Based on R.G. Keen's schematic, this board will provide approximately 18V, 25V, 33V, and -9V off of a single 9V source. Also, it has an option for a 9V sag, letting you dial in a value between 0 and 9V.
This little bad boy now has everything as the original Effects Tester, and also includes an audio probe, charge pump (-9V and 18V), and frequency generator. It makes finding those irritating issues with your circuit a breeze!