US2250613A - Amplifier energizing circuit - Google Patents

Description

y 29, 1 H. T. J. WIE GERINCK arm. 1 AMPLIFIER ENERGIZING CIRCUIT Filed July 25, 1939 AEAMPL/F/ER HENDR/KUS 7.'J. W/EGER/NCK INVENTORS D T V055 EN WW ATTORNEY.-

70 SOURCE OF A 00/0 SIGNALS T0 4.6. RECTIFIER Patented July 29, 1941 ABIPLIFIER ENERGIZING CIRCUIT Hendrikus T. J. Wiegerinck and Arnold Theo Vossen, Eindhoven, Netherlands, assignors, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporationof Delaware Application July 25, 1939, Serial No. 286,320 In Germany March 15, 1939 3 Claims.-

This invention relates to a low frequency amplifying circuit arrangement comprising an amplifying tube whose anode circuit contains the primary winding of an output transformer, the anode voltage produced by a pulsating direct current voltage being supplied to the amplifying tube through this winding.

It is well known that for simplifying and cheapening the filter circuit which is required to smooth the operating currents it is advantageous to supply to the anode of an output amplifying tube a non-smoothed and consequently pulsating direct current voltage. Consequently the direct current charge of the filter circuit is materially decreased so that comparatively small smoothing chokes, or even exclusively ohmic resistances, can be used in the filter circuit. In order to avoid, however, that in this case alternating current voltages originating from the pulsating direct supply voltage are produced in the output circuit of the amplifier, which alternating voltages would manifest themselves as alternating current hum, it is necessary to use means for compensating the interfering alternating current voltage produced in the output circuit.

'This can be achieved, as is well known, by supplying to the control grid of the output amplifying tube an alternating current voltage which has been taken from the source of anode voltage of this tube. However, the compensating circuit arrangements known to this effect essentially exhibit the disadvantage that the grid circuit of the output amplifying tube is influenced by the circuit elements required for compensation, and this generally in such manner that the frequency response curve of the amplifier becomes less favorable. An additional drawback of the known circuit arrangements is that a control of the degree of ampilfication of the amplifier by means of a variation of the magnitude of one of the circuit elements of the grid circuit of the output amplifying tube also brings about a variation of the amplitude and/or the phase of the compensation voltage supplied to the control grid so that the compensation is disturbed. Finally, the circuit elements required for compensation frequently act not only upon the grid circuit of the output amplifying tube, but also upon preceding amplifying stages. The latter is the case, for example, if the compensating voltage is taken from a resistance which is included in the common cathode return conductor for the various amplifying tubes. Consequently, very disturbing coupling phenomena may occur particularly in 7 above mentioned disadvantages are obviated. Ac-

cording to the invention, in a low frequency amplifying circuit arrangement comprising an amplifying tube whose anode circuit contains the primary winding of an output transformer, the anode voltage produced by a pulsating direct current voltage being supplied to the amplifying tube through the said winding, use is made for compensating the interfering alternating current voltages, produced in the output circuit of an output transformer, of an additional winding which is fed by the source of anode voltage of the said amplifying tube.

By a corresponding choice of the amplitude and the phase of the current flowing through the additional winding, a faultless elimination of the undesirable alternating currents produced in the output circuit is achieved. It should thereby be noted that the undesirable alternating voltages generally contain not only a component corresponding to the mains frequency, but also components corresponding to various higher harmonics of the mains frequency.

One particular advantage of the circuit arrangement according to the invention further consists in that a variation of the degree of amplification of the relative amplifying tube, as can be produced for example by means of an eccentric position of the working point of the tube, afiects the compensation of the undesirable alternating current voltages to a materially less extent than when the compensating voltage is supplied to the control grid of the tube as in the known circuit arrangements.

To obtain the phase, which is required for compensation, of the current flowing through the additional winding of the output transformer, the additional wiring is preferably connected in series with such an impedance that the series connection exhibits a substantially ohmic alternating current resistance.

According to one advantageous construction of the circuit arrangement according to the invention, the additional winding of the output transformer, which is preferably connected in series with an ohmic resistance, forms part of a filter circuit which serves to smooth a direct current which has been taken from the source of anode voltage of the said amplifying tube, said direct current being supplied to the grid electrodes'of the amplifying tube and, if desired, being further used for supplying pre-amplifying tubes.

The invention will be more clearly understood by reference to the accompanying drawing showing, by way of example, the circuit arrangement of a pentode output amplifying stage according to the invention.

In the drawing, 1 is a pentode amplifying tube, in the anode circuit of which is arranged an output transformer 2. The anode voltage is supplied to the amplifying tube through a primary winding 3 of the output transformer. The loudspeaker 5 is connected to a secondary winding 4 of the output transformer. The low frequency oscillations which are to be amplified are supplied to the control grid of the amplifying tube through input terminals 6 of the control grid circuit. The direct current operating voltages of the amplifier are taken from an existing direct current mains or a rectifying circuit arrangement, and are supplied to connecting terminals 1. A condenser 8 is connected in parallel to smooth the pulsating direct current supplied to the terminals 1.

The anode voltage of the amplifying tube I is directly taken from the condenser 8 so that the direct current voltage set up at the anode of the amplifying tube is a pulsating one. This pulsating direct current voltage brings about in the secondary circuit of the output transformer 2 interfering alternating current voltages which become manifest as alternating current hum. To eliminate the alternating current voltages brought about in the'output circuit by the pulsating anode supply voltage, the output transformer comprises an additional winding '9 which istraversed by a current taken from the condenser 8. An ohmic resistance 10 and a condenser II are connected in series with the additional winding. By a corresponding choice of the ratio between the magnitude of the alternating current resistance of the additional winding '9 and the magnitude of the total alternating current resistance of the resistance 1 and the condenser I l,the niagrlitude of the alternating voltage brought about in the secondary circuit of the additional winding 9 can be adjusted. This magnitude, of course, can also be varied by variation of the number of turns of the additional Winding 9;

If the loudspeaker has a substantially ohmic alternating current resistance, as is generally the case, the part of the anode circuit which is connected in parallel to the condenser 8 has also a substantially ohmic alternating current resistance, and the circuit of the winding '9 which is connected inparallel to the condenser 8 must have a substantially ohmic alternating current resistance in order that the phase of the current flowing through the additional winding 9 is correct with respect to the compensation. To this effect, it is necessary that the additional winding 9 should be connected in series with a corre spondingly chosen impedance. Consequently, to compensate various interfering frequencies, in the represented circuit arrangement, the ohmic resistance in this case must have a high value with respect to the sum of the alternating current resistances of the additional winding 9 and the condenser ll.

In the represented circuit arrangement the additional winding 9, the resistance l0 and the condenser H constitute parts of a filter circuit which serves to smooth the direct current taken from the condenser 8. The direct current voltage set up at the terminals of the condenser H is supplied to the screen grid electrode of the amplifying tube I, and can moreover be used for supplying further tubes present in the circuit arrangement by taking this direct current voltage from connecting terminals l2.

The condensers 8 and l l serving to smooth the operating currents of the amplifier preferably exhibit a comparatively great capacity, for example 32 microfarads. In this case a smoothing, which is suflicient for the pre-amplifying stages, of the direct current voltage set up across the condenser II will generally be achieved, if the resistance [0 has a magnitude of, say, 2000 ohms.

What is claimed is:

1. In an amplifier, a tube provided with at least a cathode, an input electrode and an output electrode, a source of pulsating unidirectional voltage, an input circuit connected to said input electrode and cathode, an output transformer having its primary windingconnected between said output electrode and said source, an output circuit connected to the transformer secondary winding, and means coupled between said source and said secondary winding for introducing into the latter a pulsating voltage component which cancels out the pulsations due to said source, a screen electrode adjacent said output electrode, said means functioning as a filter element in said source, and said screen electrode being connected to said filter means.

2. In combination with an amplifier tube having signal input and output circuits, a source of pulsating direct current voltage, said output circuit comprising a transformer provided with a primary winding and at least two secondary windings, said primary winding being connected to a point of positive potential of said source, and one of said secondary windings being included in said source thereby to introduce compensation pulsation voltage into said other secondary winding and a filter network included in said source for smoothing said direct voltage, and said one winding being included as an element of the filter network.

3. In combination with anamplifier tube having signal input and output circuits, a source of pulsating direct current voltage, said output circuit comprising a transformer provided with a primary winding and at least two secondary windings, said primary winding being connected to a point of positive potential of said source, and one of said secondary windings being included in said source thereby to introduce compensation pulsation voltage into said other secondary winding and a filter network included in said source for smoothing said direct voltage, and said one winding being included as an element of the filter network, a screen grid in said tube, and a connection from the screen grid to the output of the filter network.

HENDRI-KUS T. J. WIEGERINCK. ARNOLD THEO VOSSEN.

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