| 摘要 |
581,683. Valve amplifying circuits. STANDARD TELEPHONES & CABLES Ltd., and LEV Y, M. M. June 6, 1941, No. 7176. [Classes 40 (iii) and 40 (v)] A selective thermionic amplifier for periodically repeated pulses is arranged to amplify only those frequencies necessary for defining the form of the impulses so as to improve the signal noise ratio. The frequencies to be amplified may be harmonically related and a delay network may be used to produce the required selectivity. The amplifier may have two negative feedback paths one giving a feedback constant with frequency while the other is of constant amplitude but varying continuously in phase and may comprise a delay network, Fig. 4 (not shown). Fig. 5 shows a single negative feedback path through a Wheatstone bridge one arm of which includes a delay network D, as shown, in series or in parallel, Fig. 5A (not shown) with one of the impedances Z1 ... Z4. Fig. shows a three stage amplifier in which cathode resistance RC provides a constant feedback while a variable feedback is taken through delay network or artificial line L. In this way the line may have relatively large attenuation since by adjustment of potentiometer P the relative valves of the feedbacks may be so adjusted that the amplifier gain compensates for the attenuation in the delay network. Vector diagrams, Figs. 6, 7, 8 and 11 (not shown) are given to demonstrate the offect of the feedback circuits. The desired response may theoretically be obtained by the use of a delay network by utilising the reflection produced by an open or short-circuited output. The reduction in selectivity produced by the attenuation of the network may be eliminated by combining part of the input energy with energy passed through the delay network terminated by an impedance Z equal to the image impedance, Fig. 12. Instead of providing transformers T1, T2, the energy may be combined by arranging the output of the network in series with part, of the. input in the grid circuit of an amplifier, Fig. 13 (not shown) or energy from the two paths may be fed to separate valves with a common anode load, Fig. 14 (not shown). The network may consist of a number of sections having series elements of resistance and inductance with mutual inductance between adjacent sections and shunt resistance and capacity, Fig. 10 (not shown).
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