Replaced the rectifier discs with diodes in the ZW, question.

no the whistle is only activated with dc and when you push whistle button it temporarily activates to apply dc to track and pick up dc relay in engine!

Alan

Actually, old PW transformers used to boost the voltage to the track when you activated the whistle control.  That was to compensate for the power draw of the old AC motor in the whistling tender, they draw a significant amount of power.  The control is a two-stage affair, the first stage puts the rectifier in series with the 6V boost winding to generate enough DC offset to pick the whistle relay.  When the control is moved to the second contact, the rectifier is paralleled with a low value resistor, it's the long wire cloth wrapped affair in the transformer.  That leave a little DC to keep the relay energized and applies the full boost to the track to compensate for the power drop caused by the power consumed by the whistling tender.

I put diodes in my ZW. I never have any issues but it still accelerates the locomotive.  Same with my LW.

Just move the whistle lever half way. If still nothing, reverse the leads to the track. The diode may be installed backwards.

@Chuck Sartor posted:

Just move the whistle lever half way. If still nothing, reverse the leads to the track. The diode may be installed backwards.

You nailed it Chuck. Looks like I have some soldering to do!

Thank You!

@Chuck Sartor posted:

Just move the whistle lever half way. If still nothing, reverse the leads to the track. The diode may be installed backwards.

If you bolt a zener diode to the ZW's chassis, the whistle leads will be reversed.  This is mostly noticeable with electronic horn boards...

Mitch