Put a dab of transistor grease on the rectifier. Even tho it's overkill, It will get warm, so anything used to keep it cool is good. Where you want to put it is fine. With the amp in it's normally vertical position, it's at the top. Mine is fairly cool there. The warmest place is around the tubes (2 Ell80's and the 1 12ax7.) with the Transistor area running a close 2nd.