aperture through which the cathode 9 passesand serves as a. means for maintaining the relative positions of the control grid, screen grid and cathode. The upper extremities of the standards of the control grid 18 and 19, the cathode 9 and the upper extremities of the screen grid supports 16 and 17 pass through a washer "of mica or other refractory insulating ma terial 15 which serves to maintain the relative positlons of the cathode, control grid and screen grid. The entire assembly of the inner screen grid, control grid and cathode just described is spot-welded tosupports orstandards l3 and 14 held in the press 26. One of these standards, as 14, may serve as the terminal for the inner screen grid.

The outer screen 20 may, of course, be placed inside the envelope 1 adjacent the outer surface of the anode, but preferably consists of a metal such as zinc, sprayed or otherwise applied on the outer surface of the envelope 1 and covering practically the entire outer surface of the envelope exposed above the base except for a portion of the top where sufiicient space is left to provide the necessary insulation resistance between the control grid cap 5 and the metallic coating 20. This metallic coating serves as the outer screen grid usually placed within the envelope 1 and adjacent the anode 20. This outer screen may be, if desired, connected by means of a conductor within the base 27 to the cathode prong which is connected to the cathode cylinder by means of the contact terminal 11, although such connection is not necessary as the coating 20 may be connected to ground in other obvious ways.

In mass production utilizing automatic exhaust machines, it is desirable to provide a slot or opening 25 in the anode 21 and to bridge this slot by a wire conductor 24 in the form of a hair-pin the extremities of which are preferably spot-welded to the anode in the position shown in Fig. 1 to allow the radio frequency currents used in heating up the electrodes of the tube in the exhaust process to quickly as possible penetrate to the inner grids that these elements of the tube may be readily heated to redness during the "exhaust process. The hair-pin conductor 24 acts as the high resistance bridge across the gap in the anode and reduces the heat of the anode sufficiently to allow the grids within the anode to quickly reach the desired temperature without unduly heating the anode.

Screen grid tubes now in use employ invariably an inner screen between the control grid and the anode and an outer screen ad- 1' acent the anode but within the glass envelope of the tube and both of these screens are electrically united with a top screen or cover entirely covering the top of the anode in order that the control grid lead or terminal may be shielded.

I have found by experiment that my improved construction, whereby the control grid 7 lead is shielded through being maintained in an extension of the metallic cathode tube, produces exactly the same degree of shielding as the usual type hereinbefore referred to and at the same time evidences the same desirable low capacitance between the control grid and the anode as that in the usual tube and that, further, the electrical characteristics are in all other respects practically identical,

It will be obvious that as the inner screen grid, control'grid and cathode may be con structed in the form of a sub-assembly and introduced as such in the final assembly in the press by merely spot-welding to the-standards provided therefor in the press, that the construction in mass production is greatly simplified and consequently cheapened.

It will be further obvious that all electrodes in the sub-assembly may be definitely fixed with respect to their relation to each actly the same manner as the top anode 1 screens now used and that my construction thus simplifies the construction of screen grid tubes as now manufactured through the elimination of the upper or top cover screen to which the usual inner and outer screen grids Q are connected. My simplified construction, therefore, while producing a tube which may be more easily and cheaply constructed in mass production performs exactly similar to tubes of the same general type now in use.

Having thus completely described my invention, what I claim as new and desire to secure by Letters Patent of the United States 1s:

1. An electrode assembly for thermionic tubes comprising, a cathode in the form of a metallic cylinder, electron emissive substances on a portion of the exterior thereof, a heating element within said cylinder, a control grid without said cylinder, a terminal for said control grid insulatingly maintained within a portion of said cylinder and means for maintaining the relative positions of said cathode and said control grid.

2. An electrode assembly for thermionic tubescomprising a cathode in the form of a metallic cylinder, electron emissive substances on a portion of the exterior thereof, a heating element within said cylinder, a control grid without said cylinder, a terminal for said control grid insulatingly maintained within a portion of said cylinder and a screen grid and anode operatively associated with said control grid and cathode.

3. An electrode assembly for thermionic tubes comprising, a cathode in the form of a hollow metallic member, electron emissive substances on a portion of the exterior thereof, a heating element within said member adjacent the portion coated with electron emissive substances, a control grid adjacent said member, a terminal for said control grid passing through the wall of said member and insulatingly maintained within a portion of the interior of said member and means for a:

maintaining the relative positions of said cathode and said control grid.

4. An electrode assembly for thermionic tubes comprising, a cathode in the form of a hollow metallic member, electron emissive substances on a portion of the exterior thereof, a heating element within said member, and adjacent the portion coated with electron emissive substances, a control grid adjacent said member, a terminal for said control grid insulatingly maintained Within the interior of a portion of said member and a screen grid and anode operatively associated with said control grid and cathode.

5. A thermionic tube comprising, an enclosing envelope, a press within said envelope, a screen grid supported by said press, a control grid, a cathode comprising a hollow metallic member, a portion of the exterior surface of which is coated with electron emissive substances, a heating element within said member and adjacent said coated portion, an aperture in the wall of said mem-' ber intermediate the extremities thereof and a conductor connected to said control grid and insulatingly maintained in said aperture and extending through a portion of the interior of said member, and an anode adjacent said screen grid and supported in said press.

6. A thermionic tube comprising, an enclosing envelope, a press within said envelope, an anode supported by said press, a screen grid within said anode and supported by said press, a control grid within said screen grid, a cathode comprising a metallic cylinder, a portion of which is coated with electron emissive substances and a heater therefor within said control grid, a connection for said control grid passing insulatingly through the wall of said metallic cylinder and insulatingly extending through a portion of the interior thereof and a contact secured to said envelope and connected to said connection for said control grid.

7 A thermionic tube comprising, an enclosing envelope, a press within said envelope, a screen grid supported by said press, a control grid, a cathode comprising a hollow metallic member, a portion :of the exterior surface of which is coated with electron emissive substances, aheating element within said member and adjacent said coated portion, an aperture in the wall ofsaid member intermediate the extremities thereof, a conductor connected with said control grid and insulatingly maintained within said aperture and extending through a portion of the exterior of said member, an anode adjacent said screen grid and supported by said press and an additional screen grid electrode provided upon the exterior surface of said enclosing envelope for cooperation with said cathode member and said firstmentioned screen grid.

HENRY WPPARKER.

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