As a power amplifier pole in the power amplifier, whether it is a power tube or a power thick film integrated block, it is the largest part of the entire power amplifier. Work is large, power consumption is large, of course, the heat is also very large, so the power tube in the power amplifier has a cooling plate, and some have a fan cooling.
When these power tubes are manufactured, in order to facilitate heat dissipation, the base is basically metal, so mica sheet insulation must be added between the heat dissipation plate and the power tube. And it's got to be coated with thermal grease.
The reason behind some power amplifier chips is to insulate the circuit board and not cause short circuit, and then damage the power amplifier chip.