US2567272A - Circuit arrangement for protecting an amplifying tube against overloading - Google Patents

Circuit arrangement for protecting an amplifying tube against overloading Download PDF

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Publication number
US2567272A
US2567272A US756730A US75673047A US2567272A US 2567272 A US2567272 A US 2567272A US 756730 A US756730 A US 756730A US 75673047 A US75673047 A US 75673047A US 2567272 A US2567272 A US 2567272A
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Prior art keywords
voltage
circuit
input
output
tubes
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US756730A
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English (en)
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Buys Pieter Klaas
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Hartford National Bank and Trust Co
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Hartford National Bank and Trust Co
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    • 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
    • H03F1/52—Circuit arrangements for protecting such amplifiers
    • H03F1/54—Circuit arrangements for protecting such amplifiers with tubes only
    • H03F1/548—Protection of anode or grid circuit against overload
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
    • H03F3/22—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers with tubes only
    • 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

Definitions

  • This invention relates to a circuit-arrangement for protecting an amplifying tube, which is loaded by an impedance in class AB-, 3- or C-setting, from overloading and, more particularly, of pushpull connected final tubes in class B-setting.
  • the term contro' should be understood to mean control in the widest sense that i's'to say any control as a result of which the effective voltage supplied to the grids of these tubes (i. e. the voltage which occurs during that part of the cycle of the alternating grid voltage during which anode current passes through the tube) has a smaller amplitude than it would be the case without control.
  • a voltage proportional to the output voltage is applied to the first grid, and a voltage proportional to the input is applied to the second grid of an auxiliary tube.
  • the two voltages are in phase-opposition and their value is such that, if the final tubes are adequately loaded, the auxiliary tube does not carry anode current, even if the voltage taken from the output increases. It does, however, if this voltage decreases.
  • the anode current may be rectified and may influence the negative grid bias and consequently the mutual conductance of the final tubes and /or of one or more preceding amplifying tubes, as a result of which the effective input voltage of the final tubes decreases.
  • the effective voltage applied to the grids of final tubes l and 2 is reduced due to a voltage obtainedfrom the anode circuit of two auxiliary tubes I I and I I.
  • a rectified portion of the output voltage influences, according to the invention, the mutual conductance of an auxiliary tube I I, the input voltage being fed to a control-grid of this tube.
  • Fig. 5 The embodiment shown in Fig. 5 is different from that shown in Fig. 1 inasmuch as one of the voltages is operative in the cathode circuit,
  • the other is the grid circuit of the auxiliary tube I I.
  • the input voltage is fed through terminal 3, 4 to the control-grids of the two final tubes I and 2 operating in class B-setting (Fig. 1).
  • the anode circuit of these tubes comprises an output transformer 5, the secondary part of which is loaded by loads which are connected to terminals 6, 'I together represent a load resistance 8.
  • a voltage is taken from the second secondary winding of transformer 5 and supplied through a resistance 9 to a grid III of an auxiliary tube II.
  • the input voltage is supplied to a grid I2 of this tube through a condenser I3 and a resistance I4.
  • the phase-displacements owing to this condenser I3 and resistance I4 and those due to the resistance 9 and a condenser I5 provided, if required, in thecir-cuit connected to grid Ill are such that in the case of a purely ohmic character of load 8 the voltages set up at grids I0 and I2 are in phase-opposition. Usually only small phase displacement are allowed.
  • the amplitudes of these voltages and the bias of grids I0 and I2 are chosen to be such that with the maximum permissible value of load 8 the grids just do not carry grid current.
  • the ratio between the amplitudes of these voltages is such that at maximum load their control efiects on the anode current practically neutralize one another, so that the auxiliary tube either does not carry anode current or carries a constant anode current.
  • the curve a illustrates the power of the final amplifying tubes l and 2 obtained from the anode supply with a direct voltage U, as a function of the alternating voltage Vg sup plied to the control-grid; this power is equal to USVg.
  • Curve b represents the power S Vg R supplied to the load impedance R, curve a representing the power USVgS Vg R dissipated in tubes l and 2.
  • the anode circuit of these tubes comprises a transformer I8, on the secondary winding of which a negative feedback voltage is induced if the voltage across the output circuit of the amplifier is too low owing to an excessively small value of load resistance 8.
  • the secondary winding of transformer I8 is connected in series with the secondary winding of the input transformer l9, so that the voltage supplied to the grids of tubes I, 2 is reduced by the voltage produced across the first-mentioned winding, as a result of which the effective voltage set up at the grids decreases.
  • the voltage to be amplified which is fed to tubes l, 2, is supplied to this grid or to another grid of the auxiliary tube II.
  • the input voltage may be used for this purpose.
  • the polarity of rectifier I! is required to be reversed.
  • Fig. 5 represents, by way of example, one embodiment of the invention in which one of the voltages is operative in the cathode circuit of auxiliary tube 1 I. Otherwise the circuit-arrangement is entirely identical with that of Fig. l and has the, same reference numerals. Similarly one of the voltages may be introduced with the cathode-circuit in the circuit-arrangements shown in Figs. 3 and 4.
  • characteristic curve (1 in Fig. 2 may be closely approximated by supplying, instead of a voltage proportional to the voltage applied to the grids of tubes I 2, a voltage which is proportional 'to the output voltage of one of the amplifying tubes preceding the final tubes or proportional to the input voltage Vi of the final stage.
  • An overload protection circuit for an amplifying system having a source of desired signals, an amplifier stage adaptedior operation in class AB, B or C coupled to said source and a load impedance coupled to the output of said amplifierstage, comprising an electron discharge tube having cathode, input and output electrodes definingan input circuit and an output circuit, means coupled to said amplifier stage to derive a first potential proportional to the output voltage of said amplifier stage, means to apply said first potential to theinput circuit of said discharge tube, rectifier means coupled to the input circuit of said discharge tube to limit the amplitude of said first potential to a given value, means coupled to said source to apply a second alternating potential to the input circuit of said discharge tube, means coupled to theoutput circuit of said discharge tube to derive therefrom a control voltage at amplitude values' of said first potential below said given value, and means to vary the amplitude of said desired signals at the output of said amplifier stage proportional to the value of said control voltage;
  • An overload protection circuit for an amplifying system having an input stage providing a source of desired signals, an amplifier stage adapted for operation in class AB, B or C coupled to said input stage and a load impedance coupled to the output of said amplifier stage, comprising an electron discharge tube having cathode, input and output electrodes defining an input circuit and an output circuit; means coupled to said amplifier stage to derive a first alternating potentialproportional to the output voltage of said amplifier stage, means to apply said first alternating potential to the input circuit of said discharge tube, rectifier means coupled to the input circuit of said discharge tube to limit the amplitude of said first alternating potential to a given value, means coupled to said input stage to derive a second alternating potential proportional to the amplitude of said desired signals, means to apply said second alternating potential to the input circuit of said discharge tube, means coupled to the output circuit of said discharge tube to derive therefrom a control voltage at amplitude values of said first alternating potential below said given value, and means to vary the amplitude of said desired signals at the output of
  • An overload protection circuitfor an amplilying system having an input stage providing a source of desired signals, an amplifier stage adapted for operation in class AB, B or C coupled to said input stage and a load impedance coupled to the output of said amplifier stage, comprising an electron discharge tube having cathode, input and output electrodes defining an input circuit and an output circuit, means coupled to said amplifier stage to derive a first alternating potential proportional to the output voltage of said amplifier stage, means to apply said first alternating potential to the input circuit of said discharge'tube, rectifier means coupled to the input circuit of said discharge tube 6 to limit the amplitude of said first alternating potential to a givenvalue, means coupled to said input stage to derive a second alternating potential proportional to the amplitude of said desired signals, means to apply said second alternating potential to the input circuit of said discharge tube, means coupled to the output circuit of said discharge tube to derive therefrom a unidirectional control voltage at amplitude values of said first alternating potential below said given value, and means to vary the amplitude of said'
  • An overload protection circuit for an amplifying system having an input stage providing a source of desired signals, an amplifier stage adapted for operation in class AB, B or C coupled to said input stage and a load impedance a coupled to the output of said amplifier stage, comprising an electron discharge tube having cathode, input and output electrodes defining an input circuit and an output circuit, means coupled to said amplifier stage to derive a first alternating potential proportional to the output voltage of said amplifier stage, means to apply said first alternating potential to the input circuit of said discharge tube in a given phase, rectifier means coupled to the input circuit of said discharge tube to limit the amplitude of said first alternating potential to a given value, means coupled to said input stage to derive a second alternating potential proportional to the amplitude of said desired signals, means to apply said second alternating potential to the input-circuit of said discharge tube in phase opposition to 'said given phase, means coupled to the output circuit of said discharge tube to derive therefrom a unidirectional control voltage at amplitudeva'lues'
  • An overload protection circuit for an amplifying system having a source of desired signals, a push-pull amplifier stage adapted for operation in class AB, B or C coupled to said source and a load impedance coupled to the output of said amplifier stage, comprising an electron discharge tube having cathode, first control grid, second control grid and output electrodes, means coupled to said amplifier stage to derive a first alternating potential proportional to the output voltage of said amplifier stage, means to apply said first alternating potential to the first control grid of said discharge tube, rectifier means coupled to the first control grid of said discharge tube to limit the amplitude of said first alternating potential to a given value, means coupled to said source to apply a second alternating potential to the second control grid of said discharge tube, means coupled to the output electrode of said discharge tube to derive therefrom a unidirectional control voltage at amplitude values of said first alternating potential below said given value, and means to vary the amplitude of said desired signals at the output of said amplifier stage proportional to the value of said control voltage.
  • An overload protection circuit for an amplifying system having a source of desired signals, a push-pull amplifier stage adapted for operation in class AB, B or C coupled to said source and a load impedance coupled to the output of said amplifier stage, comprising a pair of electron discharge tubes coupled in push-pull and each having cathode, first control grid, second control grid and output electrodes, means coupled to said amplifier stage to derive a first alternating potential proportional to the output voltage of said amplifier stage, means to apply said first alternating potential to the first control grid of each of said discharge tubes, rectifier means coupled to the first control grids of said discharge tubes to limit the amplitude of said first alternating potential to a given value, means coupled to said source to apply a second alternating potential to the second control grids of said discharge tubes, means coupled to the output electrodes of said discharge tubes to derive therefrom a control voltage at amplitude values of said first alternating potential below said given value, and means to vary the amplitude of said desired signals at the output of said amplifier stage proportional to the
  • An overload protection circuit for an amplifying system having a source of desired signals, a push-pull amplifier stage adapted for operation in class AB, B or C coupled to said source and a load impedance coupled to the output of said amplifier stage, comprising an electron discharge tube having cathode, input and output electrodes, means coupled to said amplifier stage to derive a first alternating potential proportional to the output voltage of said amplifier stage, rectifying means coupled to the input electrode of said discharge tube, means to apply said first alternating potential to said rectifying means to limit the amplitude of said first alternating potential to a given value and to apply a bias voltage proportional to the amplitude of said first alternating potential to the input electrode of said discharge tube, means coupled to said source to apply a second alternating potential to the input electrode of said discharge tube, means coupled to the output electrode of said discharge tube to derive therefrom a unidirectional control voltage at amplitude values of said first alternating potential below said given value, and means to vary the amplitude of said desired signals at the output of said amplifier stage proportion
  • An overload protection circuit for an amplifying system having a source of desired signals, a push-pull amplifier stage adapted for opera-.- tion in class AB, B or C coupled to said source and a load impedance coupled to the output of said amplifier stage, comprising an electron .discharge tube having cathode and input electrodes defining a cathode-input electrode circuit and having an output electrode, means coupled to said amplifier stage to derive a first alternating r potential proportional to the output voltage of said amplifier stage, means to inject said first alternating potential into the cathode-input elec, trode circuit of said discharge tube, rectifier means coupled to said cathode-input electrode circuit to limit the amplitude of said first alternating potential to a given value, means coupled to said source to apply a second alternating potential to the input electrode of said discharge tube, means coupled to the output electrode of said discharge tube to derive therefrom a unidirectional control voltage at amplitude values of said first alternating potential below said giv en

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
US756730A 1946-06-27 1947-06-24 Circuit arrangement for protecting an amplifying tube against overloading Expired - Lifetime US2567272A (en)

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NL264766X 1946-06-27

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US2567272A true US2567272A (en) 1951-09-11

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BE (1) BE474143A (en(2012))
CH (1) CH264766A (en(2012))
GB (1) GB650721A (en(2012))

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3274508A (en) * 1963-10-14 1966-09-20 Webster Electric Co Inc Power amplifier including biasing means for reducing standby power dissipation

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2118287A (en) * 1934-05-08 1938-05-24 Rca Corp Automatic gain control circuit
US2252049A (en) * 1939-05-13 1941-08-12 Int Standard Electric Corp Linear amplifying system
US2293528A (en) * 1940-05-31 1942-08-18 Rca Corp Separating circuit
US2343207A (en) * 1940-02-07 1944-02-29 Rca Corp Wave translation device
US2413348A (en) * 1940-02-10 1946-12-31 Rca Corp Signaling system

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2118287A (en) * 1934-05-08 1938-05-24 Rca Corp Automatic gain control circuit
US2252049A (en) * 1939-05-13 1941-08-12 Int Standard Electric Corp Linear amplifying system
US2343207A (en) * 1940-02-07 1944-02-29 Rca Corp Wave translation device
US2413348A (en) * 1940-02-10 1946-12-31 Rca Corp Signaling system
US2293528A (en) * 1940-05-31 1942-08-18 Rca Corp Separating circuit

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3274508A (en) * 1963-10-14 1966-09-20 Webster Electric Co Inc Power amplifier including biasing means for reducing standby power dissipation

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CH264766A (de) 1949-10-31
GB650721A (en) 1951-02-28
BE474143A (en(2012))

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