adjustable power doodad

[hydrophidian]

I have an extra power supply laying around that I would like to use.
Problem- It doesn't have adjustable power.
It puts out 13.8 volts. I have a buddy that made a power adjustment dial to hook up to the positive line. He took a small metal box and put basically a pot from a guitar on it and made an adjuster to raise or lower the voltage going through the line.
I am looking for something a little less homemade. Does anyone know what this doohickey is called? I am having trouble locating it online without having a name for it. I went to radioshack and the retard there had no idea what I was talking about, then tried to sell me a phone!! Any help would be appreciated.
Thanks

[voodoo]

potentiometer ?rheostat?

[Chef-Ink]

I used to modify Marshall amps w/ a friend a long time ago, before there was a proper pre-amp in Marshals.

We used a "variac" sounds pretty similar.

[MontanaPiercer]

I have seen those units in the past. I don't remember who sold them, but they were sold to be hooked between car batteries and the machine to give a variable supply for the tattooist on the go / mobile units, but I haven't seen one in years.....

[ifive]

I would try a hobbie shop/store. Radioshack seems to be getting away from the old do it your self eletronics lately. I went in to the one by my house just to check out what they had and it was like walking into a cellphone store. Online Is your best bet just google -Eletronic parts-

[voodoo]

the stats and stuff r in the bins!

[Papa Gee]

Rheostat. You can get one out of an old slotcar set. Its a spring with a contact bar that slides up and down it. The closer it gets to the power source the more voltage you get to the machine.

[Cpl West]

Exactly. Just what Papa said. It's a Rheostat. The good's you're looking for in Radioshack are usually in the back of the store hanging on their pegboard displays or whatever they use. They're all pretty much the same store-to-store. If you don't see anything, just ask somebody that works there.