You may notice the casing on the end of the wires here look a lot different. This is because wires from the 70's and prior were insulted using cloth or fabric. This may make them a little more annoying to strip, so keep in mind you may need more force.

Take your standard wire stripper, and using the size gauge, take your wire and put it roughly about an inch into the hole, about the length of your fingernail.

Clamp down onto the insulation, and twist the wire before pulling upwards towards the end of the wire. The insulation will fray and eventually cut off. Your end result should resemble Picture 2.

Fabric insulation can be a little trickier to remove, even after stripped. You can used your knife to very carefully cut off the ends that remain attached without any damage to the wire, but be careful as this is a bit closer to your hand.