US2266096A - Push-pull amplifier circuits - Google Patents

Push-pull amplifier circuits Download PDF

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Publication number
US2266096A
US2266096A US275836A US27583639A US2266096A US 2266096 A US2266096 A US 2266096A US 275836 A US275836 A US 275836A US 27583639 A US27583639 A US 27583639A US 2266096 A US2266096 A US 2266096A
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Prior art keywords
point
anode
characteristic
voltage
current
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Expired - Lifetime
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US275836A
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English (en)
Inventor
Timmer Anton Leendert
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RCA Corp
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RCA Corp
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Publication date
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Publication of US2266096A publication Critical patent/US2266096A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01R—ELECTRICALLY-CONDUCTIVE CONNECTIONS; STRUCTURAL ASSOCIATIONS OF A PLURALITY OF MUTUALLY-INSULATED ELECTRICAL CONNECTING ELEMENTS; COUPLING DEVICES; CURRENT COLLECTORS
    • H01R33/00—Coupling devices specially adapted for supporting apparatus and having one part acting as a holder providing support and electrical connection via a counterpart which is structurally associated with the apparatus, e.g. lamp holders; Separate parts thereof
    • H01R33/05—Two-pole devices
    • H01R33/22—Two-pole devices for screw type base, e.g. for lamp
    • 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 electric valve amplifiers, and more especially to amplifiers of the socalled push-pull, or balanced, type.
  • means are provided whereby the working point on the valve characteristics is automatically shifted from a point on the straight portion of the anode current-grid bias characteristic towards the cut-off point on said characteristic as the amplitude of the signals increases.
  • this may be done by causing an adequate increase of the grid bias of the balance connected valves. Consequently, the amplifier will behave as one of the class A type when the signals are weak, and as one of the class B type when the signals are strong.
  • the automatic adjustment of the grid bias in dependency of the strength of the signal may be obtained by using the voltage drop across a resistance in the anode circuit, the anode current and consequently the said voltage drop increasing with the strength of the signal after the latter will have surpassed a certain predetermined value.
  • the ohmic resistance of the source of anode current usually a so-called battery-eliminator,..is so chosen, that the voltage drop obtained thereby is about just sufficient to make the working point shift from the class A to the class B point when the amplitude of the signal varies from a minimum toa maximum.
  • this difficulty may be overcome by so designing the battery eliminator that its apparent resistance decreases on increase of theload and vice versa.
  • Fig. 1 is a circuit arrangement according to one embodiment of this invention.
  • Fig. 2 is a diagram showing the shift of grid bias in the circuit according to Fig. 1;
  • Fig. 3 shows a case, where the amplifier is fed by a battery eliminator of predetermined internal resistance
  • Fig. 4 is a diagram showing the shift of the characteristic on variation of the load
  • Fig. 5 shows a case where a reduced shift of the characteristic curve is combined with a reduced shift of the grid bias
  • Fig. 6 is the correspondingdiagram.
  • the grids of the balance connected Valves V1 and V2 are biased by means of a battery C and by the voltagedrop occurring in the resistance R, through which the anode current is supplied by a battery B of comparatively small internal resistance, so that the potential at the anodes of the valves may be considered constant for all practical purposes.
  • the resistance R is so designed, that on increase of the anode direct current, e. g. as a consequence of an increase of signal strength from zero to maximum, the grid bias of the valves is increased so as to shift the working point from substantially the midpoint on the straight portion of the characteristic towards the cut-01f point, or very nearly so.
  • the grid bias on zero signal will have the value n, which is constituted by the algebraic sum of the voltage given by battery C and the voltage drop in the resistance R owing to the anode current flowing therein.
  • the distortion across R contains a great many alternating current components when the wave form of the original signal is complex, and, whether said wave form is complex or not, the distortion across R contains a, direct, current component.
  • This direct current component is persistent exactly the same way that the alternating current components persist.
  • This direct current component can, of course, be read by connecting a direct current voltmeter across R, precisely the same as thealternating current components can be read by connecting an alternating current voltmeter across R. No condenser is necessary across R to maintain the direct current component across it, for the same reason that the alternating current components are maintained therein. All spurious components across R (and the direct current component is one of them) are maintained by the non-linearity of the tubes characteristic to I which the original signal voltage is applied. Not
  • bypass condenser of capacity C shunted across R unnecessary, but such a bypass condenser is definitely a disadvantage because the time constant CR prevents the bias voltage 1 across R from properly following the changes in signal level. Due to a sudden increase in signal level which should cause the operating point to likewise quickly shift from point a. to 'point D, this shift of the operating point would become sluggish if a bypass condenser were connected across R.
  • the push-pull connected valves V1 and V2 have their grids biased, to a constant value by the battery C only.
  • the anode current is supplied by a so-called battery eliminator of a type too well known to need description.
  • Apparatus of this class usually has a comparatively large internal resistance causing the voltage supplied to the anode to be materially dependent on the load. Any decrease of the anode voltage will cause the characteristic of the valve to be shifted to the right, and vice versa. Supposing the grid bias to remain unaltered this will mean a shift of the working point of the valve towards the lower band of the characteristic, and even past it, if the anode voltage will drop sufficiently.
  • the battery eliminator is so designed that its internal resistance will keep the drop of the anode potential within such limits that the working point will not pass the cut-off point of the characteristic, provided the signal strength will not pass a certain predetermined maximum.
  • the result obtained is graphically shown in Fig. 4.
  • the grid bias supplied by battery C is constantly kept at a value it.
  • the anode current-grid bias characteristic is shifting laterally over a distance g1 from the curve P1 to P2.
  • the working point; is consequently shifted from the point a on P1 to b on P2.
  • Fig. 5 shows a way of decreasing the apparent internal resistance of a battery eliminator, leaving the usual dimensions of such device unaltered.
  • Fig. 6 shows diagrammatically, that the characteristic curve P1 is shifted laterally over a small distance Y2 to the curve P2 when the signal increases from zero to maximum.
  • the grid bias n is increased by m, which represents the entire voltage drop in the resistance R on maximum load.
  • a push-pull amplifier including apair of vacuum tubes each having a curved characteristic relating plate current to grid potential, a signal input circuit, a source of fixed bias for the grids of said tubes which is wholly independent of the plate current of said tubes and a resistive impedance common to the space current paths of said tubes for supplying bias dependent upon plate current, an improvement for' causing operation of said amplifier to change over automatically from that of a substantially class A amplifier to that of a substantially class B amplifier as the strength of input signals impressed upon the signal input circuit increases from zero to a predetermined maximum, said improvement being characterized by said bias source and resistive impedance having relative values such as to produce a total bias in the absence of input signals which is sufficient to bring the operating point of said tubes onto a substantially linear portion of said characteristic but below the point of inflection thereof whereby increasing signals produce increasing plate current, and said resistive impedance having a magnitude such that the relative values of said two bias voltages produce in the presence of maximum input signals a total bias sufiicient to bring the operating point

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
US275836A 1933-09-23 1939-05-26 Push-pull amplifier circuits Expired - Lifetime US2266096A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB26294/33A GB425696A (en) 1933-09-23 1933-09-23 Improvements in and relating to thermionic amplifiers

Publications (1)

Publication Number Publication Date
US2266096A true US2266096A (en) 1941-12-16

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Family Applications (1)

Application Number Title Priority Date Filing Date
US275836A Expired - Lifetime US2266096A (en) 1933-09-23 1939-05-26 Push-pull amplifier circuits

Country Status (5)

Country Link
US (1) US2266096A (ko)
BE (1) BE405225A (ko)
FR (1) FR769406A (ko)
GB (1) GB425696A (ko)
NL (1) NL70830B (ko)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2515916A (en) * 1950-07-18 Coded carrier signaling apparatus
US2554279A (en) * 1948-03-13 1951-05-22 Westinghouse Electric Corp Radio apparatus
US2590282A (en) * 1947-11-08 1952-03-25 Stromberg Carlson Co Variable impedance device

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4636740A (en) * 1984-04-23 1987-01-13 Kager Dennis L Control circuit for varying power output of push-pull tube amplifiers

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2515916A (en) * 1950-07-18 Coded carrier signaling apparatus
US2590282A (en) * 1947-11-08 1952-03-25 Stromberg Carlson Co Variable impedance device
US2554279A (en) * 1948-03-13 1951-05-22 Westinghouse Electric Corp Radio apparatus

Also Published As

Publication number Publication date
GB425696A (en) 1935-03-20
FR769406A (fr) 1934-08-25
NL70830B (ko)
BE405225A (ko)

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