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If other tenders don't make the noise, swap out the whistle relay with a relay from another tender, and see what happens. If the noise goes away at least you know the fix.

Is there a slight dc component to your transformer output? Does the relay have a defect that makes it responsive to your transformer power? A combination of the two? I don't know how much testing your capable of.
 

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The schematic will be fairly simple. It really isn't needed. The wiring seems fine based on you description: "Whistles ok, buzzes when the button isn't pressed.

The question is why is the relay buzzing? Either it's become sensitive to AC voltage or there's some slight amount of DC on the track that effects this relay but not the others (sensitivity differences).

Try testing it using the CW's accessory terminals. If it doesn't buzz, then the CW's variable track output is sneaking in some DC. If it does buzz, it could be the CW or the relay.
 

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The cheapest lionel transformer has the same signature as the most expensive mth. Its not the transformer.
If the scope is setup correctly, I see two instances of DC offset: (1) The "zero" point seems a little negative; and (2) The extra spike in the negative part of the wave form.

Do the accessory terminals have a similar offset?
 

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Discussion Starter #14
Thats a pic of my $4k tektronix storage scope. I put on my mth supply and it was identical. Same as lionel power max plus and cw80. Did not check my zw but was able to find problem: loose copper washers on bottom of coil. Fixed!!
 

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A stab in the dark.

In Bobs picture diagram see where it says ground?
The arm above it moves to contact the other piece, are these clean?
Sometimes these will stick together, sometimes they need a little adjusting too.
 

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Thats a pic of my $4k tektronix storage scope. I put on my mth supply and it was identical. Same as lionel power max plus and cw80. Did not check my zw but was able to find problem: loose copper washers on bottom of coil. Fixed!!
It was closer to $3850.00, but that was 1975! Not worth that now. Tools are only as good as the person who uses them.:smokin:

Glad you found the problem, and all it took was a finger!
 
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