Abstract: Provided is a voice coil wire for a sound generating device, comprising a wire body and a cavity provided in the wire body, the wire body is configured to be applied with a current signal, wherein the cavity is in a vacuum state or is filled with an insulating gas. Also provided is a voice coil, the voice coil is provided with the voice coil wire. Also provided is a sound generating device. By filling the cavity of the voice coil wire with the insulating gas or configuring the cavity to be in the vacuum state, the weight of the voice coil wire can be reduced, so the influence of skin effect on the voice coil wire is reduced, and the utilization rate of the voice coil wire is improved.

Abstract: A push-pull power amplifier includes a pair of input terminals, a pair of output terminals, a pair of matched output tubes having cathode, plate, and grid terminals, and a pair of output power supplies, all of which are connected to form a bridge circuit. A floating bias supply is coupled between the grid and plate of both output tubes. A first feedback resistor couples the floating bias supply to the cathode of the first output tube. A second feedback resistor couples the floating bias supply to the cathode of the second output tube. The floating bias supply and feedback resistors provide degenerative feedback without affecting power gain.

Abstract: An electrometric apparatus, which uses a measuring device that provides a high impedance dc signal which varies in accordance with the variable to be measured. The dc signal is amplified by at least one amplifier means and the amplified signal is applied to an indicating means which indicates the amplitude of the amplified dc signal. The supply voltage for the amplifier means is provided by a dc power supply means connected through a regulating means to positive and negative supply busses and for the amplifier means. The regulating means includes a transistor having its emitter-collector circuit connected in series between the power supply means and the positive supply bus of the amplifier means. A resistor and a Zener diode are connected in series and the series combination is shunt connected between the supply busses. A pair of series connected resistors are shunt connected between the supply busses.