GB622002A - Improvements in or relating to thermionic valve circuit arrangements - Google Patents

Abstract

622,002. Pulse and frequency modulation; valve circuits. WHITE, E. L. C., and ELBOURN, R. W. April 24, 1946, Nos. 6853/47 (divided out of 621,958) and 18366/46. [Classes 40 (v) and 40 (vi)] [Also in Groups XXXIX and XL (b)] In a circuit, Fig. 2, employing valves 1, 2 arranged with a common cathode impedance, modulation is effected by a valve 3 connected with its anode-cathode path in series with the grid-cathode path of the valve pair. The circuit is also described with respect to frequency and pulse modulation and for modifying a sawtooth waveform. With carrier frequency applied in push-pull to the grids of valves 1, 2 and low frequency to valve 3, an amplitudemodulated output appears across the anode load resistors 4, 5. The low frequency component, due to resistor 5 acting as a load to valve 3, is balanced out by employing a valve 6, coupled by cathode resistor 30 to valve 3 and fed with low frequency in phase opposition to valve 3 to supply an anode current in opposition to that generated by valve 3. Since only half the anode current variation of valve 3 passes through resistor 5, the anode of valve 6 is connected through limiting resistor 27 to a tapping mid-way along resistor 5. Cathode resistors 13, 14 are provided to linearize the current waveform of valves 3, 6 and hence the linearity of modulation. In a modification, Fig. 3 (not shown), a push-pull output is obtained by connecting a second resistor to the anode of valve 6 and to a tapping on resistor 4. A fadeover circuit, Fig. 8 (not shown), is also described (see Groups XL (b) and XXXIX). Amplitude-modulated oscillator, Fig. 5. An oscillator of the type described in Specification 540,941 employing a tuned circuit 31, 32 coupled to the grid of valve 2 is amplitude-modulated by a signal applied to valve 3. By employing a modulating signal of sawtooth waveform the resulting modulated signal may be fed through a phase-shifting device to give a spiral scan on a cathode-ray tube. The balancing valve 6 may be omitted if the output is taken from valve 1 or a tuned circuit or filter inserted in the anode lead of valve 2. Sawtooth deflection amplifier, Fig. 4. A sawtooth waveform applied to valves 15, 16 and 17, 18 appears in push-pull at the respective anodes. The waveform integrated by resistor 23 and capacitor 24 is fed to valve 20, a positive going sawtooth causing a fall in the mean potential of the anodes of valves 17, 18. The integrated waveform may be obtained from the anode of valve 16, and the amplifier may feed a cathode-ray tube of the type described in Specification 621,958. Pulse and frequency modulation. The multivibrator, Fig. 6, consisting of cross-coupled valves 1, 2 is arranged with a modulating valve 3 in the cathode lead, the conductivity of the valve determining the extent to which the grids of valves 1, 2 are driven negative and hence the time taken for the grid to receive a sufficient positive potential for the valve to conduct again. The output pulses are thus modulated in frequency and may be applied to a tuned circuit to produce frequency-modulation. Width-modulated pulses may be obtained by biassing one valve to a normally non-conducting condition, Fig. 7 (not shown), the restoration time, after triggering by a pulse such as a television synchronizing pulse, depending on the conductivity of the modulating valve. Specification 564,821 is referred to.