Double Track Operation in Dublo 3 Rail

[Titan]

Why not go for a Duette? They have a separate winding on the transformer for each controller so that the circuits are completely independent. They do have resistance mats, but seeing as they were designed to run with the motors of the time and have high/low resistance switches to address the slow speed control so should do the job just fine.They are not far off being in period too!

[Golden Fleece 30]

A Duette is what I used.

 

Garry

[Il Grifone]

 

As resistance controllers go a Duette is OK, but they still have the problem of poor control characteristic of the beasts. Effectively the series resistance will cause the voltage applied (and hence the speed) to vary with load.

 

Off topic!

 

You get the same effect with Hi-Fi speakers. The sound is superior with an amplifier with a low output impedance (rarely/never quoted as a specification for some reason ) as the speaker is damped and the cone deflection follows the electrical signal more closely.

[k9-70]

Mecanno Magazine Feb 1952 page 85 has the following information for running a second engine on three rail track. 

 

http://pdfmm.free.fr//5202.pdf

[Il Grifone]

Mecanno Magazine Feb 1952 page 85 has the following information for running a second engine on three rail track. 

 

http://pdfmm.free.fr//5202.pdf

 

 Very interesting - lots of advertisements for proper toys! I always wanted the Tri-ang 'Jabberwock' (top centre page v - 3/6d IIRC) - the few survivors are now very collectible http://www.ebay.co.uk/itm/VINTAGE-TRIANG-MINIC-JABBERWOCK-TINPLATE-CROCODILE-RARE-BLUE-1950s-WORKING-amp-key-/322186866882

 

The key item is hidden in the text of the article as each line requiring its own transformer and controller. At the time, only the bakelite cased transformer and the black resistance unit were available, which would have automatically provided separate supplies. (At least the former item is no longer safe for use due to insulation issues.)

 

EDIT 

My mistake - it was 4/11d. That explains why I never got one....

 

http://www.brightontoymuseum.co.uk/index/Jabberwock,_clockwork_(Triang_Minic)

Edited May 30, 2017 by Il Grifone

[Wolseley]

Mecanno Magazine Feb 1952 page 85 has the following information for running a second engine on three rail track. 

 

http://pdfmm.free.fr//5202.pdf

 

 

A very interesting link.  Thank you for that.  I have printed out that page for future reference.

 

The possibility of the cause of my problem being two controllers with one transformer was mentioned earlier and, yes, that was it.  One of the sliding controls on my controller packed in, and I opened up the box to see if I could determine why.  I couldn't but, while it was open, I noticed that there was only one transformer inside.  I bought myself a Gaugemaster controller and now use that and the remaining control on my old controller and all is working properly now.  I suspect that the life of my old controller is somewhat limited, so I intend to get myself another Gaugemaster one in the near future.

[Il Grifone]

Most (all?) of the Meccano Magazines are available on the site. Very interesting reading....

[sagaguy]

Interesting aren`t they,when i first found these a few years ago,i spent a long time looking for a Meccano model of the LMS 10000 which i remembered from my childhood.I eventually found it in a 1954 issue but i can`t remember which month.Interesting insight into Meccano & life history.

 

                     Ray.

[PatB]

I find it fascinating that it was, in the 1950s, entirely proper to advertise "deadly" throwing knives to teenage boys.

 

I also wonder how many generating plants BTH sold as a result of advertising in MM .

[peterfgf]

I would agree except that the centre rail should be negative with the controller in the forward position. Like 2 rail, forward is with the right hand running rail positive. ( This is why the polarity of the magnets is reversed between the 2 and 3 rail versions of Dublo locomotives.)

 

Slider potentiometers can often be serviced* by taking them apart and cleaning the muck of the track and slider contact and retensioning the latter. The dust seals work no better that on Brunel's atmospheric....

 

Some really cr rubbish components are beyond redemption (normally all plastic which doesn't appear to be the case here). 

 

A single transformer does not cause one control to affect the other (beyond slight speed variations), but will cause a short circuit if one is set forward and the other reverse. This can be resolved by isolating both circuits (all rails), but as I said before, this is a bit difficult with Dublo 3 rail. The rail joiners will come out with a little persuasion from a suitable screwdriver but then there is no location for the rails. I don't think most available insulated joiners will fit Dublo rail which has a rather large base. Possibly scale gauge 0 - they are both code 125 or thereabouts? Some tape would be needed to prevent the bases touching.

 

It looks like there is some sort of partial short between the outputs of the controller, but it's difficult to assess further at a distance

 

EDIT

 The presence of a single 2N3055 (good old standby!) power transistor suggests the outputs are not 100% independent. This would require two, one per circuit.

 

The cut-outs in the rail base are to take the wires feeding the inner circuit so that the track sits level. Dublo thought of everything (well almost).

Interesting that you say that the centre rail is supposed to be negative.  I've had my old HD 3-rail out and found absolutely no guidance anywhere on the wiring convention (other than Hornby Dublo's "change the connections round if the locomotive runs in the wrong direction").  It doesn't help that the HD controllers (A Marshall III and an A2, both with PVC sheathed mains wiring) are not marked up with positive and negative. I thought it would be more likely that the centre rail would be the positive and have followed that convention. When I fitted replacement neo-magnets (the originals had lost most of their magnetism) I made sure that the locos all went the same way.  It's not  a problem unless they run on another layout.

Peterfgf

[Il Grifone]

Interesting that you say that the centre rail is supposed to be negative.  I've had my old HD 3-rail out and found absolutely no guidance anywhere on the wiring convention (other than Hornby Dublo's "change the connections round if the locomotive runs in the wrong direction").  It doesn't help that the HD controllers (A Marshall III and an A2, both with PVC sheathed mains wiring) are not marked up with positive and negative. I thought it would be more likely that the centre rail would be the positive and have followed that convention. When I fitted replacement neo-magnets (the originals had lost most of their magnetism) I made sure that the locos all went the same way.  It's not  a problem unless they run on another layout.

Peterfgf

 

I thought it logical that the centre rail should be positive as well. It's true that no positive/negative makings are present ( I suppose they thought that it would only confuse matters, it being easy to swop the wires over*) and the only indication of the correct way to wire up is in the layout plans books which show the wires as not crossed. The ones I've tried result in a negative centre rail for forward running when this is done. I'll have to dig out my ancient literature and see what I come up with. However, if the centre rail is positive, there would be no need for reversal of the the magnets between 2 and 3 rail versions, as is specified in Dublo's own service information. 

 

* Sets were usually (always?) supplied with green wire for connecting, so it would have complicated matters to mark them. Red and black were also available as a spare - I assume this had something to do with easy availability as mains cable.

Edited May 31, 2017 by Il Grifone

[brianusa]

Its more than logical to have the third rail 'live,' as in my O layout the o/s rails are the return conductors for working accessories, etc.  Besides the 'real ' railway has a live centre rail!

 

Brian.

[Il Grifone]

Its more than logical to have the third rail 'live,' as in my O layout the o/s rails are the return conductors for working accessories, etc.  Besides the 'real ' railway has a live centre rail!

 

Brian.

 

True, but 'live' can be positive or negative or even AC. Dublo uses the tinplate base as the return which is the whole problem in this thread.

 

It's not always the case. For example, Trix trains use the centre rail as the common return and on the London Underground the centre (fourth) rail is the return with the high voltage on the outside (third) rail.

[john new]

On My Classic Train set exhibition layout back in the late 80s/early 90s I had exactly the same problem of cross shorts when I stopped using original HD control gear on insulation safety grounds and switched to Gaugemasters. Separate transformers are most definitely required.

 

However, the comments on here seem to be that 3-rail wiring is complex, I suppose it is because I grew up with 3-rail as a kid from 1955 onwards that wiring HD/common return just seems ridiculously easy in comparison with 2-rail, and it is on my modern layouts, not the HD clip ups, that oddities catch me out needing insulation breaks in seemingly odd places etc., etc.! 

 

(Edited - it was the A3 controllers I was using not the later Marshalls. I have examples of many of the HD gear from the black versions onward stored for occasional display but none get power fed to them these days.)

Edited June 1, 2017 by john new

[john new]

Of course on the old one's if they went the wrong way all you did was pull out the two push in blades and put them in the other way round. As many of us had uncoloured lighting flex as wires they had probably got twisted anyway between the screw terminals on the rails and the bladed connector at the controller. (Or the bit of wire/soldered on to a snippet of tin can after the originals got lost).

 

As a 5-year old kid things like setting plus and minus on polarity didn't matter, connect the wires, swap over at the controller blade slits if it went backwards when the lever said forwards! Simples, not like the new fangled DCC Star Ship Enterprise command desks with codes for each engine and the like.

Edited June 1, 2017 by john new

[Dublodad]

The "positive earth" of Dublo 3-rail could stem from the practice of car electrics, which up to probably the 1950's/60's were positive earth!! I believe that it was thought, at the time, to reduce corrosion in the electrical system

 

Terry

[Il Grifone]

Of course on the Marshalls if they went the wrong way all you did was pull out the two push in blades and put them in the other way round. As many of us had uncoloured lighting flex as wires they had probably got twisted anyway between the screw terminals on the rails and the bladed connector at the controller. (Or the bit of wire/soldered on to a snippet of tin can after the originals got lost).

 

As a 5-year old kid things like setting plus and minus on polarity didn't matter, connect the wires, swap over at the controller blade slits if it went backwards when the lever said forwards! Simples, not like the new fangled DCC Star Ship Enterprise command desks with codes for each engine and the like.

 

 

The Marshalls have screw terminals. It was the earlier A3 with the plug in blades. Mine came second hand and already missing the blades. I just shoved in the ends of the wire instead.

 

 

The "positive earth" of Dublo 3-rail could stem from the practice of car electrics, which up to probably the 1950's/60's were positive earth!! I believe that it was thought, at the time, to reduce corrosion in the electrical system

 

Terry

 

 

It could well be.

 

A lot were 6V as well (PITA). My dad's pre-war car even had the panels insulated from each other to avoid electrolytic corrosion. Post war they didn't bother - they either found it unnecessary or, more likely, didn't care.

[Il Grifone]

Digging through my library, I found E.F. Carter's 'Electric Model Railways'. I couldn't find a date, but it appears to be contemporary with Noah, being full of references to accumulator supplies, raised or level and inside or outside conductor rails and no mention of 2 rail at all. Apparently outside third had all the advantages and was likely to become the modelling standard.... Mention is made of shorts between pickups and closure rails with inside third 'all-level'. Dublo solved this by simply isolating the closure rails. Trix makes the blade become the centre rail, but steam roller wheels make this a  straight-forward solution.

 

He was emphatic in suggesting the running rails be solidly bonded together - still good practice and automatic with Dublo three rail though reliant on the rail joints. However the solution to the topic problem was the use of a split potential power supply - again all the advantages etc. and probably that's why they are not used any more! Basically the system has two power supplies (accumulators) wired in series one being used for forward and the other for reverse, each individual controller having two variable resistors - one connected to the 'forward' supply and one to the 'reverse'. No advantage on the face of it and none at all for simple one locomotive systems, but it does mean only two supplies are needed however large the system - a great advantage if one is messing around with accumulators.

 

No specific mention is made of the polarity of the conductor rails*, but the split potential diagram does show the forward resistances being connected to the negative supply and the reverse to the positive and thence to the conductor rails.

 

* At least I couldn't find any - I skipped the pages and pages on how to install and wire up outside third rails for various combinations of pointwork.

Edited June 1, 2017 by Il Grifone

[Wolseley]

The "positive earth" of Dublo 3-rail could stem from the practice of car electrics, which up to probably the 1950's/60's were positive earth!! I believe that it was thought, at the time, to reduce corrosion in the electrical system

 

Terry

 

 

My Wolseley 15/60 is positive earthed....

[john new]

The Marshalls have screw terminals. It was the earlier A3 with the plug in blades. Mine came second hand and already missing the blades. I just shoved in the ends of the wire instead.

 

 

oops -Thanks for the correction, I've not not had the Dublo display table set out for a while and yes it was an A3 that I first used. Duh. Old age I guess. Posts above now edited.

Edited June 1, 2017 by john new

[Dublodad]

SCARM plan of the 8 x 4 loose laid layout we ran at Milton Court Care Home - Milton Keynes, yesterday, 1st June. This is a simplified plan of a design of another group member. The plan is not geometrically correct, and also needed "Ad Libbing" during assembly. A bucket load of straight short rails are a blessing at times like this!!!!

 

Photos and a video are available on the "Hornby Dublo Trains - HRCA" Facebook page. This is a closed group, but, if you are interested in Dublo, I would recommend that you register.

 

TerrySCARM - Milton Court Version 2.pdf. 

Edited June 2, 2017 by Dublodad

[paul-dereham]

Mecanno Magazine Feb 1952 page 85 has the following information for running a second engine on three rail track. 

 

http://pdfmm.free.fr//5202.pdf

 

 

An interesting magazine as my late father in law worked for Cranes of Dereham (see article on page 55) and my Mother in Law remembers this. I live just a few minutes from the site of the works now a retail park. Also an ad for Hobbies of Dereham.

Edited June 21, 2017 by paul-dereham

[DCB]

My Wolseley 15/60 is positive earthed....

Most British Leyland and constituents cars were positive earth, I think the 1971 Marina was the first Negative earth as I cannot remember a Positive earth Alternator though my mind may be playing tricks.  We had to do something to Dynamos depending on whether they were to go on negative or positive earth vehicles. I changed a lot of dynamo cars to alternator including swapping from negative to positive earth back in the late 70s and 80s, getting the charge warning light to work correctly was a challenge.......

 

My old H/D transformer is working OK, I thought it was a marshall 3 but it has 12v controlled  12 v DC and AC connectors with spade connectors on the back. Currently in use powering a diode based voltage controlled controller, very strange to hear the cut out pinging and red light on with locos working on half throttle...

[PatB]

Most British Leyland and constituents cars were positive earth, I think the 1971 Marina was the first Negative earth as I cannot remember a Positive earth Alternator though my mind may be playing tricks.  We had to do something to Dynamos depending on whether they were to go on negative or positive earth vehicles. I changed a lot of dynamo cars to alternator including swapping from negative to positive earth back in the late 70s and 80s, getting the charge warning light to work correctly was a challenge.......

 

My old H/D transformer is working OK, I thought it was a marshall 3 but it has 12v controlled  12 v DC and AC connectors with spade connectors on the back. Currently in use powering a diode based voltage controlled controller, very strange to hear the cut out pinging and red light on with locos working on half throttle...

 

All our dynamo equipped '60s cars were +ve earth. Everything we ever had with an alternator was -ve. I remember in the early 1980s, one of the regular questions that cropped up in the "Ask a Mechanic" type pages in magazines like Practical Motorist was how to -ve earth a dynamo equipped car, usually so the enquirer could fit a modern stereo or electronic tachometer. From memory, the main thing, apart from turning the battery round, was to repolarise the dynamo which, IIRC, required the brief connection of a couple of the terminals on the inevitable mechanical voltage regulator. Or you could fit an alternator and solid state rectifier/regulator and throw the dynamo and its ancillaries in the bin, thus ensuring both an adequate supply of amps and a headache for future restorers :.

 

In hindsight I'm not sure what would happen with the starter motor. Memory tells me that the Lucas units I played with were quite magnetic, suggesting that they were permanent magnet units, but surely, in that case, reversal of the electrical system would cause it to spin the wrong way? Presumably they were actually field wound and the magnetism was just a side effect.

[Il Grifone]

Car Dynamos  - awful things! -, but quite cheap and easy to replace. I can remember parking outside a scrap yard and purchasing a dynamo for £3 (a bargain - Halfords wanted £8/10/- * exchange IIRC) and 15 minutes later I was away with the 'new' dynamo fitted - try that today! (True there's no need as alternators rarely fail!)

 

Negative earth came in with silicon based semiconductors. Germanium transistors were easier to make p-n-p required  a negative power line and convenient with positive earth vehicles. Silicon on the other hand were n-p-n and required a positive supply. (Technology moves on and this has not been the case.)

 

Field wound motors and dynamos will inevitably leave their ironwork magnetised  when run on D.C. If 'universal' or reversible care will have been taken in their design to minimise this, but when Intended for one way D.C. operation there would be no need.

 

Waffle alert!

 

* It could have been £8.50 it was around the time of the changeover. Most 12V British cars used the same Lucas unit, but I can remember problems with our Fiats. Replacements were much more expensive and differed throughout the range. We came to visit my parents in England in the eighties and the charging light came on just this side of the Channel. It was early in the morning and still dark. We managed to reach our destination (Leamington Spa) but that was all. The local Fiat agent quoted a frighteningly high figure (and IIRC didn't have one in stock anyway) so off to the breakers. Finally we found the right part (or so we thought - it fitted and worked, but really we should have had a heavier duty device. (We had the 850 (yes, really and, yes, gutless was the word*) Pulmino (minibus), but the part was from the 850 car.

* The most I got out of her was around 100 kph (60mph but it sounds more that way!), but at that speed the roadholding (or rather lack of it) did not encourage further effort....

Edited June 22, 2017 by Il Grifone