Author Topic: Overland AMD-103 Diesel - quick overview  (Read 316 times)

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Overland AMD-103 Diesel - quick overview
« on: June 07, 2019, 01:27:24 AM »
George's recent thread about resurrecting one of those made me dig up some old photos of mine.  Here is a quick review of the model, and the modifications I added to it (back when it was first offered for sale in the '90s).  That was before DCC, so I added my own lighting effects.  I originally posted this info on the Atlas Forum (which is now gone).

This was the first (brass or plastic) N scale model produced of then-new Amtrak Genesis revolutionary locomotive utilizing a monocoque body.  It was a precursor to the P42.

The model has a typical brass construction.  Detail level is quite high, and the mechanism is what is expected from brass models - not as good or quiet as contemporary plastic N scale diesel locos.  Spookshow (Mark) has his typical review available here.

The model is a good representation of the prototype.  Notice that the early examples of this loco had 3 openings over the windshield: The outer ones were Xenon strobe lights, while the center one was a red emergency beacon (like the one on F40PH locos).  But disappointingly,  those were simply represented by a decal on the cast-brass nose.  I wanted to illuminate them, so I risked milling them out on my milling machine (without making mistakes or even damaging the paint).  I succeeded.  This photo shows the finished model with the light bulbs mounted behind the "glass" covers (which are made form epoxy glue).

The rear of the model features a window for the hostler's cab. This was a feature unique to the AMD-103 (aka P40DC).  Kato's P42 models do  not have that window.

Top view.

Side views. The initial paint scheme had the red/white/blue strip which faded towards the rear of the loco.  I read somewhere that this fading was supposed to create a waving-like effect when the loco passed the observer at high speed.

My model is from the initial run, utilizing the overly-complex mechanical design.
The motor shaft, instead of driving a worm, drives a series of spur gears in each truck's gear tower. Those in turn drive a short drive shaft in the the truck, with worms on each end, finally driving the gears mounted on the wheelset axles.

Another view of the bottom side.

Because there are several gears turning at the same high speed as the motor shaft, the mechanism will always have some inherent whine.  I did take everything apart and put it back together making sure everything was in best alignment. That slightly reduced the whine, but it did not eliminate it (not that I expected that it would).

Borrowing Spookshow's image, this model has a typical brass-model rats-nest of wires.

To clean up the wiring I etched couple of PC boards.  The rear PC board was just used to interconnect the truck leads to the front PC board.  Having solder pads near the truck's pickup wires makes servicing the loco easier than dealing with original rats-nest of wires.

On the front PC board I also installed diodes (red components on the right) to obtain 1.4 Volts needed for my constant lightning circuit (remember, this is a DC loco).

I also prefer not to have wires (umbilical cord) connecting the shell to the chassis.  Whenever possible I install contacts on the chassis engaging corresponding metal pads in the shell. That way I can easily disassemble and service the model without wires getting in my way.
Those contacts (to pass the 1.4V to the shell and all the lights mounted there) are visible on top of the motor bracket.  Basically it's a small PC board with 2 pads, with flexible phosphor-bronze strips soldered to those pads.  The shell has a similar PC board with 2 pads glued inside the roof, directly over those contact strips.  When the shell is placed over the chassis those contact strips will be touching the pads on the roof, connecting them electrically.

This photo shows the flasher circuit I built and installed in this model.  Also, a small portion of the PC board with pads to connect to the chassis' contact strips glued to the roof is visible at the left edge of the photo.

Front part of the shell with all the lights installed.  Since this was before tiny white SMD LEDs were available, I used Miniatronics 1.2mm 1.5V incandescent bulbs.

Light bulbs do eventually burn out and have to be replaced. To facilitate easy replacement I used brass tube guides for the bulbs and their leads are soldered to PC board interconnects.  The bulbs are slid into the tubes until the touch inside of the light lenses on the locomotives nose. If they need to be replaced, I simply unsolder the burned bulb, pull it out of the tube, then slide new bulb into the tube and solder it to the pads on the PC board.

The 4 tubes with bulbs visible in the photo are headlights and ditch lights.  The 2 other tubes, further down, are for the strobe lights.  I also tinted the strobe light bulbs with a thin layer of Tamiya transparent blue paint to simulate "cool white" light of a Xenon strobe.

While not really visible in this photo, I also added cab walls, so if one looks through the windshield, the loco's innards will not be visible.

Maybe one of these days I'll update this model with DCC decoder and run it with my Kato P42s.
« Last Edit: June 08, 2019, 07:52:57 PM by GaryHinshaw »
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