US2406565A - Electronic amplifier and modifier - Google Patents

Description

Aug.27, 1946. R; ROWE 42,406,565

ELEC'IRON IC AMPLIFIER AND MODIFIER Filed Oct. 15, 1943' By w I I IAVTIIORN'EK' i Patented Aug. 27, 1946 UNITED STATE PATENT OFFICE My invention relates, generally, to an electronic amplifier and modifier for controlling and modifying the effective grid voltage-anode current characteristics in electron tube circuits and, more specifically, to an improved circuit for sensitive control devices. l

The designof amplifying, modulating, signalling, counting, cycling and like apparatus which depends for its function on variations in electronic tube anode-cathode voltage and current i well known in the electronic art.

In vacuum tube amplification; variations in anode current through a serially connected resistor develop a varying potential for application to the grid of th ensuing tube. In modulation, variations in the radio frequency amplifier plate voltage produce similar variations in the carrier power output. In photoelectric, inductive, capacitive and like apparatus, variations in associated vacuum tube anode currents operate serially coupled resistors, relays and other current responsi've devices. 1

In all of these and many other systems it is the variation in current or the variation in voltage, the maximum to minimum ratio, which in a large part determines the effectiveness of the control. In conventional amplifiers the variation in voltage or the voltage swing on the grid of the tube is a determining factor in the output volt age of the stage. In conventional modulators the variation in anode-cathode radio frequency amplifier voltage largely determines the percentage modulation. In photoelectric, inductive and capacitive apparatus the amount of variation in anode current largely determines the reliability, ruggednes and efficiency ofthe entire device.

I have found, however, that for many applications the variation in voltage or current, the maximum to minimum ratio, is insufficient to properly actuate the coupled device. Particularly in photoelectric, inductive and capacitive equipment fragile, expensive, sensitive relays must be used to respond to the small current changes produced. Further, these ensitive'relays usually are not designed to handl high secondary voltages and currents. Often, they are used in the control circuits of larger relays with high secondary power handling capabilities adding to the expense and complexity of the apparatus'.. Still further, sensitive relays are more susceptible to damage and faulty operation due to low contact pressure and other effects.

It is, accordingly, anobject of myinventionto;

amplify these variations in current and voltage to increase the maximum to minimum ratio.

8 Claims. (Cl. 25027) Still another object of my invention is to further control or modify these variations, the ratio, rate and slope of maximum to minimum, to effect new and'useful circuit characteristics.

The aforementioned objects and other objects ancillary thereto I prefer to accomplish, in short, by inserting serially in the master circuit a controllable resistance devic with at least an anOde', control grid and cathode together with a means for biasing the control grid of the resistive element which is responsive to current or voltage variation in the master circuit.

' Other and further objects of my invention reside in the method and apparatus employed therein as set forth more fully in the specification hereinafter following by reference to theaccompanying drawing, in which The single figure schematically illustrates a capacity sensitive circuit arrangement embodying one of the principles of my invention.

With reference to the drawing, in which oathode heaters are eliminated for convenience in drawing, master tube l is employed in a modified Hartley oscillator circuit, with variable condenser. 2 and inductance 3 comprising the resonant tank' circuit. Plate blocking condenser 4 offers a low impedance to radio frequency current, but effectively isolate the direct current component on plate 5 of vacuum tube I from the grounded tank coil assembly. Radio frequency choke 6 offers a low resistance to the flow of direct current but a high impedance to the alternating current component appearing on plate 5 of vacuum tube l. By-pass condenser l effectively shunts to ground stray radio frequency currents which are not'im-' peded by choke fi. Grid condenser 8 offer a low impedance to regenerative radio frequency current inductively obtained from tank coil 3 to provide excitation for grid 9 of tube I, but effectively isolates grid 9 from ground. I have found that shunting grid condenser 8 by a resistor as usually employed in the Hartley circuit partially impairs sensitivity of this particular-arrangement and that, especially when condenser 8 exhibits appreciable leakage conductance, additional resistance may bev omitted. The resistance from grid 9 to the cathode of tube I is somewhat critical in securing optimum circuit sensitivity and the a shown in the drawing to leads A and B, is in effect a variable resistance device across leads A and B, the resistance of which varies in accordance with th condition of resonance or anti- 3a lower than maximum value. voltage on grid26 of tube 24 decreases as determined by the IR drop acros resistor 25. Because Zof the lower negative bias on grid 26 of tube 24, anode 23 begins to draw more current through resistor 22 and more negative bias appears on grid 20 of tube I8. With increasing negative grid resonance in the link-coupled external tank circuit described below.

Pickup coils II) and I! provide link coupling to the capacity-sensitive external tank circuit com prising coil I2, condenser I3, antenna I4 and ground.

Normally closed relay I5 controls the signal-. ling, counting, cycling or like circuit to be operated by capacity variations in the external tank circuit. When the generator circuit comprising tube I and its associated components is oscillating, by proper selection of components the external tank circuit comprising coil I2, condenser' The resistance of tube I8 progressively increases I3, antenna I4 and ground can be tuned to resonance with the oscillator. Components can be so adjusted that when the external tank circuit istuned to resonance with. the'oscillator, tube I will draw maximum anode current, and when this condition of resonance is disturbed by addedcapacity between antenna I4 and ground tube I will draw less than maximum anode current.

Thus,'in a condition of resonance, current responsive relay I5 will hold open contacts I6 and I1 which control the external signalling,,counting, cycling or like circuit. Whenresonance is disturbed by a capacitance variation in the link coupled external tank circuit, the armature of current responsive relay I5fwill drop out and close contacts I6 and I1. known in the electronic art.

'However, I have found that the anode current 1 change through current responsive relay I5 from g a condition of resonance to ofi-I'esormnce as oc-. casioned by the capacity changes :which I'en-. counter is insufiicient to properly operate, the

relay which I desire to employ.

One phase of my invention resides in the hereinafter' described improvements; wherein a resistive device, vacuum tube I 8, comprising at least an anode I9, control grid andcathode ZI is inserted serially in the mastercircuit, that is to say, in series, with battery C, relay I5, resistor and. oscillator supply leads A and B; and

This circuit is well wherein. bias potential on control grid 20 is supplied by theIR drop through resistor 22 as deup termined-by the anode current of anode 23 of I vacuum tube 24; and wherein the anode current of vacuum tube. 24 is responsive to current changes 3 in ,the master circuit through resistor 25, grid j 26 and cathode 21.

V In a condition of resonance between the oscil-, j

22 and minimum bias appears on the grid 20 of tube I8 islow, a maximum voltage appears on In a condition of oiT-resonance between the oscillator and the link. coupled external circuit as occasioned bythe capacitive changes which I encounter, the anode current of tube drops to Thus, the bias lator and the link coupled external circuit the I I anode current of tube I is maximum. Thus, the bia voltage on grid 26 of tube 24 is maximum" 1 as determined by the IR drop acrossresistor 25 Because of high negative bias on grid 26 of tube 24, anode 23' draws little current through resistor tube I8. ;With low grid bias, the resistance of at each end. When weak signals and lowgrid spacing. As the. grid bias is made more negative I r to handle larger input signals, the electron flow 1 'of the grid voltage-anode current curve, the

plification factor or mu of the tube remains sub- 'and current flowing in the master circuit through the field coil of relay I5 progressively decreases to an equalization point.

controlrelay. I am able to employ less expensive, more reliable current responsive relays, .se-

cure greater sensitivity of the capacitive element and insure sh'arperand more reliable relay action. Obviously, relay I5 may be inserted serially between the cathode oi? tube I and resistor 25, above or below-the junction of cathode Z'I; or between radio frequency choke t and cathode 2I of tube I8, to further increase sensitivity by eliminating the reactive plate current component of tube 24.

Otherwise, my invention has broad application in the radio and electronic art. In the case of conventional electronic tube amplifiers, the IR voltage drop developed across a resistor inserted serially in the anode-cathode circuit is impressed on the grid of the ensuing tube. When these tubes are operated on the straight-line portion stantially constant and the maximum to minimum voltage or current ratio throughout the system remains substantially uniform- Although the peak values of current or voltage are elevated, the minimum values are similarly elevated, in a manner such that the ratio between the two remains constant. By inserting my'controlled resistive element serially in one or more of the amplifier stages, I have found that I can either increase or decrease the ratio between the maximum and minimum values of current or voltage by slight circuit modifications. Thus, it

becomes feasible to augment the amplification V factor of an amplifying stage, or modify it in a desirable manner. It is to be understood that I do not pretend to modify the inherent characteristics of a given vacuum tube, but only the effective characteristics of th circuit entity.

To reduce cross-modulation and modulationdistortion in radio receivers and to obtainother known effects, manufacturers are supplying so-' called super-control or remote cut-off amplifier tubes of a modified grid structure designed to handle both large and small grid input signals with a minimum of distortion over a wide range. As noted on page 15 of the R. C. A. Receiving Tube Manual, Technical series, PUG-14, the grid of the super-control amplifier is wound with coarse spacing in the center and close spacing bias are applied to the tube, the effect 'of the nonuniform turn spacing of the grid on tube characteristics in essentially the same as for uniform from the sections of the cathode enclosed bythe "ends of the grid is out on. The tube characterv istics are then"? dependent on the: electron flow through the coarsetsection' of the grid. As noted furthenwh'ile the curves manifest by'the super; control grid and the uniformly 'spacedgrid are similar at small grid bias and high plate current ratings, the plate current of the super-control amplifier drops mor -slowly with large valueslof bias voltage. i I i I have found that-'I am able to secure this aforementioned super-control, remote cut-off and variable mu function using a tube with a uniformly spaced grid structure if I employ the principles of my invention and insert a variable resistance element serially in th master circuit and control its resistance from current flow in the master circuit.

To amplitude modulate a radio frequency am.- plifier, the amplifier voltage is increased and reduced by the conventional modulators at modulation frequencies. ing serially, in place of the secondary of a modulation transformer for example, the variable resistance element herein disclosed I am able to accomplish the same effect when I control the resistance of the resistive device at modulation frequencies. Further, by the incorporation of a current responsive control means such as I have illustrated in Figure 1, as tube 24 and its associated components, and by designing this means to keep the proper average plate voltage on the radio frequency amplifier, I can increase the sensitivity of this modulation means to the point Where it is practical.

While I have described my invention in only several of its preferred embodiments I am aware that various alterations and modifications of the present invention may become apparent and immediately suggest themselves to those versed in the art to which. this invention is directed. Thus, any and all such alterations and modifications are to be considered within the purview of the present invention except as limited by the hereinafter appended claims.

What I claim is:

l. A circuit arrangement for amplifying the current change in a series circuit, comprising in series a source of at least substantially constant voltage, a variable resistance control device, a current responsive device constituting a load, and the anode and cathode of an electron tube, further provided with at least one control grid electrode; resistance means connecting the grid and cathode of the last named electron tube, means to supply a potential difference between the last named electrodes, said means consisting of a second electron tube with at least an anode, cathode and control grid electrode, and means for connecting the anode of the second named tube to the grid of the first named tube and the grid and cathode of the second named tube across a resistance placed in the series circuit, whereby the maximum to minimum current ratio in the series circuit .is increased.

2. A circuit arrangement for amplifying the current change in a series circuit, comprising in series a source of at least substantially constant voltage, an electron tube oscillator constituting with its output circuit a variable resistance control device, a current responsive device constituting a load, and the anode and cathode of an electron tube, further provided with at least one control grid electrode; resistance means connec ing the grid and cathode of the last named electron tube, means to supply a potential difference between the last named electrodes, said means I have found that by insertl 6 consisting-eta second electron tubeiwith at least an anode, cath'odeand controlgrid electrode,

andmeans' for'connecting the anode of the sec-' 7 on'd named tube 'to the grid of the first named tube and the grid and cathode of the second named tube across a resistance placedin the series circuit; whereby the maximum to minimum current ratio in the series circuit is increased.

3. A circuit arrangement for amplifying the currentchange in a seriescircuit, comprising in series'a sourceof at least substantially constant voltage, a variable resistance control device, a relay device constituting a load, and the anode and cathode of an electron tube, further provided with at least one control grid electrode; resistance means connecting the grid and cathode of the last named electron tube, means to supply a potential difference between the last named electrodes, said means consisting of a, sec-- ond electron tube with at least an anode, cathode and control grid electrode, and means for connecting the anode of the second named tube to the grid of the first named tube and the grid and cathode of the second named tube across a resistance placed in the series circuit, whereby the maximum to minimum current ratio in the series circuit is increased.

4. A circuit arrangement for amplifying the current change in a series circuit, comprising in series a source of at least substantially constant voltage, an electron tube oscillator constituting with its output circuit a variable resistance control device, a current responsive device constituting a load, and the anode and cathode of an electron tube, further provided with at least one control grid electrode; resistance means connect ng the grid and cathode of the last named electron tube, means to supply a potential difference between the last named electrodes. said means con-,

sisting of a second electron tube with at least an anode, cathode and control grid electrode and means for connecting the anode of the second named tube to the grid of the first named tube and the grid and cathode of the second named tube across said load.

5. A circuit arrangement for amplifying the current changein a series circuit, comprising in series a source of at least substantially constant voltage, an electron tube oscillator constituting with its output circuit a variable resistance control device, a relay device constituting a load, and the anode and cathode of .an electron tube,

further provided with'at least one control grid electrode; resistance means connecting the grid and cathode of the last named electron tube, means to supply a potential differencebetween the last named electrodes, said means consisting of a second electron tube with at least an anode, cathode and control grid electrode and means for connecting the anode .of the second named tube to the grid of the first named tube and the series a source of at least substantially constant voltage, a relay device, 'a negative impedance, and. a variable impedance control device; said last named impedance including the anode cathode circuit of an electron tube oscillator provided with a loadcircuit adaptable to resonance or anti-resonance with said oscillator, whereby the anode circuit impedance of said oscillator is con" trolled by the tuning of said load-circuit.

ROBERT G. ROWE.

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