A description is given of the requirements and design of a line amplifier for use with 3/8-in diameter coaxial cables, which is suitable for the transmission of either 405-line television on a 1-Mc/s carrier or 16 supergroups of multi-channel telephony. From a discussion of the noise and harmonic requirements it is shown that an amplifier having a gain/frequency characteristic which equalizes the attenuation of six miles of cable is necessary. The circuit design of the line amplifier, and also that of a flat amplifier for use at the terminals, is described. Some of the practical difficulties which limit the performances of the amplifiers and the associated transformers are discussed, and an indication is given of possible improvements which may be incorporated in a future design.