This paper describes efforts undertaken to upgrade ac-dc current transfer standards and calibrations at the National Research Council of Canada. The ac-dc current transfer comparator has been redesigned, using guarding techniques most advantageous for the current shunt comparisons. A set of coaxial shunts for currents between 10 mA and 10 A has been built, and characterized up to 100 kHz by a step up procedure. The operating current range was further extended, up to 100 A, by a set of commercial shunts. Furthermore, the fabrication of a set of high current coaxial shunts, with low ac-dc transfer differences, was recently initiated to replace the commercial shunts as the working standards.