A little off subject but- The first thing that came to mind when I saw the FET pic was something like an OA2 regulator tube: https://en.wikipedia.org/wiki/Voltage-regulator_tube.teemuk wrote:If it's obsolete, its not trivial to engineer a replacement.
[img:328:318]http://sub.allaboutcircuits.com/images/05269.png[/img]
silverfox.