Bell(Canada-Northern Electric) 554 Tel Touch -cannot break dial tone

[Key2871]

That slug screw etc is an attenuator to adjust or fine tune the frequency that the coil(s) out put to get the correct frequency. With out an analizer to see the correct frequency your just treading water.
An analizer will show the frequency to produce the proper tone.
I've seen WE 2500s that got dropped or other, that one of those broke and other than replacing the dial, there's no hope to get it correct. Or an analizer.