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Reply to "Whistle Waveform from Model ZW Transformer"

I have some new information, some good and one point that is confusing.

Based on the comments here I removed the resistor from my simulation of the initial whistle step, and the simulation was a very close match to the measured waveforms, except for one small issue; the polarity in the simulation is reversed relative to the measured waveforms from A and B to U.

The measured waveforms show a positive signal, while the simulation gives a negative signal. See the files:  Lionel ZW Transformer A Whistle Simulated Waveform Rev 3; Lionel ZW Transformer A Whistle Waveform 11 Ohm 220124; and Lionel ZW Transformer A Full Waveform 11 Ohm 220124. I double checked the probe connections and the polarity of the channel input on the scope. They are correct.

I've attached my Rev 3 simulation diagram and the diagram of the ZW I found on the Internet. Both have the cathode of the rectifier connected to terminal 9 of the Compensating Winding and the anode of the rectifier connected to terminal 19. 

So, my working hypothesis is that the rectifier symbol in the diagram is backwards. I measured the conduction through the rectifier used for side A of my ZW using my Fluke DVM when the Whistle/Direction switch was in the "normal run" position, and I get conduction when the positive terminal of the meter is connected to the A terminal and the negative terminal of the meter is connected to what I believe is terminal 19.  This also points to the fact that the rectifier symbol in the diagram is the reverse of the rectifier in my ZW.

In addition, as I prior design engineer myself, I think it would have been natural for the Lional engineer who designed the circuit to have the rectified whistle signal be positive instead of negative, unless there was a good reason to make it negative. 

Some of this may have been discussed in the threads related to replacing the rectifier with a silicon diode, but I have not yet read those. (Why not, the reader asks.)

Finally, I have little interest in this transformer other than keeping it out of the landfill. I'm currently trying to resurrect an old HO setup, and don't have room for both HO and O, in spite of my fond memories of our Lionel trains when I was a kid.  So, now that I know it works, at least sort of, I plan to list this ZW on eBay with all the caveats that it needs a cleaning and serious maintenance. I hope to price it low enough to encourage someone to buy and restore it.

Thanks for all your help. 

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