GB385667A - Improvements relating to automatic electric delay devices for thermionic valves - Google Patents

Abstract

385,667. Valve amplifying circuits. TAYLOR, P. H. and LAVINGTON, E., 36, Albert Road, Regent's Park, London. Sept. 2, 1931, Nos. 24652 and 25428. [Class 40 (v).] The power valve of a thermionic amplifier has its grid directly connected to the anode of the preceding stage, the correct grid bias of the power valve being obtained by a battery and resistance connected in its grid-cathode circuit. Fig. 1 shows a low-frequency amplifier 1 deriving its H.T. supply from terminals 2, 3, its anode circuit being directly connected with the grid of a power valve 26, which is supplied with high tension current from a mercury vapour rectifier 5. The transformer 7 has two secondaries 9, 40 supplying the filaments of the rectifier and power valve respectively, while transformer 12 supplies high voltage to the rectifier anode from one secondary 11 and a loud speaker field through a further secondary 18. The grid bias of valve 4 is determined by the drop across resistance 25 less the voltage of battery 29; 23 is the output transformer. The input to valve 1 is taken from a pick-up 32 through a tone compensator 33, as described in Specification 328,331, [Class 40 (v), Wireless signalling &c.]. Fig. 2 shows an arrangement generally similar to that of Fig. 1 as regards the valve coupling, but the system includes a protective relay arrangement in series with the mains supply to the rectifier anode transformer 12, whereby the supply is switched on at contacts 16, 17 after a predetermined interval, when the anode current of valve 1 through the relay coil 24 has reached a certain value. The armature 17 is held away from contact 16 by a coil 30 which is traversed by the grid current of valve 4 due to the battery 29. As the grid bias of 4 is obtained from the voltage drop across resistance 25 acting in opposition to the voltage of battery 29, the coil 30 does not release armature 17 until the bias attains the correct value. The loud-speaker field is energized from the secondary 18 of transformer 12, so that the loud-speaker is energized simultaneously with the application of H.T. voltage to the valve 4. The power stage may comprise several valves in parallel and the mercury vapour rectifier 5 may be replaced by a copperoxide or other suitable rectifier.