The 6J5 and 6SL7 tubes are still known to veterans, but the 32L7 certainly isn't. This circuit of a sound-triggered intermittent audible alarm was found on a 1947 Radio Craft. The oscillator that powers the audio power valve that has a rectifier diode is a neon lamp relaxation type. The 5 Meg potentiometer and the sensitivity adjustment. The critical components are certainly tubes and transformers. The type 47 pilot light also helps reduce filament voltage from the power grid.
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