This circuit was found in an American publication from 1965. The circuit uses components from that time. No information was given about the excitation transformer. Observe the high input power.
This circuit was found in a September 1982 Radio Electronics magazine. It was the type commonly used...
This amplifier for distributing audio signals appears in other articles on this website and even...
Many reed switches can be wired in series to perform na efficient alarm as shoen in the figure....