By inspection of your pictures, I would recommend looking at the spacing on the switch. When you push the button, the coil activates and pulls the diaphram "up", which opens the switch, cutting off power, letting the diaphram relax and the switch to close again.
The tone can be controlled somewhat by the switch preload and depth. It looks like this one uses a collar on the diaphram rather than the nut that a lot did.
Does the diaphram post move smoothly in/out of the coil?
