US2146818A - Circuit arrangement for the control of glow tubes - Google Patents

Description

Feb. 14, 1939.

W. HAHNLE CIROUIT'ARRANGEMENT FOR THE CONTROL OF GLOW TUBES Original Filed May 28, 1930 IIIIIIIIIIIJVI Gill? 5* Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE CIRCUIT ARBANGEDIENT FOR THE CONTROL OF GLOW TUBES tion of Germany Application May 28, 1930, Serial No. 456,314. Be-

newed December 18, 1936. In Germany June 1,

11 Claims. (Cl. 176124) In arrangements for the electric control of the brightness of glow tubes, for instance in so-called writing tubes for the purposes of picture telegraphy, the unsteadiness of the current potential characteristic of the glow tubes makes itself felt in disturbing manner in that the changes in intensity of the glow light do not faithfully follow 31:1 changes in the amplitude of the signal poten- According to the present invention, this fault is overcome by compensating the resistance of the glow tube through the use of amplifier tubes by means of feed-back, and insuring the stability of the circuit arrangement by means of suitable negative feed-back energy.

Due to the feed-back or back-coupling the plate A. C. of the amplifier tube feeding the glow tube is rendered independent of the resistance of the glow tube loading circuit so that the glow tube current follows the control potential linearly. The decrease in the stability of the circuit arrangement, caused by the bMk-coupling, is eliminated by negative feed-back or a counter-coupling. It will thus be appreciated that the potential returned to act on the grid of the amplifier will be equal to the difference between the feedback voltage and the negative feedback voltage. Any change in the resistance characteristics of he glow lamp will cause a change in the difference of. the two potentials fed back to the grid and by suitably porportioning these two energies, the compensating voltage returned to the grid will be just equal to that necessary to counteract the change in the glow lamp resistance. The invention is illustrated in the circuit diagrams, Figs. 1 and 2 showing two embodiments by way of example.

In Fig. '1 a receiving tube l which receives energy from the input circuit 1, and a power tube 2 are coupled by resistance 3. In the plate circuit of power tube 2 are connected a winding part 4, used as auto-transformer, of a transformer and a small resistance 5 to which is connected in parallel a transformer 6. The transformer 6 is provided with the high-ohmic loading resistance The transformer circuit contains two rectifiers 8, 8' which jointly feed the glow lamp 9 with rectified current. From transformer winding 4 branches off a line Ill on whose regulatable resistance ll may be taken oil the back-coupling. potential and impressed on'the grid of tube I. In the circuit of the back-coupling line is also disposed the counter-coupling arrangement in the shape of transformer 6 which likewise impresses on the grid of the first tube a partial amount of the plate circuit potential, of opposite phase to that returned by the connection to the potentiometer ll, of the power tube.

If in the course of the operation of the arrangement the characteristic of the glow tube moves 5 due to heating, that is, if its striking potential and its resistance value varies, the control potential is automatically changed by the back-coupling and the counter-coupling in such manner that the current is not influenced. This results from 10 the fact that the direct feed-back potential is proportional to the voltage appearing. at the output of the tube 2, while the negative feed-back potential is proportional to the current flowing through the glow lamp 9. The difference between these 15 two potentials which determines the amount of compensation, is accordingly, influenced by the resistance of the tube. For example, if the resistance of the tube increases, assuming that the output voltage of the tube 2 is held constant, then 20 the potential of the negative feed-back is less than it was formerly, since less current will flow through the lamp. Accordingly, therefore, the direct feed-backpotential predominates, causing an increased voltage to appear at the output of 25 the tube 2, which, in effect, overcomes the increase in resistance of the tube 9. If the resistance of the tube 9 decreases, then more current will flow through the lamp and accordingly, a greater negative feed-back potential is provided 30 which reduces the actual potential actuating the grid of tube I, and accordingly, the output of the tube 2 is reduced to compensate for the decrease in resistance.

Fig. 2 shows a similar circuit arrangement, ex- 35 cept that in this case howeveronly the alternating potential is fed to the rectifier circuit by means of a choke coil l2 and a condenser l3. In this arrangement the operation is enhanced by compensating the potential drop produced in the 40' pling transformer I4, whose primary winding is connected in parallel with the ohmic resistance and whose secondary is disposed in the backcoupling line.

Having now described my invention, what I claim and desire to secure by Letters Patent is the following 1. The method of controlling impedance loads varying with changes in amplitude of the current passed therethrough from an audion ainplifier which comprises supplying energy to the load from the audion output and feeding back to the audion input a voltage determinable by the changes in impedance of the load due to variations in amplitude of the output current, whereby the output current from the audion is determined from the signal potential input and is independent of the load impedance.

2. In a system for supplying current to variable impedance devices, a plurality of resistance coupled amplifiers and an input circuit therefor, a

variable impedance element in the output of the second of said amplifiers, and means associated with the output circuit of the second amplifier for feeding back to the amplifier input circuit a voltage developed in proportion to the changes in impedance of the load due to variations in amplitude of the output current whereby the eflective output from said amplifiers is determined solely in accordance with the applied signal potentials.

3. The method ofcontrolling glow tubes from,

an audion amplifier which comprises supplying therethrough, the step in the method of maintaining the output current independent of valueof the load impedance which comprises feeding back to the input of the tube a voltage of suflicient magnitude and suitable phase to neutralize the efiect of changes with amplitude in the load impedance upon the normal plate current flow.

5. A method'of compensating for changes in impedance of a load circuit energized from an audion amplifier, which comprises supplying energy to the load circuit from the audion amplifier output, feeding back to the input of the audion amplifier a portion of the output voltage thereirom, simultaneously feeding back to the audion input a counter-phase voltage variable with changes in'impedance of the load due to variations in amplitudeof the output currentirom the audion amplifier, and controlling the gain of the audion amplifier in accordance with the difference of the two out-of-phase energies fed back to the input of the audion amplifier.

q. A system for controlling the gain 4 in an amplifier for variations in impedance of the load therein due to changes in the amplitude of the current passing through the amplifier which comprises a thermionic amplifier, having aninput and an output circuit, means connecting a variable impedance to the output circuit of said amplifier, means for deriving a proportionate voltage from the output of said amplifier, means for deriving a voltagein accordance with the current flowing through said variable impedance, means for adding both of said derived voltages out of phase with each other, and means to impress the difference between said derived voltages upon the input of said amplifier.

7. In combination, a light producing device whose impedance is a function of the amplitude of current passing therethrough, an amplifier feeding the light producing device, and feedback means connected between the light producing device and the amplifier to maintain the amplitude of the current independent of the impedance of the light producing device.

8. In combination, a current responsive light producing device whose impedance is a function of the amplitude of the current passing therethrough, a source of energy for energizing the light device and feedback means for controlling the source of energy connected between the light device and source of energy to maintain the amplitude of the'current independent of the impedance of the light producing device.

9. In combination, a linear amplifier, a nonlinear current-impedance operated light producing device, feedback means connecting the amplifier to the light producing device, and means for altering the linearity oi the amplifier to compensate for the non-linearity of the light device.

10. In combination, a linear amplifier having input and output circuits, a non-linear currentimpedance operated light producing device connected in the output circuit, and means from the amplifier output circuit to the input circuit for feeding back energy to the input circuit for altering the linearity of the amplifier to compensate for the non-linearity of the light device.

11. In combination, an alternating current amplifier having a plurality of thermionic tubes, 9. variable light emitting device, a rectifier fed by energy from the amplifier and feeding energy to the variable light emitting device, a voltage feedback circuit connected between the rectifier and one of the thermionic tubes of the amplifier to control the energy fed by the amplifier to the rectifier in accordance with the energy fed from the rectifier to the variable light emitting device.

WAL'I'ER

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