 AC-operated radios using power transformers require repair and refurbishment of the power supply section before operation, as any failures are likely to stress or damage the power transformer, necessitating a costly repair.AC/DC sets using a no power transformer may be either "curtain burners" using a resistance cord to drop the line voltage, or warm/hot chassis radios using a series-string filament circuit where the voltages add up to the line voltage.They were named "AC/DC" because they operated on either AC or DC line voltage, which was not possible with a transformer-based set.