cabin car (caboose)
1914 through 1923
Tuscan (freight-car red)
2B1F2 arch bar (leaf spring; 1940s: 2A-F5 coil)
The PRR and the Pennsylvania Lines West, at that time two separate corporate entities, the latter of which was majority-owned by the PRR, had a lot of four-wheeled wooden cabin cars, when some states in 1913 outlawed the use of wooden cabooses due to their high rate of injury. Heavy engines pushing heavy trains with the wooden cabin cars caught in between being crushed. The PRR started building the N5-series of steel-bodied cabin cars. However, the Pennsylvania Lines West couldn't afford to do so, so they started converting existing four-wheeled cabin cars. They created new steel frames, but placed the wooden bodies on top. Because the new frames had to be longer, they essentially took one-and-a-half wooden cabin cars to make one new N6b car. The trucks became the more conventional archbar trucks.
The N6a cabin cars were ones that were converted from older Fort Wayne cabin cars which had an early version of the extended-vision cupola on them. These were OK far out west, but further toward the east, they didn't clear tunnels, so the N6b was created which had a rounded roof and the cupola's side walls were slanted in to make them fit the PRR's tunnels.
The N6b, which was spotted on the Chartiers branch by eye-witnesses, has two positions of the cupola. One was centered on the car's body, and one was positioned more toward one end of the car. This entirely depended on how the car was built when its body was composed of the two wooden donor cars. The Keystone article referenced below has a photo of an N6b without the exterior sheathing on it, and you can clearly make out how the two bodies were "kitbashed" to make the one car. It is rumored that the cars with the end cupola were the "kitbashed" ones and the ones with the center cupola were built from new. While about 2/3rds of the 1,100+ cars were N6a models, eventually they were all converted to N6b, so that they could be used anywhere on the PRR's system.