US1925838A

US1925838A - Push-pull signal amplifier

Info

Publication number: US1925838A
Application number: US620328A
Authority: US
Inventors: Kune Frank
Original assignee: H O BOEHME Inc
Current assignee: H O BOEHME Inc
Priority date: 1932-07-01
Filing date: 1932-07-01
Publication date: 1933-09-05
Anticipated expiration: 1950-09-05

Description

F. KUNC ?USHPULL SIGNAL AMPLIFIER Filed July l, 1932 Sept. 5, 1933.

H INVENTOR BY www( iff- ATToRNEYb,

atented Sept. 5, 1933 STATES QFIC remesa rusa-PULL srcNar. Amantea Application July l, 1932. Serial No. 620,328

l Claims.

In electromagnetic receiving arrangements for rectified alternating current signal impulses two methods are used today for converting the electrical impulses into mechanical oscillations of the armature of the receiving device, for instance of a syphon recorder, by the magnetic eld produced by the impulses. First: the armature is mechanically yieldingly biased, (such as by spring power or the like) always tending to assume a normal zero position from which it is positively deected by the impulse, but to which it returns after the impulse ceases, due to its aforementioned spring bias. Second: the armature is entirely unbiased, but the armature coil, which in the well known manner is disposed in a permanent direct current eld, is positively deflected in both directions by the signal impulse. Two modes, hereinafter denoted a and b, of carrying out the second method are in common use today.

In mode a, the armature coil is divided into two parts by a center tap, and each half is connected with the output circuit of one tube of a two-tube push-pull amplifier system of well known character, such that the output current of one tube, due to the received impulse, moves the armature positively in one direction by energizing one of the coil halves in one direction, and that the output current of the other tube, flowing on ceasing of the signal impulse, flows through the other coil half, in the opposite direction, thereby positively moving the armature in the opposite direction.

lin mode b, instead of dividing the coil itself by a center tap, a resistance, tapped in the center, is connected across the coil. This center tap is connected to the laments of the two amplier tubes by way of a common plate battery. When current flows through one tube and one half of the split resistance, a shunt path for the plate current of that tube is established around that resistance half, and which includes the other half o the split resistance and the armature coil, both connected in series. When current flows through the other amplier tube, the reverse occurs, and the rst mentioned half of the resistance, with the armature coil in series, forms a shunt path to the second resistance half which is now traversed by the plate current of the second tube, the shunt current iiowing now in reverse direction through the armature coil. It will be noted, however, that in both instances the current owing through the coil can only be a relatively small part of the total plate current owing, and therefore, given a size of amplier tubes whose output currents would normally be sumcient to ((Cl. T38-88) operate an armature of a given coil size, the number of available ampere turns in such a coil in mode b is relatively small on account of the small shunt current. Unless the number of coil turns, and thus the size of the coil is correspondingly increased, not sufficient energy is produced in such a coil, commensurate with the available tube output. Enlargement ofthe coil on the other hand would make it in weight and size practically as large as a coil employed in mode a.

With each of these older methods and modes difficulties are encountered as soon as the impulses are transmitted at'high speed, in case of Morse code signals for instance at the rate of 300 words per minute and more.

At such speeds with the rst method the reaction of the armature and coil mass becomes so great, that a spring is unable to return the armature to its normal position after each impulse, and thus the armature ceases to exactly reproduce each individual impulse transmitted.

With the two modes included in the second method, where the armature isrnoved positively 'in both operating directions, the diiculty arises that with mode "a the armature coil with its two halves amounts in reality to two full size coils, one for operating the armature in one direction and the other for operating it in the other direction. Each of these coils is entirely inactive and amounts to mere dead weight, when the other coil is energized. By this dead weight the mass of the armature is increased to such an extent, that reliable and exact signal reproduction at operating speeds, such as mentioned above, is difficult to attain, if not impossible. With mode b the armature coil, for reasons stated, being just as heavy as in mode a, the same inertia diriiculties arise at high speeds.

According to the present invention these dimculties are overcome by using only one single armature coil equivalent in dimensions to one coil half used in the second prior art method mode 'l a, and by arranging the push-pull tube circuits in such manner, that the entire tube current due to the received impulse (marking current) tra verses the coil in one direction, and that the entire tube current, which normally ows after the impulse ceases (spacing current), ows through the same single coil, but in reverse direction, thereby positively returning the armature to zero position. By this double use of a single coil for both armature operating directions, and by the flow of the entire tube current through the coil in each case, the mass of the coil is only one half of the coil mass required in the second prior art methods aforementioned, and therefore the operating speed of the armature can be very materially increased to values such as aforementioned without impairing the clarity of the signal impulse reproduction. A

My invention is illustrated in the accompanying drawing, in whichz- Fig. 1 represents a wiring diagram of an arrangement for supplying a single recorder coil with two-directional impulses, 1

Fig. -2 represents diagrammatically a recorder coil shown at c in Fig. 1 arranged in a permanent magnetic eld and connected to the recorder arm, and l Figs. 3 and 4 represent modifications of the manner, shown in Fig. 1 at II for controlling the grids of the two output tubes for producing reverse currents in the armature coil. I

Referring to Fig. 1, 10 is the primary of a transformer into which amplified audiofrequency tone signals are supplied as shown, for instance two dots and one dash. The outer ends of the split secondary l1 of this transformer are connected respectively to the grids of a two-way rectifier tube system I, comprising the two multi-electrode tubes VR1. VR2 arranged in the conventional manner, so that at the common output side 12 the signals are delivered as full wave unidirectional current impulses as shown by the rectangular graph. The arrows in this graph indicate the direction of the impulses. Accordingly, if a recorder coil c, arranged in a permanent D. C. field as shown in Fig. 2 were connected to the output side 12 of the rectifler, as is customary in the aforementioned prior art method 1, the recorder arm a would be positively moved only in one; direction, and a spring would have to be provided to return the arm to the zero line 0 0 (spacing line of tape t) after each impulse.

Returning to Fig. 1, the output connection 12 of the rectiiier system includes an ammeter 13, which should respond only when signal impulses arrive. If this ammeter respondswithout actual signal reception, it indicates that parasitic noise currents which have strayed into the line are being rectified, which might seriously interfere with the correct operation of the recorder arm. In that case the grid biasing of the .two rectifier tubes is adjusted at the biasing potentiometer 14 until the noise indications at the ammeter disappear. The system is then sensitized above the noise level. A condenser C is arranged in the common output branch of both tubes, in order to smoothen out the ripples between the rectified pulse increments.

The rectified impulses are now supplied to an intermediate control circuit II, of which Figs. 3 and 4 are modifications,'and the purpose of which is to reverse the potential relation normally existing between the grids of output tubes V1, V2, when a signal is applied to transformer 10. This control means is termed in some of the claims as a grid phase changer, inasmuch as it changes the voltage phases of the output tube grids relatively to one another.

B'efore describing the intermediate grid control system II for the grids of the output tubes V1, V2, the output circuit arrangements of the latter are first shortly described. 'I'he anode circuits of these tubes are connected in series, i. e. the filament of tube V1 is connected to the its filament to cause the normal flow of anode plate of tube V2. At the output end of the entire system a relatively high voltage (for instance of the order of 500 V.) battery +B -B is provided, which is divided into three sections B1,

current, and grid G2 of tube V2 is correspondingly negative at that time with respect to its filament, normal output current can iow only through tube V1, and thus through coil c only in the direction of the full arrow. When the potentials of grids G1, G2 are reversed, normal output current only flows through tube V2 and through coil c in the direction of the dotted arrow. Therefore, if the grids G1, G2 of these tubes should be controlled so that each grid assumes automatically the opposite potential phase of the other grid, the presence and absence of a signal impulse can be used to cause full tube output current to flowl either in one or in the other tube,land thus in coil c correspondingly in one or the other direction, and to thereby cause the armature coil c of Fig. 2 to positively move in one or the other direction. Thus, the graph of the current delivered by the rectifier tubes VR1, VR2 shown, now assumes the character shown-at the output side of the system. The full line arrows in that graph may represent the full line arrow current direction through coil c and may represent the marking impulses due to arriving signal characters, which throw the recorder pen a, Fig. 2, into the marking position, and keep it there for the duration of the character (dot or dash). The dotted arrows in the graph represent the spacing impulses, being the current impulses flowing through coil c in the dotted arrow direction, and by ,which the recorder pen a is positively returned to the zero or spacing line 0 0 on the tape t, each time a signal impulse has ceased, and the pen is kept there positively during the absence of a signal (spacing period).

Thisautomatic control of the potential phases 120 of grids G1, G2 in accordance with the arriving signal impulses is accomplished by the intermediate grid control system or phase changer II which I shall now describe, first with reference to Fig. 1.

The two parallel plate circuits of the two rectifier tubes VR1, VR2 include as common current source the battery sections B1, B2, and part of B1, the connection 14a to the latter being adjustable. The circuit portion between +B andv the rectifier plates also contains a resistance 15. The grids of these tubes are normally biased by potentiometer 14 so that when no signal current flows through transformer 1,0, 11, no plate current can flow through eitherkectier tube, and so that for the duration of a signal a full wave rectified output impulse current will flow.

The phase changer system II consists in Fig. 1 of a multi-electrode tube, in this case a triode V13, the plate circuit of which includes the two battery sections B1, B2 and the resistance 16. The grid Gp of this tube is connected at'` 12 to the rectifier output circuit through the ammeter 13, Whose purpose has already been described. Owing to resistance l5 the bias conditions of this grid with respect to its filament are such, that normally, i. e. when no rectified output currents, due to signal impulses, ow through the rectier system, grid Gp remains suiciently positive with respect to its filament, to permit normal plate current to flow in that tube. This is due to the I fact that when no rectifier current flows, still a grid-filament current fiows in tube Vp by way of +B, 15, Gp, filament, -B2, which current produces a potential drop in resistance 15 which brings grid Gp to a potential slightly higher than the filament and thus permits plate current fiow in this tube. This would permit the use of very large resistances and correspondingly higher plate voltages, without thereby unduly increasing the potential difference between Gp and its filament beyond the normal values for the type of tube employed. With higher operating potentials and higher resistances the sensitivity of the system is greatly increased, i. e. for the same grid potential variations in the rectifier tubes, we obtain larger voltage drops in resistor 15, and thus larger voltage amplitudes on grid Gp.

If now, in such an arrangement rectified impulse currents flow in addition through resistance 15, the potential drop in the latter is increased sufiicientlyrto bring point 12 and thus grid Gp to a potential with respect to its filament, considerably less positive than before, and sufficient to stop the plate current flow in tube Vp.

VThis phase changer is connected to the output tubes V1 and V2 as follows: Grid Gp and the filament of tube Vp are connected respectively to grid G2 and the filament of tube V2, and the plate of tube Vp is connected to grid G1 of tube V1. Thus normally, with no signal impulse current flowing, grid G2 is as positive with respect to its filament as grid Gp is to its filament, and therefore full output current will flow in tube V2 and thus in the direction of the dotted arrow through coil c (spacing current), which current moves the pen arm a in Fig. 2 into the spacing lineIl 0-0 and holds it there during its flow. At the same time no output current can flow in tube V1, because its grid G1 is connected to the plate end of resistance 16, (its potential variations follow the same principle as explained with respect to resistance 15 and grid Gp) and the then flow- .ing plate current of tube Vp producesa potential rdrop inresistance 16 to bring grid G1 to a potential with respect to its filament, sufciently low to prevent plate current from flowing in that tube.

y co

If on the other hand a signal impulse arrives, and rectified impulse currents flow through the rectifier tubes, the grids Gp and G2 become less positive, and thus stop the plate current fiow in their tubes, so that spacing current stops flowing through coil c. At the same time, owing to the stop of plate current fiow through resistance 16, the potential of grid G1 rises sufficiently abovev its filament potential to permit normal plate cur-` rent to flow in tube V1 and thus through coil c in the reverse direction, shown by the full line arrow. This marking current immediately flows ,on the arrival ,of the ysignal and prevails4 for the5duration. of the signalrp-V l .gA fcenter zero ammeter 24.1I 's preferably connected infseries with coil,y c, which ammeter,

,- thoughiit cannot follow'A andindicate the rrapidly reversing currents in coi1;c,,will adjustitselff. in a, meanposition, which is ,in thecenter zero Point of the scale, provided .thetwo outputcurrents of,v w the tubesl flowing through..=c oil,cv are equal.f., By., 1. locally sendingv a few signals slowly and by'obp, `serving `this instrumentfthe two anodebatteriesl `B1.,,B2 can be properly adjusted to `-rnale the two 1 currents equaLso that'the coil pull on thepen arm a in Fig. 2 is equalfin both-directions,..;

f On cessation of-'the impulse ormarking cure` rent, iiow, plate current flow Yimmediately ,stops currents lflow :the `direction of v I tube V2 ismconnected to resistance R3 yat such a in tube V1 and spacing current flow starts in tube V2, and the pen arm a is thus returned positively to the spacing line 0--0 on tape t, where it ,remains so long as spacing current flows.

It will be observed that in such an arrangement any further increase in signal strength beyond a desired minimum value to which the rectifier response is adjusted, has no effect by way of increasing the output current strength in coil c, since an increased rectified signal current only biases the grids of Vp and V2 further negative and beyond the plate current cut-off values, which occurrence of course does not manifest itself in the output current strength of tube V1, which current is a local one, its strength being determined solely by the local adjustments to suit thepartcular receiving apparatus to which it is applied. Likewise, in the absence of signal current, the plate current flow in valves Vp and V2 is solely determined by the locally adjusted constants of the circuits, and thus the current strength of both output valves V1, V2 can in my improved system not only be made equal, but can be adjusted to` suit the requirements of the particular recorder in which coil c is installed, which is also an improvement over prior art systems.

The grid potential phase changing arrangement II for tubes V1, V2 of Fig. 1 may be modified in different ways, and some other practical forms will now be described. In these modifications the output circuits of tubes V1, V2 and the signal impulse rectifier tubes VR1, VR2 are assumed to be arranged substantially similarly, and are indicatedv in these modifications only as far as is required for the understanding of these modified forms.

In Fig. 3 this phase changing arrangement consists of two resistances R2, Ra connected in parallel across the power supply -l-B -B. The plate circuits of rectifier tubes VR1, VR2 are adjustably connected at l2 and 25 to resistance R2 to supply to these circuits current from source +B -B of a potential substantially similar to that at which current is supplied to these tubes in Fig. l. While structurally dif ferent, in effect the two arrangements of these rectifier tubes are equivalent.

The arrangement further includes a multielement vacuum tubeVp whose grid Gp is connected at such a point to the resistance R2 that it will be at a potential at which the normal operating current flows in its plate circuit, which latter includes a suincient portion of the resistance R3 so as to make use of as much of the voltage amplification of Vp as is practicable.

The grids G1 and G2 of the output tubes V1, V2 are l connected as follows. Grid G1 is connected adjustably to resistance R2v at a point which imcurrent to flow in. V1 .when no` rectified signal through resistance R2. This is the spacing current flowing through coilc in Fig. 3 in the dotted arrow. The grid G2 of *point as .will impart to-,this grid a potential 'with ,respect to itsfvilament to allow `the ullplate current to flow in V2 whensignal currentflfo'ws Vand Vwhen, tube Vpv isdrawing Ino plate" current; inf

other words, whenI a signal. of minimum "strength :to which ,the rectifier still" resp'ondsisI causing fa current toiiow through .the plate circuit of -t'he-,rectifier, which includes*` a portion fthe resistance R2, and which currentisof such`;in`l

in the absence of a signal impulse current, normal plate current iiows in tubes Vp and V1, and

therefore spacing current ows through coil c.

in the dotted arrow direction, grid G2 being then sufficiently negative so that no current flows in V2. vIn the presence of impulse current, grids Gp and G1 become suiciently negative to stop plate current ow in tubes Vp and V1. Thus grid G2 assumes a more positive potential with respect to its filament and allows plate current flow in tube V2, and through coil c in the reverse direction indicated by the full arrow which is the marking current of the system.

It will be observed that also in this modification the strength of the reverse currents flowing in coil c is, as in Fig. 1, entirely independent of the strength of the actually received rectified signal currents. y

In Fig. 4 is` shown a further arrangement for reversing the potential phase relation of grids G1, G2 of the output tubes in accordance with the received rectified signal impulses.

In this modification the output tubes V1, V2 and the armature coil c are arranged with respect to the power supply +B -B the same as in the other modifications described. Instead of using a multi-electrode valve Vp in the intermediate circuit for controlling the potential phase relations of grids G1, G2, a resistance R is arranged across the local power supply +B -B. The two-way signal rectifier system VR1, VR: is in itself arranged the same as shown and described with reference to Figs. 1 and 3, but its common plate connection 12 is in Fig. 4 variably connected to point e of resistance R. The filament side of the rectifier system is variably connected to point h of resistance R. Grids G1, G2 of the output valves are respectively variably connected to points f and g of this resistance.

By properly selecting the total value of resistance R with respect to the voltage of the power supply +B -B, and by properly relatively adjusting the points e, f, g, h, reverse current signal impulses are produced in coil c in the following manner. f

Assuming first that no rectified signal impulse current flows. Point f is adjusted so that in resistance R a potential drop from +B to f (due to the grid-filament current iiow in tube V1) brings point find grid G1 to a potential still suiilciently positive with respect'to the filament of V1 to allow normal spacing current to flow in V1 and through coil c in the direction of the dotted arrow. Point g is adjusted so that at that time sufcient potential drop exists between +B and g, to make the latter point and grid G2 negative with respect to the filament of V2 to prevent plate current flow in V2.

Assuming n ow that rectified signal impulse current flows in the rectifier system. Then we create a sufiicient potential drop between the resistance portion +B, e, which is part of the rectifier output circuit, to drop the potential at f and G1 to a value sufiiciently negative with respect to the filament of V1 to stop plate current flow in V1. At the same time the rectiiier plate current, returning through resistance portion h, B, produces a sufiicient potential drop in that resistance portion to raise point a, and

thus grid G2 to a sufiiciently higher ypotential to allow plate current flow through V2 and coil c in the direction of the full line arrow, which is the oppositely directed marking current. As soon as the rectified signal impulse current ceases to flow, the potentials of grids G1, G2 reverse again, and the output system is restored to the condition rst described.

It will be noted that in this comparatively much simpler system the nature of the potential control of grids G1, G2 is such that the strength of the marking currents flowing in V2 and coil c becomes dependent upon the strength of the rectified signal impulse current iiowing at the time, because the stronger the rectified impulse current, the greater will be the potential drop in h, -B,4 and the higher will be the potential of point g and grid G2, and therefore the larger the plate current in V2 and the ,marking current in coil c.

I claim:

1. A push-pull amplifier for producing successively reversing impulse currents, comprising a pair of thermionic grid controlled output valves` having a portion of their output circuits in common, and having their anodes connected by separate paths to opposite ends of said common portion, means for normally biasing the grids of said valves at oppositev potentials relatively to one another to produce a normal output current ow in one valve through said common circuit portion in a'given direction, and means for supplying unidirectional impulses through said grid biasing means to the valve grids, for reversing the normal grid polarities of the valves, to produce for the impulse duration a normal` output current flow in the other valve through said common circuit portion in the reverse direction and a utility device operatively associated with said common circuit portion, and responsive to said reversing currents.

2. A push-pull amplifier for producing successively reversing impulse currents comprising a pair of thermionic grid controlled output valves having a portion of their output circuits in common, and having their anodes connected by separate paths to opposite ends of said common portion, a grid phase changer for normally biasing the grids of said valves at opposite potentials relatively to one another to produce a normal output current iiow in one valve through said common circuit portion in a given direction, and means for supplying unidirectional impulses through said grid phase changer to the valve grids, for reversing the normal grid polarities of the valves, to produce for the impulse duration a normal output current flow in the other valve through said common circuit. portion in the reverse direction and a utility device operatively associated with said common circuit portion, and responsive to said reversing currents.

3. A push-pull amplifier for producing successively reversing impulse currents comprising in common, and having their anodes connected by separate -paths to opposite ends of said common portion, a phase changing thermionic mula pair of thermionic grid controlled output 'valves having a portion of their output circuits tielectrode valve having its grid connected to the grid of one of said output valves to maintain said two grids at similar potentials, and having its plate circuit connected to, and arranged to bias by its plate current flow, the grid of the other output valve at a potential opposite to that prevailing at the grid of the first mentioned output valve, whereby a normal output current flow in one of said output valves through said common circuit portion in a given direction is produced, and means for supplying unidirectional impulses to the grid of said phase changing valve, for reversing the normal grid polarities of said output Valves, to produce for the impulse duration a normal output current flow in the other output valve through said common circuit portion in the reverse direction and a utility device operatively associated with said common circuit portion, and responsive to said reversing currents.

4. A push-pull amplier for producing successively reversing impulse currents comprising a pair of thermionic grid controlled output valves having a portion of their output circuits in common, and having their anodes connected by separate paths to opposite ends of said common portion, a phase changing thermionic multielectrode valve having its grid connected to the grid of one of said output valves to maintain said two grids at similar potentials, and having its plate circuit connected to, and arranged to bias by its plate current iiow, the grid of the other output valve at a potential opposite to that prevailing at the grid of the rst mentioned output valve, whereby a normal output current iiow in onevof said output valves through said common circuit portion in a given direction is produced, and means for supplying unidirectional impulses to the grid of said phase changing valve, for reversing the normal polarity of said grid, whereby the normal grid polarities of said output valves are reversed and, for the impulse duration, a normal output current flows through the other output valve and through said common circuit in the reverse direction and a utility device operatively associated with said common circuit portion, and responsive to said reversing currents.

5. A push-pull amplifier for producing successively reversing impulse currents comprising a pair of thermionic grid controlled output valves having a portion of their output circuits in common, and having their anode connected by separate paths to opposite ends of said common portion, a phase changing thermionic multielectrode valve, having a grid biasing circuit forl normally biasing its grid sufficiently positive with respect to thefilament to permit normally plate current to ow, and having its grid connected to the grid of one of said output valves to maintain said two grids at similar potentials, a grid biasing circuit for the grid of the other output valvearranged to normally bias said grid suiciently positive with respect to its filament to permit plate current iiow through said output valve, a circuit connection between the plate circuit of said phase valve and said last named biasing circuit, and means for producing by the phase valve plate current a negative grid potential at said other output valve, whereby a normal output current flow only in the first output valve through said common circuit portion in a given direction is produced, and means for supplying unidirectional impulses to the phase valve grid biasing circuit, for applying a negative potential to said phase valve grid to interrupt the plate current flow of said valve, whereby the normal grid polarities of said output valves are reversed and, for the impulse duration, a normal output current flows only through the other output valve and through said common circuit in the reverse direction and a utility device operatively associated with said common circuit portion, and responsive to said reversing currents.

6. A push-pull amplifier for producing successively reversing impulse currents comprising a pair of thermionic grid controlled output valves having a portion of their output circuits in common, and having their anodes connected by separate paths to opposite ends of said common portion, a phase changing thermionic multielectrode valve, means for normally biasing the grid of said phase valve and the grid of one of said output valves to permit plate current flow respectively through said phase valve and through said output valve and said com-- mon circuit portion in a given direction, a second biasing means connected to the grid of the second output valve for normally biasing said grid to permit plate current ow through said second valve and said common circuit portion opposite to said given direction, a connection between said second biasing means and the plate circuit of said phase valve for reversing by the phase valve plate current flow, the polarity of the second valve grid to stop plate current flow in the second valve, and means for supplying unidirectional impulse currents to said first biasing means, for varying during the impulse current flow the polarity of said phase valve grid and the rst output valve grid sufficient to stop plate current flow in said last named valves, whereby, during the absence of impulses currents, output current ows through said common output circuit portion in said given direction, and in the presence of impulse currents output current ows through said common portion in the reverse direction and a utility device operatively associated with said common circuit portion, and responsive toA said reversing currents. y

'7. A push-pull amplier for producing successively reversing impulse currents comprising a pair of thermionic grid controlled output valves `having a portion of their output circuits in common, and having their anodes connected by separate paths to opposite ends of said common portion, and an output power supply for said valves, a phase changing thermionic multielectrode valve, a iirst biasing resistance connected across said power supply, the grid of said phase valve and the grid of one of said output valves being connected to said resistance at points at which normally potentials prevail at which said grids permit plate current flow respectively through said phase valve and through said output valve and said common output circuit portion in a given direction, a second biasing resistance connected across said power supply and a connection between the grid of the second output valve and a point on said resistance at which normally a potential prevails at which said grid permits plate current flow through said second f Valve and through said common circuit portion, but opposite to said given direction, a connection between said second resistance and the output circuit of said phase valve for producing by the plate current iiow of the latter suiiicient potential drop in said second resistance to vary the potential of the second output valve grid sufficiently to stop output current flow through said second valve, and means for supplying unidirectional impulse currents through said first4 resistance for varying, due to the potential drops produced therein, the polarity of the phase valve grid and the rst output valve grid sucient' to stop plate currentl flow in said last named valves, whereby, during the absence of impulse currents, output current ows through said common output circuit portion in said given direction, and in the presence of impulse currents, output current ilows through said common portion in the reverse direction and a utility device operatively associated with said common circuitportion, and

\ responsive to said reversing currents.

8. A push-pull amplier for producing successively reversing impulse currentscomprising a pair of thermionic grid controlled output valves having a portion of their. output circuits .in common, and having their anodes connected by separate paths to opposite ends of Asaid common portion, and an output Vpowersupply for said valves, a biasing resistance connected across said power supply, a connection between the grid of one output valve and a point on said resistance at which normally a potential prevails at which said grid permitsputput current to flow in said valve and through said common output circuit in a given direction, a connection between the grid of the second output valve and a point on said resistance at which normally a potential prevails at which said second grid prevents output current ow in said second valve and through said common portion, and means for supplying rectified impulse currents through said resistance, whereby potential variations are produced at the several grid connection points on said resistance, sufiicient to reverse the relative potential values .of said grids, so that in the presence of impulse currents an output current ows only in the second valve and through said common circuit portion, but in a direction opposite to said given direction and a utility device operatively associated with said common circuit portion, and responsive to said reversing currents.

9.A push-pull amplifier for producing successively reverse impulse currents, comprising a pair of thermionic grid controlled output valves, having a portion of their output circuits in common,

and an operating coil in said portion, and having theiranodes connected by separate paths between .the two ends of said coil, -so that the output cur- 4rents-of the valves flow in opposite directions through said coil, and an output power supply for said valves, a grid biasing means connected across said power supply and to the grids of said valves, and normally adjusted to apply 'to one a pair of thermionic -grid controlled output valves, having a portion of their output circuits in common, and an operating coil in said portion, and having their anodes connected by separate paths between the two ends of said coil, so that the output currents of the valves ow in opposite directions through said coil, and an output power supply for said valves, adjusted to produce in each valve a current flow of normal strength, a multielectrode thermionic phase valve having its output circuit connected to said power supply and having means for normally applying to its grid from said power supply a grid bias which permits output current iiow in said phase valve, a connection between the grid of the iirst output valve and the grid biasing means of said phase valve for applying to the tlrst output valve a grid bias permitting output current of normal strength to iiowl when output current ows in the phase valve, a connection between the grid ofthe second output valve and the output circuit of the phase va1ve for applying to that grid a potential '-10 which willstop output current flow in the second;y valve due to a potential drop caused by the output current ow in the phase valve, and means for producing unidirectional impulse currents,

connected to said phase valve grid-biasing means 415 for reducing by the impulse current flow the bias potentials produced by said biasing means, to stop output current ow in thi7 phasevalve and in the first output valve, whereby the grid potential of the second output valve is sufficiently increased to permit output current of normal strength to iiow during the impulse current ilow and irrespective of the strength thereof.

FRANK KUNG.

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