Another alternator question

[Zoom]

I have a pair of 1930 A's both have Nu-Rex 6v alternators with the same size pulley. The Tudor has to be revved up quite a bit for it to start charging which I understand is normal. The pick up will charge as soon as the engine fires up. I'm wondering if anyone can explain why the pick up charges right away (which is nice).
Thanks
Dirk

 

[John]

Assuming that they both have the same wiring setup, the difference may be in the air gap between the rotor and stator frame of the alternator. If an alternator has never been rebuilt, this gap may be slightly closer causing the alternator to be a bit more efficient thus it will develop its voltage at a slightly lower rpm..