In reality the voltage and amperage vary on both types of machines, they are plotted on a graph known as the "volt/amper curve" On a CV machine as You increase the wire feed the machine tries to keep the voltage and arc length constant. As more wire is fed in the amperage increases to keep melting off the increased ammount of wire and maintain the arc length. The voltage does drop a little, but not much. On a CC machine, I will use stick welding as an example, If You set the amperage at say 100 amps and strike an arc the voltage changes as the arc length is changed, but the amperage doesn't change excessively from a long arc to a short arc, and doesn't get a lot higher if You stub the rod into the work. This is sometimes refered to as a "drooping volt/amper curve" and the machine refered to as a "drooper". If You tried the same thing on a [really powerfull] CV machine the amperage would varry from lower with a long arc to verry high as YOU TRIED to stub the rod into the work, BUT IT WOULD JUST KEEP BURNING OFF THE ROD, and the voltage would drop a little as the amperage increases . To see the volt/amper curve graphs for CC and CV machines look in the power supply manuals, or check the manufacturer's websites under "Owner's manuals"