Quoted from KenH:
The circuit is designed to drive at least a #44 bulb that draws 250ma.
The resistor will draw about 13 ma (I = V/R, 6/470). If you use a #47 instead, this only draws 150ma, so you would be well under 250ma total (150+13=163ma) using a #47 and leaving the resistor installed.
If you want to use a #44 though, you'd need to look up the current capability of the SCR on the Fireball Classic lamp driver board, and see if it can safely provide 263ma.
EDIT: I looked up the 2N5060 SCR, and it is rated for 800 ma max, so should be OK to leave the resistors mounted, even when using #44 lamps.
Yeah when I bought my xenon many bulbs had resistors and LEDs. I also bought it with two of the light not working. I troubleshot and found two bad scr's. replaced them and another one went. I ended up taking them all out and put #47s back in. I haven't had a problem since.
Can adding resistors cause scr's to go bad?