There will be signs if you look.
THe IRF510 is rated for 43 watts dissipation, specsheet and all.
The issue is that you have to be able to get the heat generated by that power out of the part.
Therein lies the problem as Any (and all) TO220 parts have lousy thermal resistance so it
can get very hot before the heat sink is really cooking.? ?Max temp is 150C at the die inside
the plastic that is 300F!? However keeping under 100C is better for its lifetime.? It takes
a lot of heatsink to do that.
The other issue, not paid attention too.? We know they can get hot... in a closed box where
does the heat go?? Unfortunately the answer is nowhere it just gets hotter.? I noted this with
mine and other IRF510 amps.? I could key down for 10 minutes easily on the bench in
the open and the heatsinks might hit 125F.? Put a card board box over it and it would get
to 175F after 10 minutes.? ?Airflow is important with those heatsinks 10W is fairly easy.
Hint: if the transistors are mounted to the back of the box with the right insulators
and a large flat heatsink it helps.? The other is vent hole in the box and a small 2"
fan to move the air though to the outside can also be effective.
To further make the point I have a IRF510 push pull amp (WA5EBY design) with a
8x4x1.25 inch heatsink.? With the 28V power supply it runs on 40m and 20m about
50W and 37W at 10M?out and key down for 5 minutes the heatsink (on the back
of the box out in the air) gets to 115-120F which is not very warm.? Those IRF510s?
have survived shorted coax, shorted antennas, wrong antenna for the band,?
and no coax at all at full power and continues to do so since I built it back
in 2006 on the same parts.? ?With 50W out the input power to the pair of
transistors is about 100W so theres about 50W of heat (or 25W per IRF510)
the heatsink has to remove.
So they are not fragile if not allowed to cook.
Allison
