US2067607A - Thermionic cathode space current tube - Google Patents

Description

Jan. 12, 1937. w. J. HITCHCOCK THEBMIONIC CATHODE SPACE CURRENT TUBE Filed Oct. 12, 1932 2 Sheets-Sheet l INVENTOR 9. "Mud:

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Jan. 12, 1937 J HlTCHCOcK 2,067,607

THERMIONIC CATHQDE SPACE CURRENT TUBE Filed Oct. 12, 1952 2 Sheets-Sheet 2 @Zz'gafii 5.: 65'

Wil 21 1 4! Patented Jan. 12, 1937 CURRENT TUBE V William I. Hitchcock, Scotia, N. Y.

Application October 12, 1932, Serial No. 637,433

7 Claims. (01. 250-275) The present invention relates to hot cathode space current devices such as thermionic vacuum tubes and the like.

The principle underlying the present invention resides in the design or arrangement of the electrodes with a view to improving the, thermal eiiiciency and certain other operating characteristics, as will appear from a description of one or two practical embodiments of the invention. 1

In all devices in which space currents are maintained by the emission of electrons from a hot cathode heat and light energy are liberated at the anode through condensation of '15 electrons and by the impact of electrons. An

' 25 tant results of this being to make more practical the use of caesiated surfaces or alkaline earth surfaces as hot cathodes. These and other important results, which will be apparent, are obtained by enclosing the anode entirely or 30 substantially entirely by the cathode so that heat and light liberated at the anode by the condensation and impact of electrons may substantially all be supplied by radiation to the surrounding cathode for the maintenance of the proper electron emission temperature, while at the same time enabling the cathode to be constructed of such large area as to greatly improve the emission and minimize sputtering. Such a 40 cathode may have a polished outer surface to reduce radiation, and may furthermore be surrounded by suitable radiation shielding to minimize the loss of heat and light energy through radiation.

45 The principles of the invention are applicable to many different types of hot cathode space current devices, whether high or low vacuum or 9 gas filled, but will be made sufiiciently clear by reference to examples in the form of a ther- 50 mionic rectifier and a screen grid vacuum tube as used in present-day radio circuits.

In the accompanying drawings Figure 1 is a side'elevation of a full wave rectifier tube constructed in accordance with my 55 present invention.

Figure 2 is an enlarged central vertical section thereof.

Figure 3 is a transverse section thereof on the line 3-3 of Figure 2.

Figure 4 is'a circuit diagram showing the electrical connections of the full wave rectifier tube in a standard power supply for radio receivers.

Figure 5 is a side ,elevation of a screen grid vacuum tube constructed in accordance with my present invention.

Figure 6 is an enlarged central vertical section thereof.

Figure 7 is a circuit diagram showing the connection of the screen grid tube in a typical high frequency radio receiver circuit.

Referring to Figures 1 to 4 inclusive, the hot cathode may comprise a sheet metal cylinder III of nickel, tungsten or the like, having end caps or heads ll, [2 at top and bottom, mounted within a radiation screen I3 which has the cover M at the top and the closure at the bottom. The cathode I!) may have a bright outer surface to minimize radiation, and its interior surface may be oxide-coated or caesiated, or otherwise treated for the eflicient emission of electrons. It is electrically and mechanically connected with the radiation screen l3 by the metallic spacing ring I6 at the top. The screen I3 is supported at the bottom by a pair of leadin insulators i1 and I8, of thoria or the like, which are mounted in the glass neck I!) of the bulb 20. Such lead-in insulator tubes l1, l8 pass through suitable perforations in the bottom closure l5 of the screen l3, and are secured thereto by a pair of clamping straps 2|, as clearly shown in Figures 2 and 3. A conductor 22, leading from one of the terminals of the rectifier tube and passing through the sealing neck IQ of the bulb, may be connected with the screen l3 and through it by way of the spacing ring l6, to the cathode I0.

When employing two anodes the space within the cathode i0 is divided into upper and lower chambers by the transverse partition 23, which may be of the same material as the cathode III. A cylindrical anode 24 of tubular metal construction, provided with an upper transverse wall 25, is mounted in the cathode chamber above the partition 23 upon a supporting conductor 26, which is surrounded by a collar 21 of insulation and passes through an insulating bushing 28 which is inserted through registering perforations in the screen 13 and cathode I 0. This conductor 26 passes from the insulating bushing HEB-downwardly through the neck IQ of the bulb to one of the anode terminals of the tube. A similar tubular anode 29 is moimted on a supporting conductor 30 which passes through the insulator tube l8 above-mentioned, the conductor 30 being connected with the second anode terminal of the rectifier tube. A heating resistance 3|, connected at the top to the conductor 30, is coiled around the insulator tube I8 and brought out by conductor 32 through insulator tube I! to be connected with another terminal of the rectifier tube. This heater coil 3| may be employed only in starting, or continuously, for the purpose of indirectly heating the cathode H! by radiation from the anode 29, but will ordinarily not be required after the cathode has been brought up to the emission temperature.

The circuit diagram in Figure-4 shows the heating coil 3| in the form of a filament electrically connected with the anode 29, which latter is within the tubular cathode Ill. The second anode 24 is also shown .as being located within the cylindrical cathode 10. The power supply primary coil 33 feeds a secondary transformer coil comprising the heating winding 34 and the plate supply winding 35, which latter is connected at one end by conductor 26 with the anode 24, and at the other end by way of the conductor 32, previously mentioned, to the anode 29. The cathode has the lead-in conductor 22 connected through choke 36, voltage divider 31, conductor 38, 39 and 40 to the midpoint on the winding 35 of the transformer secondary. The filter circuits are standard practice and require no further description.

The operation of the device will be apparent to those skilled in the art. Power delivered from the primary 33 and secondary 34 will heat the anode 29 which radiates heat to cathode Ill. The conduction of heat through the metal of the cathode will bring all portions of it up to emitting temperature, so that the thermionic or electron current will flow between cathode and the respective anodes 24, 29 as they alternately become positive with respect to the cathode. The impact and condensation of electrons on the anode surface develop heat and light energy which is radiated to the cathode. Since the anode in such case is necessarily at all times hotter than the cathode, it must of course be understood that the cathode employed is one which 1 emits electrons at a temperature well below that at which any substantial emission would occur from the anodes.

The example of a screen grid radio tube, illustrated in Figures 5, 6 and '7, follows in principle the construction already described in connection with the rectifier tube. A glass or pyrex bulb 56 has leading from its neck a supporting conductor 52, which is connected at the bottom with a lead-in wire 53 extending from one of the tube prongs to the radiation screen 54, which has mounted in its top an annular metallic sheet 55 with inner and outer peripheral flanges 56, 51. In the inner peripheral flange 56 is inserted an insulator 58, on which is mounted the flanged cap 59 of the cathode 60. The cathode 60 is of tubular construction, with an out-turned peripheral flange 6| resting upon an in-tumed peripheral flange 62 of the screen 54. By this construction the cathode is electrically connected with the screen 54 and through the latter to the supporting wire 52 and the lead-in 53. A second supporting wire 63 is provided to steady the mounting. The anode or plate electrode in this example is in the form of an axial rod 64 which depends from the insulator 56 at the top,

where the plate lead 65 is connected. Surroundtom of the cathode. The screen grid in thisinstance serves as the preliminary heater, and for this purpose it is connected at one end with the lead-in wire 10, which passes through the neck 5| of the bulb. The two sections of the helix may be, for example, electrically connected at the top by the metallic disk 61, above-mentioned. The other end of the screen grid is connected electrically with the metallic disk 68 at the bottom of the cathode, which latter has electrically connected with it the lead wire II. The leads 10, ll thus constitute the terminals of the preliminary heater circuit, and at the same time the connection through which the operating potential is applied to the screen grid in the receiver circuit. They are accordingly connected to the proper prongs in the base of the -tube. Surrounding the. screen grid 66 is the normal or control grid which is in the form of a helix 12, mounted between conductive supporting wires 13, 14 which pass through the insulation plug 69 at the bottom of the cathode. The supporting wire 14 is mounted in the neck 5| of the bulb. The supporting wire .13 has electrically connected with it the lead 15, which passes through the neck 5'! and is connected with the proper prong of the tube base.

The plate lead 65, above-mentioned, is shown in Figure 5 as being connected with the usual contact post 16 mounted in the top of the bulb.

By reference to Figure 7, the electrical connection of the various parts in the receiving circuit will be apparent. The terminals 10, H of the screen grid are connected across a secondary winding 11 of a heating transformer, the primary 18 of which may be switched in at the time of heating up the tube. The heating of the screen grid bringsthe cathode up to the proper emission temperature, which may thereafter be maintained by the radiationof heat from the anode, as already explained. The cathode 60 is repre-- sented diagrammatically in Figure 7 in the form of the usual filament, the screen grid being indicated at 66, the anode at 64, and. the control grid at 12. A screen grid lead wire 19 leads from a suitable tap on thepower source 80 to a midpoint 8| on the secondary winding 11. The anode lead 65 passes through plate inductance 66 to the high tension lead 82 of the power source, the cathode lead 53 connects at a suitable voltage point with the power source 89, and the control grid lead 15 connects in this instance through a grid resistance 83 and conductor 84 with the negative side of the power source 80.

Insofar as the enclosure of the anode within the cathode is connected, the advantages already pointed out in connection with the rectifier tube pertain also to the screen grid tube. There are in addition important advantages present in the screen grid tube. The electrostatic capacity between the plate and the control grid of the tube is reduced by the small area of the plate or anode. The mutual conductance of the tube is considerably improved by the relatively large emitting surface of the cathode. Caesiated or other cathode surfaces which emit at relatively low temperatures are advantageous in the oathode in the present instance, even though the 01' devices in which the operation depends upon cathode" always remains negative with respect to the anode or plate electrode. 7

The examples given are not to be taken as limitingthe scopeof the invention to the em.- pioyment o! itsprinciples in these particular types. of space current devices, since the functions pertaining to the. inventionare applicable quite generally to many diderent specific forms the application of heat to a cathode for the purpose of causing the. emission of electrons.

The anode and .cathode may each be in the form of either. a single element or a plurality of elements; that is to. say, there may be one single anode or two or more anodes, and one single cathode or two or more cathodes. In any case, however, the entire electron current from the cathode system isdirected inwardly to the anode system, in the normal operation of the tube, and the. heat developed at the anode is largely conserved and delivered by radiation and conduction outwardlyto the surrounding cathode system.

I claim: I

l. A rectifier tube comprising a cathode having a thermionic surface extending around its own emission space and provided-with an intermediate partition extending transversely across the enclosed emission space, and an anode in each of the emission spaces separated by said partition.

2. A thermionic tube comprising a substantially closed cathode having an inner surface electron emitting when heated, and an anode and a heater both disposed within said cathode, whereby said cathode may be heated to electron emitting temperature by radiation from within said cathode.

3. A thermionic tube comprising a substantially closed cathode having an inner surface electron emitting when heated, a plurality of spaced anodes disposed within said cathode, an intermediate partition extending transversely across said cathode and between said anodes to separate the latter, and a heater enclosed with an anode within said cathode, whereby said cathode may be heated to electron emitting. temperature by radiation from within said cathode,

initially from said heater and subsequently by heat radiated from said anodes during the operation of the tube.

- 4. A thermionic tube comprising a tubular sheet metal thermionic cathode closed at its ends and having an inner surface electron emitting when heated, an anode and a heater both disposed within said cathode, and a radiation screen completely enclosing said cathode, whereby said cathode may be heated to electron emitting temperature by radiation and conduction. from within said'cathode, initially from said heater and subsequently by heat radiated and conducted from said anode during the operation of the tube.

5. A thermionic tube comprising a tubular sheet metal thermioniocathode closed at its ends and having an inner surface electron emitting when heated, an anode and a heater both disposed within said cathode whereby said cathode may be heated to electron emitting temperature by radiation and conduction from within said cathode initially fromv said heater and subsequently by heat radiated and conducted from said anode during the normal operation of the the tube, and a'grid electrode disposed between I said cathode and anode and enclosed within said cathode.

7. A screen grid thermionic tube comprising a tubular thermionic cathode closed at its ends'and having an inner surface electron emitting when heated, a. control grid, a filamentary screen grid and an anode, all disposed within said cathode, whereby said cathode may be heated entirely from within to electron emitting temperature by radiation 'from said screen grid serving as a filamentary heating element when the tube is started, and subsequently by heat radiated from said anode and screen grid during the normal operation of the tube.

WILLIAM J. HITCHCOCK.

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