Whistles, Horns, and ZWs

Are you sure that when you push the whistle lever, you aren't getting a momentary break inside the ZW?  The old postwar ZWs are quite repairable except for damge to the windings.

Old transformers don't play well with newer trains with electronic controls. try moving the whistle lever only 1/2 way instead of full.

I disagree, Chuck.  Old transformers have a pure sine wave at any output voltage, which is perfect input for a DCS system or a conventional layout.  Many exterior comtrol units choke on anything other than a pure sine wave.The old ZWs would raise voltage a few volts to compensate for the load of Lionel motorized whistles.  Joe's transformer may have  bad contacts or connections at the switch or windings

The copper rectifier can be replaced with a modern diode. This will help but I do as above,half way.
   Don

Thanks for your comments.   Curiously, one of the two ZWs I use has newer diodes while the other has the old discs.  Pushing the whistle levers on any of the four throttles interrupts the power to the offending locos (not to postwar or MTH engines).  Just for the heck of it, I inserted a second Sound Activation Button in each circuit.  I already had one for bell sounds.  I thought I would try a second one to see what happened.  Result...problem solved. I sure would like to know why!

X2000

The ZW direction/whistle switch is actually a 4 position switch.  Considering #2 as the normal position, pulling the switch towards the operator gives position #1, which openes the circuit.  Pushing it away, it goes through #3, there currect is diverted through the rectifier, and when you keep pushing, you reach 4, where it adds a few additional turns of the secondary winding to compensate for the drain of the ancient motor-powered whistles, while keeping the rectifier in the circuit.  If I recall, in position #4, aser amount of current is diverted through the rectifier.  At some point ion switch movement, you may be encountering a bad contact.

The other thing the last position does is parallel the rectifier with a low value resistor to drop the DC level and allow more AC current to pass to operate the PW whistle.  The remaining DC level was just to keep the horn relay engaged.