Just a heads up, the amp openner sucks. I rarely works. The file idea is the best. The most important thing is, whether you use a file, a pen cap, the openner, or just your fingers,,, to wrap a layer of tape around the base and the head so when you open it, none of the glass falls in if you break any off. The pen cap and your fingers are the cheapest and work as well as any. The file just makes sure you get the cleanest break.