I have had the 505u since 2009.It was purchased new from a dealer in Japan.This so called grey market amp has given me nothing but great entertainment.Saved a ton of money and paid zero import fees.If have recently acquired the service manual and changed it over to 120 VAC.Quite a simple job actually.The 505u's from Japan are multi-voltage.
I do remember reading somewhere where an individual had claimed that the Japanese models had hand wound transformers and were 100 VAC only.Anyway,if someone out there wants to change their amps input voltage,let me know.