US2144226A - Discharge tube amplifier - Google Patents

Description

Jan. 17, 1939.

A. NYMAN DISCHARGE TUBE AMPLIFIER Original Filed Feb. 25, 1931 INVENTOR r z @f 6 6 2 W fexander an Y ATTORNEY.

Patented Jan. 17, 1939 UNITED STATES PATENT OFFICE DISCHARGE TUBE AMPLIFIER Alexander Nyman, Weehawken, N. J assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware 5 Claims.

This application is a division of and contains matter from United States application Serial No. 518,098 filed February 25, 1931, issued as Patent No. 1,986,597 on January 1, 1935.

In the parent application, I have described a new type of cascade amplifying system comprising substantially a plurality of amplifying valves connected in series with a suitable coupling element and an operating current source as distinguished from the usual parallel connection of amplifying valves heretofore used in the art. The advantages of an amplifier of this type residing, among others, primarily in the use of a single coupling element for an increased number of cascade stages, increased selectivity, have been set forth, and the function andoperation of such series type amplifier systems explained in detail in the parent application.

The present application relates to improvements and novel combinations of series amplifying systems of the type under discussion having for its main object to increase the efficiency and reliability of operation of systems of this type.

A more specific object of this invention is to provide means for using a series amplifier for high frequency in combination with a detector for demodulation and means for further amplification of the demodulated signal energy.

Another object of the invention is to provide means for using the same series amplifier for amplifying different frequencies or ranges of frequencies, such as first, for amplification of incoming radio frequency energy, and furthermore for detection or demodulation of the receiving signalling energy and for amplifying the received demodulated or low frequency signals.

A further object of the invention is to provide means in connection with a series amplifier for one frequency for detecting and further amp1ifying the detected signals in the series amplifier and for segregating the currents of different frequencies or frequency, ranges through their respective channels to substantially prevent mutual interference between separate frequencies or frequency ranges of the amplifier.

Still another object of the invention is to utilize a series amplifierdesigned for amplifying one frequency or a definite range of frequencies in combination with a detector and an amplifier for currents at another frequency and utilizing a portion of said series amplifier as a'coupling ele-' ment for further amplification.

Another object of the invention is to utilize a series amplifier for superheterodyne reception wherein the incoming high frequency signals are transformed into a different intermediate frequency, amplified at intermediate frequency and then demodulated to supply the audio output signals.

A further object of this invention is to utilize a series amplifier for reception of radio frequency signals according to the heterodyne method in cluding the necessary beating oscillator as an integral part of the series amplifier.

A further object of the invention is to incorporate in a series amplifier or amplifying system according to the invention, means for securing automatic volume control action.

The invention has further objects in view which Will appear hereinafter as the detailed description proceeds taken with reference to the accompanying drawing wherein:

Figure 1 illustrates a. super-heterodyne receiving circuit embodying a series amplifier according to the invention and a separate local 0scillator.

Figure 2 shows a modification of a superheterodyne circuit embodying two series amplifiers according to the invention, one operating at intermediate frequency and another at audio frequency, and an oscillator incorporated in the first series amplifier.

Figure 3 illustrates a further modified superheterodyne circuit wherein the oscillator is included in the radio frequency series amplifier chain and the intermediate frequency supplied by a separate series oscillator.

Similar reference characters identify similar elements throughout the different views of the drawing.

Referring to Figure 1, I have shown an arrangement of a series amplifier utilizing a socalled super-heterodyne connection. The general operation of a super-heterodyne includes the conversion of the received signals into another frequency known as intermediate frequency, and amplification at this intermediate frequency for further demodulation into audio frequency.

In Figure 1, the antenna 34 with a coupling coil 33 and a ground connection 35 is shown. The coil 33 is coupled to a tuning circuit comprising coil 3| and a variable condenser 32. The tuned circuit forms a part of the input circuit of the first tube of a series amplifier, consisting of tubes Tl, T2, T3, and T4. The cathode 3 of the tube TI is connected through a coupling coil I00 and a bias resistor. R2 with a bypass condenser 51, to the negative supply lead 2. The coil I00 is coupled to another coil II, which may be the output coil of an oscillator I02, the connections in the tuned circuit 3I32 and the oscillator I02.

Thus, heterodyne beats are introduced in the grid 4 of tube TI and amplified through series am lifiers T2. T3. and T4.

I have shown the grid I5 of tube T2 connected to a grid condenser I05 and a grid leak I06, the purpose of which is to demodulate the heterodyne currents of the tube TI impressed on the cathode of tube T2, so as to leave substantially only intermediate frequency on the subsequent tubes T2, T3, and T4. I have shown, moreover, a bypass condenser I01 from the plate of tube T2 and a radio frequency choke coil I08 between the plate of tube T2 and the cathode of tube T3. The object of the bypass condenser I0! and the choke I08 is to localize the radio frequency oscillations to the tubes TI and T2 and p-ermitintermediate frequency variations only to pass on to tubes T3 and T4. I have also shown a coupling element in series with the'plate I09 of tube T4, consisting of a tuned circuit consisting of inductance H0 and a condenser III arranged to be within the frequency range of the intermediate frequency. The coil H0 is coupled through the coil H2 to another tuned circuit comprising the coil I I2 and condenser H3 and the combination of the two above tuned circuits, forms the necessary coupling element with a high impedance over the intermediate frequency range necessary for successful transmission of the modulated signals; that is, it may be a range of frequency of 10 kilocycles, say, around an intermediate frequency of kilocycles, or whatever other intermediate frequency is chosen.

The design of such a filter is well known in the art and any alternative construction may be utilized. I have shown the output of the intermediate frequency coupling element connected from the coil H2 to the grid I I4 of the second detector D, which demodulates the intermediate frequency into audio frequency. To assist demodulation, a grid condenser I I5 and a grid leak II6 may be used, but this is not always necessary. The other lead from coil H2 is shown connected between a grid bias resistor II! in series with the cathode IIB of tube D and a volume control tube H0 which, as is shown, may act as arectifier for changes in the plate current of tube D.

The grid I20 and plate I2I of the tube H9 are shown connected together and bypassed to the cathode I22 of the same tube, by means of resistor I23 and condenser I24. The combination of tube H9, resistor I23, and condenser I24, is designed for a large time constant so as to give the variations of voltage, only due to sustained excessive signals. Thus, an excessive signal coming in at detector D would result in an appreciable diminution of the average plate current of this tube and a consequent reduction of the potential across the rectifier tube H9 and the resistor I23. A tap ,I25 on resistor I23 applies the reduced potential to the control grid I5 of tube T2, which acts as a first detector and, by, lowering its potential, will reduce the effectiveness of this tubeas a detector and as an amplifier, so thatthe signal amplified by tubes T3 and T4, and detected by t'ube D is also reduced.

A condenser I26 is shown bypassed from the tap I25 to the negative lead 2. The detector tube D may be coupled to a power amplifier tube P by means of direct connection from its plate I21 to the grid 9 of the power tube, and a plate coupling resistance R5 may be supplied. The power tube 'may be connected in any desired manner, for instance, as shown in Figure 5 of my above mentioned patent, and is not specifically illustrated in this diagram. Although this diagram shows ordinary three-electrode tubes used, it is quite evident that screen grid tubes could be similarly utilized and that such screen grid tubes could also be connected to the potentiometer R3, which is used for the series amplifier, in exactly the same manner as has been shown in said patent.

Referring to Figure 2, an alternative arrangement is shown in which the series amplifier consisting of tubes TI, T2, T3, and T4 may have for tube TI, a tube with a space charge grid I30, in addition to the control grid 4. In this case, I can utilize this space charge grid to produce oscillations. in the tube TI, by connecting an oscillator circuit comprising variablecondenser I03 and a coil IIJI in the circuit of the grid I30, a coil I00 coupled with IOI, and a bypass condenser I3I in the circuit of the plate 5 of tube TI. Thus, while the input circuit 3 I32 applies a potential at incoming frequency to the control grid 4, the space charge grid I30 at the same time applies an oscillation of a frequency determined by the oscillatory circuit of condenser I03 and coil IOI.

I have shown a grid bias resistor R2 with a by- T4 will receive substantially only intermediate frequency oscillations and will amplify such oscillations, as a series amplifier, due to the presence of the filter circuit consisting in this case, of three tuned circuits S3, S4 and S5, in series with the plate I09 of tube T4 and on account of the connections from the control grids of tubes T2, T3 and T4 to the potentiometer R3.

The output from the filters S3, S4, and S5 extends through a condenser I to a second detector tube D, which converts the intermediate frequency signals to audio frequency and has a grid leak resistance I33 and the following volume control arrangement. A rectifier tube I I0, similar to Figure 1 is connected in series to the cathode II8 of tube D, and a tap point I25 on a bypass resistor I23 is used to supply the grid bias to the grid I I4 of the tube D, via the grid leak I33. A bypass condenser I26 is supplied on the volume control and also a bypass condenser I24 in parallel with the rectifier tube I I9. This condenser is arranged with the resistor I23 and the impedance of tube H9 to have the necessary long time constant. The tube D may have an intermediate frequency bypass condenser I34 from plate I21 to cathode H8 and a choke coil I35, suitable to block off the intermediate frequency;

As a result, only variations of audio frequency will reach a further amplifier tube T5 in series amplifier connection with the tube D. The grid I36 of tube T5 may be supplied with a constant potential from the common potentiometer R3. The output of tube T5 and, if necessary, of a further amplifier tube (not shown) connected and in series with it, is obtained from a coupling transformer 10, which may lead further into a Cir poweramplifier'stage (not shown). It will be seen that in this case the volume control arrangement is applied to the second detector, while in Figure 1 the volume control was applied to the first detector. Either of these arrangements may have advantages, depending on the particular design of the amplifier. Thus, the connection of Figure 1 gives a more effective volume control over a wider range of amplitudes, while Figure 2,.withxa simpler oscillator arrangement, gives also a simpler volume control arrangement.

I have shown in Figure 3 another alternative arrangement in which the series amplifier TI, T2 and T3 uses the tube TI, as a radio frequency input tube, and the tube T2 as an oscillator. The tube T2 has. its grid I5 connected to a tuned circuit comprising variable condenser I03 and a coil IIlI. A tickler coil I00 is connected to the anode 6. of tube T2. A back coupling condenser I3I is used to connect the tickler coil back to the cathode I6 of tube T2. A grid bias resistor I36 may be supplied if necessary for the tube T2 used as oscillator;

The variable condenser I03 is shown to have a common control I04 with the variable condenser 32 of the input circuit 3I32, and also with the coupling circuits SI and S2, which are arranged in exactly the same manner as the circuits 3 I32 and IIl3-IIII, to give the frequency response to the two heterodyning frequencies in the series amplifier TI, T2 and T3. Thus, the heterodyning frequencies are permitted to be freely amplified up to the anode 6 of tube T3 and at the same time, certain demodulation to intermediate frequency will take place in this. series amplifier.

This demodulation will impress the potential at intermediate frequency only to a further series filter of intermediate frequency, which may be exactly similar to that of Figure 1 and consisting of a primary III] with condenser III and a secondary H2 with a condenser H3. I have shown the output of the secondary H2 applied to a further intermediate frequency series amplifier consisting of tubes T4, T5 and T6, with series coupling circuits S3 and S4, which are arranged to have a high impedance over the modulated intermediate frequency range, that is, the same range for which the first intermediate frequency filter of coil H0 with condenser III and coil II2 with condenser I I3, were designed.

The arrangement for producing the intermediate frequency by beating the incoming frequency current with the locally produced oscillations as shown in Figures 2 and 3 has the advantage that the mixing of the two frequencies is carried out purely electronically in that the two discharge streams produced by the tubes TI and T2 (see Figure 3) connected in series and one of the streams (TI) is controlled by the incoming frequency currents while the other stream (T2) is caused to vary or oscillate at a locally generated frequency differing from the incoming frequency by the amount of the desired intermediate or beat frequency, the latter being received. by the tuned circuit IIII, III for further amplification as described. In this manner, as is understood, the coupling between the incoming frequency currents and the locally generated frequency currents is purely electronic; that is, through the electron stream only, whereby the mixing effect is a direct one in that one stream affects the other in a multiplicative manner, resulting in a great efficiency of the frequency conversion and lack of distortion as compared to the systems previously known'such as shown in Figure 1 wherein the two currents, that is, the local frequency and the incoming frequency currents, are superimposed in the same grid circuit making it necessary to. operate the tube as a rectifier Withthe attendant disadvantages of distortion and others to secure a true intermediate frequency current.

Thus, the intermediate frequency signals will be freely amplified through the second series amplifier and simultaneously demodulated, resulting in audio frequency changes of impedance, which may be directly impressed upon a series audio frequency transformer ID with an intermediate frequency by-pass condenser I3'I. The output coil II of transformer I0 may be applied to further audio frequency amplifier of any suitable design and supplied, for instance, witha volume control terminal I38 and the supply terminals. I39 and I40, connected respectively to positive lead I and negative lead 2.

The volume control terminal I38 may be used, for instance, for controlling the potential of the screen grids of tubes T4, T5 and T6, by means of potentiometerR3 in an arrangement similar to that of Figure 1. I have sup-plied a choke coil I39, in order to prevent any changes of radio or intermediate frequency that may exist in resistor R3 from reaching the volume control terminal I38. I As it is necessary to use tube T4 partly as a detector at audio frequency, I have supplied, moreover, a grid bias resistor I40 in the U cathode circuit of this tube, together with a bypass condenser IM and a plate by-pass I42, which, however, may be omitted, and also a screen grid by-pass condenser I 43 which may also be omitted, without greatly affecting the operation of this device. A choke coil I44 serves furthermore, to prevent any changes at radio frequency from reaching the intermediate frequency amplifiers T4, T5 and TB.

While I have illustrated a number of modifications of the uses of series amplifier in superheterodyne circuits, I do not wish to be limited to the particular circuits or theoretical consideration outlined in the specification, except as defined in the appended claims.

I claim:

1. An amplifying system comprising a plurality of discharge valves each having a cathode, anode and at least one control electrode; a first coupling impedance; a source of high potential; said valves, said impedance and said source being in series, with the anode of one valve connected to the cathode of the succeeding valve; means for applying impulses of a predetermined frequency range to one of said valves; said impedance having a high impedance to frequencies of said frequency range; means for converting said impulses into impulses of a different frequency range; at least one further valve and means for impressing said converted impulses of the different frequency range upon said further valve; and a second impedance means in series with said last mentioned valve and having a high impedance to variations of current of said different frequency range.

2. In an electrical system comprising a plurality of discharge valves each having a cathode, an anode and at least one control electrode; a plurality of impedance means each designed to present high impedance to a different frequency range; a source of high potential supply; said valves, said impedance means and said source being in series with the anode of one valve connected to the cathode of a succeeding valve; means for applying input potential variations of a certain'frequenc'y range to' one valve of said series; and frequency changing means forming a part of said series for converting potential variations of said first frequency range to potential variations of another frequency range.

3. In an amplifying system comprising a plurality of dischargevalves each having a cathode, anode and at least one control electrode; a source of high potential, said valves and said source being in series, with the anode of one valve connected to the cathode of the succeeding valve, said valves being divided into a plurality of groups; a plurality of coupling impedances in series with said valves having different frequency characteristics whereby each of said groups amplifies currents at a different frequency range from the adjacent group, circuit means cooperating with a valve adjacent successive groups for converting the impulses amplified by the preceding group into impulses of the next following frequency range; and means for by-passing impulses of a pre-determined frequency range from portions of said amplifying series transmitting impuses of a different frequency range.

4. An electrical system comprising a plurality of discharge valves each having a cathode, anode, and at least one control electrode; a source of high potential; said source and said valves being in series, with the anode of one valve connected to the cathode of the succeeding valve; means whereby one of the valves within said series acts as a frequency converter to change the input frequency range applied to the first of said valve series into a different frequency range; at least two impedance means connected in series With said valves and said high potential source and designed each to present high impedance to said first and second frequency ranges, respectively, whereby part of said series operates at more than one frequency; and by-passing means around the other part of saidseries effective for currents having a frequency transmitted by the remaining portion of said series.

5. An electrical system comprising a plurality of discharge valves each having a cathode, anode, and at least one grid electrode; a source of high potential supply; a first impedance; means for applying high frequency modulated input signals to one of said valves to produce amplified potential variations across said impedance; circuit means connected to another of said valves which is adapted to. act as a detector oscillator heating with the high frequency signals to produce intermediate frequency signals; a second impedance connected to another of said valves which is adapted to produce amplified potential variations at intermediate frequency across said second impedance; and means for by-passing currents of said intermediate frequency around said first valve operating at high frequency.

ALEXANDER NYMAN.

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