If your goal is just to install Qsampler, there's a PPA which Rui always
keeps up-to-date with the latest version. The applications and libs are
in separate repos with the same signing key, not sure if you need both
Thank you for your reply, Roger. I was sent a personal e-mail advising me
to install qttools5-dev-tools. This included /usr/lib/qt5/bin/lupdate.
After doing so, the source code compiled and installed without error. As I
mentioned, I was missing something obvious. Still, unless you know it, you
don't know it....