(Contributed by Ray McClure, W8CNL)
The "IF-Shift" IC-751 is identifiable by the concentric IF Shift/Notch control (instead of PBT/Notch).
Remove the top and bottom radio covers. Just on the top of the main board, under the top cover, to the left of the two 9 MHz IF filters, you will see a lone brown (or black) wire going to a jumper pin. It is J17. Simply remove the wire from the pin, and tape it so it will not short-circuit to anything. Then you have PBT with the center at the detent at the top. You can still turn PBT off by turning the knob fully counter-clockwise, just like the IF shift.
All credit should go to Bruce, K1XR, who sent me this modification a couple of years ago.
It works great here, compared to the IF shift.
73 de Ray, W8CNL.