Differance between Ar 636 rx and 636A rx
 

I have two Carbon z T-28's. I just got one used from a guy about one week ago. One has an AR636 receiver the one I got recently has an AR 636A receiver. I am interesting in knowing what the difference between the two rx's is. I know the AR636A has a built in Gyro or stabilizer. I have a feeling the AR636 does not have one.