Dead-Rail Conversion of a Sunset 3rd Rail Allegheny 2-6-6-6 Locomotive with MTH Proto-Sound 3


Don’t jump to conclusions; MTH did NOT manufacture the C&O 2-6-6-6 Allegheny with MTH Proto-Sound 2.0 (PS2.0) I found on eBay. Instead, it’s a brass locomotive produced by Sunset 3rd Rail (Figure 1) and converted to PS2.0 (see MTH PS2.0 Upgrade Manual). See Figure 2. The retrofit replaced the original tender QSI-OEM Digital Soundboards, the wiring harnesses for the tender and locomotive, and the Suethe smoke units and their voltage regulator board in the locomotive.

Figure 1: Sunset 3rd Rail C&O Allegheny box info
Figure 2: Original tender Proto-Sound 2.0 electronics and harness wiring

It was a well-done conversion, so I was very reluctant to tear out the tender PS2.0 control board, and the wiring harnesses in the tender and locomotive. The PS2.0 conversion used an MTH smoke unit that has both fan speed and smoke intensity controls.

Figure 3: MTH Smoke Unit with funnel

The CVP Airwire receiver boards I typically use for dead-rail conversion don’t have this level of smoke unit control. And, the PS2.0 board used a speed encoder on the locomotive motor’s flywheel to synchronize the PS2.0 board’s sound. See Figure 5 for the speed encoder reader and flywheel strip and 5b for additional electrical connections.

Figure 4: Original Constant Voltage Unit wiring with dead-rail modifications indicated
Figure 5: Speed encoder, flywheel strip, and electrical connections for the Constant Voltage Unit.
Figure 5b: Locomotive harness wiring after modifications connecting the Constant Voltage Source to Battery +/- and replacing incandescent bulbs with LED’s

All of these built-in features were pretty nice, but I still wanted a dead-rail conversion.

Hmm… Looking around, I found out that Proto-Sound 3.0 (PS3.0) had DCC/DCS control options and the wiring harnesses are the same for PS2.0 and PS3.0 boards (see for instance MTH PS3.0 Upgrade Manual). Things are looking up. Then I found a great site, Ray’s Electric Trainworks, that provides PS3.0 replacement boards and great support.

My thought was this: if I can upgrade the locomotive to PS3.0, then I can take the following steps. Jumper the PS3.0 board to DCC operation, disconnect the original rail power/communication wiring, and re-connect the rail power/communication wiring to the DCC outputs of a CVP Airwire CONVRTR-60X receiver (CONVRTR Users Guide). Easy, right? Not so fast.

Ray at Ray’s Electric Trainworks was a great help: he steered me to the right PS3.0 card that I needed for the tender, and he loaded the Allegheny sound file for me. Otherwise, I would need a bunch of DCS infrastructure to load the sound file. And, he gave me a rebate for the old PS2.0 card! Great guy.

OK, I have the PS3.0 card from Ray. The PS3.0 card came mounted in its plastic carriage that is screw-mounts on the tender chassis through pre-existing holes. The heatsink orients a bit differently between the PS2.0 and PS3.0 – no big deal – I just needed to drill a hole in the tender chassis in a slightly different place. The PS3.0 doesn’t use a Ni-MH battery, so out it went. That was a good thing, too, since I needed the real-estate for the replacement LiPO battery that would supply power to the control boards, lights, smoke unit, and the locomotive.

Locomotive Modifications

Here is a diagram of the locomotive wiring harness from the MTH PS3.0 Upgrade Manual with my annotations.

Figure 6: Locomotive PS3.0 wiring harness with modifications indicated

Since I wouldn’t be sending track power to the tender, I cut the Ground Lead and Pickup Roller Leads wires. I re-purposed them by connecting these harness wires to the Constant Voltage Unit, which is a heat-shrink blob whose input leads were cut from their original chassis connections (see Figure 5 again).

While I was at it, to reduce power consumption, I removed the incandescent cabin and headlight bulbs, and I replaced them with Yeloglo LED’s (see Yeloglo description) whose + input was in series with the Yeloglo’s 470-ohm resistor for 10-16 Volt operation. Yeloglo LED’s have an excellent yellowish output reminiscent of incandescent light.

Tender Modifications

The diagram below shows the tender’s wiring harness with my modifications.

Figure 7: Tender PS3.0 wiring harness with modifications indicated

Continuity testing revealed that the locomotive Roller Pickup Leads and the Ground Lead connected to Pin 1 and 3 of the 7-pin connector, respectively.

Note that BOTH locomotive and tender Ground Leads (both are black) that are input to the PS3.0 on pins 3 and 4 of the 7-pin connector, respectively, MUST BE DISCONNECTED FROM THE LOCO/TENDER FRAMES AND CONNECTED to the “B” DCC output of the CONVRTR. This pair of connections was the trick. I initially connected ONLY the Ground Lead coming from the locomotive (pin 3 of the 7-pin connector) to the CONVRTR, and it did NOT work! I don’t know if only connecting pin 4 of the 7-pin connector would work – I didn’t try it.

Similarly, I disconnected the red wire that is input to the PS3.0 on pin 1 of the 7-pin connector (which originally connected to the locomotive Roller Pickup Leads) from the plug bundle that connects the tender to the locomotive, and I connected it to the “A” output of the CONVRTR.

The “harness side” of the two cut wires originally going to the Pickup Roller Leads (red) and Ground Lead (black) on the locomotive, were connected to switched Battery + and Battery – (ground), respectively, to provide power to the locomotive’s Constant Power Unit.

Note: “Switched B+” means battery power coming from the Battery’s + terminal that is turned on or off with a switch (you want to be able to turn off the power!). “Battery – (ground)” means the connection to the Battery’s negative terminal that is usually grounded to the tender chassis by a battery charging plug.

A picture is worth a thousand words, so studying Figures 6 and 7 will give you the story of what wiring cuts and re-connections that are needed to convert a Proto-Sound 3.0 steam locomotive to dead-rail.

Other Dead-Rail Conversion Details

Of course, there are other aspects to the dead-rail conversion that are required. These aspects include the addition of battery power and CONVRTR connections and removal of center-rail pick-ups and electrical connections that are part of a typical 3-rail to dead-rail conversion for an O scale steam locomotive. These conversion aspects are discussed in another blog.


In summary, if you have a locomotive with the PS3.0 installed, conversion to battery-powered DCC operation and radio control (dead-rail) is straightforward once you know the few wiring cuts and re-connections you need to make. The DCC operations for this particular locomotive can be found in the MTH document “Premier 2-6-6-6 Allegheny Steam Engine .” What you preserve with the PS3.0 is good DCC functionality, the original sound, and coordinated smoke – and that’s a pretty nice combination.