This was the first really high quality North American prototype locomotive model from Arnold. And as such, it pretty much sounded the death knell for their earlier (and much more primitive) attempts at N scale locomotives (their "baldwin switcher" and "F9" models). Internally, the FP9 chassis and mechanism appear to share the same basic design as Arnold's European V200 diesel (actually sharing many of the same parts). However, this was not simply a "stick a new shell onto an existing mechanism" type of operation. The FP9 chassis was clearly designed specifically for the FP9 and, as such, has never been used in any other model.
These models were originally imported by Revell (a relationship that lasted until around 1972). These early units can be found in cardboard Revell packaging. Post-Revell, these models were imported primarily by Walthers (although there were probably other importers as well). These models were packaged in the familiar Arnold plastic jewell box with the orange paper inserts (that, annoyingly, don't actually say what's inside the box). Arnold was eventually acquired by Rivarossi and the entire line of Arnold N scale locomotives pretty much vanished from the face of the earth when Rivarossi went bankrupt and was liquidated circa 2006. I'm not aware of any major revisions to this model (Arnold's modus operendi apparently being to design a locomotive and then run with it... for decades).
This is a very solid locomotive in all respects. The shells are nicely painted and detailed, and the mechanism is quite good. All wheels are geared and provide pickup. Throttle response is very smooth and slow speed creep is excellent. The all-metal chassis provides plenty of heft and pulling power. Internally, nothing is soldered. And although a couple of wires serve to move current around, they are quite stiff and not connected to any moving parts. The motor is an enclosed "can" job (and presumably a 3-poler). A non-directional headlight is mounted on the front of the chassis.
On the downside, the couplers are "Rapido" style (obviously), and mounted to the trucks - a pretty typical arrangement for 1960s-era locomotives. Also, all of the gearing is metal, so these things are extremely loud (I mean barbershop razor loud).
Arnold offered dummy versions of both the "A" and "B" units (although the "B" units came along a little later). The couplers on the "B" unit are molded right into the trucks and are somewhat differently sized/shaped than typical Rapido couplers. An "A" chassis cannot be used to power a "B" shell without major modification.
These models are easily distinguished from Arnold's earlier "F9" models. Among other differences, the early 1960s F9s had flat metal truck sideframes (no detail whatsoever) whereas these have detailed plastic truck sideframes.
Reviewed: 11/67 Model Railroader ("The new Rapido diesel is a considerably improvement over the original F-type diesel produced by this firm. The new model is fashioned after EMD's FP9 freight-passenger 1750-horsepower unit. The model is well proportioned and in general follows scale dimensions; some liberties have been taken to accommodate the mechanism and couplers. The front truck sits back about a scale 18" and the rear truck forward about 6", making the truck wheelbase closer to the F9 wheelbase then the FP9. Over all, the appearance is good. The ready-to-run model comes painted and lettered. The body is a one-piece plastic casting with all details cast on. The winterization hatch over the rear fan should be about 12" higher rather than flush with the roof - a correction can easily be made with scrap polystyrene, wood, or cardstock. Clear plastic material simulates cab windows. The plexiglass headlight and number boads are illuminated by a 12-volt lamp in parallel with the motor. The mechanism of this unit is considerably better than the one used in Rapido's early F-unit diesel. New sideframes are close copies of those found on the prototype as opposed to the blank sheet metal trucks of earlier models. Wheels scale 48" in diameter (prototype wheels are 40" in diameter) and with the .040" deep flanges are nearly 5 feet in overall diameter. The oversize wheels are not too apparant when the model is on the rails. The frame is a one-piece zinc alloy casting to which the trucks, motor, electrical contacts, and lamp are ingeniously attached by an interlocking system of components. Rapido autocouplers are truck-mounted front and rear. A new, improved drive is quiet and smooth. All eight wheels are powered through a combination worm-and-gear/spur-gear drive; all eight wheels are used for electrical pickup for the 12-volt DC permag motor. Our test sample had a slight lurch when starting... Speeds are on the high side, but control is good. Full wheel-slip current is on the safe side, but the superstructure is so completely filled with frame and mechanism that there is no room to add more weight for pulling more cars. The model should handle 25 to 30 average N scale freight cars... This smooth-running model retails for $14.98, powered and lighted. It is available with B&O, NP, PRR, or SF color scheme and lettering. Dummy units are $4.98 each.")
Discussed: 01/68 Model Railroader ("The most interesting change in the new Revell/Rapido line is an entirely new diesel based on the EMD FP9 prototype. The running gear for this engine is an adaptation of one of Rapido's newest designs first offered in strictly European-prototype diesel and electric locomotives. There was a problem here. The more common F9 diesel prototype is too short, when reduced to N scale, to fit over the newer Rapido chassis. Some clever individual discovered that the full-size FP9 was about 4 scale feet longer than the F9; and the Rapido engineers were off and running with a new American-prototype locomotive. Briefly, the older Rapido F9 offered only four-wheel traction and no truck detail. Its appearance could, at best, be considered semiscale. The new Revell/Rapido FP9 has eight-wheel power, plus more weight for traction and excellent truck detail. The detail and proportions are much in keeping with that expected of a scale model... To allow proper operation... the couplers were mounted on the trucks... This forced the designer to make the pilot pivot with the front truck... We prefer this front coupler-pilot arrangement to the alternate of an oversize coupler pocket. The rear coupler protrudes too far, so that the gap between car and locomotive is greater than between car and car. This mounting needs to be redesigned to improve its realism. The extra weight in the new FP9, plus its eight-wheel drive, allows it to pull about 30 cars... a 30% improvement over the older F9. No B unit is offered this year, but a dummy A is available.")