IC706 Tune Device
In common with most Icom rigs, the “TUNE” button on the IC706 is designed for use with an external Auto-ATU (usually supplied by the Transceiver Manufacturer) and provides a 10 watt carrier to enable tuning. No Tune facility is intentionally provided for use with manual tuners. This feature seemed to disappear with Valve PA’s and Pi-Tank couplers.I normally use a Z-Match tuner with balanced feeder, so need some RF output to enable me to tune the ATU for the best match.
Various circuits have been published for devices to “fool” the IC706 that it’s connected to an Icom AH-4 tuner or similar and there are also at least 2 commercial gadgets available. Most circuits I’ve seen have a high component count, using either a couple of transistors or even the 555 Timer IC. I found an excellent circuit by Larry, WA2EHZ which is a real Engineer’s solution – simple, elegant and does the job with 2 passive components and a $1.19 Molex Connector from Radio Shack.
