Try a good paper developer, e g Ilford Universal. Dish develop with
constant agitation at 1:9 at 20 C.
It is difficult to say how long the development should be, but if the film
was over exposed by two stops in relation to silver gelatine printing, the
development time for a density range of about 1.8 should be about two
minutes.
It does sound, however, as if you have underexposed the originals for long
range negs. Or perhaps the 2.4 indicated that you had just developed for
too long
But with Tri X probably the best way to overcome the difficulty is to
develop for silver gelatine and then build up the contrast by making a
silver gelatine interpositive by contactingonto FP4 and then an
internegative, again contacting onto FP4, building up the contrast at each
stage.
You did not say what your preferred film was but I would suggest that
sticking to FP4, for long density range negs, is going to give the
required result.
Terry ing