Full Wave Bridge Power Supply
 

To build a 9VDC power supply use a 6.3vac transformer, a full wave
bridge rectifier and 3300uf capacitor. Depending on the current your
radio needs, if this is a transistor radio I would think a 1 amp
transformer and a 50V 1 amp full wave bridge rectifier would suffice.
Parts should be found at your local Radio Shack. You can also use a
12VCT (center tapped transformer) and 2 diodes to do the same thing.

Regards,
Sal