This circuit produces a pulse when the voltage in the regulator exceeds a certain value depending on the components. PUT is not a common component today. The circuit is from a 1970 EEE.
This experimental amplifier was found in the 1960 Mullard transistor reference manual. The...
This circuit from Motorola is from 1968, appearing elsewhere on this site. The transistors admit...
This circuit triggers the LED when the monitored battery voltage drops below 9 V for 12 V...