These are very nice.
I have a little Bischoff bipolar dynamo (or motor). I name it due to one shown in Heinrich Rehse's Katalog No. 77 with all the Bischoff engines and accessories he sold ca 1904. That said, there is no identifying mark on it so I cannot be certain of it's origin.
Is it similar to the large or to the short one above...?
Can you please post a pic of it...?
I have a short video of it here.
Enjoy,
Gil