I can't speak directly about FT-8, but I have tried to use my amp on other digital modes (using fldigi), and have experience a couple of different issues. For a long time it would keep kicking out into BYPASS for some unknown reason. The antenna is resonant, and I tried it straight, as well as through my HF-AUTO, and the same behaviour. Ultimately I discovered that if I set up the levels differently in the transceiver it would stop kicking out. I am only looking for about 100 watts, so I only drive it with 5W. Now that it has stopped that behaviour I can use it, but the temperature climbs like a rocket! Keep in mind that many of the other modes require longer continuous transmissions, and so after about a minute it is up over 50, and a 2 minute transmission puts it in the red (over 70). In the end I think this amp is not really suited to any digital work, and I now just go direct at 25W. Given I got this amp for some SSB use, and decidedly being able to run 100-200W in digital modes, I am disappointed. My expectation was that trying to run a 1KW amp at 100W would not be any strain on the amp at all. Good luck with FT-8, maybe with it's shorter transmission times it will work for you.
