US2235677A - Amplifier for signal transmission - Google Patents

Amplifier for signal transmission Download PDF

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Publication number
US2235677A
US2235677A US177375A US17737537A US2235677A US 2235677 A US2235677 A US 2235677A US 177375 A US177375 A US 177375A US 17737537 A US17737537 A US 17737537A US 2235677 A US2235677 A US 2235677A
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Prior art keywords
tubes
amplifier
bridge
class
bias
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Expired - Lifetime
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US177375A
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English (en)
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Gubin Samuel
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RCA Corp
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RCA Corp
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Priority to US177375A priority Critical patent/US2235677A/en
Priority to CH209779D priority patent/CH209779A/de
Priority to DER103926D priority patent/DE704724C/de
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Publication of US2235677A publication Critical patent/US2235677A/en
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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
    • H03F3/42—Amplifiers with two or more amplifying elements having their DC paths in series with the load, the control electrode of each element being excited by at least part of the input signal, e.g. so-called totem-pole amplifiers
    • H03F3/44—Amplifiers with two or more amplifying elements having their DC paths in series with the load, the control electrode of each element being excited by at least part of the input signal, e.g. so-called totem-pole amplifiers with tubes only

Definitions

  • My invention relates to amplifiers for signal transmission and more particularly to class B amplifiers used as modulators in transmitting.
  • An object of my invention is to obtain a high- 5 er utilization factor in output transformers used in class B amplifiers.
  • a further object of my invention is to provide an amplifier circuit of the class B type for modulation that makes possible the reduction in size and simplification in design of an output coupling transformer.
  • a still further object of my invention is to provide, in combination with a novel class B amplifier circuit, a transformer characterized by tighter coupling and lower phase shift than heretofore possible for use with class B amplifiers.
  • Another object of my invention is to provide I a balanced amplifier circuit characterized by an output transformer that has no center-tapped primary winding with the attendant disadvantages.
  • Another object of my invention is to provide a class B amplifier circuit wherein tubes are used in series for the purpose of obtaining operation by a high voltage plate supply of twice the voltage normally used.
  • Still another object is to provide a bias supply at ground potential for A. (2., in combination with my improved class B amplifier wherein the U0 cathodes of certain of the tubes are operated at a high A. C. potential above ground.
  • the conventional class B or push-push amplifier
  • FIG. 1 is a circuit diagram in simplified form of a thermionic amplifier made in accordance with my invention
  • Fig. 2 is a more detailed circuit diagram, with certain modifications, as actually built by me in accordance with my invention,
  • Fig. 3 is a diagram of a circuit for supplying grid bias to certain tubes shown in Fig. 1.
  • thermionic vacuum tubes I, 2, 3 and 4 preferably of the class B type, are connected in a bridge circuit resembling somewhat a single phase full wave bridge power rectifier system.
  • An early form of bridge amplifier, using a single tube in one arm and resistors in the remaining arms is shown by Adair Patent 1,383,275.
  • the control grids of the tubes in opposite arms are excited, or driven, in phase for each input half cycle, respectively.
  • grids of tubes I and 3 are driven in phase and positive in direction during one half of the input signal Wave by means of an input coupling network, e. g. secondary-windings 5 and I, respectively, of an input driving transformer 9.
  • the grids of tubes 2 and 4 are driven in phase and in a positive direction by secondary windings 6 and 8 during the other half cycle.
  • the primary ll of the input transformer is connected to a source of signal energy as to an audio amplifier driver tube not shown.
  • the grids of the class B amplifier tubes are biased, preferably negatively, as by means of cells l3, or other known equivalent, in accordance with the teachings of A. V. Loughren Patent 1,699,110. In some cases it is desirable to employ a positive bias. The operation is such that little or no plate current flows in the no signal condition. However, in this arrangement the apparatus may be greatly simplified (see Fig. 2) by using tubes of the class B zero bias type, made and used in accordance with the teachings of L. E. Barton Patent 2,084,181. Since the oathodes of tubes 3 and 4 are at a high A. C. poten- 5o tial relative to ground, the grid bias supply, as from rectified alternating current is complicated, and the use of zero bias tubes is quite desirable.
  • the power supply for the anodes P is represented diagrammatically by a battery l5, which may be a rectified power supply source, connected across one diagonal of the bridge.
  • the cathodes F of tubes 3 and 4 are at high alternating potential and require insulation by some means such as indirectly heated cathode type tubes, as shown, or by means of filament type tubes heated by A. C. employing low capacity filament heating transformers, (Fig. 2).
  • the signal input secondary windings, 5, 6, 'l and 8 must be properly poled relative to each other in order that tubes in one pair of opposite arms are driven in phase, for one half cycle while those in the other pair of arms are driven in phase during the other half cycle.
  • the output transformer H has its primary it connected as shown across the other diagonal of the bridge, and the secondary ill to the load.
  • the plate current paths are traced as follows: When the signal voltage on the grids of tubes I and 3 increases in a positive direction, current fiows, in conventional terms, from the positive end of supply source l5, through the tube 3, through the primary l9, through tube I, all in series, back to the source, negative end, the flow being indicated by arrows in full line.
  • the grids of tubes 2 and 4 are similarly excited 180 degrees later, the plate current flows in the opposite direction through the primary winding, the current path through tubes 2 and 4 being indicated by arrows in dotted lines.
  • tubes 5 and 4 have their space current paths connected in series, the cathode of tube I being connected to the negative end of the source [5, the anode of I to the cathode of tube 4, and the anode of tube 4 to the positive end of source IS.
  • tubes 2 and 3 have their space current paths connected in series, the cathode of tube I being connected to the negative end of the source [5, the anode of I to the cathode of tube 4, and the anode of tube 4 to the positive end of source IS.
  • tubes 2 and 3 have their space current paths connected in series, the cathode of tube I being connected to the negative end of the source [5, the anode of I to the cathode of tube 4, and the anode of tube 4 to the positive end of source IS.
  • tubes 2 and 3 have their space current paths connected in series, the cathode of tube I being connected to the negative end of the source [5, the anode of I to the cathode of tube 4, and the anode of tube 4 to the positive end
  • a 750 watt output modulator circuit as built by me according to the above teachings, although slightly modified. Like reference numerals correspond to similar parts in Fig. 1.
  • Four filament type RCA 805 zero bias tubes were employed, and were energized from a 3000 volt plate supply.
  • the filaments were energized by power transformers the secondaries only of which are shown at 21, 28, 29 and 30. While separate windings 21 and 28 are shown, a single winding of an ordinary transformer could obviously be used for filaments of tubes l and 2 if the negative end of the anode supply is grounded. However, the windings 29 and 30 for tubes 3 and 4 are well insulated from ground and are designed to offer low capacity to ground, or primary, for high audio frequency potentials.
  • the input signal transformer diifers from that in Fig. 1 in that two separate transformers were used, being of a type readily available. Electrically the arrangement is similar to Fig. l. The primaries are shown connected to a driver stage using RCA type 845 tubes connected in pushpull relation.
  • the input and output transformers were designed in accordance with the teachings of class B amplifier practice. However, in the output transformer, since the tubes are in series, the reflected load resistance is made substantially twice the optimum load resistance per tube as determined in accordance with such class B practice.
  • One way of isolating the bias apparatus from the mains, which are substantially at zero signal potential, is the use of large reactors in series with the leads connecting to the mains. This method may require expensive reactors of special design to maintain high impedance at all signal frequencies and yet to have low impedance to the mains frequency where grid regulation is required of the bias source.
  • a bias supply which may consist of a battery, generator, or rectifier of A. C. is shown at 3
  • Associated with the bias source is a capacity to ground, 42, which prevents the use of the bias rectifier directly in the grid circuit.
  • a filter consisting of elements as shown in Fig. 3 performs the desired function of isolating the grid from ground for signal potentials, the terminals 23 and 24 being adapted for connection to the terminals 23 and 24 of Fig. l in place of the cell i3.
  • a similar bias supply circuit is adapted to be connected to the terminals 23' and 24 of Fig. 1.
  • the inductors 35, 36, 3'! and 38, resistors 43, 44, 45, 46, 47, 48 and 50 and capacitors 39, 40, 4!, 42 and 49 which comprise this network are proportioned so as to form constant resistance networks,
  • my invention effects a reduction in distortion as well as a reduction in the size of the modulation transformer or reactor used in a class B amplifier combination. While it may appear that the number of tubes has been increased as an offset to the above advantage in size economy, such is not the case. For a given output, say 750 watts, two pairs of parallel connected tubes of the type disclosed above, or two tubes of double the power rating would ordinarily be used. So what I have done is to arrange this given tube complement in such manner as to obtain new and unusual results as above set forth.
  • the reduction in size of the modulation transformer for a given power output becomes very important in transmitters where the transformer is of the large coil cooled type like those used in A. C. power stations. It will further be seen that I have solved the problem of grid bias supply in the case of class B amplifiers having their inputv electrodes operated at a potential that is high above ground for A. C. or signal potentials.
  • While my invention has been illustrated and described for purposes of convenience in its present preferred application to audio frequency amplifiers of the class B type, it is not intended that my invention shall be limited thereto but may be applied to other amplifiers, e. g. those operating at radio frequency, and wherein it is desired to simplify the apparatus and reduce the distortion. While my invention has been disclosed in connection with thermionic vacuum tube devices of the conventional type as amplifiers it is not intended that I shall be limited to such devices. While I have disclosed an output coupling transformer, I can use an output inductor or a resistor, which may be the load itself. This is made possible by the fact that the output is undivided as distinguished from the conventional divided output circuit, as illustrated by Colpitts 1,128,292. Although I have shown four tubes as constituting the arms of a bridge, a lesser number of tubes can be employed and still maintain undivided output circuit condition.
  • a signal amplifier of the balanced type comprising, in combination, two pairs of thermionic tubes connected in bridge relation, an input coupling. network arranged to control in phase a pair of tubes in opposite arms of the bridge during a half cycle of input signal energy and the other pair of tubes during the other half cycle of energy, and an output transformer connected across a diagonal of said bridge.
  • one of the tubes has its input electrodes operated at a high A. C. potential above ground, and a bias supply at substantially A. C. ground potential for said input electrodes.
  • a signal amplifier of the balanced type comprising, in combination, a source of signals, four thermionic tubes arranged in the four arms of a bridge, respectively, a high voltage supply of space current connected across one diagonal of said bridge, an output coupling means connected across the other diagonal of said bridge, signal means for causing space current to flow alternately through said coupling means, in series through one pair of tubes in opposite arms of the bridge and through the coupling means in one direction, and serially through the other pair of tubes and said coupling means in the reverse direction.
  • a bridge signal amplifier of the balanced type comprising in combination, a plurality of thermionic tubes disposed in arms of said bridge, an output coupling device connected to terminals across a diagonal of said bridge, said terminals being at high A. C. potential above ground, one of said tubes having its cathode connected to one of said diagonal terminals, a bias supply at ground potential for A. C., and means connecting said bias supply to the input electrodes of said tube while maintaining said electrodes at high A. C. potential above ground.
  • a balanced type amplifier comprising a pair of thermionic devices connected in series and having cathode, control and anode electrodes, an input coupling network for exciting said devices in phase as signal frequency potentials, and an undivided output load circuit comprising an inductor connected at one end to the anode of one of said devices and at the other end to the cathode of another of said devices.
  • a signal amplifier comprising in combination, a plurality of thermionic tubes arranged to operate as a balanced amplifier, an anode supply source connected to supply space current to said tubes in series relation, and an undivided output coupling circuit with end terminals connected to electrodes of said tubes in series therewith and characterized by the absence of any intermediate terminal connection tosaid tubes or supply source, whereby full utilization of said coupling means is effected.
  • a class B amplifier comprising in combination, a plurality of amplifying devices included respectively in the arms of a bridge, an anode supply connected across one diagonal of said bridge, output coupling means connected across the other diagonal, and an input coupling network arranged to control in like manner the tubes in one pair of opposite arms of said bridge but in reverse phase to the control of the tubes in the other pair of arms for causing alternating flow of anode currents in said output coupling means.
  • said output circuit comprises an inductor the end terminals of which are directly connected to the output electrodes of said tubes but with no space current flowing in said circuit in the no signal input condition.
  • inductor is the primary of an audio frequency transformer, characterized in that the coupling between primary and secondary is substantially tighter than in the case of a divided primary winding.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
  • Microwave Amplifiers (AREA)
US177375A 1937-11-30 1937-11-30 Amplifier for signal transmission Expired - Lifetime US2235677A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US177375A US2235677A (en) 1937-11-30 1937-11-30 Amplifier for signal transmission
CH209779D CH209779A (de) 1937-11-30 1938-11-28 Gegentaktverstärker vom Typ der B-Klasse.
DER103926D DE704724C (de) 1937-11-30 1938-12-01 B-Verstaerker fuer groessere Leistungen, insbesondere fuer Modulationszwecke

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US177375A US2235677A (en) 1937-11-30 1937-11-30 Amplifier for signal transmission

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US2235677A true US2235677A (en) 1941-03-18

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2561425A (en) * 1949-06-30 1951-07-24 Edward J Stachura Balanced push-pull amplifier
US2895018A (en) * 1954-01-06 1959-07-14 Arthur L Tirico High fidelity push-pull amplifiers
DE1084316B (de) * 1958-06-24 1960-06-30 Sueddeutsche Telefon App Kabel Verstaerker- bw. Oszillatorstufe mit mehreren gleichstrommaessig in Serie gespeistenTransistoren gleichen Leitfaehigkeitstyps
US3157839A (en) * 1962-02-01 1964-11-17 Harry B Brown Transistorized bridge amplifier with a bias compensating circuit therefor
US6809586B1 (en) 2003-05-13 2004-10-26 Raytheon Company Digital switching power amplifier

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2561425A (en) * 1949-06-30 1951-07-24 Edward J Stachura Balanced push-pull amplifier
US2895018A (en) * 1954-01-06 1959-07-14 Arthur L Tirico High fidelity push-pull amplifiers
DE1084316B (de) * 1958-06-24 1960-06-30 Sueddeutsche Telefon App Kabel Verstaerker- bw. Oszillatorstufe mit mehreren gleichstrommaessig in Serie gespeistenTransistoren gleichen Leitfaehigkeitstyps
US3157839A (en) * 1962-02-01 1964-11-17 Harry B Brown Transistorized bridge amplifier with a bias compensating circuit therefor
US6809586B1 (en) 2003-05-13 2004-10-26 Raytheon Company Digital switching power amplifier
US20040227568A1 (en) * 2003-05-13 2004-11-18 Habboosh Namir W. Digital switching power amplifier

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Publication number Publication date
CH209779A (de) 1940-04-30
DE704724C (de) 1941-04-05

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