This low power circuit was obtained from an American 80's documentation. The circuit indicates the voltage of a battery being trimmed by the trigger point. The transistors can be the BC549.
This 45 to 90 Hz hum elimination circuit was obtained from a 1980s documentation. The operational can...
This circuit uses a triac to detect the level of a reservoir, and a sensitive SCR connected to the...
The components used in this 80's circuit are uncommon today. The circuit is intended for...