1929 A: 12volt alternator on 6 volt system??

[dwhitehead]

Cranks but won't start condition. I see a 12 v alternator with a 6 volt battery, lights are still 6 volt. There is a 30 amp fuse on top of the starter that keeps blowing so I'm not sure the solenoid is getting power. Pretty soon the battery was unable to crank the starter.
I took the battery to be tested and it failed.
Does anybody know a reason why a 12 volt alternator might have been installed during the "to the frame" rebuild. Unable to ask the man who did the work for my father-in-law. Dad did drive it in this configuration and always kept it on a 6 volt trickle charge.