Found in an American documentation from 1969, this circuit makes use of a pair of matched transistors of the time. The circuit supports modern equivalent components.
This circuit is from a April 1991 Popular Electronics. The magazine no longer exists, but the...
This circuit is a variation of the previous one, containing a modulation input. The components are the same....
These 6 to 12 V source with current up to 100 mA was found in Radio Electronics magazine from June...