6600 pops household circuit breaker when keyed in tune mode with over 5 watts

Had similar issues with my 6500. RF coupled into the ac power line triggered my arc interrupter breaker. Depends on power level and frequency.

Try a good dummy load. Check your antenna SWR. Try an un-un coax isolator etc.

GL es 73 Martin AA6E

I originally had the same sort of problem using my 6500. I who worked as an electrician in our family business at one point of my life, installed a 200A 40 breaker panel in the house, all new wiring, and a lot of expensive ARC Fault / GFI breakers. Back in my electrician era I installed a lot of panels and new breakers, and in those days GFCI outlets were the thing and there were no ARC fault breakers.

WELL, when on 40m pop and the whole shack went down.... I had quickly installed the radio (As it was my new toy) and station grounding, lead RFI ferrites and chokes were just not installed as it was day 1 an upgrade from a FLEX 1500.

I changed out the ARC fault for a standard breaker and it's still in there 7 years later. HOWEVER, the station got a straight shot through the floor to the foundation, through a hole right to an 8 ft x 5/8" copper ground rod. I installed ferrites on about everything that comes out or goes into the radio... And am meticulous with station grounding and RFI protection. This is especially important when you need to interface with remote coax switches driven with USB cables to computers.

First thing would be get the ARC fault out of the shack, so that you can get on the air. and then make sure whatever RF you do make, gets out of the shack through feedlines correctly and then decouple everything. My favorite ferrite is a DXE slip over the coax and then install connector unit.

Through this process, I still managed to BREAK, my 8877 amp when the 6500 locked in full transmit, crashed the computer and recently my little dual 3-500 FT8 amp blew up when the station again locked in transmit when the coax switch freaked and locked the computer on. The end result was a complete rebuilding of my station into heavily grounded racks on one side of the room, and the shack computer op desk now 15 feet away from the radio, power supplies, tuners and switches. When you start adding even more power, your RFI procedures become even far more critical !!! You can see what I've done on my ZED Page... and I'm still working on the rebuild. Good luck with everything. Erika DD