I know it's an old post but I am chiming in. So it happens to be that I own AD-6900 model "U". It is designation for Japan and South/North American market. Voltage being pre-set (no option available on the backplate for manual voltage selection) to 110V, 60Hz. So, here it goes: model "E" has 4 selectable options for voltage select (110/120/220/240); models "K" and "G" has 120/240 only. Mine, as mentioned, model "U" has no selectivity. Probably your model "C" (well, theoretically what logic implies) is that it is most likely pre-set to one of voltages left which may be 22/ or 240. But I just may be wrong. Look into it on the net. I also ask many things here because this is great place for all hi-fi questions! The right place to be. Sometimes, like in this case, there is a waiting period but it only goes so far on some items. This AIWA being old deck adn higher range one, not many left alive today. In other words, very obscure one. So, not many people having great insight in this matter. Me included. ;-)
BTW, I bought mine well over a year ago. Maybe even two years now. I sent it to my tech who literally dismantle it completely, restored to mint, brand new condition and now it works as the day it left the factory. Brand new. Literally brand new. He replaced all that needed to be replaced. Again, literally everything. To the smallest screw or some tinly little spring, all rubbery parts, all electrolytics, all mechanical parts, all motors either checked, lubed or refurbished. A restoration process of 4 months and many, many working hours. I bought it to restore it to it's former glory. And let me tell you! Man, what a machine! Simply gorgeous. Super advanced for it's age. Built like a tank. Very little of them still 100% working. Very nice piece to have and collect.
I don't know which are you. An avid collector or just hi-fi lover and user of that deck. Whichever it is, this deck is worth bringing back to it's original glory! ;-)
Best of luck to you and the deck!
Krešo
