The circuit for the U67 is very unique compared to other
microphones. The historic BV12 transformer is built very differently than your standard microphone output transformer.
Designed with a Primary, Secondary and Feedback winding, the Feedback is a voltage sensing or feedback circuit that if engaged
as an output by itself will cause the transformer to behave in a non-linear fashion. It is advised that one familiarize
themselves with the technical aspects of a U67 before emarking on a DIY project.
The T67 provides the same flexibility as the BV12, the advantage being on a PCB board is that it is easier to make
the necessary connections to utilize the T67. All of the windings are attached to pins and are essentially open loops.
You must connect two Primary pins (and two Secondary and two Feedback) in order to create a loop with two terminals (see picture
to left). Tying the Primary and Secondary together creates a 7:1 output ratio while tying the Primary to the Feedback
creates a 22:1 output ratio.