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April 21, 1936. W. A. Harris 2,038,285 | NVENTOR April 21, 1936. W. A. HARRIs 2,038,285 PARALLEL PUSH-PULL CONVERTER CIRCUITS Filed Oct. 7, 1934 3 Sheets-Sheet li r n s sUQQQQQQQQQr | NVENTOR WILL AM A. HARRS ATORNEY April 21, 1936, W. A. HARRIS 2,038,285 PARALLEL PUSH-PULL CONVERTER CIRCUITs Filed Oct. 17, 1934 3. Sheets-Sheet 2 AZz 2 5 Zocal as?/ZZA70e-/s/ Dé/FC70e Aay. 3 35 / S. AA7AC/A Local a.c.1470 NVENTOR WILLAMA, HARRS by f6 alon-2-1- ATTORNEY Patented Apr. 21, 1936 2,038,285 UNITED STATES PATENT OFFICE 2,038,285 PARALLE, PUSH-PULL CONVERTER CIRCUITS William A. Harris, Belleville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 17, 1934, Serial No. 748,606 5 Claims, (C. 250-20) My present invention relates to signal frequen between the same voltages impressed on the other cy changer networks, and more particularly to device. parallel push-pull converter circuits adapted for Still another object of the invention is to pro use in superheterodyne receivers. vide a superheterodyne converter circuit which 5 Spurious couplings between the local oscillator includes an electron discharge tube provided with 5 and Signal frequency circuits of Superheterodyne a pair of diode electrode sections and an elec converter networks cause considerable difficulty. trode section including at least one grid, the last This has been found especially troublesome in section having circuits operatively associated Converter netWorks used in multi-range receivers, therewith to enable it to function as a local OS () and wherein the converter network utilized a 6A7, cillator, and the diode sections having circuits 10 or pentagrid, type tube. Most of the spurious for rendering them operative as a parallel push couplings, in the latter case, have been found to pull converter network. be due to the effect of modulation of the space Still other objects of the invention are to in charge, in the vicinity of the signal control grid, prove generally the efficiency of converter net at the local oscillator frequency. It was, addi works, and to particularly provide such networks 15 tionally, found that some spurious coupling was which are not only reliable in operation, but eco caused by residual inter-electrode capacitances nomically manufactured and assembled in Super Within the converter tube. heterodyne receivers. - NOW, I have discovered that the effect of such The novel features which I believe to be char undesired Spurious couplings, whether due to ca acteristic of my invention are set forth in partic 20 20 pacity and/or Space charge coupling, can be prac ularity in the appended claims, the invention tically eliminated by employing a pair of con itself, however, as to both its organization and Verter tubes, or elements, in the converter net method of operation will best be understood by Work, and reversing the phase relation between reference to the following description taken in local oscillator voltage and signal voltage in one connection with the drawings in Which I have 25 25 of the tubes with respect to the other. indicated diagrammatically several circuit organ Therefore, it may be stated that it is one of the izations whereby my invention may be carried primary objects of this invention to provide a con into effect. Verter network for a superheterodyne receiver In the drawings:- wherein the network includes at least two tubes, Fig. 1 shows a circuit diagram of a converter 30 Or devices, arranged in circuits such that if the network embodying the invention, signal voltage is applied to the appropriate elec Fig. 1A shows an alternative local Oscillator trodes of the two devices in a parallel arrange circuit for the network of Fig. 1, ment, then the local oscillator voltage is applied Fig. 2 illustrates a modification of the network in push-pull fashion, and, conversely, if the os shown in Fig. 1, 35 3 5 cillator voltage is applied to the two devices in Fig. 3 represents another modification of the parallel, signal voltage is applied with the devices invention, in push-pull. Fig. 4 shows a further modification, Another important object of the present inven Fig. 5 graphically shows the phase relations in tion is to provide a combined local oscillator Figs. 1 and 2. 40 40 first detector network for a superheterodyne re Referring now to the accompanying drawings, ceiver, wherein the network includes a pair of wherein like reference characters in the different pentagrid tubes arranged in parallel push-pull figures represent similar circuit elements, there relation, and the connections between the tubes is shown in Fig. 1 that portion of a Superhetero are such that the phase relation between the os dyne receiver preceding the second detector. The 45 cillator voltage and signal voltage is reversed in signal collector, radio frequency amplifier and One of the tubes as compared to the other. intermediate frequency amplifier are schemati Another object of the invention is to provide cally represented. Those skilled in the art are a method of substantially minimizing, or elimi well aware of the construction of these networks. nating, the effect of capacity and/or space charge The radio frequency amplifier may include one, 50 couplings in superheterodyne converter networks, or more, tunable stages. The network between the method including impressing upon one of a the tunable amplifier and the intermediate fre pair of electron discharge devices employed in quency amplifier includes the subject matter of the network local oscillator and signal voltages the present invention, and functions as a com bined local oscillator-first detector circuit. The 55 5 5 in phase opposition relative to the phase relation 2 2,038,285 latter includes a pair of tubes , 2 having their of condenser 23 and resistor 32, while grid S' circuits so arranged that the effect of spurious is connected to the junction of resistor 33 and couplings between the local OScillator and signal condenser 25. circuits is practically eliminated. It will be observed that the Oscillator anode of This is accomplished by connecting the signal each of tubes and 2 is reactively coupled to its 5 control grids 3 and 4 of the tubes in parallel with asSociated oscillator grid by the oscillator circuit the tunable signal input circuit 5. The latter in f8, and capacities 23 and 24, or 25 and 26. Fur cludes a variable tuning condenser 6 connected thermore, it will be seen that the oscillator elec between ground and the high alternating voltage trodes of tubes f and 2 are arranged in push-pull O side of circuit 5. The cathodes of tubes , 2 are relation, while the signal input circuits are ar O connected together, and grounded through a re ranged in parallel relation. In other words, the Sistor T shunted by a radio frequency by-pass phase relation between oscillator voltage and sig condenser 8. Part of the biasing voltage for the nal voltage is reversed in one of the converter signal control grids 3 and 4 is obtained from the tubes as compared to the other. The two tubes 5 drop in this resistor, and additional biasing volt if and 2 are substantially alike in characteristics, 5 age -E1 may be supplied as indicated. This and this arrangement results in a practical elimi additional bias may be derived from an automatic nation of capacity and/or space charge coupling Volume control circuit. The intermediate fre aSfar as their effects on the circuits are concerned. quency Output of the two tubes is derived from a The tubes and 2 are of the pentagrid converter 20 circuit 9 maintained fixedly tuned to the oper type of tube. Such tubes are well known to those 20 atting intermediate frequency by a condenser f0. skilled in the art, and need not be described in The plate f l of tube f and the plate 2 of tube 2 any detail. They are known as 6A7 type tubes, may be connected respectively to the two sides of and the electron coupling phenomenon occurring circuit 9. The following input circuit 9', also Within the Space current path of each tube has 25 tuned to the intermediate frequency, is coupled been disclosed by J. C. Smith in application serial 2 5 to circuit 9. No. 654,421, filed January 31, 1933. In using The center tap on the primary coil of the cou pentagrid converters, such as the 6A7 type tube, pling transformer M1 is grounded through a path in multi-ranged receivers considerable difficulty including lead .8' and condenser 3. The lead 3' has been experienced due to coupling between the 30 is further connected to a point of positive voltage OScillator and radio frequency circuits. As stated : E3, and thus the plates , 2 are maintained at a before, most of the spurious coupling of this desired positive voltage. The signal grid of each nature appears to be due to capacity and/or tube is disposed between a pair of positive screen Space charge couplings. The circuit arrangement grids thereby providing a positive shielding field shown in Fig. effectively eliminates the effects 35 around each signal grid. The screen grids of the Of Such spurious couplings, and, therefore, ren 3 5 tubes are connected to a point of positive voltage ders the Superheterodyne type of receiver employ E2 through a lead f4, and a radio frequency by ing converter circuits more efficient in operation. pass condenser 5 is connected between ground Each of the tubes in the circuit of Figure 1 and the lead -4. The value of E2 will, in general, Operates in a conventional manner. Thus in the 40 be less than the value of E3.
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