Introduced: 1989 (Kato/Japan version), 1998 (Atlas Classic version), 2003 (revised Atlas Classic version)
Atlas's first U25B model was manufactured by Kato (Japan). The chassis/mechanism design is basically identical to the 1988 Atlas/Kato RS-1 model, so no innovations there. On the other hand, it's shell was indeed the first in N-Scale to feature separate side sill / handrail assemblies.
These models come in two different flavors - "Phase IIa" and "Phase IIb". I'm told that the differences between the two shells basically boil down to minor variations in the battery boxes and the heights of the various side-panel doors.
Features of the Kato version include a split-frame metal chassis, dual-flywheels, split-frame metal truck assemblies, blackened wheels, all-wheel drive (no traction tires), and all-wheel pick-up. The motor is a closed-sided 5-poler. All gearing is plastic. Directional lighting is provided by PC boards mounted on either end of the chassis. The couplers are truck-mounted Rapidos (open pilots). Wheels are low-profile and have no problems on Code-55 track.
Performance on these models is most excellent. They run smoothly and quietly at all throttle levels. Pickup is flawless, slow-speed creep is superb, and pulling power is impressive. The top-end speed is a bit high, but that's a minor nitpick. And running characteristics aside, these things just flat-out look great (especially as compared to other 1980's diesel models).
Trivia - in 1994, N Scale of Nevada introduced a $99 GE B39-8 conversion kit for this Kato-made mechanism.
Atlas ultimately severed their ties with Kato in the mid-90s, and in 1998 this locomotive was re-released as part of the new "Atlas Classic" line (redesigned, retooled, Chinese-manufactured remakes of the old Kato-made models) -
The Atlas Classic shells are virtually identical to the previous Kato-made shells - the main difference being the introduction of full pilots and shell-mounted couplers (still Rapidos, though). On the other hand, the chassis/mechanism is completely new -
These Atlas Classic U25B's have all the niceties we now associate with "modern" Atlas diesels - low-friction pickup, current-conducting metal strips sandwiched between the fuel tank and the chassis, DCC-Ready frame (available with factory-installed decoder), etc. And as nice as the old the old Kato models ran, these new ones run even better (a bit smoother and quieter).
In 2003, Atlas re-issued their U25B with new "slow-speed" motors, Accumate automatic couplers, and "white" LED's -
Removing the shells on the Kato version requires a bit of gentle prying with a small screwdriver. Start on one end and work your way around. Eventually the shell will come free. The Atlas Classic shells are a bit easier. I can generally wiggle them off by taking hold of the fuel tank with one hand and the shell with the other.
Grade: A (all versions)
Kato version reviewed: 5/89 Model Railroader: ("N scalers will be happy to find that a superb model of this hard-working locomotive is available. Atlas has once again worked with Kato to produce a good-looking model that runs very well. It's also a very accurate model, with its major dimensions matching those on (drawings) of the prototype... The body is made of four components that snap together: the main hoods, cab, handrail and walkway assembly, and a sill assembly. The two-piece frame and walkway arrangement is a clever bit of design and molding work that makes painting the unit easy. For while the outer visible areas that must be painted are made of styrene like the hoods and cab, the walkways, treads and railings that don't need to be painted are cast in a tough engineering plastic that doesn't take paint very well. This provided rugged railings and allows paint to be applied where it belongs.
"Mechanically, the unit follows the proven design that Kato has used so successfully in the Atlas Alco diesel models. Two cast-white-metal frame pieces, separated by insulated bushings, clamp over the motor, brass flywheels, and worm assemblies. The wheels on both trucks are driven and pick up current through wipers that rub against their backs... Our sample was a fine-running unit that didn't require any final adjustments. It started easily and ran smoothly and continuously at its minimum speed. As the speed was increased, the model went on operating well. The brass flywheels are a real advantage as the unit coasts over dirty spots, even at slow speed... This is a fine addition to the roster of N scale engines. Atlas even offers two versions of the U25B, changing the body and sill castings to match the prototypes! Like other Atlas/Kato diesels, this U25B will please many modelers. Phase IIa: undec, Santa Fe, Pennsylvania, Union Pacific and Conrail. Phase IIb: undec, Burlington Northern, Erie-Lackawanna, Seaboard System and Rock Island. Price: $79.95")