Bill,
Just use a 12 volt voltage regulator and a small heat sink. It costs $0.35 from Jameco.com (part 7812T) and the heat sink is $0.99 (part 326713). The voltage regulators can handle up to 35 volts and put out 12 volts at 1 amp, more than enough for the dukes system.
From: Bill Maddox [mailto:reddog@smwireless.net]
Does anyone have a 28v dukes outflow valve that will trade for a 12 volt Dukes wants 4000 for the conversion Bill Maddox