US1872109A - Multistage amplifier - Google Patents

Description

Aug. 15, 1932.

P. BORlAS 1,872,109

MULTISTAGE AMPLIFIER Filed July 5, 1929 i i l ln-wwa, N

5 HIM AAAllA I P01614770 =02) zzif INVENTOR ,Paud Bart/ad, BY

ATTORNEY Patented Aug. 16, 1932 UNITED STATES PAUL BORIAS, 0F PARIS, FRANCE MULTISTAGE AMPLIFIER Application filed July 5, 1929, Serial No. 376,249, and in France July 5, 1928.

The present invent-ion relates to amplifiers, and, more particularly, to coupling means for multi-stage amplifiers.

A multi-stage amplifier has been disclosed in application Serial No. 254,988, filed February 17, 1928 which possesses novel characteristics to be briefly referred to. The reactance of the plate circuit for the frequency to be received is eliminated with the result that all reaction due to the internal capacitance of the tube is prevented, inasmuch as the plate is at an alternating current potential practically of zero value.

More specifically the amplifier arrangement in the said application comprised a series resonant coupling between stages, the coupling including an inductance in series with a resistance and a capacity in shunt with the latter. As will be readily noted this arrangement does not transmit the higher frequencies and leaves a residue of amplification for the lower frequencies.

Now, it is well known that attempts to insure high quality of reproduction of audio or musicalfrequency currents is attended,

in the audio stages, with difiiculties of filtering out the radio frequency currents which.

still exist at the output end of the detector tube.

detector tube and the first audio stage.

Another important object of the invention is to provide a couplmg arrangement between the audio stages which will successfully fiLer out residual radio frequency currents which exist at the output ends of preceding stages. The invention will bebetter understood from the following description by reference to the accompanying drawing in which,

Fig. 1 shows a multi-stage amplifier embodying a series resonant coupling,

Fig. 2 shows a novel form of coupling arrangement to a succeeding audio stage,

Fig. 3 shows a graphic representation of t the operation of the amplifier shown in Fig. 2.

As stated above, there has been disclosed interposed between the plate and filament of tube 1.

A coupling capacity C is inserted in the lead brought to the grid of tube 2, while the potential of the latter with reference to the filament is determined and governed, for example, by means of a grid-leak resistance It. For the working frequency, the reactance of impedance L is compensated by the reactance of impedance C. To apply to the plate of the tube 1, the necessary direct current potential, the said plate is connected with a suitable source of potential by way of an impedance Z (resistance or inductance) which will not result in an'appreciable shunt for the radio frequency current, since the branch or shunt L C forms an impedance sensibly of zero value for this current. It will be noted that this coupling arrangement leaves aresidue of amplification for the lower frequencies, while it does not transmit the higher frequencies.

' In Fig. 2, I have shown an arrangement for connecting a detector tube D with a subsequent amplifier tube A. Between the plate of tube D and a suitable point of the supply sources (not shown), there is established a connection comprising, in series, a reactance coil or choke-coil L at the plate end and a capacitive reactance C on the source end adjustable as in Fig. 1. The plate of tube D is associated with the positive pole of the plate source by way of a resistance R.

It is possible without great inconvenience to dispose in shunt-to the resistance R an adjustable condenser G with a view to enhance the filter action, or else a back-feed or tickler coil P in series with the condenser C A connection or lead associates the grid of tube A with a point between Land C, said connection comprising the coupling condenser C The potential of the grid of tube A is fixed by curve will have a a pulsation 0 R is made equal to p (where p isv the internal resistance of the tube), and further Under these conditions, the amplifying shape as shown in Fig. 3. This curve deviates but little from the ordinate l t/2 (where it represents the coeflicient of amplification in volts of the tube) for all values of the pulsation being less than al Butitfalls off very rapidly to zero for the values of the pulsation above (0 The graphs 1, II, or Ill are obtained according to whether the resistance R is not shunted; is shunted by the capacity C or shunted by the capacity C in series with a reactance coil P.

As will be understood without departing from the spii -t underlying this invention, it is possible to adopt, according to the end aimed at, values, o er than those hereinbefore indicated, w .h are adapted to and chosen for he conditions under which amplifiers are usually employed in radiophony. The invention and its application will be found particularly useful and eilicient in connection with superheterodyne receiver sets, or sets operating on the frequency-changing principle in which appear beyond the detector not only musical or audio frequency currents, but also radio frequency currents and currents of an intermediary frequency, of rather large values, which are generated by the action of the oscillator or the local modulator.

There are a. number of evident modifications of the invention that will be quite apparent to those skilled in the art. F or example, since the condenser C is designed so as to transmit conveniently audio frequency current, it does not matter whether the condenser C is disposed as shown in Fig. 1, or else is connected after the capacity C in relation to That is to say, for example, in parallel relation with the resistance R.

ln lieu of triodes it is also possible to use two-grid tubes or multiple-electrode tubes, without the herein disclosed coupling means losing its special pro )erties. While I have indicated and described a system for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications in the circuit arrangements, as well as in the apparatus employed, may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is 1. In an amplifier of lower frequencies resulting from the detection of higher frequencies, a coupling between tubes comprising a series resonant circuit tuned to a definite low frequency and comprising an inductance in the output circuit of one of the tube-s and a capacity in the input circuit of a following tube, coupling means between said capacity and the grid of the said followingtube, and a resistance included in the circuit comprising the plate of the first named tube and its source of potential, the equivalent impedance of the said resistance and the internal resistance of the first tube being equal to the impedance of the inductance of the series resonant circuit at the said tuned low frequency;

2. In an amplifier low frequencies resulting from the detection of higher frequencies, a coupling between tubes comprising a series resonant circuit tuned to a definite low frequency and comprising an inductance in the output circuit of a tube and a capacity in the input circuit of a following tube, coupling means between said capacity and the grid of the following tube, and a resistance equal to the internal resistance of the first named tube and included in the circuit comprising its plate and its .source of potential, this resistance being twice the impedance of the inductance of the series resonant circuit at the said tuned low frequency.

3. In an amplifier of lower frequencies resulting from the detection of higher frequencies, a coupling between tubes comprising a series resonant circuit tuned to a defiite low frequency and comprising an inductance in the output circuit of one of the tubes a capacity in the input circuit of a following tube, coupling means between the capacity and the grid of the following tube, and a resistance inserted in the circuit comprising the plate of the first named tube and its source of potential, the equivalent impedance of the said resistance and the internal resistance of the first tube being equal to the impedance of the inductance coil of the series resonant circuit at the said tuned low frequency, and the said resistance bein shunted by a variable impedance.

' PAUL BORIAS'.

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