This circuit was taken from Maxim documentation from the 1990s. It can be implemented on the basis of modern operational amplifiers. Power supply doesn't have to be symmetrical.
This simple circuit with a unijunction transistor at the time appeared in Radio Electronics...
This circuit was used to reinforce radio signals for listening on the phone, making it possible to listen...
This circuit was found in General Electric documentation from 1968. The circuit uses triac from the...