Патент USA US2122772код для вставки
July 5, 193s. 2,122,772 E. GREEN THERMIONIC AMPLIFIERFiled Oct. 29, 1932 2 Sheets-Sheet l #F294 à m œ BY ' EMME > l r ' M014, ATTORNEY July 5, 1938. v E_ GREEN ' 2,122,772 THERMIONIC AMPLIFIER Y Filed Oct. 29, 1952 2 Sheets-Sheet 2 l _@ l 4 6,’ 1/ / l? ‘?’ Ö l/ f; c; z l v‘ ‘L :i l, :L l/ y is ”2 à@ E; ’i . +?fï INVENTOR ‘ ERNEST G BY /fë ' l ATTORNEY 0,7 Patented July 5, 1938 2,122,772 UNITED STATES PATENT OFFIQE 2,122,772 THERMONIC' AMPLIFIER Ernest Green, Chelmsford, England, assigner to Radio Corporation of America, a, corporation of Delaware Application October 29, 1932, Serial No. 640,280 In Great Britain October 29, 1931 3'v Claims. (Cl. 179-171) This invention relates to thermionic amplifiers and more particularly to thermionic amplifiers of what may be termed the multi-tube or multi-valve per stage type i. e. amplifiers wherein a plurality 5 of tubes are provided in a single stage of ampli flcation. In thermionic ampliiiers embodying a plurality of tubes in a single stage of amplification, and as at present in common use, difficulty is often eX perienced in practice, owing to the fact that the individual tubes will not share the alternating current load equally unless their electrical char acteristics are identical. For example, where a single stage of ampliiication comprises a plu 15 rality of triodes in parallel, if theseparate tubes are of slightly different internal characteristics they will not ordinarily share the alternating cur rent load equally with one another. For this reason it is usual to require that tubes which are 20 intended to work together in a single multi tube stage, shall be “matched”, but this is always a more or less expensive requirement, and where large tubes are in question the additional ex penditure may be prohibitive. Similar requirements as regards “matching” 25 for alternating current load apply not only to par allel tube circuits but also to so-called push pull circuits as ordinarily employed. It is, of course, also desirable in most cases to “match” as regards the direct current compo 3 O nents of anode or plate current, but this presents no difliculties, and may be accomplished quite simply by the usual method of providing where necessary, different values of grid bias for the different tubes e. g. by providing grid bias bat 35 teries of diiferent Values for the different tubes or, where automatic grid bias is in question, by arranging the tube grid circuits to receive dif ferent values of potential from a grid biasing ceding stage of amplification or other source of Voltage to be amplified that the input alternat ing current voltage applied to different tubes is different and is in each case suited or adjusted to the characteristics of the tube in question, so that the said tube will take its correct proportion of the total alternating current load. The invention is illustrated in and explained in connection with the accompanying drawings which show diagrammatically various arrange 10 ments in accordance therewith. Fig. l is a circuit diagram of a parallel con nected resistance coupled ampliiier; Fig. 2 is a diagram of a theoretical circuit of the input voltages; 15 Fig. 3 is a circuit diagram which is a modiñ cation of Fig. l; Fig. 4 is a circuit diagram of a transformer coupled ampliiier; Fig. 5 is a circuit diagram of a push-pull ampli 20 lier; Fig. 5 is a circuit diagram of another modifi cation of the circuit arrangement shown in Fig. 3. Referring now to Figure l which shows one way of carrying out the invention, a parallel anode connected resistance-capactiy coupled thermionic ampliñer comprises an input impedance consist ing of the usual resistance M one end of which is connected at GB- to the negative terminal of a suitable grid bias source (not shown) and the 30 other end of which is connected through the usual coupling capacity C1 to a preceding stage or other source of voltage to be ampliñed. The parallel stage now described consists of three triodes V1 V2 V3 in parallel (though of course there may be any other number of tubes) the anodes of the triodes being connected together and through an anode resistance R to the posi tive terminal of a source of anode potential (not vide an improved arrangement whereby the ne shown) the junction point of the anode resistance 40 R and the anodes being also connected through the customary coupling condenser C2 to the next cessity for accurately “matching” thermionic stage. 40 resistance or its equivalent. The present invention has for its object to pro tubes in a multi-tube amplifier stage is avoided. The invention is applicable alike to parallel tube 45 The three grids of the tubes are eifectively con nected each to a different tapping point T1 T2 or T3 on the input resistance M the leads to the grids a degree of balance of such accuracy as to render of the tubes Vi, V2, containing each a supple mentary bias battery b1 or b2 to maintain equal direct current anode feeds to the three tubes. circuits and push-pull tube circuits and provides the said invention applicable to circuits of large power. This applicability to circuits of large 50 power is very important for it will be appreciated that, for example, in the case of tubes in parallel, it is possible if any substantial disparity be tween tubes exists, for the individual alternat ing current loads of the tubes to Vary so much so that in some circumstances the load on some of the tubes may even be negative, i. e. some of the tubes may “drive” the others. According to this invention, the input elec trodes of a plurality of tubes arranged in a com 60 mon amplifying stage are so connected to a pre The cathodes are connected together and to thei ‘ negative terminal of the anode potential source in the usual way. The above described circuit is, from the point of view of the present invention, the electrical equivalent of the theoretical circuit shown in Figure 2 which theoretical circuit consists of a plurality of parallel paths each path consisting of an alternator, and a resistance in series, the three parallel paths being in parallel across a common load resistance R. The voltage of the 60 2 2,122,772 alternator in each branch of the equivalent cir cuit is, as indicated in Figure 2, the product of the alternating input voltage eg1 or e‘gz or egg to the appropriate tube multiplied by the amplifica tion factor 1u, ,uz or ¿la of that tube. The resistances in series with the equivalent vand the output from the stage is taken off as in the usual way through an output transformer OT whose primary is connected between the common anode point and the high tension source (not shown). In a still further circuit modification shown in alternators are the internal resistances of the ' Figure 5' in which the invention is applied to a tubes in question and are represented by R1, R2, by R. In carrying out the present invention the input four tube amplifier consisting of two tubes V1”’, Vz'”, and V3”’, V4”’ in parallel and two (V1”’ Va’" and V2”' V4"’) in push pull each grid is coupled through its own coupling condenser Cl'", tapping points are so chosen that the terminal voltages across all the alternator-resistance secondary TS of an input transformer the “push” R3. 10 The common load resistance is represented branches in the equivalent circuit are equal when the load is shared equally. This condition is ob viously satisfied when the proper bias battery values are chosen and the direct current through the tube equalized a condition for obtaining equal alternating current through the tubes will then 20 be where . etc. or expressed in general terms for the case Where there are n tubes . tubes being connected to different tapping points upon one side of the electrical centre EC of the transformer secondary and the two “pull” tubes being connected to points upon the other side of the electrical centre. Each grid is also directly connected to its o-Wn grid resistance R91 Rg‘z Rgs or R94 the other end of which is connected to a 20 suitable point upon a common bias battery B” the cathodes of the four tubes being connected together and to the electrical centre of the trans former secondary. The output circuit of the stage consists of a centre tapped output trans 25 former OT’ arranged as in the usual way. Figure 6 of the accompanying drawings shows 30 The above condition is the condition for ac curate adjustment. Clearly however, when the value of R is very much greater than a tube re sistance divided by the number of tubes suñicient accuracy will be obtained by making _eene Cz'", 03”’ or 04"’ to a different tapping upon the ` a still further circuit arrangement in accordance with this invention, this circuit being a modifica tion of the arrangement shown in Figure 3. In Figure 6, V1’ V2’ V3’ are three tubes connected in parallel, each tube having a separate grid re sistance R91 R92 or Roa the ends of these resist ances remote from the respective grids being connected to tapping points upon a common bias 35 battery B.. Input to the grids of the tubes V1' V2’ V3’ is taken through coupling condensers C1’ . . etC. Figure 3 shows a circuit of a modification 40 which is suitable for use as the main modulator stage of a choke controlled modulated carrier wave circuit having input modulating potentials which are applied across three condenser cir cuits. The condensers are connected at the side of the preceding stage in parallel, each con denser circuit consisting of a condenser C1', Y C2’ or C3’ connected on the grid side in series with a resistance Rc1-Roz or Rga the other end 50 of which is connected to a point on a common grid bias battery B. The modulator stage con sists of a plurality of tubes V1’ V2’ V3’ hav ing their anodes connected in parallel, each grid is connected to a tapping point T1’ T2’ or T3’ 55 upon the appropriate resistance there being, of course, as many parallel input condenser circuits as there are tubes. The anodes of the tubes are connected together and through a choke L to the positive terminal of the anode potential 60 source (not shown) the high frequency stage HFS to be modulated being connected as in the usual way between the common anode point and the common cathode point of the modulator stage. The invention is also applicable to transformer C2’ C3' from tapping points T1’ T2’ T3’ upon an anode resistance AR connected in the plate cir cuit of a preceding tube PV. 40 The invention is obviously applicable to stages consisting of any desired member of tubes in par allel or in push-pull or any combination of par allel and push-pull. Having now particularly described and ascer tained the nature of my said invention and in what manner the same is to be performed I de clare that what I claim is: 1. An amplifying system comprising a plurality of tubes, each having an anode, a cathode and a grid, means connecting the anodes’of the tubes directly in parallel, means connecting together the cathodes of said tubes, an alternating cur rent output circuit connected between the par allelly connected anodes and said cathodes, an alternating current input circuit, means con necting the cathodes of said tubes to said input circuit, means connecting the grids of said tubes to points of different alternating current po tential in said input circuit, and means for sub 60 jecting each grid to a different direct current po tential with respect to its associated cathode. 2. An amplifying system as described in claim 1 characterized by the fact that the grids are connected to the input circuit by way of a plu coupled amplifiers and in one such circuit ar~ rality of direct current blocking condensers. rangement shown in Figure 4, the grid of each tube V1", V2”, Vs” of a parallel connected stage is connected through a coupling condenser C1', 3. An amplifying system as described in claim 1 characterized by the fact that the input circuit comprises a transformer, and also by the fact that the grids are connected to the secondary of said transformer by way of a plurality of direct current blocking condensers. 70 C2', C3’ to a different point on the tapped sec ondary TS of an input transformer. The grid side of each coupling condenser is connected througha separate resistance R1”,»R2”, R3" to a suitable point on a common bias battery B' ERNEST GREEN.