Link, this is supposedly the first 1.50S sold, according to a lady at Horizon, it has no letter designation, it has an 11.24 to 1 compression ratio. The next series marked (B) on the right lug had lower compression. Don't confuse the latest 1.50B model with the early B. Note different cam housing on the latest B series. Picture #1.
Detailed test by Clarence Lee,
http://sceptreflight.net/Model%20Eng...20FA-150S.html