I have an old ZW transformer whose whistle function barely works with several new engines. Is there some kind of addition that allows me to use the ZW but can sound the whistles and bells?
jefny
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First thing would be to change the old metal rectifier disc for a solid state diode. This should fix the whistle issue.
http://tranz4mr.com/ZW_Whistle_Diodes.html
Next would be to add a sound activation button for ringing the bell. Lionel 6-5906. Although I'd suggest replacing the wire with heavier gauge wire if running multiple locos.
I use this combination on my RW. Works great.
Otherwise get 2 sound activation buttons and wire them in series. The instructions that come with the buttons show how to set them up to activate the whistle and bell.
An old zW will not activate the Bell function. Only the whistle / horn. Your rectifier discs might be shot. If so you should replace them, or better yet, replace them with newer diodes.
Make your own whistle/bell box.
This is just something I whacked together from junk box parts years ago.
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John, what parts do you have there ?
Well, those are 3A diodes. If you're going to duplicate it, I'd make two small suggestions. Use 6A diodes, and also add one more diode to the string where I have the arrows. I've been told that for bulletproof operation one more diode drop was needed. I never had a problem with this setup, but I do see other versions with six diodes in each string, better save than sorry. 
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John,
Are you selling them? Way to busy to build my own! Just wait till you move you will see what I mean. Still can't find some of my tools.
PCRR/Dave
Nope, I just built that one because we were discussing it.
John - remind me (us) - this is wired in series with the track power? The push buttons are both NO, right, so the AC waveform passes through the diode string - when pushed, they create a DC offset superposed on the AC(?) to trigger either the bell or whistle(?)
Also, when activated, does the locomotive slow down?
It is in series, and the locomotive doesn't slow down as the DC offset is really added to the track voltage. Since the diodes are all in the circuit when it's not active, track power is going through all of them, when you press one of the buttons, it creates an imbalance of the diodes and adds the DC offset.
The only downside, if you consider it that, is you need about 3-4 volts more track voltage for a specific speed as the diodes are dropping that much voltage.
