Page 12 - January February 2012

Tsunami Sound for Athearn’s U50
This is a cautionary tale. Athearn’s new HO scale model of the General Electric U50 locomotive comes in both Union Pacific and Southern Pacific versions, these being the only roads to purchase this 5000 hp double diesel. Commonly known as “Whirlybirds” because of the noise made by the two equipment blowers and associated fans located at either end of the long hood, they were essentially two GE U-25B locos joined back-to- back, with two GE FDL-16 prime movers providing the 5000 hp. The running gear came from traded-in 4500 hp gas turbines, hence the unusual B+B–B+B wheel arrangement on a span bolster. (After GE introduced the U50C the designation became U50D.)
Athearn have utilised the gas turbine chassis as the basis for the U50, incorporating similar provision for twin 1- or 1.25-inch speakers, but unlike the gas turbines, the U50 possesses a nar- row hood with walkways. This means that there is little room to enclose a speaker in a baffle, and if an attempt is made to use the circular Soundtraxx plastic baffles, the hood cannot be re- placed on the chassis because the speaker enclosures will prevent the walkways from resting on the flat edges of the chassis. I discovered this by allowing my enthusiasm to over- come my intelligence.
Athearn’s U50 is in their “Ready-to-Roll” line and as such it comes “DCC and sound ready”. This means it has the afore- mentioned provision for speakers, plus both eight-pin and nine-pin decoder sockets on the PC boards. There may just be room for a small DCC decoder above these boards, but certainly not for the fairly large Soundtraxx Tsunami I was intending to install. Soundtraxx has recently introduced a new Tsunami TSU-1000 decoder with twin FDL-16 sounds specifically for the U50. It is part number 827124 and I obtained my example from Sunningwell Command Control. This is a Universal style or wired decoder, not a replacement board. It includes a capacitor to smooth out power supply. (For an alternative, I believe that QSI may make a “drop-in” decoder available for the U50 in the near future.) In retrospect, the simplest installation (for those with confidence in their soldering abilities) might be to remove the Athearn PCBs completely, and the 1.5 volt lamps, and hard- wire in the Tsunami and replacement LEDs. However, I decided to go with the “ready-to-roll” concept and utilise the existing components.
The first step is to take off the body shell. There are four cross- head screws on the underside of the chassis, two above each front and rear truck. Once these are removed, the loco shell can easily be lifted off the power chassis. But care needs to be taken because the wires for the headlight remain attached to the rear or main PC board “B”. These are connected by plastic tabs that simply pull off, and the wires can then be pulled out and the shell put aside until it comes time to replace it. (I discovered that the reason why the 1.5-volt lamps in Athearn’s models produce such feeble light is that the power connections on the PCB only provide 1.0 volt DC to the lamps!)
Once the shell is out of the way, one is confronted by a mass of wiring. Carefully locate the nine-pin socket on the front PCB “A”.
There is a jumper board installed in the socket that has to be removed. (One must remove the jumper whatever DCC decoder is being installed, and whichever socket is being used.) Gently pull the nine-pin socket and its attached wires up and free from the front PCB. This socket will remain wired to the rear main PCB “B”. It will now be obvious that there is simply insufficient room for the Soundtraxx Tsunami decoder anywhere other than where the front PCB “A” is located. So remove the two small screws that hold the PC board to the metal chassis, and lift up the board, taking care to retain all the wire connections intact! Since I didn’t wish to discard this PCB, an alternative location had to be found for it: swing it around and, using double-sided adhesive tape, mount it upside-down below the rear main PCB “B”. One needs to slot it between the grey wires
Tom Watson (NMRA-BR Member Aid Officer)
from the rear truck pick-ups, but there is ample room for it to hang above the rear gear tower worm cover. The sticky tape acts as effective insulation from the top board, and no adverse effects such as overheating have manifested themselves to date. Fortunately the wiring is long enough to allow this relocation without difficulty.
Now that the front PCB is out of the way, the Tsunami decoder can be installed in the vacated space. The Tsunami comes with two purple speaker wires and two wires (red and black) attached to a capacitor at one end, and the usual eight wires for power and functions at the other. These have to be disconnected so that the decoder can be plugged into the nine-pin socket. In order to do this it is necessary to very carefully cut around the purple heat-shrink covering of the decoder where the wires are plugged in, so that the wires can be unplugged as a unit. Just sufficient material must be removed to allow a small screwdriver (or similar tool) to lever out the eight-wire harness. (It is my understanding that Soundtraxx will allow this much of the protective covering to be removed from the decoder without voiding the warranty.) Once the harness has been disconnected, the decoder can be plugged into the nine-pin socket on the loco and attached to the chassis in place of the PCB using double- sided tape plus some black insulation tape. Mount it upside- down (ie flat side up) so as not to interfere with the loco shell when that is replaced.
One is now faced with the question of where to put the capaci- tor. My first thought was to place it under the decoder and on top of the front worm cover. However, it was soon evident that it was a tight fit and inhibited the free movement of the gear tower. So let’s pull it back out and leave it hanging whilst we have a look at the speakers.
It is common knowledge that speakers will only deliver their proper performance if they are enclosed in an appropriate baffle. This is an air-tight (and thus sound-wave-proof ) enclosure around one side of a speaker, thus ensuring that the pressure waves from one side of the speaker are not cancelled out by those from the opposite side. In a diesel this enclosure is often provided by the loco body shell itself, or by the fuel tank. It was clear that mounting the speakers in the U50 would be much easier if one first removed the cab assembly from the front (it can be levered off with a bit of care; and you might wish to paint the dials etc and add some crew members). Also disconnect the back-up lamp wires from the rear PCB. Then unscrew the two yellow blower and fan housings and set them aside. This allows one to get at the pre-drilled front and rear speaker de- pressions. As mentioned, because the shell of the U50 has massive openings at front and rear, top and sides, my first thought was to enclose 1-inch Soundtraxx speakers (part #810054) in Soundtraxx baffles (part #810110). When assem- bled, these worked a treat and looked to be a nice fit in the chassis. Until I came to replace the shell; at which point I realised I had been stupid because the baffles were preventing the shell from sitting on the chassis correctly.
No doubt there will be others who will use smaller speakers or enclosed hi-bass speakers, but I was determined to use my two 1-inch speakers. So (with some difficulty) I removed the speakers from the baffles and simply glued them in place over the speaker openings using Adair Shops “Sound Bond Glue”. This is flexible pink white-type glue, which makes an effective seal around the speakers (available from Model Junction). Alternatively one could also have used Soundtraxx self-adhesive 1-inch gaskets (part #810119). Connect the speakers in series, with one purple wire from the decoder going to the positive terminal on the front speaker and the other purple wire going to the negative terminal on the rear speaker. Solder a connecting wire from the negative terminal of the front speaker to the positive terminal of the rear speaker. Ensure that this wire does not interfere with the mechanism and as far as possible runs
12 ROUNDHOUSE