My first train was an AF 3/16" scale O gauge 3 rail freight headed by a PRR K5 #561. Dad was in the 47th Infantry Div and returned home to Lake Ronkonkoma, NY from Germany in February 1946. For Christmas that year Santa left a 4 car American Flyer freight set under the tree headed by the American Flyer K5. I wasn't quite 3 years old and fell totally under the spell of the electric train. I understand that set was produced by Gilbert using left over pre-war components. Unfortunately the following year's American Flyer's catalog featured only 2 rail S gauge trains. The path to expanding the Christmas set was not clear. Dad decided to go with Lionel for new equipment and track. For Christmas 1948 Santa delivered three Lionel O-27 green streamlined passenger cars. To enable the Flyer K5 to pull the Lionel passenger cars Dad machined a dummy knuckle coupler with an under side pin that fit into a hole he drilled on the upper surface of 561's link coupler. To pull AF freight cars I could lift off the dummy knuckle and couple up to the AF tinplate car's link couplers. Over the next 6 years (and with a move to a house with a basement) Santa delivered a number of Lionel locomotives, operating cars, and accessories. Occasionally I'd bring out the AF train but eventually 561's e unit failed and the locomotives's final disposition is unknown. By the time I was in 5th grade Dad convinced me to build an HO layout with him and we traded the Lionel trains in for HO equipment at a local (Bay Port, NT) hobby shop. For the next 12 years I was into HO. Years later we moved to the DC area I had the good fortune to visit John Armstrong's O scale railroad in 1971. I was totally taken by the mass and detail of O scale models. Since then it's been Pennsy O scale 2 rail all the way. I AF K5 561 with infecting me with Pennsyitis - an incurable passion.
Four years ago I was able to purchase a very clean AF 521 and a set of cars that matched my first train set. At this time of the year I set up a small table top 3 rail Xmas tree layout in my basement train room. Dad passed on several years ago - but seeing the AF train running under the tree never fails to bring back warm family memories.
An accurate scale model of PRR K5 5698 has never been offered in O scale so several years ago I commissioned master craftsman and friend Frank Miller to build one for me. Below is a shot of AF 521 side by side with 5698 on my railroad. As a young kid I never faulted the look of a 3/16th scale model on O gauge track. 
