Carbon microphone used in association with a headphone (not present) to form a valveless amplifier. It was probably manufactured by New Wilson Electrical Manufacturing Co. Ltd in 1927.

The bar replaces the diaphragm of a headphone earpiece so the bar now vibrates instead of the diaphragm. The earpiece is connected to the output of the radio (usually a crystal set). The movement of the microphone bar changes the resistance between the microphone terminals (ie the resistance between the screw and the carbon). A pair of headphones (for listening) is connected via the microphone terminals to a battery.

A control knob allows adjustment of the sensitivity of the microphone part.

Physical Description

A rectangular metal shaped object with a black disc attached to one side with a screw. There is one terminal on the body and another on the black disc. Internally there is a carbon block mounted between two nickel plated ends joined by a blunt ended oval shaped piece of magnetic material. The screw, on the opposite side, can be adjusted to optimise the pressure between the carbon and the contact for maximum sensitivity.

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