I did the agc-off mod on a '570 cupla years ago -- worked fb. Sold the rig cuz of filter leak-around on c-w, in favor of an '850 with all kinds of i-f analog filtering. No leaks there, due to multiple-freq filtering. Still debating outboard a-f filtering for the '850, and TKS V.M. for advice from K8AC and all u others re this subject. 73, Dave, K3BHJ