Soviet line voltages

Up until the 1950s, most (maybe all) of Ontario and some portions of the US near Niagara Falls used 25 Hz electric power. I just did a Google of when the conversion to 60 Hz took place. I discovered that at least a few industrial users continued to use 25 Hz long after the conversion of residential use to 60 Hz in Ontario some time in the 1950s. At this point, there seems to be little, if any, 25 Hz production of electric power left at Niagara Falls. And YES!, I also remember the flicker from lighting when 25 Hz was used even though I was about 20 years old at the time. That was around 55 years ago (I turned 75 in July). If I remember correctly (as you stated above), while the flicker from mercury-vapor lamps was excessive, the flicker from ordinary incandescent lamps or bulbs was noticeable, but quite acceptable, having seen only 25 Hz powered bulbs all of our lives. I don't remember the transformers having a rattle, but then I was not very concerned at the time. Jerome Fine