That is a good article on three terminal regulators. They give the best results because the output doesn't vary much with the load.
The radios can be converted to 12 volt operation. You need a power transformer out of an old 12v tube radio, a 12 v vibrator and a set of 12 v tubes. The old GM Sonomatic radios turm up on Ebay all the time in the 12 v form.
