I have a question about your 545S mic. it seems that the 545S mic gets described in a few different ways. My question, is the shure 545S impedance mic and the 545S series 2 unidyne 3 the same mic? I don't know if these descriptions are a different way to describe what era they were from or what.
The current model of the 545 is the 545SD-LC. It is a Unidyne III design.
Any Shure mic with 545 in the model number is a Unidyne III design.
Series 2 has never been used in the 545 model number.