by Allen Hazen
The 2000 hp PA-1 (and PB-1) passenger units of 1946-1949 were built under three different specification numbers: Dl-305, Dl-305A, Dl-305B. (Sorry, I've forgotten whether 305 was for the PA and 306 for the PB, or 304 the PA and 305 the PB: in either case, the series of Blank, A and B "submodels" is parallel for the cab and booster units.) At least one of the technology upgrades marked by the change in specification had to do with a change in the model of GE traction motors used. I was looking at a variety of sources (Kirkland's Alco volume, Steinbrenner's Alco Centennial book, and "Passenger Alcos" whose author I seem to be having a "senior moment" about) last night, and there seems to be some confusion about the particular traction motor models involved. One source said the Dl-305 had the 746 motor, with the change to the 752 in the Dl-305A, whereas another said the first submodel had the 726, with a change made to the 746 in the A-submodel (in which case the 752 would have been introduced in the B-submodel).
So my question is...
A contemporary trade-magazine article describing the first PA (Santa Fe 51) which I have seen gives the 726 as the traction motor used. The 746 (apparently a more expensive, more elaborately ventilated, model) and the 752 (apparently a massively upgraded 726) would both have been higher output models. I can IMAGINE an initial use of the 726 (which was successfully used in the New Haven's Dl-109 fleet), followed by a decision to use something more robust, with the 746 (which had been introduced in 1945 on the Erie-built units GE built for FM), followed at last by the 752 (cheaper than the 746, but a new design that hadn't been available when the PA was designed. But does somebody KNOW?
Background (from the related query about Erie-built t.m.s I have just posted to the FM forum): By the late 1940s, GE seems to have standardized on the 752 as its basic motor for large locomotives: Alco's, Baldwins and FMs after Westinghouse quit, GE's own U-series. Before that... Pre-war Alco Dl-109 had either 730 (for exclusively passenger service) or 726 (for dual service, as on the New Haven). According to a post to some Railroad.net forum a while back, the 752 was an upgraded and improved version of the 726 (fairly major upgrade, given the tractive efforts cited (in Kirkland's Alco volume) for 726 and 752 equipped Alco FA-1, though the upgrades made between 1950 and the 752AH used on GE's Dash-9 freighters without changing the model number are surely greater!). According to a "Trains" magazine article on FM locomotives from a few years back, one of the things that made it difficult for FM to compete was that they had chosen the 746 motor, which was more expensive (I think it had more elaborate ventilation features). At a GUESS: in 1945, when the Erie was introduced as a dual-service use, suitable for heavy freight, FM decided they wanted something more robust than the 726, and the 746 was what GE could offer them, only later achieving comparable performance from a cheaper, 726-derived, model, the 752. BUT THAT'S JUST SPECULATION.
So my question is...
A contemporary trade-magazine article describing the first PA (Santa Fe 51) which I have seen gives the 726 as the traction motor used. The 746 (apparently a more expensive, more elaborately ventilated, model) and the 752 (apparently a massively upgraded 726) would both have been higher output models. I can IMAGINE an initial use of the 726 (which was successfully used in the New Haven's Dl-109 fleet), followed by a decision to use something more robust, with the 746 (which had been introduced in 1945 on the Erie-built units GE built for FM), followed at last by the 752 (cheaper than the 746, but a new design that hadn't been available when the PA was designed. But does somebody KNOW?
Background (from the related query about Erie-built t.m.s I have just posted to the FM forum): By the late 1940s, GE seems to have standardized on the 752 as its basic motor for large locomotives: Alco's, Baldwins and FMs after Westinghouse quit, GE's own U-series. Before that... Pre-war Alco Dl-109 had either 730 (for exclusively passenger service) or 726 (for dual service, as on the New Haven). According to a post to some Railroad.net forum a while back, the 752 was an upgraded and improved version of the 726 (fairly major upgrade, given the tractive efforts cited (in Kirkland's Alco volume) for 726 and 752 equipped Alco FA-1, though the upgrades made between 1950 and the 752AH used on GE's Dash-9 freighters without changing the model number are surely greater!). According to a "Trains" magazine article on FM locomotives from a few years back, one of the things that made it difficult for FM to compete was that they had chosen the 746 motor, which was more expensive (I think it had more elaborate ventilation features). At a GUESS: in 1945, when the Erie was introduced as a dual-service use, suitable for heavy freight, FM decided they wanted something more robust than the 726, and the 746 was what GE could offer them, only later achieving comparable performance from a cheaper, 726-derived, model, the 752. BUT THAT'S JUST SPECULATION.