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Hi, Does anybody know exactly how a 6-5906 sound button works? I took one apart (there are 2 screws under the bottom sticker).
I understand how whistle controllers work & diodes work. However, diode #7 is a direct link to the in/out wires when button is pushed. The other 6 diodes are in series like when you string diodes as a volt dropping device. I don't get it. It seems like #7 would carry all the load since it would have much less resistance?? Why the other 6?
The switch is a simple on/off contact. Not pushed, the switch is closed bypassing the diodes. Pushed, the switch is open forcing current to pass through the diodes making 100% pulse dc. So far as I can see there is no provision for "make up" current as on a 167 whistle controller, or in the extra whistle winding in a multi control transformer with whistle button.
Maybe some of the electroinics experts can clue me in?
Very best, Don Johnson
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The sound activation button uses 6 diodes in one direction and
one diode in the other direction to produce the small DC offset
to operate the horn or bell. The transformer button uses one diode
and a resistor to produce the offset. The resistor in the transformer
has the same effect as the 6 diodes in the sound button. There is no
voltage increase in the sound button as there is in the transformer
so operating the sound button will cause the train to slow down.
Hi PA & Dale. Thank you for such a prompt reply.
PA, You are most correct about the diode #7 being opposite from the others. I was up way too late working with this stuff! After a fresh look & now see what you mean.
The train tends to slow somewhat with the sound button. Depending on the loco, & load. (Polar Express, Thomas, Willaims GP9). The ones with an electronic sound/speaker slow much less than the Polar with can type whistle motor.
The sound button nearly or often stalls postwar 2025.
This all started when I decided to see if I could work out a diode system of some sort for my PW ZW to work good on both postwar & modern trains. Understanding bell is neg. dc, I didn't care much about the bell.
Now I have 2 CW80s which I've never taken apart, but they work both the postwar & modern whistles ok. All the modern locos keep the exact same speed while blowing whistle/horn. The 2025 slows slightly. The fold back light comes on while blowing whistle with 2025 so the tranformer is over working but whistle still works pretty good.
Is it possible to acchive this with a PW ZW? That is my goal. How does the CW80 do it? I have no idea.
Another thought I had was if I got the transformer worked out is, modifying a 167 whistle controller to trigger just the bell. The retro look of the 167 fits my theme better than a new sound button.
Dale, Thanks for the link to the sound button plans. I'm starting to understand this a bit better.
Very best, Don Johnson
A 167 should work to activate the bell without any modifications if you reverse the wires. The 167 does drop the voltage to the track through an inductor so that there can be a voltage "boost" during whistle operation to compensate for the drop across the diode and parallel resistor.

There are apparently 3 types of 167s - with and without circuit breaker, and reduced resistance for early smoking locomotives.
The 167 was designed for use with transformers without a whistle button.
The transformer had a higher output voltage so there was an inductor inside
the 167 to drop the extra voltage. When the horn button was pressed, the inductor was shorted out and the diode/resistor circuit reduced the voltage
to keep the speed constant.

The circuit was designed in the 1930s when there were 2 motors, engine and whistle, to load the resistor in the controler enough to keep the train speed
constant. New trains with electronic horns and small can motors do not have
enough load to drop the voltage across the resistor in the controler to keep
the speed constant or generated enough DC offset to operate the horn.

Replacing the resistor and diode with a Zener diode corrects all the problems
but does cost more.
Hi PA, Hmmm, Interesting. Again you have my full attention.
I know little about zener diodes other than my old Triumph motor cycle uses one to shunt over-volts to a heat sink to control charging.
How is the zener used in the whistle control? The way the bike shop manual tells it, it's open circuit until volts reach a threshold, then closes. That's my understanding of it.
How would one put this in the whistle circuit?
Very best, Don Johnson
Zener diodes are used as voltage references or voltage regulators.
Zener diodes pass current in the forward direction with .7v drop.
In the reverse direction, zener diodes do not conduct until the
breakdown voltage is reached then they will conduct and drop the
zener break down voltage.

Replacing the disc rectifier and resistor with a 12 volt zener
diode corrects problems caused by a 1930s whistle system used with
present small can motors and electronic horns.

With small can motors there is not enough load current thru the resistor
to compensate for the voltage increase when the whistle button is pressed
so the train speed increases. There is also not enough voltage drop to
generate enough voltage off set to operate electronic horns.

The zener diode corrects both problems without depending on the load current
thru a resistor, no speed increase and horn operation with no train operating.
I used 10 watt zener diodes or 50 watt zener diodes in the ZW transformer. The
zener diode is not a cheap fix like replacing the copper disc rectifier with
a silcone diode. The zener diode works very well when there is very little load
on the track so the train does not speed up and the horn will still operate.
So... Are you saying disconnect the resitor wire & replace disc with a zener? That would be easy.
Again, how with this work with PW whistles?
Seems it should work fine.?? According to Lionel service info the resistor wire simply bypasses the resistor to reduce current flow through it to keep it from overheating. My thought is if the diode can take full current that resistor would not be needed.??
Very best, Don Johnson
The shunt resistor does more than just reduce the power through the diode. It provides quite a bit of current in the direction opposite to the diode flow so that the current is not just halfwave rectified, but rather more like AC with bigger humps on one side than the other to create the small DC component required to HOLD the whistle/horn relay (not activate it.)

The ZW and the 167 both have the two-stage activation button that first puts halfwave rectified voltage to the whistle/horn relay to activate it, then adds the resistor to restore some of the missing part of the halfwave waveform.
Originally posted by Dale Manquen:
The shunt resistor does more than just reduce the power through the diode. It provides quite a bit of current in the direction opposite to the diode flow so that the current is not just halfwave rectified, but rather more like AC with bigger humps on one side than the other to create the small DC component required to HOLD the whistle/horn relay (not activate it.)
I'm still waiting to see how this Zener diode gets wired in to maintain compatibility with both the old and new whistle designs. Smile
Most of the electronics talk here is over my head, but for years I ran two 5906s from one throttle of a KW. I had a center-off switch for each block so I could use the horn/bell button throttle for modern engines and the KW's lever for postwar stuff.

It worked, but as noted 5906s aren't really stout enough for that much juice. I eventually cooked one and then switched over to a new Williams transformer that I'm happy with. I still run accessories off the KW, and I still have a choice of throttles - I use the new unit's adjustable accessory control to move engines on sidings while the big throttle runs the main.

I am surprised nobody has made a more substantial add-on sound button - maybe one that lets you choose to add some "jump" voltage or not.
Hi, On a side note, I always noticed my right PW ZW whistle worked much better than the left. Now, the left is a diode repl. & the right is old disc.
However... I was runing several switchs & their controllers off track power on the right throttle. 8 112 switches with 022 controllers.
The left throttle was track only.
The service manual talks of adding bulbs to track power to help whitles.
So... for a little experiment I decide to make up a test set with some automotive light bulbs. 21w & 5w. Very interesting. 2) 21w bulbs hooked to track power was remarkable. Every postwar & modern train worked quite well. Even my new General with train sounds worked quite well.
Thomas was most surprising. Without the bulbs running just loco alone the whistle wouldn't sound & he would take off like a jack rabbit from the 5v. With the bulbs the whistle worked 100% of the time & no speed change. He's a good puller, with a heavy train, still no speed change. That surprised me.
I added a 3rd 21w bulb still good. Several 2300 PW passenger cars with him or other locos still good.
I tried 30w of bulbs. That was on the cusp of threshold for working. Seemed like they all liked the 2 21w better. The amps was about 3.5 for the 2 bulbs not including train. I didn't check total train & bulb amps yet.
The heat from the bulbs is tremendous.
Not suggesting adding 80w of consumers to the transformer is a good idea, but was an interesting experiment.
Agian, I want to get some zeners.
Very best, Don Johnson

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