US1789664A - Electrical amplifier system - Google Patents

Description

Filed Aug. 8, 1927 INVENTOR ATTORNEY Patented Jan. 20:, 1931 UNITED STATES SIDNEY Y. WHITE, OF NEW YORK,

N. Y., ASsIGNDR 'ro EDWARD H. LOFTIN, AS

'rnns'rnn ELEGTRICAL AMPLIFIER SYSTEM Application filed August 8, 1927. Serial No. 211,292.

neighborhood of 30 in the positions of VT My invention relates generally to electrical amplifier systems, and has for a particular object the eflicient amplification of electrical en ergy irrespective of its character of move- 5 ment.

Another object is to provide an amplifying system substantially devoid of natural periodicities' within the limits of the frequencies of alternating currents generally encountered in practice, including the very high frequencies of so-called short wave radio signaling, and thereby eliminate distortion due to circuit discrimination in favor of one frequency over other frequencies in broad band amplifying,

as is required in line and radio telephony and like practices.

A further object is to provide a system that in large part requires no interchanging of apparatus in shifting its use as an amplifier from a range of frequencies of one order to a range of frequencies of entirely different order, and at the same time employing apparatus that is simple, inexpensive and permanent.

A. particular object is the preservation of tonal quality in the amplification of sound conveying currents for sound reproduction now so extensively in use in numerous ways.

Numerous uses and advantages will be ap- 3o parent from the description to follow in connection with the accompanying drawings.

- Fig. 1 diagrammatically illustrates a complete amplifying system including connections rendering it suitable for use in connection with a radio broadcast receiver or like use. Fig. 2'illustrates the system in modified form as to one of the control elements. Like reference characters represent like elements in the two systems so far as possible.

The figures show three electrode vacuum tubes VT VT and VT, connected in tandem, the filaments being heated from a common circuit energized in a well known manner from a source indicated as +A, A. Tubes VT and V'I preferably have very high amplifying ability, but may be of low power with respect to tube VT at the output end of the system. For example, I have had unusually good results in my system with tubes having an amplification constant in the and VT and so-called power tubes having amplification constants in the neighborhood of 3 to 8 in the position of VT On the other hand, with tubes having amplification, constants in the neighborhood of 8 and below in the positions of VT and VT the results have been relatively less satisfactory.

Tube VT is shown to have its plate circuit energized in a normal manner from a source B indicated for convenience as a bat: tcry, and I preferably employ the normal rated plate potential of the particular type of tube at this point. Tubes VT and VT are shown to have the unusual arrangement of plates connected directly to grids of succeeding tubes through sources'of potential, indicated for convenience as batteries, B and B respectively, the positive terminals of the batteries being connected plate-wise. High resistances R and R connect the negative terminals of these batteries to the positive side of the filament heating current system as indicated at the points I) and 0 respectively.

The potentials of sources B and B and thevalues of resistances R and R are determined largely by the nature of the succeeding tube in the series and more particularly with respect to its grid bias or initial gird potential characteristic for normal operation. For example, with a tube requiring a. normal grid bias of about 40 volts'in position VT I employ a potential at B in the neighborhood of 67 Volts and a resistance at R, in the neighborhood of 1-4 megohm, while with a tube requiring a grid bias of about 1 volt in position VT I employ a. potential B of about 4 volts, and a resistance at R in the neighborhood of 1 megohm.

However, I can alter the values of these resistances over a wide range without correspondingly altering the potentials of the-batteries, but find it desirable to maintain the ratio of the resistance values substantially constant in making such variations. In operation the current drawn from the sources B and B is so small that dry batteries can be used with an operating life substantially equal to shelf life.

It is well to note at this point that the high am lification tubes I have mentioned as prefera ly employed in positions VT; and VT:

do-not begin to give any noticeable amplification when cascadedin the usual manner 5 in well-known systems until the ;plate energizing potential reaches thene hborhood of 100 volts, and in fact are rated or normal operation at 180 plate volts; so that the very low potentials I use would render these tubes totally inoperative as amplifiers in such other systems. In fact, I have obtained very good results without the useof any source atB but relying entirely upon the potential derived from connecting resistance R, to the positive side of the filament system, as at point b.

For normal operation the filamentlate impedance of the high amplification tn 5 I use in ositions VT and VT, is extremely high; t at is, of the order of several hundred thousand ohms. At the very small plate currents in my mode of operation this impedance increases to megohms.

In ion of the figures shows as a mat- 251 ter 0 fact that not all of the abnormally low potentials of sources B and B isapplied between the filament and plate electrodes of VT and VT respectively. Because of the presence of resistances R and R which have values of the order of the filament-plate impedances of their respective tubes, the total applied potentials are divided about equally between the filament-plate impedances and the associated resistances; or in other words, the potentials on the plate of a preceding tube and grid of a succeeding tube are near equality and about one-half of'the total applied potential. This accounts for the preceding mentioned requirement that the potential of B greatly exceed the normal required grid bias potential of VT The input-circuit of tube VT is shown to include a variable circuit L C through which the tube can be selectively energized with currents to be amplified, the currents being derived as shown in Fig. 1, from any source through connections 1 and 2, and be ing transferred to the variable circuit through the combined electromagnetic-electrostatic coupling including the inductive relation between coils L and L5 and 'the.

5 VT in Fig. 1, and resistance R condenser connection for cascaded amplifiers a. permanent change in grid bias or initial tecting the loud speaker w nding from the dlrect current component in the plate circuit, though with a proper design of winding the loud er may be connected directly in the p ate circuit as shown in Fig. 2

The operation will be' understood from the following discussion: In the usual form of tential of the grid of the first tube will not sfiect the steady or permanent current flow in the plate circuit of. the last tube, but merely change the steady or permanent current flow in the plate circuit of the tube whose grid bias is modified. In my system a ermanent modification of the grid bias 0 tube VT will carry through the system and permanently modify the plate current of'tube VT which may be accounted for as follows: With the grid bias of tube VT; made so highly negative that no space current flows, with the result that the plate impedance is practically infiinite, no current can flow from battery B through resistance R to alter the grid bias of tube VT The grid of tube VT is positively biased through the connection of resistance R to the positive side of the filament, as at point '6, so-that space current flows in tube VT under the potential of battery 13 This current flows through re sistance R to create a negative difierence' of potential overcoming the positive bias on the grid of VT,, which bias is derived from the connection of resistance R to the positive side of the filament, as at point 0. This neg- 'ative bias thus produced on the grid of tube VT holds down the current flow in the plate circuit of this tube, and if the values of the resistances and the potentials of the batteries are properly chosen, current flow in the plate circuit of VT can be substantially eliminated by reason of a bias on the grid of tubeVT By lessening the degree of negative bias. of tube VT current is caused to flow in the plate circuit of tube VT in accordance with the degree of lessening of the negative bias, and I have found that such-a small change in this grid bias potential is necessary to change the current flow in the plate circuit of tube' VT from zero to 20 milliamperes that there results a power amplification in the system of extremely highorder. It will be recognized that this is direct current amplification through the over-all system, for so long as the new bias on tube VT is maintained the current. in the plate circuit of VT, continues to flow. Y

It is ap arent however that if the bias of tube V 1 be set to maintain a iven current flow in the plate circuit of any alteration of this bias no matteuhow slow or fast, will correspon ingly amplifiedly alter the current flow in the plate circuit of VT so that the system, in addition to being an amplifier of direct current, is equally well an amplifier of alternating current or varying current of any character. Since the system is substantially devoid of inductance and capacity other thanthat of the distr buted type contained in the necessary wiring and connections, which for practical purposes is negligible, it is to all intents and purposes an aperiodic system,j-even for the highest of frequencies in practical use.

In operating the system as an ampllfier v of alternating currents it is desirable to inticular tube, this in order that alternating itially bias the grid of tube VT to such degree that the plate current flow of tube VT is maintained at about the middle of the plate current characteristic curve of the parvariations will occur on the substantially straight portion of the curve extending both ways from this middle point.

In operating the system as an amplifier in a radio receiver, as shown in Fig. 1, the high frequency modulated radio signals are selectively impressed upon tube VT by means of tunable circuit L 6 It is well to bring out at this point that the system is an efficient rectifier in addition to its ability as an amplifier, with the result that a continuous wave, modulated or unmodulated, impressed upon tube .VT is rectified and has the eliect of permanently altering the initial bias of VT in proportion to the strength of the incoming continuous wave. In view of this fact it may be that if the system is so initially biased as to bring the plate current flow of tube VT to the middle of the plate current characteristic, the additional bias due to an incoming continuous wave will change this point of operation to some removed point with respect to the middle of the characteristiccurve, and it is quite likely to happen in the case of nearby powerful stations that this point is moved so far as to cause the alternating current variations to operate in the'region of one or the otherof the bends of the characteristic curve,

which results in distortion in a well known manner.

In view of these conditions it is desirable to be able to alter the initial bias of tube VT to permit of bringing the point of operation on the characteristic curve at about the middle for any intensity of incoming signal. It is a simple matter to provide the grid circuit of tube VT with a battery and potentiometer to permit of adjusting the initial grid bias to a proper value for combination with the incoming continuous wave, and

T then.

for unskilled operators, are undesirable, I

have provided means for automatically overcoming this-dificulty, shown in one form in Fig. 1 and in another formin Fig. 2. In Fig. 1, I provide a vacuum tube VT having its filament in series with the plate circuit of tube VT and choose a vacuum tube VT of such filament heating characteristics that the filament just commences to be sufiiciently hot to emit electrons at about the plate current value of VT which represents operation at the middle of the characteristic curve; However, by means of a resistance R in shunt to the filament of tube VT I can adapt commercial tubes not having precisely the exact filament heating characteristics to satisfy the requirements for satisfactory performance.

In series with the plate and filament connection I place a source of potential B and a resistance R and connect these elements as shown so that any change in current flow through the resistance R due to electron emission in't'ube VT, altering the over-all resistance of the combination will result in changing theinitial bias on tube VT Thus if the plate current of tube VT tends to permanently increase for any reason the filament of tube VT will heat up to emit electrons, thereby increasing the conductivity between filament and plate to permit more or less current to flow from battery B. through resistance R and thus increase the negative bias on tube VIZ, which negative bias will immediately cause the plate current of VT to subside, and in this way to remain at some predetermined fixed value irrespective of the strength of the incoming signal or other cause tending to increase the plate current.

It is to be noted that this arrangement will not prevent the plate current of tube VT momentarily increasing to represent signal efiec-t's. because such signal effects take place at such high frequency that there is no possibility of the temperature of the filament of tube VT responding. It does, however, most effectively prevent any efiect tending to produce a permanent change in the plate current from accomplishing the undesired result.

I show tube VT as a three electrode tube converted into a two electrode tube in effect by connecting the grid directly to the plate It so happens that there is available a coin-' a comnierciall available t of power tube T of Fig. 1 may be of high frequency charsuitable for t e osition ,4 In fact, the actor, tuned or not, to transfer hi h. fre-' particular tube ,T, should be operated with a plate current of'approximatelv 20 milliamres. The particular tube VT, requires a filament current of approximately milliamres for normal operation as an amplifier,

ut begins -to emit electrons at about the 20 milliamperes mentioned. i The auxiliary device of -Fig.- 2 for main taining constant operation comprises a resistance R, in the grid circuit of tube VT so connected that the plate current of tube VT, must pass therethrougha .The value of.

this resistance is so chosen that when the desired plate current of tube VT, is had the difference of potential across the resistance will be correct for combining with any other difierence of otential to give the proper grid bias to tube V l If the late current of tube VT, tends to increase or any reason, the difference of potential across resistance R will increase and thereb offset the effect. To prevent resistance R i'om producing the same limiting effect on signal variations a by-pass condenser C, is connected between the filament and the plate circuit as shown, and a choke coil CH is inserted in series with the plate circuit, thus shunting signal variations from the resistance R The objection to this arrangement of Fig. 2 is that the use of condenser C and choke coil CH introduces elements having frequency characteristics into the system, which procedure tends to destroy to somev extent the aperiodic character of the system. a

The amplified high frequency modulated currents arrive at audio 'fre uency transformer T in Fig. 1 in rectified orm, and this transformer acts to filter the low frequency modulations from the rectified high he quency current for delivery to the loud speaker LS. It is obvious that the transformer T and loud speaker LS have freqency characteristics and serve to lessen the aperlodic character of the system, but since these are the only elements in the system so acting acterlstios are extremely small compared to existing systems employing a large number of such transformers. However, loud speakers are now available having such construction that it is not necessary to prevent the steady direct current of the plate circuit from "flowingthrough the winding, so that it is possible to insert such loud speakers directly in the output circuit as shown in Fig. 2, and thus do away with another element tending to lessen the aperiodic character of the system.

In employing the system for amplifying high frequency modulated currents as described it is not necessary that the rectifying characteristic of the system be utilized for detecting the nodulations The-transformer the frequency discriminating char-.

quency currents to a succeedin recti yin or other detecting device. Furt er ampli cation at low frequency after detection may be carried out utilizing the t pe of system herein described or other we I known audio f uency amplifyin systems. Where the highest standard 0 tonal quality is demended I prefer the herein described type of amplification throughout.

I claim: 7

1. An electric amplifier stem including a plurality of three electro e vacuum tubes connected in cascade, means for applying a biasing potential to the grid electrode of the first tube of the series, means for creating a substantial current flow in the plate circuit of.

the last tube of the series, means linking said tubes and coo crating therewith" whereby the effect of said iasing potential is transferred from tube to tube in the series with alternate- 1 reversed effects to produce a plate current film in said last tube responsive to said biasing otential, and means for maintainin the biasing potential to the grid electrode 0 the first tube of the series of such polarity and magnitude that the steady component of the .plate current flow in the output circuit of said last tube is maintained at substantially the midpoint of its plate current characteristic curve.

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 tube of the series, means linking said tubes and cooperating therewith to transfer the efiect of said 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 potent1al,and means responsive to said plate current flow for determining the I degree of said biasing potential.

3. An electrical amplifier system including a plurality of three electrode vacuum tubes connected in cascade, means linking said tubes whereby a potential bias on the grid electrode of the first tube of the series controls the degree of plate current flow in the last tube ofthe series, and means responsive to said plate current flow for determining the degree of said biasing potential.

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

5. An electrical system including a pluralfor creating a plate current flow in one of said tubes, and means for creating agrid biasing potential for another of said tubes including a heated cathode electron discharge device having its cathode ener ized by said plate current flow and means or making a potential derived from the resulting current flow in said electron discharge device effective on the grid of said other tube.

6. An electrical amplifier system including a plurality of three electrode vacuum tubes connected in cascade, means for creating a plate current fiow inthe plate circuit of the last tube of the series means for creating a biasing potential on the grid electrode of the first tube of the series, means linking said tubes and cooperating therewith to'transfer the effect of said grid biasing potential through the system whereby said plate current flow is responsive thereto, means for impressing a modulated carrier current potential on the grid of said first tube, and means for limitingthe effect of rectification in the system of said carrier current on said biasing potential and plate current flow including means operated by said plate current flow for altering said biasing potential.

7. Anelectricalamplifiersystemincluding a pair of three electrode vacuum tubes connected in cascade by means including a direct connection between the plate of the preceding tube and the grid of the succeeding tube, and a source of direct current potential connected to be negatively impressed on the grid of said succeeding tube with respect to its cathode by Way of the filament-to-plate impedance of said preceding tube and said direct connection, the potential of said source being of the order of double that required as a grid biasing potential in the normal operation of said succeeding tube asan amplifier.

8. An electrical amplifier'system including i a pair of three electrode vacuum tubes connected in cascade by means including a direct connection between the plate of the preceding tube and'the grid of the succeeding tube, a source of direct current potential connected to be negatively impressed on the grid of said succeeding tube with respect to its cathode by Way of the filament-to-plate impedance of said preceding tube and said direct connection, the potential of said source being of the order of double that required as a grid biasing potential in the normal operation of said succeeding tube as an amplifier, and a-high resistance directly connecting the grid of said succeeding tube to its cathode.

9. An electrical amplifier system including a pair of three electrode vacuum tubes connected in cascade by means including a conductive connection between the plate of the preceding tube and the grid of the succeeding tube, a source of direct current potential connected to be negatively impressed on the grid of said succeeding tube with respectto its cathode by way of the filament-to-plate impedance of said preceding tube and said conductive connection, the potential of said source being of the order of 150 per cent of that required as a grid biasing potential in the normal operation of said succeeding tube as an amplifier, and a high resistance connecting the grid of said succeeding tube to a point of positive potential of lesser magnitude than said first potential.

10. An electrical amplifiersystem including a plurality of three electrode 1 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 po tentials difierent from one or more of the other of said tubes, means for supplying negatively to the grids of succeeding tubes a direct current potential of the orderrequired 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.

11. An electrical amplifier system including a pair of three electrode vacuum tubes and means connecting said tubes in cascade relation, said means including a source of direct current potential and conductive connections for energizing the plate electrode of the preceding tube and the grid electrode'of the succeeding tube therefrom, the potential of said source being of the order of double that normally required for energizin the grid electrode of said succeeding tube foroperation as an amplifier.

- 12. An electrical amplifier system including a pair of three electrode vacuum tubes and means. connecting said tubes in cascade relation, said means including a source of direct current potential and conductive connections for energizing the plate electrode of the preceding tube and the grid electrode of the succeeding tube therefrom, the potential of said source being so low that its application to the plate electrode of said'preceding tube produces operation on the plate current characteristic curve of said tube below the lower bend'thereof.

13. An electrical amplifier system including aplurality of three electrode vacuum tubes connected for cascade amplification through conductive connections between the plate electrodes of preceding tubes and the grid electrodes of succeeding tubes, direct current means capable of energizing the plate electrode of the last tube of the series for operation at substantially the mid point of the' plate current characteristic curve of said tube, directcurrent means for energizing the grid electrodes of said tubes, said means bein con- ,point of the plate current characteristic nected to said electrodes by way of sai conductive connections and in series with the filament-to-plate impedances of reced ng tubes, the potentials of said means mg incapable of operating said preceding tubes beyond the lower bend of the plate current characteristia; 1

curves thereof, and means impressing a biasing potential on the grid electrode 0 the first tube of theseries of such. polarity and value as to fix the steady current flow of the plate circuit of said last tube at about the mid curve thereof.

14. In a direct coupled amplifier system, the combination of a source of energy, a pluralit of electron tubes, impedance output and mput circuits couplin said tubes in cascade, and means for energizin electrodes of said tubes so that the cathode-p ate impedance of each preceding tube is of the same order as the impedance input tothe next succeeding tube of said cascade.

15. In a direct coupled amplifier system, the combination of a source of energy, a plurality of electron tubes, impedance output and mput circuits coupling said tubes in cascade, and means for energ1zing electrodes of said tubes so that the cathode-plate impedance of each preceding tube is of the sameorder as the impedance input to the next succeeding tube of said cascade, the cathodeplate impedance of each preceding tube and the input impedance to the'succeedipg tube being determined as functions approaching as a limit, in-so-far as practicable, the cathode-grid im ance of the succeeding tube. 16. In a irect coupled amplifier system, the combination of a source of energy, a plurality and input circuits coupling said tubes in cascade, means for energizin the electrodes of said tubes so that the cat ode-plate impedance of each preceding tube is of the same order as the impedance input to the next succeeding tube of said cascade, and means series related between the space current path of the last tube of said cascade and said source for determining the grid bias of one or more tubes of said cascade.

17. In a direct coupled amplifier system,

the combination of a source of energy, a plurality of electron tubes, impedance output and of electron tubes, impedance output cathodes, impedance output and input circuits coupling said tubes in csacade, and means for energizin electrodes of said tubes so that the cathode-p ate impedance of each preceding tubeis of the same order as the impedancev the combination of a source of energy, a plurality of electron tubes, impedance output and input circuit coupling said tubes in cascade, means for energizing electrodes of said tubes so that the cathode-plate impedance of each preceding tube is of'the same order as the impedance in ut to the next succeeding tube of said casca e, and means series related between the space current path of the last tube of said cascade and said source for determining the grid bias of one or more tubes of said cascade, said means being substantiall nonresponsive to signal current energy therethrough.

20. In a direct coupled amplifier system, the combination of a source of energy, a plurality of electron tubes, impedance output and input circuits coupling said tubes in cascade,

. means for energizing electrodes of said tubes so that the cathode-plate impedance of each preceding tube is of the same order as the impedance in ut to the next succeeding tube of said casca e, and means series related between the space current path of the last tube of said cascade and said source for determining the grid bias of one or more tubes of said cascade, said means consisting of a discharge tube having a plurality of electrodes, the cathode of which is series related between the space current path of said last tube and said source, another electrode being connected directly to the grid of one of the tubes of said cascade, and means for producing a potential across the space discharge path of said discharge tube.

21. In a direct coupled amplifier system, the combination of a source of energy, a plurality of electron tubes, impedance output and input circuits coupling said tubes in cascade, means for energizing electrodes of said tubes so that the cathode-plate impedance of each preceding tube is of the same order as the impedance input to the next succeeding tube of said cascade, and means series related between the space current path of the last tube of said cascade and said source for determin- .ing the grid bias of one or more tubes of said cascade, said means consisting of a discharge tube having a plurality of electrodes, the cathode of which is series related between the space current path of said last tube and said source, another electrode connected di- I rectly to the grid of the first tube of said casends, and means for producing a potential across the space discharge path of said d1scharge tube.

22. The method of energizing an amplifier 5 system including an output tube and an amplifier tube, which consists in controlling the average intensity of the space current of the output tube by the intensity of the space current of the amplifier tube, and controlling the average intensity of the space current of the amplifier tube by the average intensity of the space current of the output tube. v

23. 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 out-put tube b a rise 1n the space current of any odd num ered tube of said cascade, and producing a decrease in the average space current of said odd numbered tube by the rise in the space current of said output tube. v

24. The method of energizing an amplifier systemincluding an 'odd number of tubes including an output tube and a plurality of amplifier tubes arranged in cascade, which consistsin 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 rise in the average space current of any even numbered tube of said cascade by the rise in the space cur- 35 rent of said output tube. r

25. 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 space current'of the output tube by a decrease inthe average space current of any odd numbered tube of said cascade, and producing a rise in the space current of said odd numbered tube by the decrease in the space current of said output tube. 26. 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 55 decrease in the average space current of said output tube.

In testimony whereof I aflix my signature.

SIDNEYY'. WHITE.

8 v SCLAIM 1-,789,664.-S'idney Y. White, New York, N. Y. ELECTRICAL AMPLIFIER SYSTEM:

Patent dated January 20, 1931. Disclaimer filed February 19, ,1935, by

the assignee, Radio Corporation of America.

Hereby disclaims that part of the specification of said patent which consists of claims 2, 3, 4,10, 22, 23, 24, 25, and 26, which are in the following words:

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 tube of the series, means linking said tubes and cooperating therewith to transfer the effect of said 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 determining the degree of said biasing potential.

3. An electrical amplifier system including a plurality of three electrode vacuum tubes connected in cascade, means linking said tubes whereby a potential bias on the grid electrode of the first tube of the series controls the degree of plate current flow in the last tube of the series, and means responsive to said plate current fiow for determining the degree of said biasing potential.

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

10. An electrical amplifier system including a plurality of three electrode 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 supplying negatively 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 wayof the filamentto-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. 22. The method of energizing an amplifier system including an output tube and an amplifier tube, which consists in controlling the average intensity of the space current of the output tube by the intensity of the space current of the amplifier tube, and controlling the average intensity of the space current of the amplifier tube by the average intensity of the space current of the output tube.

23. 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 numbered tube by the rise in the space current of said output tube. i 24. 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 rise in the average space current of any even numbered tube'of said cascade by the rise in the space current of said output tube.

25. 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 space current of the output tube by a decrease in the average space.current of any odd numbered tube of said cascade, and pr'bducing a rise in the space current of said odd numbered tube by the decrease in the space current of said output tube.

26. The method of energizing an amplifier system including an output tube 1 and an amplifier tube arranged in cascade, which consistsin producing a decreasein 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 decrease in the average space current of said output tube.

.[Oficial Gazette March 19, 1985.]

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