This is the last of the temp tests...
So I moved the transistors to the point of where they are completely in contact with the heat sink. I did not fill in the hole because in this installation the transistor is not covering the hole.
Final results:
~ Delta temp between transistor tab and heat sink
Transistor mounted with silicone pad, heat sink drilled, transistor positioned completely over aluminum. Delta T = 5 deg.
Transistor mounted with silicone pad using screw on existing hole. Delta T = 15 deg C
Transistor mounted with Kapton pad and thermal grease using screw on existing hole with paint removed from AL. Delta T = 15 deg C
Transistor mounted with Kapton pad and thermal grease using screw on existing hole with paint on AL. Delta T = 15 deg C
Transistor mounted with Kapton pad only using screw on existing hole with paint on AL. Delta T = 34 deg C
Typical heat sink temp after warm up is 37-40 deg c.
So then I placed a thermocouple on the Q203 (I THINK, COULD BE Q205) put the covers on and flipped it over.
It runs around 53 deg c with the music gently playing. I did not check the board temp.