Hi Bill,

Many thanks for that - I was about 75% of the way there yesterday but it was getting late and the neural fade was pronounced :)  Anyway, I am happy to report that, having set the NOSHAPING environment variable, my Class D amplifier is happy.  No hiccuping at the FST4(W) transmission start, even with the hardware signal level gate disconnected.  I'll give it a more thorough waveform checkup later but it looks good at this point.

I guess  that with time and experience the switch may find its way to the WSJT-X GUI but it works well enough in the present form. 

Thanks again to you and the team, and 73,
Peter.