given all the rectifiers on the board it's certainly power supply and what is on the sink is likely all regulation.
Far left is a 7915 which is a negative 15V regulator, third is a 7805 which is a positive 5V regulator and two larger ones are PNP power transistors and could be driven by smaller regulator components, they maybe the as end of a high current regulation of some sorts. Most common amp sections will have a PNP and a NPN transistor... also a LOT more support components.
The power amp section is buried deeper.