Ive worked on a few 10B's and I would send it back to AC. BTW that tuner was designed by Dick Sequerra. Every tuner that came off the assembly line had to be trouble shot. No 2 are alike. I received this info. from a 2 hr. conversation with the late Sid Smith. Sid worked for Marantz for many years and was responsible for the output transformer designs on the 8B. He told me he went through almost 50 incarnations of transformer before he arrived at the one they used in the amp.
G.Garfield
G.Garfield