US2010253A - Amplifier - Google Patents

Description

L.. E. BARTON Aug. 6, 1935. l v

AMPLIFIER Filed Dec. 29., 1933 vGoflr/a'oL e/D vous: o

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f-Mysinyent ,n.relatesf to amplifiers and particu: larlv to amplifiers, such-,ias athosegofr. the ,-ftriggerlj type, adaptedrgto control ,electricalfdeyicea l .1 @Atv the presenti-timer; e1eetricgdischarseltube am,- fame-- chemicalllelays.`A @In the@ iftriggerf typeaofiampliner. fithegoutpu of; the jfamplierlf' suddenly changesV to, acertain` aluefinfresponse vt a prei determined change; .invvoltage :applied 'to the.; amt-i; pliferinput circuit. Triegerfiamplifiers:arefes: peoiallw tuseulwinfcircuits:requiring:,anonfand oir relayiaetienrsueh-:as zloavelmroiindisupioression circuits in radio receivers, and` Ytheliirreplaemg much moref sensitive and. eliabl than` rnef :hanicah:re-.-

proved :i LA further .,obieotiofnmy"invention-i a improvoed.ramplifier-ofthe,ftrggertY me becmanufaoturedyatiaflow costa i `Aetill further;object;ofmyiinventionust 1p vde anivimprovedftriegeramplerfwhich may be Controlled by changes inalternatine. current f; the. `prefer embodiment ggorniyginvention; llutilize. en eleotliopdisohareetubeofthenentode type in combination witharectiner. circuit s oconneotedV :that it leoneses @the i :eontrolrfgridf offV the pentodet-to beoomeibiesedmoreneeativelyaasthe alternetingfieurrent output-o helpento e inereeses. i4 n i n 1r,

`Tlhe.pentodo is i perated With-1a ylow.. Qltaeeepplied to its \,anede 5 whereby, the l 1v gain: of v the pentodeincreasesas the anode; oltage` increases. The oheneeein aaode,f,vo1tageisobteinediabyyinserting a resistorinthe,anode;` circuitso that a largefplate lenfreint invthe. pentodei eausesa llarge voltage drop across the resistor and a correspondto. rovde typewhleh the-pent de cooed i With the outputeireuit. Y to the reotier. Circuiti-e predetermined voltage. applied to the pentodes ieontrol grid-causes ,the control grid to. become more-negative whereby; the plate currentpdecreases andyahigher voltage is applied tothe anode ofythefpentode.` vIYhiS; in: creases the gain of the pentode, the control grid becomes still more negative,pand;the 1:gainlfis further increased until` the` decrease in r gain4 caused by the negative biason then-,controlfgridequals the increase in :gain 1 `caused fby; the t increase in v oltagegappliedtothe anode v Other objects,v `featuresfand advantages ofglmy invention will appearl fro-m the -Afoliowingi` description taken infconnecton withkthe` accompanying drawing in which, f

a y y N. J., assignm-- droJ Qorpprationfo America,v al orporation t Delawar t New York,` N.

ateristis of and A#the secondarywindngs "are f tned i tol that frequency f by lneansbffcondensers 'f 43 and 4 5 Q respectively] S4 jl',` j "j .i yif henan alternating voltage ise impressed upon the Iamplinerf l'inputl fcr'cu-it, f' it is amplified inthe pentode section v9Vandthe"anfiplied*output; of `this Isection isltransferred through theftransformer 35 :and: impressed? upon the-*elements A5' and" 1 of fthe? diode 'lrectif-ieri The; amplied energyisimpressedupon Asaid rectifier elements through afco'nductor V4.1 which connectstheldiode plate 15Jtoone-.eterminal of thefsecondary windiing 4|, and throughvaiconhection'fffrom-the cathode v'l 'tov the othex=.=termina1 Aof the'isecondary 41,*1whi'ch connection may Abe tracedf'froni the cathode 1 through iaself` .biasing vresist'or'fd 1' to ground,` through ground to 'the llower :terminali of a resistorl5I`fv(whch may have a `resistance off the orderfof one megohm) and through thev resistor 5 If' to the said 'other terminal fof the secondary.` 4L

The sole function of the diode rectifier 3 is to increase the negative bias on the control grid I3 of the pentode section when -energy is impressed upon the amplier input circuit. Since a flow of current through the diode rectifier causes the upper end of the resistor 5I to become negative, the control grid I3 also becomes more negative because of its connection to the negative end of the resistor 5I through a high impedance resistor 53.

The self biasing resistor 49, the resistor 5I and the plate resistor 31 are preferably shunted by condensers 55, 51 and 59, respectively, for bypassing alternating current having the frequency of the input voltage.

It will be apparent from the foregoing description that as soon as an alternating control voltage is impressed upon the input circuit of the pentode 9, the control grid I3 of thel amplifier becomes more negative because of the current ow through the circuit of the diode.

It should be noted that the change in bias on the control grid I3 depends, to a certain extent, 1

upon the voltage drop produced in the selfbiasing resistor 49, since this voltage drop is in series with the voltage drop along the resistor' 5I of the diode circuit. That these voltage drops are in series will be made evident by tracing the direct current path of the pentode section input circuit. It may be traced from the control grid I3 through the secondary winding 25, the high impedance resistor 53, through the diode circuit resistor 5I to ground, through ground to the self-biasing resistor 49, and through the selfbiasing resistor 49 to cathode 1.

When there is no alternating voltage being impressed upon the amplifier input circuit, the plate current of the pentode 9 is large, since the only negative bias on the control grid I3 is that due to the self-biasing resistor 49, and this negative bias is comparatively small. Consequently, there is a large voltage drop in the plate resistor 31, whereby 'the upper end of resistor 31 is at a comparatively low positive potential with respect to ground. This potential may be supplied through an output circuit 6I to a circuit or device (not shown) to be controlled by the alternating voltage input. At the same time, the gain of the pentode 9 is low because of the low voltage on its anode I9.

As soon as an alternating voltage is impressed upon the input circuit, the amplifier 9 supplies signal energy to the diode 3, the voltage drop in the diode circuit resistor 5I increases the negative bias on the control grid I 3, wherebythe plate current of amplifier 9 decreases and the upper end of the plate resistor 31 becomes more positive with respect to ground. Thus a higher voltage is applied to the output circuit 6I It will be apparent that, at the same time, a higher voltage is applied to the anode I9 of the pentode.

It should be noted that although the decrease in plate current tends to cause a reduction in the biasing voltage drop across the self-biasing resistor 49, the increased negative bias provided by the current iiow through the diode circuit resistor 5I is much greater than any decrease in bias due to reduction in plate current.

The above described action of the diode-pentode circuit whereby the upper end of plate resistor 31 becomes less negative in response to a. voltage impressed upon the input circuit is preferably made a trigger action by giving plate resistor 31 a proper resistance value. This trigger action depends upon the fact that the increase in gain caused by the increase in the plate voltage is greater than the decrease in gain caused by the increase in negative bias on the grid. In practice, a tube of the type known as RCA 2B? has been found satisfactory for use as the tube I.

Figure 2 shows a family of plate curves for a particular vacuum tube having the characteristics which are preferred in practicing my invention. The operation of my amplifier will be better understood by referring to the load lines Ri and Rz drawn through the plate curves, the load line Rr being for a plate load of 25,000 ohms and the load line R2 being for a plate load of 50,000 ohms. For the purpose of explanation, it will be assumed that the plate load is equal to the resistance value oi' the plate resistor 31.

Under the condition of no input voltage to the amplifier, there is only a small negative bias on the control grid I3 and the plate current is correspondingly high, whereby the voltage drop in resistor 31 is so great that the pentode 9 is operating at a very low plate voltage. At this low plate voltage the amplification of the pentode is comparatively low, as will be seen by referring to the intersection of the load line R1 with the plate curve for a bias voltage of minus one volt. It will be apparent that, if the voltage impressed upon the input circuit swings the grid one volt each side of the bias potential, that is, between zero volts and minus 2 volts, there is a compartively small change in the plate voltage, as indicated by the spacing between vertical lines 63, 65 and 61.

As previously explained, the input voltage causes the negative bias of the grid I3 to increase. Assuming the input voltage has increased the bias to minus 3 volts. it will be seen, by referring to' the spacing between vertical lines 61, 69 and 1I,

that a grid swing of one 'volt each side of the bias voltage causes a greater change in plate voltage than was caused by the same grid swing at the lower bias potential. A further increase in negative bias on the control grid I3 causes the tube amplification to increase still further and the output voltage may increase very rapidly (depending upon time constants of the circuits of condensers 59 and 29) up to a certain point. The curves show that as the bias increases to some value beyond the region minus of -5 volts, the change in plate voltage for a given grid swing begins to decrease, that is, the amplification of the'lpentode 9 begins to decrease. In other words, at this point the increase in amplication due to the increase Vin plate voltage becomes less than the decrease in amplification due to -the increase in negative bias on the control grid, and the amplifier has reached a stable condition where the output voltage is a maximum.

The operation of the amplier along the load line R2 is the same as described above except that for the higher load resistance a greater voltage input is required to trigger oi the amplifier. This is because a given input will cause a smaller change in plate voltage than in the case where a smaller load resistance is used, as will be apparent from the curves. I

It will be understood that in place of the double tube shown in Figure 1, separate pentode and diode tubes may be employed.

Various other modifications may be made in my invention without departing from the spirit and scope thereof and I desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and set forth in the appended claims.

--I climfasfmYmVm-OD? I'rrc bihaitionfanelectric discharge device av g` an 1n `t ircuitandan output circuit,

, .device,havingfaplurality of electrodes including a control gfridlandan anode and having the characteristic that at low anode voltages its gama-increases with increase of anode voltage. means for applying a negative bias to said control grid means for increasing saidv negative bias in response to an increase in alternating voltage applied to said input circuit, and a resistor in said output circuit in series with said anode whereby the anode voltage increases as said control grid becomes more negative.

2. In combination, an electric discharge device having an input circuit and an output circuit, said device having a plurality7 of electrodes including a control grid and an anode and having the characteristic that. over a certain voltage range, the gain of said device increases with increase in voltage applied to said anode, a resistor in series with said anode, and means for making said control grid more negative in response y to an increase in alternating voltage applied toincrease in gain caused by the resulting incrase in anode voltage.

3. In combination, an electric discharge device having an input circuit and an output circuit, said device having a plurality of electrodes including a control electrode and an anode and having the characteristic that, over a certain voltage range, the gain of said device increases with increase in voltage applied to said anode, a rectifier having an input circuit and an output circuit, said rectier input circuit being coupled to said rst output circuit, said rectier output circuit being so coupled to said first input circuit that said control electrode becomes more negative in response to an increase in the alternating current output of said discharge device, a resistor in series with said anode, and means for coupling a work circuit to said resistor.

4. Apparatus according to claim 3 characterized in that said discharge device has the further characteristic that over said certain range the decrease in gain caused by said control electrode becoming more negative is less than the increase in gain caused by the resulting increase in anode voltage.

5. A trigger amplifier comprising a vacuum tube of the suppressor grid type. Said tube having a plurality of electrodes including a control grid and an anode. said tube having an input and an output circuit, a. rectifier, means including said rectifier for giving said control grid a negative bias which increases in response to an increase in alternating current output appearing in said output circuit, and means in the anode circuit of said tube for increasing the voltage applied to said anode in response to a reduction in the plate current of said tube.

6. An amplifier according to claim 5 characterized in that the voltage applied to said anode has a value such that an increase in said voltage causerJ an increase in the gain of said tube.

7. In combination, an electric discharge device having a plurality of electrodes including a pair of principal electrodes and a third electrode, means for .producing a direct current flow between said principal electrodes, means for applying a biasing potential to said third electrode in accordance with a ow of alternating current between said principal electrodes whereby said direct current flow is varied, and means for controlling the voltage across said principal electrodes in accordance with said direct current iiow. said electric discharge device having the characteristic that its gain increases with increase of voltage across its 4principal electrodes.

8. In combination, an electric discharge device of the pentode type having a pair of principal electrodes, a control grid, and two auxiliary grids, means for producing a unidirectional current now between said principal electrodes, an input circuit connected to said control grid and one of said principal electrodes whereby an alternating voltage impressed upon said input circuit will produce an alternating current component in said unidirectional current flow, means for applying a biasing potential to said control electrode in accordance with said alternating current component whereby the direct current component of said unidirectional current iiow is varied, and means for controlling the voltage across said principal 4electrodes in accordance with said direct current component.

9. In combination, an electric discharge device of the pentode type having a pair of principal electrodes, a control grid, and two auxiliary grids, means for producing a unidirectional current flow between said principal electrodes, an input circuit connected to said control grid and one of said principal electrodes whereby an alternating voltage impressed upon said input circuit will produce an alternating current component in said unidirectional current flow, means for biasing said control grid an increasingly negative amount in response to an increase in said alternating current component whereby the direct current component of said unidirectional current flow is decreased, and a resistor connected in series with said principal electrodes whereby the voltage applied across said principal electrodes increases with decrease in said direct current component.

10. In combination, an electric discharge device having a plurality of electrodes including a pair of principal electrodes and a third electrode, said device having pentode characteristics, means for producing a direct current flow between said principal electrodes, means for applying a biasing potential to said third electrode in accordance with a ow of alternating current between said principal electrodes whereby said direct current iiow is varied, and means for controlling the voltage across said principal electrodes in accordance with said direct current flow.

11. In combination, an electric discharge device having a plurality'of electrodes including a pair of principal electrodes and a third electrode, said device having', the characteristic that its curve of plate current plotted against plate voltage is concave downward, means for producing a direct current iiow between said principal electrodes, means for applying a biasing potential to said third electrode in accordance with a flow of alternating current between said principal electrodes whereby said direct current flow is varied, and means for controlling the voltage across said principal electrodes in accordance with said direct current ilow.

12. A trigger amplier comprising a vacuum tube having an amplifier section and a rectier section, said amplier section including a control electrode and having a plate circuit including a series resistor, a biasing circuit including said rectier section, means for transferring energy 5 from said plate circuit to said biasing circuit, and means 4including a resistor in said biasing circuit for increasing the negative bias of said control teristic that its amplifying ability increases with an increase in plate voltage.

LOY E. BARTON.

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