Rather than hard wiring another dedicated mic, I’ve moded a few white and black faced Johnsons with a 4 pin Jack. I mounted most of these jacks on the back or side. Besides destroying originality, it’s too difficult to achieve a clean looking install on the face because of the thickness and corrugated design. While trying other mics, keep in mind these old tube radios are designed for high impedance crystal or ceramic mics. Unless it's powered, the common 500 ohm dynamic mic that’s made for a solid state radio will not provide enough audio. A powered D104 will work fantastic on your white face, surprisingly even with the gain turned near maximum.