We found this Vox in a 1969 Motorola documentation. Transistors support modern equivalents and the SCR can be a TIC106. The reset is done by a push button.
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....