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Recently a friend gifted me a Lionel 6-18018 (Vintage 1992, #4501, 2-8-2 Southern RR Mikado) Based on provided instructions, This Locomotive and Tender utilizes a Lionel 5906 controller (included in the box) to activate the Bell.

The Lionel 6-18018 (Vintage 1992, #4501 is of the Lionel LLC - Richard Kughn/Neil Young era and is a conventionally controlled Locomotive (i.e., variable voltage Transformer).

I have a KW Transformer that is deemed compatible with the Lionel 5906 Sound activation Button for sounding the Bell.

I have attached, for reference, selected sections of the O&M Instructions included with the #4501 Mikado, these provide wiring detail for adding the 5906 Sound Activation Button. (Figure 5 for “AC Transformers with built-in Whistle Actuator”.)

It is my understanding, based on previous Forum “Posts”:

  • Activating the Whistle control on the KW “adds a negative DC bias to the center rail, the sound activation the button (5906) adds a positive DC bias to the center rail.”

Based on the O&M wiring instructions (attached) I added the 5906 Button to the KW circuit and, using a Fluke 115 Digital VOM, set to DC, verified the expected DC bias polarity. (The Red test lead of the Fluke connected to the center rail and Black lead connected to the outer (common) rail. The result:

  • As expected, Activating the Whistle control on the KW “adds a negative DC bias to the center rail, the sound activation the button (5906) adds a positive DC bias to the center rail.

After the above verifications, I placed the Locomotive and Tender on the track. However, I did not get the expected results.

  • Results: KW activates the bell and the 5906 button activates the bell. No whistle activation.

I removed the 5906 Button from the circuit and connected only the KW to the track and verified again with the Fluke 115 connected to the center and outside rails that activating the whistle control on the KW adds a negative DC bias to the center rail. I placed the Locomotive and Tender on the track.

  • Results: Activating the Whistle control sounds the Bell (versus the whistle).

Without going into detail, I tried various wiring configurations (eg., reverse wiring of the 5906 button etc.) but never achieving the expected results. (If interested, I can also post those wiring configurations and results - although never the desired result.)

The only and very unconventional configuration that achieved the desired result was wiring the 5906 Button in the circuit as instructed and reversing the “A” and “U” terminations at the KW. This in effect reversed the anode and cathode orientation of the diode in the KW and the diodes in the 5906. However, it connects “A” (power) to the common “outside” rails and “U” (common) to the “center” rails.

(At one time I found a schematic of the 5906 Posted on the OGR Forum. However, I have not been successful in recent searches to find this Posting/circuit.)

I did find a “Posting” that states “The Sound Activation Button uses six diodes in one direction and one diode in the other direction.

As a “double check” I verified the KW diode orientation based on the Lionel Service Manual by visual inspection and manually tracing wiring. For reference, I have attached page 1 of the Lionel KW Service Manual that I used which provides a schematic of the KW whistle control when activated.

(As a sidebar, several years ago I replaced the original KW rectifier with a NTE5994 Stud mount rectifier rated 600 V max and 40 A max – overkill I know.) Based on my “double check”, the diode orientation is per the KW Service Manual.

Out of curiosity, I unboxed my original Lionel 671 Turbine and Tender. (Santa brought the 671 and KW at the same time.) The whistle operated as expected with A to center rail and U to outside rail. Subsequently, I reversed the A/U connections at the KW. The whistle of the 671 sounded as expected (i.e., the 671 was not “A” and “U” orientation selective as is the 4501 Mikado).

It appears the 4501 Mikado of the Lionel LLC - Richard Kughn/Neil Young era electronic design is sensitive to DC positive/negative orientation but are not consistent with previous Lionel Transformers.

I have another steam locomotive of the Lionel-FunDimension era that has a motor driven whistle. I modified the wiring (switched wires) in the tender to make it compatible with the KW (i.e., It would not respond to the KW unless I swapped A and U Connections at the track. Therefore, to keep the KW and Service Manual schematic consistent, I modified the wiring in the tender).

I am open to more test configurations if desired. Please let me know.

My goal is to understand and resolve this puzzle electrically and technically.

How do I overcome the seemingly puzzled wiring related to the 4501 Mikado???

Thanks for your support.


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I purchased a refurbished KW that had the diode replaced. It was put in backwards, so my "whistle" control activates the bell. A poster here with a handle something like "ADXRob" said that the Lionel manual has a misprint, and shows the diode backward from what it is actually supposed to be.

Hi Ken,

Thanks for your “tip” – regarding a possible “Lionel Service Manual Misprint” related to the Diode orientation on the schematic. Your reply prompted me to review the ZW schematic and search the OGR Forum for similar ZW issues related to the Diode orientation.

Since the KW and ZW are of the same era, it is likely any error in the schematic drawings may have been carried over to other Transformer schematics as well.

In my search I found a previous OGR Forum posting, dated 1/22/22, by Forum member “vroberts”, titled “Whistle Waveform from Model ZW Transformer”.

In the various replies and discussions “vroberts” writes the following on 1/24/22.


“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 a prior design engineer myself, I think it would have been natural for the Lionel 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.”


However, this reorientation is in conflict with the statement below that is in my original posting that I found in a general search of the topic.

  • Activating the Whistle control on the KW “adds a negative DC bias to the center rail, the sound activation the button (5906) adds a positive DC bias to the center rail.”

However, I plan to “open up” the KW and swap the diode orientation and report the results. This will provide a positive DC bias on the rails versus a negative bias for the whisle control. As noted in my original post, my vintage Lionel 671 was not DC polarity sensitive.

I “opened” the KW and reversed the orientation of the diode/rectifier (i.e., the anode is now connected to the compensating winding and resistor) which now places a positive DC bias on the center rail.

A live check of this change provided the desired results. The 4501 Locomotive and the 5906 sound button operate as expected (i.e., the KW activates the whistle and the 5906 button the bell).

For my own purpose and documentation, I revised the schematics on pages 1 and 2 in the original KW Lionel Service Manual to depict the correct orientation of the Diode. And I created a cover sheet to document my revisions.

I have attached my revised document for use by others as needed.


@Ken Wing posted:

Credit where credit due, I believe my info came originally from @ADCX Rob

Yes, while the pictorial diagrams are obviously correct, the original schematics for multi-control transformers show the wrong polarity of the rectifier.

This has come back to bite "rebuilders" who follow the schematics and replace the rectifiers with silicon diodes... it wouldn't make any difference running equipment made prior to 1972 but starting then, it does matter.

Last edited by ADCX Rob

Thanks. Rob for the confirmation. Without the tip from Ken, based on your original original post, I am sure I would still be working on my "puzzle". I have been "programmed" over the years to trust the documentation. And back in the early days I replaced the disc rectifier at least twice and achieved the expected results - so in a way I set myself up.


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