"Peter has a radio, but it is faulty."
Translation:Péternek van rádiója, de rossz.
We understand if you say so but it would rather belong to another context in which the radio is in the focus, like:
- Gézának tévéje van. Péternek rádiója van, de (az) rossz. Géza has a TV. Péter has a radio but it's faulty.
or another example
- (Gézának egy jó rádiója van). Ugyan Péternek (is) rádiója van, de (az) rossz. (Géza has a good radio). (Though) Péter has a radio, (too), it's faulty.
Hahaha and there can be a problem with "de rossz" in the end if you don't use "az" like in my example (or just simply say Péternek rossz rádiója van), because "de rossz!" can mean "Damn! It's so bad!" but with a lot of sarcasm. So you are actually kind of envious of him that he has a radio :D