US2006872A - Series oscillator - Google Patents

Description

July 2, 1935. A, NYMAN SERIES OSCILLATOR Filed May 27, 1951 6 Sheets-Sheet 1 POWER FMFLI F'IER Frequency INVEHTOR Hlexand er Nymqn.

HTTORNEY July 2, 1935; A. NYMAN 2,006,872

[SERIES OSCILLATOR Filed May 27, 1931 6 Sheets-Sheet 2 mvsnr'on fllexander Nqman,

HTITORNEY A. NYMAN 2,006,872

SERIES OSCILLATOR,

Filed May 27, 1951 e Sheets-Sheet 4 119 i m 114== m F1936 I 30 #IP -/20 Ell - IHVENTOR 466 I W Y. fllezander Hyman.

HTTORHEY July 2,1935. A. NYMAN 2,006,872

' I SERIES OSCILLATOR Filed M21127, 1931 6 Sheets-Sheet 5 22 9 (-Q-QQQ] 202 [HVEHTOR fllexander Hyman July 2,1935. I A. mm 2,006,872 SERIES QSCIVLLATOR Filed May 27, 1931 s Sheets-Sheet e mvErg'ro fllexander Nqmqn HTTORNEY Patented 2, .1935

AleTxander Hyman, Dobbs Ferry, r5.

by mesne assignments, -to Radio Y., assignor,

Corporation f of America, a corporation of Delaware Application my 27, 1931, Serial No. 540,257 g My invention relates to novel apparatus for and methods of signalling systems and more palticularly relates to ratusfor operating an electric a novel method of and appaal oscillator and Electrical-oscillators heretofore used in transmitting.stations have comprised either a single thermionic valve .with an associated tuned circuit or a plurality of thermionic valves connected in parallel.

In either case, theelectrical characteristics of the oscillator circuit are such that the frequencies fluctuate over a very wide range and this; serious fluctuation of the frequencies very undesirable as it tendsto cause atransmitting stationto radiate frequencies which varies from its own as signed frequency to frequency within the fre-' quency range assigned to'some other transmitting station, resulting in interference.

Because of this, strict regulations of "the trans-' mitting stations have been issued compelling stations to operate close to the assigned frequency.

Heretofore, the method of holding theoscillating frequency within the assigned frequency range has been by means of crystals, tuning forks, and other complicated apparatus which need careful attention to hold the frequencies over a smaller range of fluctuations and are expensive in constructlonand operation. 7 4

Accordingly, an object of my invention is to provide a novel method of operating an oscillater which will prevent frequency fluctuation.

Still a further object of my invention is to pro-3 vide an oscillator which inherently oscillates only within a narrow frequency band.

Still a further-object of my invention is to provide an oscillator comprising a plurality of thermion'ic valves connected in r 'In the present oscillators the arrangement is such that the oscillator is adapted to'operate only one-frequency range. It is often desirable, howfrequency ranges.

ever, toutilize the'same oscillator for a plurality of oscillating frequencies. :Accordingly, a further object of my invention is to provide an oscillating circuit which will simultaneously oscillate at a plurality of different Another object of'm'y invention is to provide a series oscillatorffor generating a plurality of oscillating frequencies simultaneously.

In any oscillator the fundamental. feature is the feed back arrangement whereby output en- 4 ergy isfed back into the input circuit to set up and maintain the oscillator in oscillation.

I have discovered ,a novel apparatus for and method-of prodding oscillations Oneobject of my invention, therefore, is to provide an oscillator in which feed back is obtained by applying a porto a portion of the series amplifier circuit.

.A further object of my invention is to provide in a oscillator means for feeding the out- Y put of the last series tube to ceding series tube.

Still a further object of my invention is to provide means in a series oscillator for applying part series amplifier to the cathode of a tube of the series amplifier;

Still va'further object of my invention is to provide means in a oscillator for feeding bacl'; part of the output energy of one of the series tubes of the oscillator simultaneously to the cathode and grid of a preceding tube.

A further object of my invention is a push-pull series oscillator.

Still a further object of my vide an electro-magnetic feed back in a series oscillator. j v 4 Another object of my invention is toprovide an electrostaticfeed back in a series oscillator.

p ce n to provide the grid of thepreinvention is to proof the output energy of the last tube of the series oscillator in which a series tuned circuit is connected in series with a series amplifier.

In series oscillators, the problem of modulation is somewhat different than that present in the usual oscillator heretofore used.

Accordingly, an object of my invention is to provide novel apparatus for and methodsof modu lating oscillations in a seriesfoscillator.

H A further object of my inventionis to modulate by changing the impedance of-the tuned. circuits in a. series'oscillator.

A further object of my invention is to provide frequency modulation in a series oscillator.

A further object of my invention is to modulate the output energy of a'series oscillator by vary ing the impedance of one of the thermionic valves of said oscillator. v V till a further object of my'invention isto provvide modulation in a series oscillator by a capacity varying means.

.A further object of my invention is to provide a novel methodof modulation which comprises varying the capacity in the feed back circuit.

Another object of my invention is toprovide a novel method of modulation which comprises the 1 a Variable voltage supply to a series oscillator in accordance with the desired modulations.

A further object of my invention is to provide a method of modulation of series oscillator by connecting it in series with a series amplifier to which modulating signals are conveyed.

Still a further object of my invention is to provide a novel power amplifier.

Another object of my invention is to provide a power amplifier in which tubes of different energy characteristics are used.

A further object of my invention is to provide a novel method of cutting ofi undesired frequencies in a modulated carrier frequency system. 7

Still a further object of my invention is to provide novel means, in a series oscillator circuit, for broadening the range of frequencies at which it is operated in accordance with requirements.

Figure 1 is an elementary diagram of a series oscillator.

Figure 2 consists of curves illustrating the amplification characteristic of a series amplifier compared to other amplifiers.

Figure 2a is a curve showing the variation and impedance of a tuned circuit with a frequency.

Figure 3 is a form of series oscillator adapted to operate simultaneously at a number of difierent frequencies.

Figure 3a illustrates the modulating means applicable to circuits of Figure 3.

Figure 4 is a complete diagram of a series oscillator in combination with a novel power amplifier and modulating means.

Figure 5 consists of diagrammatic charts illustrating the voltage relations in various. parts of a series oscillator.

Figure 6 is a diagram of a series oscillator show.- ing novel potential bridges and modulating means.

Figure 7 is an alternative form of series oscillator and modulating, means therefor.

Figure 8' is'a further alternative form of series oscillator showing a double function of modulation and oscillation.

Figure 9 shows an alternative form of oscillator with a series connected modulator.

Figure 10 shows a push-pull series oscillator with series modulating means; Figure 11 shows an alternative form of push-pull series oscillator with push-pull modulating means. Referring to Figure 1 which illustrates the simplest form of oscillator; this comprises broadly a plurality of thermionic valves I, 2, and 3, connected in series with each other in such a fashion that the ancde of the first tube l is connected to the cathode of the valve 2 and the anode of 'ther-' mionic valve 2 in turn is conductively and directly connected to the cathode of the valve 3. The control electrode or grids of thermionic valves I, 2, and 3 are maintained at predetermined fixed potentials by means of connections taken therefrom to the taps of a potentiometer 4.

In order to insure that the control electrodes are maintained at the predetermined fixed potentials, the control electrodes are further grounded through condensers 5 and 6. Energy for the oscillator tubes and the potentiometer 4- is supplied from the potential leads 8 and 9 connected to the opposite terminals of the potentiometer and through the tuned circuit H to tubes 3; 2, and I.

A. Theoscillator circuit is completed from the output circuit of 'the tube 3- through the parallel tuned circuit ll comprising a variable condenser is inherently stable.

to the input of the first tube 1.

Such a circuit will operate as a series amplifier with regard to potentials applied to the grid of tube 1 of a frequency to which circuit H is tuned. In this circuit a condition of oscillation is established by feeding back a predetermined percentage of the output potential in the last stage 3 of the oscillator through the variable condenser 16 to the control electrode of the first thermionic valve i. I

Inasmuch as the output potential of the thermionic valve 3 is in phase with the output potential from valve l, a phase reversal of the output potential which is to be fed back to the grid of tube 1 is necessary. This is accomplished by tapping the inductance l3 at some intermediate point thereof for the supply connection 9 so that the feed back potential applied to the control electrode of tube i is reversed in phase with respect to the output potential from tube 3.

I2 and inductance l3 through the condenser H p A biasing resistor H for the first tube i is bytothe input of a power amplifier 2i which is here diagrammatically illustrated as any well known form of amplifier and modulator may be used. The output energy of the oscillator is then radiated over the antenna 22 in any well known manner.

The advantages of this form of oscillator; namely, a series connected oscillator, can best be explained by reference to Figures 2 and 2a.

' Figure 2 discloses the gain obtained in a series amplifier and explains the stability of suchan amplifier with regard to frequencies'when used as an oscillator. The curve shows the amplifica tion as a function of the ratio of tube impedance Rp to the impedance of the tuned circuit Z.

' The curves were obtained by mathematical calculations which show with the series amplifier the gain or amplification expressed as the ratio of output voltage to input voltage to be as follows:

in which a is the amplification constant of each tube.

Z is the impedance of the tuned circuit at the operating frequency.

R2 is the energy component of Z at the operating frequency.

Xz is the reactive component of ating frequency.

' R1) is the internal impedance of the tube at the operating frequency.

n is the number of stages of amplification, and

Z at the oper-.

aooasva ratio: R,

On the other hand, with a parallel amplifier of a number of stages with a corresponding number of tuned circuits, the amplificationfalls off relatively -slowly, illustrated for three stages in the curve 26 and expressed by the formula:

' tuned circuit will varywith frequency, giving a maximumat the resonant frequency F. If the i 80% of-the amplification atthe resonance point maintains a stable oscillating condition, then, as.-

shown by the dotted line in Figure 2, the parallel amplifier would permit a very large variation of the above ratio corresponding, for instance, to the range of variation of Z from a to b of Figure 211. While with a series amplifier the corresponding range of variation of ratio is much narrower, as indicated by points 0 and d of Figure 2a. This latter is due to the fact that a further reduction of the impedance of the tuned circuit reduces the amplification below the 80 which was assumed to be necemary for maintaining oscillations.

It is clear from Figure 2a, therefore, that the oscillations for a fixed condition of the tuned circuit must take .place. at a frequency within the range determined by-the points c and d while with a parallel oscillator the corresponding range is much wider, as indicated by points a and b.

I have'found from practice, that the series amplifier has istics, in 'accor ance with the above explanation, and also thatiif .a feed back circuit is supplied, the oscillation will maintain its frequency at a very stable value while the oscillations cannot, at the same. time, be easily suppressed or changed in frequency by changes in the varioustube potentials. One theory for explaining this stability is as follows:

The changm of frequency that'occur inan ordinary single tube oscillator or an oscillator comprising a number of tubes connected inparailel is. caused to a large extent by varlationsof the tube impedance caused by such factors as variation in filament potential, in grid biasing potential, or in plate potentials at which the tube operates. v

However, in a series amplifier, where a number of tubes are connected in series, I if the electronic current on one of these tubes has changed, for instance, due to the change of filament emission, there is an immediate readjustxtremely sharp' tuning character- I have found that affects the oscillating characteristics and which is represented by the slope of voltage and current characteristic at the operating point, that is, the

' electrode, tubes 25,

dynamic impedance of the tube may remain .practically the same. Therefore, the operating fre-' quency will also remain constant.

Figure 3, shows a modification in which several frequencies are generated simultaneously. Three 25, and 21 are connected in series relation substantially in the manner as in Figure 1 so that the anode of tube is connected to the cathode of the next succeeding tube 26, and 'so on. The anode of tube 21 is connected in series with a plurality of tuned circuits 23, 29, and 30, each of which comprise an inductance and variable capacity and is tuned to an individual frequency.

Three adjustable condensers 3|, 32, and 33, each adapted to compensate for the effect of the 0 tube capacities of the thermionic valves 21, 26,' and 25, are connected from the plate circuit of tube 21 to the cathode lead of each of these respective tubes. Condensers 35 and 36 are con nected respectively from the grids of tubes 21 and 2G to the negative lead 3. The function of condensers 3|, 32, 33, 35, and 36 is discussed in detail in reference to diagrammatic Figure 5 below. e

The remaining connections for the oscillator itself are similar to those shown in Figure 1, including'the potentiometer 33, bias resistance 31, and a bypass condenser 38. Instead-7 of a feed back condenser i6 as in Figure 1, an inductive feed back by means of a coil 39 coupled to the inductances of the tuned circuits 28, 29, and 30 isused in this circuit. In practice, however, I have found that it may be possible to omit the coil 39, as the condensers 3|, 32, 33, 35, and 38, serving to supply the capacity current between I the elements, can be so chosen as to supply an ment of the grid potentials as secured from acommon potentiometer, and of the plate potentials is secured from a common? scurcemf plate current, by means if which. the change in electronic emission caused by the change of filament of the tube, as voltage to current on the particular tube, may

measuredby the ratio of stable potential lsautomatically compensated. Forexample, if the filament potential has dropped, with operation of the system at the frequency of cirexcess of current to the connections between the tubes, and thereby create oscillations in accordance to .the resonant frequencies of the circuits 28,-29, and 33;

In an'ordinary type of oscillating circuit, it is conceivable that several oscillating systems are introduced and that oscillations would be created at several frequencies. Howeve ingeneral, due

to the ability of an ordinary oscillatorto swing 50 over a fairly large range of frequencies for the same timed circuit, if several circuits are included in the tuning path, it is likely to oscillate at a frequency correspondlng'to the summation of all inductance and all capacity elements instead of at three definite frequencies.- 0n the other hand, with a series amplifier as has been explained in connection with Figure 2; the circuit relations are such that the circuit oscillates at exactly the resonance frequency of the'tun'ed circuit and the swinging of the frequencyis prevented by the- ,nature of the circuit connections.

It follows from this also, that the variation of impedance of the tube elements caused by oscillations of: the frequency of, say circuit 23, would not interfere or affect the effectiveness of circuit 23 in interposing a hlgh'impedance at its own resonant frequency and time maintaining oacilv lations at its frequency. On the other hand, the

circuit 23 considered at the frequency of circuit 23, will be equivalent to a relatively large capacity or relatively small inductance in series with the tuned circuit 23, and will in no way affect the cult a.

z Similarly, circuit 30 will interpose a high impedance at its own resonance frequency and, provided suitable feed back means, will oscillate at that frequency, while at the frequency of circuits 28 and 29 it will merely interpose a low reactive or capacitative impedance.

The oscillating circuit for the three frequen-- cies includes all of the three circuits, so that the same current flows therethrough Onthe other.

hand, the voltages generated in the tube circuit is impressed respectively on circuit 28 at its frequency, on circuit 29 at its own frequency, and on circuit 35 at its own frequency.

This 'voltage, being the measure of the energy circulating in the corresponding tuned circuit,-

can be abstracted from this circuit by suitable coupling means, and I have shown three possible alternatives: The coil Ml coupled to coil 28, con-.

Thus, included in circuit 28 is a radio frequency.

bypass condenser 45 shunted by the equivalent of a series modulating resistor which will change the eilective resonance impedance .of circuit 23 and thereby the amplitude of the resulting modulations. The modulating resistor may comprise a microphone, but in the preferred form, cou-s' pling condensers l6 and 49. are used, the other side of which may-be connected to the output circuit from an audio source such, for instance, as is illustrated in Figure 3a in which the terminals 41 and 48 correspond to the terminals 41 and 48 of Figure 3.

This circuit may consist of an amplifying tube 50, the grid of which is supplied with audio frequency source, while the plate circuit is connected to terminal 41, The plate power to the tube #9 is supplied through a choke coiljl. Accordingly, the modulating resistance includes, at radio frequency, condensers l6 and 49 and the resistance of tube 50. And since this resistance is modulated by the audio frequency applied to the grid of tube 50, a correspondingly varying resistance effect is introduced into the tuned cir-.

cuit 28. In practice, such a connection may be used to introduce frequency modulation by proper choice of the values of various condenser elements.

Connected in circuit 30 are similar condensers 46' and 49' connected to terminals 41' and 48,

which may be again supplied with the modulating resistor in accordance to Figure 3a. In this case this modulating resistor is in parallel with circuit 30 and must have, therefore, a relatively high impedance value approximating the tuned impedance value of circuit 30. The variation of this shunting modulating resistor will then modulate the oscillations at the frequency of circuit 30. This arrangement may again serve as a frequency modulating means.

Connected to circuit 29, there is a keying arrangement including a relay 52 operated from the battery 53 by means of-key 54,. In the normal non-operating position, the circuit of relay 52 is closed and the relay is thereby energized,

short-circuiting the contacts 55 and 56, and thereby short-circuiting the circuit 28.

Thus, no scillationsof the frequency of the circuit 2! will be generated. However, when the impress on the grid of tube 25 a purpose as the condenser ,with Figure 5. .{bridge circuit across the tuned circuit 84, may also be utilized for establishing oscillating conditions, as explained in connection with Fig- -ure 5 in which casethe inductance 66 may be key is depressed the relay 52 is deenergized, the short circuit across the contacts 55 and .56 is removed, and the impedance of circuit 29 is interposed'in the series oscillator circuit, thereby generating oscillations of the frequency of circuit'fll.

An alternative'mcdulation scheme which will simultaneously modulate all of the three frequencies and which includes control elements of tube '25 and the secondary of an audio frequency transformer 51 bypassed by condenser 58, is also shown. This audio frequency'transformer may a be supplied from any suitable source of audio frequencies "or other control currents, and will voltage correspendingv to the audio frequency oscillations. Thus, .the impedance of tube 25 will be varied in accordance with this impressed voltage and thereby, as explained in connection with Figure 2, the oscillations at all of the frequencies will be varied. If the modulation of all of the circuits is not desired, the transformer jb'l is merely omitted and the grid ground.

These methods of modulation possess certain limitations in so far as they control directly the ratio of tube impedance to the impedance of the tuned circuit and as thedegree of amplification through the series circuit is dependent on this ratio, a change in the above ratio above a certain limit would entirely stop the oscillations.

I have, however, shown the alternative ways is connected directly to of modulation without theselimitations audit will .be understood that these alternative systems can be also applied to the circuits of Figure, 1 and Figure 3.

In Figure 4 thereis shown a further modification of series oscillator in a system more adaptable to power circuits where the energy to be transmitted will require large power tubes and relativelyhigh voltages and currents. Undersuch condition, it is desirable to confine the generation of oscillations to a so-called master oscillator of relatively lowenergy and then amplify and modulate the oscillations generated as above in a power amplifier and modulator,

. This system comprises a series oscillator sim- ,ilar to that of Figure l and consisting of three series tubes BI, 52, and 63 connected in series with a tuned circuit 64 and a bypass condenser 65 across'the power input terminals 8 and 9; Connected to the cathode of tube GI is an inductive element 66 and a biasing resistor 61 bypassed by condenser 68. -.,The inductance 66 may serve in a manner similar to the-inductance 39 of Figure 3 for supplying the feed back potential to the cathode'of tube 6|. The gridof this tube is held at the ground potential and therefore the creation of oscillations in the series amplifier will be in accordance with the general theory, as explained in connection with Figure 1.

Bypass condensers 69, 10, ll, 12, and 73 supply the necessary capacity currents to the tube elements, as discussed in detail in connection These condensers forming a omitted; The potentiometer 34 serves the same arranged to gen-- being of the type suitable for large energy 05-.

i cillations and having relatively high voltage and relatively high current carrying capacity. of course, the tubes I and 11 may also have energy capacity inexcess of the tubes GI, 02, and 58, as they form an intermediary step between the master-oscillator and the final tube I8 of the power oscillator. A resistor I9 is connected between the grid I5 andthe ground connection which, in cooperation with bypass condenser I9, will in general be sufficient to supply the necessary grid bias to tube I5, but additional grid bias may be introduced by a cathode resistor 80 with a bypass high frequency condenser II. The power supply for the series amplifier is obtained from terminals 82 and 03 which is in serieswith a filter arrangement comprising an audio frequency bypass condenser 04, an audio frequency choke coil 85, a radio frequency choke coil 06, and a radio frequency bypas condenser- 81. The function of this filter will be described below. A potentiometer consisting, as shown, of two parts, 08 and 89, applies the proper bias potential to the grid of tube II, and to the grid of tube 11, and serves also to supply the biasing potential to a tube 90 of the modulator and compensator circuit, to be described below.

Since the power tube I0 will in general carry a current in excess of the current which may flow through tubes I6 and II, a compensator circuit is provided comprising tubes 00 and SI connected in series, and a bridge arrangement consisting of condensers 02, 93, and 94 by means of which the cathodes of tubes 90 and 9| are supplied with a potential from the output lead 95 of tube in phase with the currents flowing through the tubes I6 and 11.

Thus, the resistance of the tubes 00 and SI is varied to have, at any instant, a constant proportion to the resistance of tubes I6 and I1, and insure a proportionate division of the current of tube between the two circuits of the tubes I6 and "and of the tubes 0| and 0|.

The circuit of tubes so and er may be utilized for modulation purposes in the following manner: Connectedto the grid 95 of tube 9| is the secondary 86 of a modulation transformer, the primary 91 of'which has terminals 90 to which audio frequency or any other control modulation may be applied. To separate the radio frequency from the transformer secondary 95 there is provided abypass condenser 99, and in series with the secondary 05 there is connected a radio frequency choke coil III. I have, furthermore, shown the connection of grid IOI of tube 90 to a tap I02 on the resistor 00, and through a grounding condenser. I03, to negative lead 83.

In this way, audio frequency potentials are applied to grid 95 and amplified by tubes 90 and II in the usual series amplifier connection so that the impedance of tubes' 90 and SI is in- ,creased or reduced in proportion to audio frequency modulations taking larger or smaller proportion of the total current flowing through tube II.

It is, of course, evident that the audio frequency modulations on tubes 90 and SI are also impressed the cathode of tube I8 and there- 'i'ore the output of tube I8 is modulated in accordance with this impresed voltage.

The function of choke coil 05 will now become evident as a coupling inductance for the audio frequency changes in potential due to theseries audio frequency amplifier consisting of tubes BI, 90, and I8. The radio frequency choke 'coil 05 blocks the passage of radio frequency currents to the input terminals 02 and 83 while the radio frequency bypass condenser 81 returns the radio frequency currents to the negative lead 83. An audio frequency bypass condenser 04 serves to return' the audio frequency currents to the negative lead 03.

A condenser I09 may be provided to supply the capacitative current to the tubeelements of tubes II and 90 while 'a condenser I 09' will supply the capacitative current of the elements of tube 15.- A condenser I03 may be also provided for grounding the grid of tube I8.

While the circuit described refers to the tubes IIi, II, and I8 as a series power amplifier in which the power tube I8 carries an excessive current which must be provided by the compensator consisting of tubes 90 and SI, it is evident that the same series of tubes, that is I6, II, and II, may be used directly as an oscillator. In that case, the feed back system, which will be'described below in connection with Figure 5, may be pro vided by asuitable choice of condensers I09, I09, I03, I03 or some other alternative form of bridge, as discussed in connection with Figure 5. If the tube I8 under these circumstances is a tube carrying a current in excess of tubes I5 and 11, then a compensator consisting of tubes 80 and SI may be also provided connected identically to this figure and this compensator may again be used as a modulator of the oscillations created in the oscillator I6, 11, andfIB. Again, the bridge of the compensator consisting of condensers 92, 93, 94, I03, and 99 can be arranged for the proper feed back service so that the tubes of the com pensator 90 and SI will also create oscillations. The tubes I8, 90, and SI will then be acting both as a modulator and as an oscillator.

The output circuit of tube I8 includes a tuned circuit comprising a condenser I04 and an inductance I05. The inductance I05 may be coupled to the antenna circuit, for instance, by means of a secondary coil I05 in series with an antenna I01 and a ground connection I08.

The tuned circuit may include also an adjustable resistor I06 with suitable taps at I01 and I08. The object of the resistor I06 is to widen the responsive range of frequency of the tuned circuits I04 and I05 to include the full range of modulation of tube I8. This range would thus include the side bands caused by the modulation of the high frequency currents in this circuit. The resistance of circuit I06 as well as the tuning of the circuits I04 and I05 and I06 can be adjusted to include the carrier with all of the side bands or merely the carrier with the side bands on one side, or even to include merely the side bands on one side of the carrier. It is evident,

.of course, that the tuned circuits I04, I05, and

I 06' can also be modified to any other type of radio frequency filter which, in conjunction with Figure 2a is widened and the operation of this amplifier, which is ordinarily limited as explained in connection with that figure to the range between such points as c and d, will be extended overa wider frequency band.

In other words, the power amplifier can be made responsive to as wide a range of frequencies as is desired for the practical operation of the transmitting set. Thus, for instance, if the carrier wave and one range of side bands are to 'be suppressed and the remaining side bands to be transmitted, the circuit of I04, I05, and I06 is merely tuned to a frequency intermediate of the desired side bands and the flatness of the tuned circuit, as determined by resistor I06, is arranged to have the points 0 and (1 cover the desired frequency band.

In Figure 5 a theoretical explanation is made of another system of feed back, applicable to se. ries oscillators. In this diagram the. abscissa represents the voltages on the different parts of the circuit and the ordinate represents the parts of the circuit, as illustrated on the left hand side of this figure, marked A, including the tubes A, B, and a tuned circuit T, in a series amplifier connection including a potentiometer 4 and a grid biasing resistor 11 connected to the cathode of tube A.

Referring to part B, Fig. 5, when a direct current is applied to this series amplifier, the voltage distribution will be in accordance with the curve Oaobuv, the voltage drop being distributed over the resistor H, the tube A and the tub B, while no voltage drop occurs on the line In) across the tuned circuit T.

The cathode of tube A will be at the potential indicated as 00 on the abscissa while the grid of this tube is as shown, connected to the ground potential 0. Similarly, the grid of tube B is shown to be connected to a potential marked g on the abscissa. a0 is the potential of the anode of the tube A and the cathode of tube B, while he is the potential of the anode of tube B.

Assuming that a change is applied .to the cathode of tube A. If this change is at a frequency to which the circuit T is tuned and between the limits or and 01 then the voltage on the system will vary from the curve oaibiv to the curve 0a1biv. This can be explained as follows: As the potential of the cathode of tube A is changed from 00 to 01 the amplification of tube A will raise its anode potential from do to 111, increasing the difference of potential from grid to cathode of tube B from the value gao to the value 9111.

The tube B will then amplify this changed potential so that its anode potential will have changed from be to In and the difference between the original voltage relation and the present voltage relation expressed by the value 170171 is impressed on the tuned circuit T. Similarly, when the cathodehas changed from C0 to 0'1, the cathode of tube B will change to m and the anode of tube B to bi.

In practice, however; I have found that owing to the distributed capacity of the tube elements to each other and the tube elements to ground,

the amplification does not entirely conform to this relation but is rather smaller, as indicated by dotted lines cab: and oaz'bz. The circuit is inherently stable insofar as the tube amplification is reduced by the inherent capacity of the tube.

It is evident, however, that as the output of tube B is connected to a tuned circuit T, including an inductance, this inductance can be made to supply the capacity currents of tubes B and A, and I have secured this by connecting elements, such as Z and Z which may be condensers \or combination of condenser and resistors, which bypass the cathode to anode of each of the tubes A and B.

Assuming for simplicity that Z and Z are condensers in series, then it will be seen that condensers Z and Z and the bypass condenser 18 are in parallel with the tuning condenser of the circuit T since the supply leads of the circuit are bypassed by a large condenser M. The capacity current of these condensers is thus supplied by the inductance of the tuned circuit T when it is operating at the resonance frequency. For theoretical consideration, it may be assumed that the elements Z and Z include also the distributed capacities of the tube elements and the tube elements to ground. There is shown, on the part marked C of Figure 5, separately the radio frequency potentials existing in the series oscillator. Thus, the curve OAzBzV corresponds to the voltage generated in accordance with the curves oazbzv, and oaz'bzv according to part B of this diagram. Radio frequency potential VB; exists across the tuned circuit and is applied to the bridge circuit ZZl8 and by choosing the proper values for the bridge capacity or resistors, this voltage may be given a distribution corresponding to curve OAJBZ.

Since the central point w of the bridge is connected between the tubes A and B, the potential 0A3 of this central portion is applied to the cathode of tube B, and thus the tube B can be made to amplify to anew potential B3, giving a final voltage across the tuned circuit VB: and a distribution of 'the voltage across the condenser bridge as OA4B3. The potential at point w is therefore raised to 0A4, and further amplification will take place. At the same time, the potential of the cathode of tube A as determined by the drop through the condenser l8, will be raised to a higher value so that the amplification of tube A is also raised. Such a capacity bridge will, therefore, cumulatively raise the amplification of the series system until a final value of radio frequency voltage 'is reached, such as OClAlBlV, shown at'part B of Fig. 5 which represents its resulting output.

It is seen, from Figure 50 that the radio frequency potential across tube A is represented by a value clAl while the radio frequency potential on tube B is represented by the value AlBl. The diagrammatic derivation from the series amplifier connection shows these voltages to be unequal in value. This need not be so however, since the grid of tube B can be supplied by another bridge, such as is illustrated in part A of Fig. 5, by impedance elements X and X with a potential which would give the amplification in tube B of the same magnitude as that in tube A. Thus, Figure 5D shows for two equal tubes, equal voltage increments CiAi for tube A and AiBi' for tube B, which require equal grid potentials 001' and GAi' on the two tubes.

It is quite evident that since the grid of tube A is grounded the impedances X and X can be chosen to give the desired value G on the grid of tube B, while the impedance Z, Z and I8 will give the potentials C1 and A1 on the cathodes of the respective tubes A and B. It is quite evident also that the particular combination of impedances such as X, X, Z, Z need not be utilized. but alternative bridge constructions may be also supplied to secure the necessary potentials on the va ious elements.

' tentiometer I28 to the grid of tube III.

I have illustrated already such alternative arrangements in Figure 3 as applied to a three stage oscillator and consisting of condensers 3|, 32, and 33 for the cathode circuits. The bridge for each cathode is then completed through the distributed capacity of all of the cathode connections to the negative lead 8. I have also shown condensers 35 and 36 which form a bridge arrangement for the grids of tubes Hand 25 respectively through the tube capacities of the respectlvefigrids to their respective cathode and anode elements.

I have also shown an alternative arrangement in Figure 4 where the condenser bridge 38. 69, 10, H, 12, and 13 supplied by capacitative current from the tuning circuit 84 through the bypass condenser 65 forms a bridge on which any desired radio frequency potential can be secured and an arrangement of taps from the different points of this bridge to the various tube elements of the tubes GI, 62, 63 is also shown. Thus, an oscillating condition can be established either in Figure 3 or in Figure 4.

This oscillathzg condition will be practically independent of he frequency to which the tuning circuit, such as circuit 64 of Figure 4 or tuning circuits 28, 28, and 30 of Figure 3, are adjusted.

Figure 6 illustrates the application of this system of feed back to a practical oscillator including three-tubes, III), III, H2, in series with the tuned circuit II3 with a return con nser H4. The direct current is applied to terminals I I8 and H9, the terminal II! being positive, and the output may be derived from the terminal I20 connected to the tuned circuit and to the anode of the tube II2 through condenser I2l.

The feed back arrangement may include an adjustable condenser I22 forming a part of a condenser bridge including also condensers I23, I24, and I25. By means of this bridge the suitable potentials are applied to the cathodes of all of the tubes while a similar bridge comprising condensers II5, II 6, and II1applies the correct potentials to the respective grids. Asshown, however, the grids may have a feed back in parallel with the condenser elements consisting of a potentiometer I26 in series with a tube I21 with taps from the cathode of tube I21 to grid of, tube H2 and .from an intermediate point on the po- Either the resistance element alone or the capacity elements alone may be used, or the combination of the two. The tube I21 may be replaced by a suitable resistor except when it performs a special function as follows:

- The resistance bridge may be utilized as a part of a modulating system in which the grid I29 of tube I21 is supplied with modulating'transformer I30. The return from the modulating transformer I30 is to a tap over a portion I28 of.

grid bias to gr d I29.

It is evident that modulating potentials are applied to transformer I30, they are impressed on the grid of- I21 and will change the impedance of this tube, thus.varying the feed back potentials applied to the gridsof tube III and H2. r

As an alternative. the tube I21 may be connected below the-potentiometer I26; that is, between the negative lead I I8 and the grid of tube III which will also result in effective operation. With this type of connection, it is possible to omit the usual potentiometer, such as potentiometer 4 of Figure 1 as the steady potentials to the grids will be supplied from the feed back potenpotentiometer I25 sizcient to give the correct tiometer I26 and the cooperating tube I21. Thus, the connection departs in this respect from the usual series amplifier circuit, but in general, unless this specific system of modulation is used, such a connection is not desirable as the oscillator is evidently bypassed by the resistor I28 and the tube I21, and, therefore, an extra load is imposed on it. I

An alternative manner of modulation utilizing the capacity bridge consisting of condensers I22, I23, I24, and l25 'is also shown. This can be accomplished by introducing the equivalent of a capacity element variable in accordance with modulation in series with condenser I22 and consisting of a primary I3I of a radio frequency transformer, the secondary I32 of which is connected via the condenser I33 to the anode and cathode of a tube I34. This tube has a suitable energy supply, such as a battery I35 and a choke coil I36, and a grid input consisting of the audio frequency transformer I31 the primary of which may be supplied with modulating currents while the secondary is connected to the'grid of tube I34 and through a tap on the potentiometer I33 across a biasing battery I38 to the cathode of the same tube. The value of potentials of batteries I38 and I35 is chosen in such a way that the dynamic impedance of tube I34 to radio. frequency will vary with the variations of the impressed modulation potentials from transformer I31. The effect of condenser I33 in series with impedance I34 will be to apply these modulations through the transformer I3I and I32 to the f ed back c rcui ond nse I22. While bat eries. are shown at I35 and I33, any other suitable energy supply may be used instead.

It is also evident that the impedance characteristic of tube I21 should be arranged with the same object in view; that is, that its impedance will vary with the variation of the potential impressed by transformer I3Il. As the operating characteristics of tubes are well known, such a choice of a suitable tube and suitable potentials are quite easily accomplished. ,In this way, I have shown two alternative ways of modulating by inserting modulating means in the special feed back arrangement of a series oscillator.

As the eflect of modulation of tube I34 on the feed back of condenser I22 is to change the capacity current flowing through this condenser I22. it will result in hangin sli htly the freflu ncy of the o eratin vsf m aim-' th c denser I22 in series with the bridge I23, I24, I25 is supplied with capacity current from the tuned circuit II3. Thus, I have secured a frequency modulation system which can be arranged by a suitable choice of the condenser I 33, the transformer I 3| and I32 of the cooperating-impedance of tube I34, relative to the other capacities in the tuned circuit, to secure any degree of. modulation that may be desired.

Referring to Figure 7, another' a rangement of series oscillator is shown in which the principle of capacity bridge feed back il ustrated in Figure 6 and discussed in connection with Figure 5, is further extended to include feed back bridges of opposite phase applied to the grid and the plate circuits. Tubes I40, I. and I42 are connected in series with grid biasing resistor I43 to. a tuned circuit including an inductance I44 and the tuning condenser I45. The inductance I44 may be supplied by direct current via a tap I45 through a radio frequency coil I46 and an audio frequency coil I41 from the terminal I48, while the resistor I43 is connected to the negative terminal I43.

The coil I44 may be coupled to the output coil I or its output may be derived by any alternative means, such as illustrated in Figure 3-.

The terminals of the tuned circuit I44--I45 are connected to two capacity bridges. The capacity bridge including condensers I5I, I52, I53, and I54 correspond to those illustrated in Figure fi and explained in Figure 5, and includes means for applying suitable capacity currents and suitable potentialsto the intertube connections and to the cathode of tube I40. The condensers I55, I56,-

I51, and I56 are shown connected to the opposite side of the tuned circuit I44-I45 and will therefore apply potentials to the grids opposite in phase to the plate and cathode potentials, and thus increase their feed back effectiveness.

Since the condenser bridge connected to me grid circuit carries an opposite phase of radio frequently from the bridge connected to the oathode circuits, it is evident that the condition shown in Figure 5D cannot be met with regard to the potential of the grids of tubes HI and I42. This connection will be more satisfactory if the tubes chosen for this circuit are graded with regard to their potentials so that thegrid of each tube, although receiving a potential of a phase opposite to the cathode potential will bear the correct ratio to the corresponding plate potential.

In other words, if the tubes are graded with regard to potentials in accordance to their amplification, so that tube I40 will have a relatively low voltage, tube I4I a larger voltage, and tube I42 still a larger voltage, then it is evident that the potential between the grid of, say, tube I42 and its cathode, although almost double the potential of the cathode of tube I42 with regard to lead I49, may be just correct to give the oscillating condition within this tube.

This circuit in this way will be equivalent to a graded parallel power amplifier of oscillations in which the oscillations of small power are passed on to a larger tube which amplifies them further, and from that tube to a larger tube still, with the exception that oscillating conditions are provided for all of the tubes on the same oscillating circuit I44 and I45 and therefore that the frequencies in all of the oscillators are determined by the same tuned circuit. In other words, there is no interstage coupling and the current in all of the oscillators is substantially the same.

The grids of tubes HI and I42 are further shown connected to the potentiometer I59 for securing the proper steady potential bias, the potentiometer I59 being supplied from the terminals I48 through the choke coil I41 and from the terminal I49. The grid of tube I40 may be supplied with a steady potential from the negative lead I49 via a radio frequency choke coil I60. I have thus established a double feed back on the series oscillator consisting of tubes I40, I, I42, and I have found that by this means a very effective and powerful oscillation of definite frequency can be se'- cured.

In order to modulate such an oscillation, I have shown a series amplifier consisting of tube I6I, I62, and I63 connectedto the same power supply terminals I48 and I49 through the choke coil I41. The radio frequency currents are prevented from passing into this amplifier by the choke coil I46 and are confined to the oscillating system including inductance I44, condenser I45, and the two bridge systems. The grids of tubes I62 and I63 may be connected to a separate potentiometer I64 but could be also supplied from the potentiometer I69 if the latter were connected directly to terminal I48. In that case, choke coils and grounding condensers would be necessary in the leads from the grids of tubes MI and I42.

The grid of tube I6I is connected to a modulating transformer I66, the primary of which may have any desired modulating currents applied to it. Bias resistor I65 insures the proper steady potential to the grid of tube I6I. The effect of the modulating amplifier of tubes I6 I, I62, and I63 is to impress to the input tap I45 and potentiomj eter I59 of the series oscillator a varying potential depending on the modulating potential of transformer I66, and thus, vary the output of the series oscillator in accordance with this modulation.

and the plate and gridbridges, the impressed modulation will merely affect the amplitude of these oscillations.

Referring to Figure 8, I have shown another modification of series oscillator which utilizes an additional tuning circuit on the negative side of the series amplifier for the purpose of sharpening the definition of frequency as generated by the oscillator. As discussed in connection with Figure 2, the steadiness with which the frequency is held at a definite value is dependent on the ratio of tube impedance to the impedance of the tuned circuit. Thus, if in series with the tube impedance, another impedance is inserted and it has tuning characteristics such that its impedance is lowest at the tuning frequency and increases as the frequency deviates from this value, the above ratio becomes more dependent on frequency and therefore, the steadiness of the frequency is enhanced.

As shown in Figure 8, I utilize for this purpose a so-called series tuning device consisting of an inductance I10 in series with condenser HI and connected to the negative side of a series oscillator comprising tubes I12, I13, and I14. The positive side of tube I14 is connected to a parallel tuning device including the inductance I15 and a tuning condenser I16. It is to be understood that the tuning circuit |15I16 may be adjusted to the same frequency as the tuning circuit I10 and IN. The other elements of the oscillator include the potentiometer I11 connected to the supply terminals I19 and I80 with taps to the various grid connections and a bypass condenser I16 to return the radio frequency currents from the tuned circuit I15 and I16 to the negative line I19. The positive line I80 supplies the tuned circuits I15, I16 and therethrough the series oscillator.

I have shown for tubes I12, I13, and I14 the so-called pentode tubes, the inherent characteristics of which is that of low impedance which makes them particularly suitable for series oscillator. The first and second grids of the pentode are shown connected to, suitable points of the potentiometer I11, whili-"the third grid is in the usual manner internally connected to the cathode of each tube. I have further shown bypass condensers from the various grids to the negative supply lead I19 and bypass condensers I8I, I82, and I83 to the cathodes of ,-the three tubes. These condensers are arranged again to have such values relative to the capacities of the tubes as to form the capacity bridges for securing the correct operating potentials on'the various elements in accordance with the considerations discussed in connection with Figure 5D. The circuit may be, thereby, render'ed inherently oscillatory. But I have provided, in addition, a further feed back arrangement. bY Providin As the frequency of the oscillator is in this 3 case defined by the oscillator circuit I44 and I45,

inductive coupling between the inductance I and the tuning coil I 15, as indicated by the arrow I84.

Since the condenser I1I isolates the cathode of tube I12 from the negative supply line I19, it is necessary to supply a bypass around the condenser I1I, which may be an inductance or a resistance. But I have shown as a preferred form a tube I85. the cathode of which 3s connected through the resistor I86 to the negative line I19, and the anode of which is connected to a tap I81 on the coil I10.

The tube I85 is, therefore, in series with the tubes I12, I13, and I14 and will cooperate with those tubes to form a series amplifier for modulating of the series oscillator. a modulating transformer I88, the primary of which may be supplied with suitable modulating currents and the secondary of which is connected to the negative line I19 and the grid of tube I85 may be used. Thus, the applied modulating potentials are amplified in the tubes I12, I13, and I14 and applied across the choke coil I89 in the positive lead I80, in such a way that the oscillator is subject to a modulating variation of potential. A bypass-condenser I90 permits theaudio frequency variations to return from the positive lead I80 to the negative lead I19. A coil I9I may be coupled to the coil I and utilized either for further amplification or for transmission purposes. I have thus combined in the same series connected tubes, the functions of an oscillator, an amplifier for modulating currents, and the modulator.

The arrangement of Figure 8 can be conveniently utilized for the purpose of suppressing is taken into account and the frequency im-- pedance characteristics of the tuned circuits I15 and I16 is modified in a manner exactly similar to that of the tuned circuit I04, and 105 of Figure 4 by inclusion of a resistor similar to resistor I08 of Figure 4.

However, the suppression of the carrier wave can be accomplished independently of such a change in the frequency characteristic of circuit I15 and I16. Instead, the tuned circuit I10 and HI may be adjusted to have its resonance point about the center of one of the side band rangesl Then. at the other side band range, this same tuned circuit imposes a relatively high impedance in series with the tube impedances and prevents any oscillations of this second half of the side band range in the oscillator. .In such aform of operation, I would prefer to omit the feed back arrangement illustrated by the arrow I84 which would necessarily tie up the tun'- ing characteristics of the two tuned circuits.

The .operation of such an oscillator modulator combination with suppressed-side band may be explained, for example, as follows: The normal connection of the oscillator including the tuned circuits I15 and I16, the three tubes I12, I13, and I14, and their capacity bridges, will have a definite oscillating frequency. The modulating tube I85, acting through the same tubes I12, I13, and I14 as amplifiers at modulating frequency, will modulate the output of oscillations so that theoretically all of the side bands will be present in this modulated wave.

For this purpose However, as the tuned circuit consisting of inductance I10 and condenser I1I is impressing a high impedance for the side band frequencies on one side of the carrier, these particular side bands will be reduced in amplitude or completely.

.of transmission that the suppression of one half of the side bands results in an increased output of the whole transmitting system without any sacrifice of the clarity of reception provided at the receiving circuit the suppressed range of side bands is re-established.

Referring to Figure 9, I have shown another arrangement for modulating a series amplifier in which the modulating circuit is connected in series with the series oscillator. I have shown a two tube oscillator comprising the tubes 200 and I in series with a tuned circuit consisting of inductance 202 and a tuning'condenser 203.

I have also shown a radio frequency return condenser 204 which connects to the cathode of tube 200 through a bias resistor 205. I have also shown a capacity bridge consisting of condensers 206, 201, and 208 by means of which the distributed capacity of the tube elements is included in the oscillatingcircuit.

The feed back arrangement in this case is shown by means of a coil 208 connected between the return to the cathode of tube 200 and the id of the same tube, and the arrow 2I0 indicates that this coil is inductively coupled to the inductance 202 of the tuned circuit. A potentiometer 2II is also connected from the return lead 2I2 to the positive lead 2I3. There is also a radio frequency condenser 2I4 to supply the grid of tube 20I with proper radio frequency potential. This grid is also connected to a suitable tap 2| 5 on potentiometer 2 to supply it with a proper steady potential.

The above description covers a complete two tube series oscillator. 'It is seen from the diagram that this oscillator is directly in series with tubes 2I8, 2I1 which constitute a series modulating amplifier. This amplifier utilizes the tubes 200 and 20I as a resistance coupling element for its molulations and has a return audio frequency path through the condenser 2H! and the biasing resistor 2I9. The latter may also be bypassed by suitable condenser 220; The grid of tube 2I6 may be supplied from a modulating transformer 22I, the primary of which is fed with suitable modulating currents, and the secondary of which i connected to the negative line 222 and the grid of tube 2I8. The grid of the tube 2I1 is connected to a tap point 223 on a potentiometer 224' which, as can be readily seen, is in series with the potentiometer 2H and an audio frequency choke coil 224. Of course, instead of connecting the potentiometer 224 in series with 2, it is also possible to extend this potentiometer and supply with a positive potential from the terminal 2I3. Choke coils 225 and 226 isolate the modulating amplifier from the radio frequency oscillator, audio frequency bypass condensers 221 and 228 may be also supplied to steady the potential lines 2I2.and. 2l3 a potential is applied to the series oscillator varying in accordance with the modulatedirequency, and the oscillator output will be accordingly varied. The tuning coil 202 may be coupled to an output coil 229 for further amplification, or for use in a transmitting antenna.- 7

.' Figure 10.' shows another modification of a series modulating arrangement in which the-oscillator is of a push-pull type; that is, the oscillator is split into two parallel channels and arranged so that while'the current in one of these channels is increasing, the current in the other channel is. decreasing.

I have shown an oscillator consisting of tubes 233, 23l, 232, and 233 and a tuning circuit consisting' of inductance 23 4, and a tuning condenser 235. The tubes .230 and 23l constitute one channel of the oscillator while the tubes 232 and 233 the other channel of the oscillator, and the two are connected respectively to the opposite points of the tuning circuit 234 and Y235. A centertap 236 on the coil 234 connects the oscillator to the positive supply 231. In this oscillator it is not necessary to supply any potentiometer for grid potentials. The diagram shows that the grid of tube 23l is directly connected to the anode 'of tube 232 and the grid of tube 233 to the anode of tube 233.

- Similarly, the grid of tube 233 is connected to the negative terminal of oscillator channel 232, 233 at point233 while the grid of tube 232 is connected to the negative terminal of the oscillator channel 233 and 2" at the point 239. Blasing resistors 243,2, 242, and 243 are respectively connected to the cathodes of the tubes 233, 23l, 232. and 233. In this'way, for a steady con dltion, the grid of each of the tubes is receivinga biasing potential from a tube in the other channel. Butwhen the oscillations are established while the cathode of, say, tube 231 is rising inpotential the cathode of tube 233 and the anode of tube 232 are'fallingin potential, and therefore the grid of tube 231, which is connected to the anode of tube 232, is receiving a potential in the opposite phase to the cathode of tube 23!, and a condition is established for powerful oscillations, since on each or the tubes the cathodes and anodes are driven to opposite potentials.

It may be desirable in this case to have different.

voltage ratings on tubes 23! and 232 as compared with .23! (and 233 for the'same reason as was explained in'oonnection with Figure 7.' Capacity bridges, consisting of condensers 244, 245 on theehannel 233 and 23!, and consisting of 243, 241 on the channel 232 and 233, is also supplied to take care of the capacitative current. An interchannel condenser 243 is arranged between points 233 and 233 by means of which a return path is formed for the capacitative currents that may circulate through the capacity bridges. T

the negative potential is applied to the push-pull oscillator.

. For modulating purpom, tubes 23! and 232 are connected in a series-amplifier circuit with the cathode of tube-23L supplied from the negative lead 233 and a biasing resistor 234' while the grid of tube 231 is fed froma modulating transformer 235 with suitable potentials. The grid of tube-13.2 is asuitable tapron a potentiometer 233 across the power mply- It is seen, therefore, that themodulating p have also shown coils 24s and 233anda connection at point 233 through i accordance with the principle discumed. with connectedto.

. may serve for output purposes.

Referring. to Figure 11, I have shown a further modification. using a push-pull series oscillator and a push-pull series modulator, the modulator comprising tubes 213 and 21! in one channel and tubes 212 and 213 in the other channel, each series connected to the negative. supply 214 and a positive supply 215. The negative supply leads contain a biasing resistor 216 for the first channel and a biasing resistor 211 for the second channel. The positive supply lead 215 is connected to a center tap on a push-pull transformer primary 213. The two ends of the transformer 213 are connected directly to the anodes of tubes 21! and 213. A potentiometer 219 is also connected to the center tap and serves to supply the correct biasing potentials to grids of tubes 2" and 213 from potentials of opposite phases from a transformer 23 I the primary of which is supplied with suitable modulating currents. The secondary 232 of the modulating transformer is connected on one side to the positive supply lead 215 and on the other side to the input tap 233 of the push-pull series oscillator. v

This series oscillator, includes the tubes 234 and 235m one channel and the tubes 233 and 231 in the other channel. The anodes of tubes 235 and 231 are respectively connected to -'opposite ends of the tuning inductance 233 of which point 233 forms the center tap and a tuning-condenser 238 is also connected across these opponte ends. The center tap 233 supplies also'a potentiometer 233, the other end of which is connected to the negative supply lead 214. Biasing resistor 23l is supplied for the first channel and biasing resistor 232 for the other channel. Capacity bridges similar to those of Figure'9 are shown for each of I thechannels and serve the same purpom. The grids of tubes 234 and 233 maybe supplied from' a feed back coil 293, which may beinductively coupled to the tuning coil 233. The center, tap of the coil 233 may be connected to the negative lead 214 so that the opposite ends will supply opposing potentials to the grids of tubes 234 and 233. The arrow 234 indicates the magnetic con- 'pnh between mass m which must be, of

course, ofsuch aseniethatthepotentialofthe grid of, say, the tube 234 is in the oppositephase tothepotentialoftheanode ofiaibelli.

The feed back coil 233 may be omitted if the capacity bridges are armfiged to have feed back will form, in connection with he capacity of tubeelements 01' tubes 23! and 231, a bridge circuit across the timed circuit 233 and 233to' securetheoorrectpotentialoneachoffllegrids ,thesetwogridschwenofsmhavaluetlntit' 20" rality of discharge devices having anode, cathode corresponding to diagram Figure D. Thus, the oscillations in the series oscillator will be in opposite phase but of full magnitude in the two channels. v

In this way I secure a powerful oscillator which needs no return circuit, as the oscillations are confined within the circuit so thatthe output lead and the secondary 282 need not carry any radio frequency current.

As a. further protection, however, I interpose a choke coil 2% in this supply lead. The coil 288 may be coupled to an output coil 299 for further amplification or transmission.

Although I have illustrated my invention as applied to an-oscillator, it will be understood that it has other adaptations in electrical circuits and these come within the scope of my invention.

I claim ,1. An oscillation generator comprising a pluand control electrodes; a source of current therefor; a resonant circuit; said devices, said circuit and said source being in series through the anode of one device being connected to the cathode of the succeeding device and a potentiometer con nected across said source provided with tap connections to said control electrodes to maintain predetermined fixed potentials thereat.

2. An oscillation "generator comprising a plurality of discharge devices having main electrodes; a source of current therefor; a predetermined resonant circuit; said devices, said circuit and said source being connected'in series; control electrodes for said devices; a potentiometer connected across said source and tap connections from said potentiometer to said control electrodes to secure predetermined fixed biasing potentials.

thereat; and a feedback circuit connection from said resonant circuit to the control electrode of the firstdischarge device. I I

3. An oscillation generator comprising a plurality of thermionic discharge tubes having cathode, anode and control electrodes; a source of current therefor; a parallel resonant circuit;

said tubes, said resonant circuit and said source,

being connected in series with the anode of one tube being directly connected to the cathode of the succeeding tube; afeedback circuit connection from said resonant circuit to the first tube; means for maintaining constant predetermined direct potentials relative to said source at the control electrodes of said tubes; and further means for securing proper relative high frequency potentials at the various electrodes of said tubes, said first means consisting of a potentiometer connected across said source and tap connections from said potentiometer to the control electrodes of said tube, and said further means comprising an impedance bridge connected across said resonant circuit and tap connections from said bridge to the electrodes of said tubes. 1

4. An oscillation generator comprising a plurality of thermionic discharge tubes having cathode, anode and control electrodes; asource of current therefor; a parallel resonantcircuit;

said tubes, said resonant circuit and said source being connected in series with the anode of one tube being directly connected to the cathode of the succeeding tube; a feedback circuit connection from said resonant circuit to the first tube; means for maintaining constant predetermined direct potentials relative to said source at the control electrodes of said tubes; and further means for securing proper relative high frequency potentials at the various electrodes of said tubes; said last means comprising a series of condensers connected across said resonant circuit and connections from said condensers to the cathode electrodes of said tubes.

' 5. An oscillation generator comprising a plurality of thermionic discharge tubes having cathode, anode and control electrodes; a source of current therefor; a parallel resonant circuit; said tubes, said resonant circuit and said source being connected in series with the anode of one tube being directly connected to the cathode of the succeeding tube; a feedback circuit connection from said resonant circuit to the first tube; means for maintaining constant predetermined direct potentials relative to said source at the control electrodes of said tubes; and further means for securing proper relative high frequency potentials at the various electrodes of said tubes, said last means comprising a seriesof condensers connected across said resonant circuit and connections from said condensers to the control electrodes of said tubes.

6. An oscillation generator comprising a plurality of thermionic discharge tubes having cathode, anode and control electrodes; a source of current therefor; a parallel resonant circuit;

said tubes, said resonant circuit and saidsource being connected in. series with the anode of one tube being directly connected to the cathode of the succeeding tube; a feedback circuit connection from said resonant circuit to the first tube; means for-maintaining constant predetermined direct potentials relative to said source at the control electrodes of said tube; and further means for securing proper relative high frequency potentials at the various electrodes of said tubes,

said last means comprising a series of condensers connected across said resonant circuit and connections from said condensers to the anodes of said tubes.

'7. An oscillation generator comprising a plu-. rality of discharge devices, each having cathode, anode and a control electrode; a source of current therefor; a plurality of resonant circuits each tuned to a different frequency; said devices, said circuits and said source being I in series with the anode of one device being directly connected to the cathode of a succeeding device; means for maintaining the control electrodes of said devices at predetermined fixed potentials and feedback circuit connections from said resonant circuits to the first of said devices wherby said series circuit is maintained in multiple oscillating condition.

' ALEXANDER NYMAN.

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