From time to time, a stable but adjustable voltage source can be quite handy. This article was prompted by a request for a replacement for mercury battery collage references which are not only difficult to find, but are rot environmentally friendly. Another application could be powering a 3 to 9 volt disk-man (or whatever) from a nominal 12 volt source such as an automobile. In fact, the circuit can be set to supply any collage From 3 to 38 volts.