GB289165A - Improvements relating to the electrical sound reproduction of gramophone and like records - Google Patents

Abstract

289,165. Miller, R. J. Jan. 24, 1927. Magnetic and electrostatic instruments, - A combined electrostatic and electromagnetic sound - box is actuated by a stylus to set up simultaneously potential variations in a condenser and current fluctuations in a coil which fluctuations are impressed on an amplifying circuit so as to bring out both the low and the high tones. As shown, the stylus holder 1, Figs. 3 and 4, made of light material such as fibre or aluminium alloy is mounted by pivots 5 to brackets 2 secured to a block 3 extending between the limbs 4 of a magnet, and springs 17 secured by screws 34 engage recesses in the holder to centralize it. The holder carries one electrode 12 of a condenser the other electrode 13 of which is carried bv, but insulated from, a magnet pole 11. Leads pass from the respective condenser plates to terminals 15. The stvlus holder also carries a coil 6 surrounding- a soft iron core 9 carried by the block 3, and having its ends connected to terminals 7. Alternatively, an armature carried by the stylus holder may move within a fixed coil. The reproducer is supported to track a record, and leads from terminals 15 are taken to terminals 19, Fig. 5, of a valve circuit for connection to grid and filament respectively. The H.T. positive 28 is connected to one of the terminals 19 to maintain a working potential across the condenser. The output circuit of the valve acts through a transformer 22 the secondary circuit of which is shunted by two resistances 24, 25, and the coil terminals are adjustably connected to these through terminals 23 so as to impress the current fluctuations in the coil on the output coiinected to terminals 26.