You absolutely must use filter capacitors, and you really should use a full wave bridge rectifier. Since you have no input filter capacitor, but you DO have an output capacitor, about half the time your regulator chip is powered IN REVERSE!!! This is because the charge on the output capacitor is greater than the incoming voltage most of the time- only during the peaks does the input voltage exceed the voltage on the output capacitor. Rebuild your circuit, use a full wave bridge rectifier and an input filter capacitor. You would also do well to put a large inductor (like a noise filter choke for automotive audio systems) inline with the input, since the raw output of a little alternator like that can easily create transients in the 200 volt range. Incandescent bulbs don't really care, but semiconductors do.
Cheers!
Chip Shults My robotics, space and CGI web page -