DURANGO & RIO GRANDE SOUTHERN RAILROAD - AUSTRALIA
SLIMTRACKS NARROW GAUGE WORKSHOPS
PRESENTS
“HOW TO WIRE A K27 HON3 LOCOMOTIVE WITH SML’s & TSUNAMI”
PART 2 – The Tender
By Laurie McLean Photos by the author
Oh she’s a woman alright, & made of steel,
Bright shiny lights & curves you can feel,
She can give you a whistle to see if you look,
But this lovely lady doesn’t know how to cook!
Take her out on the road, for a test run,
Together the two of us are going to have fun,
We’ve polished her up to make her look good
Hope she behaves like a good loco should?
With her tender behind, coupled at rear,
Just move over ‘Casey’ & let this bloke steer,
Sit back & relax, and have a D-Wheat,
She’s looking so good and traveling sweet.
G’Day again cobber’s, so you’re back for PART 2, the “Tender Behind”.
Got the Durango Wheat’s ready…. nice & cold are they?
In this second part we will be running the wires from the decoder to the tender & installing a
speaker inside that “black-box”. (It’s only a flight recorder if it’s tested on a banister test-track)
Now, we have checked the wheel gauge on the loco & tender wheels have we not? Very good.
Now remove the 4 screws holding the tender body to the floor – you did put them in a little see-thru
container with a lid on it didn’t you? Let’s not loose a screw now, we’ve only got started.
Notice anything – empty space? – No, not my glass, the space we intend to place the speaker. It’s
been measured & we have agreed to fit one of Tony’s Train Exchange Mini Oval Speakers inside.
What’s that – enclosure you say?...... of course, every speaker MUST have an enclosure otherwise
the sounds are poor & we all want the very best sound coming from our expensive Micro Tsunami
don’t we? Well, we will be making our very own enclosure & testing it in a moment.
Notice anything else? Have you checked the swing of the trucks to see if any of the wheels are
touching the body? Those “floating trucks” are a bit funny to try & get level but they do sit well on
the tracks. The 2 beams running down the middle of the floor have been shaped to clear the wheels
– notice the curved grooves where the trucks swing? PSC have had these cut away for clearance but
we need to make sure that there is no chance of a short – I hate SHORTS! Check they are clear.
Now that we have checked that the trucks will clear when they swing we need to take them off.
Careful – don’t loose the spring around the screw-pin – Woo-up a bit, we forgot to mark the trucks
before we take them off – let’s do this first. The insulated wheels are on the Engineer’s side on the
tender (& most brass) & the pick-up wheels are on the Fireman’s side. I place a tiny white dot in the
trucks & a corresponding white dot on the under floor so I know which way to put them back.
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DURANGO & RIO GRANDE SOUTHERN RAILROAD - AUSTRALIA
FIG.1
FIG.2
See the tiny white dots – they tell me which way to replace the trucks. (Handy hint.)
Figure 1 shows the tender body & the floor – AND, the extra wire I added to each bolster.
Why? I hear you say……… Well we need to get a reliable electrical pick-up so we don’t have a
“Leaping Lizard” hopping & spluttering along the track. We want smoothness for our little lady.
Because of the design of the “floating trucks” & with the Die-cast” metal body & floor we also have
a steel spacer/bearing washer that sits between the brass truck & the die-cast floor.
Not a good electrical path – it’s going to tarnish & get muck under it over time. So, extra pick-ups.
The draw bar pin is secured into the die-cast & transfers the electrical L/H rail power through it via
the draw bar to the locomotive.
Now we used the existing black wire on the loco by removing it from the motor terminal & placing
it on with the extra wipers we fitted on the locomotive. So, we need to use as much as what is
available to keep constant electrical paths getting to the decoder reliably. If one pick-up misses
collecting the L/H power we know that there are 2 or 3 other wipers or wheels that will keep things
running.
So, to get a better & more reliable electrical path for the current to flow through & to be able to
constantly reach the decoder, the “jumper” wire has been added to the brass on each truck. I will see
how this goes & if it plays up I will add another #30 wire to be directly soldered to the draw bar
itself. This would fix it if the steels washers don’t provide the flow path correctly.
Right then, we have taken care of the pick-ups & the trucks. Sweating by now….let’s have a “DW”
The speaker & its enclosure (speaker box) need to go inside the cavity in the tender body.
Because of the sloping angle of the coal plate, this prevents the use of a regular enclosure & speaker
combination. It is best to use the biggest size speaker that will fit inside. The detail PSC provided in
the tender is too good not to show off so the gusset plates will be seen & just half a coal load filling
the bin. Hmmm…..my glass is half empty too…..I’ll fix this now….hic
So, we need to make a custom speaker box/enclosure that will fit the contour of the body.
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DURANGO & RIO GRANDE SOUTHERN RAILROAD - AUSTRALIA
To do this, we first test fit the speaker by itself inside the body. Note where the speaker sits in
relation to the body, it must be under the edges. It can’t stick out past the body or the floor won’t go
back on.
FIG.3 Test fitting speaker – it sits UNDER the edge.
In the photo above FIG.3 you can see how the speaker fits, it’s under the body edges – just!
This will work as it sits just enough under the body. The thickness of the styrene sheet from which
we will be making the enclosure will take up the gap & make it sit flush with the floor.
FIG.4 The styrene enclosure being made.
Because of the coal plate (die-cast metal) being at an angle, the box needs to conform to the angle
shape so one end of the box will be short & the other long - tapered.
So we make the box with a taper. FIG.4 shows 3 sides already made. The left-hand side is 10mm
high & the right-hand side (end) is 6mm high. Now we want the speaker to sit evenly & flat against
the floor when the body is screwed back on so we need to work this out. The gap remaining under
the speaker to the body has a piece of cork to “take-up” this distance or gap & it keeps the speaker
parallel to the floor, flush & in place.
The cork does 2 things.
Firstly it holds the speaker & enclosure in place without it jumping around inside the tender body &
keeps it gently against the floor with its holes to let the sound out. It helps absorb noise also. Make
sure the speaker cone is clear of the floor otherwise it won’t perform correctly. If the speaker you
have chosen has the cone sticking out the enclosure will need to be built so it holds the cone off the
floor.
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DURANGO & RIO GRANDE SOUTHERN RAILROAD - AUSTRALIA
An option would be to use contact cement or silicone to hold the speaker & enclosure onto the floor
itself. I prefer to keep things simple – but there are other ways to do this.
Secondly, the cork stops vibrations or harmonics. Vibrations & harmonic sounds can upset what we
are trying to achieve – that is good noise free sounds. A little “padding” reduces any chance of
these.
You could use a springy material such as medium density foam that doesn’t loose its shape to fill
the void & help keep the speaker against the floor; I used 2 pieces on each side of the enclosure.
In this case we are only placing the speaker in the tender, if we were placing a decoder as well, we
need to allow air to circulate & prevent the decoder overheating. There are fore’s & against’s
involved with filling the tender box. A decoder’s worst enemy is a short followed closely by heat.
Squeezing a decoder & a speaker into a tender means there MUST be ventilation –on my old brass I
drill 1/8” holes for the speaker & to allow some air movement to allow the heat from the decoder to
dissipate.
FIG.5 The finished enclosure box.
In FIG.5 you can see the wires which are hanging with 2 clips pulling on them. I have cut away the
material just where the 2 holes are & where the wires come out. The speaker needs to sit flush & so
that the wires would not interfere with it sitting flush I cut away the sides just enough to allow the
speaker to sit flat on the floor.
The 4 small holes were filled with silicone & left overnight to dry – this seals off the box so the air
movement behind the speaker fabric moves & has a resistance created inside the sealed box. This
makes the sound work properly. There are technical reasons regarding the air behind the speaker but
all I know is that it definitely needs to be sealed 100%. (I’m no expert on this so check elsewhere).
Now we have to run the speaker wires back to the 2 purple wires of the decoder which will be via
the PCB terminal that was placed on the side of the motor.
What must be worked out next is to make sure that where the wires exit the tender & “jump” across
to the loco, that they DO NOT inhibit the free movement of neither the front truck swing nor the
swing between the loco & tender.
Also, where to drill more holes for the wires to run needs to be worked out.
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DURANGO & RIO GRANDE SOUTHERN RAILROAD - AUSTRALIA
Keeping the wires parallel to the track from the tender to the loco or vice versa is the best way of
avoiding the wires inhibiting the movement between the 2 bodies. If the wires are too tight across
the “gap” then the loco or tender may derail due to the wires not flexing sufficiently.
If the wires come out from either the loco or the tender at angles then this also will cause running
problems caused by the way the wires are run.
This is a very important matter if our locomotives are going to work properly & have plenty of free
natural movement. This is of course mainly on curves & many of us run tight curves so get this part
right – keep the wires parallel to the track!
Each type of loco & manufacturer differ as the configurations are all different however if “hard
wiring” is to be accomplished, then the loco & tender relationship must allow for free movement &
the way the wires are run is very important.
Now we are talking about just 2 speaker wires because we fitted the decoder in the boiler. But, what
if a rear light is to be fitted? Well, we will need a Yellow & a Blue wire also running between the 2
bodies – that’s now 4 wires.
Let’s keep things balanced here & let’s drill one hole on the left & one hole on the right. We can
now have 2 wires in each hole – or just 1 in each if just the speaker.
How do we best run the wires?
There are 2 ways this can be accomplished. The wires can be “crossed “X” under the draw bar or
they can be run straight. If the wires need to be “gathered” together to hold them, then a piece of
black heat shrink tube can be placed over the wires before they are soldered at the ends. This piece
of heat shrink is left to “float” the wires through it DO NOT shrink it as this will cause the wires not
to flex & possibly cause tension between the loco & tender.
On the tender the 2 wires will represent the water hoses so there will be a wire on each side.
FIG.6
FIG.7
The holes were drilled & countersunk each side so no sharp metal edge could cut through the tiny
#30 wires. The sketch in FIG.6 shows the new holes are 3.5mm in front of the existing screw holes.
FIG.7 shows 2 styrene blocks that were ACC’d to keep the wires parallel.
NOTE: The drilled holes were drilled at an angle to prevent a 90 degree bend in them.
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DURANGO & RIO GRANDE SOUTHERN RAILROAD - AUSTRALIA
FIG.8 The styrene block (unpainted) & wire run.
FIG.9 The foam block in coal bin.
Here she is all screwed-up; we’ve finished with the “internals” & the speaker, and after a little filing
of the box edges, sat flush with the floor.
Fig.8 shows the styrene block & how the wires sit. FIG.9 shows the foam that was cut to fit down in
the coal bin – stuck with a dab of contact cement.
It’s your turn to get us a “coldie” each from the fridge mate! This is still thirsty work.
Now the tender is nearly finished, we just need to glue the real coal I picked up in Colorado, all
smashed into a nice scale size, into the tender. A half load to show of the detail.
Now, the 2 speaker wires need to run UNDER the draw bar & into the boiler to the PCB terminal
we placed inside in Part 1. Like a brewery –“it never runs out of beer” – well we don’t want to be
mean with the wire runs. ALWAYS leave wires longer than the point ‘A’ to point ‘B’ run so that
when you need to take things apart for maintenance it’s easy & no wires are ripped off.
I tucked & left about 1.5 inches of extra wire inside the tender & the same for inside the loco boiler
– there is room behind the motor for this. Solder the 2 speaker wires onto the terminal to join the 2
Purple wires from the decoder.
We need to test things again before we reassemble – test the beers too! ….sip, sip……
Testing as we go is a really good way of teaching ourselves about new model projects. It one step at
a time at first then we become absolute wiz-kids at the game & can show others – how to model not
drink Durango Wheat’s I mean!
So, we coil the SML wires up & gently, very, very gently manage them into the smoke box &
because we have our wire long we don’t rip the tiny SML wires from the connections.
Make sure that a piece of insulation tape is placed onto the boiler body where the PCB terminal is
so it can’t short to the body. Now slide the boiler back on & using our tweezers, push the excess
wires in as we fit the boiler. There ya-go! It’s all back together, a few screws later & it’s all done.
Be careful – it’s hard-wired together now so we must lift the loco & the tender together.
If you like, you can solder a short piece of brass wire onto the draw bar pin to stop the draw bar
coming off – I have found this helps a lot.
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DURANGO & RIO GRANDE SOUTHERN RAILROAD - AUSTRALIA
FIG.10
FIG.11
Here’s how the coal looks in FIG.10 – Old Mighty Mike is shovelin’ it around some – the coal I
mean!
Fig.11 is a shot showing things from a different angle to help you along.
FIG ure I’ll have another Durango Wheat.
What a pretty girl – all lit up.
Well I hope that you have enjoyed working along with me on this tiny project.
I certainly hope you try fitting sound decoders & maybe SML’s too, it’s not that hard to do.
The PSC part number for the brass casting Class-markers is # 3124, $ 3.25 / pr.
Thanks for your company & cheers for the drinks cobber.
Your friend down-under,
Laurie
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