Block Working in Miniature - The Triang Bell Signal Set

Author: David Ward
Date: 7 September 2009

In my travels recently, I was fortunate enough to come by a Triang Bell Signal Set. I am unable to recall any other company that offered operating miniature bell signal instruments (block instruments) as a model railway accessory, and for this reason alone, the set offered by Triang is particularly worthy of note.

On the big railway, block instruments were utilized in conjunction with ‘block working’. Under this method of safeworking, a railway is divided into absolute intervals of space known as ‘block sections’, with the access to each section being controlled by a signalbox. Each signalbox is provided with a block instrument to assist the Signalman in enforcing the principal rule of allowing only one train within a block section at any one time. To achieve this, the block instruments at both ends of a block section are electrically connected, and via the transmission of a series of specific bell codes, the Signalmen at both ends of the section are able to communicate in order to achieve the object of the system.

The Bell Signal Sets were offered for sale by Triang between 1964 and 1967.

The set comprises two block instruments and an associated wiring loom that any quality British car manufacturer of the time would be proud of! Uncontrolled 15v AC is required to power the equipment.

The block instruments stand about 8 centimetres in height (31/4 inches ) and are based on the standard British Railways 3-position block instrument in use extensively throughout the UK during the mid sixties. The instruments were known as the 3-position type because the indicating needles could be positioned at three separate positions, depending on the state of the line ahead (ie: ‘Line Clear’, ‘Normal’ or ‘Train on Line’).

As a comparison, the remaining VR block instruments still in use between Craigieburn and Seymour are of the two-position type, in that the indicating needles only display two indications (ie: ‘On Line’ or ‘Cleared’).

For obvious reasons, the bells of paired Triang instruments maintain a different tone.

The ‘Model Railway Constructor’ advert of 1964 announced that:

‘This set is designed to bring realism to model railway operation. It makes it possible for two operators to communicate by means of the bell code by using ‘Block Instrument Units’, following a similar procedure to that which has been used for many years in the majority of British Railways Signalboxes.

It may be said that the operators could call to one another and thus dispense with the need for block instruments, but the correct use of the instruments adds a fascination to model railway operation which needs to be experienced to be appreciated and is most impressive from the onlooker’s point of view’

A ‘fascination’ which, for obvious reasons on a real railway, was an absolute necessity!

Operation of the instruments is quite simple, in that the manipulation of the indicator switch on one instrument automatically controls the position of the block indicator on the opposing instrument. This operation can be achieved at any time and from either instrument and is not subject to any pre-conditions relating to track occupancy.

The official Triang operating instructions are detailed a little more elaborately.

Box ‘A’ wishes to pass an Express Passenger Train to Box ‘B’ -

  1. ‘A’ taps out 1 beat to ‘B’ (‘Call Attention’).
  2. ‘B’ acknowledges by repeating the signal back to ‘A’.
  3. ‘A’ taps out four beats (‘Will you accept Express Passenger Train?’).
  4. If ‘B’ is prepared to accept, he repeats the signal back, allowing the train to proceed.
  5. ‘A’ then taps out two beats (‘Train Entering Section’).
  6. ‘B’ acknowledges by repeating back signal. When the train has passed his section, he taps out two beats, followed after a brief pause by 1 beat (‘Train Out of Section’).
  7. If ‘B’ is unable to accept the train, he does not reply to the 4-beat signal from ‘A’. After a while, ‘A’ repeats the series of signals from the beginning - 1 beat, ‘Call Attention’ - until ‘B’ is ready to accept the train.

One fundamental aspect absent from the authorized operating instructions is that the Signalman at Station ‘B’ is also required to place his indicator switch to the ‘Train on Line’ position immediately prior to/after acknowledging the bell code listed in step 3. Failure to do this could result in a train being admitted into a section without authority... a serious offence on the big railway, which in some instances has led to disastrous consequences.

Triang advertised common bell codes for use and these are indicated in the table below:

Common Bell Codes

MessageBeats on Bell
Opening Signal Box5 pause 5 pause 5
Call Attention1
Express Passenger Train4
Local3 pause 1
Express Freight3 pause 1 pause 1
Empty Coaching Stock2 pause 1 pause 1
Light Engine2 pause 3
Mineral or Empty Wagon Train4 pause 1
Train Entering Section2
Train Out of Section2 pause 1
Obstruction Danger6
Closing Signalbox7 pause 5 pause 5

Those of you who have visited a VR Signalbox in the past will perhaps recognize some well known bell codes in the list above, as generally all were developed by and applied within the Railway Clearing House Standard Rules and Regulations of 1897. The current Victorian Rail Network Rules and Procedures in use today is based on this document, hence the similarities.

But back to the Bell Signal Set... the obvious question here is how popular were the sets to budding railway enthusiasts in the mid sixties?

According to Pat Hammond’s magnificent book, ‘The Story of Rovex: Volume 1, 1950-1965’, the bell signal set equated to the same price as one of the newest additions to the Triang line of the time, the North Eastern 4-6-0 B12 express passenger locomotive.

From a general perspective, it is difficult to understand how any child could find the operation of a block instrument superior to that of controlling an electric loco at speed. It is unknown how many bell signal sets were sent to Australia for sale, but brochures I have from the prominent model railway retailers of the time do not list the set as a regular item in stock during the period of production.

Triang ceased production of the Bell Signal Set in 1967. Upon cessation, approximately 3,850 sets had been manufactured.

Due to their limited production, the items have consequently become quite collectable and, when they do become available, command generous prices at auctions or on Ebay.

And with this final comment on perhaps one of Triang’s most eccentric accessories, I’ll finish by transmitting the 7-5-5 bell code to you all via print. An acknowledgement of the bell code in this instance will not be necessary!

Below picture - The Triang Bell Signal Set, showing the two block instruments, wiring loom and box.

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