hifi engine

ROTEL RX1603; trying to identify boards

I have a strange home brew amplifier on my bench. Seems like it was built from scavenged parts.The only identification i have sofar is the transformer which is labelled ROTEL RX1603 Reciever.
I don't know how tall that unit was but the power amp module looks too tall for a 70's reciever. More like something from a big American power amp, Phase Linear etc.
The board is certainly Japasese in style, but other than that there are no obvious markings.
I don't need a service manual as it is all working but a identifying the biasing procedure would be useful as the amp runs really hot for it's power output. There are three pots.
does anyone have any internal pictures to help with identification? I could also post some to see if anyone recognises the internals.
Regards Hywel