I built a Metro 2203 and it has the 400V tap on the PT. I was using the 490V but tried the 400V tonight. If my math is correct, I'm looking for 41 mA at 422V as opposed to 36mA at 490V. For some reason, I barely got the 36mA with the bias pot almost all the way up. Now, with 422V, I'm only getting 12mA with the pot fully cranked. I have a 47K resistor attached to the pot; make it a smaller value? The other two resistors in the circuit are 15K and 27K.