(Perhaps this should have gone on the Alco forum, but the Railroad.net index says this forum is for GE locomotive "technology.")
The Alco 500-series (531,538,539, each in normally aspirated and turbocharged versions) was used in new locomotive production for thirty years, from the demonstrator switcher 600 of 1931 to the last RS-1 light roadswitcher in 1960. The overwhelming majority of the locomotives with these engines had General Electric electrical equipment. (In the 1930s a few customers got switchers, and GM&O three streamlined-train power cars, with off-brand electricals, but GE-equipped units outnumbered "off-brands" 56 to 28 among units with the 531 engine, built 1931 to 1938 (with one unit(*) completed in 1939), and 81 to 15 among those built with the 538 engine from late 1938 to mid 1940.)
Six different models of GE main generate were used with these engines.
For normally aspirated engines
--The GT526 was used from the start, and for all but the last 531-engined switcher. (All these were rated at 600hp.)
--The GT551 was used on the last 531-engined switcher and on those-- some rated 600hp and some 660hp-- with normally aspirated 538 engines.
--The GT552 was used on the "low profile" 660 hp switchers (S1,S3, MLW S10 and S11) introduced in 1940. Since the 551 was, at the time, a new design, incorporating whatever lessons Alco and GE had learned in seven years of switcher production, I assume the 552 was internally a duplicate of the 551, the model change reflecting the different support arrangements for a generator attached to an engine recessed into the frame.
For the supercharged engines
--GT542 on switchers starting in 1937, some with 531T engines and some with 538T. (All the GE-equipped 531T powered locomotives were rated 900hp. (So were most of the W'house equipped 531T units, but one was uprated to 100 hp.) Some 538T units were rated 900hp, some 1000hp: power rating was apparently negotiated between Alco and the customer for each order, and the installed equipment was basically the same.
--The GT542 was also used on Rock Island 624, the prototype of the Dl-10-whatever 2000 hp passenger unit, which had 538T engines.
--The GT553 was used on "low profile" 1000 hp switchers and RS-1 (and MLW RS-13) light road switchers with the 539T engine. Since GE had revised the design of the lower-rated generator (from the GT526 to the GT551) a couple of years earlier, the GT553 probably incorporated similar design updates as well as the support arrangements for use with a low-mounted engine.
--The production DL-10? units used 539T engine, but mounted above the deck. (Don't ask me why Alco didn't use the 538 engine, which stayed in production for stationary and marine applications.) They used GT557 generators. At a guess, this is internally the same as a GT553, but with different mounting arrangements.
(Based on data in John F. Kirkland, "The Diesel Builders, volume two: American Locomotive Company and Montreal Locomotive Works," Interurban Press, 1989.)
(*) This was an Alco plant switcher, utilizing an engine that had been used as a stationary test engine: Kirkland says it "appears to have been built largely from surplus obsolete equipment and intended only for use as a Schenectady in-plant switcher." For the history of technical developments, therefore, it is best regarded as a distraction.
The Alco 500-series (531,538,539, each in normally aspirated and turbocharged versions) was used in new locomotive production for thirty years, from the demonstrator switcher 600 of 1931 to the last RS-1 light roadswitcher in 1960. The overwhelming majority of the locomotives with these engines had General Electric electrical equipment. (In the 1930s a few customers got switchers, and GM&O three streamlined-train power cars, with off-brand electricals, but GE-equipped units outnumbered "off-brands" 56 to 28 among units with the 531 engine, built 1931 to 1938 (with one unit(*) completed in 1939), and 81 to 15 among those built with the 538 engine from late 1938 to mid 1940.)
Six different models of GE main generate were used with these engines.
For normally aspirated engines
--The GT526 was used from the start, and for all but the last 531-engined switcher. (All these were rated at 600hp.)
--The GT551 was used on the last 531-engined switcher and on those-- some rated 600hp and some 660hp-- with normally aspirated 538 engines.
--The GT552 was used on the "low profile" 660 hp switchers (S1,S3, MLW S10 and S11) introduced in 1940. Since the 551 was, at the time, a new design, incorporating whatever lessons Alco and GE had learned in seven years of switcher production, I assume the 552 was internally a duplicate of the 551, the model change reflecting the different support arrangements for a generator attached to an engine recessed into the frame.
For the supercharged engines
--GT542 on switchers starting in 1937, some with 531T engines and some with 538T. (All the GE-equipped 531T powered locomotives were rated 900hp. (So were most of the W'house equipped 531T units, but one was uprated to 100 hp.) Some 538T units were rated 900hp, some 1000hp: power rating was apparently negotiated between Alco and the customer for each order, and the installed equipment was basically the same.
--The GT542 was also used on Rock Island 624, the prototype of the Dl-10-whatever 2000 hp passenger unit, which had 538T engines.
--The GT553 was used on "low profile" 1000 hp switchers and RS-1 (and MLW RS-13) light road switchers with the 539T engine. Since GE had revised the design of the lower-rated generator (from the GT526 to the GT551) a couple of years earlier, the GT553 probably incorporated similar design updates as well as the support arrangements for use with a low-mounted engine.
--The production DL-10? units used 539T engine, but mounted above the deck. (Don't ask me why Alco didn't use the 538 engine, which stayed in production for stationary and marine applications.) They used GT557 generators. At a guess, this is internally the same as a GT553, but with different mounting arrangements.
(Based on data in John F. Kirkland, "The Diesel Builders, volume two: American Locomotive Company and Montreal Locomotive Works," Interurban Press, 1989.)
(*) This was an Alco plant switcher, utilizing an engine that had been used as a stationary test engine: Kirkland says it "appears to have been built largely from surplus obsolete equipment and intended only for use as a Schenectady in-plant switcher." For the history of technical developments, therefore, it is best regarded as a distraction.
