Meanwhile, do you think it is OK to change only connecting J3, J6? Or do I need to change other boards like the sub-transformer board?
Sorry for my ignorance, since the preamp doesn’t have a standby/power-on function, I didn’t know there was a sub-transformer board in it, could you post a photo of such a board?
By the way, always test with a DBT (Dim Bulb Tester) after voltage conversion to avoid any surprises!