This circuit was found I a 1965 Radio Schack documentation. The transistors are from that time, admitting equivalents. The transformer has 500 ohm primary and secondary depending on the speaker.
This CMNOS crystal-based circuit generates a 2 Hz signal. It was found in the October 1994 issue of...
This well-known circuit triggers a relay when light striking the phototransistor is cut off. The...
Using transistors at the time, this circuit was found in a 1970s documentation. Transistors support...