hey i have a good method which does not cause the amp to pop and send glass pieces everywhere...
get a pair of wire strippers, put the neck of the amp in the stripper made for 10 gauge wire apply on a (slight) amount of pressure while slowly spinning the amp... this will score the amp and the top will almost fall off... that amp glass is the sharpest stuff on the planet, even the smallest piece hurts like hell when its hiding in the carpet !!!:angry: LOL !!