Sqealing = bad preamp tube. I have tried different tubes in it, put in an NOS rectifier which was nicer than the stock one... hard to describe HOW it was nicer, but definitely nicer. Also put a Tung-Sol 12AX7 in V2, and that warmed the boost tone up a little. But honestly, the stock tubes sound very good, and I heard very LITTLE DIFFERENCE in swapping out tubes, in any of the positions. The NOS rectifier is a keeper tho.