Used as a detector, its output being applied to a d.c. amplifier circuit. A pair of 4mm sockets allow connection to a 1mA meter for quantitative work. A gain control is also provided. Identical dimensions to the transmitter. The transducer is of the same type as used in the transmitter but in this case used as a detector, its output being applied to a d.c. amplifier circuit. A pair of 4mm sockets allow connection to a 1mA meter for quantitative work. A gain control is also provided so that the output from the receiver provides full scale deflection of the meter under maximum signal conditions. Requires 9V PP9 battery (not supplied).