I do not know the difference. I would guess length. My 282 has 11077 armature.
The armature tested good but it wasn't. Is your 290 motor getting hot? Try an
armature from one of your other engines. That's how I found my problem. Changing
parts till I hit on the culprit.
Look up parts diagram and find an engine that you might have with same armature and switch them out.
Looked up different its called the blue wire version. W/out oil slinger. Spec is 2&11/32 length 5/32 diam shaft copper blue coat #27 wire -75turns-resistance 1.5-1.6 ohms can be used for many steam engines.
Lets be careful, here are the armature facts. XA5969 is the number of the first postwar steamer armature. It was used from 1946 through 9/49. beginning in 10/49 an oil slinger was added to the armatures and the number XA11077 was introduced, but many XA5969 armatures were made after 10/49 with oil slingers. The oil slinger armatures are 1/16" longer and require a different brush bracket to work. the laquer wire insulation changed from clear to purple in 1951. The color means nothing other than it looks different. All purple armatures have oil slingers.
Beginning in 4/51 Pul-Mor armatures were introduced, unfortunately with the same XA11077 number. These are easy to identify because they have very narrow pole gaps. These Pul-Mor armatures will work in a non Pul-Mor Atlantic or 290. They are completely different than the super armatures referred to as the "big motor."
I neglected to mention there were several other armatures used as well. Such as the two versions of the DC motor armatures. They look identical but have a much higher DC resistance and should not be used in the universal motor engines.
I don't know what it costs to have an armature rewound. Not many people do it.
I found an old guy that repaired armatures but he never called me back. I think
he got sick and maybe died. I think it would be cheaper to just buy another one.
But before you do that you need to try an armature from one of your other locos.
Then if your 290 runs fine then get one. I bought a chassis with complete motor
for 19.95 plus shipping to get mine. A used one should be fine. They either work or they don't.
Any idea what year your 290 is from. I didn't think 290s were made in the 40s. But I don't know.
Maybe its the wrong armature. Try another armature.
I ran across 2 11077 armatures and bought them. They are brand spanking new.
From an old time train shop that went out of business. Probably will never need
them. Armatures don't go bad that often. But good addition to my parts dept. I
did have a bad armature so it does happen. I still have my bad armature and it is in
a baggy marked BAD. I am using a used armature in my 282. It runs so good I didn't
even try one of the new armatures.