开云体育

After assembling a QDX rig for a local ham I received a couple of the QDX PA mod PC boards made by WB2CBA which have the FDT86256 mosfets. They have a max voltage of 150V compared to the 60V of the BS170. Since I like to experiment I decided to try and adapt one of the boards to my QMX+. I filed off the two "tabs" opposite the mosfets being careful not to file off? any of the traces. It fit perfectly where the BS170's were. After some testing it seems to work well. My QMX+ is presently wired for 9V and I have a Buck-Boost converter stuck on the back set at 10V so I can use any battery I like from 5V-30V. On 80m-30m I can easily get 5w with the 10v input. Since I like to "play with fire" I plugged in my 12.6V battery and got 6.5w-8W on the lower bands. The mosfets stayed very cool....into a dummy load. While playing on FT8 with my Hexbeam and low SWR sometimes the finals got warm and actually got pretty hot on some of the higher bands but kept work fine.?

? ?If anyone else out there can or wants to give it a try, especially if you have the proper test equipment please let me/everyone know what you found.

The info for the PC boards are here... ?

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Tim - K5DEZ

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And as you can obviously see, I added a couple small heat sinks using a thin coat of contact cement to hopefully add a bit more metal mass. Just make sure they do not touch.

Tim - K5DEZ

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The usual problem with (not entirely sure why) beefed up ?FETs is poor 10 metre performance

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Do you have any measurements ?for this Mod ??

My output wattage on the original finals was a bit low anyway. With the larger FETs it was still about the same but with the ability to run at a higher input voltage if desired, it was easy to make up any differences plus a bit more. I did some preliminary checks and overall the output is better except like you said the higher bands suffer a bit. For me, it is good enough and gives me some leeway for output. The lower bands 80m, 40m 30m do extremely well. They are up to 7W-9W range. I believe they are 10W components so there is a lot more overhead and with the 150V max voltage they are less likely to burn out. For now that's my story an I'm sticking to it until I break something else. Experimenting for me is part of the hobby. YMMV.

Tim - K5DEZ

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