US2270295A - Amplifier - Google Patents

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Publication number
US2270295A
US2270295A US316913A US31691340A US2270295A US 2270295 A US2270295 A US 2270295A US 316913 A US316913 A US 316913A US 31691340 A US31691340 A US 31691340A US 2270295 A US2270295 A US 2270295A
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US
United States
Prior art keywords
circuit
feedback
output
tubes
tube
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US316913A
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English (en)
Inventor
John B Harley
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AT&T Corp
Original Assignee
Bell Telephone Laboratories Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to BE442189D priority Critical patent/BE442189A/xx
Priority to NL60229D priority patent/NL60229C/xx
Priority to NL115824D priority patent/NL115824B/xx
Priority to NL57913D priority patent/NL57913C/xx
Priority to US316913A priority patent/US2270295A/en
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to GB1287/41A priority patent/GB544175A/en
Priority to FR884047D priority patent/FR884047A/fr
Application granted granted Critical
Publication of US2270295A publication Critical patent/US2270295A/en
Priority to CH272950D priority patent/CH272950A/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/26—Modifications of amplifiers to reduce influence of noise generated by amplifying elements
    • H03F1/28—Modifications of amplifiers to reduce influence of noise generated by amplifying elements in discharge-tube amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/34—Negative-feedback-circuit arrangements with or without positive feedback
    • H03F1/36—Negative-feedback-circuit arrangements with or without positive feedback in discharge-tube amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/26—Push-pull amplifiers; Phase-splitters therefor
    • H03F3/28—Push-pull amplifiers; Phase-splitters therefor with tubes only
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B15/00—Suppression or limitation of noise or interference
    • H04B15/005—Reducing noise, e.g. humm, from the supply

Definitions

  • AMPLIFIER Filed Feb. 2', -1940 s sheets-sheet 2.”
  • the excess noise resulting from the use of negativefeedback in the above manner is eliminated by introducing into the input circuit of the tube to which the feedback is applied, a second ripple potential of the proper magnitude and phase to balance the ripple potential reach@ ing the tube over the feedback path. This may be done in various ways such as by dividing the ripple potential of the suppl;7 sourcel ⁇ in the proper proportions between the inputv and output circuits.
  • a second feedback connection from each'output tube may be used to feed back both ripple and signal potentials in a positive sense to amid-
  • the ripple potentials fromthe two tubes will be .of the same phase and of the proper magnitude to balance out the ripple due to the first negative feedback connection but the signal potentials of the ⁇ second feedback circuit will oppose each other and produce no net effect in a properly balanced circuit.
  • the second feedback circuit may be crisscrossed from Fig. 1 is a typical stabilized feedback amplifier with an imperfectly filtered power supply;
  • Fig. 2 is a simplified equivalent of the circuit of Fig. 1; c
  • Fig. 3 is a feedback amplifier with one means according to the invention for introducing into a low level part of the circuit a hum voltage which balances out thehum voltage fed back over the feedback path;
  • Fig. 3A shows a simplified equivalent of one side of the circuit in Fig. 3;
  • Fig. 4 is a push-pull amplifier with a positive feedback circuitfor balancing out the hum voltage of the negative feedback circuit
  • Fig. 5 is a push-pull amplifier with two negative feedback circuits feeding back hum voltages which are applied to the amplifier in .opposite phase so as to balance out in the input circuit.
  • Fig. 1 the vacuum tube I I is energized from an alternating current source I2 by means of rectifier unit I3.
  • a ripple or noise voltage Esc due to imperfect filtering of the power supply appears across the condenser I4, its magnitude and direction at a given instant being represented by the associated arrow.
  • a negative feedback circuit comprising a resistor I5 and a condenser I6 extends from the plate to the grid of the tube I I. With this circuit open the voltage Esc will set up a ripple current through the transformerv II and the tube and this circuit will produce a voltage drop eac across the primary of the transformer in the direction of the associated arrow and of a magnitude equal to EML R0 +L where L is the effective load impedance and Ro is the plate resistance of the tube.
  • the voltage eac will induce a voltage in the secondary winding of the transformer I'I and if the feedback path is connected to this latter winding ,instead of to the Vplate of the tube, as shown, this induced voltage will be fed back along with thev signal output and reduced by the feedback action in the same proportion as the signal so that the ratio of power supply noise to signal in the amplifier output is not'increasedby this type of feedback connection.
  • the circuit of Fig. 1 may be represented by the simplified equivalent circuit of Fig. 2 and in accordance with feedback amplifier theory as explained, for example, in Patent 2,102,671 to Black, December 21, 1937.
  • the attenuation constant for the voltage Ess applied to the grid of the tube the output transformer which is very nearly equal to is therefore ev-i-eac.
  • Go is the grid circuit impedance of the tube.
  • C is the effective input impedance externally of the tube.
  • Rn is the internal impedance of the plate circuit of the tube.
  • L is the effective lcad impedance
  • f is the impedance of the feedback circuit.
  • 4 are usually of large capacity and low impedance at hum frequencies as compared with R0 and L and are therefore neglected in this discussion.
  • the hum or ripple voltage V1 applied through the feedback path to the grid circuit due to the power supply hum voltage Eac is This voltage at the grid is amplified by the tube and modified in the usual manner by feedback action as a result of which a component voltage V2 of opposite polarity appears at the grid.
  • the circuit of Fig. 3 comprises two push-pull stages with an input transformer 2
  • the input pentode tubes are self-biased by the cathode resistors 2l and 28,
  • a stabilizing negative feedback circuit which is preferably of the type disclosed in Patent 2,123,241, granted to meJuly 12, 1938, extends from the plate of each output tube to the cathode of the corresponding input tube through resistors 39 and 40, respectively.
  • a portion of the ripple voltage existing across the condenser 38 is applied to the input circuit of the tubes 24 and 25 by means of a condenser 4
  • the instantaneous ripple potential drop Eg across the condenser 43 increases the bias on the grids of the tubes while the potential drop Ep across condenser 4
  • Fig. 3 is of the push-pull type, the invention is, l
  • condenser 4I will ordinarily be determined on the basis that it forms a part of the main power supply filter and when this has been decided the value of condenser 43 is readily 45 calculated from the above expression for the ratio of the condensers.
  • the voltages applied to the screens 44 and 45 of the tubes 24 and 25 are subjected to lteringby resistor 46 and con@ denser 41 in addition to the filtering in the plate supply lead so that the power supply noise comfponents in the screen grid current are negligible as compared with those in the plate current to these tubes.
  • the resistor 46 and condenser 41 are also effective in reducing the ripple potentials in plate supply for the voltage amplifying tubes 22 and 23 and still further filtering for these plate currents is effected by resistor 48 and condenser 49.
  • FIG. 4 The use of positive feedback to eliminate the excess power supply noise caused by the negative feedback is illustrated in the circuit of Fig. 4.
  • are impressed through the input transformer 62 on the grids 63 and 64 of the push-pull tubes 65 and 66 and from the plates of these tubes by means of the usual coupling condensers 61 and 68.
  • connects the plate circuits of the output tubes to the load 12 and power for all of the tubes is supplied from the alternating source 13 by a conventional rectil-ler unit 14.
  • a stabilizing negative feed back connection including a high resistor 15 extends from the plate of the output tube 69 to the cathode of tube 65 and a similar path including the resistor 16 connects the plate of tube 10 to the cathode of tube 66 whereby negative feedback potentials are produced across the cathode resistors 11 and 18 and applied to grids 63 and 64, respectively.
  • the ripple voltage Ea@ across the filter condenser 19 sets up noise currents which produce potential drops. ep and ep in the output transformer and due to the negative feedback connections additional noise components tend to appear in the output circuit as described above. There is, however, a second feedback path through resistors 80 and 8
  • resistors 11 and 18 The value of the resistors 11 and 18 is determined by feedback considerations as explained above and in cases where they do not provide sufficient self-bias for the tubes 65 and 66 the necessary additional bias may be readily obtained by connecting the cathodes of the tubes to the power supply through resistors 83, 84. These resistors will ordinarily be large as compared with resistors 11 and 18 and their effect on the circuit at noise frequencies need not be considered.
  • the circuit of Fig. 5 comprises an input transformer impressing signals from the source 9
  • the output circuits of these tubes are delivered to the load 98 through the transformer 99 and the amplifier is supplied with power from the alternating source
  • the rectifier may be of the voltage doubler type which may be used without a transformer and connected directly to the power source thereby reducing the cost and weight of the amplifier and eliminating inductive pick-up which is one common source of power supply noise in the signal circuit.
  • 04 of the tubes 96 and 91 are connected through resistors
  • the tubes 92 and 93 are biased in part by the potential drop due to the plate current flowing in the resistors and
  • a stabilizing negative feedback connection including resistor
  • Signal energy fed back over this circuit will develop across resistors and
  • a second negative feedback circuit comprises resistors
  • 9 are preferably all of the same value and resistors
  • are also of the same value so that the two feedback paths each carry one-half of the total feedback required for gain reducing purposes.
  • Theripple potential Esc is applied to all four of the feedback connections and-since the paths are all of the same impedance the rip- ⁇ ple potential developed across resistorv llwill balance the' ripple potential across resistor Ill so that no noise potential is applied tothei grid circuit of tube 92 over the fed back connections.
  • 19 and H2 will be equal but of opposite polarity in the grid circuit of tube 93.
  • This circuit therefore, permits the use of negative feedback without increasing the noise level and it has the additional advantage that the signal feedback is negative in both circuits thereby avoiding any sacrifice of the margin against instability;
  • an amplifier having an input circuit including a source of signals and an output circuit including an output impedance a vacuum tube in the amplifier having ⁇ a grid, an
  • anode and a cathode a source of direct current for the amplifier having noise components, connections from the source of direct current to the cathode and through the output impedance to the anode, a negative feedback circuit from the anode and cathode to a point in the amplifier between the tube and said signal source, whereby undesired noise components are fed back along with the signal currents and amplified to produce in the output impedance a noise level greater than would exist in the absence of feedback, and means for impressing on the grid of the tube noise potentialsfrom the current source equal in magnitude but opposite in phase to the noise components impressed thereon by the feedback circuit.
  • a vacuum tube having a grid, a cathode and a plate, an input circuit connected to the grid and cathode, an output circuit connected to the plate and cathode and including an output impedance, a source of current having undesired noise components connected to the cathode and to the plate through the impedance, a negative feedback path connected to the plate of the tube and feeding back noise components along with the signal and two condensers connected directly in series across the source of current dividing the noise component potentials of the source between the input and output circuits of the tube, the ratio of the impedance of the con-denser in the input circuit to the impedance of the condenser in the output circuit being substantially equal to l+ Roz, u (Ro-l-LMZg-I-f) to balance out in the input circuit the noise components fed back over the feedback path.
  • ⁇ having undesirednoise components connected to the tubes,means forreducing the noise components of the current rfor the voltage amplifying tube, a negative feedback circuit connected to the output circuit of the output tube and feeding back to the voltage amplifying tube, along with the signal, noise components from the current source of such phase and magnitude as to increase the noise level in the output circuit above the level existing in the absence of feedback, and means for applying -to the input circuit of the output tube a noise potential from the current source for balancing out in said input circuit the potential produced therein by the noise components in the feedback path.
  • an input circuit an output circuit, two input vacuum ⁇ tubes having input circuits connected in push-pull to the input circuit, two output vacuum tubes connected in push-pull between the input tubes and the output circuit, a source of current for the tubes, a separate impedance in the input circuit of each input tube andan impedance common to the input circuits of the input tubes, negative feedback connections from the plates of the output .tubes to the separate impedances, and a positive feedback connection from the plate of each output tube to the common impedance.
  • a system according to claim 5 in .which the separate irnpedances are each substantially equal to the common impedance and the impedance of each positive feedback connection is substantially equal to twice the impedance of each negative feedback connection.
  • a source of signals an output impedance, a plurality of tandem, push-pull, vacuum tube amplifying stages having input and output electrodes connecting the source to the impedance, a source of current for all the tubes having noise components and supplying current to the output electrodes of the tubes of the last stage through portions of the impedance and separate negative feedback paths from the output electrodes of each tube in the last stage to the input electrode of each tube in the rst stage.
  • a source of signals an output impedance, an input stage comprising two push-pull tubes each having a grid and a cathode, an output stage comprising two pushpull tubes each having a plate, said stages being in tandem and connecting the source to the impedance, a source of current for the tubes supplying current to the plate electrodes through the impedance, two resistors in series between the grid and cathode of each input tube, connections from the junctions of the resistors to the source of currents and negative feedback connections from the plate of each output tube to the grid of one input tube and to the cathode of the other input tube.
  • An amplifying system comprising a pushpull, vacuum tube input stage, a push-pull, vacuum tube output stage, a source of signals connected to the input stage, an output impedance connected to the .tubes of the output stage, a source of current having noise components connected to the tubes of the output stage through portions of the impedance, two ⁇ feedback paths from the output tubes to each input tube, said paths carrying signal currents of opposite phases and noise components from the current source of the same phase, and means in the input circuit of each input tube for reducing the gain of the amplier in accordance with the sum of the signal currents in the two paths and for balancing out the effect of the noise components in each input tube.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Amplifiers (AREA)
US316913A 1940-02-02 1940-02-02 Amplifier Expired - Lifetime US2270295A (en)

Priority Applications (8)

Application Number Priority Date Filing Date Title
NL115824D NL115824B (fr) 1940-02-02
NL57913D NL57913C (fr) 1940-02-02
BE442189D BE442189A (fr) 1940-02-02
NL60229D NL60229C (fr) 1940-02-02
US316913A US2270295A (en) 1940-02-02 1940-02-02 Amplifier
GB1287/41A GB544175A (en) 1940-02-02 1941-01-31 Improvements in negative feedback thermionic amplifiers
FR884047D FR884047A (fr) 1940-02-02 1941-03-29 Systèmes amplificateurs d'ondes électriques
CH272950D CH272950A (fr) 1940-02-02 1942-09-16 Dispositif amplificateur d'oscillations électriques.

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US316913A US2270295A (en) 1940-02-02 1940-02-02 Amplifier

Publications (1)

Publication Number Publication Date
US2270295A true US2270295A (en) 1942-01-20

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Family Applications (1)

Application Number Title Priority Date Filing Date
US316913A Expired - Lifetime US2270295A (en) 1940-02-02 1940-02-02 Amplifier

Country Status (6)

Country Link
US (1) US2270295A (fr)
BE (1) BE442189A (fr)
CH (1) CH272950A (fr)
FR (1) FR884047A (fr)
GB (1) GB544175A (fr)
NL (3) NL57913C (fr)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2473423A (en) * 1945-06-18 1949-06-14 Submarine Signal Co Antihunt electrical servo system
US2523240A (en) * 1947-11-18 1950-09-19 Tesla Nat Corp Balanced feedback for symmetric cathode followers
US2583552A (en) * 1944-04-29 1952-01-29 Sperry Corp Motor control circuit mixer
US2677015A (en) * 1952-06-03 1954-04-27 Us Navy Frequency shift measuring circuit
US2714137A (en) * 1944-10-12 1955-07-26 George S Dzwons Stabilized amplifier
US2751548A (en) * 1951-09-06 1956-06-19 Charles F Gunderson Ripple compensator
DE1014596B (de) * 1952-11-18 1957-08-29 Hasler Ag Gegentakt-B-Verstaerker mit Gegen- und Mitkopplung
US2934715A (en) * 1956-09-17 1960-04-26 Marconi Wireless Telegraph Co Grid bias control for class-b amplifier
US3053934A (en) * 1959-04-21 1962-09-11 Erie Resistor Corp Amplifier system for stereo sound
US3324407A (en) * 1964-06-29 1967-06-06 Crosley Broadcasting Corp Amplifier of the transformer-output type with regenerative feedback networks for reducing low frequency distortion

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2583552A (en) * 1944-04-29 1952-01-29 Sperry Corp Motor control circuit mixer
US2714137A (en) * 1944-10-12 1955-07-26 George S Dzwons Stabilized amplifier
US2473423A (en) * 1945-06-18 1949-06-14 Submarine Signal Co Antihunt electrical servo system
US2523240A (en) * 1947-11-18 1950-09-19 Tesla Nat Corp Balanced feedback for symmetric cathode followers
US2751548A (en) * 1951-09-06 1956-06-19 Charles F Gunderson Ripple compensator
US2677015A (en) * 1952-06-03 1954-04-27 Us Navy Frequency shift measuring circuit
DE1014596B (de) * 1952-11-18 1957-08-29 Hasler Ag Gegentakt-B-Verstaerker mit Gegen- und Mitkopplung
US2934715A (en) * 1956-09-17 1960-04-26 Marconi Wireless Telegraph Co Grid bias control for class-b amplifier
US3053934A (en) * 1959-04-21 1962-09-11 Erie Resistor Corp Amplifier system for stereo sound
US3324407A (en) * 1964-06-29 1967-06-06 Crosley Broadcasting Corp Amplifier of the transformer-output type with regenerative feedback networks for reducing low frequency distortion

Also Published As

Publication number Publication date
GB544175A (en) 1942-03-31
NL57913C (fr)
BE442189A (fr)
NL115824B (fr)
NL60229C (fr)
FR884047A (fr) 1943-07-30
CH272950A (fr) 1951-01-15

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