USA Trains has finally released its model of the SD70MAC.  Those that model modern railroads now have another large diesel to add to their roster.  The AC designation on this locomotive means that this unit in real life has AC traction motors instead of the usual DC variety.  This prototype has been produced by General Motors (EMD) from 1992 to the present, and is used by a great number of railroads across the country.  Similar in design to the Dash-9, manufactured by General Electric, these units push out 4000 horsepower with later models turning out 4300 horsepower.  AC traction motors are simple when compared to their DC counterparts, but need very expensive inverters to generate the AC power that they require.  The EPA put an end to the production of the original SD70MAC, and the locomotive was replaced by the newer more environmentally friendly unit designated as the SD70ACe.  This review will use parts of reviews written by others, and will also contain my own observations and comments based on tests on a borrowed unit.  The loco that I borrowed for this review was painted in the Susquehanna scheme, and I only had one week to play with it.
    Looking at a picture of the model does not do it justice.  To many, it looks a lot like the Dash-9 at first glance, but all "comfort cab" diesels look similar, and all are descendents of the original homely Geep that EMD produced in the 1940's.  What impressed me first was the fact that "unpacking" instructions are included so that you do not damage any of the fine details that come on the locomotive.  The packing allows you to store and transport the locomotive in its original styrofoam with the handrails on.  Other manufacturers should take note of this.  However, once you add the pilot details, you have some carving to do on the foam to get the locomotive back in the box. As usual, the snowplow and the brake hoses are a pain to install, and require CA glue to keep them in place, but once they are on, they make the model really look good.  I will not go too much into the great height debate, since this has been beaten to death on many of the forums.  Needless to say, the Aristo Dash-9 sits a little high, and the USA SD70MAC might sit a tad low.  Of course with the two different gear ratios, it would be tough to run both locomotives together, since USA locomotives tend to run faster than Aristo locomotives at any voltage.  If you do try to run them in tandem, place the USA locomotive in the lead.
    The Susquehanna locomotive that I tested had clean crisp paint and graphics.  The paint is quite bright, and I am not quite sure if it matches the prototype.  I would probably spray my USA model with a coat of Floquil Flat to get a more satin finish, and to tone down the brightness.  All the labeling on the doors and trucks is crisp and very readable.   The locomotive comes in a variety of roadnames.  Once again USA has painted the locomotives for road names that did not run the SD70MAC.  Roads such as the UP, SP, D&RGW, CSX, and CONRAIL do not have this model locomotive, but USA's paint jobs on the models looks good.  CONRAIL actually has the SD80MAC models, and the other railroads mentioned above run the Dash-9.  The ATSF, BN, and BNSF do have these units, and paint jobs are very accurate as far as these roads go.
    The detail of the cab is exceptional, but is populated by the same "clones" that USA uses in all their locos.  A repaint of the figures to more modern clothing and colors is a must for this loco, since modern engineers do not wear blue overalls and engineer caps. One figure is sitting at a computer screen, and the other must be a conductor.  Many of these locos have three crew members, with one being a brakeman which could be added by the modeler.  I especially like the safety chains on the trucks of this model.  This is a first for any model manufacturer, and a feature that many people add themselves. Of course, all the cab doors open including the one on the nose.
    The six wheel trucks use the same drive system that the original SD40-2 and PA used, which many people dislike due to the fragile nature of the mechanism.  Constant handling seems to be detrimental to this type of truck arrangement, and many people are disabling the drive on swiveling wheel set on each truck to prevent future problems.  This is a two handed model due to its length. Surprisingly it is a lot lighter than the Dash-9, and derives some of its traction from the infamous rubber traction tires that USA likes to use.   If I was going to own and run one of these diesels, I would change the traction tires out for solid wheels, remove the sliders, and add weight to the model so that it weighs what the Dash-9 does.
    Once again the switches for the lights, smoke, motor, and optional sound system are on the bottom of the loco.  I have heard many complaints about this location, and it has been suggested that they be re-located to the top of the locomotive under a removable hatch similar to what Aristo did with their SD-45, and what they will have on their E-8/9.
    The fuel tank has a plug which runs to a circuit board for an optional sound system.  I have found that with both Aristo and USA, it is better to hook your sound system track power leads directly to the power pick up wires on the trucks.  This is because some circuit boards are "funky" and cause a lag in throttle response with either Phoenix or Sierra sound systems.  This means that your loco is moving at a good rate before you get throttle up sounds, and when you shut down it also takes time for the sound system to respond.  There is some component on some of these boards that causes the problem, but I have not taken the time to find out which.
    The locomotive is a smooth runner, and the motor noise is minimal.  I could make the loco crawl down the track right out of the box.  I forgot to mention, that I opened up the gear boxes to make sure the were properly greased.  Luckily they were, but I don't take chances after killing the gears in a Geep because the factory lube had dried out.  USA made good on that one, but I am sort of anal, and like to make sure everything is right before I turn on the power.  The ditch lights are a cool feature on this locomotive.  At slow speeds they alternate, which is a real nice effect.  If I were to put a Sierra sound system system into this loco, I would have to disable this feature since Sierra allows you to have the ditch lights flash alternately or in sync, and also  flash when the horn sounds for grade crossings.  The new USA smoke unit puts out a decent amount of smoke, which is pushed by a fan.  Aristo has had this feature for years, and it gives the smoke some motion similar to a real diesel exhaust.
    Minimum diameter curves is 8 feet according to the book, but I think the loco would look better and be "happier" on at least 10 foot diameter.  Even with the supplied hook and loop couplers, the lead car kept derailing on 8 foot diameter curves until some weight was added to the car.  The train ran perfectly on the 10 foot diameter curves with no derailments.  A Kadee #831 coupler fits perfectly on this locomotive.  Once you make this conversion, the 10 foot diameter curve is a must.  One of the disadvantages of squeezing these large diesels around small diameter curves is the extreme wear and tear on wheels and gear boxes.  Replacement of these is not cheap, so take this into consideration before you buy.   Over several hours of running, this locomotive continued to run smoothly and without any problems.
    Once again we have a scale diesel that meets the needs of the modern railroader.  The exceptional attention to detail by the manufacturer is a definite plus. My pros include this extremely high level of detail, smooth motor operation, scale fidelity, and crisp lettering on clean smooth paint.  My cons are the swiveling wheel set drives on the trucks, the paint schemes that do not reflect the prototype, and the difficulty of adding pilot details.
In all, a great diesel that will please many a mainline modern railroader and is a great companion to the Dash-9 on your roster.