Yes, it’s Marx. They were issued as a AA unit in lithoed metal 1950-1954. It is full O scale and it was designed to compete with Lionel in fact, when it was sold separately, it came with a die-cast knuckle adapter which enabled it to pull Lionel cars.
It is a very smooth runner and it looks far better than the picture. As for value, I’m afraid I don’t know. Mine is part of a freight set - caboose, boxcar, tank, and hopper.
Strangely enough I 've seen a set of those on a swap in Europe a year ago. Though they should run properly, my opinion is that the Lionels are much nicer to look at. That’s because every detail of the engine is lithographed on it and the window and nose section is clamped in it, which is not a smooth connection.
But I’m no collector…
An antique store in my town has an AA set of these, along with a few cars, some track, a lithographed metal tunnel, and a steel bridge (can’t remember if a transformer was included) for $100.
This was my fathers first train set and in turn it was my first set. I really loved this one and have strong feelings for it still. This set was the set that ran around the tree when I was a kid. It looked Christmassy with red and silver twin deisels and a green box car and black hopper and gondola cars followed by a red caboose.
They are supposed to by FT units because of the portholes on the side. The A unit will not connect with cars if you don’t have the B unit with the Marx compatible coupler. The A and B are visully the same and share the #21. In a pinch you can run it with a tender if you don’t have the B unit because that is the rear coupler type on this one. Another funny thing about this one is the trucks look like they have three axles each but really only have two axles. I guess this made it easy to use these trucks in the later plastic E units they made. There were some matching Santa Fe passenger cars in a similar litho style.
One thing to consider is that these should be runn on tracks without turnouts unless you have some Marx ones because the wheels are made wider than usual with an inside gear. They will run fine with these cautions and seem near indistructable. If you find a clean set go for it.
Paul, anytime you have a real tough question about Marx and it is not answered here on the forum, the Kruger Street Toy Museum in Wheeling, WV most likely can answer your question. Many of the Marx Toys were made just south of Wheeling in Moundsville, WV. They have just about one of everything that Marx ever made.
Each year there is a train show-flea market at Wheeling and of course Marx is at many tables. Also, I see a lot of Marx at the shows around Central Ohio. After looking for about two years for a specific hopper car with specific stampings and couplers, I found it at a little show here in Columbus last month. I have seen the Santa Fe engines on several occasions.