US2066902A - Method of and means for producing oscillations - Google Patents

Description

Jan. 5, 1937. TZ 2,066,902

'METHOD- OFAND MEANS FOR PRODUCING OSCILLATIONS Filed May 24, 1934 2 Sheets-Sheet l M I Z040 0M0 (mm r sax/ea 0/050 (WERE/W.

sou/9c! INVENTOR JOHN L. REINARTZ ATTORNEY Jan, 5, 1937.

J.- L. REINARTZ 02 METHOD OF AND MEANS FOR PRODUCING OSCILLATIONS- Filed May 24, 1934 "2 Sheets-Sheet 2 a/kicr cue/e50 2. 5? 5 F@\ f 14 1 K r INVENTOR JOHN R EINARTZ BY gwl/ v ATTORNEY Patented Jan. 5, 1937 UNITED STATES PATENT OFFICE John L. Reinartz, Manchester, 001111., assignor to Radio Corporation of America, a corporation 7 of Delaware Application May 24, 1934, Serial No. 727,215

2 Claims.

This invention relates to a method of and means for producing oscillations of constant frequency and, if desired, multiplying the frequency of the oscillations so produced. More in detail 5 the present invention relates to a method of and circuit arrangements for utilizing efficiently thermionic tubes of the multi-electrode type heretofore commonly used in class B operation, in class C operation as oscillation generators, amplifiers and/or frequency multipliers. In general, the tubes involved are of the type comprising a cathode, a control grid, one or more additional grid-like electrodes and an anode.

Class B tube operationis characterized by the condition that a relatively low plate current is maintained when no excitation is supplied to the control grid of the tube. When a signal of sufficient magnitude is applied to the grid, there will be no plate current flow over a substantial part of the negative cycle of said signal. Current,

however, .will flow during the positive or less negative portion of the cycle of said signal. Ideal class B operation is attained when the alternating component of plate current is an exact replica of the input signal for the half-cycle when the grid is positive and the plate current flows during 180 electrical degrees of the applied signal.

Tubes of the type described above when used in class B operation generally have their grids connected directly together and to the cathode by Way of the input impedance. No biasing potential source is necessary, the tubes in operation relying on the potential produced by grid rectification of the signal wave in the grid circuit.

Tubes of the type described above have also been used in class A operation. When so used, the control grid is excited by the wave to be amplified. The auxiliary grid electrode is connected directly to the anode electrode so that in effect we. have a triode. In some instances when these tubes are used as class A amplifiers the screen grid electrode being nearer to the cathode draws exceedingly heavy current and is destroyed.

This defect, of course, would not hold where the additional grid electrode is tied to the control grid.

With class C operation of the tube the bias applied to the grid electrode is appreciably more than necessary to cut oil the plate current to zero when no exciting voltage is applied to the control grid, so that the plate current flows in the tube for appreciably less than one-half of each cycle. In this case jabs of current appear in the anode circuit during much less than degrees of the applied wave. Class C operation is attained with extremely high plate circuit efliciency.

An object of the present invention is to provide 5 a new method of and circuit arrangement for operating thermionic tubes of the class described above as oscillation generators and operating said tubes in said circuit as class C relays.

Another object of the present invention is to 10 provide a method of and. circuit arrangements for producing high frequency oscillations in a thermionic tube of the multi-grid type and for impressing said oscillations on an output circuit which is coupled to the generating circuits by 15 the electron stream only of the tube. In this circuit, changes or variations in the load coupled to the output circuit have no effect whatever on the constants of the frequency generating and determining circuits. 20

Another object of the present invention is to provide an oscillation generator utilizing a multigrid electrode of the type described in which the control grid, cathode and one or more grid-like electrodes make up a conventional triode in which 25 oscillations may be generated of a frequency determined by the constants of the circuits connecting said electrodes or by an additional frequency determining element and in which an output circuit electro-magnetically separated from, 30 but electronically coupled to the prior electrodes and circuits may be connected between the anode and cathode of the tube.

Another object of the present invention is to provide a circuit arrangement as described in 35 the preceding paragraph in which the circuit be tween the anode and cathode of the tube may be tuned to the fundamental frequency generated in the triode operation of the tube or to a multiple of said frequency. 40

When exceptional stability is desired in the circuit briefly described in the two preceding paragraphs, the anode electrode and circuit may be further dissociated from the triode portion of the tube and the circuits thereof by connecting 45 neutralizing condensers between the desired electrodes in the triode portion of the tube and the anode.

In the triode portion of the tube sustained oscillation may be assured by connecting coupling 5 condensers between the control grid and grid-like electrodes of the tube to produce a feed back of energy from the grid-like electrode adjacent the anode to the control grid electrode. In a pushpull arrangement the control grids of each tube 55 may be fed energy from the grid-like electrode of the other tube.

Numerous otherobjects of the present invention and advantages derived from the use thereof will become apparent from the following detailed description thereof when read in connection with the attached drawings throughout which like reference symbols indicate like parts insofar as possible and in which,

Figure 1 shows, for purposes of illustration only, an oscillation generator circuit in which tubes of the type described above are connected in a novel manner to produce oscillations of substantially constant frequency and to apply the same to a load circuit in such a manner that variations of said load have no effect on the constancy of the frequency producing circuits.

Figure 2 shows a modification of the arrangement of Figure 1.

Figure 3 shows an oscillation generator including thermionic tubes of the multi-grid electrode type in which certain electrodes of the tube are connected for triode oscillation generation,

while other electrodes are connected in an output circuit coupled only by the electron stream of the tube to the prior circuits; while,

I Figure 4 shows a modification of the arrangement of Figure 3.

Referring to Figure 1, A and B are a pair of thermionic tubes having cathodes K, control grids I and I 2 and anodes 3 and 3. The grids 2 and 2 are connected as shown in pushpull relation by a circuit IE comprising an inductance L and a tuning capacitor C. Grid I of tube A is connected as shown by way of a feedback capacitor FB to grid 2' of tube B, while grid I of tube B is connected as shown by way of a feedback capacitor FB to grid 2 of tube A. The circuit I 0 is tuned to the frequency it is desired to generate and is preferably preponderantly inductive in character. Due in part to the impedance of this circuit and in part to the feed back supplied by the condensers FB sustained oscillations of the desired frequency are developed in the circuit I0 and the electrodes I, 2, I and 2.

A circuit 20 comprising an inductance M and tuning capacitor D is connected as shown between the anodes 3 and 3 of the tubes A and B. This circuit 20 may be coupled in any manner to any load shown diagrammatically at 24. The oscillations produced in the circuit I 0 are impressed by way of the electron stream in the tubes A and B to the circuit 20 which is magnetically isolated with respect to the circuit It]. The control grids of the tubes derive their biasing potentials by way of resistances R connected as shown between said control grids and the cathodes. No separate biasing potential source is necessary. The anodes and grid-like electrodes of the tubes derive their positive potential from a direct current source connected as shown to points intermediate the terminals of inductances L and M respectively.

In actual practice it was found that a considerable change of the load on the anodes of the tube resulted in no change in the frequency generated and in the amount of direct current flowing in the control grid circuits. Moreover this is true whether the circuit DM be tuned to the fundamental frequency to which LC is tuned or to a multiple frequency in.

In the arrangement of Figure 2 a single tube A has its control grid I connected as shown by way of a resistance R to its cathode K. A freand auxiliary grid electrodes 2 and quency determining piezo-electric crystal PC is connected as shown between grid I and the oathode. The grid-like electrode 2 of this tube is connected by way of a circuit LC to the cathode of the tube. This electrode 2 serves as the anode of a triode system in which oscillations are produced of a frequency determined by the crystal PC. In this arrangement the circuit LC is preferably tuned to a frequency slightly above the frequency of the crystal so as to increase the impedance of this circuit and thereby insure the production of sustained oscillations in the tube. The anode 3 is connected as shown by way of an output circuit 20 to the cathode of the tube. Here, as in the prior case, the anode is coupled to the frequency determining circuits only by way of the electron stream of the tube. The cir' cuit 20 is electro-magnetically isolated from the other circuits of the tube. To further insure decoupling between the different elements including the anode electrode 3, and its circuit 20, the screen grid 2 and the frequency determining circuit CL a neutralizing capacitor NC is connected as shown between the anode 3 and the grid 2 by way of the circuit CL. It will be noted here that by using this tube in applicants novel circuit results are obtained equivalent to the use of two tubes. The tube first serves as an oscillation generator and then as an amplifier in case the circuit 26 is tuned to the fundamental frequency or as a frequency multiplier in case the circuit 20 is tuned to a harmonic fn.

In operation oscillations are produced in the circuits connected with electrodes K, I and 2 of a frequency determined in part by the piezoelectric crystal PC. These oscillations appear in the circuit CL from which they may be utilized if desired. However, it is preferable to place no load on the circuit CL and to derive the useful oscillations from the circuit 20. This insures a more constant operation in the triode portion of the tube.

In order to eliminate to a great extent the harmonies which may be present in the tank circuit 20 of the device of Figure 2, I make use of a pushpull arrangement as shown in Figure 3. The thermionic tubes A and B have their control grids I and I connected as shown by way of resistances R to their cathodes K. A frequency determining piezo-electric crystal PC is connected between the control grid electrodes I and I. The grids 2 and 2' of the tubes A and B are connected as shown in pushpull relation by a frequency determining circuit CL which may be tuned to substantially the frequency of the crystal PC. A positive potential is applied between grids 2 and 2 and the cathode by connecting the positive terminal of a source to a point on the inductance L and the negative terminal of the source to the cathodes of the tubes A and B. The electrode system, which is similar to a triode, and circuits so far described when energized produce sustained oscillations of constant frequency. The anodes 3 and 3' of the tubes A and B are connected in push-pull by tuned tank circuit 20 as shown. The positive terminal of the direct current source is connected to a point on the inductance M. A load circuit may be coupled to the inductance M. The oscillations produced in the triode portion of the tubes and appearing in CL are transferred by way of the electron stream only of the tubes A and B to the anodes 3 and 3, and from the anodes to the tank circuit 20. The oscillations in the tank circuit 20 may be impressed on the load circuit. The tank circuits 20 may be tuned to 75 the fundamental frequency, that is, to the frequency of the crystal PC or to a harmonic thereof. Due to the pushpull arrangement many of the harmonics which might be present in the arrangement shown in Figure 2 will not be present in the circuits of Figure 3. To further insure that there is no coupling between the output circuit 20 and anodes 3 and 3 other than by way of the electron stream in the tubes neutralizing capacitors CN may be connected as shown between the anode of the tube A and grid 2 of tube B and between the anode of tube B and grid 2 of tube A. In operation it was found that there was no reaction whatever present on the grids 2 and 2' when the tank circuit is tuned through resonance. The generator operated in a stable manner to produce oscillations of a constant frequency and to amplify or frequency multiply the same. Moreover, it was possible to key the plate circuit of the generator with no appreciable change in the frequency as determined by the triode system including CL and a. piezo-electric crystal PC.

In some cases it is not desirable or not practical to use piezo-electric crystals in the circuits. 1 have provided a novel circuit by means of which sustained oscillations of substantially constant frequency may be obtained without the use of a frequency determining element such as a piezoelectric crystal. Such a circuit has been shown in Figure 4 wherein the electrodes of the tubes have been spaced out to show more clearly the separation between the various circuits and the circuit arrangements.

The grid electrodes l and l of tubes A and B are connected as shown to the cathodes K by way of biasing resistances R. The grids 2 and 2 of tubes A and B are connected as shown in pushpull relation by a tuned tank circuit CL. This circuit is tuned to the frequency of the oscillations it is desired to generate and determines said frequency. Positive potential is supplied to the electrodes 2 and 2' by way of a connection between a point at the electrical center at L and the positive terminal of a direct current source, the negative terminal of which is connected to the cathodes K. The grid electrode 2' of tube B whichis serving as the anode of a triode system is connected by way of a feed back condenser FB to the electrode l of tube A. The electrode 2 of tube A, which is acting as an anode of a second triode system is connected by way of a feed back condenser FB to the grid l of the tube B. When the circuits are arranged as shown and energized as shown the grids 2 and 2' serve as the anodes of a triode system in which sustained oscillations are produced of a frequency determined by CL. The anodes 3 of tubes A and B are connected as shown in pushpull relation by a tank circu't 20. The positive potential for the anodes 3 is supplied by way of a connection between the electrical center of M and the positive terminal of the direct current source. The sustained oscillations produced in the triode system and appearing in the circuits CL are impressed by way of the electron stream to the anodes 3 and from 3 to the tank circuit 20. The tank circuit 20 may betuned to the fundamental frequency F or to the harmonic FM. The oscillations may be applied from N to any load circuit 24. Here again changes in the load circuit or in the tuning of the tank circuit 20 cause little or no effect on the frequency generated in the triode portion of the tube. Moreover changes in load or in tuning of the tank circuit can be prevented entirely from affecting the frequency of the oscillations produced if the anode of each tube is connected as shown by way of neutralizing condensers CM to the grids 2 and 2' of the other tube.

A separate source of direct current is shown connected between a point on the inductance L connected with the grids 2 and 2'. When using a high capacity circuit CL connected with grids 2 and 2' and when this tank circuit CL is supplied from a separate direct current source which cannot change when the anode circuit 20 is keyed, then there is no change in the current drain in the circuit connected or no change in the frequency produced in the triode portion and radiated from 20.

It will be noted that in all of these electron coupled oscillators and/or frequency multipliers, no grid biasing potential source is utilized. Moreover, in each of the circuits shown the oathodes of the electron coupled oscillator tubes are maintained at ground radio frequency potential. This is of considerable importance because it lends to stability of operation and helps to insure production of oscillations of constant frequency. Moreover, from a practical standpoint, as will be readily understood, it is of advantage to have the cathode which is heated by low fre-.

quency or direct current at ground radio frequency potential. If the cathode must be operated at high radio frequency potential, as is the case in electron coupled oscillators known heretofore, considerable precautions and added expense are involved in insulating or raising the cathode and its heating circuits and sources above ground potential.

Having thus described my invention and the operation thereof, what I claim is:

1. An oscillation generator of the push-pull type comprising a pair of electron discharge tubes each having a cathode, an anode, and at least two grid electrodes, including a control grid and a screen grid, a tank circuit interconnecting the two anodes, a second tank circuit interconnecting the screen grid electrodes, an input circuit for each tube disposed between the oathode and the control grid thereof, each said input circuit comprising means for maintaining a negative bias on said control grid with respect to the cathode of such value that less than 180 of each cycle of an applied excitation wave is available to render the tube conductive, two symmetrically disposed feed-back capacitors each intercoupling the control grid of one tube with the screen grid of the other tube, means including a direct current source for so polarizing said electrodes each with respect to the other as to activate said tubes, and means including two symmetrically disposed capacitors each intercoupling the screen grid of one tube with the anode of the other tube for neutralizing the inter-electrode capacitances of said tubes. 7

2. An oscillation generator according to claim 1 and further characterized in that the two said tank circuits are so tuned that the resonant frequency characteristics thereof bear a harmonic relationship, one to the other.

JOHN L. REINARTZ.

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