I have an older ICOM A22, my headset adapter includes both headset jacks and
a smaller 3mm plug for a PTT which I had to order for that size plug. Keying
the 3mm PPT works the headset mic.

I do not know if installing the headset adapter jacks to the A22 disables
the radio's on board mic, I believe that it will because I also have the
"speaker/mic" combination that I use in sail planes, clipping the
speaker/mic to the seat belt and letting the radio sit beside. That
connection disables the "on board" mic and it is the same style plug set for
the headsets adapter.

BT

"B A R R Y" wrote in message
...
I use my A24 lots, for listening to ASOS, communicating to aircraft at
fly-ins, ordering fuel, etc... I rarely use it with a headset.

The other night, I had a full-on comm failure and needed to use it
while aloft, with a headset. It took me a few minutes to remember,
but my radio keys only the radio's onboard mic when keyed with the
onboard PTT, not the headset mic. To use it with a headset, I need to
put the radio to my mouth and talk into the radio, the mic in the
headset is not used. My adapter is a genuine Icom product, with
phones, mic, and PTT connections. I'm only connected to the phones and
mic jack.

Can anyone confirm to me that an external PTT will in fact key the
headset mic?

My Googling has come up with lots of yeas and neahs in conflict.