How to determine hot wire in old 110v Al wires

[electro]

I am replacing old receptacles (two prongs porcelain) with new GFCI outlets, but didn't know which cable is the hot one. Any hint?

[ramfan]

Electro
You can go to any home repair store and by a circuit or line tester for under $20 it will light up and buzz when placed over the hot wire,All you do is place it in the prong it will only light up on hot only,not nuetral or ground.The power must be on,so just place tester in outlet socket for safety.Ckeck on a none good circuit first always prior to use.

[electro]

Thanks for your hint. Sometimes we forgot simple solutions.