'A' or 'B' circuit generator?

This is so embarrassing, I must just be getting old; I can't remember
if the generator in my '61 C-172 is an A or B circuit. Worse, I
forget which one is which. Does the 'A' supply controlled voltage
to the field and the 'B' does a controlled "ground out" of


A circuit field tied to voltage source inside generator and regulator
switches resistance in and out of circuit to ground to control field
current. Grounding field terminal produced full output.

B circuit field is grounded inside generator and regulator switches
resistance between field terminal and voltage source to control field
current.

Cheers:

Paul
N1431A