As my ICOM-706 MK2G is slowly dying I was looking for an option to do some HF operations with a simple antenna setup. For the IC-706 I used an ICOM AH-4 automatic tuner. This unit is basically compatible with the IC-705 if you are able to build a simple adapter cable.

Internal wirig colors of ICOM AH-4

I used a spare connector of former 5.25” computer drives to connect the AH-4 side. In order to fit I chamfered one side with a sharp knife. It is not optimal but makes the connector suit into the AH-4 plug. The control lines are connected to a 3.5” stereo headphones plug and carry the signals GND, START and KEY. The power supply is on a separate cable directly connected to the battery. The wiring is documented on [1].

Homebrew adapter cable

Contrary to [1] in my case it was not necessary to first power the AH-4 before the IC-705. Instead the corresponding symbol appears in the FUNCTION menu seconds after the AH-4 control wire is connected.

IC-705 FUNCTION Menu with Active TUNE button

So the AH-4 will still be in use after its companion IC-706 died.

References:

[1] https://www.fbnews.jp/202007/ww02/