[jason701802]

The simplest way to take care of this would be to just use a ~5 volt source to power the servo tester. Unless you have 5 volt source, the easiest way of getting 5 volts would by using a lm7805, $1.59 at RadioShack. Connect the left most pin to the power supply, the middle to ground, and the right one to the voltage input on the servo tester.

Better yet, if you haven't already bought the servo tester, find one with a regulated 5 volt supply or just make one yourself, it can be a great learning experience. There are many circuit diagrams for servo testers online (and probably even a few on Chief Delphi) that are based on the 555 timer chip (the same as the servo tester you linked to).