Found in a 1965 CQ magazine, this circuit uses period components. The unijunction transistor can be a 2N2646 and the relay has voltage according to the supply.
Found in Popular Electronics from the 1980s, this circuit uses two operational amplifiers from...
This circuit was obtained in a 1974 documentation. It shows how to use a JFET as a low intensity...
The telegraph communication system has been out of use for a long time, so the montage presented has...