Originally Posted by Air&Road

That would not be a difficult solid state circuit to design, but would it be cost effective? There is a commonly used 5V regulator in a TO-5 case that is used for on board voltage regulation. There might be a 13.5 volt version if someone were to research it. Or one of the semiconductor desing manuals might show a way to use passive components to fine tune the voltage point of a regulator chip near that voltage level.