US2306749A - Amplifying system - Google Patents

Amplifying system Download PDF

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Publication number
US2306749A
US2306749A US394572A US39457241A US2306749A US 2306749 A US2306749 A US 2306749A US 394572 A US394572 A US 394572A US 39457241 A US39457241 A US 39457241A US 2306749 A US2306749 A US 2306749A
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US
United States
Prior art keywords
amplifier
anode
grid
impedance
stage
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
US394572A
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English (en)
Inventor
James L Potter
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.)
General Electric Co
Original Assignee
General Electric Co
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 BE473731D priority Critical patent/BE473731A/xx
Application filed by General Electric Co filed Critical General Electric Co
Priority to US394572A priority patent/US2306749A/en
Priority to GB6940/42A priority patent/GB556051A/en
Application granted granted Critical
Publication of US2306749A publication Critical patent/US2306749A/en
Priority to FR942898D priority patent/FR942898A/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • 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
    • 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

Definitions

  • My invention relatesto an amplifying system and particularly to a multi-stage amplifying system of the feed-back type.
  • a class B amplifier i. e., one in which anode current fiows in the individual tubes only during half cycles of the applied voltage, presents a-load impedance to the driving source which varies appreciably over each cycle due to the varying grid currents drawn during portions of. each cycle. Therefore, if the proper grid excitation is to be supplied to its input, itis necessary for the driver stage to have low internal impedance. For perfeet voltage regulation of the driver stage under these conditions, its apparent internal impedance should be exactly equal to zero. If such is the case, the output voltage of the driver stage will always be proportional to the input voltage regardless of the value of its external load impedance.
  • a combination of positive and negative feedbacks is utilized in a multi-stage amplifier for the attainment of this result.
  • a particular form of impedance network is interconnected with two cascaded amplifying stages. This network functions to provide a degenerative feedback between the grid and anode circuits of each stage controlled by its own anode current, and a regenerative feedback between the stages which is controlled by the anode current in the second stage.
  • Another object of my invention isto provide a simple and efllcient feedback amplifier in which the apparent anode impedance of the output stage may be given a desired value differing materially from its, actual resistance.
  • a further object .of my invention is to provide an improved: amplifier of this general, type H wherein the apparent anode impedance of the output stage may be made substantially equal to .zero,.and the voltage gain through the amplifier thereby made independent ofvariations in the output load impedance.
  • Still another object of my invention is to provide" an improved multi-stage amplifier which has a combination'of positive and negative feedbacks and which is stable in operation and readclas B amplifier or the like.
  • Fig. 1 diagrammatically represents aelass B push-pull amplifier with a two-stage driver amplifier embodying my invention
  • Figs. 2-5 are curves representative of the operating characteristics of a particular experimental amplifying system embodying my invention.
  • the secondary winding. of the 1 transformer I0 is coupled to the input of a-voltage amplifier having two stages H and I2.
  • amplified signal voltages are supplied-from the output of this amplifier to the input circuit of a push-pull class B amplifier B through, a coupling transformer
  • the output of the amplifier is supplied to any suitable utilization device, not shown, through the output coupling transformer It.
  • the output of the amplifier l3 may be supplied to a sound reprowill further be observed that the resistor R3 is ducer, or the amplifier l3 may be used as a class common to the grid and anode circuits of both B modulator for a radio transmitter.
  • the first stage II comprises an electron disback to the grid circuit of Ti which is proporcharge amplifier T1 which is illustrated as a 5 tional to the anode current in T2.
  • This voltage triode having a cathode 16, control grid 11, and is regenerative and tends to increase the gain of anode l8.
  • Signal voltages e. are impressed bethe amplifier. tween the grid I1 and ground from the secondary By adjusting the values of the various resistors, of the input transformer In.
  • Cathode I5 is conthe apparent anode impedance of the amplifier nected to ground through two resistors R1 and T: may be given various desired values. If the Rain series.
  • the anode I8 is connected to ground positive and negative feedbacks are properly prothrough a coupling resistor R0 and a suitable portioned, the efiective internal impedance of the source of anode operating potential, represented amplifier T: can be made just equal to zero.
  • the suppressor grid 2i is inover their operating ranges, a close approximaternally connected to the cathode 2
  • i i the manner and the screen grid 23 is connected to anode current of the tube T1, and considering the the anode 25 so that the device T: effectively 25 second tube T2 and all feedback eflects, functions as a triode amplifier.
  • is connected to ground through w a resistor R: and the previously-mentioned re- 30 amplificatmn fact T1 sistor R3.
  • the push-pull amplifier la fl@i. (2) comprises two duplex triodes T: and T4 connected R1 2+ZO+ i+ a) (m+ 1) in parallel, on one side of the amplifier, and simi- Where ar duplex triodes T5 and To connected in parallel, on the other side. It will, of course, be 0 52:3: $5 5 fg'lgfigggggg: gi' i g into apparent to those skilled in the art that by using the primary winding of transformer a plurality of amplifiers connected in parallel increased power output may be supplied from the Equations 1 and 2 may now be solved in terms of transformer I5.
  • the anode current for the am lifier T must fio through the resistors R1 andpm ,1 the ,1 R3 iRe+ Rl+Ro (2+ 1 1IR.1+RO+ R.+R, (m+ sistors R1 and R3 are unbypassed, this provides umz o a degenerative feedback to the grid l1 which is proportional to the anode current in tube Ti and
  • the quantities of (Ril-I-RB) and (RH-Rs) are the substantially uniform at all signal frequencies in required bias resistances for each amplifier. the operating range.
  • the flow of anode Hence, their value is known for any given types current in the device T: through the resistors R2 of tubes. However, it must be taken into considand R3 provides a uniform current-controlled eration that the anode current of both amplifiers degenerative feedback to its control grid 22. It flow through the resistance R3. Therefore, in
  • this type of amplifier is also advantageous when working into an impedance which varies with frequency, because it tends to flatten the frequency response.
  • anode impedance of the driver 65 amplifier T2 in Fig. 1 By making the anode impedance of the driver 65 amplifier T2 in Fig. 1 appear nearly equal to zero, a reduction in harmonic distortion in the class B amplifier I3 is also secured. It may even be found desirable in somecases to make the anode impedance of the driver T2 appear somewhat negative so that an actual rise in voltage is obtained when the grids of the class B amplifier 13 are at maximum positive values. This will tend to compensate for the curvature generally occurring in the plate characteristic in this region and, also, to compensate for the losses in the coupling transformer l4.
  • a type 6L7. tube was used for the amplifier T1, a triode-connected type '6F6 tube for the amplifier T2 and type 6N7 tubes for the amplifiers Til-T6.
  • the curves of Fig. 2 are'actual test curves taken with this apparatus showing the harmonic content at the output transformer l5 plotted against the feedback resistance Rs, which controls the current regeneration between the stages II and I2.
  • the power output from the amplifier 13 was held constant at about 33.2 watts.
  • the apparent anode impedance of the amplifierTz was equal to zero when the feedback resistance R; had a value of about ohms. For values of R above 45 ohms, the apparent anode resistance was negative and below 45 ohms, positive.
  • Fig. 3 shows experimental curves for this same apparatus, with R3 equal to about 45 ohms, and illustrates the variation in anode current I, and grid current I; for the amplifier l6 plotted against signal volts input to the first stage II of the driver amplifier.
  • Figs. 4 and 5 show the 70 tion:
  • the driver tube T2 was working at maximum output.
  • the harmonic distortion could have been reduced still further by utilizing a driver tube of greater capacity. 7
  • first and second thermionic amplifiers means for coupling said amplifiers in cascade relation comprising a coupling resistance R0, said amplifiers havin internal anode resistances Rpl and R z respectively and amplification factors Ill and 2 respectively, degenerative feedback resistances R1 and R2 common to the grid and anode circuits of the respective amplifiers, and a regenerative feedback resistance R3 common to the grid and anode circuits of both amplifiers, said resistances having values determined substantially by the rela- 'll-2 0 whereby the gain through said amplifiers is substantially independent of the value of output load impedance -in the anode circuit of said second amplifier.
  • a driver amplifier for a class B amplifier or the like comprising first and second thermionic amplifying devices T1 and I: each having an anode, cathode and control grid, said devices having internal anode resistances R131 and Rp2 respectively and amplification factors n and 12 respectively, resistance coupling means between said devices comprising a load resistor R0 for T1, a degenerative-regenerative feedback network in said amplifier comprising three resistors R1, R2 and R3 connected in a Y, the free terminalsof R1 and R2 being connected to the cathodes of T1 and T2 respectively and the free terminal of Rev being connected to a point of reference potential, connections from the grids of Ti.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
US394572A 1941-05-22 1941-05-22 Amplifying system Expired - Lifetime US2306749A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BE473731D BE473731A (fr) 1941-05-22
US394572A US2306749A (en) 1941-05-22 1941-05-22 Amplifying system
GB6940/42A GB556051A (en) 1941-05-22 1942-05-21 Improvements in and relating to amplifying systems
FR942898D FR942898A (fr) 1941-05-22 1946-10-30 Perfectionnements aux amplificateurs du type classe beta

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US394572A US2306749A (en) 1941-05-22 1941-05-22 Amplifying system

Publications (1)

Publication Number Publication Date
US2306749A true US2306749A (en) 1942-12-29

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ID=23559517

Family Applications (1)

Application Number Title Priority Date Filing Date
US394572A Expired - Lifetime US2306749A (en) 1941-05-22 1941-05-22 Amplifying system

Country Status (4)

Country Link
US (1) US2306749A (fr)
BE (1) BE473731A (fr)
FR (1) FR942898A (fr)
GB (1) GB556051A (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2429124A (en) * 1944-04-12 1947-10-14 Arma Corp Electrical amplifier
US2578613A (en) * 1947-01-24 1951-12-11 Rca Corp Second and third harmonic generator

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2429124A (en) * 1944-04-12 1947-10-14 Arma Corp Electrical amplifier
US2578613A (en) * 1947-01-24 1951-12-11 Rca Corp Second and third harmonic generator

Also Published As

Publication number Publication date
BE473731A (fr)
FR942898A (fr) 1949-02-21
GB556051A (en) 1943-09-17

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