I had to put a new bias pot (the external one) on my Nak BX-300. Before I replaced it I could bias TDK D (1990s), TDK SA (any vintage), Maxell XLII (any?), Sony Metal XR (2000s) just fine but any true CrO2 tape wouldn't bias correctly. I should also try a few more tapes I had touble with (80s...