If Tim says class A, he ought to know
I would say the 859 was nominally 13 watt, and later (869) 15 watts, Half 32 watts is 16 so I suspect it is. Also I would imagine if the amp was run significantly into class B it would mess up the DC feedback and introduce strange artefacts with the 2 feedback loops. I haven't studied the circuit enough to state that with certainty but it would seem likely.