Re: 50 Watt Amp Final Transistors


George Korper
 

Hans describes testing six to come up with one, What is the manufacturing difference that makes
the difference and is it consistent? I know it is cheap. Has any manufacturer come up with the same
specs in a better package? Or do similar transistors go for a lot more money? Just want to know to
learn more about these devices, I read the manual and understand Han's logic. Do the Yeasu's and Icom's 
make their own? QST could sure help out by doing a long article on this! 
Also do these Mosfet's do better on 40 than 20?

On Sun, Mar 1, 2020 at 7:04 PM Glen Leinweber <leinwebe@...> wrote:
My old National Semiconductor data book shows the IRF510 chip size....
98 thou x 87 thou
2.5mm x 2.2mm
The heat-generating area is a bit smaller than that.
Drain is bonded to the metal tab directly while the source
and the gate are attached with flying leads that conduct very little
heat away.
That chip is a tiny heater bonded to a far bigger slab of metal, which in
turn is molded to the IRF510's black epoxy.

That 3.5 C/W junction-to-tab heat spec is likely due to the small chip
size. The much larger contact area of metal tab -to- heatsink likely
means the tab runs just a bit hotter than the heatsink under it.

We used to rely on the black anodizing on the heat sink as an insulator.
Although the aluminum oxide is very thin, it is a remarkably tough insulator.
This was for 60W Class AB audio, where two transistors bore the heat load.

Not saying you should try this because I don't know the quality of that
heatsink extrusion - a little scratch can cause mayhem. As always,
follow Hans' excellent instructions.

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