Also, the bulb I tried was an indicator bulb, so probably 21W. I think (from my A-level physics) it would therefore draw more than 1A with a 12v supply. So I won't be surprised if the fuse has blown!
Trying to draw 21watts would completely swamp that transformer. 50/50 whether the fuse would blow, the resistance of the windings would likely be enough to limit the current and avoid the fuse being blown.
You may or may not see a spark shorting the wires, depending on where in the sinewave you short them.
For testing if the transformer has an output, assuming the push is illuminated, you could use the lamp in the bell push. Or if you are careful not to press it whilst testing - connect the push itself.