Greetings from Holland to Michael down there!  Jazz flute ranks and
vibratones cannot be tuned with the pallets open.  The large leak hole
is so near to the pipe mouth (actually it is opposite to it) that the
pipes will not sound with open pallet!

Tuning these pipes against another (octave) rank with pallets closed
will give a pleasant sound with the tremulant off; however, to the
listener the effect will be as if the rank is tuned too high as soon
as the tremulant is switched on.

The best, and to my opinion only, way to tune these ranks is with
tremulant on, and against a steady-sounding sub-octave.  Tune the pipes
till your subjective ear is pleased, and then it will hopefully please
the other listeners too!

Sure, I know that this method does not sound very scientific, but
science cannot be the cure of everything...

Hans van Oost, Netherlands