Southern Pacific class AC-6

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Southern Pacific class AC-6
Type and origin Power type Steam Builder Baldwin Locomotive Works Serial number 61353, 61354, 61382-61389, 61416, 61426-61429, 61491-61494, 61535-61538, 61543, 61544 Build date May–December 1930
Specifications Configuration: ​  • Whyte 4-8-8-2 Gauge 4 ft 8+1⁄2 in (1,435 mm) standard gauge Driver dia. 63 in (1,600 mm) Adhesive weight 517,000 lb (235,000 kg; 235 t) Loco weight 639,500 lb (290,100 kg; 290.1 t) Boiler pressure 250 psi (1.7 MPa) Feedwater heater 6S Worthington Cylinder size 24 in × 34 in (610 mm × 864 mm) (bore × stroke)
Performance figures Tractive effort 124,300 lbf (553 kN)
Career Operators Southern Pacific Railroad Class AC-6 Number in class 25 Numbers 4126 – 4150 First run July 10, 1930 Retired 1953 – 1955 Disposition scrapped

Southern Pacific Railroad's AC-6 class of steam locomotives was the third of the railroad's classes built with a 4-8-8-2 wheel arrangement. Like the earlier AC-4 and AC-5 classes, the AC-6 class were cab forward locomotives. The AC-6 was slightly larger than the previous classes with a higher boiler pressure and tractive effort rating.

In 1947 and 1948, this class was rebuilt with cast steel frames, increasing the overall weight to 648,000 lb (with 523,600 lb on the drivers). At this time, most of the locomotives in the class were also equipped with larger cab windows that became standard for SP's cab forward locomotives beginning with the AC-8 class. One of those locomotives that had been turned from AC-6 to AC-8 was the number 4146.

This class was removed from active service between 1954 and 1955 and they were all scrapped by March 1956.