The sensor is S1 in this alarm that we found in a Radio Electronics magazine from May 1971. Several sensors can be used in series. The SCR supports equivalents from the 106 series.
This small commercial radio for the MW band with germanium transistors was found in Japanese...
This circuit is from 1992 documentation. The transistor can be a TIP42 with a good heat sink for...
This speaker overload protection circuit was found in Radio Electronics from the 1980s. The...