Chris,
I assume that AWR is a typo and should be SWR.? If that is correct, then the answer is both, though we have yet to find the specific impedance of an SWR that produces a high enough voltage to take out the BS170s.? The power dissipated by the Class D amp in the QDX and QMX is susceptible to the impedance it sees from the low pass filter (LPF).? This changes with the load that is connected to the LPF.? An ATU will go through many load combinations to find the lowest SWR.? Through that process, the magic SWR that fries the BS170s may be presented.
For my QDXs (I have three operational), I have installed a Zener diode on each of the two sides of the Class D amp to protect from overvoltage.? I do not know of a way to protect from excessive power (current) in the same manner.? ?The pads are on the QMX to install the Zener diodes.? I have not done so yet; I am waiting for the SSB firmware to break out the QMX again and play with it.? I have the easier-to-repair QDXs to play with for digital modes, and I am not a CW op.
73
Evan
AC9TU
