Hartke LH500 bass amp. One of those hybrid bass amps you always see that has a tube or two in the preamp and then a big, powerful solid state output section. Big heat sink is on the right with fan to keep those output transistors cool when trying to push 500W. Not an easy task. Airflow and fan placement are very important in amps like this if they are to be reliable.
This board got all burnt up when this thing failed. The amp did not fail, but the fan, an output transistor, and a 10 ohm/2W resistor did. Not sure if the fan caused the transistor to fail or if it was the other way around, but this thing needed a little hardwiring because the board was so damaged. 2SC3117 transistor seemed impossible to find but as a last resort I called Hartke and they supplied it without a problem. Awesome support! Here is the Hartke LH500 schematic. Actually it is for LH1000 but same amp except twice as many transistors in the output section for double the power, wow.