US2450009A - Multiple stage thermionic valve - Google Patents

Description

Sept. 28, 1948. A. J. MADDocK MULTIPLE STAGE THERMIONIC VALVE Filed May 13, 1943.

ode for a succeeding section of the tube.

Patented Sept. 28, 1948 MULTILE STAGE THERMINIC VALVE Alan Lulian li/iaddocli, London, England, assignor to Standard Telephones land Cables Limited, Londen, England, a British company Application May 13, 1943, Serial N0. 486,897 in Great Britain May 22, 194:2

6 Claims.

This invention relates to thermionic valves and tion in valve `apparatus and increase the eiciency thereof.

Accordingly the invention resides in a multistage thermionic valve so constructed that the heat generated at the anode of one stage or section due to losses in that section and which has hitherto been wasted, is utilised to raise the teinperature of said anode tol such a value that it emits electrons and which then acts as the cath- A plurality of sections may be used, the cathode of each section, except the rst, deriving itsenergy for 4raising its temperature to the required degree from the electron stream impinging thereon said cathode constituting the anode of the preceding section. The sections may be arranged to function as succeedingampliiier stages in an amplitying or transmitting system, or as parallel units of an amplifying stage, or as one unit of one amplifying system and one unit of another, or as several stages or combination of stag-es as will be described hereinafter.

An advantage of the multi-stage Valves according to the invention is that the eiiiciency is increased since the power for heating cathodes is materially reduced, the necessaryl power being derived from what would, in a normal singlestage valve construction, be heat wasted from the anode voltage supply or supplies. Furthermore the demands upon and size of the anode cooling system is materially reduced as now only the last section anode will require cooling so that a vgreat saving in initial and upkeep costs canbe effected, especially in large equipments where the cooling system may involve considerable apparatus.

A further advantageiis that whatever direct cathode heating power is needed for the first section or stage ta-kes place at a relatively lo-w magni'tude so that direct heating by alternating current may be carried out, still further raising the eiiciency and reducing cost by eliminating rectiflers or motor generator sets. No eXtra power is drawn from the sources of anode tension since it is the normal losses that are utilised for heating the cathodes.

Yet another advantage is that the number of valves required in an amplifying system is rei duced as also is the number of mountings required for'same.

At short wavelengths a still further advantage is that the succeeding valve sections arein close proximity, thus reducing materially the distance 'f (Cl. Z50-27.5)

between the input and output terminals of the coupling circuits. This is also advantageous at all frequencies in reducing the overall size of the equipment.

.Still another advantage is that the principal cathodes of the valve are of equipotential form and thus potential drop across the cathode is avoided and furthermore more uniform and rolbust types of construction vof the multi-stage valve can be obtained than with the normal type having nlamentary cathode. This also gives the possibility of constructing valves of lower anode impedance and higher mutual conductance.

Various constructions of valves embodying the invention will now be described. Like parts are given the same designations in all the gures.

In the drawings Fig. 1/ shows in schematic form a two section valve constructed according to the invention;

Fig. 2 shows an arrangement in which the cathanode takes the form of a grid;

Fig. 3 is similarto Fig. 2 except that the width of the electrodes constituting the gridV is at right angles to the electron path in the tube; and

Fig. i shows onestructure which is possible in the present invention.

Figure 1 shows, in schematic' form, a two-sec,- tion valve constructed according to the invention the principles of operation may be outlined as follows. Only external sources of power are sho-wn on this diagram, other connections` to circuits such as R. F. or L. F. are omitted.

The valve consists of the two separate sections V1 and V2 in which both sections are represented as tricdes but limitation to such construction is not implied, it being evident that diode, tetrode, pentode or other construction may be adopted for either or both sections. The first section V1 has cathode Crheated by the source of power F1 so that it behaves as va thermionic emitter and electrons are accelerated towards the anode CA1 which is at a positive potential with respect to C1 hy virtue of the anode supply source HT1; control oi the current is effected by the .grid G1 and its associated bias supply B1.

The electron stream from C1 impinging on the :anode CAi raises the temperature of the latter and if CA1 is made of suitable proportions and "dimensions it may be heated to such a tempera ture that electrons are emitted therefrom and it becomes the cathode of the second lsection V2 of the Valve, which section likewise has anode and grid A2 and G2 with associated sources of power H'I'fl` and B2. The heating of cathode CA1 is thus Qbtained lfrom power delivered thereto by the sheet or other perforated construction.

supply HT1 and can thus be heated by a high voltage supply with a small current (the space current across V1 between C1 and CA1) in contradistinction to the low voltage, heavy current utilised heretofore to heat the usual llamentary cathodes of the present types of Valves.

Now it will readily be understood that input and output circuits may be added to each section of the valve, independently of the other and output power be delivered from the respective anodes. Thus, for example, if a certain R. F. voltage is applied to the grid G1 then R. F. power well be delivered into suitable circuits by the Ianode CAi but at the same time the latter will be heated due to the losses which always occur in a thermionic amplifying device and th'e power available for heating will be the difference between the total input to the device from the source I-IT1 and the output power delivered by the Ianode CA1 to the associated output circuit and its load.

In normal valves this power delivered to the anode is expended in raising its temperature and serves no useful purpose but is waste heat and must be carried |away by air or liquid cooling so that a considerable loss of energy occurs, not onli7 in the waste h'eat itself but also in the energy necessary to circulate the cooling medium and, in some cases, to cool this latter and for which purposes elaborate and costly apparatus is necessary.

This invention utilises what would otherwise be j wasteheat and obtains th'e necessary heating of the cathode of the second section of the valve therefrom. This section may then be used as amplier or other stage in the normal manner and power be delivered by the anode A2 to its associated output load. At A2 again, heat will be generated which, if this section forms the last valve of the .amplifying chain, must be got rid of `by the usual means but may, if further stages or sections are required, be utilised to raise the tem i perature of Az so that it may form the cathode of a further section to the valve and so on. Thus the normally wasted power which appears as heat at each anode of a valve is utilised in the present invention to form the heating power necessary for the succeeding cathode. High overall eilciencies can. thus be obtained and a considerable `amount of equipment is rendered redundant which is important from the point of view of cost and maintenance.

For convenience of reference the electrode which' acts as anode for one stage and cathode for the next and is heated by the power losses occurring at the former is herein termed a cathanode or thermionic cathanode to indicate that it is raised to such a temperature that electron emission takes place therefrom.

The cathanode may have a form resembling a grid of spiral wires, strips, tapes, or punched In particular such construction might be employed when the size of anode is such that the area must be reduced in order to attain the desired temperature for its operation as a cathode. Furthermore, limitation to pure metals or alloys for the anodes which also act as cathodes is not implied as the surface which acts as cathode may be coated with electron emitting material such as the alkaline earth oxides, carbonates, etc., in a manner Well known in the art or the material may be such' that an enhanced emission may be obtained due to the presen-ce of some active material in the .body of the metal. e. g. thoriated tungsten may be be similar, e. g, one cathode might be oxide-coated, one thoriated tungsten and another pure tungsten.

Active material aixed to an anode may also be used of which an example is the use 0f a helix of wire for the anode inside which is xed a stick of active material such as barium or strontium silicates, Zirconates, or the like.

Since the anode is at a high temperature, it will also emit electrons into the space wherein its normal function is that of an anode so th'at, if large grid currents or reduction of anode current are to be avoided, the anode potential should not be allowed to swing below that of the nearest electrode to it. An additional grid or grids may be inserted in any of the types described, the function of which is to introduce a low potential element near to the anode so that shielding of th'e control grid takes place and emission cur rent is reduced. This gridor grids may be employed more or less solely for this purpose or may form the additional grids to render the section a tetrode or pentode or other multi-electrode stage and particularly in the latter case will the reverse current be practically suppressed, but at the same time a higher anode voltage swing may be employed without this current becoming appreciable.

Since the second stage derives its cathode temperature from th'e heating of the anode of the rst stage and as it is normally desired that the currents in any stage shall be space charge-limited rather than temperature-limited, it is necessary so to proportion the dimensions of an anode, which acts as a cathode, in relation to the power being dissipated thereat so that its temperature is high' enough to give this condition and also, of course, to give an emission current per unit area of its surface consistent with reasonable life. However, in certain applications, it may be desired that the emission of the cathode be increased at the same time as an increase of current occurs in the rst stage. This is readily arranged since the increased current gives a greater heat dissipation at the anode and hence a high'er temperature for this element acting as the next cathode with resulting enhanced emission for the next stage.

All the sections may be contained in one envelope and the whole be evacuated so that each section functions as a vacuum valve or the whole may be gas or vapour-filled so that each section acts as a gas or vapour-illed valve. Alternatively any element acting as anode and cathode may be used to form a barrier and isolate two spaces one from another so that one may be gas or vapour-filled and the other evacuated. Thus combination of Valve types and functions is available.

In addition to the elements forming the valve sections of the device it may also be desired to introduce circuit components such as inductances, capacitances or resistances, into the envelope to act as coupling elements between one section of the valve and another this being particularly useful at very high frequencies, or to act as decoupling elements or elements to damp out oscillations which might occur in the amplifying system.

The grid form of construction of the cathanode is advantageous in that it not only allows the construction of a valve with given dimensions, the pitch and width of the wires, strips or tapes forming the grid being adjusted to obtain the requisite area, but also provides spaces through attacco :which heat radiation from the inner electrodes- `particularly the grid-,may take place `and thus rhelpto-maintain electrodes which should not emit below a temperature at which any considerableemission takes place. The material forming the main surface of the cathanode in this grid type of construction may be made of wires, strips.

.tapesor of sheet punchedintoparallel strips and .l 5urthermore, that side of the elements which faces towards that section of the valve for which this electrode acts as anode, may be treated to j- `reduce the vemission on thatside since copious emission vfrom an anode is not usually desired, or the elements may be of such material that their natural emission is low but the presence of active coating on the cathode sides gives the requisite emission for the side where emission is desired.

As already mentioned it is of advantage also to allow as free radiation of heat as possible from any grid structures contained within such a cathanode and for this reason the strips of the cathanodes may be formed edgewise or radial to the axis of the valve thus presenting a small radiating surface to the inner grid assemblies and providing wide spaces through which heat 3 radiation can take place. Such a construction is shown in Fig. 2 in which a two section triode is shown with lamentary cathode C1 for the rst section, grid G1 and anode CA1 which latter also acts as the cathode for the second section having grid G2 and anode Az. The cathanode CA1 is formed of strips placed edgewise, i. e. with their longest dimension parallel to the general iield between anode CA1 and cathode C1.

In a preferred construction, howevery the strips or helical grid wires forming the cathanode are arranged across the direction of anode to cathode eld in order to intercept the maximum number of electrons and to assist in this the strips are located opposite the spaces in the grid wires of that section of the valve for which the cathanode acts as anode. This construction is illustrated diagrammatically in section in Fig. 3 in which C1 represents the cathode of the first section, G1 the grid and CA1 the anode-also acting as cathode for the next section. The strips or wires a, forming CA1 are so disposed as to be opposite the spaces in the grid G1 and the field of force between anode and cathode is as designated by F, which also represents the paths the electron streams will follow; the field would be practically the same if CA1 were formed of sheet as the electrons are focussed by the action of the charged grid G1. Thus through the interstices b of the cathanode CA1 practically no electrons will pass and enter the second section of the valve so that this construction gives a device in which no interaction occurs between one section and the other as a result of the electrostatic field: this would be further helped by placing the grid wires G2 of the second section opposite the spaces b as then shielding of the first section from any field from the anode A2 of the second section would take place and furthermore the strips a of the cathanode CA1 are opposite the spaces in the grid wires G2 of the second stage, thus allowing the emission from the elements of CA1 to be utilised to the full. The spaces b provide gaps opposite the grid wires G1 through which heat radiation can take place and thus the grid G1 Amay .be Amaintained .at .a temperature belowthat at Which emission takes place therefrom. Additional reduction can be obtained by treating the grid G1 inknownmanner to reduce its emission yand/or constructing it of such `material that the emission therefrom is small. lAs mentioned before, the `side of .CA1 lnearest to C1 may be similarly .treated .to reduce emission from this hot electrode intothe space ybetween CA1.and C1.

Additional screening between sections .canbe .effected by Ithe interposition of a grid of vwires or strips inr each of the'spaces b as indicated either .at p1, po, or pa in Fig. 3 and such'grid may beat .the same or nearlythe same potential as CA1. It will have the effect of forming a barrier fora few lines of force which might tend to pass from one section to the other but being in a practically `field-.free spacewill not appreciably aiect v the characteristics of either section and will also not become heated to emitting temperature since practically no current passes thereto due to the focussing action of the grid G1.

The construction of one embodiment of a tube according to the invention and having twosections is shown in Fig. 4 in structural form. This is a double-ended construction. The electrodes are shown as of the coaxial cylindrical type, the heater for the first cathode being shown at C1 supplied by the feed line C11. This heater may, of course, operate as the cathode itself. The grid of the first section is shown at G1 and the lead thereto at G11. It may be supported by tie-rod RG1 sealed through the envelope as shown. The anode CA1 of the first section which also functions as the cathode for the second section may comprise the concentrically arranged strips as shown. The lead thereto is CA11, CA1 being supported by tie-rod Resi sealed in as shown. Grid Po is supported in the spaces of CA1 by tie-rod R110 which may be sealed through the envelope and connected by plate P1 to the tie rod of CA1 as shown. The concentric grid of the second section is designated G2 and lead thereto as G22. It is supported by tie-rod RG-i, the grid wires being positioned in line with those of G1. The concentric anode of the second section is designated A2 and, it will be observed, is shown as forming a part of the envelope of the valve.

Fig. 4 is intended to indicate only one of the forms a valve embodying the invention may take and does not constitute any limitation on the design as other designs may be employed to suit conditions and modifications will be clear to those skilled in the art. If the cathanode is of helical grid structure the -Wires -of helical grids G1 and G2 would of course be aligned with corresponding cathanode spaces.

While Fig. 4 illustrates one embodiment in which the nal anode A2 forms part of the outer envelope of the valve and so can be cooled by aditional external means such as a flow of air or liquid, such construction is not the only practicable form. The whole electrode system may also be enclosed inside the envelope.

What is claimed is:

l. A thermionic valve device including a cathode, a cathanode spaced from said cathode and comprising a plurality of spaced cathanode surfaces of discrete dimensions, a rst grid electrode mounted between said cath-anode and said cathode, the conductors of said grid electrode being positioned in line with the apertures between said cathanode surfaces, an anode spaced from said -cathanode surfaces on the side thereof remote from said cathode, and a second grid electrode mounted intermediate said cathanode and said anode.

'2. A thermiom'c valve device in accordance with claim 1 in which the conductors of said second grid electrode are positioned in line With the apertures between said cathanode surfaces.

3. A thermionic valve device in accordance with claim 1 further comprising a. third grid structure positioned in the apertures between said cathanode surfaces.

4. A thermionic valve device in accordance with claim 1 in which 4said rst and second grids, s-aid cathanode, and said anode form substantially -close'd surfaces concentric With said cathode. 5. A thermionic valve device in accordance With claim 1 in which the active surfaces of said cathanode are substantially perpendicular to the electron path in said device.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,419,547 Ehret June 13, 1922 1,655,270 Hull Jan. 3, 1928 1,864,591 Foster June 28, 1932 2,283,639 Kling May 19, 1942 2,348,814 Herriger May 16, 1944

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