10:27 PM
@rdtsc . Early era vacuum tube units, (1930's and 40's) used input isolation transformers. After that when the radios went to using 5 tubes (all American five), there was no isolation transformer. And this was done in the era when a 120 volt outlet had only two pin receptacles.
No ground receptacle. The radio metal chassis therefore was either line (live) or ground, depending upon which way the 115 volt plug was plugged in. It was common for the plastic knobs on radio to break and fall off. Tuning or volume adjustment was shocking. However, never knew anyone who was injured
Of course after you got shocked, you reversed the plug in the outlet, and then you marked the plug and receptacle so to make the chassis grounded. Didn't need a new plastic knob over the metal controls
