Minitrix DC Devices

When Minitrix came to the market in 1964, there was no “Command Control” such as Märklin Digital, Trix Selectrix or DCC.  The Minitrix trains were controlled with Direct Current (“DC”). When you want to change a train’s operating direction, you flipped a switch, the track polarity changed and the train ran in the opposite direction.

Now, of course, things have changed, but the DC heritage remains in the Minitrix product line, available for those who are reluctant to switch over to command control. There are several devices that enhance the operation of a Minitrix DC layout.


Although not a “device”, and although Minitrix does not manufacture overhead catenary wires, the use of catenary wires allows you to operate two locomotives on the same railroad at the same time. At least one of these locomotives has to be an electric type, and both could be electrics if that is what you want.

Key to this type of operation is fitting the railroad with catenary; in Europe, there are at least two manufacturers of catenary for N-Scale; Vollmer and Sommerfeldt

Also key to successful operation is paying attention to the color coding of the Minitrix wiring system.  “Red” and “Blue” are the track power colors.  In a catenary installation, one transformer controls both rails, with a blue wire going to the “Blue” rail” and a red wire going to the “Red” rail.  The second transformer also has a blue wire connection to the “Blue” rail, while the red wire is connected to a terminal mast which feeds power to the catenary overhead.

In the illustration above, note that both locomotives have their “Blue” connection on the same rail. The right hand locomotive is collecting current from the “Red” rail (even though its pantograph is raised), while the left locomotive takes its power from the overhead wire, which is controlled by the right-hand transformer.

It is important that the left locomotive also be configured for overhead operation.  There is a switch on the Minitrix electric locomotives which selects between either two-rail or one rail and catenary:

The selector switch is usually on the locomotive roof, and is often marked “O” and “U” (over, under). As noted, the locomotive can have its pantograph raised but if the switch is set for “U”, it will still be takings its power from both rails.

Blue Common

With the Minitrix color coding system, the “Blue” becomes important at signals.  Note that the train stopping segments used with layout automation use the blue rail for halting trains.  This is so that both locomotives on a catenary layout will stop at signals, regardless of their transformer control.

DC Devices

Minitrix developed several ingenious devices to use with the Direct Current model railroad.


6627 Line Rectifier

Deceptively simply, yet incredibly useful, the 6627 Line Rectifier (now 66627) has the spring terminals on the top and contains a single diode inside.  The diode acts like a one-way valve, allowing electricity to flow in one direction only.  This device has a number of helpful uses. Here, a basic application:

Used in this application, the 6627 allows a train to approach an end-of-track bumper.  Once the train reaches a certain point, the track power is turned off by the diode of the 6627.  When the track polarity is reversed, the power is allowed by the 6627 to flow; because the polarity is different, the train operates in the opposite direction.

In a similar application, a two track locomotive engine house is fitted with a 6627 on each track.  Second-generation Minitrix turnouts can be set to be “current routing”, which means that track power will only go the the track with which the turnout is aligned.  The other track will be dead. In this situation, you could bring a locomotive into the engine house, with it stopping at the end of the track.  The track power is turned off, the turnout set to the other track and the power turned back on.  When the polarity is reversed, a locomotive parked on the second track will then back out of the engine house.

The 6627 Line Rectifier is very useful indeed.

6629 Stop Controller

The 6629 (now 66629) Stop Controller automatically stops a train at a defined section of track.  After a period of time, the train starts back up and proceeds.

A sliding switch allows you to set the duration of the train stop. And, the 6627 can be connected into the defined stopping section so that trains going in the opposite direction do not stop.

6631 Braking Resistance Unit

The 6631 (now 66631) Braking Resistance Unit is used to slow trains in a defined segment of track.

The 6631 allows you to slow trains which are going through a restricted speed area, such as through a village that has train speed limits. It also is used to slow trains which are going down hill:

Once again, the handy 6627 is used, in this case to direct the slow speed function of the 6631 only to trains which are going down hill. Trains going up hill get full power, while those going down hill do not.

Again, as a reminder, these devices do not work in the command control environment.  In the case of the 6631, command control eliminates the need for this device since most locomotives are fitted with load-compensating decoders, which regulate the train’s speed automatically in relation to the throttle setting.

In the case of controlling a second locomotive from overhead catenary wire, this too is rendered obsolete by the character of command control. While two locomotives can be controlled in the DC environment with overhead catenary wire, many more can be controlled with command control.  As an aside, several manufacturers recommend that all locomotives be operated from the rails rather than from the overhead wire.  While it is possible to do so, there have been reports of reliability problems with overhead wire operations and command control.

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