Instructions from ON7WP:

Remove the three notch/connector assemblies on the right.  (replaced by
stainless steel screws, the single one on the left was only opened to check
the content).  They consist of a small coppertube and a small strip.  You
only have to adjust the lenght of the strip to the copper tube (I think I
made it slightly longer) in order to get the notch at the good side of the
pass frequency. 

It's one of the best duplexers i ever measured for 1.6 Mhz shift.  Do you
know any sources to acquire these?   

73's

Pedro, belgiums most famous repeater guru...