Abstract: An apparatus for providing regulated direct current to magnetizing coils of a non-destructive magnetic testing apparatus for detecting welding defects in pipe, which includes a variable output auto-transformer, a rectifying and filtering circuit, a meter relay for detecting direct current output magnitudes from the rectifying circuit at upper and lower bounds of a predetermined range required for proper operation of the testing apparatus, and a synchronous motor for adjusting the output of the variable transformer, in response to a control signal from the meter relay, until the direct current magnitude is within the predetermined range.