Solid state AB amp?

Is that the one they use in submarines? 

YBA calls "class Alpha," which means that the driver stage is class-A but the output stage is class-A/B
Read more at https://www.stereophile.com/solidpoweramps/831/index.html#84RYQxlcHp4utR9l.99

Thought that class A could be running alone
atmasphere would you explain what that means?

class A means that the output transistors never go into cutoff. In your case the output transistors cutoff at slight more than half of the output waveform.  This is to prevent any distortion at the critical point where the signal goes from positive to negative and vice versa. Class A makes significant heat since the transistors are on all the time; class AB makes a lot less heat and also more power.

The following excellent article by Nelson Pass may be of interest:

https://www.passlabs.com/press/leaving-class

Regards,

-- Al

Thanks guys