Identification of an AC transformer
It's an AC/AC transformer, the rectifier was probably on the red/black lines. Usually Yellow\Green lines are for AC mains (according to international standards, but it also depends on the age of the device). 

Your best bet is to hook up a signal generator, and see what the step down ratio is if you want to use it. 

The other thing that will be of use is any markings on the outside of the clock that specify the current and voltage (you need the current) because that will give you a good idea of the saturation point of the transformer and how much power can be run through it. 

EDIT:

I didn't see the blue black line in the picture which is not clearly indicated:
The primary is most likely blue brown and there are two secondaries, in this case red/black are one secondary and the other secondary is yellow/green


Source: https://airlinktransformers.com/post/chassis-mounting-toroidal-transformers-technical-notes