Hmm. It may be the output hybrid amplifer. I earlier did research on this and there is a guy who reproduced a better than original amplifier replacement. I was lucky with mine.
He used to manufacture and sell the amplifiers but no more. However he has kindly provided the component list, schematic and PCB layout to build one. That is a project within itself.
Here are the links.
http://www.dasarodesigns.com/product...012-1820-0150/
http://www.dasarodesigns.com/project...012-1820-0150/