Bachmann Cravens Class 105 DMU


Another loco aimed mainly at our extended "Little Histon" layout, to enable post 1967 period running up to closure of the station.


Sourcing the Bachmann Cravens unit:

Having confirmed that these units were regular users of the Cambridge to St Ives line, sourcing the now fairly old Bachmann product, in the correct livery for the late sixties, looked a potential problem. However, much to my surprise I discovered virtually the entire range still available in new condition from Olivias Trains. I opted for the Preston-Colne unit in BR blue with yellow ends and with a head code window below the main windscreens.  Next job is to add DCC sound and improved lighting, then customise the destination labels. 



Hatton's photo of the DMU showing the 1967 BR blue color scheme.


This follows the successful earlier Class 108 DMU arrangement:

With Bif's Class 105 sound project on board an ESU LokSound V4, driving a conventional 4 ohm 40x20 speaker.  The speaker is mounted in its standard enclosure, facing downwards, semi-recessed under the floor of the trailer car. The top of the motor housing has been modified by removing the side & rear walls with a hack saw & file, to make sufficient room for the V4 decoder to fit sideways on, between roof and motor housing.

I am using an ESU LokPilot FX function decoder in the rear car to drive the lights, as this decoder can track the soft switched lighting, used in the front car LokSound decoder. The rear car decoder fits within the toilet enclosure. A pair of miniature 2 way connectors link the two cars electrically. One connector for the speaker wires and the other to link the track contacts of the two cars together to provide 16 wheel contact reliability. A link is used to disconnect the track feed to the rear car decoder, to enable separate programming of the LokSound while still connected to the speaker while both cars are on the track. (The rear car can be programmed separately on dedicated track, when the connector plugs are removed.)  

A cab light is installed within the power car.

A driver has taken up residence in the front cab and a few passengers are distributed in both cars.

The outer tension lock couplers have been removed.

The destination boards are now  "St Ives" and "Cambridge".

The motor feed coils and capacitors have been removed. 

All bogies will be hard wired in the event of poor conduction via the contact tabs or excessive tab vibration noises.


The circuit.


A Cravens DMU at Histon Station in 1967.


Running Lights:

Decades before the introduction of modern dual function LED combined rear and front marker light fittings..... The Class 105 operated on a similar basis..... except that the light source was a pair of fairly dim conventional bulbs mounted one above the other (top red, bottom white) within a common circular housing employing a flat glass front.  Bachmann's interpretation is via closely located shrouded chip LEDs, red and yellow, close behind the lens of each light.


Destinations updated


Internal Coach Lighting:

The roof mounted compartment lighting circuit includes all series resistors, so can be powered directly from the decoder function output. However, the Bachmann lighting solution is only marginally better than on the 108, so I've used a similar technique to replace it with chip LEDs, fed via the Bachmann resistors. Decoder Aux1 switched by key 4 activates the lights in both cars.


Fitting the speaker:

Unlike the power car, the trailer car has a plastic floor. So that has to be the primary target location for the speaker hole. Near the centre of the car, the under-floor furniture can conceal a protruding 40x20 enclosure from virtually any direction (as long as the car stays on the rails.) The PCB between the floor and the seat mouldings has to again have the centre portion removed and the missing tracks replaced by wires running beside the speaker enclosure.  The speaker enclosure can be inserted through the gap cut in the PCB right up to the seat moulding underside. The standard ESU 50344 20x40 enclosure is nicely hidden in this location, by the surrounding engine, radiator and under floor tanks etc.


Showing the modified motor housing and the trailer car speaker location


Motor Control CVs:

The motor control is fine tuned via a number of relevant CVs. I found some jitter present at very low speed so I've made some changes to largely eliminate the issue. There are probably other combinations that would do the job, but these are the ones I am now running with:

CV Value CV Value CV Value
2 1 51 5 29 14
3 60 52 40 49 19
4 30 53 66 124 4
5 255 54 200    
6 90 55 40    
    56 150    


Passengers join the train


Re-Arranging the Function mapping:

TBA.... but probably identical to the 108:

Charlie's website Function List:

Bif confirms that since this was posted, The manual gear change is now on Key 7 and the on-board toilet flush is on Key 8.

(Also handbrake on/off is now on F16 and F17.)




0 Running lights
1 Sound on / engine start
2 Hi Horn
3 Lo Horn
4 Internal lights
5 Despatch whistle
6 Right away signals
7 Manual gear change
8 Door slamming
9 Wheel flange scrape
10 Cab light
12 Brake application
13 Buffering up
14 Toilet flush
15 Firebell or buzzer
16 Handbrake on
17 Handbrake off
18 Detonators
19 Reduce volume to 50%

Revised map to put the most useful functions in the 0 to 9 range.



Supplier website links:
 Web Link (click below)    Items concerned
Olivias Trains    Class 105 Sourced here.
DC Kits D&E Videos    Source for Bif LokSound V4 and ESU speaker.
Digitrains    Source for LEDs


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