Here are some stories about putting DCC decoders in small locomotives.
Southern Pacific C-9 2-8-0 #2765
Crossing First Street in San Jose
This locomotive is a brass import from the 1980's. This was the first locomotive I'd converted to DCC, first locomotive I'd converted to sound, and my first brass locomotive. Messing with the locomotive was always traumatic, such as when I broke a piston rod, or when I had to disassemble the whole locomotive for painting. Still, I'm very pleased with how it's come out.
2765 has a Soundtraxx decoder in the engine's boiler. A 1 inch speaker is located in the whaleback tender, facing down through holes drilled in the floor. Both headlights are wired, and two LEDs in the firebox provide fire effects. Having the decoder in the boiler made wiring the locomotive easier, for it cut the number of wires needed. There are currently three wires between the tender and locomotive -- two for the speaker, one for the headlight. Four wires would have been needed if the decoder was in the tender -- power, both motor leads, and headlight -- and the firebox effects would have needed at least two additional leads. However, the decoder takes the space normally filled by a lead weight, so the locomotive doesn't pull as many cars as it should. The firebox effects are neat, but they're just not so special that I'd use them again.
Wires from the locomotive are routed on the left and right sides, and run through holes in the left and right front corners of the tender floor. The holes are small and can barely fit the miniconnectors I used. Separating the tender and locomotive is a painful job requiring multiple tweezers to guide the miniconnectors through the holes.
I painted the locomotive with Floquil paints. The base color is the lightened black often suggested in the model press. I used a slightly lightened Floquil graphite for the smokebox and firebox; the color's almost the same tone as the black. This was a happy coincidence, for it makes the locomotive resemble photos from before 1946. (After 1946, SP painted the fronts of the smokebox silver, making the front of the locomotive much brighter.) I'm really happy with the weathering on the locomotive; the running gear has a gray dusty appearance. I used dry-brushing and an airbrush to add white deposits from evaporating wire and black stains from oil spills.
Southern Pacific C-26 #3444
Lightly-modified Bachmann Spectrum plastic locomotive
3444 pulls a freight train past the Market Street Station
Even though the Bachmann locomotive isn't a Southern Pacific prototype, my minimal changes give it an SP feel. Most importantly, I didn't try to do anything requiring major reworks. The locomotive certainly doesn't look like a common SP consolidation; it's much too "chunky" and the ladders on the front end certainly aren't a common SP feature. To get around this, I looked at the uncommon Consolidations in "Century of Southern Pacific Steam", a great book showing the range of Southern Pacific locomotives. I found the class C-26 locomotives matched the Bachman well. These locomotives were built for the El Paso and Southwest railroad, and inherited by the SP when they bought the EP&SW. The locomotives went to the SP's Mexican subsidiary in the 1920's, but saw some use in the States during World War II.
To make the locomotive resemble the C-26, I added number boards and converted the tender to oil by making a new oil bunker top from sheet styrene. The paint job made the greatest change -- the graphite smokebox and red fittings completed the transformation. I again tried to use a lightened black as the base color. However, I'm not happy with the final color. I'm not sure if I chose too light a color, if the Polly-Scale paints just look different than Floquil paints, or if the plastic model just is destined to look different. I didn't bother to paint the running gear; it's still a darker black.
Sheet styrene oil bunker on stock tender
The Bachmann was already wired for DCC, but I did some further modifications. I added a Soundtraxx DCC decoder. The decoder's in the tender along with an edge-port speaker pointing out the front of the tender. Both of these squeeze into the tender. The decoder is at the back, double-stick taped to the tender, and arranged to one side to miss the screw securing the tank body to the frame. tender. The speaker fits at the front of the tender. The existing circuit board in the tender was removed; the decoder's hardwired to the connector for wires from the locomotive and to wires from the tender rucks. The worst part of installing the decoder was accidentally pinching the wires to the headlight when disassembling the engine. The tender connector's fragile -- wires have broken in the past.
Inside the Bachmann tender
It's a great locomotive -- it runs well and can pull more cars than many of the brass locomotives.
Southern Pacific T-31 4-6-0 #2358Westside Model Company brass import from the 1970's
I'd hoped to put a Soundtraxx decoder in this locomotive. The biggest problem was access -- the decoder and speaker had to fit in the Vanderbilt tender, but the tender was soldered shut. I created access by unsoldering a sheet covering the top of the oil tank and cutting an access hole in the top of the oil tank structure. I could then maneuver a Soundtraxx decoder into the water tank portion of the tender, and place a speaker in the oil tender.
The top of the oil tank is removable to reach the DCC decoder.
The actual details of cutting open the tender was pretty low tech -- I pointed a pistol-type soldering iron at the top of the oil tank and kept heating it til the solder melted and the top let go. I cut the access hole with a dremel; if I remember correctly, I used a drill to put holes along the edges of the cut, and finished off with a cutoff wheel. The original oil tank top had stripwood strips added so it could be placed back on the top of the oil tank.
I never figured out a good way to get the sound out of the tender, and eventually gave up on sound. The locomotive currently has a Lenz LE130XF back-EMF decoder powering a can motor.
Four wires run between the locomotive and tender: two for the motor, one for the headlight, and one for track power. I use a Circuitron 4 pin connector for the locomotive-tender connection.
My primary modifications for this locomotive was to repaint it and replace the headlight and tender backup light so both could be illuminated. The tender light was the most interesting -- the back of the tender was soldered shut. When I replaced the old headlight, I also drilled holes so its wires could be routed through the tender deck, then through a hole at the bottom of the tank. The light's wire then ran inside the underframe (which was detachable), then back into the front of the tank to reach the DCC decoder. I only needed to route one wire -- all my headlights are 12 volt bulbs, with one wire connected to a DCC decoder's function output and the other to one track (or, in the case of this locomotive, straight to the body of the tender.) This approach keeps the voltage on the bulb low. There's also one less wire to route.
Southern Pacific S-12 0-6-0 #1234Sunset brass import from the 1970's
234 curves onto Fourth Street for the street running down to industries south of San Jose. The large building behind the locomotive is the Richmond Chase Cannery.
Decoder mounted on top of motor
Adding DCC to this locomotive was easy, but there was simply no way to put sound in it. The cylindrical tender can't be opened as far as I can tell, so I instead had to put the decoder in the engine. The N-scale Lenz decoder (I don't remember the exact model)is placed just above the small open frame motor. Only the front headlight is powered. The back headlight isn't powered because there was no good way to route a wire to it. On the positive side, because the decoder's in the engine, there's no need to run any wires between the engine and tender -- the drawbar connection supplies the power from one rail. On this locomotive (and all the others), I use a microconnector for the headlight lead so I can separate the boiler and frame for maintenance and painting. The other lead from the bulb gets soldered to the locomotive body -- usually the back of the smokebox.
I bought this locomotive secondhand, and did very little work on it -- I even kept the pure black paint job, even if the locomotive's darker than any of my others. My one change was to put a bulb in the front headlight. Rather than drill a hole into the existing solid headlight, I instead unsoldered it and replaced it with a Precison Scale hollow headlight, then placed a bulb inside that. The smokebox got a new coat of graphite paint after the soldering.
Unsoldering the headlight was a bit of an adventure. My pistol-style soldering iron couldn't generate enough heat. The previous owners of our house had helpfully left a plumbing-style propane torch, so I tried that out. As soon as I lit it and pointed the torch at the locomotive, the huge flame made the old headlight casting glow red then fall off. I'm amazed more parts didn't fall off the locomotive.
In Progress: Southern Pacific T-1 4-6-0Bachman 4-6-0 high-boiler plastic locomotive
My next project is to make a Bachmann 4-6-0 into a believable small SP engine. I'll probably try to add a few key details as I did with 3444. I'm not sure what to do with the tender. Bachmann sells a nice Vanderbilt tender, but I don't know how to fit both a speaker and Soundtraxx decoder. The internal space is broken up with screws and plastic, so it's not an easy task. The alternative would be to convert the square tender that came with the locomotive into an oil tender. This would make installing a sound decoder much easier.Lessons learned
So what have I learned from all these installations?• The hard part of installing a decoder (especially a sound decoder) is routing the wires. There's almost always room for the decoder, but the wires coming off the decoder add a lot of bulk to the decoder; routing the wires neatly and in a way that permits disassembly, is much worse. Think about wire routes, and use tape to secure wires in place when possible. For example, the microconnector for 1234's headlight is actually taped to the top of the gearbox to keep it out of the way.
• I've found it easiest to use 12 volt bulbs for headlights, with one wire grounded to the frame. The lights are still adequately bright, and one less wire makes installation so much easier.
• For the last decoder installations, I've used a Circuitron 4 pin plug between the tender and locomotive. I've used the same pins for the same purpose; this is very helpful because I can test that the tender wiring is correct by connecting it to an already-working locomotive with the same plug. I'm thinking of converting the rest of my locomotives to use a standard plug.