You're probably thinking of the E12S. It was pretty much electrically
identical to the early E15 except for the fact that they left the field
weakening components off of Card # 1, therefore it only has 3 forward
speeds. To give us a bit of a better grasp:
First production model by GE was E15 with Card #1 - Early (Jan?) 1970
Second production model was E12S with Card #1 - Approx. Sept. 1970 (Last
batch of these approx. April 1971)
Third production model was E20 with Card #4 - Approx. April 1971
Fourth Production model was E12 WITH NO Transistorized cards - Approx.
June 1971