I was wondering how do the whistles in post war Lionel tenders work. What happens when you operate the whistle control on the transformer to make the whistle operate?
The whistle signal in a postwar whistle is something like a DC offset in the normal AC current sent to the track. This trips a DC solonoid which caused the whistle to blow.
This is a general, conceptual explination. I’m sure somebody else will give a better answer.
The transformer changes the voltage that it puts out, from a symmetrical sinusoidal waveform, the average of whose instantaneous voltage is zero, to a waveform that has a non-zero average, which is to say, a DC component. Inside the tender is a “slugged” relay, which is one which has a couple of copper disks around its pole piece. These shield the pole piece from the fluctuating magnetic field produced in the coil by the AC voltage but do not hinder at all the steady component produced by the DC component. This causes the relay to operate. It connects the whistle motor to the track voltage; and the whistle blows.