Help me understand......

[Zinc]

Okay. I'm looking into getting a Rocktron Voodu Valve for my guitar rig. I thought that this could be only run through a power amp, but I emailed rocktron and the guy said it would be fine to run it through my 100w Ampeg VL-100h tube head and 4x12. So my question is what is the point of power amps? If you get a power amp and a preamp, does that cancel the need for a regular tube head? So can you run any preamp through a regular tube head? I'm confused....PLEASE explain....