GB325833A - Improvements relating to electron discharge amplifying apparatus - Google Patents

Abstract

325,833. Carpenter, R. E. H. Nov. 28, 1928. Thermionic amplifiers. - Use is made of the phase opposition in voltage between the input and output circuits of a thermionic valve to secure " push-pull " amplification, the output voltages being symmetric about a neutral point which is a symmetric with respect to the input. As shown in Fig. 2, the voltage at the point 11, derived from the anode of valve A, is in opposite phase to that at the point 12 which is taken from the the anode of valve B. The point 13 is at the potential of the input terminal 2. To maintain the two outputs at equal amplitude, the grid voltage of the valve B is taken from an intermediate point 10 on the anode resistance 3 so as to compensate for the amplification factor of the valve A. For fined adjustment the grid input of valve B may be taken from a tapping 8a, on the leak resistance. To minimize " hum when the valves are energized from the mains, a symmetrical cross-connection from a tapping 37, Fig. 5, on the anode resistance 9 may be taken to the grid of the valve A. In a modified arrangement, Fig. 6, the necessary fractional grid voltage is fed to the valve B from a tapping 41 on a high resistance 40 shunted across the anodes of valves A, B. A symmetrical cross-connection (not shown) may also be taken from the opposite side of the centre point m to the grid of the valve A to eliminate " hum." In order to ensure a uniform overall amplification, a circuit comprising a resistance 43, Fig. 7, in series with a tuned loop circuit 44, 45 may be inserted across the anodes of an intermediate pair of valves G, H. This circuit is tuned so as to shunt the lower frequencies more readily than those higher frequencies normally attenuated by capacity leakage. The final output currents may feed separate loud-speakers, or may flow through branch circuits comprising different impedances. Specification 314,605 is referred to.