Don't know for sure but, in general, a class A/B amp will operate in class A up to where the output current is about twice the bias current. The ML 436 idles at half the rated power output at 8 ohms so I am guessing that means it's biased close to 1 amp. Therefore the class A operation is twice that squared times 8 ohms or 32 watts.
That's a guesstimate.
That's a guesstimate.