This circuit was found in February 1976, Radio Electronics magazine. The circuit is powered by 12 V and consists of an intermittently triggered timer.
The presented circuit monitors a line indicating if it is busy if there is an extension. The...
This high-powered megaphone circuit is from a Radio Electronics from December 1964. Note the use...
This linear circuit was found in a 1965 Electronic Design. The transistors are from that time....