Patent GB-373973-A (GB)
Title: Improvements in photograph pick-up arrangements
IPC: H04R19/06
Filed: 1930-11-26
Abstract: 373,973. Wireless receiving apparatus. DUBILIER CONDENSER CO. (1925), Ltd., Ducon Works, Victoria Road, North Acton, London. - (Assignees of Nyman, A. ; 10, East 40th Street, New York, U.S.A.) Nov. 26, 1930, No. 35584. Convention date, Dec. 7, 1929. Void [Published under Sect. 91 of the Acts.] [Class 40 (v).] In a gramophone reproducing arrangement, an electric pick-up is used to modulate the oscillations produced in a high-frequency circuit of a wireless receiver, the modulated oscillations being detected and amplified in subsequent stages. Fig. 1 shows a receiving circuit in which the first high-frequency amplifier 7 is converted to an oscillator by switching in the circuit 8, 6, 9 across the plate and grid, the oscillation frequency being controlled by circuit 10, 11. The vibrations of the stylus 3 vary the inductance of coil 6 by movement of a metal plate 5, the changes in impedance of circuit 6, 9 causing changes in coupling and corresponding amplitude variations in the oscillation. Fig. 3 shows a circuit in which a variometer type of pick-up is used. As shown in Fig. 3a, the stylus 3 is secured to the moving coil 21 connected in series with the fixed coil 20, the pickup being connected in the feed-back circuit from the plate of valve 7 through condenser 24 to the primary of the input transformer 23. The operation is similar to the arrangement of Fig. 1. Fig. 4 shows a method of adapting a screen grid amplifier to oscillate by opening the screen circuit at 29. The modulating circuit 30, 24 is connected across the winding 23 and effects frequency-modulation by varying the effective constants of circuits 10, 11. The pick-up employed with this arrangement comprises a toroidal coil 32, Fig. 4a, with a small gap 33 in which oscillates a metal plate 34 secured to the stylus 3. To reduce the considerable sensitivity of the circuit of Fig. 4, the circuit 23, 24, 30 may be made non-resonant near the oscillator frequency. As an alternative, the variometer may be directly connected across the grid and filament of valve 27 in series with inductance 10 or condenser 11. In Fig. 5 a condenser pick-up 40 and variable resistance 43 form a regenerative coupling between the plate and grid of the valve 7 to produce amplitude modulation in the circuit 44, 11 of the oscillator 7. The condenser pickup and resistance may be replaced by a variable condenser and a carbon granule type resistance pick-up, Fig. 5a (not shown) ; the condenser or resistance pick-up may alternatively be connected in a circuit coupled to inductance 44. The condenser pick-up may be connected in the same way as the pick-up 30, Fig. 4, for frequency modulation which may be converted to a mixture of amplitude and frequency modulation by detuning the input circuits of valves 15, 16, Fig. 1, from the oscillator frequency. A resistance pick-up 50 may be used for amplitude modulation as in Fig. 7, the resistance 51 being provided to control regeneration. The coil 23 may be coupled to the output coil 12 instead of 10 ; alternatively the pick-up may be directly included in circuit 10, 11 or other part of the oscillating system.