Shortly after take-off, whilst climbing through 6000 feet, the left AC generator light illuminated and could not be reset. A loud vibration was heard and felt from the left engine. Visual inspection revealed black smoke coming from the generator vent, and remnants of red hot generator windings against the grill of the vent. There were no fire warnings but the engine was shut down to prevent further damage. The aircraft returned to Sydney where an uneventful single engine landing was carried out. Examination of the generator revealed that the drive end bearing had failed, allowing the rotor to contact the stator. The drive shaft however was reported to be in good condition, having failed to shear and disconnect the generator from the engine as intended. This matter has been referred to the Civil Aviation Authority for resolution with the manufacturer to ensure that the design of the generator drive shaft is suitable for the application.