With the help of Graham and the service manual on Beoworld, I turned a 120V Beogram 7000 into a 220V Beogram 7000, by changing the tappings and soldering a new powercord to the transformer. The fuse was already a 700mV, so did not need changing. Now it works perfectly. Thanks again Graham!
Now another one: Can a U.S. Beogram 8002 (120V) be modified to be a European Beogram 8002 (220V) in the same way? I checked the Beogram 8002 service manual, but it looks a lot more complicated than the Beogram 7000 one. Thanks in advance for your suggestions!!!