DCC Loco Conversions - 29 - Dublo & Wrenn City

Although of the same prototype class as the earlier Dublo Duchess there are differences to the body and chassis between the Dublo Duchess and City models including the service sheet so I have written this conversion up as a separate model.

Installation of a decoder is straightforward, modifying the chassis to insulate the original brush holder takes most of the time.

Very Important - the chassis was modified as in articles 22 and 23, failure to do so can destroy a decoder.

https://platform1mrc.com/p1mrc/inde...-22-dublo-wrenn-brush-holder-extraction.6017/

https://platform1mrc.com/p1mrc/inde...23-dublo-wrenn-brush-holder-replacement.6025/

My Dublo City of London required a replacement armature for which I substituted a Wrenn part, however the Wrenn commutator diameter was 1/4 inch diameter as opposed to the original 3/8 inch Dublo commutator. To accommodate this change the replacement brush tubes were lengthened to 21.5mm, otherwise the usual replacement process above was implemented.



Both City models had defects which needed rectification which are included in article 32, "Trips and Tips", (Ref 29.1), here I focus on the DCC conversion.

After resolving issues I had with these locos they were both happy to use the RoS-6D decoder

For details of connecting to this decoder please refer to Solution 1 of article 26, (Ref 29.2), mounting varies as below.

Hornby Dublo - City of London

This loco was different to all my other open frame motored locos in that it does not have a notch in the top of the chassis to release the armature, I first considered that perhaps the armature was fitted before the driving wheels so proceeded to create the 'missing' notch. However whilst doing this the armature fell out!

Examining this puzzle (much like those linked metal shaped puzzles that used to be in Christmas crackers) I found that there is a way of releasing the armature without a notch or removing wheels (an absolute last resort).

Normally the armature is released commutator end first once the top bearing was removed.

Image 2 shows the armature in it's running position, ready to be extracted.



Image 3 shows the armature lifted out of the bottom bearing with the worm gear end of the shaft visible between the chassis and the right hand side driver, (did not work going to the left hand side).



Image 4 shows the armature in the same position but from the left hand side illustrating that the top of the armature shaft is now free of the chassis.



Image 5 shows the armature extracted from the left hand side.



Wrenn City of London

Dismantled and reassembled in the usual way for this type of mechanism

Both City Locos

In both cases the RoS-6D decoder was fixed directly to the chassis, as this stage was common to both City locos I am showing only the Dublo chassis.









Summary

The two examples of a City loco I had gave me many hours of fun to repair, especially as the the armature in the Dublo City decided to give up and take the decoder with it while I was setting the speed CVs. Some over oiling of both as they were worked on in parallel gave me some grief with BEMF which I did not realise until trying 2 more decoders.

Otherwise both work happily with the RoS-6D, real grief was with the Dublo and Wrenn 2-6-4T locos please see "Issues" of Ref 29.2 if you want to see how much these vintage locos can drive you bananas.

Jim

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References

29.1 DCC Loco Conversions - 32 - Dublo & Wrenn Trips & Tips

https://platform1mrc.com/p1mrc/inde...o-conversions-32-dublo-wrenn-trips-tips.6102/

29.2 DCC Loco Conversions - 26 - Dublo & Wrenn 2-6-4 Tank

Solution 1 - Rails RoS-6D decoder (connection)

https://platform1mrc.com/p1mrc/inde...o-conversions-26-dublo-wrenn-2-6-4-tank.6066/