Configurable tube interstage transformer for driving power output stages. Two identical secondary windings are provided which may be used in parallel for maximum current or in series for maximum voltage drive to SE output stages. The two windings may be used for independent drive of parallel SE stages or used as a phase splitter for PP stages. Two primary windings may be used in series or parallel to give two ratio options. Best performance is obtained when driven from a low impedance. A resistive load across the secondary may be helpful in damping the leakage resonance which can vary due to the grid capacitance of the driven stage.