Hi;
The Class-A output prior to Class AB for a 3B SST is about 1.5 Watts. On a 4B SST it's around 2.5 to 3 Watts.
Btw, these amps don't ever switch to 'Class B', they always have some bias running. The distortion typically runs in the low thousandths of a percent at 20K at any power level below clipping.
Hope this helps!
Chris Russell, writing for James Tanner