Hans,
?I have QCX V1 and I adapted for usdx and used it with 1x BS170 without any problems many months. The PA efficiency is 60 to 70% which does not create significant excess heat.
?Actually that QCX is my QRPp rig which I still enjoy. I know that usdx is not the QCX firmware though I think they share the same QCX ghetto class E PA design regardless of firmware as hardware topology.
I like to experiment and this suggestion was through my experiments that I carried out so ?here is the disclaimer listen to Hans and do not try this at home if you are not into experimental ham radio operation!:)
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73, Barb
Barb WB2CBA