Horn/Whistle circuit

I think you mean "bell" when you say "horn."

When the DC offset is one direction, it activates the whistle (steam) or horn (diesel). When it is the other direction, it operates the bell.

Lionel misprinted some technical information in the past about diode orientation. As a result, I purchased a rebuilt KW transformer with a diode replaced backward that operates the bell but no whistle.

It sounds like you may have followed the same incorrect information and installed your diode backward.

You can either reverse the polarity, or Train Tender sells a disk that reverses the polarity that you can install on top of the backward diode, if that's the type of diode you have.

Positive DC offset is for the horn/whistle, negative DC offset for the bell.  You can power the track and use a DC voltmeter to measure the offset.  Modern transformers will have either + or - 2 to 2.5 volts, postwar transformers will have + 2-3v pickup voltage and about a 0.5-1 volt hold voltage depending on how far the whistle handle/button is pushed/turned.

Thanks gentlemen,

Yep, diode installed backward in an LW transformer. Wondering though would it matter if I used it that way with a Postwar shaded pole relay? Are they polarity sensitive?

Thanks again

AC

@ACGilbert posted:

Wondering though would it matter if I used it that way with a Postwar shaded pole relay? Are they polarity sensitive?

They are not.

Polarity didn't matter until the 1972 introduction of the electronic whistle for the 8142 & 8206, when Lionel/MPC reinforced the convention they started in the 1930's - + offset for whistle control.