I'm curious why you replaced the Microphone's electret 'capsule' with the one provided in the kit?
Aren't these mic's all electret anyway?
I've bought a couple of these on eBay - one for an ACTUAL Beofeng radio and another for ... 'experimentation' just like this, so I appreciate your work!
I've found them for as cheap as USD$2.89. Quality: be prepared to repair.
The first one I bought - worked perfectly.
The second - PTT is fine, Speaker fine... No transmit. Solution: solder a little piece tinned buss wire to join the electret in. Bad solder join or bad PCB trace.
This is a SUPER idea, BTW. The BitX20 kit I have has a 4-pin (old) Kenwood-style connector, which indeed, will support a Speaker in the Mic.
Mike Yancey, KM5Z
Dallas, Texas, USA