This is the circuit for the HM-10ª, an instrument sold by Heathkit. The circuit is from a Radio Electronics from May 1963. The indication is by an analog instrument.
Linear Technology's LT213 circuit, which suggests this application in 90s documentation, is not...
This is the patent for the zener diode regulator circuit by David B. Dean of Austin published in...
This circuit is from a 1967 publication. The configuration holds true for modern transistors having...