You can also use a big 6 volt power transformer wired as a bucking transformer to drop the voltage down a bit - see:
http://www.allaboutcircuits.com/vol_2/chpt_9/5.html
Just find a transformer capable of handling the current. Connect it according to the diagram (primary to secondary on one side, connected to the line, other end of primary connected to the line and the load, and the other end of the secondary to the load). Check it with your meter before plugging the set into it, if wired wrong you'll add six volts instead of subtracting it!
-Ian