US2084180A - Radio signaling system - Google Patents

Radio signaling system Download PDF

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US2084180A
US2084180A US586874A US58687432A US2084180A US 2084180 A US2084180 A US 2084180A US 586874 A US586874 A US 586874A US 58687432 A US58687432 A US 58687432A US 2084180 A US2084180 A US 2084180A
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output
circuit
amplifier
grid
current
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Loy E Barton
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RCA Corp
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RCA Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
    • H03F1/04—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in discharge-tube amplifiers
    • H03F1/06—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in discharge-tube amplifiers to raise the efficiency of amplifying modulated radio frequency waves; to raise the efficiency of amplifiers acting also as modulators

Definitions

  • the present invention relates to radio signaling systems and more particularly to systems of that character embodying electric discharge devices as audio frequency amplifiers and modulators.
  • the demand for higher power output occurs chiefly in connection with the output stage of 15 the audio frequency amplifier, while in transmitting apparatus it occurs both in connection with the power amplifier and in connection with the modulator, used in conjunction with the power amplifier, to apply the modulating or audio frequency signal to the carrier wave.
  • pedient has the disadvantage that it involves a omultiplicity of tubes and associated apparatus, with corresponding complication and cost. This is particularly true in connection with transmitters arranged for substantially 100 percent modulation and having appreciable power output, for the reason that the power requirements for a suitable modulator therefor is of a corresponding magnitude and cost.
  • the average antenna current may remain the same, but the effective value of the current increases, therefore, increasing the average power input to the antenna.
  • This increase in antenna power must be supplied (a) by the modulators employed, (b) by an equivalent increase in power, (c) by an increase in the plate current to the power arnpliiier tubes, or (d) by an increase in the average efficiency of the power amplifier tubes.
  • the increased power may best be obtained by method (a) above, in supplying the increased power in the form of audio frequency power to the anode or plate circuit of the radio frequency power amplifier.
  • modulators heretofore and at present may often include a plurality of high power in balanced and in multiple rel tubes connected ation, with attendant high cost of operation as well as initial cost.
  • the classification 4 is based upon the operating characteristics depending upon values of grid bias, excitation, allowable distortion, and other features.
  • a type of amplifier known as a class "A amplifler is the type most used in receiving apparatus in the usual audio and radio frequency ampliflers, and in which'the average value of plate ⁇ appreciably when a signal is impressed on the tube grids, and the grids are usually not driven positive.
  • the distinguishing characteristic is that the output alternating current voltage bears a linear relation to the input alternating current voltage.
  • a type of amplifier known as a class B" amplifier, is one which is usually employed as a radio frequency output amplifier in a transmitter, and its distinguishing characteristic is that the power output is proportional to the square of the excitation grid voltage.
  • the electric discharge devices or tubes employed therein are biased to essentially plate current cut off or slightly above, and the average value of direct plate current varies with the input alternating current voltage. The plate current flows only during the positive swings of the input voltage. I'Ihe grids may be driven positive until the output voltage begins to deviate from a linear relation with respect to the input voltage.
  • the plate circuit Since plate current flows only during one-half of the cycle, the plate circuit must be tuned to preserve the input wave form or if an audio or an aperiodic amplifier is desired, two tubes must be used in a typical push pull or balanced arrangement in order that plate current to one or the other of the tubes may flow at all times.
  • the excitation may be strong enough to swing the grid or grids positive and thus produce an appreciable rectified grid current. Rather heavy loads are therefore placed on the preceding amplifier by the large amount of grid excitation required to overcome the grid losses in the tube.
  • the output efficiency is very good because of the fact that the peak plate or anode current'may be comparatively high for peak positive voltage swings on the grid and the instantaneous direct current resistance of the tube is low during the half cycle the plate current flows.
  • a third type of amplifier known as a class amplifier, is a, special type ⁇ of radio frequency amplifier or oscillator and is one in which the output varies as the square of the plate voltage within certain limits.
  • the tubes are biased to about double the value for plate current cut off and the grid is driven to a degree such that l small changes in input voltage does not appreciably change the output Voltage.
  • the excitation peak voltages must be sufficient to drive the grid considerably positive in order to secure large amplitudes of plate current. This results in a very high emciency of tube operation due to the fact that the internal direct current resistance of the tube is very low during the time of plate or anode current flow.
  • the grid excitation losses are relatively high and the preceding stage must deliver enough energy to supply these losses.
  • the grid excitation may go so far positive that saturation 2,084,180 A further lconsideration oi' amplifiers and may be 'reached for a relatively large portion of the cycle.
  • the class C type of ampliner is considered to be the most efficient type for transmitters, but the plate' circuit must be tuned if sinusoidal voltage output is desired. For constant input voltage, the output voltage or antenna-current is proportional to the plate voltage. Therefore, this type of amplifier is well adapted to plate modulation. If enough energy is taken from the output o1' a class C amplifier to drive its grid, the ampliij'ler becomes tor, l
  • power required for modulation purposes may be in the order of the power output of the output amplifier.
  • the present power output requirements from the amplifier of a radio receiver may be in the order of several watts, while for operating a plurality of loud speakers or other devices for wide sound coverage, the audio frequency power requirements may often be in the order of several hundred watts. ⁇
  • the present. invention relates more particularly to the class type of amplier as the output stage of an audio frequency amplifier unit for signaling systems, and has for a further object to provide an audio frequency electric discharge amplifier or modulator of that type from which a higher undistorted output power may be obtained at audio frequencies than has heretofore been obtainable by known means or arrangement of electric dischargeV devices in an amplifier, while taking advantage of the desirable operating characteristics of a normal class B amplifier.
  • an amplifier of the above character capable of delivering a high undistorted audio frequency power output may be adapted to use as a modulator of high power transmitters, as an output amplifier in radio receiving apparatus and the like, and that it may permit the use of ordinary electric discharge devices or tubes of the so called battery type to deliver relatively high audio frequency power in battery and portable receiving apparatus, with economical current consumption.
  • the plate or anode dissipation must be kept within rated or normal values.
  • the class A type of audio frequency amplifier or modulator which is extensively used at the present time, does not satisfy all of the above conditions.
  • the maximum plate or anode dissipation occurs while the amplifier is receiving no signal current and the maximum anode efficiency is relatively low, being normally not over 25 percent at maximum output.
  • the result of the high anode dissipation is that the output or power tubes must be large, and in general a relatively high anode voltage is required.
  • a plurality of such tubes, and at least two in balanced or push pull relation, are required in the usual amplifier. In the last case,the tubes must be of a higher power rating to obtain a higher power output. This type of amplifier is therefore usually uneconomical in the power required for the anode supply.
  • the output or power tubes are biased to essentially anode current cut off and when the input electrodes or grids are properly biased and driven by signal currents to substantially zero bias swing, the first three of the above conditions are satisfied to a fair degree.
  • this type requires relatively low audio frequency power from the signal source to operate it, and the input system thereto may be the usual relatively high resistance type.
  • An amplifier of the class B ⁇ type does not in itself satisfy the fourth requirement above mentioned.
  • an audio frequency amplifier by which a relatively high audio frequency output, for exampleof f'lve to ten times the usual or normal output, may beobtained Without increasing the size, rating, or number of electric discharge devices employed therein, and without increasing the anode potential or anode dissipation.
  • An amplifier of this typel may be used as a source of high audio frequency power for plate modulation of a transmitter as hereinbefore described, and may be applied to any signaling system requiring a relatively high'audio frequency output, with a minimum of equipment.
  • Figure l is a circuit diagram of an audio frequency amplifier embodying the invention.
  • Figs. 2 and 3 are curve diagrams illustrating operating characteristics of the amplifier shown in Fig. l;
  • Fig. 4 is a circuit diagram of equivalent circuits representative of the input and output circuits shown in Fig. l;
  • Fig. 5 is a circuit diagram of a modulator embodying the invention as applied to a broadcastv transmitter having a high power output amplifier of the class C type;
  • Fig. 6 is a wiring diagram of an audio frequency amplifier embodying the invention and adapted for battery operation;
  • Fig. 7 is a circuit diagram of equivalent circuits to those shown in Fig. 6;
  • Fig. 8 is a circuit diagram of an alternating current amplifier or modulator embodying the invention and applied to a short wave transmitter system.
  • an improved class B audio frequency amplifier embodying the invention includes an output'stage I0 and a driver stage II therefor, which are so coupled and controlled, that by means of an electric discharge amplier or vacuum tube I2 of relatively low power output in the driver stage, which may be of the class A type for example, the output stage may be driven substantially to the limit of the emission or space charge of the electric discharge devices or tubes therein for maximum audio frequency power output.
  • the latter tubes also may be of normal l power rating as will be seen hereinafter.
  • the amplifier I2 receives audio frequency signal voltage from any suitable source such as input terminals I3 which are connected with it through a suitable input or grid circuit I4, whereby audio frequency signal potentials applied to said terminals or to the input of the amplifier, are amplified by the device I2 and through its output or anode circuit indicated at I5, are applied 'to the output stage I0.
  • any suitable source such as input terminals I3 which are connected with it through a suitable input or grid circuit I4, whereby audio frequency signal potentials applied to said terminals or to the input of the amplifier, are amplified by the device I2 and through its output or anode circuit indicated at I5, are applied 'to the output stage I0.
  • the output amplifier stage consists essentially of two tubes I9 and I'I connected in push pull or balanced relation between push pull input and output coupling devices I9 and I9 respectively, and biased for class B operation, as indicated.
  • the grid bias supply indicated is preferably of relatively'low direct current resistance.
  • the output stage is provided with a suitable anode voltage or plate supply source as indicated in the drawings.
  • the anode voltage supply source 10 should have good voltage regulation under wide load variations, as it should be understood that the load current increases with an increase in the amplitude ofv applied signal voltages in this type of amplifier.
  • the output stage is provided with an input circuit or'system, including the coupling device i9 and the output circuit I5 of the driver stage, having a relatively low impedance in itself, whereby the signal voltage is permitted to carry the grids of the tubes I6 and I1 therein, far into the positive range of operation, without a reduction of the available signal voltage and hence distortion, because of the impedance drop in such input cir'- cuit or system, and without excessively loading the driver stage.
  • the driver or lrst stage of the ampliier is preferably but not necessarily, transformer coupled to the output stage.
  • device I8 is a transformer having a step down ratio from a primary winding 20 in the anode circuit I5, to each side of the secondary winding 2
  • the step down ratio of the coupling device or input transformer I8 for the output stage is arranged to permit a relatively low reflected impedance, over from the anode or output circuit I5 of the driver stage, in each half of the input or grid circuit 22 of the amplifier I 0, in series therewith. Therefore, when the grids of the tubes I 6 and I1 are driven into the positive range, the low effective input resistance permits grid current to flow without seriously affecting the shape of the signal or input voltage wave as applied at the input terminals I3 of the amplifier.
  • the impedance ratio of the input coupling means is such that the current requirements of the grid circuit 22 are met without overloading the driver stage II and introducing distortion, and, is further of an order such that the anode circuit impedance of the driver stage reflected over into each half of the grid circuit 22 of the output stage III in series therewith, is substantially less than thelgrid to cathode impedance of the electric discharge device I9 or I1 in the output stage connected with that half of said grid circuit, when drawing maximum grid current through said circuit.
  • the output or power amplifier devices I6 and l1 are preferably of the type having a higher,
  • the output tubes I6 and I1 are arranged to be operated in accordance with class "B operation. That is, the control electrodes or grids are biased to substantially anode or spacecurrent cut off as indicated by the legend in the drawings, Fig. 1.
  • the bias source is located inthe grid circuit 5 22, and is common to both devices I9 and I1.
  • the input or grid circuit 22 for devices I6 and I 'I is provided by a winding or impedance 2I, this being the secondary of the coupling device or transformer I9, and is mid- 10 tapped as indicated at 24 for application of the biasing potential, in the usual manner for push pull circuits.
  • the load connected with the output stage is also arranged to have a relatively low impedance 15 with respect tothe internal impedance of the output stage. .
  • the output circuit of the power stage is arranged to have a low ini-' pedance with respect to the internal or plate lmpedance of the electric discharge'devices therein.
  • the output circuit of the power or output stage I0 includes a balanced output or anode circuit 25 for devices I6 and Il, a source of load therefor indicated by output terminals 26, and the output coupling device or transformer I9 which is inter- 25 posed between the circuit 25 and the load, as an impedance transforming means.
  • the anode or operating potentials for the de;- vices I6 and I'I areapplied through a mid-tap connection 28 on the primary winding 21 of the 30 output transformer or coupling device, and the anode circuit 25, in the usual manner for push pull amplifiers.
  • the plate or anode supply source which may be connected between the cathodes and the tap 29 should, as indicated, have good regulation for the reason that in operation the devices or tubes I6 and I I draw a varying load current in response to changes in the impressed signal voltage.
  • the grid'or input circuit per se as distinguished from the entire input circuit or system, of the power amplifier or output stage must be of low resistance and the input circuit as a whole must be of low impedance, so that the power or cur- 45 rent requirements of the tubes through the grid circuit may be met without seriously distorting the wave shape of the signal applied to the driver stage, and the reected load back into the output circuit, or the output circuit impedance, must be 50 kept low with respect to the internal impedance of the output tubes in order that the tubes-may be driven to the limit of their emission or space charge, without distortion in the plate circuit.
  • the output power is limited by the plate dissi- 55 pation, the maximum direct current to the plate, or the maximum allowable grid voltage swing within the distortion limits. If the grid voltage swing limits the output because of distortion, it does so, by swinging in a positive direction until 60 it approaches the minimum instantaneous plate voltage. When the two voltages approach each other, the direct current of the grid rises very rapidly with any increase in grid voltage swing.
  • the plate or anode current swing for a given ex- 65 citation depends upon the load resistance in the plate circuit. 'I'he load resistance, then, bears a very important relation to the tube loss, the maximum power output and the power required to drive the grid, as will be seen herein- 70 after.
  • Fig. 2 29 and 30 are plate or anode-current,l grid-bias curves for tubes I9 and I 1 respectively, of Fig. 1.
  • the curves are plotted with respect to a grid bias scale or zero 75 plate current line 3I, and an ordinate .32 representing plate current and grid current scales.
  • the curve 29 is plotted from data obtained by varying the applied grid potential and reading the corresponding anode current for one tube such as tube I6, inthe circuit 25 of Fig. 1.
  • the plate current curves are taken with load, that is with a load at 26 reected over in series with one tube in the plate circuit 25.
  • the zero bias line for curve 29 is indicated at 33 and it will be noted that the normal anode current for class B operation is indicated at 34 through which is drawn the normal negative bias line 35. It will also be noted that the negative bias is such that the point 34 on the curve 29 is substantially at zero or cut off for the anode current.
  • the anode current increases along the line 29 to a maximum point such as the point 36 for example.
  • the total grid swing for such operation is indicated at 31, which includes the negative range 38 and a considerably larger positive range 39. 'I'his is thegrid or input signal voltage swing, A, for the tube I6.
  • each tube is carried far into the positive range and that after the zero bias at line 33 is passed, the grid begins to draw. an increasing amount of grid current indicated by the curve 40, a point of maximum slope on which is indicated at 4I.
  • the lower curve 30 for the tube I1 is the same as the upper curve 29 except that it is reversed and shifted along the bias line 3I until the curves 29 and 30 coincide as nearly as possible to a line 42 drawn through the straight portion of the upper curve 29.
  • the bias potential indicated .at the point 43 through which the straight line 42 passes in crossing the zero plate current line or the grid bias line 3I, is the proper normal negative bias potential to use for the two tubes I6 and I1 having characteristics substantially as shown.
  • the bias may be adjusted until the anode current is obtained as indicated by the curves.
  • the relation of the plate or anode current curves 29 and 30 of Fig. 2 is an indication of the operation of devices I6 and I1 respectively in the circuit shown in Fig.v 1.
  • the plate or anode current of that tube increases with the swing, and ows through one half of the primary winding of the output device I9.
  • the output voltage for this half cycle bears a linear relation to the input voltage to the amplifier.
  • the above tube becomes idle because its grid becomes more negative and the other tube functions in a manner similar to the first except that the anode .current ows in the other half of the output winding of the device I9, and the output voltage is therefore 180 d ⁇ e grees out of phase with the first half wave.
  • the input coupling device or transformer I8 delivers current to the grids of the output tubes from only one side of the secondary at any particular instant, which must be considered in the design of this device.
  • the plate current 29 of the tube I6 which may be designated as IbA, increases, and as the grid becomes positive, grid current designated as IcA, flows according to curve 40.
  • IbA As the signal reverses, Ib. decreases and as it passes the common bias line, IbA becomes zero and plate current Ibis of the other tube I1 increases according to the curve 30. Therefore, each tube functions over one-half cycle, While the other is practically idle.
  • the load impedance applied at 26, which either the tube I6 or the tube I1 is working into is calculated as if only one tube is supplying the total power from one side of transformer primary 21, but in calculating plate dissipation, each tube functions for one-half the time sothat the total plate loss is divided between the two tubes.
  • the plate current input to the output tubes resembles a true full-wave rectified current
  • the power input to the plate of the output tube is:
  • IpmEb power input in which 1pm: peak plate' current (alternating current) .f Eb: plate or anode supply voltage (direct current) 0.637 1pm: Ib or average plate current
  • the power output may be represented as:
  • Epm approaches Eb as a limit, then the e'iciency becomes 78.5 percent for half-sine-Wave outputs.
  • the output power from (2) is:
  • the plate current is not limited as in the class A amplifier, so that a load resistance for maximum power output is such a value that the limit of emission is approached.
  • the minimum instantaneous plate voltage Ehm and the allowable plate dissipation y are also factors which determine the load resistance.
  • 'I'he input resistance of the amplifier is indefinite, as with a class A amplifier with the grids driven positive, but a minimum -value can be obtained from the grid current curve 40 of Fig. 2, being in the present example, point 4I for a maximum positive signal voltage swing.
  • 'I'his may be used to indicate the input series resistance that may be permitted for a given degree of distortion.
  • the minimum input resistance is calculated from the maximum grid current and also the voltage swing required for this current.
  • the slope of the grid current curve must also be considered because if this resistance represented by the slope of the curve is low compared with the effective grid series resistance, considerable distortion will result. This is especially true if the operating bias is considerably negative as indicated.
  • alternating current component of the anode or plate current Ip, the alternating current plate voltage Ep, and the alternating signal voltage Eg, applied to the grids of the output tubes are plotted as ordinates against time, in curves 44, and 46 respectively.
  • the curve 45 for the plate voltage is shown with respect to the normal applied anode or plate potential En indicated by a line 41, while the cathode potential or zero axis is indicated by a line 48.
  • the normal negative grid bias potential with respect to the cathode line 48 is indicated by a line 49, about which as an axis, the curve 46 is drawn.
  • a line 49 about which as an axis, the curve 46 is drawn.
  • One half cycle of the alternating cur- 40 rent component of the alternating current anode or plate current Ip is shown and is drawn with respect to a line 50 corresponding to the normal anode or plate current indicated in Fig. 2 at point 34 on curve 29.
  • the grid current and grid voltage may be estimated for the above conditions. Incidentally the above condition for minimum plate voltage is a condition where the space charge limitation and emission limitations are practically equal. 2. With the above data, which may be esti'- mated from'standard data sheets of characteristie curves of available tubes, the minimum input resistance Rg is estimated between the grid and the cathode at the point of maximum positive grid swing. The peak grid voltage swing is also estimated. 3.
  • the next step is to provide a means in the input circuit for supplying the required grid current without appreciably affecting the voltage input wave, even though at times the grid current in the output stage may be zero or the input resistance may be very high.
  • the permissible input regulation may be chosen at ap-l proximately 10 percent, from which the eil'ective resistance in series with the ygrid of each output stage tube approximately may be one tenth ⁇ of the value of the minimum grid to cathode resistance, for maximum positive grid voltage swing in response to a signal wave. 10
  • the transformer or input device I8 is designed with a proper ratio for this purpose, and to permit the use of a tube in the driver stage that, without overloading, will 16 supply the necessary input signal voltage at the known impedance of -the tube, to the primary 28 of the input transformer I8 for the output stage.
  • the above features may be used successfully to the limit or the output of the tubes, if a load re- 30 sistance is used, such that vwhen maximum plate current fiows, the voltage drop in the load resistance causes the plate voltage to drop from the value Eb (Fig. 3) of the plate voltage supply to the minimum value Ehm (Fig. 3) as determined 35 by emission and space charge. It has been found that such desirable loading of the output tubes yrequires that the load resistance be 'made lower than the plate resistance of the output tubes. This is a feature of the improved class audio 40 amplifier, which is highly desirable and effective in providing a maximum power output economically.
  • is the minimum resistance of grid to cathode or the internal input impedance of one of the output tubes, which may be 60 called Rg.
  • the total input or grid voltage change or swing on each output tube is the swing indicated at 38 plus that indicated at 39, with a minimum resistance Rg. Rs, or the resistance of-the input 55 circuit in series with the grid of one output tube, must be appreciably lower than the resistance Rg, and is preferably of the order of one-tenth oi' Rg, as hereinbefore pointed out, although it is not limited thereto.
  • no. shunt resist- 00 ance must be permitted except to improve the frequency characteristic and the coupling device in the input circuit is designed to provide, in itself, this desired effective input resistance in series with the grids of the output tubes when 65 coupled with the stage.
  • the maximum alternating plate voltage Epm delivered to the load across the primary 21 of the output device I9, or the maximum voltage decrease from the plate supply Eb is determined by the minimum allowable plate voltage Ehm which will cause the peak plate current to flow. This is dependent upon the space charge of the tube and is limited thereby. Ehm is then, the. minimum plate voltage necessary to obtain peak emission or as nearly peak emission as safe operation permits, the peak plate current being 1pm.
  • the load resistance Rp for each of the tubes I6 and I1 for the time it operates is:
  • the underlying thought in the above design is that of providing a class B output amplifier, with input and output circuits including suitable coupling means, whereby a maximum power output is provided without appreciable distortion of the signal wave applied to the driver stage in the input circuit.
  • a coupling Vmeans such as a step-down transformer so designed that a reflected series impedance Rs, over from the preceding driver stage, is of a lower value than the impedance of the grid circuit between the grid and cathode of each tube in the output stage, when said grid is at a maximum positive potential and drawing a maximum grid current.
  • a coupling means such as a transformer, is provided whereby the reected load Rp back into the plate circuit of the output stage is of a lower value than the internal impedance Tp of each of the output tubes, in series with the plate circuit.
  • the direct current resistance of the grid or input circuit of the output stage must be relatively low, together with the source of bias potential, to prevent distortion, because of voltage drop in the elements of the circuit.
  • the anode potential supply must have good regulation.
  • a low impedance grid circuit as a part of the input circuit for the output stage, is provided without resorting to artiiieial loading means such as a shunt resistance, in connection with the grid circuit. 'I'he loading effect of such resistance upon the grid circuit and upon the driver stage, would seriously introduce distortion or introduce practical limits into the design, whereby the desired operating characteristics would not be obtained. Chief among the disadvantages of such a circuit would be the lowering of the applied signal voltage to the output stage and additional load upon the driver stage.
  • an audio frequency amplifier in which a class B type of output stage, and a driver stage therefor, are connected in cascade between a source of signal potentials and a source of load for maximum power output, limited only by the space charge or emission of the output devices.
  • the output stage includes electric discharge devices in balanced or push pull relation, and a coupling device, preferably a transformer, is arranged to couple the anode circuit of the driver stage with the grid circuit of the output stage.
  • the impedance ratio of the transformer is such that the current requirements of the grid circuit are met without over-loading the driver stage and introducing distortion, and furthermore, is of such an order that the anode circuit impedance of the driver stage, or operating impedance, reflected'over into each half of the grid circuit of the output stage in series therewith, is substantially less than the grid impedance of the electric discharge device connected with that half when drawing maximum grid current through the grid circuit.
  • an impedance changing or transformer means having an impedance ratio such that the load impedance, or operating irnpedance, reflected back into each half of the anode circuit of the output stage may be substantially less than the anode impedance of 4the electric discharge device connected with that half, and in series therewith, whereby the electric discharge devices in the output stage may be driven to the limit of their emission or space charge.
  • the grid or input circuit including the secondary of the coupling device orvtransformer, must be of low impedance so that the power or current requirements of the tubes through the grid circuit may be met without seriously distorting the wave shape of the signal applied to the driver stage, and the reected load back into the output circuit, or the output circuit impedance, must be kept ,low with respect to the internal impedance of the output tubes, whereby the tubes may be driven to the limit of their emisimpedance between certain points such as themid-tap 24 and a point 5I of Fig. 1 representing the input impedance Rs, must be substantially less than the impedance betweencertain other points l2 and Il, representing the grid impedance R.. 'I'he impedance R. is the reected .im-
  • the entire input circuit may be reduced to the which terminals 56 represent the signal voltage applied to the output stage.
  • This Signal voltage as indicated, will be the mu or amplification factor of the tube i2 multiplied by the value of the applied signal voltage at terminals I3, and by the turn ratio of transformer i8, Fig. 1.
  • 'I'he circuit 64 of Fig. 4 is thus the equivalent of and serves to illustrate the fundamental values of the input circuit shown in Fig. 1.
  • Coupled to the output stage is the load impedance as provided between the terminals 26, and which when reflected back into the output circuit of the ampliner, appear in each half of the output circuit, such as between points 28 and.
  • This reflected load impedance over into the output circuit is preferably relatively low with respect to the internal impedance oi' the corresponding output tube, such as the tube I6 for example, between a point 60 and the point 53, being the plate to cathode or internal anode impedance of the tube.
  • 'I'his output circuit is represented in Fig. 4 by the circuit 6I in which the impedance 62 is the reflected load impedance between points 59 and 28, for example, in the output circuit 26, and the impedance 63 is the internal impedance 'of the tube between the points 60 and 59 as above pointed out.
  • the signal voltage delivered by the output tube is applied as indicated by the terminals 55 and is, as indicated, the mu or amplification factor of the output tube multiplied by the signal potential En applied from the driver stage to the output stage.
  • the potential available in the output circuit will be 20x160 or 3200 volts, oi' which, 1300 volts may exist between points 28 and 59 across the load, and the remainder of which, 1900 volts, may exist between points 60 and 53 or across the tube in the output circuit.
  • the 1300 volts or Epm will leave an instantaneous minimum potential Ehm on the plate oi' 700 volts.
  • this last named voltage may be and preferably is, the minimum anode potential necessary to maintain a maximum ilow of plate current as determined by the space charge of the particular tube.
  • the impedance of the output circuit should be and preferably is such that a maximum plate current Ipm may flow with minimum instantaneous applied potential. It will thus be seen, as hereinbefore pointed out, that the power output is affected by the load impedance and by thespace charge of the tubes employed. It is also atlected by the emission limits of the tubes. and the load impechnce must be such that the platerv dissipation of the tube is not exceeded.
  • the values of the circuit elements ofthe input and output circuits of ldgs. 1 and 4 may vary in different installationspdepending von the character of work to be amounts of power to be transmitted, but in any case impedance R. must always be less than imf pedance R. and the impedance R@ must always be less than the impedance rp for maximum power output.
  • an'l audio frequency power output may be obtained, which is many times larger than the output available from the same number of tubes in an ordinary class "A" or class B amplifier. This is chiefly for the distortion of the applied An amplifier of this character is therefore particularly well adapted for use as a modulator in a broadcast transmitter.
  • a radio frequency powex amplier of the class "C type is indicated at 64 and includes a plurality of electric discharge amplifying devices 65 connected in parallel with a' tuned radio frequency input circuit 66, through a coupling device 61 and radio frequency input terminals 68.
  • the output or anode circuit indicated at 69 is also parallel connected with the devices 65 and is coupled with a radiating system 10 through a suitable output coupling device 1I.
  • Audio frequency modulating signals are applied to the anode circuit 69 to modulate it, through a modulator 12, which includes a driver stage 13 and an output tween audio frequency input terminals 15 and the anode circuit 69.
  • stage 14 rascade connected, be-
  • the audio frequency input terminals 15 are suitably coupled to an input circuit 16 for the driver stage 13 by an audio frequency coupling device or transformer 11.
  • an audio frequency coupling device or transformer 11 Between the output circuit of the driver stage indicated at 18 and the input or grid circuit of the output stage indif cated at 15J, a second audio frequency coupling device is interposed and is designed to provide an impedance relation between circuits 18 and 19 substantially like that provided by device I8 lin Fig. 1, and for the same purpose.
  • an output coupling device 8l is connected to provide a load impedance arrangement in the output circuit 88 substantially like that provided by device I9 in Fig. 1 and--for the same purpose.
  • a radio frequency choke coil 82 and a suitable bypass condenser 83 serves as a filter to isolate the anode circuit 69 from the modulator 12.
  • electric discharge devices indicated at 84 are arranged in balanced relation between the input coupling device 80 and the output coupling device 8
  • the driver stage includes two devices 85 arranged also in balanced relation as distinguished from the single driver tube utilized in Fig. 1.
  • this arrangement in the driver stage h-as the advantage that the generated voltage from plate to plate in the output circuit thereof is doubled for a given input voltage between grid and cathode on the output stage, and the step-down ratio of the input coupling device 80 may then be increased by two, or an impedance ratio of four.
  • the plate resistance of the driver stage in series with the primary or coupling device 80 is only increased by two. Therefore, the net gain may be one half of the eiective resistance in series with the grid, such for example as resistance Rs of Fig. 4.
  • tubes known as radiotrons type 'UV-211 have successfully been employed in the driver stage at 85 with tubes of the type UV-851 used at 84 in the class B modulator stage 14, while in the RF power amplifier 64, tubes of the UV-204-A type have been used at 65.
  • These tubes are designated only by way of example, since their characteristics are well known and thereby the values employed in the design of the modulator may more readily be appreciated and understood.
  • the coupling device 80 is preferably a stepdown transformer having a turn ratio of substantially 5 to 1, or 10 to l, to each side of the secondary. This provides an impedance ratio of substantially' 100 to l and with an internal plate impedance Rp in the driver stage of substantially '7000 ohms, thus providing a reflected impedance over through the coupling device 80, in series with the grid circuit 19, of substantially 70 ohms. As compared with the internal impedance Rg of the d-evices 84 in the output stage, of 800 to 1200 ohms, this impedance is relatively low, as will be seen. The impedance of 800 to 1200 ohms, of course, is measured at a maximum positive potential on the grid which in the present example was substantially 80 volts. ⁇
  • the calculated load over from'the load circuit 68 is provided by the power amplifier 84 and is sub'- stantially 2200 ohms.
  • is so designed that a turn ratio of 'one to 1.4 from each side of primary to secondary is provided, and an impedance ratio of one to two.
  • the reilected impedance, Rp, of the load, over into each half of the output circuit 80 is then approximately 1100 ohms, which, as will be seen, is lower than the internal impedance of the output tube associated therewith.
  • an output of approximately 1500 watts is obtainable from the two tubes, which is more than sufficient to modulate to percent the 1000 watt station, provided by the remainder of the equipment including the RF amplier indicated at 64.
  • the grids of the devices 84 have in practice been drivenl into the positive range to such an extent that relatively high values of grid current'were obtained.
  • this grid current at substantially 80 volts positive, on a positive signal swing reaches as high a value as milliamperes.
  • the direct current resistance of the grid or input circuit 19 must be maintained at a relatively low value, otherwise serious distortion may take place.
  • the directA current resistance of the bias potential source must be kept low. It may further be interesting to note that the corresponding power output of the same tubes 84 in a class A type of amplifier and at a maximum output rating, is approximately 200 watts. Therefore, the greater power output from the modulator above described is more readily apparent.
  • cathode supply circuits have been omitted.
  • the source of cathode current supply is indicated at 86 and is a generator driven by a suitable motor 81.
  • the positive terminal of the generator 86 should be understood as being connected to all of the cathodes, although as above mentioned, the connection lead is omitted.
  • the opposite or negative terminal of the generator is connected thru a common grounded supply lead 90 to all of the cathodes as indicated, and serves as a grounded cathode return lead for all circuits. In practice this connection is provided by making all connections to ground.
  • Anod or plate potentials for the amplifier tubes 6 and the class B modulator tubes 64 are supplied by a suitable high voltage direct current generator 9
  • serves to raise the voltage supplied by the generator 9
  • and 91 are connected in series by a lead 99 and generator 91 is in yturn connected with the common ground lead 90 as indicated at 99, whereby the operating anode potentials are applied between the cathode and anodes of the tubes supplied by said generators.
  • a direct current generator, or generators, are employed in the system of the present example for thel reason that they provide good. regulation under a varying load condition imposed by' the operation of the class B amplifier 14. An anode supply source of this character also has a large power capacity.
  • rectified alternating current may be em-.
  • and 91 are also driven by a suitable motor
  • 04 is suitably by-passed to the ground lead 90 by a by-pass condenser
  • 'I'he arrangement is such that the grid circuit 19 of the class B modulator 14 is isolated from the bias supply
  • one side of the filter means is connected with the cathode return lead 90 thru a return lead
  • This last is preferably a storage battery or other suitable means for the purpose o'f providing a stabilizing reservoir of extremely low resistance in the grid circuit return, or in the grid circuit of the class B modulator 14.
  • an additional bias adjusting battery or bias means is provided in connection with one tube. In the present example this is a battery 89 in the grid circuit of one tube.
  • the grid circuit be of relatively low resistance and this also includes the source of bias potential, whereby variations in the amount of grid current drawn by the tubes 64may have no appreciable eilect upon the appliedsignal potentials to cause distortion.
  • This precaution 4in the other portions of the transmitter is not as essential, hence in the present example a battery reservoir is utilized only in the position shown,
  • any suitable bias supply means may be employed, and in the present example this may be a simple battery indicated at Likewise it should be noted that the source of bias potentials
  • the anode or plate potential supply for the driver stage 13 is supplied by the generator 91 thru a tap connection lead I2 between it and the generator 9 I.
  • 2 which, together with a
  • the anode potential or current supply lead 93 in the modulator stage 14 is also suitably by-passed by a condenser H5. In each case the by-pass connection is to the common grounded cathode supply lead 90.
  • ammeters 96 and 95' are respectively included in the plate circuit of the class C output amplifier 64 and in the output modulator 12.
  • the plate current may be adjusted to substantially 40 milliamperes, while the plate current through meter 96 is sub- 'stantially one ampere, with tubes of the UV-85l type at 84 and tubes of the UV-204-A type at 65.
  • a Variation in the current through the meter 95, in response to signals may be taken approximately as an indication of the modulation being applied to the amplifier 64, since the plate current increases proportionately with an increase in the value of the applied signals.
  • the plate potential applied to the vclass B" amplifier 14 and to the output amplier 64' through the supply lead 92 is approximately 2000 volts as delivered by the generators 9
  • 2 is approximately 1000 volts.
  • the filament potential supplied by the generator 86 is approximately 15 volts.
  • is approximately 115 volts.
  • vis substantially 80 volts negative, the voltage being reduced from that provided by the generator by the series resistor
  • The. biasing potential supplied by the source is that required to operate the devices 85 as normal class A ampliers.
  • the class C amplifier 64 is provided with the usual oscillator circuit in connection with the ⁇ tuned circuit 66, having a grid leak and condenser combination, I
  • radio frequency signals from a suitable source are supplied to the terminal 68 of the class C radio frequency amplifier 64 and are transmitted through the radiating system 'l0 as a carrier wave.
  • the value of the signal strength may be measured by a suitable meter I9 in the radiating system.
  • Audio frequency signals for modulation are applied to the terminals 'l5 of the modulator 12 and are amplified in the successive stages 'i3 and 14.
  • the amplified output is supplied to modulate the plate circuit 69 of the amplifier 64 through the coupling means provided by the output device 8
  • the power output is several times that obtainable from the same devices when used in an ordinary class A amplifier. This is for the reason that the impedance of the input circuit in circuit 19 is relatively loW, whereby the devices 84 may be driven far into their positive grid bias range without distorting the input wave.
  • a load impedance reected into the circuit 80 is such that the output of the devices 84 is limited only by the space charge or the emission.
  • the impedance of the load is such that the emission limits of the devices 84 are not exceeded.
  • a transmitter of this character has the advantage that the radio frequency amplifier and the modulator may be substantially separate units as shown, and may be coupled for plate circuit modulation by an isolating coupling device such as a transformer. Furthermore, by the proper design of the input and output coupling devices of the output stage of the modulator, the amplifier devices employed therein may be driven far beyond their normal useful range of operation to produce a power output many times in excess of that ordinarily provided, thereby materially reducing the cost of manufacture and operation of a transmitter for a given power output.
  • class C radio frequency amplifiers are primarily plate circuit modulated and the class B amplifier of the present invention is adapted to operate in connection with various loads by the choice of a suitable impedance matching means, such as a transformer, the class B amplifier of the present invention is particularly well adapted for use in combination with the class C type of amplifier employed in transmitters.
  • a class B amplifier embodying the invention in its adaptation for battery operation is indicated at
  • This amplier is similar to that shown in Fig. l and includes an input device
  • is connected with a driver stage including an amplifier device
  • Anode potentials for the two stages are provided by suitable sources indicated by terminals
  • 26 is a common cathode return terminal and grid biasing potentials are supplied between it and a third terminal
  • 20 is obtained from a tap
  • a biasing potential is applied to the driver stage or to the tube
  • 32 are of such values that they serve to operate as coupling resistors in connection with the device l23.
  • 28 are dependent upon the values of the resistors
  • Audio frequency signals are applied to this amplifier thru the terminal
  • 28 is lthe B minus terminal
  • 26 is the negative A and the positive 221/2 volt terminal of the B battery
  • 21 is the positive 180 volt terminal of the B battery. It will be seen that this provides a B battery voltage upon the anode circuits of the devices
  • 'Ihe amplifier employs tubes of the Radiotron UX 230 type, having a filament consumption of 120 milliamperes as against 260 milliamperes for a standard battery operated amplifier.
  • the maximum power output is approximately 1.2 watts with approximately 7 milliamperes average fB battery drain with a signal being transmitted.
  • the above standard battery amplifier has a normal output of about .35 watts and a B battery drain of approximately 16 milliamperes.
  • each tube In response to an applied signal, the plate current of each tube increases as the signal potential increased in a positive direction upon its grid. Grid current begins to flow at about one volt positive and increases to approximately 1.5 milliamperes at 20 volts positive. The maximum plate current for this -grid voltage is approximately 25 milliamperes.
  • Each tube alternately functions to take the load as its grid becomes positive, the operation in this respect being the of the driver stage reflected over in series therey mately milliamperes.
  • 25 of the type above mentioned is approximately 9000 to 10,000 ohms, while the input or grid impedance is approximately 12,000 to 14,000 ohms fora maximum positive grid swing.
  • is one to .75 for each side of the secondary, or an impedance ratio to each grid of one to .45 step-down.
  • This provides an input or grid circuit for the stage
  • 20 is indicated at and includes the impedance with by the coupling device
  • Across the circuit is the grid impedance Rg of each one of the devices
  • the signal potentials delivered by the driver stage to its outputvcircuit for transfer to the output stage may be indicated by potentials which may exist between input terminals
  • 20 for maximum power output is substantially 3750 ohms on each side, although it may be lowered in the present example to 2500 ohms for a maximum power output.
  • substantially 4000 ohms, as shown, is believed to be more generally satisfactory and safer from an operating standpoint, as approximately this value insures against excessive plate current on peak signals.
  • the load impedance becomes a limiting factor in the control of the plate current.
  • 22 is such that a 2.7 ohm output device may be employed at
  • a loading device including a. winding and a condenser in series therewith, as indicated, respectively, at'
  • the values of the load and plate impedance in the output circuit are indicated at
  • is substantially 9000 ohms, while that of the load indicated at
  • 20 may be considered as being applied at the terminals
  • Themaximum gridcurrent depends upon the power available to drive the grids positive.
  • the grid current forfa 2500 ohm load at a positive bias potential of 20 volts is approximately one milliampere, which represents a resistance for the in- Therefore, the voltage. from the driver stage must not drop appreciably when such load resistances are encountered.
  • the minimum resistance as calculated from the slope of the current grid voltage curve is about 14,000 ohms as indicated above.
  • the plate current must increase With power output. 'I'his requires that the plate current supply source be adapted to provide a constant voltage, with good regulation.
  • the power requirements for a battery operated amplifier of this character may best be understood from the fact that with an output of 1.2 watts the input power to the plate circuit is approximately 18.7 milliamperes at 158 volts or 2.96 watt for continuous sine wave output. ⁇ The plate efficiency for the average load atfull output is about for sine wave inputs.
  • a transmitter having a modulation system provided by a class B modulator embodying the invention is shown in connection with an alternating current source of operating potentials.
  • the radio frequency system includes a crystal oscillator
  • the class C amplifier like that shown in Fig. 5, is plate circuit modulated and for this purpose is provided with a plate current connection
  • Audio frequency modulation is applied to the circuit
  • the amplifier is provided with an input coupling device
  • 56 receives its operating current or potential from a supply lead
  • 62 are heated from the source
  • 64 is aprovided for the cathode lheating transformer
  • 61, respectively, from the rectifier are connected with the cathodes of devices
  • 66 in association with a suitable by-pass condenser
  • 69 will hereafter be considered.
  • 55 should preferably be designed to couple the devices
  • medium power tubes should be used in the output stage of the speech amplifier
  • 10 is employed in the anode circuit of each of the devices
  • 52 prevent radio frequency currents from entering the transformer
  • 58 for the class B tubes is adjusted to such a value that each tube draws a normal plate current of approximately 20 to 30 milliamperes for the type of tubes above mentioned, this being substantiallyv plate current cut off for such tubes.
  • 58 represents any suitable source of C bias having a low resistance as described in connection with the preceding embodiment of the invention, and is preferably a heavy duty type of B battery.
  • is placed in circuit with the anodes of the devices
  • may be taken as a fair indication of the percentage modulation.
  • is arranged in two sections
  • the type of connection depends upon the type of tubes used in the class C radio frequency amplifier
  • the above described system of modulation in connection with a class C" amplifier is of relatively low cost and of simple construction and has a relatively high radio frequency power output with 100% modulation. Furthermore, the use of the meters in circuit, as indicated, particularly the meter
  • or anode supply circuit of which it forms a part is the usual type of full Wave rectifier.
  • 68 is a special design to improve regulation, and the filament transformer
  • the filaments of all of the tubes may be left on while the plate supply is turned off, thereby requiring a minimum time to start when placed again in operation.
  • 68 is preferably of the iron core type in series, as shown, with the rectifier source, and is tuned as by the condenser
  • 69 there should be no filtering between the rectifier and the resonant filtering element because it is arranged to operate upon an appreciable alternating current component. Any addi-l it near toits saturating point, since a change of reactance for regulation purposes must be proportional to an increase in the load current.
  • 69 may be omitted if the reactor is so designed that its impedance decreases vrapidly with an increase in direct current.
  • the regulation is aided somewhat by providing for a normal load current, or from 10 to 20% of the output current derived from the plate supply source.
  • a normal load current or from 10 to 20% of the output current derived from the plate supply source.
  • the filter is tuned until the inductance oiiers a maximum impedance at the chosen frequency which reduces the output voltage to a minimum.
  • the choke coil is also'designed so that it tends to saturate as the load current is increased so that it tends to introduce a lower reactance in the circuit for greater load currents, while at the same time the change in reactancev detunes the circuit, which also tends to sharply reduce the impedance of the circuit yto maintain the tube voltage more nearly constant regardless of the tube current 'within the power range of the plate supply means.
  • 14 functions as a normal filter condenser and should be relatively large to effectively by-pass the A. C. components -to currents to the class B modulator.
  • An audio frequency amplier including, in combination, a pair of electric discharge devices each having an anode, a' cathode, and a, control grid, said devices being connected in balanced relation to each other and being connected to be biased to substantially anode current cut off, an input circuit of low alternating current impedance with respect to the grid impedance of each of said devices when drawing a maximum grid current, and an output circuit of low alternating current impedance with respect to the anode impedance of eachof said devices.
  • An audio frequency amplifier including in combination, a pair of balanced electric discharge devices, an input circuit therefor and an output circuit therefor, said input circuit having a lower alternating current impedance in series with the input electrodes of said devices than the lowest input operating impedance of said devices effected by high signal amplitudes causing current flow to said electrodes, and said output circuit having a lower series alternating current impedance than the output impedance of said devices, by an amount sufcient to permit said devices to be driven in response to signals to the limit of their emission or space charge.
  • An audio frequency amplifier system including in combination, an input circuit therefor and an output circuit therefor, and means arranged for connecting between said circuits a pair of electric discharge devices in -balanced relation as an amplifier biased to substantially anode current vcut off, said means providing in said input circuit stantially to zero, an input coupling device in the input circuit adapted when connected with a driving source of signal potentials to provide an alternating current impedance in series with each half of the input circuit of a valuel substantially lower than, and having a direct current resistance of a value one-tenth of the value or less of the internal impedance of each of said electric discharge devices when drawing a maximum grid current, and an output coupling device connected with said output circuit having a coupling ratio such that when connected with a load source the series alternating current impedance provided thereby in each half of the output anode circuit may be substantially less than the internal or anode impedance of the device connected therewith.
  • means for connecting a pair of electric discharge devices in balanced relation and for biasing the same to essentially space current cut off said means providing series input and output alternating current impedance in connection with the input and output electrodes of said devices of values lower than the lowest internal operating input -and output impedances respectively of said devices, whereby signal potentials may be applied to each of said devices, having maximum positive values and the anode current of each of said devices is limited only by the space charge or by the emission characteristics of said devices.
  • An audio frequency amplifier including, in combination, a pair of electric discharge devices each having an anode, a cathode, and a control grid, said devices being connected in balanced relation to each other and provided with means for biasing the same to'substantially anode current cut off, an input circuit of low alternating current impedance with respect to the grid impedance of each of said devices when drawing maximum' grid current, and an output circuit of low alternating current impedance with respect to the anode impedance of each of said devices,
  • said input circuit further being of relatively low direct current resistance, said output circuit alternating current impedance being of such low value, that the output anode current of each of said devices is limited by the space charge or emission characteristics thereof, and said anode circuit including a source of anode potental supply having a predetermined relatively high regulation.
  • An electric discharge amplifier having a balanced grid circuit and a balanced anode circuit, means for biasing said amplier substantially to anode current cut off, an input coupling means connected with said grid circuit providing aos-1,180
  • an alternating current impedance in series therewith of a value lower than the internal input impedance of said amplifier when drawing maximum grid current and an output coupling device for an alternating current load circuit adapted to provide a load impedance, lower than the output impedance of output anode, whereby the output anode current of the amplifier is limited by the space charge or by the emission of the electric discharge devices therein and whereby a grid potential variation is permitted to a value whereat the anode current becomes so limited.
  • a balanced electric discharge amplier device In an audio frequency amplier, a balanced electric discharge amplier device, an input transformer and an output transformer pertaining thereto, providing input and output circuit' alternating current impedance values therefor substantially lower than operating values of the internal input and output operating impedances of said device when drawing grid current.
  • An audio frequency ampliiier including in combination, a step-down input transformer and a step-down output transformer adapted to be connected with a pair of electric discharge devices of the vacuum tube amplier type in balanced relation thereto, the first named transformer providing a lower series input circuit alternating current impedance than the lowest input operating impedance of either of said devices, and the second named transformer providing a lower series output alternating current impedance than the output impedance of either of said devices.
  • a balanced input and a balanced output transformer ar- .ranged to be connected with a pair of electric discharge amplier devices having input and output electrodes, each half of the secondary of the balanced input transformer having an operating alternating current impedance lower than the lowest alternating current impedance of said amplifier devices to be connected therewith between their respective input electrodes when drawing current in response to signals of high amplitude, and the balanced output transformer having a lower alternating current impedance in each half of its primary than the internal impedance of the amplifier device to be connected'therewith between its output electrodes and lower than is permissible for class A operation thereof.
  • An audio frequency amplifier including, in combination, a pair of electric discharge devices each having an anode, a cathode, and a control grid, means providing a balanced signal input circuit connected between said control grids and the cathodes of said devices, the alternating current impedance of said input circuit being substantially less than the input impedance of said devices when the grids are driven into the cxtreme positive range of grid potentials by the peak of the signal wave to be amplified, a balanced output circuit connected between the anodes and the cathodes of said devices, a loadg flected load impedance having a value lower than the output impedance of said devices, when' said grids are driven into said extreme positive range of grid potentials.
  • An audio frequency amplifier including, in combination, a pair of electric discharge devices each having an anode, a cathode. and a control grid, said devices being connected in balanced relation to each other, an input circuit for said devices of low alternating current impedance with respect to the grid impedance of each of said devices when the grids thereof are made positive with respect to the cathodes by the magnitude of the applied alternating current energy, a balanced output circuit connected between the anodes and the cathodes of said devices, a loud speaker, and coupling means linking said output circuit and said loud speaker for determining the alternating current load impedance of the loud speaker reflected over into the output circuit, said reflected load impedance having a value lower than the output impedance of said devices, when said grids are made positive by the magnitude of the applied alternating current energy.
  • a pair of power output electron tubes an electron tube driver for said power output tubes, an impedance adjusting transformer connected to couple said driver tube to said output tubes, said transformer having an impedance ratio whereby the driver tube output impedance reflected into the input circuit of said output tubes is substantially lower than the grid impedance of the output ⁇ lower than the anode impedance ofsaid power J output tubes when said grids are driven into said positive bias range by a strong signal.

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US586874A 1932-01-15 1932-01-15 Radio signaling system Expired - Lifetime US2084180A (en)

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US728267A US2063290A (en) 1932-01-15 1934-05-31 Radio signaling system

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3648186A (en) * 1970-03-24 1972-03-07 Kahn Res Lab Amplification system
US20080031480A1 (en) * 2006-08-04 2008-02-07 Siemens Audiologische Technik Gmbh Hearing aid with an audio signal generator
EP2747280A1 (fr) * 2012-12-24 2014-06-25 Samsung Electronics Co., Ltd Dispositif électronique et son procédé de commande

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3648186A (en) * 1970-03-24 1972-03-07 Kahn Res Lab Amplification system
US20080031480A1 (en) * 2006-08-04 2008-02-07 Siemens Audiologische Technik Gmbh Hearing aid with an audio signal generator
US8411886B2 (en) * 2006-08-04 2013-04-02 Siemens Audiologische Technik Gmbh Hearing aid with an audio signal generator
EP2747280A1 (fr) * 2012-12-24 2014-06-25 Samsung Electronics Co., Ltd Dispositif électronique et son procédé de commande
US9413304B2 (en) 2012-12-24 2016-08-09 Samsung Electronics Co., Ltd. Electronic device and control method thereof

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