[Arran]

 I had a Victor 118 with that problem once, it means that part of the speaker field coil is shorting to the basket, which means 200+ volts of B+ between you and the chassis. It really has nothing to do with the inherent design of the set so much as an insulation breakdown in the speaker, it's not supposed to do that. Knowing the way these early AC sets were normally designed the chassis was likely slightly positive with respect to ground, the true negative would be at the center tap of the power transformer, so you weren't at full potential but still more then enough to give you a good jolt, or kill if you had a bad heart.
Regards
Arran