US2079444A - Operating point control for thermionic devices - Google Patents

Operating point control for thermionic devices Download PDF

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Publication number
US2079444A
US2079444A US5744A US574435A US2079444A US 2079444 A US2079444 A US 2079444A US 5744 A US5744 A US 5744A US 574435 A US574435 A US 574435A US 2079444 A US2079444 A US 2079444A
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United States
Prior art keywords
modulator
voltage
envelope
rectifier
amplitude
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Expired - Lifetime
Application number
US5744A
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English (en)
Inventor
George W Fyler
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General Electric Co
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General Electric Co
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Filing date
Publication date
Application filed by General Electric Co filed Critical General Electric Co
Priority to US5744A priority Critical patent/US2079444A/en
Priority to GB3872/36A priority patent/GB466831A/en
Priority to FR801750D priority patent/FR801750A/fr
Application granted granted Critical
Publication of US2079444A publication Critical patent/US2079444A/en
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
    • H03C—MODULATION
    • H03C1/00—Amplitude modulation
    • H03C1/62—Modulators in which amplitude of carrier component in output is dependent upon strength of modulating signal, e.g. no carrier output when no modulating signal is present

Definitions

  • Theoperatingfpointof the amplifier, or modusmallaveragevalueand an increaseinoverall class A type, and its objectristo provide means 5 for and methods of changing the ⁇ operating point lator,..tube.may .be varied in several Ways to ob. ta.in..the Vabovedescribed,.result.
  • Fig-'"1'- illustrates curves showing ways in which'the operating pointw of a'class-A orsirnilarfamplifierflor modulatory may be changed as the ltube isfoperated between ⁇ maximum signal condition andminimum vor: zerosignalzfcondition;and .FigJZll isia circuit t diagram .fV
  • B2, B3, B4 andBs indicateaoperating pointsfor zero signal.-. : The clfiange-fofthe operating. point from A to B1 is made by a change in the gridbias voltage impressed. on the *,tubeathe.- plate lvoltage beingV .-.maintained substantially,x 1 constant.
  • this .method .of changing..the ...operatingpoina the external plate impedance of the tube must be low for direct current, the resistance of the audio frequency choke coil in the plate circuit being necessarily low for this purpose.
  • the change from A to B2 is made by varying the plate voltage, the grid bias voltage being maintained substantially constant, and the change from A to B3 is made by varying both the grid bias and the plate voltage.
  • the changes from A to B4 and to B5 are made by a change in grid bias alone when the external direct current impedance of the tube is approximately the same as thealternating current impedance.
  • a radio frequency carrier supplied from any suitable source (not shown) is impressed on the input circuit I0 of a radio frequency power amplifier II the output circuit I2 of which is connected to an antenna.
  • Modulating potentials in the usual audio or voice and music range of frequencies having the usual minimum frequency of the order substantially of 25 to 30 cycles per second and supplied from -a microphone or other suitable source (not shown) are impressed on the inputl circuit I3 of an amplifier I4.
  • the intensity of the sound, in the audio or speech and ⁇ music range of frequencies, impressed on the microphone is not ordinarily constant but varies at a relatively slow rate, therefore the amplitude of the envelope of the audio signal potentials impressed on the input circuit I3 correspondingly varies, this variation occurring :at relatively low frequencies, including the abovementioned so-called syllabic frequencies, below the minimum of the audio frequencies.
  • the output of amplifier I4 is impressed, as through leads I5 and input transformer I6, on the input circuit I'I of a class A modulator I8, the plate circuit I9 of which is connected to the plate circuit I2 of radio frequency power amplifier II.
  • the grid-cathode or input circuit I1 comprises a resistance-capacity network which will pass these relatively low frequencies, this network having a resistor 26 in series inthe circuit and a capacity 2
  • Plate voltage for the power amplifier I I and the modulator I 8 is supplied preferably from a suitable A. C. power source (not shown) through a main rectifier, indicated generally by the numeral 22, comprising the rectifier elements or tubes 23 and 24 having anodes 25 and cathodes 26, the latter tubes 24 further including grids or control electrodes 21.
  • a filter means 28, including a choke vcoil 29 and a condenser 36 is cnnected between the rectifier 22 and the tubes I8 and II, the cutoff frequency of this filter being in the neighborhood of 20 to 25 cycles.
  • the filter 28 is adaptedV to remove the 'ripple due to the '60 cycle supply. 'Ihis filter however, having the cutoff frequency above stated, offers negligible impedance to frequencies below this minimum.
  • the rectifier 22 is connectedv to the plate circuit I9 of modulator I8 through the laudio choke 3
  • control means for varying the output of the current source which supplies plate current for the tubes f3 and II, this current source in the present embodiment of the invention being the main rectifier 22.
  • control means comprises a recti1ierfilter circuit including a rectifier 32 and a lowpass filter 33 having a cutoff frequency sufiiciently low to offer a high impedance to frequencies in the audio signal or speech and music range but offering negligible impedance to the relatively low frequencies which characterize the variations in amplitude of the audio signal envelope.
  • the input of the rectifier and filter circuit is connected to the audio amplifier I4 through a transformer 34.
  • the control means further includes a resistor 35 connected across the output terminals of the rectifier-filter circuit.
  • One extremity of resistor 35 is connected to the positive end of a constant grid bias voltage means, as battery 36, the negative end of which is connected to the grids 27 of rectifier tubes 24.
  • the other eX- tremity of resistor 35 is connected to the cathodes 26 of tubes 24 through lead 31.
  • the total bias voltage impressed on grids 2l is, therefore, theV voltage determined by the fixed voltage of battery 36 and the varying voltage drop ⁇ across ⁇ resistor 35, the larger the drop across resistor 35 the less negative the grid bias impressed on grids 27.
  • a voltage limiter means is connected across resistor 35 comprising a rectifier 38 and a fixed voltage means, as abattery 39, in series with the rectifier 38.
  • thecarrier frequency impressed on power amplifier II is modulated in the usual manner by audio frequenciesfrom modulator I6 transmitted thereto from the microphone or other signal source through audio amplifier I4.
  • A. C. power, three-phase in the present instance, which is impressed on the rectifier 22, is rectified in the rectifier 22 and filtered in lter 28, and the resulting direct current is supplied to the plate circuits I2 and I9 of the tubes II and I 8.
  • alternating components corresponds to the audio frequencies in the voice and music range, for eX- ample the range above substantially 25 to 30 cycles.
  • Another set of alternating components corresponds to the recurring variations in amplitude of the envelope of the audio frequencies.
  • 33 is a low pass filter offering a high impedance to the frequencies in the usual audio range, above 25 to 30 cycles, but offering negligible impedance to the relatively slow variations in amplitude of the audio signal envelope, therefore the alternating components in the range above 20 to 25 cycles are suppressed and only the components corresponding to the variations in the amplitude of the audio signal envelope are allowed to pass. Consequently a direct current is caused to fiow through the resistor 35, this direct current varying from a maximum to a minimum in accordance with the envelope amplitude variations. During a period of maximum amplitude of the envelope the direct current fiowing in resistor 35 is a maximum and the drop -of the audio signal envelope.
  • amarrar resistor 35 is so poledv with reference to bias battery 36 that the drop through the resistorA 35 opposes the voltageof the latter ⁇ bias battery.
  • rectiiier 38 in seriesacross resistor"3 ⁇ 5 operates to prevent greater voltagedrop across"'the”re sistor than is determined,v by the vvoltage'of bat#l tery 39, this battery being so poled with reference to the 'resistor 35 as to tend to'o'ppose the'voltage drop inthe resistor.
  • the lter 28 permits the increaseof output'since 28 is a low-pass filter offering negligible impedance to frequencies corresponding to the relatively slow variations in the amplitude Since, in modulator tube' I8, the plate current which ows through vresistor. in s'eries in the plate-cathode circuit is Vat 4its maximum, vthe voltage drop through this 'resistor 20 is high and the negative ⁇ grid bias voltage in tube ⁇ I8, due to the drop in resistor 28, is at its maximum.
  • the operating Vpoint for class A modulator tube I8 is designated in Fig. l by the point A represent- ⁇ ing the operating point for maximum" signal.V
  • the plate voltage'of amplierI I and modulator I8 being at a minimum and the negative grid bias of modulator I8 also at a minimum
  • the operating point of class A modulator I8 is shown in Fig. 1 bythe point B3 which represents the point for minimum ⁇ or zero amplitude of the envelope of the audio signal potentials;
  • the operating point of class'A modulator tube I8 changesfautom'atically along the'line 40 connecting-the'point 4A of Fig. l, representing i maximum amplitude .of the envelope of the audio signalv potentials; -andpoint B3, representing minthat the modulated amplifier plate voltage, the modulatorplate voltage and plate current are reduced 50% at zero modulation. Also letit be assumed that the plate voltage rises to normal "in proportion to the 'amplitude of the audio modulation. The following table gives the plate power for a 500 kw.
  • the -modulator eiciency being'assumed to be 40% with '100%modula ⁇ tioni Y Power am- Total Percent Modulator
  • the ntotal'plateinput power is 634 kw. for the modulator andvmodulated power amplifier.
  • The' reduction ofthe radio frequency carrier to 50% of its maximum or1normal value will not cause noticeable distortion in a receiver which picks ⁇ up the signal radiated from the transmitter.
  • the apparatus illustrated herein provides a substantially distortionless. systemfor Vreducing peaks of modulation, thereby preventing to a certain extent overloading distortion in receivers.
  • the modulator and modulatorpower amplifier is capable of'twice the average modulation (assumed as 25%) and ⁇ one-half the maximum modulation amplitudes without undue distortion. ⁇ v ⁇ 'I'his tends to prevent eiectively overmodulationof the transmitter on sudden-'modulation peaks.
  • a transmitter powered-similarly to the aboveassumed system but having class B modulator apparatus takes the following power,A assuming the same power amplifier eiiiciency as in therst case, andr 54% modulator eciency at 100% vmodula-
  • the transmitter having the class B modulator power amplifier system takes, under the 25% average Vmodulation condi-W. tions, 45% more power than thetransmitter hav ingthelclass A modulator power Iamplifier system.. in accordance with my ⁇ 'inventionu
  • the 'apparent eicienciesfor the similar class B. and theclass A Cyr amplier and modulator systems are 54.5% and 79% respectively.
  • the yearly power saving is $18,600 for the herein described system inA accordance with my invention, over the -transmitter having the class B modulator system.
  • the transmitter apparatus illustrated 4in Fig. 2 may be operated as hereinbefore described to vary the' plate voltage of the power amplifier and modulator tubes in accordance with the amplitude of the envelope of the audio signalpot-entials in the audio input, but without variation of the-.grid bias voltage of the modulator IS.
  • the operating point of class A modulator tube I8 and power amplifier tube Il changes automatically along the line 4I connecting the maximum operating point A of Fig. 1 and the point B2, the latter point representing minimum or zero amplitude of the envelope of the audio signal potentials.
  • radio transmitter apparatus and methods of operation thereof in accordance with my invention that as compared particularly with apparatus including class B modulator systems, less audio harmonic distortion and at the same time VHbetter overall-efficiency results from the use of class A modulation devices with varying operating points.
  • a signalling system comprising a thermionic device, means to impress on said system modulating potentials in 'the audio frequency range, said potentials having an envelope varying inl amplitude, and plate voltage supply means for lsaid thermioriic device including a rectifier having a control electrode, of a second rectifier and means to supply currrent thereto from said first-named means.
  • a modulated carrier wave system comprising an audio input circuit, means to impress on said system modulating potentials of audio frequency, said potentials having an envelope varying'in amplitude, a modulator, and means including a rectifier having a control electrode to supply plate'voltage to said modulator, of means to shift the operating point of said modulator from a point corresponding to the maximum value of said modulator potentials to a point corresponding to substantially zero value thereof, said last-named means including a second rectifier and means lto impress voltages thereon from said first-named means, a low-pass filter connected to said second rectifier having its cut-off point below the Voice frequencies of said modulating potentials, means to impress bias voltages on said control electrode varying in accordance with the frequency variations passed by said lter, and means responsive to the plate voltage of said modulator to vary the grid bias thereof.
  • a modulated carrier wave system comprising a carrier frequency amplifier and means to impress a carrier frequency thereon, an audio input circuit and means toimpress modulating potentials of audio frequency thereon, said potentials having an envelope varying in amplitude, a modulator, voltage supply means for said amplifier and modulator including a rectifier having a control electrode, means to impress on said modulator said modulating potentials from said input circuit, and means comprising said modulator to modulate said carrier frequency in said amplifier with said modulating' potentials, of means to shift the operating point of said modulator from a point corresponding to maximum audio signal impressed on said input circuit to a point corresponding to substantially zero audio signal, said last-named means including a second rectifier and means to impress voltages thereon ⁇ from said audio input circuit, a low-pass filter connected to said second rectifier having its cut-olf point below the voice frequencies of said modulating potentials,
  • a source of modulating potentials of audio frequency comprising a rectier device including a control electrode, a rectier-lter circuit and means to supply voltage thereto from said modulating potential source, said circuit being arranged to pass those frequency variations only which correspond to said amplitude variations of said envelope, and means to impress bias voltages on said control electrode varying in accordance with the frequency variations passed by said rectier-iilter circuit, thereby to control the plate voltage impressed on said thermionic tube in accordance with said variations in amplitude of said envelope.
  • a thermionic tube having a plate circuit, an alternating current source, a source of modulating potentials of audio frequency, said potentials having an envelope varying in amplitude, a rectifier connected to said alternating current source and comprising a plurality of tubes including control grids, a lter connected to said rectifier adapted to pass only a direct current having superposed thereon alternating components of low frequencies of the order of the frequency of the variations in arnplitude of said envelope, means to connect said filter to said plate circuit, bias voltage means for said grids comprising a constant voltage source and a resistor in series therewith, a rectifierlter circuit, means to connect the input of said rectifier-filter circuit to said modulating potential source, and means to connect the output of said rectifier-lter circuit to said resistor, said rectifier-lter circuit being adapted to supply to said resistor a direct current having an alternating component superposed thereon corresponding to said envelope amplitude variations, Whereby the voltage impressed on said plate circuit

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
US5744A 1935-02-09 1935-02-09 Operating point control for thermionic devices Expired - Lifetime US2079444A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US5744A US2079444A (en) 1935-02-09 1935-02-09 Operating point control for thermionic devices
GB3872/36A GB466831A (en) 1935-02-09 1936-02-08 Improvements in and relating to the control of thermionic devices
FR801750D FR801750A (fr) 1935-02-09 1936-02-08 Système de modulation

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US5744A US2079444A (en) 1935-02-09 1935-02-09 Operating point control for thermionic devices

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US2079444A true US2079444A (en) 1937-05-04

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FR (1) FR801750A (fr)
GB (1) GB466831A (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2429649A (en) * 1942-04-10 1947-10-28 Fed Telegraph Co Modulator distortion correction
US2555015A (en) * 1948-05-25 1951-05-29 Products & Licensing Corp Voltage regulator
US3579238A (en) * 1971-02-20 1971-05-18 Andrew V Haeff Automatic power control of a pulse modulator

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5422859B2 (fr) * 1972-12-30 1979-08-09

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2429649A (en) * 1942-04-10 1947-10-28 Fed Telegraph Co Modulator distortion correction
US2555015A (en) * 1948-05-25 1951-05-29 Products & Licensing Corp Voltage regulator
US3579238A (en) * 1971-02-20 1971-05-18 Andrew V Haeff Automatic power control of a pulse modulator

Also Published As

Publication number Publication date
GB466831A (en) 1937-06-07
FR801750A (fr) 1936-08-14

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