I have an old Voice of Music 1450 tube amp. I need some help with wiring. I want to update it with newer wire. Its the wire that runs from the head to the speaker cabinet. In the picture you see 3 screws. Above them are numbers (left to right) 0, 4, and 8. What does this mean and which wire screw is positive and which one is negative. The 4 screw doesn't have anything to it. I'm thinking that the 4 is positive for if you wanna use 4 ohm speakers, the 8 is positive for if you wanna use 8 ohm speakers, and the 0 is negative. Correct me if I'm wrong. But here's the picture.