The fan that I installed yesterday was driving me nuts. It was noisy, both acoustically and electrically. And I would occasionally get my fingers in the blades. Not good. While it did seem to keep the IRF510 from getting too hot, I knew that a real heatsink would do better thermally.
But how was I going to attach the sink to the transistor? That tab on the IRF510 goes to the collector, so if it touches a grounded heat sink, you get a short. A nylon screw and some mylar between the transistor tab and the heat sink is one option. But I didn't have a nylon screw. So I decided to just keep the heat sink electrically insulated from the chassis.
This project required me to refresh my memory on how to tap a 4-40 hole. I went back and watched the short video I made on the tribal knowledge that Pete had shared with me. Out came the Tap and Die gear and the machine oil. The process went very smoothly.
Here is what I did to get the heatsink in place:
1) After removing the original heatsink, I gently bent the leads on the IRF510 so that the transistors outer edge would be flush with the edge of the PC board.
2) I put a strip of thick tape (Gorilla Tape) along the lower side of the heat sink. This will keep the heat sink from shorting to the chassis.
3) I placed the heatsink where I wanted it, and carefully marked where the mounting screw (through the transistor's tab) should go.
4) Drill! Tap! (see video) https://www.youtube.com/watch?v=LuqliWT1k5A
5) I applied some heat sink compound (or Desitin!) and then attached the transistor to the heatsink.
6) I put a few drops of glue between the heatsink and the board and the chassis, just to mechanically stabilize it a bit.
7) Bob's your uncle.
It seems to work great. The MOSFET stays cool. even after long "old buzzard" transmissions. And I notice no stability problems. It was fun to put to use some tribal knowledge and refresh a mechanical skill.
73 Bill N2CQR