This NiCd baterry charger circuit schematic can charge 6 volts as well as 12 volts NiCad batteries. It uses a transformer which can deliver 4 to 5 A current between 12.6 and 15 V. Ordinary chargers ...

Now the battery charger is set and ready to go. Read a commentary on this article by Anoop Hegde: If You Build A Smart Battery Charger Using a Single-Transistor Circuit, Beware the Consequences.