And now I'm replying to my own post...

After I had read the datasheet a bit better and also rebootet my brain , I don't know if there is much point in making the board with the 6651... That chip is only a fan controller where you set the speed and the chip keeps the fan at the preset speed. It doesn't contain a temperature sensor, so either it would need to rely on the built-in temperature sensor in the Empeg or it would need an external temperature sensor. The fan wouldn't be PWM controlled either, it would be voltage controlled, as PWM and tach signals doesn't mix very well...

And since Ben has already made boards with the temperature controller, so unless people want this type of board and someone makes the patch for Hijack, I'll just stop this project. But if someone wants some boards, it wouldn't take long to do the layout and make some boards, since I can make them at home...

Stig