Going from memory here - but there is only one screw/knob on my 7700 to open the back & top of the lamp housing. Once inside, you'll see it's a standard halogen or similar (they are easy to get from audio/visual stores, or on ebay).
My enlarger has a simple cord running from here to an external transformer -- nothing special, just 240v to 12v. As I said, you can buy these pretty much anywhere.
Depending what yours is configured for, this transformer may be all you need to turn it from 120v to 240v. Just check the lamp itself to figure out what transformer to get...
Happy to help if you have more details.