The present invention relates to methods and apparatus for removing coatings from generally opposed first and second major surfaces of a substrate. In one embodiment, the controller includes an analogdigital converter configured to provide samples of a rectified voltage waveform corresponding to a rectified sensed voltage of the power converter. The apparatus includes a draw down unit and a control system for closed loop control of the draw down unit. The device includes a handle oriented perpendicular to the axis of the tube and a moveable trigger that can be grasped by the fingers of the operator while his palm is against the handle. Since the level shifter outputs voltages substantially corresponding to voltages which the first and second power sources supply respectively, a range of the output voltage may be extended.