Before they became mini-Shinkansen lines:

[Sacto1985]

I just found a couple of zenmen tenbō videos of travel on the Ōu Main Line from Fukushima to Yamagata and Tazawako Line from Morioka to Ōmagari, both before they were converted to mini-Shinkansen lines:

 

Fukushima to Yamagata

 

 

Morioka to Ōmagari

 

 

You can understand the changes needed to accommodate the mini-Shinkansen trains.

 

For comparison, here is what these lines look now, upgraded to mini-Shinkansen service:

 

Yamagata to Fukushima

 

 

Morioka to Ōmagari

 

 

Because the line upgrade to mini-Shinkansen service, JR East had to modify a number of 701 Series train sets so the rail gauge on the modified train sets are 1,435 mm, not the original 1,067 mm.

 

Speaking of the Ōu Main Line, due the storm damage on the line between Shinjo and Ōmagari in July 2024, there is now serious consideration by JR East to just dismantle the 20,000 volt 50 Hz AC overhead power on that part of the line. Given that they were using 701 Series train sets almost exclusively on that part of the Ōu Main Line anyway, they would replace them with additional 110 Series or even EV-G400 train sets in non-electrified service. (I doubt they will dismantle the 20,000 V 50 Hz overhead power on the Uetsu Main Line south of Akita, since JR Freight trains regularly use that line.) YouTube member ayokoi talked about the change in this video:

 

 

[miyakoji]

Good finds Sacto.  I've always been interested in those regular types (701 and 719 I think) that were converted to or built as 1435 mm gauge.