US2241925A - Thermionic amplifier - Google Patents

Thermionic amplifier Download PDF

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Publication number
US2241925A
US2241925A US266129A US26612939A US2241925A US 2241925 A US2241925 A US 2241925A US 266129 A US266129 A US 266129A US 26612939 A US26612939 A US 26612939A US 2241925 A US2241925 A US 2241925A
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United States
Prior art keywords
amplifier
feedback
impedance
networks
gain
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Expired - Lifetime
Application number
US266129A
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English (en)
Inventor
Roche Alleman Holly
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International Standard Electric Corp
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International Standard Electric Corp
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Publication date
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Publication of US2241925A publication Critical patent/US2241925A/en
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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
    • H03F1/34—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
    • H03G—CONTROL OF AMPLIFICATION
    • H03G9/00—Combinations of two or more types of control, e.g. gain control and tone control
    • H03G9/02—Combinations of two or more types of control, e.g. gain control and tone control in untuned amplifiers
    • H03G9/04—Combinations of two or more types of control, e.g. gain control and tone control in untuned amplifiers having discharge tubes
    • H03G9/06—Combinations of two or more types of control, e.g. gain control and tone control in untuned amplifiers having discharge tubes for gain control and tone control
    • H03G9/08—Combinations of two or more types of control, e.g. gain control and tone control in untuned amplifiers having discharge tubes for gain control and tone control incorporating negative feedback

Definitions

  • This invention relates to thermionic amplifiers and more particularly to such amplifiers in which a feedback circuit is provided for feeding back waves including those of the range of; transmitted frequencies from the output to the input of the amplifier to reduce the gain of the amplifier below the value it would have without feedback, in order to reduce unwanted modulation and/or non-linear effects and to render the gain stability greater than it would be without feedback.
  • the invention consists more particularly in improvements in or modifications of feedback amplifiers in which the feedback voltage applied to the input is obtained froma tapping 'ona reactive potentiometer which is shunted across the feedback path and the impedance of which is large compared with the impedance presented to it by the feedback path.
  • Such an arrangement provides a, simple means of adjusting both the gain and equalization ofthe amplifier.
  • one or more networks is or are also incorporated a in the feedback path, which network or networks is or are so designedthat the phase and gain characteristics of the amplifier outside the operating range are modified in such manner that instability is prevented whilst leaving the gain substantially unaffected in the operating range.
  • the network or networks is or are shunted across the feedback path in series with an impedance which is low compared with the impedance of the reactive potentiometer.
  • the potentiometer comprises a reactive portion and a resistive portion the latter being included in the grid circuit of a, valve of the amplifier and in which a low impedance is shunted across the potentiometer, the network or networks is or are inserted between the junction of the resistive portion and the low impedance and the cathode of the valve.
  • FIG. 1 this shows an amplifier of the kind described in British Patent No. 472,256 but only sufiicient of the circuit is shown for a proper understanding of the present invention.
  • the output bridge consists of the resistance RH shunted by condenser Cit, the resistance R56, the resistance R55 and condenser C12 in series and the plate cathode impedance of the valve'va.
  • This is. a. balancedah idac and the-c ndenser Cl8 is made variable for adjustment of the output impedance, athigh frequenciesandthe resistance Rl5 is also made slightly. variable to give a measure of output impedance adjustment over the whole frequency range, as, described in the above-mentioned patent.
  • the feedback voltage is. taken across thev di-.-. agonals of the output bridge in thenormalmanner.
  • the elements CH9 and B25 in para11el: are insertedto give enhanced stability at the lower end of the frequency spectrum, as described. in British Patent. 499,315 complete.
  • The. resistance R23. is a. low impedance shunt whose. value. is smallv compared. with. the. impedance of. R22 and the equalising network (consistingof R26, L8 and C2! in parallel) in series.
  • the frequency range covered by a typical amplifier for use in an open wire carrier broadcast channel is 34-425 kilocycles.
  • the stability correcting networks comprising elements CH9, R25, R24 and L9, have no effect on the frequency characteristic in this range.
  • the equalising network consisting of the elements R26, Lil and C2! is inserted in order to correct the gain frequency characteristic of the amplifier for the losses introduced by the line separating filters which are used to separate the 3-channel equipment from the broadcast channel.
  • Thetype of correction obtained is shown in Fig. 3 in which the gain in db. of the amplifier is plotted against frequency in kc. It will be seen that over the range 34 to 42.5 kc. the variation is approximately 3.3 db. with the highest gain at 34 kc.
  • the equaliser has been made variable by providing a small adjustment on the condenser C2 i.
  • the feedback voltage is taken from a tapping on a high impedance potentiometer shunted across the feedback path.
  • the high impedance potentionmeter shunted across the feedback path comprises the feedback resistance R22 in series with the equalising network consisting of R26, L8 and C21 in parallel.
  • R23 is a low impedance shunt across the diagonals of the output bridge.
  • any networks or impedances inserted in series with R22 will have a negligible effect on the feed back voltage because R22 is already high in impedance compared with R23. This is borne out in practice and no increase in stability is obtained by the insertion of correcting networks in series with R22.
  • Fig. 2 An alternative position for the correcting networks is shown in Fig. 2.
  • the correcting networks are placed between the junction of R22 and R23 and the cathode lead as shown.
  • the feedback voltage is corrected by the'insertion of the stabilising networks because these are in series with R23 as well as R22.
  • the values of the various components comprising the stabilising and equalising networks to give a curve such as that shown in Fig. 3, may be as follows:
  • the design of the amplifier is such that if the equalising element is shorted out, a flat gain over the range 34 to 42.5 kc. of 60 db. is obtained.
  • a negative feedback amplifier circuit for amplifying a given range of frequencies which comprises an amplifier having an input and output channel, a feedback channel energized from said output channel, a reactive potentiometer of substantially higher impedance than said feedback channel bridged across said energized feedback channel so as to draw a current therefrom, a
  • circuit branch of substantially lower impedance than said potentiometer also bridged across said energized feedback channel so as to draw a substantially larger current therefrom, connections from one side of said feedback channel and from an intermediate point of said potentiometer respectively to said input channel, and a network connected to be traversed by said substantially larger current and proportioned to vary the gain of the circuit only outside said given range and in such sense as to increase stability.
  • a negative feedback amplifier circuit according to claim 1, wherein said network is serially connected in said lower impedance circuit branch so as to be traversed solely by said substantially larger current.
  • a negative feedback amplifier circuit according to claim 1, wherein said network is serially connected in one side of said feedback channel so as to be traversed both by said substantially larger current and also by said current through said potentiometer.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
US266129A 1938-04-21 1939-04-05 Thermionic amplifier Expired - Lifetime US2241925A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB2241925X 1938-04-21

Publications (1)

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US2241925A true US2241925A (en) 1941-05-13

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Application Number Title Priority Date Filing Date
US266129A Expired - Lifetime US2241925A (en) 1938-04-21 1939-04-05 Thermionic amplifier

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US (1) US2241925A (da)
DK (1) DK57406C (da)
FR (2) FR846917A (da)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE963622C (de) * 1954-11-07 1957-05-09 Lorenz C Ag Schaltungsanordnung zur Neutralisation von HF-, insbesondere ZF-Stufen in Brueckenschaltung, bei der die Abstimmkapazitaet des Anodenkreises von der Anode gegen Masse geschaltet ist
US3423690A (en) * 1965-04-09 1969-01-21 Int Standard Electric Corp Terminating network for a negative feedback amplifier

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR900025A (fr) * 1943-07-29 1945-06-18 Thomson Houston Comp Francaise Perfectionnements aux amplificateurs à contre-réaction

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE963622C (de) * 1954-11-07 1957-05-09 Lorenz C Ag Schaltungsanordnung zur Neutralisation von HF-, insbesondere ZF-Stufen in Brueckenschaltung, bei der die Abstimmkapazitaet des Anodenkreises von der Anode gegen Masse geschaltet ist
US3423690A (en) * 1965-04-09 1969-01-21 Int Standard Electric Corp Terminating network for a negative feedback amplifier

Also Published As

Publication number Publication date
FR846917A (fr) 1939-09-28
DK57406C (da) 1940-03-26
FR50345E (fr) 1940-03-16

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