Indicated for powering circuits with operational amplifiers, this source was found in Popular Electronics. The output voltage depends on the transformer used, as well as the current.
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...