Ming Da MC 84C07 Power Question - 220/10 - Please Help

Hello to any of you current or former 84C07 users.

I just bought an 84C07 used here on Head-Fi, and one thing is perplexing me.  The power specifications on the back say 220V/50Hz - in two locations - once on the transformer and once above the IEC socket.  The photo on the Pacific Valve site (this was not bought through Pacific Valve) has a sticker covering up the 220/50 saying 120/60 above the IEC.  Mine does not have that.  Is there any chance that this amplifier actually is configured for 220/50 but still functions on 120, though not at its optimum?  Or would feeding the amp half its required voltage mean that it obviously would not function properly.  Also, are there any other Ming Da owners out there that have noticed this power rating inconsistency or lack of appropriate stickers?

Thanks Much, Peter

I'm hearing a slight hum through my Ultrasone HFI-650 headphones, with a bit more emphasis on the left channel.  They are rated at 32 ohms, so I guess that means they are pretty sensitive.  I plan to use the amp with Sennheiser HD580 phones.  Do you think with these phones (300 ohm impedence) the hum will be less?

Thanks MoodyRN - you've been more than helpful, and set my concerns at ease!

Peter