A, Introduction

Model 106 (aka 146) - Single Track Block

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A Introduction

B Dwgs-Const
C Const Steps
D Operation
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 1-trk (Mdl 106)
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Sections shown below on this page:

1. Related Sections
2. Summary
3. Logic Diagram
4. Drawing Set
5. What The Drawing Set Produces
6. Comments About Building This Block
7. The Four Construction Phases
8. Electrical Comments
9. Track Planning For Best Visual Effect

1. Related Sections

  • Section A1, (this section) Single Track Block - Description
  • Section A2 , Single Track Block - Drawings
  • Section A3, Single Track Block - Step-By-Step Instructions - Constructing Phase 1
  • Section A4, Single Track Block - Operating Instructions & Phases 2, 3 & 4
  • Section A5, Single Track Block - All Drawings PDF - use this section for PRINTING

    This section makes reference to the following drawings, which can be viewed in the next section, KEY drawings:

    • Sheet 3, Schematic Drawing (Phases 1, 2, and 3)
    • Sheet 4, Track Unit Assembly
    • Sheet 7, Parts List
    • Sheet 9, Template for Control Unit

2. Summary

The Model 146b Single-Track Experimenter's Block is the simplest of the three control systems discussed in this bulletin. The purpose of this Experimenter's Block, is that you can it up on a temporary loop of track, and get acquainted with automatic multi-train operation.

The following figure shows the completed Model 146b Single-Track Experimenter's Block.

Figure 1 - Model 146b Single-Track Experimenter's Block
As implied in the figure, this block can be built in 4 "phases". Phase 1 is the simple starter version, Phase 2 adds a rheostat and slowdown Section, Phase 3 (optional) adds capacitor, and Phase 4 adds the signal lights.

3. Logic Diagram

The following figure, Logic Diagram for Single-Track Automatic Block, explains how this unit controls 2 trains on the same track.

Figure 2 - Logic Diagram


4. Drawing Set

NOTE: You can build this automatic block using the instructions and reduced-size drawings included in the Bulletin B9702, starting on page 25, or using the copies at the end of this section on the web. As an OPTION, you can order Item 4. Item 4 includes several of the drawings already included in the bulletin, but full-size and in color, plus the template.

Item 4 -- U_BLD_M Drawing Set for Model 146b Single-Track Experimenter's Block

Two 11x17 colored drawings & laminated template

Colored, Laminated Template


Figure 3- Item 4 Drawing Set
Item 4 includes the following:
  1. Colored Sheet 4, Track Unit Layout
  2. Colored Sheet 9, Full Size Pattern for Control Unit
  3. Template -- Colored, plastic-laminated copy of the lower half of Sheet 9, Phase 2 Control Unit -- Standard Version w/Slowdown.

This plastic-laminated, color template shows where all parts and wires go -- you can see some of the detail in the above figure. The template is designed to be glued to the wood base of the control unit. For easy assembly, all parts and wires are shown full size in their proper location. You just attach the parts and run colored wires over top of their colored outlines.

5. What The Drawing Set Produces

Figure 4a shown above, shows the completed Model 146b Single-Track Experimenter's Block. The following figure shows the completed control unit and track unit assemblies -- note they are built as separate subassemblies.

Figure 4 - Model 146b Block - Subassemblies


6. Comments About Building This Block

This unit, as with previous Ingram Autocontrol designs, uses all electromechanical components -- no electronics. The parts are all readily available from Shiloh Signals, LGB, Radio Shack, and Newark Electronics.

A standard LGB switch motor and relay, activated by standard LGB track contacts, controls the switching on and off the DC track power.

You can use any good-running, properly-geared locomotives right out of the box, with no modifications except adding a magnet to the bottom to activate the track contacts.

This Automatic Block is essentially "plug and play" when used as a portable control unit and track unit combination. You just hook up the AC power, and attach the one remote track contact 'T2'.

This unit has the capability to control a minimum of 2 trains on a single mainline. You can also completely depower it so it acts inert -- that is, acts just like a section of ordinary straight track.

Videotape Demonstrations

The videotape "Video Textbook for G Scale Automatic Display Ideas" (Item 2, Basic Videotapes 1 & 2V9202) demonstrates how an automatic block operates, using an earlier Model 944 unit.

I suggest you watch the videotapes to "get a feel" for how it operates. Section 3 contains a list of people who have at least one of the videotapes.


This Automatic Block is intended to be an "experimenter's block", to get you familiar with automatic block operation. After constructing and operating this single-track Automatic Block, you may want to use the other available plans to build a two-track Automatic Switching Block, a 4-track Zellner Yard, or custom configurations of your own design.

You can use this completed block to operate an additional train with the either the 2-track or 4-track switching blocks.

However, if you instead decide not to proceed any further with the automatic controls, the parts used to build this Automatic Block are easily "recyclable" to other model railroad uses.

Skills Required To Construct

As long as you can cut a wire, strip the insulation off the end, and connect it to a screw terminal following explicit diagrams, you can probably build this block. All the construction is done by screwing things together, except 2 solder connections to the rheostat.


7. The Four Construction Phases

You can construct this block in 4 separate phases as follows.
  1. Phase 1 -- Starter version without slowdown block

    You can construct a simple-as-possible "Starter version" to get familiar with how this block works. Sheet 3, Phase 1 -- Starter Circuit without Slowdown, shows the schematic. Sheet 9, Phase 1 Control Unit -- Starter Version, shows the actual control unit layout.

  2. Phase 2 -- Standard Version With Slowdown Block

    Later you can later add a rheostat and a few wires to expand the control to add a "Slowdown Block". Now trains will approach a red block at a reduced speed, and also start-up at a reduced speed when the block changes from red to green. Sheet 3, Phase 2 -- Standard Circuit with Slowdown, shows the schematic. Sheet 9, Phase 2 Control Unit -- Standard Version w/Slowdown, shows the actual control unit layout.

  3. Phase 3 -- Standard Version Plus Capacitor (OPTIONAL)

    As of Oct 96, I was still experimenting with the capacitor circuit -- it seems to work well with some trains & layouts, and on others I have observed some jerking as the engines enters the stop block. So you may want to skip this step unless it sounds really appealing.

    You can add a capacitor wired in parallel with the locomotive motor. Sheet 3, Phase 3 -- Circuit With Slowdown Plus Capacitor, shows the schematic. Sheet 4, Automatic Block Track Unit Assembly, shows the wiring -- you add wires 7B, 7C, plus the capacitor.

    When the block changes from Red to Green to start up the locomotive stopped on the block, the uncharged capacitor will drain some of the current away from the locomotive as it charges up, and thus result in a smoother locomotive start. When the next locomotive enters the stop block, the charged capacitor will discharge its energy back into the block, and thus cause the locomotive to drift to a smoother stop.

  4. Phase 4 -- Adding Signal Lights

    You can add red and green signal lights to the block, that will indicate the "state" of the block. Sheet 9, Phase 2 Control Unit -- Standard Version w/Slowdown, shows the wiring -- you connect the lights to terminals 2, 15, and 16.


8. Electrical Comments

AC Current And DC Current

This block uses both AC and DC current.

The AC current is what powers the controls of the block, and the signal lights. The block gets its AC current from the two wires connected to the knife switch K0, which are connected to the AC output of the transformer. The AC wiring is standard LGB circuitry, just like you use to wire your track switches, except we use the track contracts activate the switch motor, instead of the orange 5175 momentary switch control box where your finger pushes the button.

The DC current is the track current that the block controls by switching it off and on, to stop and start the locomotives. The block gets the DC current from the left (+) rail of the mainline just in front of the block, and returns it to the left rail of the stop block and the slowdown block.

AC Control Voltage

Probably the most important factor in getting reliable operation of these control units, is supplying it with a good "healthy" source of AC control voltage. This AC control voltage (rectified to DC) is what powers the switch motor 'M3' that operates the relay.

LGB's "standard" control voltage is 18 volts AC. LGB transformers AC output measures 18 volts. This works fairly well for indoor operation where everything is clean, but I think that there is not much margin of error.

There have been occasions when I have been demonstrating my units at shows, where my 110v ac power connection has been at the end of a series of long extension cords, and have I watched in dismay and frustration as the switch motors on my control unit repeatedly failed to reliably change. And this was indoors -- with no dirt to contend with.

Increasing AC Control Voltage

I have observed that increasing the voltage to 20 or 22 or 24 volts, appears to improve the reliability of the operation of the switch motors. Blue Streak transformers, which a lot of people seem to have, produce about 20 volts AC. Thus Blue Streaks are a good source of AC power. I currently use a discontinued version of a San-Val pack that supplies 22 volts AC.

A way you can increase the voltage to 24 volts, is to get one of the little plastic lawn-sprinker transformers you can buy in hardware stores.

Voltage Recommendation

I recommend you use the minimum voltage you can, starting with the "stock" 18 volts, to get reliable operation of the switch motors. At 24 volts, I believe the track contacts may wear out a bit sooner. By "wear out", I mean they start to frequently stick in the closed position -- see page 34, Sticking Track Contacts for discussion.

The Shiloh Signals searchlight signals with LED s can be ordered to handle up to 24 volts. But you have to be careful about overheating any bulbs that may be in the circuit (such as you have if you use the LGB signals 5092, 5094, 5095, etc).

If you use 24 volts and fail to use the resistors to reduce the voltage to the bulbs, you may burn them out and melt the plastic housings.

Byron Fenton (who has built several of these units with Ed Zellner) cautions that if you use 24 volts, you must use a 220 ohm 1/2 watt resistor in series in the wire powering a two bulb unit -- such as the semaphore arm. Byron advises you use a 100 ohm 1/2 watt resistor in series in a wire powering a one bulb unit, such as the 3030 indicator light -- the 220 ohm resistor will also work.

BOOSTER: The LGB 52750 Booster is designed to provide more positive operation of switch motors. However, per LGB catalog 02996 "Lights may not be connected to the EPL Booster", but should be on a separate circuit. For this reason, I do not use the Booster with these controls, although you could if you modified the circuits to keep the lighting circuits separate from the circuits that actuate the switch motors.


9. Track Planning For Best Visual Effect

You may want to give some thought to the "visual effectiveness" of the track plan you use with this block. The reason I mention this is, the effects of a single-track block operating on a simple oval loop can be subtle -- that is, with a train on one side of the loop and another train on the other side, a casual observer may never realize there is more than 1 train running.

A way to emphasize the fact that there are two trains on the same loop, is to configure the track plan so the viewer's eye is forced to see both trains at once. You can do this by using an elevated crossing, or a crossover, or a dogbone -- set them up so, at some point, one train passes close by the other, and the observer cannot fail to notice that there are 2 trains on the loop.

The following 2 figures show examples of a dogbone and elevated Figure 8, configured so the viewer sees both trains in the same scene. In fact, as the viewer observes engine 5 passing by on the mainline as it travels over Contact T2, engine 1 on the stop block will start up, for "added drama".

Figure 5a -- Visual Emphasis of Two Trains by Dogbone

Figure 5b -- Visual Emphasis of Two Trains by Elevated
This page created 8/2003, modified 12/8/2009 by (bottom include)
James R. Ingram , Williamsport Pa, Voice Mail 570-322-7597