Trix Twin


The Basics Explained


By Trix Collector

Box label prewar 2

1936   box  label

© Copyright 2004-2006 Garry Lefevre, all rights reserved



To Site Introduction


US Twins2

The US Twins : an example of how Trix produced two complimentary locos.

Quite often locos were produced in pairs, a passenger and a goods loco differing only in colour




Why “Twin” –    Wiring a layout -    AC or DC –   Wheels - Track



Over the years I have been asked questions and advice from new and experienced collectors.  This section will attempt to answer those most common frequently asked and give advice, ( my own views), on collecting and running and repairing Trix Twin.  You may not always agree with my views but do tell me and I may add your comments and ideas for the benefit of all Trix fans.  Hopefully, both old hands and new converts will find parts of interest and use to their own approach to the hobby.  To successfully collect and indeed decide which to run Trix Twin, Trix Express or modern Trix there are a few  key facts to digest first.   So lets kick off with the basic difference between Trix Twin and other model railway systems.




Quite simply “Twin” is because two trains can be independently run and controlled remotely on the same track without interfering with each other.  This may seem rather simple when one compares modern digital systems enabling dozens of locos to be run simultaneously, but in 1935 “Twin” running was sensational as was the ability to reverse the loco by remote control.  Prior to this the only manufactured HO system was the Bing Table Top railway; started in 1922 these clockwork trains developed into locos with electric motors but each required track to be insulated between each running loco.  Reversing a loco was achieved by means of a lever sticking out of the side of the loco.  In 1935 Trix Express in Germany brought out the system we know in England as Trix Twin.  The sensation was locos could for the first time in HO be remotely reversed from a controller without touching the loco and two could be run on the same track independently.  More of this story can be seen in the “History of Trix Twin in pictures”.


The basic Trix  instruction book from 1936 shows how the system works :


basics 1

The above diagram is taken from the first instruction book.

The principle illustrated is that each loco picks up the current by means of collector shoes, both use the centre rail as a common, connection and each uses a different outside rail for the other connection.  Hence each rail must be insulated from the other two.  The instruction book goes on to show how the collector shoes should be fixed to the loco :-


basics 2


Wiring a basic layout :


So as to control two locos, one needs two controllers.  The  instruction book goes on to show how to wire this up:


basics 3



How to wire up electrical operated points is next covered in the book :-

basics 4


Note: post war points had two connections from the lever to the point.



How can I have more than two locomotives on the same layout  ?


Once again the instruction book shows how :


basics 5



One needs to be careful in planning layouts with reverse loops.  These are possible if one uses only one loco and one controller on the layout, hence “Twin” running is not possible under independent control unless insulating sections are used.   TTR explained this in their introduction leaflet sold with each set :-


Track plans 5




AC  and DC explained or why don’t modern locos run on a Trix Twin layout


I am frequently asked to explain another oddity about the early ( 1935 to 1955) Trix locomotives.  They were designed for AC ( Alternating Current ) not DC (Direct Current).   AC you get from the mains and only need a transformer to reduce the voltage to 14 volts to run TTR : NEVER connect the mains direct to the track !.  But modern systems need a rectifier as well to convert the electricity to DC, the type of electricity you get from a battery.  The advantages of DC is that all you need to do to reverse a loco on the track is reverse the current by changing the connections for the loco to reverse.  This is done inside the controller.  The TTR AC system is more complex.  This requires the current to flow through the motors windings in a different sequence, hence the change must be made inside the loco for it to reverse.  A full explanation can be found in a number of publications by Trix, but for the purposes of this section it is sufficient to know that TTR achieves the reverse by means of activating a relay inside the loco.  On the Trix controller a button ( pre-war) or a lever ( post war) is pressed which interrupts the current.  This causes the relay to function, first causing the loco to stop and the second time to reverse.  The disadvantage of the TTR system is that if the current is interrupted by accident the loco can stop and go into its reversing sequence, as when track is dirty causing the pick up shoes to loose electrical supply. 


So why wont DC locos work on a TTR system ?  The reason is that they do not have the additional electrical wirings inside the loco to create the magnetic field round the motor.  DC locos rely on a permanent magnet to provide this magnetic field, which cannot work with a current fluctuating from positive to negative as with AC systems.  Whilst DC motors are more reliable as the current can be temporarily interrupted without the loco going into reverse, but it also means they will not run on the TTR ( or Märklin) systems.  However the good news is that TTR locos will work on both AC and DC providing you have the means to interrupt the current to activate the reverse.  Now I will explain how you can combine AC and DC together on the same track and even modern digital !


How to combine AC and DC on the same layout :


The key to doing this is to realise each circuit needs at least one independent connection from the controller to the loco via the track but can share a common return.  Trix has the advantage that each rail is insulated from the other two, thus it is quite easy.  Here’s how :-

basics 6

This configuration will enable a DC loco to pick up the current on the one outer rail  and the AC loco to pick up its current from the other outer rail.  Both use the centre rail to return the current.  This can be used for example where you have a traditional TTR AC loco and a more modern DC 3 rail loco such as a Britannia or one of the range of modern Trix Express locos.  Note it will not work if the loco is Hornby,  Märklin  or similar where the outer wheels are not insulated from each other.


With only a slight change it is possible to run modern 2 rail DC locos with one TTR  AC loco.  Just use one of the outer rails as the common return and the centre rail for the TTR loco only.  In the above diagram just switch the green wire to the centre socket in the rail and the red line to the outer rail currently used by the green wire.


Note for the locos to each run through points you will need to use the universal points described above.  Since it is almost certain the 2 rail DC loco will have fine scale wheels.


To be really ambitious you can apply this same basic principle to running modern digital locos and one Trix AC loco together :-


basics 7

Note that points or any other device using the centre rail for a common return, such as uncoupler rails will need a separate wire feed to replace the return through the centre rail.  Universal points already have this feature.  If the device has hard wired the connection to the centre rail it MUST be disconnected.


All modern Trix locos made in the last few years have sockets built in to take a micro chip that converts the loco to digital.  This is a whole topic in itself and is out of place in this basic TTR collectors guide, but is mentioned here to show one of the advantages of the old Trix 3 rail system enables even the most modern systems to be used on the same layout.


WARNING :  Because of government regulations, I have to state here that it is recommended wiring is carried out by a qualified electrician.



What is meant by coarse wheels and fine scale wheels,

Or why cant I run TTR and Hornby on the same track


In 1935 Trix Express and hence Trix Twin was designed with children ( of all ages !) in mind.  Running at speed and robust design was needed.  Therefore the wheels had deeper flanges than more modern wheels which attempt to get closer to a more realistic scale appearance. 


wheel flange1


Clearly the rail height differs; examples of the two different types of track needed are shown below:-

Flexible track 1

Fine scale is on the left and Trix Express on the right



These deeper flanged wider wheels required track to match, hence the points have a larger gap at the frog than needed for fine scale.  Quite simply this means that the older Trix coarse wheels will not run on modern track and modern fine scale wheels will not run though the TTR points without derailing, but fine scale wheels will run on the early TTR track providing there are no points in the circuit.  The good news is there is a solution to run the two together.  In the late 1950’s TTR brought out points with a universal design that allows any size wheel flange to run though the point.  These points have point blades which are longer than normal so that the top of the bald closes the gap at the frog enabling any size of wheel flange to pass through the point without derailing.   These are much sort after by collectors, it is a pity nobody makes them now days.  About the same time Wrenn also produced a similar point to their own design.


Universal point1

A TTR leaflet






All TTR and Trix Express track is 3 rail with a rail profile much higher than for more modern model railways. The profile is 3.2 mm compared with about 2 mm for modern model railways.  This restricts the use of other makes on the same track but it can be overcome – more of this below.


In 1935 the first TTR used track mounted on black bakelite which clipped together enabling layouts to be easily put together and taken to pieces again.  The track is very robust although it needs constant cleaning and can suffer from rust if stored in damp conditions.


Pre-War bakelite track

bakelite track 1

Although not shown a ½ curve rail was also made


In the late 1950’s Trix introduced in England and Germany more modern looking track with individual sleepers made out of fibre pressings. The rail was still made of tinplate.  Soon after an improved design using nickel silver rail on a plastic base was introduced in Germany.  This is much more reliable with smooth joints and improved electrical contact. Both these two types can also be used to quickly put together a layout and dismantle again. But it is not as easy or as reliable as the bakelite track used in this way.  A permanent layout with the track permanently fastened down is really needed for this more modern track.


Late 1950’s early 1960’s fibre based track

fibre track1


To overcome the problem of combing coarse TTR wheels and fine scale wheels on the same layout Trix introduced universal points in the late 1950’s.  See above for more details.



Britannia passenger train 1

A Britannia with Western Region coaches

This loco was one of several produced with both coarse and fine scale wheels




See more practical tips




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