US2697796A

US2697796A - Electron tube structure

Info

Publication number: US2697796A
Application number: US38384A
Authority: US
Inventors: William W Eitel; Jack A Mccullough; Harold E Sorg; Clayton E Murdock; Paul D Williams
Original assignee: Eitel Mccullough Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1948-07-13
Filing date: 1948-07-13
Publication date: 1954-12-21
Anticipated expiration: 1971-12-21

Description

DCC- 21, 1954 w. w. EITEI. ET AL ELECTRON TUBE STRUCTURE Filed July 13, 1948 /fAQ//f k M. h C w 0 9 0 T. 5 N N U d Q Edmmdwa O WHMQMHT WEEN .A Adm .mk/www Wm@ vn B i;

United States Patent O ELECTRON TUBE STRUCTURE William W. Eitel, Woodside, Jack A. McCullough, Millbrae, Harold E. Sorg, Redwood City, Clayton E. Murdock, Millbrae, and Paul D. Williams, Palo Alto, Calif., assignors to Eitel-McCullough, Inc., San Bruno, Calif., a corporation of California Application July 13, 1948, Serial No. 38,384

6 Claims. (Cl. 313-247) Our invention relates to further improvements in the electron tube structure disclosed in our copending application, Serial No. 11,916, now Patent No. 2,688,707.

The principal object of our present invention is to provide a tetrode having improved power capabilities in the higher frequency ranges.

Other objects are to provide an improved electrode combination for a tetrode, including an anode, cathode, control grid and screen grid, and to provide an improved terminal arrangement for such electrodes on the tube envelope.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of our invention. It is to be understood that we do not limit ourselves to this disclosure of species of our invention, as we may adopt variant embodiments thereof within the scope of the claims.

Referring to the drawing:

The single figure is a vertical sectional view of a tetrode embodying the improvements of our invention.

In `terms of broad inclusion, our improved electron tube structure comprises an envelope having an anode a1 one end and a cathode terminal coaxial with the anode at the opposite end. A screen grid terminal ring is interposed in the envelope wall intermediate the anode and cathode terminal, and a control grid terminal ring is interposed between the screen grid terminal and the cathode terminal, the screen grid terminal and control grid terminal and cathode terminal all being coaxial. A cylindrical cathode, control grid and screen grid are concentrically mounted in the envelope coaxial with the anode, these electrodes being connected totheir respective terminals. In our preferred tetrode the cathode is of the thoriated tungsten type and is heated by electron bombardment from a filament located within the cathode. The cathode terminal is preferably a tubular member and terminals for the filament are preferably brought out through a stern in the cathode terminal.

In greater detail, and referring to the drawing, our tube structure comprises an evacuated envelope having an external anode 2 at the upper end and a tubular cathode terminal 3 at the lower end. The anode is of metal such as copper and preferably has a cylindrical cup-shaped body 4 and an integral upturned flange 6 terminating in a downturned sealing ring 7. A metal exhaust tubulation S on the anode body is pinched off at tip 9 after evacuating the envelope.

A screen grid terminal ring 10 of metal having an external contact surface 11 is arranged below the anode, and an envelope section 12 of vitreous material such as glass is sealed at its upper end to sealing ring 7 and at its lower end to the screen grid terminal ring 10. A control grid terminal ring 13, having an external contact surface 14 of smaller diameter than surface 11 of the upper ring, is arranged below the screen grid terminal ring 10, a glass envelope section 15 being sealed between the two grid rings. Another glass envelope section 16, preferably of U-shape, is sealed along its outer periphery to the lower edge of control grid terminal ring 13 and along its inner periphery to a sealing flange 17 on the cathode terminal 3.

As shown, the cathode terminal projects downwardly beyond the envelope section 16 to provide ample contact surface for circuit connection, the terminal 3 being preferably of copper. By this cathode and grid terminal ar- ICC rangement there are provided three coaxial terminals of different Contact diameter located below the anode, namely, the screen grid terminal 10 which lies immediately below the anode, then the control grid terminal 13 which is intermediate and has a contact surface smaller than that of the screen grid terminal, and then the cathode terminal 3 which is lowermost and has a contact surfacesmaller than that of the control grid terminal. Such an arrangement of cathode and grid terminals, all coaxial with the anode, provides a terminal arrangement which is particularly well adapted for linear or cavity type high frequency circuits.

A cooler at the upper end of the tube for forced air cooling the anode comprises core 17, say of copper, surrounding the anode body 4 and secured thereto by cadmium solder 18. Radially extending cooling fins 19 on the core are held by retaining sleeves 20, and a cap 21 on the core completes the cooler assembly. The outer sleeve 20 of the cooler provides a convenient terminal connection for the anode, which anode terminal is thus also coaxial with the cathode and grid terminals. It will also be noted that the external contact surface of the `anode terminal is of larger diameter than that of the screen grid terminal. In other words, the contact surfaces of the anode terminal, screen grid terminal, control grid terminal and cathode terminal are of successively smaller diameter. If desired a water jacket may be used for cooling the anode in event a water cooled rather than an air cooled anode is preferred.

Cathode 22, control grid 23 and screen grid 24 are cylindrical electrodes disposed coaxially within the anode body 4. The grids are preferably of cage-type wire construction. Screen grid 24 is supported by a conical metal bracket 25 on a flange 26 secured to the screen grid terminal ring 10, and control grid 23 is similarly supported by a conical metal bracket 27 on a ange 28 secured to the control grid terminal ring 13.

Cathode 22 is of the indirectly heated type, preferably of carburized thoriated tungsten, and may conveniently comprise a cylinder of thoriated tungsten sheet such as that disclosed in the copending application of Paul D. Wililams, Serial No. 4,648, or the type disclosed in the copending application of Harold E. Sorg, Paul D. Williams, and Donald F. Drieschman, Serial No. 38,1l4. The cathode cylinder is arranged coaxially with the cathode terminal 3 and is supported on the latter by a sleeve 29. The supporting sleeve is preferably of tungsten welded to the cathode cylinder and secured to the upper rim of the cathode terminal in a suitable manner, as by a clamping ring 30 held by screws 31.

The means for heating the cathode preferably comprises a filament 32 arranged to heat the cathode cylinder 22 by electron bombardment. A helical filament of tungsten wire is preferably employed and is arranged to project coaxially within the cathode cylinder, a biflar filament being preferred. This filament is supported from a stem 33 within the cathode terminal 3 and having three upwardly projecting

tungsten rods

34, 35 and 36. The center rod 34 extends through the filament and is welded to the upper ends of the filament strands, while the two shorter rods 35 and 36 are welded to the lower ends of the filament strands.

Stem 33 preferably comprises a tubular glass section 37 having a press 38 through which the

rods

34, 35 and 36 are sealed. The lower end or glass section 37 is sealed to a metal sleeve 39 which in turn is secured to a flange 41 on the lower end of the cathode terminal 3. All of the niet-al-to-metal connections are preferably brazed to insure Vacuum tight joints. Flexible extensions 42 on the lead-in rods 35 and 36 are connected to concentric -

terminals

43 and 44 supported by an insulating disk 46 fastened to the end of cathode terminal 3 as by a retaining ring 47. The filament terminal 43 is preferably a pin located centrally of the tubular filament terminal 44, it being noted that these filament terminals are both coaxial with the cathode terminal 3 so that all fit with coaxial line circuitry.

By this arrangement separate terminals are provided for the filament 32 and there is no interference with the cathode circuit because the filament connections are `brought out through the hollow cathode terminal. Suitable airpassages 43 are preferably provided in disk 46 to` permit forced `air circulation in the stem structure. In the operation of our tube a source of current is connected to the

terminals

43 and 44 to heat the iilament to its electrony -emitting temperature, and the cathode cylinder 28 is maintained lat a sutliciently positive potentialwith respect to the filament to eifectl heating of the thoniated tungstenl sheet tothe desired temperature by electron bombardment from the filament. The operating temperature of the cathode cylinder 2S is preferably around. l-650 C. brightness temperature, and the operating temperature of lilament 32 (using unthoriated tungsten wire) is preferably around 1809 C.

InV theI interest of thermal eiciency the ends of the cathode cylinder are confined by suitable heat shielding. This is done by completely closing the upper end of the cylinder withVA atungsten cap. 49 welded to the cylinder wall, andL by providing an apertured tungsten disk 51 welded at the lower end of the cathodecylinder. Disks 52` andy 53 mounted on the center rod 34 adjacent the upper andv lower ends. of the cathode cylinder complete the shielding arrangement. The lower disk 53 cooperates with the aperturedpiece 51 for closure purposes vand the upper. disk A52protects the cap 49vagainst excessive bombardment.` These

disks

52 and 53 are preferably of carbon or graphite to suppress electron emission from their surfaces. Flared skirt 54 projecting from the base of supporting sleeve 29V provides still further shielding. A thermally eiiicient cathode is thus obtained and, what is equally important, uniform heating of the cathode cylinder 2S. along its active length is assured. These are very important consider-ations in. a thoriated tungsten cathode of the character described because of the relatively highy operating temperatures involved. A metal cup 56 securedv to center rod` 34 and iitted over the inner end, of stem. 33 protectsv the glass of the stem against heat andy stray electron bombardment.

We claim:

1. A tetrode comprising `an` envelope having a cylindricalyanode at oneend and a cathode terminal coaxial with the anode at the opposite end, a cathode in the envelope comprising a cylinder. coaxial' with and connectedA to said terminal and projecting into the anode, a control grid andv screen grid inthe envelope coaxial with the cathode cylinder, a terminal ring for the screen gridY interposed in the envelope wall between the anode and cathode terminal, anda terminal ring for the control grid.' interposedv in the envelope wall between the screen grid. terminal and cathode terminal, said control gridterminal having an external Contact surface of smaller diameter than that of the screen grid terminal and said cathode terminal having an external contact surface smaller than that of the control grid terminal.

2. A tetrodecomprising an envelope having an anode at one end and a tubular cathode terminal coaxial with thel anode at the opposite end, a cylindrical cathode in the envelope connected to said terminal and comprising a cylinder including thoria and tungsten, a control grid andV screen grid in the envelope, a terminal ring for the screen grid interposed in the envelope wall between the anode and cathode terminal, a terminal ring for the control grid interposed in the envelope wall between the screen grid terminal and cathode, terminal., a iilament in the cathode for heating said cathode by electron bombardment, and terminals for said tilament. supported on the cathode terminal and coaxial therewith.

3. A tetrode comprising an envelope having a cylindrical external anode at one end and-.a cathode terminal coaxial with the anode at the opposite end, a cathode in theenvelope comprising a cylinder` coaxial with and connected to said'terminal and projecting into the anode,

a control grid and screen grid in the envelope coaxial with the cathode cylinder, a terminal ring forn the screen grid interposed in the envelope wall between the anode and cathode terminal, a terminal ring for the control grid interposed in the envelope wall between the screen grid terminal and cathode terminal, and a terminal on the anode, said anode terminal and screen grid terminal and control grid terminalV and cathode terminal being coaxial and having external contact surfaces of successively smaller: diameter in the Aorder named.

4. A tetrode comprising an envelope having a cylindrical anode at the upper end and a tubular cathode terminal coaxial with the anode at the lower end, said tubular terminal extending into the envelope and having an outer end projecting externally of the envelope to provide a cylindrical Contact surface, a cathode in the envelope projecting into the anode and comprising a cylinder coaxial with and supported on the inner end of said tubular cathode terminal, a control grid and screen grid in the envelope coaxial with the cathodeV cylinder, and terminal rings for said grids interposedin the envelope wall between the anode and cathode terminaland sealed along their upper and lower edges to said envelope to provide cylindrical contact surfaces coaxial withthat of the cathode terminal.

5. A tetrode comprising an envelope having a cylindrical anode at the upper end and aV tubular cathode terminal coaxial with the anode at the lower end, said tubular terminal extending into the envelope and having an outer end projecting externally of the envelope toprovide a cylindricall contact surface, a cathode in the envelope projecting into the anode and comprising a cylinder coaxial with and supported on the inner end of said tubular cathode terminal, a control grid and screen grid in they envelope coaxial withthe cathode cylinder, terminal rings for said grids interposed in the envelope wall between the anode and cathode terminal and sealed along their upper and lower edges to said envelope to provide cylindrical contact surfaces coaxial'with that of the cathode terminal, said cathodercylinder including thoria and tungsten, and a filament in the cathode for heating thev cathode cylinder by electron bombardment.

6. A tetrode comprising an envelope having a cylindrical anode at the upper end and a tubular cathode terminal coaxial with the anode atV the lower end, said tubular terminal extending into the envelope and having an outer end projecting externally of the envelope to provide a cylindrical contact surface, a cathode in the envelope projecting into the anode and comprising a cyl.- inder. coaxial with and supported on theinner end of said tubular cathode terminal, aV control gridand screen grid in the envelope coaxial with the cathode cylinder, terminal rings for said grids interposed in the envelope wall between the anode-and cathode terminal and sealed along, their upper and lower edges to said envelope to provide. cylindrical contact surfaces coaxial with that of the cathode terminal, said cathode cylinder4 including thoria and tungsten, a filament in the cathode for heating the cathode cylinder by electron bombardmen, a stem supported by the tubular cathode terminal, and conductors on the stem supporting saidlament.

References Cited in the file ofthis patent UNTED. STATES PATENTS 1 l l s l