A multiplier - square-law detector is described which has fewer limitations than existing types. It is shown that the gain of an emitter coupled amplifier (longtail pair) is proportional to quiescent current. This property makes it possible to obtain accurate wideband multiplication. Test results are given for a unit designed for radio astronomy application which, when used as a square-law detector, has an input dynamic range of over 40 dB. It is noncritical in adjustment and operates at frequencies up to 50 Mc. A single thermistor is used to maintain gain within 2% from 10 to 50°C.