I am sorry to hear your 50W amp is not working. I wish I could be more positive, but your information appears to indicate to me:
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IRF510 FETs have failed short-circuit between Drain and Gate.
BS170, Q6, has failed short-circuit between Drain and Source.
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To confirm (1), remove the 14V supply from the amp and measure DC resistance between Drain and Gate.
The L10 and R13 voltages in TX and RX that you noted are the ones that we see when Q6’s Drain and Source are short circuited.
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I assumed the 1 or 2W output you saw is the output from your QCX+ mini, reduced by the attenuator, then passed through the (short-circuited) IRF510s and reappeared at the amplifier output.
