We need more heavy motive power for preliminary op sessions, so I’m back to finishing the Century 425. There is little space in the long hood because Overland soldered a cross support member that blocks much of the access. In the cab there seems nothing to offer support.
I’ve been experimenting with several solutions, none of which looked good. Most involved mounting 1206 surface-mount LEDs to the back of various stacks of white styrene. All produced horrible bright spots. Some previous locomotives received elaborate light boxes that spaced the LEDs away from the diffuser, but particularly in the rear of this locomotive I couldn’t fit anything comparable.
A few weeks ago it finally came to me to use a light pipe. A strip of 1/16" polycarbonate, ripped from an 8x10 sheet procured at a home store, was ACC’d to the back of a 0.015" thick white styrene diffuser, sized to fit the inside of the shell, and with enough overlap on the inside for glue.
Onto the light pipe two 1206 2700K warm white LEDs from Mouser were glued. The assembly, held down to the work table with tape, offered a perfect platform for attaching wires. These two LEDs, each of which drops about 3 Volts, are hooked in series. Then each end’s LEDs get wired in parallel, and fed through a single 1K Ohm resistor. There will be plenty of light, and because these LEDs came from the same reel (batch), and were made by Cree instead of a random Chinese vendor, they are very well matched to each other. Unlike siblings at the dinner table, they share current equally.
Once each was assembled and tested, I packed gray never-hardening modeling clay around the back to serve as a stray light dam. The clay also helped hold each fixture in place prior to adding a drop of ACC in each outside corner to permanently hold it in place.
Here’s an inside view of the rear light package. Each number board has 2 LEDs, one each for the two rear headlights, white and red 0402 class light LEDs on each side (white and black wires, respectively. Finally there is a single walkway light not visible near the bottom-center threaded mounting hole.
In the last photo we see the number boards from the outside. Prior to adding black background decals, the perimeter of the white area will receive black gloss paint to hide any gaps around the decals.
Yes, the upper headlight is loose and has slid outside of its brass investment casting. It will receive additional glue before the rear headlights are also packed in gray clay.
A Tang-Band 1925 speaker module will attach with double-sided tape, firing down, to the crossbar in the second photo, and another that is just the right distance inside the shell. Sound primarily exits open radiator intake air louvers on either side.
FYI the tiny 0402 LEDs were procured from German eBay seller LEDBaron. Each received a small blob of ACC to insulate the solder joints so that they would not short to the brass shell and cause a regrettable problem.