problems switching transistor variable voltage power supply.

i'm new to the forum arduino and electronics. im workin with a basic tank circuit. two inductors in series and a capacitor in parallel with a 9v battery. i am controlling the circuit on and off with a npn transistor. i have a diode in place as if the cuircut were a dc motor. not sure if it is needed? the base of the transistor is connected to pin 9 on the arduino. no resistors in place. i have a potentiometer connected to analog pin 0 and use it to vary how long pin 9 is off( as in the blinking LED example).
this works as i would expect and my coils (inductors)pulse.

i usually use this tank circuit with a variable voltage power supply. 2-24 volts. im not sure the amperage. hoping to test soon. but I'm guessing 4-5 amps max. so un hooked my battery and tried the variable power supply. now pin 9 is dead. i.e. it does not shut off. verified by running a blinking LED code. all other pins seem to work correctly. =( .

so i started looking for other circuit diagrams while i wait for a new atmega chip, some have resistors in place between the pin out and transistor. but im not to sure where to find a solution.

heres a link to a pic . i'm trying to use the arduino to replace the mechanical switch.
the transistor i'm using is TIP3055.