The primary impedance of a transfomer in an application, as seen by the source, is the primary no load impedance in parallel with the transformed load. The ”primary no load impedance” for a gapped tube amp transformer is the primary inductance. The ”transformed load” is the secondary load as seen from the primary winding (Load * (turns ratio)*(turns ratio)). Thus, the transformer by itself does not have an impedance that can be used without a context.
