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MH-31 Mods

The only thing about the FT-817 that I don’t like is the lack of talk power from the MH-31 microphone and the fact that there isn’t a speech processor.

There are a few published articles about converting the microphone to an electret condenser and this for me seemed a good way to go.


I followed the method used by George Smart M1GEO and used a Panasonic WM-53B insert, I am very pleased with the results.

The first thing to do after removing the cable is to remove the back of the microphone which is held on with 3 screws.


A further 3 screws hold the PCB in place.


The microphone is a push fit into the front moulding of the microphone body, this needs to be unsoldered from the PCB and then the resistor, capacitor and the 2 wires to the switch need to be removed.



I then fitted a 10nf capacitor and an 8.2K resistor to the bottom side of the PCB.

To the top side of the PCB I fitted 1uf and 50nf capacitors, wired so that the switch would switch in either value in series with the microphone output.



The new Panasonic insert is only 10mm in diameter so I cut out a perspex disc to the same diameter as the original insert. This enabled the new insert to be fitted as a push fit with no glue or holes being drilled in the microphone body.


Finally the PCB was mounted back into its original position and the 2 wires from the insert soldered back onto the microphone wire pads.

The Panasonic insert is polarized so ensure that the + side is connected to the pad which is connected the the new 8.2K resistor.