I've heard a pair of deep sockets work well, using the diameters that match best with the amp bottom and head. No chance of crushing the amp or cutting yourself. Better leverage for a nice easy clean break, as well. As others have mentioned, you can score the neck with a variety of devices, but I've heard that a $5 amp cutter is very convenient. Of course I have absolutely no personal experience, and in no way endorse taking any substance that may be illegal or harmful to your health. Always consult your doctor.