The paper discusses the design and engineering details of two types of demodulator equipment which will operate from a p.a.m. system, and could be used, for example, in the field of electronic telephone exchanges. Apart from normal circuit-elements the equipments contain only semiconductor diodes and transistors. The equipments described will provide electrical characteristics conforming to different levels of performance such as might be required for local or trunk routing. They are both designed to operate on a 100-channel system and will provide gain of the signal information of about 40 dB.The effects of variations in device parameters and environmental conditions on electrical performance are considered in some detail, and the results achieved in practice are discussed in relation to the standards of performance likely to be required. Special attention has been paid to the stability of the semiconductor parameters with life, and the effect of this on the long-term performance of the circuits. A preliminary investigation to determine life trends of the type of transistor specified has been undertaken, and the results obtained are presented and discussed.