PA-1 traction motors

[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.

[Ol' Loco Guy]

746 was a larger (size) motor than 726/752, originally spec'ed for electric locomotives. These two are not physically interchangeable within the same truck frame.

Remember that the FM locos you speak of were spec'ed as dual service thus they had to be able to maintain high speeds in passenger service and
have low enough MCS in order to pull heavy freights up grade. Hence, the need for the larger motor, which its attendant ability to dissipate heat without insulation breakdown.

Alco passenger units were seen as pure passenger units and the need for a low MCS (< 10 mph) was not there.

Also suspect that GE prefered to keep the 726/752 for Alco/GE production, while offering the more expensive 746 to 'outsiders.'

Appropo of nothing, much of FM's locomotive engineering staff came straight from LaGrange- Jack Weiffenbach, George Derrig, Hank Schmidt-to name a few. So, read between the lines here.

A final note-in 1953, Alco and GE went their separate ways. Around the same time, GE equipment began to show up in BLH and FM products.

[Ol' Loco Guy]

As the 746 was originally used in electric locos, it may have had a more complicated field structure in order to effect proper commutation. Consider that a DC traction generator makes 'pure DC', while the electric locos of the time made 'dirty DC' that had to be 'cleaned up' with gadgets like smoothing reactors.

So, while this field structure was essentially superfluous in the FM units, it was still reflected in the cost.

The other thing to know about DC traction motors is that there is a delicate balance between the amount of copper that can be 'stuffed' into a fixed volume and the amount of insulation required. Simply stated-more copper=more more power=more tractive force. Insulation materials have improved greatly over the last fifty years. So, what I am trying to say is that an incremental design change can alter 'performance' greatly.

[Allen Hazen]

Ol' loco guy--
Thank you for your comments. When I tried rechecking my "sources" last night (my next post will document) I found some remarks on the 746 motor which confirm some of what you point out.
In the March and April 1987 issues of "Trains" there is a two-part article on the Fairbanks-Morse diesel locomotive story by Robert Aldag (who worked for F-M, starting as a "sales engineer" and ending as head of the locomotive program, for most of the period of F-M's activity in the locomotive business). The March installment discusses the Erie-builts.
He makes the same point that you do, that the Erie was intended as a dual-service locomotive, suitable for heavy freight lugging, and with only four motors this meant F-M was trying to put a third more power into each motor than the competition did in freight units at that time, so they needed a whopper of a traction motor. (The discussion is interesting: he suggests that, whereas engine h.p. was the limiting factor with most diesel locomotives of the time, the transmission was the hard bit in the Erie, and that the Erie was thus, as an engineering problem, more analogous to the problems of electric locomotives.) The GE 746 was what was available; he says, as you do, that GE had developed it for use in heavy electric locomotives: adding the detail that it was particularly for the Virginian's and the Great Northern's.
((This would be the Virginian BBBB type -- EL-2? -- and the Great Northern's 2D+D2. Both of these were motor-generator designs, and so (???) analogous to diesels in that the traction current is from an on-board generator rather than directly from the overhead. Do you think this is relevant to your remark in your second post about the 746 possibly having a more complicated field structure? A priori, as a non-professional, I would have thought the traction motors on a motor-generator locomotive would have gotten a diet of "pure DC" just like those on a diesel electric. ???))
Aldag concludes his discussion of the Erie-builts by arguing that they were too expensive to build profitably. He points to the 746 motor -- "far heavier and somewhat more costly than the GE 752" -- as one of the Erie's high-cost features, and suggests that the 752 might have done as well. (To which last I reply that CERTAINLY the 752 would have sufficed for PASSENGER Erie-builts, though I'm not sure how the earliest iteration of the 752 would have done at 500 hp/motor in drag freight, but that in any event the 752 was not available in 1945 when the first Erie-builts were built.)
Thank you again for your comments: I always find your posts to Railroad.net forums among the most interesting!

[Allen Hazen]

(This is the "bibliography" to my initial post.)
The contemporary trade-journal articles ("Railroad Mechanical Engineer"?) referred to were reprinted in a "Model Railroading Cyclopedia," which is where I saw them. I'm not, right now, on the same continent as my copy, so can't give exact references. I've gone over the articles on the Erie-builts and the PA-1 repeatedly: I'm sure they say the F-M had 746 and the Alco 726 traction motors.
Jim Boyd's "Passenger Alcos" (Morning Sun Books, 2002-- and forgive me for forgetting Jim Boyd's name the other day!) agrees with Kirkland's "The Diesel Builders, volume two: American Locomotive Company and Montreal Locomotive Works" (Interurban Press, 1989) that the first PA/PB-1 (the Dl-304 and Dl-305) had 746 motors: 746A2, to be exact. Also that the next version, the Dl-304A/Dl-305A (first unit built 30 November 1946), switched to 752 motors. (Pp. 30,35 in Boyd's book, pp. 129-131 in Kirkland's.)
Kirkland comments "This change appears to have been the end result of performance data that was obtained in the course of road testing the two prototype units on the Lehigh Valley, before the models PA-1 and PB-1 were placed in production. The model GE 752 motor was of an advanced design that permitted substantially increasing the locomotive's haulage ratings."
Steinbrenner's book, on the other hand, says on p. 253 that "GE 726 traction motors were used in initial production of each of the locomotive models [sc. FA, PA]", and p. 255 that the initial PA design had a GT566C1 generator (everybody agrees on that) and four GE 726 traction motors, and that the first units of the next variant "delivered to the Gulf Mobile & Ohio, No. 290-291... were built to the DL-304A specification, indicative of an upgrade to the GE 746 traction motor."
--
Kirkland's book also (pp. 118,121) says that the initial FA/FB-1, the Dl-208/209, had 726 (with an option of 731!) motors and a GT564B generator, and that the next variant, the Dl-208A/209A, first units delivered in February 1947 changed this to the GT564C, and that "Coincidental with this change, the model GE752 traction motor with 74:18 gearing was made standard." (The wording is odd: was the 752 available as an option before being made standard?) So it seems that the 752 probably became available at the end of 1946.

[Typewriters]

I have, up until now, never heard of the 726 motor in an ALCO 244-engined locomotive. Only 752 and 746, so this is interesting. One wonders where this data originally came from. No listings I have here for any 538 or 539 engined units show anything other than 731 motors.....

If I consult a textbook from way-back-when, I find a speed-tractive effort table (among many other things) obtained from ALCO-GE for the 2000 HP twin-engined locomotives which are commonly referred to as the DL-109 series, even though we now know they're all not. This table clearly specifies "4 GE 730 Motors." The contemporaneous switchers are listed with 731 motors. If it helps any, the same textbook lists the continuous amperage rating on the road units as 700 amps.

It appears from the diagrams in this book that the units mentioned may be an earlier variant; so, then I get out my NYNH&H manual for road units of the 0700 class (these are DL-109's) and find the continuous limit also to be 700 amps, with the short time ratings essentially the same. Yes, this can be limited by other things, but perhaps it can help in our search for data.

Turning to the 244 engine locomotives, in manual TP-400, we find on page 830 (rev 8/49) a table giving all of the transition, overspeed and trip relay settings for all 244 engined locomotives up until that time. In this manual, the only traction motors listed for 1500 HP units are 752's. Two colums show 746 motors for 2000 HP units, both also having 64/23 gears and 42" wheels. (There is also a column for 752 motors, 61/22 gears and 42" wheels -- everything else has 40".) Thus, there is no indication in this manual that anything other than 746 and 752 motors were used.

I also wonder about some of the data regarding motor capacity. It's known that in the Erie-Built Fairbanks-Morse units, the continuous amperage rating was 1050 amps. The early 752 motors were rated 900 amps, and after 1950 the upgraded 752 was rated 1085 amps. If we assume system voltage to be about the same (which I'll check out) then the strongest motor is the later 752, with the 746 between it and the early 752.

(A few minutes separate this and my previous material.) I just checked through my son's manuals, and his all show 900 A continuous for 1500 HP and 2000 HP road locomotives with 244 engines, including back to mid 1947. I would wonder if perhaps only the very first GM&O FA units had some other traction motors.

At least -- this is what I have here, in original materials!

-Will Davis

[Allen Hazen]

Dear Will Davis--
THANK YOU! I think your information may be very useful here.
Kirkland gives various continuous ratings, but no amperages. Do you know if there is a simple formula for converting? Even for an approximation (as in: plug in a guess at some motor-specific parameter)?
539-engined switchers seem to have had 731 motors, and the 251-engined switchers generally had 752: the exception, according to (I think this is where I saw it) Kirkland, being the MLW 1000 hp switcher, which was built both with 731 and with 752.
As to 538-engined switchers... On the basis of the "Extra 2200 South" Santa Fe roster (sorry, not on right continent to get exact reference) and, I think, the New York Central diagram book online at George Elwood's "Fallen Flags" site, I think the High-hood switchers had traction motors with model numbers in the 200 series. I have wondered, but without ANY relevant information, whether the "new" 731 motor apparently introduced on the "low-profile" switchers of 1940 was really a new motor or just a new system of motor model-numbering...
Kirkland and at least one other source (an article in a model railroad magazine, which I won't be able to get a reference for until I get back to my usual office in May) agree that the "Needle-nose" passenger units (don't you like the skillful way I dodge the debated question of their specification numbers?) were available with either 730 or 726 motors. I think they are independent sources: each contains information not in the other.
Kirkland says that the FA/FB-1 initially had an option of 731 motors; doesn't say if any were actually built with this option.
Sorry I can't say more: this post was mainly confessing the limitations of my knowledge!

[Typewriters]

Right on, Allen, and good catch. The motors for the NYC high-hoods were GE 287 model. These were built 12/38 through 5/39. Interestingly, the old tri-power units are listed with model 286, if anyone's keeping tabs.

Immediately following the high hoods, you have the 539 engine units, all listed with subvariants of the 731 motor.

The book I mention lists the dual-engine road units (DL-105, DL-109 I suspect) with GE 730 motors. Note that --- 730. I have found two things to be true in this little investigation; one, that this is the only place I find any reference to a 730 motor, and second, that I find NO reference to any 726 motor. I am becoming curious where, in original manufacturer materials, I'd have to look to find a 726. One wonders if this isn't some kind of misprint somewhere. You know how it is; one single railfan source prints one wrong thing, and then it spreads like wildfire, and soon everyone's quoting something that's wrong. Not saying yet that this is the case here --- but you and I (and everyone) know that this happens.

So, then, if you combine my previous post with your data and my further data here, it would seem as if the road unit DL-103/5/7/9 locomotives were fitted with 730 motors for sure, with the possibility of some yet-undetermined other motor, be it a 726 or the known 746. The PA units were fitted, it appears with 746 very early and rarely, and 752 for the majority, and the FA units fitted with 752 again for the most part, with the earliest units perhaps being fitted with either the 726 or 746.

Confusing, eh? Of course, we all know that what's SPECIFIED is not always what's actually built. You will find many unbuilt specifications, and so I wonder if the table given in the actual ALCO-GE manual, listing only 746 and 752 motors for 2000 HP passenger (244) units, and only 752 for 1500 HP freight units, isn't correct after all.

It looks as if we might have to find something official concerning these early units to nail down traction motor model numbers. Anyone out there have a listing of just which 2000 HP and 1500 HP units would be included in this group? IE, the group which do NOT have 752 motors? Perhaps then we can locate railroad-specific materials to give us the answer, or else find out what the root of the mentioned authors' information really is.

-Will Davis

[tgibson]

Here is a site which mentions the 726 traction motor:

http://www.magnus-farley.com/prodref.html

Hope this helps,

[Allen Hazen]

Dear T. Gibson--
Thanks!
Comments:
(i) I think we can take this as confirmation that the 752 was a development of the 726: the 726 has parts shared with (what I take to be) the earliest versions of the 752 (A, C, E1).
(ii) Do you suppose there are many 726 motors out there to seel spare parts for? Since the last domestic locomotives to use it were some of the first Alco FA-1 and RS-2 (and ***maybe*** PA-1), I wouldn't expect many to be still in use on locomotives, but there are other applications for electic motors of the size of locomotive traction motors.
---
I will post more of what I have found in a day or two (after copying down stuff from books I don't want to have to lug to where I have computer access).
---
One thing. Since Kirkland mentioned the 726 as used on Dl-109 in FREIGHT service, and the New Haven famously used its as dual-service, I
had ASSUMED that the New Haven's Dl-109 had 726 motors. I've found a bit of confirmation: the Summer 1977 (I think) issue of the NHRHTA magazine, "The Shoreliner," has an article on the New Haven's Dl-109, with a table showing them all as having had the gear ratio (62:21 I think) which Kirkland cites as used for 80mph top speed with the 726 motor: the gear ratio for this speed with 730 is different. (Part of the "Shoreliner" writeup is a reprinting of an article by Win Cuisiner that had appeared in some earlier issue-- date not given-- of "Extra 2200 South". It isn't clear whether the table with the gear ratios is part of this reprinted material.)

[Allen Hazen]

I've been trying to find more in my files (which are mostly "railfan scholarship": I can, but won't bother unless someone is interested, give specific references: for the most part, old "Extra 2200 South").
George Elwood's "Fallen Flags" railphoto site has excerpts from both the Pennsylvania Railroad and New York Central locomotive diagram books: there is no consistency in the sorts of information recorded (motors are sometimes just 752, other diagrams specify form, etc etc etc). But:
---
Typewriters quoted above limiting amperages for some GE traction motors:
700A for what's in Dl-109 (probably 730)
900A for "early" 752 (maybe 754A and 752B?)
1050A for what's in Erie-builts (746)
1085A for post-1950 752 (752C? or 752E1?)
I can add some later developments:
1195A for 752E6 through 752E9
1260A for the 752AF
(The 752 model progression seems to have progressed from E1 to E3 by the mid 1950s: Alco's RSD7 and GE's "small" turbines for UP had the E1, the RSD15 and the "Big Blow" had the E3. The 752E6 is no later than the mid 1960s, being used on some but not all U25B and contemporary Alco types. The 752E7 came by about 1967: it was used on Alco C636 and some C630. The E8 was used on some U23B, so dates from no later than 1977. The 752AF was introduced, along with the GTA24 alternator and the Sentry wheelslip system, on the B36-7 in 1980.)
---
The 752 was used with the 74:18 gear ratio from the beginning up to the mid 1980s. (Apparently this tooth-size limited it to 750hp/axle, so GE went to the 83:20 gearing-- very nearly the same ratio-- for the 752AF.) Top speed with this ratio was initially 65mph, upped to 70mph no later than 1962 (PRR's RS-27, with 752E3 motors, is shown as having the 70mph top speed).
---
At last I get to continuous tractive efforts. For ease of comparison, I am glad to have found a bunch of four-motor locomotives all with 74:18 gearing!
Initial FA-1 (with ?? 726 ?? motor): 34,000 lbs at 13.5mph
Later FA-1 (752A or 752B): 42,500 lbs at 11 mph
FA-2 (752C1 motors): 52,500 lbs at 9.4mph
RS-11 (?? 752E3 ??): 53,000 lbs at 10 mph
RS-27 (752E3): 50,800 at 14mph.
(The FA-1 was nominally a 1500 hp locomotive: at the continuous ratings given it was putting out 1224 of 1247 hp, neatly bracketing the traditional 82% efficiency quoted for American DC-motored diesel-electrics. The two versions of the FA-1 quoted had GT564B and GT564C generators; I hope the differences in generator model are just a matter of "peripherals" -- replacing belt-driven with gear-driven auxiliaries, etc. The three later locomotives have GT581 generators and 1600, 1800 and 2400 hp ratings.)
---
Fonally, some generator stats (from New York Central diagram book):
GT566C1 in a PA-1:maximum voltage 790, full load voltage 735, capacity 1400kw.
GT566C1 in a PA-2:max 780V, full load 755V, capacity 1550kw. (Don't ask me why things change with the same generator; there are a few other anomalies in the NYCRR diagram data.)
GT564C1 in FA-1: max 900V, full load 850V, capacity 1050kw
GT581A1 in FA-2: max 865V, full load 845V, capacity 1100kw.
---
I have more, but this post is already too long! Later.

[Allen Hazen]

--Just to show why you should always use GE traction motors and not off brands (grin!), the Pennsylvania Railroad had some of its EMD F-3 locomotives delivered with special low (65:12) gearing for helper service (Class EH-15). With this gearing, the F-3 had a top speed of only 50mph, but managed a continuous rating of ... 42,500 lbs at 11 mph. Which is, of course, the same as the (752 motored) FA-1 with 65mph, 74:18 gearing! Most PRR F-3 had 62:15 gearing that allowed them 65mph (Class EF-15), but this gave them a contiuous rating of 32,500 lbs at 14.25 mph: not even as good as an FA-1 with 726 motors.
---
Ol' Loco Guy, a while back, pointed out that the 746 motor was biggerthan the 752, and that the two were NOT interchangeable in the same truck frames. One hopes, however, that the truck frames can be modified to accept the other motor: Doyle McCormack,after all, is using Erie-built trucks in refurbishing a PA, and I suspect 746 motors are hardto find these days. ... At least in external appearance, the rear trucks on 5-axle C-liners were the same as those on the Erie-builts, so this truck could apparently be modified to accept GE746, Westinghouse 370 or (on the last CPA16-5 for CN) GE752motors.

[Typewriters]

It looks by the reference Mr. Gibson gave, which is a site offering bearings, that there is at least some parts compatibility between the 726 and 752, and it would probably be safe to assume that the 752 is an improved 726 from all that we have now.

One could also easily assume that advances in materials and design would allow the smaller frame motor, ie the 726, to equal (900A) and then later surpass (1085A) the larger and thus theoretically more expensive 746 motor; that's how you'd decide to drop the 746 and modify the 726 into the 752 if you were GE and looking at making profit.

I think then we can safely assume that at least a few early 244 units might have had "other" motors, meaning that there could have been some 1500 HP freight units around with 726 motors, and that there were 2000 HP passenger units around with 746 motors.

(I am loathe to use model numbers here. ALCO manual TP-406 is in my hand right now, which states on its front cover "2250 HP Diesel-Electric Passenger Locomotive," and on its front page "this manual covers basic operating instructions to assist the Engineman in the efficient handling of the 2250 HP Passenger locomotive models: PA1, PB1." You see why our modern-day "application" of model numbers is ... well.... suspect.)

My son's large-format maintenance manual, April 1947, lists only the 752 motor. (5GE 752A1 to be exact.) It's for the 1500 HP road units.

HOWEVER, close inspection of his "1500 RO" --which is the very early-style operators' manual for what we call the FA -- dated 5/47 has a different ammeter from all of the other manuals. (Including his 8/47 version of exactly the same manual.) Actually, these manuals of this style have two ammeter illustrations; the first, in the operating section, and the second in the dynamic braking section. Usually, they match; in this one, they don't. The one in the dynamic braking section is the usual, familiar one, with 900 A limit, meter topping out at 1400 amps.

In this 5/47 manual, the loadmeter illustration in the operating section tops out at 1200 amps. The continuous limit appears to be 750 amps -- this is where the yellow range starts, and yellow (that's the 90 minute range) tops out at 900 amps.

THUS, we have a problem. If this is a misprint, or mistake, it was then corrected in the later manual. But from where does that illustration come? Perhaps it was mistakenly carried over into the 752 range of manufacturing dates, and was originally in a manual for an FA with 726 motors. You'll note the close approximation to the 700 A limit on the DL-109. (Naturally, amp limits can be not just due to motors, but also due to generators, cabling, cooling -- but it's a start.)

That oughta fuel your imaginative fires, eh? I missed that different ammeter when I looked before. But I'm sure now that it's VERY different, and will help nail down what we're looking for.

-Will Davis

PS The 1500 RO could be called the "black cover" manual of early ALCO-GE manuals, whereas the later ones begin to have colored covers.

[EDM5970]

Going back to Allen's endorsement of GE motors over "off brand", I have a little story to share. I'm involved in an Alco restoration project, and we have equipment on a shortline that has a nice bunch of GP-9s. The shortline is doing much of the heavy work for us, like truck and TM swaps, using their jacks and truck transfer table.

The MM there and I were talking about TMs; his forklift can handle an EMD motor and axle combo, but not a GE combo. No numbers are available, but he feels that the GE 752 motor weighs twice what an EMD motor weighs.

This goes back to something that I once researched and maybe posted here a long time ago. The first EMD motor (D-7?) was based on an earlier GE design (716?), to the point that you could put an EMD armature in a GE frame, etc. To my knowledge, and I'm not all that up on EMDs, the early D-7 is the same physical size as the later D-77. If so, the D-77 is a highly developed descendent of the 716, with newer, thinner insulation and lots of copper crammed into it. Or am I stretching things a bit here?

Another interesting point is that there are a lot of GE U-boats and -7s, etc, running around with Blombergs that were modified or specially built to
accomodate GE 752 motors. Yet on the shortline above, the EMD motors do just fine, at 400 plus HP each.

Will, I've also seen illustrations that don't quite match, but that may be because Alco/GE may have used a stock photo from their files. My favorite picture is the very distinguished gent, with suit and tie, listening to a generator bearing with a listening rod. Not my usual locomotive attire, I buy expendable, used work clothes at the flea market!

[Allen Hazen]

EDM5970--
Thanks! I've been trying to find more relevant information in my personal library (I'll make a big post in a few days), and did manage to dig up ONE reference to the GE 716: it was apparently the traction motor used on one of the first streamliners, Union Pacific's M10000. Given the low power (600hp? 900? I forget) of this locomotive (well, articulated train power car) I had assumed that it would have used a smaller traction motor than that used on, e.g., early EMD E-units, but....
I'm not sure of my memory here, but I think Kalmbach's "Our EMD Scrapbook" (compilation of old "Trains" articles, mostly-- I think-- by David P. Morgan) somewhere says that the basic EMD traction motor was pretty much a copy of the GE motor they had been using before opening the La Grange plant and making their own electrical gear, and that EMD armatures "until recent times"-- this was probably published in the late 1960s-- were interchangeable with armatures from GE motors of the 1930s.
As for weights, the GE 752 may be somewhat heavier than an EMD motor, but I doubt it's twice as much. (My impression is that traction motors for typical American diesel-electrics all weigh around three tons, give or take a few hundred pounds: but if someone with actual numbers wanted to post them....)
Anyway, thanks!