901 series

The 901 series, later the 209-900, 209-910 and 209-920 series, is a group of three Japanese ten-car commuter electric multiple units operated by the East Japan Railway Company from May 1992 to August 2007. Acting as the prototype for the 209 series, the three sets were used on services on the Keihin-Tōhoku and Negishi Lines until they were retired.
==History==
The 901 series was designed in 1992 as a prototype "new-generation train" for use by the then-newly formed JR East. Three ten-car sets were built in 1992; sets Ura101, Ura102 and Ura103. Ura101 was built by Kawasaki Heavy Industries, Ura102 was built by Tokyu Car Corporation and Ura103 was jointly built by Kawasaki Heavy Industries and JR East's Ōfuna Works.
All 3 sets entered service on 7 May 1992, with sets Ura101 and Ura103 carrying a special headboard to commemorate the event. The sets were refurbished in 1994 to make them more in-line with the mass-production 209 series sets for which they served as the prototype for, and were reclassified; Ura101 was reclassified as the 209-900 series set Ura90, Ura102 as 209-910 series set Ura91 and Ura103 as 209-920 series set Ura92.
All three sets were based at Urawa Depot (now Saitama Depot). The sets were slowly retired from 2006; set Ura90 retired on 28 August 2007, set Ura91 retired on 19 December 2006 and set Ura92 retired on 7 March 2007.
==Design==
The 901 series uses a modern design with an unpainted stainless steel body very much like most JR East commuter trains; their appearance is identical to the 209-0 series sets that would soon follow.
It is said its exterior design was heavily inspired by the Milan Metro 8000 series sets.
==Specifications==
Construction is of stainless steel. Cars are 20 meters long and 2.87 meters wide. All 901 series sets were different in some way or another, including the variable frequency drives used.
Ura90 used a power transistor-based system made by Fuji Electric that made a quiet hiss when accelerating from idle; the system was later changed to a gate turn-off thyristor variable frequency drive made by Mitsubishi in 2001 as the power transistor system was unable to respond to the digital ATC signal produced on the Keihin-Tōhoku Line. This same GTO system was adopted by the full-production sets. 
Ura91 used a more generic GTO-VVVF system manufactured by Toshiba, while Ura92 used a three-level GTO-VVVF system made by Mitsubishi; the Mitsubishi system was adopted by the full-production 209 series sets.
Other than the above differences, each set has its own unique differences when it comes to bodywork. Ura90 had big one-piece side windows, pneumatically-operated passenger doors and screw-type air compressors, Ura91 had two-piece side windows, electrically-operated passenger doors and reciprocating-type air compressors and Ura92 had two-piece side windows, pneumatically-operated passenger doors and reciprocating-type air compressors along with ductless air conditioners.
==Preservation==
The following 901 series cars have been preserved:
Car number	Manufacturer 	Date manufactured	Date retired	Previous sets	Location 	Notes
KuHa 901-1	Kawasaki Heavy Industries	March 1992 	August 2007 	Ura101, Ura90	Tokyo General Rolling Stock Center, Tokyo, Japan	Ex KuHa 209-901, renumbered back to KuHa 901-1; preserved near depot's main gate
== Gallery ==
File:901 A KuHa 901 1 2010.jpg|KuHa 901-1 (ex-Ura90) on display at the Tokyo General Rolling Stock Center in August 2010
==References==
*Wikipedia.org
Category:Electric trainsets
Category:JR Group trains
Category:Built in 1992
Category:Scrapped locomotives