This high quality circuit with complementary symmetry was found in an Electronics World of 1966. It can be made with modern transistors like the BD or TIP series.
We found this touch control on a Popular Electronics from 1970. The circuit makes use of an...
This very low frequency circuit was found in a 1964 Electronic Design. Transistors may be modern...
This circuit, from the 1990 Motorola Dataar Databook, can be implemented with other comparators. The...