Q for John or Dale

Did you do a search for "Zener" in the forum?  A quick search turned up this thread and there are many more.  

I did, in fact I read way to much. That,s why in wanted John or Dale's  input.

But thank you for help too.

Greg

How does the zener diode avoid the speed change that we experience with the diode ladder?

With the Zener diode, you remove the boost winding effect.

John,

Have you forgotten what a rookie I am:-) 

Can zener diodes be used in the external bell/whistles controllers instead of the diode ladders so that we avoid the speed changes?

I've never looked into Zener diodes for the external whistle box, but I can envision how it would work.  However, that would not change how the external box operates over standard diodes, just potentially reduce the component count.

John,

I was thinking more in terms of how those who install them in the ZW claim that there is no speed change when they blow the whistle. How is that possible? I would love it I could maintain constant speed with an external controller.

Denny

When they're in the transformer, the whistle control has an extra winding that boosts the voltage to account for the old post-war whistle current.  This was to keep the speed up with the additional current draw.  Nowadays with electronic whistles, that isn't really a factor, so with a standard transformer, the speed increases.  With the Zener diode, it inserts the DC offset to trigger the whistle, but also drops the extra boosted voltage so that the speed remains fairly constant.

John,

Thanks for a clear explanation.

Denny