A temperature-controlled soldering iron, wire cutters and possibly a 1-1.2mm miniature drill bit to widen the holes for the upgraded bridge rectifier legs. A voltmeter will be useful. However, do not use an oscilloscope unless you have either a) differential probes or b) an isolating transformer to power the Valhalla or Acis boards – these power supplies are not isolated from the mains power so experience and caution are required when working on them.