New guy!!

I am new to this hobby but not the obsession with tractors. My question is, I just purchased 2 B models. From what I can tell one is a 1950 (serial # B263494) and one is a 1939 (serial # 62845). Can someone verify these for me.
Another question: I was told by the seller, who knew nothing about them, that the '50 was a 6 volt system. I bought a 6 volt battery and it turned over very slow. On a hunch I put a 12 volt battery in it and it spun over beautifully. How do I tell whcih it is? When it was runnign with the 12 volt I turned the lights on and they worked fine. If it was a 6 volt system wouldnt the bulbs blow?

Thanks for any help!!!