US2071759A - Electron discharge tube system - Google Patents

Description

Feb.'23, 1937. N. MINORSKY ELECTRON DISCHARGE TUBE SYSTEEM 5-Sheets-Sheet 1 Filed June 25, 1926 FIG: I.

' LYVEN OR. Nicolai mmorsioy, B y

1 WITNESSES:

@ziwzafl ATTORNEYS.

Feb. 23,1937. I N. MINORSKY 2,071,759

ELECTRON DISCHARGE TUBE SYSTEM Filed June 25. 1926 5 Sheets-Sheet 2 .FJZC-E K WITNESSES: :19 INVENTOR:

ATTORNEYS.

Feb. 23, 1937.

-N. MINORSKY ELECTRON DISCHARGE TUBE SYSTEM Filed June 25, 1926 W TIYESSES:

5 Sheets-Sheet smmvrom JYMZMJ m'zwrsiiy,

ATTORNEYS.

Feb. 23, 1937. N. MINORSKY v 2,071,759

ELECTRON DISCHARGE TUBE SYSTEM 'Fild June 25. 1926 5 Sheets-Sheet 4 I FIQJLC INVENTOR.

Nicolai Minofsky,

A T'TORNEYS Feb. 23, 1937. N. MINORSKY ELECTRON DISCHAR GE TUBE SYSTEM Filed June '25, 1 26 5 Sheets-Sheet 5 Q x a Q Q NH QN N q H mm v I. N \N M w MMW MMN PW 'HHHHHI I INVENTOR. Nicolai Minors WW ATTORNEYS;

WITNESSES .the filament to change its potential from the- Patented Feb. 23, 1937 UNlTED I STATES PATENT OFFICE- ELEO'IRON'DISCHARGE TUBE SYSTEM Nicolai Minorsky, Narberth, Pa., assignor to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application June 25, 1926, Serial No. 113,508

12'0laims.

systems was the necessity for many 3 and verylarge grid batteries, which are diflicult to adjust when several stages of amplification are used.

The present invention resulted from work designed toward eliminating diflicultiesinherent in former systems, and incidentally provides a tube system with entirely new properties differing from those of an ordinary amplifier. Under certain conditions, the system behaves abruptly, similar to the action of an electric contact. switch.

It is further found that by its use, an electron dischargetube is associated with circuits in such a way that both the grid and the filament may change potentials; and in particular the grid is caused to change its potential from an input, and

output of the tube, so that a regenerative effect may be obtained, either directly or reversely as the direction of change of potential at the grid may. be established.

A res istance coupled amplifier circuit tubes, in-which-the tubes receive their space current and grid biasing potentials from a common direct current source, in such manner that the regulation of the tube circuits produces reactions from this common source and its associated elements upon the tube circuits themselves, whereby the cumulative or regenerative effect is obtained.

A peculiar feature of this invention is the fact,

as set. forth above, that the tube systemhas the characteristic of acting, under certain circum-- stances, as an electric contact switch rather-than in the usual continuous or gradual manner of electron discharge tube circuits: this is hereinafter termed the contact effect, as by it a dis continuous and instantaneous circuit-making and circuit-breaking performance may be produced,

similar to the action of an electric contact is provided having a? plurality of electron discharge switch. This phenomenon may be employed in controlling and regulating apparatus associated with such a circuit, whereby an instantaneous and decisive action may be obtained at a pre-' determined and adjustable point, and substantial quiescence or continuity of action at other points. To this purpose, the circuits are provided to establish a single point of stability in the output of'the system at each of a plurality of applied grid potentials, and these individual values for stability are separated by graph distances corresponding to a large space current variation in the tube as it passes from one grid potential differing very little from the first.

This invention may be employed in conjunction with various electrical controlling systems, in which a supervising instrument such as a bolometer, a thermostat or'thermometer, a pres- [sure gage, a Pitot or Venturi tube, a photoelectric cell, or other hydraulic, centrifugal electrical, mechanical or optical device is employed to govern an electric circuit including a regulator such as a trip-out relay, voltage or current regulator for a direct or alternating current generator, speed controlling device, etc., whereby the regulation is accomplished.

The invention is illustrated by way of example in the accompanying drawings, which demonstrate the circuits employable and several applicationsof the phenomena produced thereby, to theregulationof electrical machinery: but it will be understood that these illustrations are not limitations.

In the drawings:

Fig. I is a circuit diagram of the arrangement of a system according to the invention, having three three-electrode electron discharge tubes.

' Fig. II is a graphic diagram of a phenomenon which may be produced in the circuit of Fig. I. Fig. III is another graphic diagram illustrating the principle of the phenomenon.

Fig. IV is a further graphic diagram illustrating the result of the phenomenon when the circuit is associated with a regulator for an electric generator.

I Fig. V is a circuit diagram similar to Fig. I, with the tube system employed to regulate a direct current generator.

Fig. VI is a modification of the circuit shown in Fig. V. v

Fig. VII is a circuit diagram of the application of the invention to the regulation of an alternating current generator. I

Fig. VIII is a graphic diagram illustrating the I5. The filaments 4, 5, 6 are therebymaintained O rectifying and regulating eflect of the apparatus shown in the diagram of Fig. VII.

Fig. IX is another circuit diagram of an arrangement similar to that of Fig. VII.

Fig. X is a circuit'diagram resembling Fig. I, in which the speed of an electric motor is supervised and controlled.

Referring to Fig. I, the'electron discharge tubes I, 2, 3 have the filamentary cathodes 4, 5, 6; the grids 1, 8, 9; and the anodes I8, II, I2. The tubes I and 2 are preferably high amplification tubes, while the tube 3 is a power tube. The filaments 4, 5, 6 are heated by individual sources of electricity, such as the separate secondaries I3, I 4, I of the transformer whose single primary winding 5| is connected to an alternating current supply main 58.

The potentiometer I1 has the end terminals I6 and I8 across which is applied a direct current from a source of such energy, e. g., the generator I9. The cathodesor filaments 4, 5, 6 are connected respectively to the points I6, 28', 2I on this potentiometer by the respective conductors 52-, 53, 54 which, with the illustrated employment of an alternating heating current, are connected to the middle points of the secondary windings I3, I4,

at negative potentials; filament 4 being at the negative potential of generator I9, while filaments 5 and 6 may have their potentials varied by sliding the contacts 28, 2I along the potentiometer I1.

The anode circuits of the tubes I, 2 are connected by wires 55, 56 through the respective fixed resistors 24, 25 to the points 22, 23, which represent sliding contacts on the potentiometer I1.

The points 26, 21 intermediate the anodes-I8, II

and the resistors 24', 25 are connected by wires 51, 58 to the grids 8, 9 of the succeeding tubes 2, 3, in their respective relations. The anode I 2 of the tube 3 is connected by wire 59 through a coil 28" to the end point I8 of the potentiometer I1 which is at the positive potential of the generator I9. The coil 28 constitutes the output of the system, and maybe the field coil of an excite'r; the trip coil of a relay, etc.

The staggering of points I6, 28, 22, 2| with regard to each other eliminates the necessity of having biasing'batteries, but requires the use of separate sources of heating current.

The grid 1 of the tube I is connected to a terminal 29; and the input potential for the system is applied between points I6 and 29. In order totromotive force of a battery 38 applied across them, as regulated by the potentiometer 3 I, since generally the grid 1 must be biased at a certain negative potential with respect to the point I6 or the filament 4. The potential applied across points 29 and I6, by slight variation at the critical condition of the system, produces the phenomenon of the contact effect, and this potential will therefore be hereinafter called the trigger voltage.

The tube I is normally at the potential difi'erence between points 22' and I6 on the potentiometer I1; the tube 2 at the potential difference between points 23 and 28; and the tube 3 at the potential diflerence between points I3 and 2I.

These potential differences 22'I6, 23-28, I8--2Iv are staggered with respect to each other by the amounts corresponding to the. potential drops across the overlaps 28-I6, 2I28, respectively.- By moving the sliding contacts, it is possible to, so control these differences as to eliminate the 350 volts.

necessity for grid biasing batteries between point 26 and the grid 8 on the one hand, and between point 21 and the grid 9 on the other.

If desired, the current from the generator or source I9 may be kept constant by a ballast device I9 of well known type.

The system shown in Fig. I may be operated in any one of three ways: (1) as a resistance-coupled resistance is very high, so that the plate currents therein are generally negligible as compared to the plate current of the power tube 3, which itself must be negligible as compared to the current flowing through the potentiometer I 1: in such event, changes in the several plate currents, or in any of' them, will not cause any appreciable change in the distribution of current along the potentiometer.

In an actual test, the potentiometer I1 had a total resistance of about 350 ohms; the generator I 9 delivered a steady potential difference of about The tubes I and 2 were Western Electric type 102-D tubes, and tube 3 was a Western Electric 101-D power tube. The plate resistors 24 and 25 were each of about 200,000 ohms. The tube I worked under the potential difference between I6 and 22, and tube 2 under that between 28 and 23, which were staggered so that the controlling point 26 of tube I was about 1 volts below the potential of the filament (point of the second tube, which corresponds approximately to the middle point of the rectilinear part of its characteristic. The alternating current mains 58 were fed by 110 volt, 60 cycle current. Thus the plate currents in tubes I and 2 may be of the order of 1 milliampere or less; the plate current in tube 3 of the order of 2030 milliamperes; and the potentiometer current 1 ampere.

Assuming that the potential of the grid 1 of tube I is increased by a small amount inany way, e. g., by moving the sliding contact of the potentiometer 3|; the increased potential of the grid 1 will cause an increased space current to fiow between filament 4 and anode 18 of the tube I, witha resultant decrease of the potential of the point 26 and at the grid 8 of the tube 2. The space current in the tube 2 will decrease, so

that a correspondingly increased potential will be applied at point 21 and the grid 9 of the tube 3. The space current in the tube 3 will accordingly increase, and hence the plate current flowing through the output coil 28. In the instance above, the plate or output current variations in tube 3 will be of the order of or 30 milliamperes.

The amplification obtained is linear, i. e., a small variation of the input voltage on tube I will produce a proportional variation of the plate current of tube 3, provided the sliding contacts 28, 2|, 22, 23 have been located at such positions that the initial point of performance is approximately at the middle-oi the rectilinear portion of the characteristic curve o i' the respective tube.

When'the points 28, 22, 2. are once adjusted,

may readily be calculated in the known way.

2. If the plate current variations of the power tube 3 are approximately of the same order of magnitude as the current, flowing through the potentiometer, for example the current through the potentiometer being about one hundred milliamperes and the plate current variations of the tube '3 around 20-50 milliamperes, the tube 3 constitutes a variable resistance connected in parallel with the section 2I--l 8 of the potentiometer N. Then, by Kirchofis laws, for the parallel resistances (tube 3 and section 2l-I8) in series with the section 2I-'-|6 of the potentiometer, a decreased resistance .of the tube 3 will cause an increase of the current flowing between points I6 and 2|, so that the potential at point 2| increases in' proportion. Likewise, the potentials of points 20 and 22 increase and the potentialdifference between points 2| and I3 decreases, in proportion. This redistribution along the potentiometer causes important reactions upon the tubes in the system.

Firstly, the effect of variation in the plate current in tubes I and 2 upon the potential and current distribution along the potentiometer I1.

the tube 2 decreases. The increased conductance of the tube 3 causes the redistribution ofpotentials indicated above, and the potentials of thepoints 20,:2I, 22, become more positive. The filament 5 is connected to point 20, and its potential is accordingly increased. The space current in tube 2 therefore decreases because (1) the grid potentia becomes more negative, and (2) 'the fllament p ential becomes more positive. This constitutes a distinctive feature of the invention and contributes to produce a greater increase by amplification than is the case when the potential of the filament remains constant, and gives the regenerative effect, since the filament potential of tube 2 depends on the current flowing in the succeeding tube. The opposite effect is obtained in the tube 3, so that when the potential of the grid 9 increases, the potential of the filament 6 also increases, so that the amplification in the tube 3 is slightly decreased. The final eifectwhen -three tubes are-employed, as shown in Fig. I,

is a gain of amplification because the gain in the tube 2 considerably outweighs the loss in the tube 3. The first tube is not in such'case affected by the regeneration; as its filament 4 is maintained at the fixed potential of the point I6. In case more than three tubes be connected in a similar manner, there will always be a gain of amplification, since the regenerative eflect in each subsequent tube will be less than that inthe' preceding tube, and there is always a gain in the second tube where the regenerative eflect first appears: and

the same gain of amplification is obtained if only two' tubes be employed, thesecond being'a power tube, although the result is notthen so apparent as with three tubes.

3. The third method of operation is the most' important, and constitutes" an entirely new method of employing electron discharge tubes with associated circuits. This method is a fur- The space ther development of thesecond, in which the amount of regeneration is increased above a certain criticalvalue, whereby the performance of the system becomes abrupt and discontinuous;

there is a substantially instantaneous passage from a condition at which a certain amount of plate current flows through the output coil to a condition at which a widely diiferent amount flows, and this passage is provoked by a very small change of the applied potential. These amounts of current remain fairly constant when the applied potential departs in the respective direction from this critical value. The abrupt eflect greatly resembles that of a contact switch in making or breaking a circuit; and hence is called the "contact eflect.

.the same critical value whether the input potential is increasing or decreasing in value.

lIl

It usually occurs at substantially j This is represented by the graphic diagram of I Fig. II in which the plate current in tube 3 and the applied grid potential on tube I are plotted as coordinates. If the grid potential on tube I be originally negative, and be steadily increased from a value A to a critical value B, the plate current in the tube 3 changes but very little in passing from the value K to the value N. A discontinuity however occurs at the critical value B, so that a further increase of grid potential in the tube causes the plate current in tube 3 to jump abruptly from the value N to the value M, which generally is that of the saturation current in the tube 3. A further increase of applied grid potential on tube I to the value .0 produces substantially-no further change of the plate currentv in passing from the point M to the point Q.

When the applied grid potential on tube I is decreased from an initial value C, an inverse action occurs. As the potential approaches a critical value B which is very close to the critical value B with an increasing grid potential, the plate current abruptly drops from the value M which is substantially equal to the value Q, to a value N. A further decrease of grid potential from the value 13 to the value A produces substantially no further change of the current. The points M, M and N, N are very close together,

and respectively represent substantially the same current values. In practice, it has been found possible to make the zone B-B' very narrow, and

its position'within the range A-C may be varied at will.

In an actual instance, this potential difference I was varied from 5 to 20-30 millivol 14nd in one particular instance was reduced to 0.1 millivolt; witha plate current variationin the last stage of about 3540 milliamperes in each case. The

potentiometer I! had a resistance of about 3500 ohms, resistors 24, 25 about 200,000 ohms each. and the grid bias potentials were about 1% volts as before. 'The phenomenon is very erratic when the grid potential lies between B and' B: There a is no actual grid control and the plate current moves from high to low value upon the occurrence I of extremely slight changes.

The slightest increase at B, or decrease at B acts as a'trigger to release the "contact eflect".

The position of this range B'B may be shifted f to another place by changing the staggering 01 the fllament;potentials, by changing the plate resistors 24, 25, etc.; but forgiven parameters, it is constant to a remarkable degree of precision, and the discontinuity always occurs at a strictly identical point of the grid voltage of the first tube.

This contact effect" appears to require no spontaneous alternating current self-excitation, though of the same nature as the self-excitation of a. shunt-wound direct current generator.

When a generating and a receiving circuit ex,-

change energy, the equilibrium may be defined as stable when a small departure of the system from this equilibrium position disappears spontane- In Fig. III, the curve G is plotted from the plate current I and the grid voltage V; of the tube 3 of Fig. I; and the straight line P represents the effect of the reaction to the potentiometer due to the variationof the plate current in the tube 3. This variation appears as explained above as a variation of the filament potential of tube 3, i. e. as an equivalent opposite variation of the grid potential of this tube, and can therefore be represented on the same diagram as the characteristic curve G of this tube. In this case G is the generator curve, and P1 and P2 the receiver curves:

At N, the slope of G is less than the slope of Pi,

and the system is stable, and the same is true at M with respect to P2.

The theory shows that for a variation of the grid potential of tube I there is a displacement of the straight line substantially parallel to itself from P to P Line P intersects the curve G only at the point N, while line P intersects it only at the point M: these points N and M in Fig. III correspond to those in Fig. II. Although generally lines P and P are curved'instead of straight, the same remarks hold: and the maximum sharpness occurs when the shapes of the curves P P are substantially identical with the shape of the curve G, in which case it is sufflcient to give the slightest change at B or B in Fig. II to the grid potential of tube I to release the phenomenon through the whole range from N I to M in Fig. III, or vice versa.

' The- tubes 2 and 3 therefore have a mutual controlling action upon each other; when one is a maximum, the other is at a minimum, and vice versa, In practice, it is preferable to have one or the other at a saturation value at all times.

.When tube 2 is at. saturation, the tube 3, with its opposite characteristic in the circuit system of the present invention, is delivering a constant current of minimum value (i. e. the graph from K to N in Fig. II) and when tube 3 is at saturation, (graph from Mto Q in Fig. II) its reaction upon tube 2 reduces the current in this latter tube to a minimum. Hence thetvalues of current output from tube 3 are dependent upon the saturation currents in tubes 2 and 3, and are substantially constant at a maximum or a-mmimum.

The contact effect" therefore occurs where the electron discharge -tube is-associated with circuits which afford at two widely separated positions stable current equilibrium separated by a zone of instability, and whereby the passage from one position to the other is accomplished by means of a very small variation of applied potential which displaces the receiver curve from its position P determining current stability att e value N to the position P determining such stability at value M.

It may be stated that osclllograms show that the time for passage from N to M or from M' to N is of the order of one two-thousandth of a second.

strate the method of obtaining the contact effect", and hereinafter a number of applications of this contact effect to the regulation and.

control of mechanisms will be described.

Fig. V represents the application of this contact effect to the voltage regulation of a direct current generator 34.. The, electron discharge tube system and its circuits have the same reference characters in Fig. I, and the output of the last tube 3 passes'through the coil 28 which in this instance is the field coil of a direct current exciter 35 which is connected by the conductors 60 with. the auxiliary field 36a of the generator 34. It will be understood that the generator 34 may have the customary main fields 36. The control winding 36a has a sufficient value in ampere-turns to counteract the'eifect of the armature reaction in the generator 34 during the regulation. Connected in parallel across the generator terminals 38, 38 is a source of reference voltage 31 such as a battery whose voltage may be maintained very nearly constant, and the purpose of which is to determine the magnitude of the voltage to be maintained-by the generator 34 at all loads. The negative terminal of the source 31 is connected tothe negative terminal 38 of the generator 34; and the positive terminal of the source 31 is connected to the grid 1 of the tube I, while the end terminal I6 of the poten tiometer I1 is connected by a conductor 6| with the positive terminal 33 of the generator 34. It is preferred to connect a small regulating battery 30 in shunt of a potentiometer 3| in the circuit between the reference battery 31 and the grid 1 of the tube, so that the exact potential of the batteries 31 and 30 may be closely regulated. The load on the generator 34 is conventionally represented by the lamps 42. I

The operation of this voltage regulating system is as follows: E

Assuming that initially the-generator is at a condition of no load and that its terminal voltage is exactly equal to the electromotive force of the source 31. The potentiometer 3| for this particular position must be adjusted so as to imthe voltage of the generator 34.is determined by the main winding 38.

If a load 42 is placed upon the generator, its terminal voltage decreases and no longer annuls the effect of the reference battery 31; the grid I voltage of the tube I increases accordingly and goes beyond the critical value B in Fig. II. In passing the value B the plate current abruptly jumps from the value N to the value M, releasing the transient: in thisv way, the plate current of the tube 3 flowing through the output coil 28 is suddenly increased in value, whereby the exciter 33 will deliver current through the conductgr 30 and the auxiliary winding 36a of the generator .34, with a resultant increase in the voltage from the generator. As this generator voltage increases, it will restore the mains to the initial condition of predetermined constant voltage. On the other hand, when the voltage of the generator increases in proportion to the reference voltage until they are equal to each other. again, which is equivalent to the decrease of the applied grid voltage on tube I from C to beyond B in Fig. II, the reverse phenomenon occurs and the current flowing through coil 28 'now drops from the value M to the value'N", so that the auxiliary winding 36a no longer receives current from the exciter 35, and the generator again is excited by its main winding 36 alone.

This action resembles that of a Tirril regulator of the well known type employing vibrating switch contacts: oscillation will usuallyoccur in the same manner as with this device. Such'oscillation is represented in Fig. IV, in'which' the upper graph a represents the fluctuation of the current through the coil 28 and the middle graph b represents the corresponding fluctuation of the voltage across the generator terminals while the lower graph represents the load on the generator. If at a certain instant S the generators output increases from to Ii, the plate current through thecoii 28 will remain atits maximum value for a slightly longer time than at its mini- 30 mum value, but the voltage E of the generator will maintain'substantially the same value as be-. fore, with but a slight minimum fluctuation. If at a time T, the load is increased to a greater value 12, at which the current through the coil 28 continues, this particular value I: of generator current correspondsto the maximum range of the regulator, beyond which it cannot maintain a constant voltage E across the generator terminals. If at a certain time U, the load on the 4o generator. is further increased to the value I3,

the regulator cannot deliver a greater excitation than for the current value 12, and a drop of voltage across the generator begins at this point. The regulator thus has a well defined rangewhich varies according to the constructional dimensions given the parts, and may be made adequate for any particular purpose.

It is apparent that the connections shown on Fig. V between the positive terminal of the gen- 50 erator 34 and the filament 4 on the, one hand, and. between thepositive terminal of the source of reference voltage 31 and the gridff'l on the other hand may be reversed with regard to each other if the connections 01, the auxiliary fieldwinding 36a. be reversed with regard'to the terminals of the exciter 35. In a similar manner, the condition represented on Fig. IV may be modifled in various ways, and for example, its performance shown at theleft from the point S 4 may be made to correspond to the full'load condition, and its performance represented between the points T and U will correspond to the position of no load; in which case the action of the coil 28av must be diflerential with respect to that of the main field winding 36 of the generator 34.

Many other connections and combinations of a the above described elements are of course possible without departing from the general method of regulation shown in Fig. IV. Instead of obsource as the battery 31, it is possible tO' obtain it from the potentiometer H as shown in the diagram of Fig. VI. In this only two tubes "are employed, representing the second and third 7 tubes in the circuit of Fig.1. The fi ament 5 taining the reference voltage from a separate of tube 2 is shown in Fig. VI as being connected to a point 20, which is separated from the negative terminal l6 of the potentiometer I! to obtain a potential difference equal to the ohmic drop between these two points. The negative terminal 38 of the generator 34 is connected to the point It, and the positive terminal 39 to the grid 8 of the tube 2 by a conductor 62. The

potential difference between the points l6 and 20, will maintain the grid potential of tube 2 normally while the terminal voltage to the generator 34 supplies the small; voltage necessary to counteract. this and to produce. the potential at which the contact.efiect is released. In this case, the potential difference between the points 16 and 20 will act as. an adjustment thereof may be made by sliding contact 2IL along the potentiometer. The method of operation of the circuit in Fig. VI is therefore as follows:

Assume that initially the generator voltage 38-39 is slightly below the critical voltage 3 ,at which the contact effect" is released in the system formed by the devices 2 and 3. If the \voltage of the generator 34 increases, the potential of the grid 8 of the tube 2 will be increased and the contact effect will be released, the current jumps to the full saturation value in tube 2, and'for reasons previously explained, the current in the tube 3 will drop abruptly to a low the reference voltage, and

' Fig. V, and thus diminish the excitation of the auxiliary field 36a of the generator 34. As soon as the voltage of the generator 34 decreases by a very small amount, the effect is produced in the opposite direction. The equilibrium at the point of given voltage will thus be dynamical as in the above case, although an arrangement according to the diagram of Fig. VI will be less sensitive than that of Fig. V, since not only is a lesser number of stages employed but also the potential of the filament of tube 2 (point 20, on the potentiometer l1) increases at the same time that the plate potential is increasing, and vice versa; it is, however, sumcient for practical industrial purposes.

It is possible to obtain the utmost precision of' voltage regulation with the employment of an additional tube l in front of tube 2, according to the general diagram shown in Fig. VI. For this purpose, the arrangement is made specifically the same as in Fig. I, except that the staggering of the potentials between the points l6 and 20 will occur as in Fig. VI..

VII shows another example for the voltage regulation by an alternator 34 'utilizing the same principle of the contact effect. The load 42 is supposed to be balanced between the phases, as is usually the case, so that it is suflicient to regulate the voltage of only one phase. A small potential transformer, with a primary winding 48' connected across one phase of the alternator, has a secondary connected at one terminal to the point It or the potentiometer II, the other end of this transformer secondary being connected to the grid 1 of the vacuum tube l which in this instance operates as a rectifier since suitable negative bias isobtained on the grid of this tube by the potential difference between the points l6 and I6, oi. the potentiometer I]; in order to obtain the direct current control required for the release of'the transient or contact effect, the

plate circuit of the tube I may contain any suitable filter system comprising the inductance 4i in series with the coupling resistor 24, which is 6 connected at eachend by the condensers 42, 43 with the terminal IS. The remaining elements are connected exactly as before, and the performance and operation may be explained in connection with Fig. VIII, in which H represents the represents the potential drop between points [6 and Iiiv of the potentiometer H. The wave K produces a rectified wave is which is smoothed out by the filter system so as to obtain a practically steady direct current of amplitude In which passes to the resistor 24 and the potential of the point 26 differs from that of point 22 by the ohmic drop of this current along the resistor 24.

The potential of the point 26 is therefore'substantially constant, and varies only with corresponding variations in the potential wave X. If the potential at the, generator rises to the new value K on Fig. VIII, a new rectified wave k is produced which in turn is smoothed out by theifilter system so as to obtain the direct current of amplitude I through the resistor 24. If the constants-of the circuits of the several tubes are properly proportioned, as set forth above, this rise of potential will release the contact efiect" or transient as before: and again a very small change in the amplitude of the potential wave at the generator will produce a very great change in the current output of the system, and this 00- curs at a very fixed and constant point of the operation when once established. A steady voltage is therefore maintained across the alternator terminals in spite of any fluctuations of the load.

In Fig. DI, such a system is employed to control the excitation of a three-phase alternator in accordance with the condition of the loads upon all three phases, In this case the voltage regulating transformer has the primary phase windings 40, 40 40 associated with the respective secondary phase windings 40, 40 40 which are each coupled to the grid of a respective tube I, I, I". Thefilaments of these tubes are-supplied in multiple with current from the secondary winding 13 of a transformer with its primary II connected to a source 50. The middle point.

of winding I3 is connected as before toa point '6 on the potentiometer l1, so that'the control potential is determined by the drop along the potentiometer I! from point l6 to point It. The tubes I, l I act as rectifiers, and the current passing through each of them is smoothed out by the choke coils 4|, 4l 4| and the bypass condensers 10, 10, 10 for the respective tubes, and the condenser 1| for the common output. It is preferred to connect this common output through a further choke coil 4| to the grid of the tube 2 in a manner similar to that described heretofore. The neutral point of the secondary windings 40", E0, 40 is connected to the negative terminal l6 of the potentiometer. The operation is substantially the same as before, and the potential at the common output point 26 of the tubes I, I, l controls the restof the'system. The other connections are the same as before.

While the foregoing illustrations have shown the employment of such a system for regulating output potentials in generators, it must he stood that many other uses are possible. ,For example, in Fig. X is shown a system employed forthe speed regulation of an electric motor-J30. The field coil 8| of this motor is its nor al shun under biasing potential on the last tube of the series,

time the motor departs in speed in one direction or another from its predetermined value, even if by only a small amount.

It is clear that any other device may be employed to impress varying potentials upon the grid of tube I, and that the system may be so regulated that at a predetermined value of potential, a very small change will cause a very great change in the output current of the tube 3, i. e. the contact eifect".

Although specific examples of the arrangement and connection of the various parts, and dimensions thereof, are given by way of examples which have been found operative in practice, yet it will be recognized that the invention is not limited to these illustrations, but may be modified within the scope of the appended claims.

Having thus described my invention, I claim:

1. In a system employing a plurality of electron discharge tubes each having a cathode, a grid and an anode, independent means for exciting said cathodes, a, potentiometer, a source of current connected to the ends of said potentiometer, a ballast device in series with said source and potentiometer arranged to maintain the direct current therethrough substantially constant, intermediate taps on said potentiometer, and conductors from said taps to the cathodes, grids and plates of the respective tubes, the conductor from the cathode of the first tube being spaced from the adjacent end of said potentiometer whereby a" bias potential is applied between the grid and cathode of such tube, the resistance of said potentiometer being so designed that the direct current therethrough is considerably greater than the total space current of said discharge tubes.

2. An electrical amplifier system. including a plurality of three electrode vacuum tubes connected in cascade, means for applying a biasing potential to the grid electrode of the first tubeof the series, means linking said tubes and cooperating therewitl'rto transfer the effect ofsaid biasing potential to the grid of the last tube of the series to produce a plate current flow in said last tube responsive to said biasing potential, and

.means responsive to said plate current flow for for determining the degree of said biasing poten-' tial.

4. An electrical amplifier-system including a plurality of three electrode vacuum tubes connected in cascade, means for impressing a fixed grid electrode of the first tube of the. series, means linking said tubes whereby a potential bias on said grid electrode controls the degreeofplate current flow. in the and means responsive to plurality of said plate current flow for altering the degree of said biasing potential. v

5. An electrical amplifier system including a threeelectrode vacuum tubes connected in cascade including conductive connections between the plates of preceding tubes and the grids of succeeding tubes, one or more of said tubes requiring for normal operation as amplifiers grid biasing potentials different from one or more of the other of said tubes, means for suppiyingnegatively to the grids of succeeding tubes a direct current potential of the order required for biasing the grids of said succeeding tubes'for said normal operation as amplifiers by way of the filament-to-plate impedance of and the conductive connection to the plates of succeeding tubes, and high resistances connecting the grids of said tubes to their respective cathodes.

6. The method of energizing an amplifier system including an output tubeand an amplifier tube which. consists in controlling the average intensity of the space current of the output tube by the "intensity otthe space current of the amplifier tube, and controlling the average intensity ofthe space current of the amplifier tube by the average intensity of the space current of the output tube.

7. The method of energizing an amplifier system including an odd number of tubes including an output tube and a plurality of amplifier tubes arranged in cascade, which consists in producing a rise in the average space current of the output tube by a rise in the space current of any odd numbered tube of said cascade, and producing a decrease in the average space current of said-odd in the space current of said output tube.

8. The method-of energizing an amplifier system including an odd number of tubes includin an output tube and a plurality of amplifier tubes arranged in cascade, which consists in producing a rise in the average space current of the output tube by a rise in the space current of any odd numbered tube of said cascade, and producing a- -nectioi1s between the of said last mentioned rise in'the average space current of any even, numberedtube of said cascade by the rise in the space current of said output tube. v 9. The method of energizing an amplifier system including an odd number of tubes including an output tube and a plurality of amplifier tubes arranged in cascade, which consists in producing a decrease in the average output tube by a decrease in the averagespace current of any odd numbered tube of said cascade, Y

and producing a rise in the space current of said odd numbered tube by thev decreasein the space current of said output tube. I

10. The method of energizing an amplifier system including an output tube and an amplifier tube arranged in cascade, which consists in producing a decrease in the average space current of the output tube by a rise in the average space current of said amplifier tube, and producing a decrease in the average space current of said amplifier tube by said space current of said output tube.

11. An amplifying circuit comprising a potentiometer having its terminals connected to the opposite leads of a potential supply source; vacuum tubes connected in cascade, each having. an anode, cathode, and control electrode; the anode of one tube being directly connected to the control electrode of the succeeding tube; conelectrodes of said tubes and said potentiometer at such points'th'at the voltage control electrode due to anode current is compensated; and means for separately and independently heating the cathodes of said tubes to emitting temperature.

12. 'In a vacuum tube system comprising a plurality of cooperating thermionic vacuum tubes; means for coupling said tubes to form an amplifying, circuit; means whereby of said tubes are operated at substantially the same potentials but at idiflirent portions of the voltage gradient and separ te independent and insulated heating sources for maintaining said cathodes at emitting temperature.

NICOLAI space current of the the cathodes 20' decrease in the average

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