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uBITX -Regarding the PA transistor heatsinks.

 

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I can see the insulation argument to why these are installed hanging on to the IRF510s but this puts a large mechanical load on the transistor legs and increases the risks of damage especially if one tried to use the uBITX as a portable, even as a SOTA rig.

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One could fit a larger heatsink that was fixed to the chassis/casing or PCB and one would then have to add rectangular insulating washers between the transistors and the heatsink.
These changes would increase the parallel drain(s) capacitance to ground

?

What sort of negative results should/could one expect from these measures?

?And could one fix'em?

?

I envisage these positive results:-

-?????? better mechanical strength

-?????? easier to provide controlled cooling of the heatsink.

-?????? a slight increase of weight

?
Someone has suggested use of? very beefy 6400BG heatsink, this has two solderable pins installed in the one end of the profile. However the uBITX board has no room for these.
 

I was lucky in the box I put my uBITX in was just large enough to fit the display out? a hole in the front and the heat sinks out the back.? When I changed the final transistors the tab was at ground.? Then I bought a large heat sink and fastened it to the box and bolted the transistors to it.? That gave me a heat sink about 3 inches tall and 4 inches long with some vertical fins.

On Fri, Jun 1, 2018 at 3:31 AM, Peter LB0K <lb0k@...> wrote:

?

I can see the insulation argument to why these are installed hanging on to the IRF510s but this puts a large mechanical load on the transistor legs and increases the risks of damage especially if one tried to use the uBITX as a portable, even as a SOTA rig.

?

One could fit a larger heatsink that was fixed to the chassis/casing or PCB and one would then have to add rectangular insulating washers between the transistors and the heatsink.
These changes would increase the parallel drain(s) capacitance to ground

?

What sort of negative results should/could one expect from these measures?

?And could one fix'em?

?

I envisage these positive results:-

-?????? better mechanical strength

-?????? easier to provide controlled cooling of the heatsink.

-?????? a slight increase of weight

?
Someone has suggested use of? very beefy 6400BG heatsink, this has two solderable pins installed in the one end of the profile. However the uBITX board has no room for these.

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