Finally had a chance to get the PA up and running, add variable output power control to the DDS, and connect the two together. Everything's working very nicely and I can now easily adjust output power between <100mW and 10W (and more). I bought an old (and very sickly) power/SWR meter, and calibrated it to 10W, so at least I have a rough indication of power level.

No output low-pass harmonic filter yet, but harmonics are approx. -40dBc at second and -25dBc at third, so probably won't cause too much interference. For now I'll keep the output power to around 1W to be on the safe side. Actually, the old 12V lead-acid battery I'm using to power the PA is knackered so most of the time I'm probably only making half that...

On my very first FT8 transmission I got a QSO - so clearly it works! And now getting spots well in excess of 5000km on FT8.