Simplest and cheapest way is with a 6-12 volt converter. I have a '35 and ' a '36 both are 6 volt systems. I use a 12 volt converter to play a modern 12 volt radio. These converters have been trouble free for years. If you get a chance check this:
http://www.ebay.com/itm/Ford-Model-A...tWKXUh&vxp=mtr
Tom