[codefox1]

Agree, most likely a partial short in the secondary winding, and ultimately could be a hazard. Of course you could carefully note and disconnect all windings, remove the transformer, open the bells, gently loosen paper shielding and inspect connections from leads to windings. They often corrode, dunno why, but at this junction you have little to lose. Well, you can always resolder 'em, and replace the leads if they are worn or ratty. Not familiar with this model, but if you have enough space, any transformer that is roughly electrically equivalent (or better) and will physically fit in the set can be used.