This circuit was found in the component's own manual, which is not very common nowadays. Note that the circuit requires the use of a symmetrical power supply.
With 3 transistors, we found this receiver in a documentation from 1966. The circuit has an output...
This sonic relay or vox was found in a Popular Electronics from the 90's. The power MOSFET can be of...
This tri-state comparator was found in a circuit manual from the 1980s, but it can be easily...