US2056852A - Electrical signaling system - Google Patents

Description

Oct. 6, 1936.

H. R. HAYDEN ELECTRICAL SIGNALING SYSTEM ,Filed Feb. 4, 1929 INVENTOR m ATTdRNEY.

Patented Oct. 6, 1936 ELECTRICAL SIGNALING SYSTEM 7 Harold R. Hayden, Brooklyn, N. Y.; Elsie G.

Hayden executrix of said Harold R. Hayden,-

deceased Application February 4, 1929, Serial No. 337,294 -8 Claims. (01'. 250-27) This invention relates to electrical systems employing three-electrode vacuum tubes as repeaters or amplifiers.

The system herein disclosed is a multi-stage signal receiving system, employing a detector stage followed by several stages of audio frequency amplification, and each of the audio'frequency stages is coupled to the preceding stage by a so-called impedance coupling; the last audio frequency stage serving to operate a loud speaker of other signal-translating device. Each stage of the system includes a three electrode vacuum tube, the plate circuit of which is energized from a source of fluctuating direct current, such for example as from an alternating current supply; system through a rectifier and filter. The filaments of the several tubes may be supplied with direct current from any suitable source, such as a battery or if desired means may be provided for maintaining the battery charged from the same source of alternating current as supplies the plate circuits. I may, however, if desired, supply the filament of the tubes with alternating current.

The use of 1 alternating currentas a source of supply for the tube circuits tends to create disturbing current variations in the outputcircuit of the last tube, thus interfering with-the satisfactory reception of signals. With'the plate circuits of the tubes supplied from a source of alternating current through a rectifier and filter the current supplied to the tube circuits, although unidirectional, issubject to variations of low frequency which tend to produce a disturbing noise in the loud speaker. This effect is more pronounced in systems employing a plurality of stages arranged in tandem and coupled to one another by audio frequency couplings, as in the case of a multi-stage audio frequency amplifier; because the low frequency hum variations inthe plate circuits of the first stages arereadily carried over through the audio frequency couplings to the grid circuits of succeeding stages and are amplified in the succeeding stages. Similarly when alternating current is employed in the filaments of the tubes, the alternate heating and cooling of the filament as well as other effects caused by the alternating current in the filament, tends to cause disturbing current variations in the tube plate circuits, which tendency is more pronounced in the case of multi-stage audio frequency amplifiers.

One important object of the present invention is to provide a system of this general character wherein a. source of fluctuating'current is employed for energizing one or more of the tube circuits and wherein disturbing current variations in the plate circuit of the last stage are substantially reduced or eliminated.

A further object of my invention is to provide a receiving system with the parts so constructed andarranged that the tube circuits may be: supplied from a source of fluctuating current or potential and the disturbing effects caused by the fluctuations in the supply will be balanced out in the receiving system so that little or no disturbing variations will occur in the plate'circuit of the last tube. A

In systems constructed in accordance with my invention, which are designed to eliminate hum, I make use of an interstage coupling so constructed and-arranged that disturbing current variations in an earlier stage are reversed in phase and the reversed variations are caused to oppose in their effect, the effect of similar disturbing current variations in a later stage. that form of invention disclosed I employ as couplings between successive stages, reactance couplings or the so-called impedance couplings. These couplings serve to impress on the grid of the following tube, potential variations which are dependent upon potential variations at some part of or point in the plate circuit of the preceding tube. By proper construction and arrangement of the couplings or of the circuits with which they are connected I am able to cause variations occurring in a preceding stage to oppose similar variations arising in the following stage, and a further object of my invention is to provide a system of this character wherein the opposing variations are of substantially equal magnitude and substantially degrees out of phase with one another, whereby the opposing variations substantially balance and neutralize one another, as will be more fully explained hereafter.

Further features of myimproved signal re- In the drawing reference character I 0 represents an antenna adapted to receive signal waves.

' The antenna is grounded at I I through a Winding I2 positioned in inductive relation to a winding I3 included in the grid circuit of a detector tube I6. Connected across the terminals of the winding I3 is a condenser I8 which is adjustable to tune the grid circuit of the detector to the frequency of incoming signals to be received. For the purpose of providing a finer tuning adjustment, I may, if desired, employ a smaller condenser I9 in shunt to the condenser I8. One sideof condenser I8 and I9 is connected to the filament of tube I6 and the other side is connected to the grid of tube I6 through an adjustable-condenser 20 of small capacity and, in parallel with the condenser 20, a high resistance 2| which is also adjustable. t Connected in series with the plate of the detector tube I6 is a winding 22 positioned in in N0. 1,881,357, October 4,1932.

Theplate circuit'of tube I6 is coupled to the grid circuit of the first audio frequency amplifying tube 30, through an impedance coupling 3I consisting of an inductance or inductive impedance32 in the-plate circuit of, tube I6, a resistance 33 in the grid circuit of tube 30 and a condenser 34 connecting similar terminals-of the impedance and resistance, as shown.

The grid circuit of the second audio fre-v quency amplifying tube '40 iscoupled to the plate circuit of the tube 30 by' an impedance coupling 4I comprising an impedance 42,,resistance 43 and 'condenser 44, connected as shown; Similarly thegrid of the amplifier tube 46, which in the system shown, is in the last stage of amplification, is coupled to the plate circuit of tube 40 by an impedance coupling 41 comprising an impedance 48, resistance 49 and condenser. The highly amplifiedcurrents in the plate circuit of the final amplifier tube 46, serve to operate a loud speaker, or other signal translating device 52. The loud speaker may be shunted by acondenser 53 of small capacity. 'If desired, the resistance 49 of the coupler 41-may be shunted by a resistance 55 which is adjustable to control the volume of sound in the loudspeaker.

Heating current for the filaments of the detector and amplifying 'tubes is supplied from a source of current connected to the terminals +A and A. This source 0f current may be a battery ordirect current lighting mains. In 'certain cases also I may employalternating current in the filament heating circuits.

The +A terminal .is connected to the positive terminal of each filament through a conductor 6| and the -A terminal is connected to the negative terminal of each filament through a conductor-62 and a rheostat B4 in each local filament circuit.

The grids of the amplifier tubes are connected to the negative side of the filament supply through conductors 69 and I0. I find when employing 3M A tubes and using a five volt source of supply for the filaments, that with adjustment of the rheostats 64 to include several ohms in the filament circuits, the arrangement shown gives a satisfactory grid biasing voltage for the amplifier tubes. It will of course be understood that I may, if desired, to secure the gridbiasing voltage, employ a potentiometer across the filament supply with a tap or taps to the respective grids. Also I may, if desired, employ a grid biasing battery. The system? shown, however, has the advantage that such additional grid biasing meansunnecessary. The grid of detector tube I6 is connected to the positive terminal of the filament of this tube through the winding I3 and the, grid biasing resistance 2 I.

Connected across the inductance 32 and source of filament supply is a condenser I06 of small capacity, whichforms a path of low impedance for the high frequency components of, the detector tube plate current.

For the purpose of supplying direct current for energizing the plate circuits of the tubes, I provide a rectifier 80, adapted to be, energized from asource of, alternating current indicated at 8|, which-source may be the usual alternating current house lighting mains, and connected with the output circuit of the rectifier 8B is a filter 82;

Reference character 93 represents the primary of an alternating current transformer, supplied from the mains 8|. Reference charactersBBand 81 represent respectively low and .high voltage secondaries-of the transformer. The rectifier 80 in the ,form of invention shown comprises a vacuum tube 89, the plate and grid of which are connected with one terminal of the secondary winding BI and the filament of. which is connected across the secondary winding '86 through a current controlling rheostat: 9|. Theother terminal of the secondary winding 81 is connected to the .positive terminalxof the filament supply through a conductor 93 which forms the negative-supply .conductorifor the plate circuits from the rectifier and filter. One terminal of the secondary 86 is connectedthrough a reactance coil 94 of relatively high impedance to'the conductor 95 which forms 'the positive terminal conductor ofthe filter; Connected across the filter output circuit at opposite sides of the reactance 94 are high capacity :conden'sers '98 and 99, ofsay-approximately 2 mid. capacity each, more or less; and also connected :across the "output circuit between the .conductors 93 and 95, are three parallel circuits, each comprising an adjustable resistance, I00, I 01 and 1102, respectively, of relatively high value, such for example as 10,000 to 100,000 ohms, and in series with each resistance a high capacity condenser, 303, I04 and "I05, respectively. Condensers 103, I04 and I will ordinarily be of considerably less capacity "than the condensers 98 and 99. -All condensers employed may, .if desired, be theusual by-pass condensers .of relatively low voltage test.

Leading from a point between the resistance I02 and condenser I 05 is a=conductor III) which connects through the reactance 32 and winding 22 with the plate of the detectortube. The plates of the remaining tubes are connected to a point between the resistance fIIlIand condenser Why 7 V conductor II2 supplies to the plate circuits of the amplifier tubes a relatively higher voltage, such for example as '75 volts. The conductor 95 or the tap. I20, which connects with a point between the resistance I00 and condenser I03 may, with the resistance I00 properly adjusted, be employed, whenl higher plate voltages are required, as for example when a power tube is employed in the last stage of amplification. When the detector stages are preceded by one or more stages of radio-frequency amplification, I may energize the radio-frequency tube plate circuits from the tap I20 or tap II 2. It will be understood that adjustment of the resistances I00 to I02 permits adjustment of the voltages of the taps over a relatively wide range to satisfy the requirements of the various tubes. While I have shown three taps in addition to the positive terminal conductor 95, it is obvious in certain cases that this number of taps is not necessary. Thus with the rectifier and filter designed to give proper voltage, I may supply the plates of one or more of the tubes, taking a higher voltage, directly from the terminal conductor 95.

The condensers I03 to I05 may also be adjustable to vary their effective capacities. Thus, in place of each of these condensers I may substitute a fixed condenser and a variable condenser in parallel therewith.

The rectifier. and filter as above described may be built as a separate unit and designed to be connected with the receiving system by a conductor cord or cable containing the various output conductors.

In considering the operation of my improved. system, in eliminating hum due to variations of current supplied by the filter to the tube circuits, it is to be noted that the hum current variations in the plate circuit of any tube except the first, are the result of two effects, that of filter voltage variations applied directly to the plate circuit of that tube and that of filter voltage variations supplied to plate circuits of preceding tubes, and carried over to the grid of that tube. Thus a momentary rise in voltage applied by the filter to the plate circuit of the last tube, would, if acting alone, cause an increase in current in the plate circuit. If, however, simultaneously with the increase of the voltage applied directly to the plate circuit of the last tube, the effect of the increase in filter voltage as applied to the plate circuits of the preceding tubes is to cause the potential of the grid of the last tube to become less positive, these two effects will oppose one another and reduce the resultant current variations in the plate circuit of the last tube. If the amplitude of the variations of grid potential and filter voltage variations applied directly to the plate circuit are properly related in value, these two effects may be caused to cancel one another. It is one feature of the present invention to secure this result or to so fix or control the relative values of these two effects with respect to amplitude and phase, .that current variations in the plate circuit of the last tube are maintained at such low amplitude as not to mask or materially interfere with the reception of signals.

Referring to the drawing the couplings shown are reactance couplings, comprising coupling condensers 34, 44 and 50. These couplings serve to transfer to the grids of the succeeding tubes potential variations which are proportional to the potential variations of that point of the preceding tube plate circuit which is connected to the coupling condenser. Thus, due to a rise in the filter voltage applied to the detector tube plate circuit, there is a rise in potential at the point 34 and a resulting increase in the potential of the grid of tube 30. The increase in potential of the grid of tube 30 causes a decrease in the internal impedance of the tube tending to allow more current to flow through the plate circuit of this tube and also tending to decrease the potential of the point 44' in the plate circuit, which is connected to the coupling condenser 44. Due also to the rise in the filter Voltage, this voltage, applied directly to the plate circuit of tube 30 causes an increase in current in the plate circuit and a tendency to increase the potential of the point 44'. The point 44 is thus subject to two effects, one tending to raise its potential and one tending to lower its potential. If these two effects are equal and opposite, there will be no change of potential of the point 44' because of variations in this filter voltage and therefore no variations from this source will be passed on to the grid of tube 40. If the effect of variations in the grid of tube 30 predominates over the effect of filter voltage variations applied directly to the plate circuit of tube 30, the potential at the point 44' will decrease. If on the other hand, the filter voltage variations applied directly to the plate circuit of tube 30 predominate over the effect of the grid variations of tube 30, the potential of point 44' and consequently the potential of the grid of tube 40 will increase due to the rise of filter voltage.

It will thus be seen that by control of the amplitude of the voltage variations delivered directly to the plate circuit of tube 30, or of the amplitude of the variations in the grid potential of tube 30 and by control of the phase displacement of one of these variations relative to the other, the effects of these two variations may cancel one another or the two may combine to produce a resultant effect in phase or out of phase with. one or the other of the two effects.

In considering the potential variation at the point 34' due to variations of filter voltage, it is to be noted that these variations lag with respect to the variations in filter voltage, due to the inductance of the coupling impedance 32. Similarly the voltage variations at the point 44, due to filter voltage variations applied directly to the plate circuit of tube 30, lag with respect to these filter variations, due to the inductance of coupling impedance 42. Also it is to be noted that variations of the grid potential of tube 30, caused by potential variations of the point 34, lead with respect to the potential variations of point 34', due to the capacity of the coupling condenser 34.

The potential variations at the point 50 in the plate circuit of the tube 40 are likewise dependent on variations of potential of the grid of tube 40 and variations of filter voltage applied directly to the plate circuit of this tube, and whatever variations result from the combined effects of the two former variations are carried over to the grid of the last amplifier tube.

The quantitative values of the potential variations at points 34, 44, and 50 may be expressed very closely as follows:

Neglecting the effect of the small condenser I06, and letting e be the voltage variations of the filter output circuit, that is, the variations between conductors 93 and 95, To the value of resistance I02, C0 the capacity of condenser I05, r the impedance of the detector tube, Z1 the impedance 32, then the potential variations at the point 34' will be dVl ez' and if dV1' represents the potential variations of the grid of tube 30, then where'n represen'ts-the value of the resistance 33 and C1 the capacity of condenser 34.

The voltage variations dV1 on the grid of tube 3!] will be amplified by the tube 30, and cause varying potential effects at the point 44 in the plate circuit of tube 30. These latter effects will combine with the varying potential effects at this point, caused by the varying filter voltage applied directly to the plate circuit of tube 30. q The direct effects at the point 44 may be expressed quantitatively by an equation similar in form to Equation (1). Assuming that the resistance IDI is adjusted to a low value so that substantially the entire filter voltage is applied to the plate circuit of tube 30, the direct effect at the point 44 may be expressed quantitatively, as

2 m -i- Z2 where rz is internal impedance of tube 30 and Z2 is the value of impedance 42. With the assumed conditions the actual potential variations, dVz, at the point -24 which is the sum of the direct and indirect effects at this point will be n I z 2p nz i 2) where 2 is the amplifying factor of tube 30.

Similarly, under these conditions the resultant variations at the point in the plate circuit of tube 4%! will be By properly relating the electrical quantities in the system as expressed generally in the above equations, variations may be introducedinto the grid of the last tube, the effect of which when combined with the eifect of variations in the filter voltage applied directly to the plate circuit of the last tube, will so reduce the current variations in this plate circuit that no audible hum will be produced in the telephone or loud speaker. The system above described represents one embodiment of my invention wherein this result is attained and wherein signals may be received by the system and amplified efficiently.

Not only may the opposing variations in the plate circuit of the last tube be made of equal amplitude, but they may if desired be made opposite in phase .to the variations which they opposed.

By proper construction phase displacement caused for example by the coupling condensers may be compensated for and the potential variation passed on through one or more of the tubes be completely neutralized. Thus in order to compensate for theflphase displacement of the indirect effects due to the coupling condensers, different coupling impedances may be made of different values, so that the direct effects at one or another of the points 44 and 50' shall be displaced from the indirect effects by 180 degrees or more or less as desired. In this connection it is to be noted that the plate circuits which are coupled to a following stage, eachcomprises a resistance at one side of the coupling p0int, namely'the tube resistance, and a reactance and resistance at the other side of the coupling. point. The phase of the direct effects at the coupling point with respect to the phase of the filter voltage variation is dependent on the relation of the in-' ductance to the total resistanceof the plate circuit and with a given phase displacement, the amplitude of the direct effects at the coupling point, with reference to the amplitude of the filter voltage variations, depends upon what proportion of the total resistance is at one side of the coupling point. It is therefore apparent that by properly arranging the resistance at opposite sides of this coupling point and by properly relating the inductance of the plate circuit to its total resistance, the direct effects at the coupling points may be made of the amplitude and phase required for neutralization. Furthermore, the system provides a number of adjustments Whereby these'eifects may be controlled and at the same time secure efiicient reception of signal.

Thus, the rheostats for controlling the currents in the individual filaments provide a means for controlling the internal impedance of the tubes independently of one another by changing the grid bias of the tubes and by controlling the supply of electrons emitted from the filament.

Also adjustmentof the grid leak resistance 2| controls the internal impedance of the detector tube and thus controls the direct effect at the point 34. control the voltages supplied to the plates of the several tubes and thus control the direct effects respectively at the point '34 and at the points 44 and 50'.

Inasmuch as variations'in the earlier stages are amplified insucceeding stages, the same adjustments in the earlier stages produce 'much greater effect in the output circuit of the last tube than corresponding adjustments in the later stages. The arrangement in the filter circuit'of the resistance I02 in series with the detector plate circuit and the condenser 105 across the detector plate circuit is of decided advantage. The condenser which does not permit the passage of the direct component of the filter current, 'forms a by-pass for the varying component, thus acting to reduce materially the variationsapplied to the detector tube circuit and at the same time avoids excessive consumption of current from the filter. In this connection it is to be noted that the filter does not comprise any connection across the filter output which will permit the passage of the direct component of the filter current.

It will be seen from an inspection of the foregoing equations that hum may be controlled by adjustments other than those above mentioned. Means may be provided for varying the values of the impedances in the plate circuit, adjustable rheostats may be placed in the plate circuit at Similarly the rheostats I00 and llll one or at both sides of the coupling points, thus providing means for controlling the direct effects at the coupling points. The circuit disclosed provides means for opposing the canceling disturbing current variations of altered phase whether the phase alteration is caused by an impedance coupling, transformer coupling, or coupling of any other type.

The phase displacement of the indirect effects due to the coupling condensers may be lessened by employing coupling condensers of greater capacity. I, however, find certain advantages in employing coupling condensers of relatively small capacity. By eliminating the condensers and employing the so-called direct coupling, I eliminate the phase shift from this source.

Inasmuch as hum is eliminated by causing the effect of variations in filter voltage applied to one part of the system to oppose or cancel the effect of filter variations applied to another part of the system, the amplitude of the filter variations may be changed without affecting the hum, thus making it possible to employ relatively cheap filters wherein the output voltage is subject to relatively large periodic variations. In one system built by me, the condensers have an aggregate capacity of 5.75 mfds. and I find that I can reduce this capacity by a substantial amount without affecting the reception, detection and amplification of the received signals.

For heating the filamentsofthe system disclosed, I may, if desired, employ alternating current and eliminate disturbing current variations arising not only from the filter variation, but also from the variations in the filament heating circuits. One embodiment of such a system would include an alternating current source of supply for the filament heating circuits, such for example as another secondary winding on the supply transformer which is connected to the filaments of the amplifier tubes to supply alternating current therethrough, and as a detector tube I may employ an alternating current tube of the indirectly heated type. The grid circuits are connected in the usual manner, employing potentiometers across the alternating current supply and suitable means is provided for supplying the requisite grid biasing voltages.

The alternating current in the filaments tends to cause fluctuations in the plate current due to variations in the supply of electrons and their flow to the plate. Thus the periodic cooling of the filament at times of low current tends to diminish the emission from the filament. Other effects tend to produce the same result as for example the magnetic effects due to the change in current in this filament. When these effects causemore current to flow in the plate circuit of a tube coupled to a succeeding tube by an impedance resistance or other coupling of the character shown, the potential of the coupling point in the plate circuit is lowered and as a result the grid potential of the succeeding tube is lowered. This tends to cause a decrease in the plate current in the following tube. If simultaneously with this tendency to decrease the plate current in the following tube, there is a tendency to increase the plate current in the following tube due to the effect of the alternating current in the filament of the following tube, these two tendencies will oppose one another, and can readily be controlled so that there will be no variations in the output circuit of the last tube. In a system such as that shown any residual variations derived from the filament heating currents, such as might be caused by differences in magnitude or phase of the direct and indirect effects, can be substantially eliminated by introducing from the filter opposing variations of the proper amplitude and phase and of the same frequency which frequency will generally be twice that of the alternating current which supplies the filaments and rectifier.

I may, if desired, employ in connection with the system shown in the drawing one or more stages of radio-frequency amplification preceding the detector stage. In such case the coil l2 may be in the plate circuit of the last stage of radio frequency amplification. The first stage may be coupled to the antenna circuit and the successive stages of radio-frequency amplification may be coupled by radio-frequency transformers constructed as described in my copending application above referred to.

I preferably include in series with the primary 8| of the supply transformer, a resistance H5 which is adjustable to compensate for changes in the voltage of the supply mains 8|.

Having now described my invention, what I claim and desire to secure by Letters Patent is:

1. A multi-stage vacuum tube signal repeating system, having a detector stage followed by a plurality of stages of audio amplification, couplings between successive stages, at least one of said couplings being an impedance coupling, a means for energizing the plate circuits of the several tubes, consisting of a rectifier, a filter connected to said rectifier, said filter offering substantially infinite shunt resistance to the flow of direct current and comprising a reactance in its output circuit, condensers across said output circuit at opposite sides of said reactance, a connection across said output circuit beyond said reactance, said connection comprising a resistance and a condenser in series therewith, the plate circuit of the detector tube being connected across said last named condenser and connections for supplying the plate circuits of the amplifier tubes from said filter, the parts being so constructed and arranged that disturbing variations supplied by the filter to the detector plate circuit, when carried forward through the impedance coupling, serve to eliminate disturbing variations supplied to subsequent stages whereby hum is eliminated from the output circuit of the system.

2. In a multi-stage vacuum tube amplifier, a loud speaker, a source of current adapted to supply to the system currents which are subject to variations which tend to cause hum in the loud speaker, an impedance coupling connected with the plate circuit of a tube and adapted to produce in its output circuit variations which oppose in phase variations supplied from said source to a circuit succeeding said coupling, said coupling comprising a reactance which tends to cause such opposing variations to differ in phase from the variations supplied to such succeeding circuit by an amount other than and impedances of different values in the circuits preceding and succeeding said coupling for causing such oppos-' ing effects to differ in phase by substantially 180 whereby hum in the loud speaker is eliminated.

3. In a multi-stage vacuum tube amplifier, a loud speaker, a source of current adapted to supply to the plate circuits of the system, currents which are subject to variations which tend to cause hum in the loud speaker, an impedance coupling between two of the stages, adapted to produce at the stage succeeding said coupling, variations. Which oppose in phase variations supplied from said source to said latter stage, said coupling comprising a reactance which tends to cause such opposing variations to differ in phase from the variations supplied from said source to such succeeding stage by an amount other than 180 and impedances of different values in said stages for causing the opposing effects in a succeeding stage to differ in phase by substantially 180,

whereby hum in the loud speaker is substantially eliminated.

4. An inductance coupled multi-stage vacuum tube signal receiving and amplifying system having audio frequency amplifying and detector tube signal receiving and amplifying system having audio frequency amplifying stages and a detector stage with couplings which serve to reverse the phase of preceding grid potential variations, means for energizing plate circuits by current subject to fluctuations which tends to produce disturbing variations in the output circuit, means for relating the fluctuations in their respective circuits so as effectively to eliminate disturbing fluctuations in the output, said means comprising a filter for reducing the fluctuations supplied to the plate circuit of a detector tube to a small fraction of those supplied to the plates of later tubes, and means for compensating for slight phase shifts through the couplings whereby variations carried forward from one stage to another are of substantially opposite phase to those supplied directly to a later stage.

of said couplings being inductance couplings and.

the inductances of different couplings having predetermined different values whereby the effect of variations supplied to a later stage through a subsequent stage are substantially 180 out of phase with variations supplied directly to said later stage and the alteration of phase caused by said couplings is compensated for and disturbing variations in the output circuit of the system are eliminated.

7. In a multi-stage vacuum tube amplifying system, means for energizing tube circuits from a source of varying potential which causes disturbing variations in the plate circuits of the tubes, couplings adapted to transmit said variations to subsequent stages in altered phase, two of said couplings being reactance couplings and the reactances of different couplings having predetermined different values whereby the effect of variations supplied to a later stage through a later stage and the alteration of phase caused HAROLD R. HAYDEN.

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