Electrical hearing aids
T. S. Littler · The journal of the Institution of Electrical Engineers. Part 3, Communication engineering · 1944
An account is given of the problems involved in the design of electrical hearing aids and components. Details of a number of circuits, both portable and non-portable, typical of modern practice, are included, and methods of measuring effective amplifications are discussed. Finally, special adaptations, such as tone-control adjustment and automatic gain-control, are considered.