This CMOS circuit was found in a Popular Electronics from the 80's. The circuit consists of a counter that has its output activated when the selected key combination is pressed.
Suggested by General Electric in a 1980s publication, this circuit is intended for coupling...
We found this flasher with two transistors in a 1992 publication. The transformer is the driver type...
This source, obtained in a 1973 publication, uses a low power transistor to regulate the output...