This is how mine sounds on 18v. The coil only throws the little hammer in one direction so it relies on deflection to strike the bell on the left on the rebound . For this reason it helps to tweak the arm so the hammer is biased towards the left bell when in the idle state . The little screw on the side sets the "throw" by adjusting when the current to the coil is broken. You will notice that also moves the arm so it's a dance to get it right.
I found it easier to tune it by adjusting the screw while the bell is ringing. You can tell if both bells are in play by touching them one at a time while it's ringing. If touching the bell has no affect on the sound it's not in play. I'm sure mine's not working perfect either. Chuck is right, it's closer to a "buzz" than a ring.
