I've looked around for a good, cheap souce for the rheostat, R3. The closest thing I could come up with is part number (RWV) 200-66HS500 Rheostat, 500 Ohm, 1W, multi-turn, wire wound, inductive element at www.surplussales.com for $5 (see link). This part is just to dial in the voltage, correct? Will this be replaced with a unique resistor once the value is determined?.....Colin