US2556883A - Reactance tube circuit - Google Patents

Description

June 12, 1951 R. E. MOE 2,556,883

REACTANCE-TUBE CIRCUIT Filed Feb. 25, 1 948 Inventor: Robert E. Moe,

byW-ZDM H is Atto'rhey.

Patented June 12, 1951 York 2,556,883 UNITED STATES PATENT OFFICE REACTANCE TUBE CIRCUIT Robert E. Moe, Syracuse, N. i'r assigncr'to General Electric Company, a corporation of New Application February 25, 1948, Serial No. 10,773 s Claims. (01. 250-36) sible to reverse the positions or R and C and change their values and thus achieve a 90 'degree phase shift in the opposite direction, but the residual component is still degenerative. An inductance may be inserted'in this circuit to give the desired 90 degree phase shift, but this combination is frequency-sensitive and is not applicable over a wide band of frequencies.

It is an object of my invention to provide a reactance tube circuit that has 'a negative-resistance residual component.

Another object of my invention is to provide a reactance tube circuit that aids the oscillator rather than loading it.

Afu'rther object of my invention is toprovide a reactance tube circuit that'is efiective throughout a wide range o'f frequenci'es.

The features of my invention which I believeto be novel are set forth with .particularity in the appended claims. My invention itself, however, together with further objects and advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawing in which Fig. 1 is a schematic diagram of a typical reactance tube circuit; and Fig. 2 is a schematic diagram of a reactance tube circuit embodying my invention.

Referring now to Fig. 1, I have shown a reactance tube circuit using a pentode discharge device I having an anode 2, a cathode :3, a grid 4, a grid and a grid 6. The cathode 3 is connected to ground and the grid 6 is connected to the cathode 3. The anode voltage is supplied from a suitable B+ supply represented conventionally by bus I8, through a radio frequency choke I-I A unidirectional control voltage for grid 4 is supplied from a suitable control source (not shown) through a resistor 9. The grid 5 is supplied from the 13+ supply by a resistor l2 "and is 'by-passed to ground through a capacitor [3.

The output of an oscillator: 15, having a tuned circuit comprising a capacitor 4 6 and inductance I1, is connected, through a coupling capacitor 14 and blocking capacitor l0, across the phase shifting network'comprising the resistance] and the capacitor 8. The common terminal of the capacitors'and the resistor 1 is connected to the grid '4. The oscillator [5 may be any suitable self-excited oscillator of which various types are i choke 28. Control grid 26 is connected to ground.

well known to those skilled in the "art. "If'the re- -sistance 1 is, for example, ten times the impedance of the capacitance 8, the phase shift of of the resultant voltage on the grid 4 of the reactance tube l is 84.3 degrees (lagging) from the voltage across the tuned circuit. This causes a similar current to flow in the anode circuit which is also across the tuned circuit. Thus,

where I1) is the anode current, gm is mutual conductance, X0 is the capacitive reactance, and E1; is the anode voltage. The effective impedance Z is then Now the 45,000 ohm term represents an equivalent inductive reactance across the circuit, in "series with a 500-ohm pure resistance. This is a result of the incomplete phase shift of the RC circuit. This effect can be reduced by making R in which case the phase shift will be 89.4 degrees and Z=500+i50,000 ohms (4) In the latter case, however, the reactance effect "is reduced and will be equivalent to the impedance of 3 micromicrofarads at 1,000 kilocycles. The "effect of the additional resistance is to 'load the tuned circuit of the oscillator, in addition to the shunt effect of the phase shift network RC, so that the amplitude of the oscillator varies markedly with the value of the unidirectional control voltage applied to the grid l of the reactance tube I through the resistor 9 which is high in comparison to the resistor 1. Actually, in most instances with this arrangement, it is not possible to obtain the desired amount of frequency shift before the oscillator stops oscillating completely. 7

Referring now to Fig. 2, I have shown a reactance tube circuit embodying the invention which comprises a discharge device 20 which, for illustration, I have shown as a double triode such as a commercial type 6J6. One section 20a has a cathode'ZZ, control grid 23 and anode 24 and the other section 201) has a cathode'25, control grid 3'6and anode 21. The oscillator I5 is represented asfthe same type as in Fig. 1. The upper end of inductance H is connected to the anode 21 through a coupling capacitor 2 I.

Anod'e potential is supplied-from the B+ supply bus 18 to anode 21 through'aradio frequency The cathodes 22 and 25 are tied together and are connected to ground through a radio frequency choke 29. The anode 24 is connected directly to the 13+ supply. The phase shift network, comprising resistance 1 and capacitance 8, is the same as in Fig. 1. The control grid 23 is also again connected to a suitable source of unidirectional control voltage through resistor 9.

Essentially, the reactance circuit of Fig. 2 comprises a cathode-follower section 20a, driving a grounded-grid amplifier section 201), such that an increase in voltage on grid 23 produces a decrease in plate current at plate 21.

Is can be seen from the above description of Fig. 2 that the anode current through the anode 21 is 180 degrees out of phase with the voltage at the grid 23. Assuming the effective plate load m to be 50,000 ohms and the reactance device 20 to be a type 6J6 with a a of 35 and a plate resistance r of 7,000 ohms for each section, then- Thus, it may be seen that this circuit introduces a negative resistance in series with an equivalent capacitance across the tuned circuit of the oscillator, which compensates for the losses in the resistor 1 that shunts the tuned circuit. In other words, it aids the oscillator rather than loading it down. I The control voltage on the grid 23 can, therefore, be varied over a much wider range without any appreciable change in the amplitude of oscillations.

It should be understood by those skilled in the art that the invention is not limited to a doubletriode circuit, which is shown merely for purposes of illustration. A pentode might be used for the section 201) which would increase the control effect because of the higher gain that could be realized due to its higher plate resistance.

While a specific embodiment of my invention has been shown and described and certain modifications suggested, it will, of course, be understood that various other modifications may be made without departing from the invention. The appended claims are, therefore, intended to cover any such modifications within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A reactance circuit comprising first and second electron discharge devices each including an anode, a cathode and a control electrode, said devices having their cathodes connected to a common reference point through a common cathode load impedance so that a voltage applied to the control electrode of said first device produces an anode current change in said second device 180 electrical degrees out of phase therewith, means for impressing an alternating voltage between the anode of said second device and said point, and means comprising a phase shift network interconnecting the anode of said second device with the control electrode of said first device for feeding said voltage between the control electrode of said first device and said point, said network producing a voltage phase shift of less than 90 electrical degrees in the voltage impressed on the grid of said first device,

thereby to cause the effective impedance at the anode of said second device to consist of a reactive component and a negative resistance component.

2. A variable reactance circuit comprising first and second electron discharge devices each including an anode, a cathode and a control grid, said devices being coupled together through a common cathode impedance, said second device also having a separate load impedance connected to its anode, whereby a voltage variation at the grid of said first device produces an in-phase voltage variation at the anode of said second device, means for impressing an alternating voltage on said anode of said second device, means comprising an alternating-current phase-shiftin network connected across said second device and said cathode impedance in series, said network having an intermediate point thereon at which a corresponding alternating voltage appears with a phase shift of less than electrical degrees, with respect to said first voltage, a connection from said intermediate point to the grid of said first device, thereby to produce a correspondingly phase-shifted voltage across said cathode impedance and to cause the effective impedance across the anode of said second device and said cathode impedance in series to consist of a reactive component and a negative resistance component, and means to vary said second impedance comprising a source of control voltage connected to the grid of said first device.

3, A variable reactance circuit for controlling the frequency of a, high frequency oscillatory system, comprising first and second electron discharge devices each having a cathode, an anode, and a control grid, said devices being coupled together through a common cathode impedance connected from their cathodes to a reference point, means connecting said anodes to said point through sources of anode operating potential, said second device also having a separate anode load impedance and having its grid connected directly to said point, means for impressing high frequency voltages from said oscillatory system between the anode of said second device and said point, means for impressin low frequency and unidirectional control potentials between the grid of said first device and said point, a phase shifting network connected from the anode of said second device to said point comprising a resistive and a reactive element in series, and a connection from the grid of said first device to a point on said network located between said resistive and reactive elements and at which high frequency voltage appears with a phase shift of somewhat less than 90 electrical degrees, whereby the effective impedance connected across the system has a negative resistance component as well as a reactive component.

ROBERT E. MOE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,140,339 Travis Dec. 31, 1938 2,181,909 Peterson Dec. 5, 1939 2,248,132 Smith July 8, 1941 2,253,470 Rath Oct. 7, 1941 2,441,504 OBrien May 11, 1948 2,469,194 Delvaux May 3, 1949

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