I also photographed Tobu 9000 Series on Tokyu Toyoko Line.
9102F set in my photograph was the first-made mass-production model of 9000 Series and was manufactured in 1987 and refurbished in 2007.
In 2024, 9000 Series is one of the rare armature chopper control carriages, as well as JR West 201 Series, Hiroshima Electric Railway 800 Series, and Hiroshima Rapid Transit 6000 Series. Armature chopper control was put to practical use in the 1970s and was mainly introduced among subway carriages. In the 1990s, variable frequency drive became popular and profitable for maintenance. Though many carriages were gradually converted from ACC to VFD (for example, Tokyo Metro 6000, 7000, 8000 Series, Kyoto Municipal Transportation Bureau 10 Series, and Transportation Bureau City of Sendai 1000 Series), 9000 Series wasn't done.