One of my "better improvements" was adding lost wax casting marker lamps. My first attempt was to use diodes in series with the Rivarossi motor to power the 1½ volt micro bulbs. Two diodes in series creates a 1.4 volt drop, perfect for 1½ volt lamps. That worked for many years until I remotored my articulated fleet. The new Rare Earth magnet motors draw less then ¼ of the original Rivarossi motor thus the diode trick doesn't work at creep speeds. I needed a new way for constant voltage to power the 1½ volt marker lamps.
As I'm a retired Electronic Techie it was time to use some of my electronic knowledge. The obvious answer was to build a LM317 regulator with a 1.4 volt output. Using the 1 mm diameter micro bulbs the current draw is 20 ma per bulb so 40 ma is a piece of cake for the 1.5 amp rated LM317. I originally installed the regulators in my locomotives using the frame/weight as a heat sink to get rid of the heat from the LM317.
As time passed I wired all of my locomotives for DCC operation. Because I only have a few DCC decoders I move them around to the "locomotives of the hour" making use of my 8 DCC decoders.
About a year ago I picked up a couple more 1970s version Rivarossi Cab Forwards that I put on my display shelving and recently decided to restore them and put them into service. Over time I have found several better solutions for my end product. I have done quite a bit of research on DCC over the last year and was kicking around some wiring changes to my locomotives and this is a good opportunity to test my ideas.
My plan is to use DCC Function 3 to control the marker lights, under normal route scheduling the marker/classification lights would be off. Thanks to the NMRA DCC design folks it's rather easy to do. By using pin 3 on the 8 pin DCC connector and adding a green wire to the tender cable I can control the marker lights with the F3 command. Now things get even better, the 1.4 volt regulator can be removed and replaced with a shunt regulator. Removing the regulator allows more room for additional weight in the locomotive.
I have had a problem making baffles for the DCC sound decoder speakers that give good bass response so I came up with a rather easy way to accomplish that too. I use 28 mm 1 watt speakers in my tenders and by using a ¾" PVC pipe cap I solved the baffle problem too. It requires a bit of cutting and filing but it sounds fantastic, it's best baffle I've come up with so far.
I cut the PVC pipe cap to ¾" high and drilled a 3/16" hole in the side to pass the speaker wires.
The pipe cap is 1¼" in diameter so for it to clear the tender sides I took ⅛" off the sides with a file. My glue preference for this type of project is Crafters Amazing Goop, it is very strong but remains somewhat flexible and with sharp #11 blade the glue can be removed with the aid of long nose pliers.
The tender is ready for assembly, I need to do a bit of clean up to the shell details and it's ready to put behind a Cab Forward or AC9.
This is the finished drawing of my DCC wiring diagram for my Dual Canon EN22 motor Rivarossi locomotives. The 1.4 volt LM317 regulator has been removed and replaced with a 1.4 volt shunt regulator to power the marker lamps in the locomotive. The regulator consists of a DF005 bridge Rectifier in series with two 470Ω ½ watt resistors in parallel and powers the marker lights on and off with DCC Control Function 3.
After final checkout everything is functioning correctly. I'm not wild about shunt regulators but for this purpose it works very well. The circuit draws 50 milliamps max from the decoder to operate the two 20 ma bulbs in parallel at 1.4 volts.
The PDF file and AutoCad DWG of my drawing is available for download from my Google Drive by clicking here.
Important Update
Do not attempt to plug the connectors together between the boiler shell and the frame with the power on!
It took me an hour to remove and replace the marker bulbs after accidentally touching the 1.4 volt contact with the 12 volt contact to the number boards.
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