100 mile Bruce,
My 2N does the same thing. It seems slow to charge.I replaced the belt with a ribbed belt and it did not really help. Tightness can be a problem as mentioned by another forum member. I run an old Wincharger system at my man cave in northern Minnesota and have worked on 6 volt generators for about 50 years give or take. You mentioned the tractor has seen a lot of use so your commutator may have to be cleaned up a bit. The spaces between the copper bars used to be mica.The spaces may have to be cleaned if the copper has worn down riding more on the spacing material than on the commutator bars. I cleaned one of my Wincharger generators and it helped a lot. Hope this helps!
Mr. T. Minnesota