US2158248A - Electrical amplifying system and method of operation - Google Patents

Electrical amplifying system and method of operation Download PDF

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Publication number
US2158248A
US2158248A US743610A US74361034A US2158248A US 2158248 A US2158248 A US 2158248A US 743610 A US743610 A US 743610A US 74361034 A US74361034 A US 74361034A US 2158248 A US2158248 A US 2158248A
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tube
potential
grid
biasing
current
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US743610A
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English (en)
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Numans Johannes Jacques
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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
    • 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

  • the invention relates toamplifiers with thermionic tubes with three or more electrodes for the distortionless amplification of electric oscillations.
  • Such amplifiers may be used in combination with loudspeakers for the reproduction of sounds (e. g. in the acoustical cinematography), or for the modulation of oscillations of a difierent frequency (e. g. in telephony transmitters) etc.
  • the invention relates more in particular to such amplifiers whereby a negative grid bias can be chosen in such a manner that the thermionic amplifier tube is adjusted approximately in the middle of its characteristic.
  • the negative grid bias can also be chosen to such a value l5- -that the tube is adjusted at the bottom region of its characteristic; in this case preferably two tubes are used working in a push pull combination, in order to avoid serious distortion.
  • the latter method is known from the British Patent The practice has learned that in such amplifiers very serious distortion occurs if an attempt is made to increase the output by increasing the amplitude of the signal voltage to such a degree 'that grid current is produced.
  • the invention aims to decrease this distortion considerably, respectively to nullify it altogether.
  • Fig. 1 shows a known amplifier circuit comprising means for applying a negative biassing potential to the control electrode of the amplifier.
  • Figs. 2, 3 and 4 show circuit arrangements according to the invention.
  • Figs. 5, 6 and 7 show graphs explaining the operation and advantages of the amplifier according to the invention.
  • This grid potential-apparatus may consist of a rectifier with smoothing apparatus.
  • I indicates an input transformer; 2 a, thermionic tube, 3 an output transformer; 4 a source of anode potential which is shunted by a condenser 6; 5 a source of grid potential of the kind already referred to above; 8 a. potentiometer for adjusting the required negative grid bias, and 1 a blocking condenser for blocking the negative grid potential and forming at the same time a bypass for the alternating potential of the signal.
  • This increase of the negative grid potential is 10 the result of the fiow of the grid current of the tube 2 through part of the resistance of potentiometer B, so that an additional potential is produced in it.
  • the steady negative grid potential is thus increased and the result is that the oper- 15" ating point on the characteristic of tube 2 shifts to a region where distortionless amplification is no longer possible.
  • the point to which the grid potential Vg1 is adjusted (at zero grid current) is at about 235.
  • the curve A indicates the increase in the negative grid potential Vgi of tube 2 when a grid current Igi flows; the figure clearly indicates that 3 this variation of grid potential is in fact considerable; under these circumstances serious distortion is found in practice to occur in this circuit.
  • age-current-characteristic exhibits a thresholdvalue and of which the internal resistance is small, so that the value of the grid potential is practically exclusively governed by the magnitude of this threshold value and is practically inde- 5o pendent of the grid current it carries.
  • a suitable device for this purpose is a gas filled tube e. g. a so-called glow discharge tube, of which several may, if desired, be used in series.
  • this glow-discharge tube may 55 An attempt may be made minimize this dis 351,1;
  • potentiometer 8 the potential is adjusted in such a way that a discharge occurs through the glow-discharge tube; it is important for the proper operation that this should occur. If grid current flows during the operation of tube 2, it will flow through the glow-discharge tube; this will produce only a very small change of potential across the glowdischarge tube becauseas is well knownthe potential across the glow-discharge tube is unafiected by the current between very large limits.
  • a drawback of the method which has just been suggested is that the potential across the glowdischarge tube has a fixed value which depends on the construction of the glow-discharge tube.
  • a thermionic tube with three or more electrodes can also be used as a threshold apparatus.
  • a circuit arrangement for this purpose is shown by way of example in Figure 2.
  • the auxiliary tube is herein marked 9; the grid potential of this tube can be adjusted by means of battery l0 and the anode voltage can be adjusted by means of the potentiometer 8.
  • the grid potential of tube 9 can be adjusted by means of battery l0 and the anode voltage can be adjusted by means of the potentiometer 8.
  • a current will flow through this tube only when the anode voltage is above a certain value. Consequently the tube 9 may be employed as a threshold apparatus.
  • the threshold value may be adjusted by adjustment of the grid potential of tube 9.
  • tube 9 in the circuit arrangement of Fig. 2 may be explained as follows.
  • the potential between the cathode and anode of tube 9 may be adjusted by means of the potentiometer 8 to such a value that the desired grid bias for tube 2 is obtained. Further the grid potential of tube 9 may be adjusted by means of battery It to such a value that a small current is flowing from the source of grid poapplied to the grid of tube 2 that grid current occurs in this tube, the potential between anode and cathode of tube 9 will show a tendency to increase because of the combined resistances of the tube 9 and the potentiometer 8. The tube '9, however, is then operated above its threshold value which means that its conductivity is rapidly increased.
  • Fig. 6 The effect of the tube 9 may be further explained with the aid of Fig. 6.
  • the current Iaz through the auxiliary tube 9 is plotted as abscissa and the potential Vaz between cathodeand anode of the auxiliary tube 9 is plotted as ordinate.
  • This potential is, of course, equal to the grid potential Vgr of tube 2.
  • Curves a and b indicate two characteristics of tube 9, plotted at difierent values of the grid potential Vgz of tube 9.
  • the threshold character can be readily seen; as this figure indicates, with the circuit of Figure 2, at a very high value of vaz Vgi, only a small current Iaz flows, but nevertheless the increase of V0.2 with an increase in M2 is only comparatively small.
  • the curve a is substantially flatter to the right right of P1 than to the left of P1 with the result that in the manner indicated, the value of Vaz can be kept constant to a better degree.
  • the grid potential of tube 9 is influenced by the potential between anode and cathode in such a way that with increasing potential the negative grid potential of tube 9 is decreased.
  • the passage of current through tube 9 increases as is necessary; the potential between anode and cathode of tube 9 is thus kept more constant.
  • Vaz and Vg2 the grid potential of tube 2 change from 258 to 330.
  • the dotted line D (which relates to Fig. 3) indicates how the grid potential Vgz of tube 9, which is equal to the potential across the resistance H and which is plotted on the right hand abscissa, decreases when the current through tube 9, which is equal to the grid current 191 of tube 2, increases.
  • circuits according to the invention is especially apparent in the case of push-pull amplifiers which are adjusted by means of negative grid potential, to Work on the bottom region of the characteristic; under these circumstances a comparatively small increase of thenegative grid potential would result in very serious distortion.
  • both of the tubes working in pushpull should be capable of being adjusted individually to the required anode current because the tubes are seldom absolutely identical to one another.
  • a push-pull circuit according to the invention is shown.
  • I indicates the input transformer supplying the signal voltage to the push-pull tubes 2.
  • Negative grid bias is supplied to these tubes from the source of grid potential 5 by way of the potentiometer 8, the resistance M, the potentiometer l5 and the secondary windings of the input transformer I.
  • I2 and I3 are two auxiliary tubes each serving for the same purpose as the auxiliary tube 9 in Fig. 2 and in Fig. 3.
  • auxiliary potential E in the manner suggested is due to the fact that in this case the source of potential 7 E hardly needs to deliver any current and is therefore unloaded; in many cases this is a considerable practical advantage. If the auxiliary potential E is connected directly into the path of the grid current of the tubes 2, the potential E would be afiected whenever a grid current flows because this grid current would have to flow through the source of potential E, thereby reacting on the source E.
  • An electrical amplifier including. a thermionic amplifier tube having a. control electrode, a biasing circuit comprising a source of biasing potential adapted to apply a negative biasing potential to said control electrode, and means associated with the biasing circuit and adapted to prevent an undue increase of the negative biasing potential which might otherwise be produced on the occurrence of grid current flowing to the control electrode of the thermionic amplifier tube through the resistance of its source of biasing potential, said means comprising an auxiliary thermionic tube comprising a grid electrode and having its output circuit arranged in parallel to the source of biasing potential with its anode connected to the cathode of the thermionic tube, and auxiliary means for biasing the grid electrode of the auxiliary thermionic tube toimpart to said auxiliary tube an electric voltage-current characteristic presenting a threshold discharge voltage, and a low resistance.
  • An electrical amplifier including a thermionic amplifier tube having a control electrode, a biasing circuit adapted to apply a negative biasing potential to said control electrode, an auxiliary thermionic tube comprising a grid electrode and being associated with said biasing circuit, the anode of the auxiliary thermionic tube being connected to the cathode of the amplifier thermionic tube, and means for biasing the grid electrode of the auxiliary thermionic tube and causing the bias produced thereby to be controlled by grid current of the thermionic amplifier tube flowing through the biasing circuit of said amplifier tube.
  • An electrical amplifier including a thermionic amplifier tube having a control electrode, a biasing circuit adapted to apply a negative biasing potential to said control electrode, an auxiliary thermionic tube comprising a grid electrode and being associated with said biasing circuit, the anode of the auxiliary thermionic tube being connected to the cathode of the amplifier thermionic tube, and means for biasing the grid electrode of the auxiliary tube and causing the negative bias produced thereby to be reduced by grid current of the thermionic amplifier tube flowing through the biasing circuit of said amplifier tube, so as to produce an increased current conductivity of the auxiliary tube.
  • An electrical amplifier including a thermionic amplifier tube having a control electrode, a biasing circuit comprising a source of biasing potential adapted to apply a negative biasing potential to said control electrode, an auxiliary thermionic tube comprising a grid electrode and having its output circuit arranged in parallel to that section of the biasing circuit comprising the source of biasing potential, with the anode of the auxiliary thermionic tube connected to the cathode of the thermionic amplifier tube, and
  • biasing circuit comprising a source of biasing potential adapted to apply a negative biasing potential to said control electrode, an auxiliary thermionic tube comprising a grid electrode and having its output circuit arranged in parallel to that section of the biasing circuit comprising the source of biasing potential with the anode of the auxiliary thermionic tube connected to the cathode of the thermionic amplifier tub-e, and means for biasing the grid electrode of the auxiliary tube and causing the negative bias produced thereby to be reduced on the occurrence of grid current of the thermionic amplifier tube flowing through that section of the biasing circuit of said amplifier tube comprising the source of biasing potential.
  • An electrical amplifier including a thermionic amplifier tube having a control electrode, a biasing circuit comprising a source of biasing potential adapted to apply a negative biasing po- -tential to said control electrode, an auxiliary thermionic tube comprising a grid electrode and having its output circuit arranged in parallel to that section of the biasing circuit comprising the source of biasing potential with the anode of the auxiliary thermionic tube connected to the cathode of the thermionic amplifier tube, and means for biasing the grid electrode of the auxiliary thermionic tube and causing the bias produced thereby to be controlled by grid current of the thermionic amplifier tube flowing through that section of the biasing circuit of the amplifier tube that comprises the source of biasing potential, said means comprising a resistance connected between the cathode of the auxiliary thermionic tube and the source of biasing potential for the thermionic amplifier tube.
  • An electrical amplifier including a thermionic amplifier tube having a control electrode, a
  • biasing circuit for said control electrode comprising a source of biasing potential, an auxiliary thermionic tube having its anode connected to the cathode of the thermionic amplifier tube and having its output circuit arranged in parallel to that section of the biasing circuit comprising the source of biasing potential, and a resistance provided between the cathode of the auxiliary thermionic tube and the source of biasing potential, a, point of said resistance being connected to the grid of the auxiliary thermionic tube.
  • An electrical amplifier including a thermionic amplifier tube having a control electrode, a biasing circuit adapted to apply a negative biasing potential to said control electrode, an auxiliary thermionic tube comprising a grid and be-- ing associated with said biasing circuit with its anode connected to the cathode of the thermionic amplifier tube, means for biasing the grid electrode of the auxiliary tube, and further means enabling the control electrode biasing potential of the thermionic amplifier tube to be varied, said further means comprising connections enabling a potential different from the biasing potential to be introduced into the grid circuit of the auxiliary thermionic tube.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
  • Control Of Position Or Direction (AREA)
US743610A 1933-09-13 1934-09-11 Electrical amplifying system and method of operation Expired - Lifetime US2158248A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL432618X 1933-09-13

Publications (1)

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US2158248A true US2158248A (en) 1939-05-16

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US743610A Expired - Lifetime US2158248A (en) 1933-09-13 1934-09-11 Electrical amplifying system and method of operation

Country Status (5)

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US (1) US2158248A (fr)
BE (1) BE405172A (fr)
FR (1) FR778460A (fr)
GB (1) GB432618A (fr)
NL (1) NL43268C (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2504480A (en) * 1946-01-21 1950-04-18 Bendix Aviat Corp Amplifier bias system
US2540313A (en) * 1945-06-01 1951-02-06 Hartford Nat Bank & Trust Co Apparatus to control the gain of a signal amplifying system
US2552136A (en) * 1945-06-13 1951-05-08 Gen Electric Linear amplifier system
US2777018A (en) * 1954-10-15 1957-01-08 Du Mont Allen B Lab Inc Direct-coupled amplifier
US2783376A (en) * 1950-10-03 1957-02-26 Wilbur A Hane High speed positive pulse generator
US2817716A (en) * 1954-03-05 1957-12-24 Melvin B Freedman Gain control circuits
US2965854A (en) * 1956-02-20 1960-12-20 Bergson Gustav Electro-meter amplifier

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE754298C (de) * 1935-07-04 1952-07-17 Emi Ltd Niederfrequentes UEbertragungssystem mit selbsttaetiger Amplituden-regelung durch eine quer zum UEbertragungsweg geschaltete Impedanz-Mehrgitterroehre

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2540313A (en) * 1945-06-01 1951-02-06 Hartford Nat Bank & Trust Co Apparatus to control the gain of a signal amplifying system
US2552136A (en) * 1945-06-13 1951-05-08 Gen Electric Linear amplifier system
US2504480A (en) * 1946-01-21 1950-04-18 Bendix Aviat Corp Amplifier bias system
US2783376A (en) * 1950-10-03 1957-02-26 Wilbur A Hane High speed positive pulse generator
US2817716A (en) * 1954-03-05 1957-12-24 Melvin B Freedman Gain control circuits
US2777018A (en) * 1954-10-15 1957-01-08 Du Mont Allen B Lab Inc Direct-coupled amplifier
US2965854A (en) * 1956-02-20 1960-12-20 Bergson Gustav Electro-meter amplifier

Also Published As

Publication number Publication date
BE405172A (fr)
GB432618A (en) 1935-07-30
FR778460A (fr) 1935-03-16
NL43268C (fr)

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