I am surprised that no one suggested a Grado for the Dual 505-2 , The person I acquired the Dual from had an MT+ Grado mounted on it. I was considering upgrading the stlus but NO ONE even suggested a Grado. Was wondering why?
I believe your 505-2 like my 506-2 it has the ULM Ultra Low Mass arm and the Grado would not be a good match, maybe that's why. You might want to consider an Ortofon OM 5,10,20 etc. depending on your budget.