After power ground balancing my Silver umax and Compadre, I started picking up some signals in the pebble area of a school tot lot and finally found a black rock about the size of a quarter. Taking it back home, I tested it in a/m mode with my Royal Sabre, which I believe you said had the true a/m mode. The threshhold immediately went into the null, so I surmised I had set both too far negative. Turning the pot ccw, the rock quit making signals. With the Compadre, I could null out the rock as I did with the Royal and a penny would still be found under it, as with the Silver umax. Turning the Silver umax to min. disc. instead of a/m, the penny could still be heard, albeit with a more broken sound. I'm hoping I've found my Homestead rock.