GB233737A - Improvements in and relating to electrical valve amplifiers - Google Patents

Abstract

233,737. Priess, W. H. Nov. 14, 1923. Thermionic amplifiers.-Relates to multi-valve amplifiers for the amplification of currents of radio or audio frequency in which the inter-valve couplings comprise transformers or choke coils, and consists in employing at the several stages couplings resonant ' to different frequencies, and combining therewith potentiometer control of the grid potentials, so as to vary the damping of the couplings, and consequently vary the sharpness of resonance. The object is to secure approximately equal amplification for a range of frequencies, thereby securing freedom from distortion in dealing with audio frequencies, and in the case of radio frequencies enabling a set to receive efficiently over a wide range of wave-lengths. Fig. 1 shows the application to a two-stage radio-frequency amplifier, the transformers A, B and the input circuit K, I being resonant at different frequencies. The grid potentials are adjusted by a potentiometer H shunted by condenser K<1>, and filament current is supplied from a transformer T. Condensers K<2>, K<3> and a resistance R are connected across the filament leads, and the grid circuits are connected to a point between the condensers and to a tapping on the resistance. The potentiometer for varying the grid potential may be connected across the filament battery, and mav have separate sliders H, H<1> for the several grid circuits. This arrangement is shown in Fig. 5, in which also the first high-frequency transformer A is replaced by an inductive or non-inductive resistance R in the plate circuit of the first valve and a resonant choke coil L<10> in the grid circuit of the second valve. The positions of the elements R, L<10> may be reversed. A condenser C<10> is connected between the plate of the first valve and the grid of the second. A crystal or like rectifier D, or a valve with grid leak, may be used as a detector, and the resulting low-frequency currents may be amplified by additional valves, or the radio-frequency valves may be utilized also for the amplification of the audio-frequency currents in the manner described in Specification 234,025. When two or more stages of audio-frequency amplification are employed, the resonance of the intervalve couplings is graduated. A reaction cricuit described in Specification 234,025 comprising an adjustable inductance, a resistance, and a capacity all in series may be connected between the plate of one high-frequency valve and the grid of an earlier valve; and a similar circuit may be connected between the plate of the detector valve and a variable tap on the grid coil of that valve. Electromagnetic reaction may also be employed from the plate circuit of the first valve to its input or aerial circuit. The filament rheostat may be employed for adjusting the grid potential of some or all of the valves in the manner described in Specification 234,024. The transformers are. preferably constructed as described in Specification 234,023.