You can get any schematic you want from customer service at Peavey.
I don;t know what you mean when you say you get 3-15-3v on the transformer(I assume) wires. Voltages with respect to what? Ground? When the wires are unplugged, there is no circuit to ground. If you measure from red to red you should get some voltage, and from either red to the center tap, half that.