An old Hornby power controller restoration

[high_vacuum_house]

Good evening,
A quick restoration this afternoon as the weather was bad. This time it was a Hornby railway power controller from the mid 1980's

I purchased this to make up a model railway layout and upon power up was completely dead from the variable supply to the tracks. Tapping it and wiggling the switches would make it cause brief spurt of power.

It is a vey simple supply with 15V AC output for signals and point motors and a variable DC supply for the track to run locomotives. The power switch really just switches the bridge rectifier from half wave to full wave supply. The speed controller is little more than an in-house made wirewound resistor.

To open it 6 rivets have to be drilled out of the case, the 2 switch dollys need removing and the power knob removing as well.

The 2 switches (one for direction change and one for low and high power) are not a bought in part from a component supplier, but made in house and are easily disassembled.

Here was the cause of the almost dead supply. The switch sliding contacts were brass strips and tarnished. This came up well with some Brasso. The other major problem was with the springing of the moving contacts. The sponge strips they used had deteriorated over many years and had lost all of its springiness so that the contacts were not being pressed onto the fixed contacts. I found some silicone sleeving was an ideal replacement for the old sponge and once fitted into the contact carrier, the sliding contacts were making good contact with their fixed contacts. You can see the difference in the third picture.

After cleaning the case, switch dollys and the power knob, reassembly was straightforward and I replaced the drilled out rivets with 4BA nuts bolts and washers to complete the work. The power controller now functions faultlessly now.

[high_vacuum_house]

Finally after the case and controls being cleaned and then reassembled.

[Cathovisor]

They're mid-70s - I had one with my train set in 1976.

Never as good as the offering from Hammant and Morgan.

[Uncle Bulgaria]

I like the replacement with BA - just what I'd have done!

[The Philpott]

Reminds me I must get my Hammant & Morgan Safety Minor sorted out. (Originality set aside as a nice chunky Paignton knob with chromed pointer is now in place on the front!)

Dave

[emeritus]

I bought a Hammant & Morgan Duo for £2 at a charity shop a few years ago. It gets occasional use with its 12 V DC auxilliary output connected in series with my Farnell L30-2 when I need around 42V when periodically cycling the three SLA batteries that power my electric bike to check their capacity. Charge using the H&M and L30, discharge using three 12V 21W bulbs in series. It is also used to control the speed of my 12V Expo Mini drill.

[duncanlowe]

I had one similar, back in the 70s too. Not sure if it's in the loft, but if it is this will be a great guide to reviving it.

[SiriusHardware]

This controller comes from the original peak period of my childhood / early teens interest in model railways and at the time I was quite the Hornby fan and I wanted an all-Hornby setup including the controllers, but when I went specifically to buy a controller like the one which is the subject of this post the owner of the model shop persuaded me to buy a Hammant and Morgan 'Duette' instead.

I had something of a model rail revival about a decade ago and I spotted an H&M 'Duette' like my original one in the 'shed shop' at Grosmont on the North Yorkshire Moors Railway. It was clearly second hand, priced at £40 and I couldn't talk them down, they were adamant they would be able to get the asking price for it. So those H&M units are still well regarded after all this time, although maybe not so much sought after now because DCC (Digital Command and Control) seems to be very popular now.

[Cathovisor]

Depends. H&M controllers are sought after by Hornby-Dublo collectors instead of the "classic" A3 controller - for newer models with analogue control. Gaugemaster feedback controllers are favoured where folk don't want the expense of DCC.

[Graham G3ZVT]

Mine was an A2 like this



I got it in 1959 and it disappeared along with a load of scrap metal from the cellar of my late in-laws house about 15 years ago. I still have the engine from the set, but I won't risk posting a locomotive picture.

The transformer spent more time being abused with my electrolysis and electroplating experiments in later years.

I too drilled out the rivets, it was to replace the mains lead, but it was long enough ago for 4BA to be far more likely to be at hand than M3/M4.

[SiriusHardware]

A friend (early 1970s) had a hand-me-down-from-Dad Dublo set complete with 3-rail track mounted on tinplate 'ballast'. The controller was either an A2 or A3 judging by images I have seen recently, including in the post above. I can't be sure which, it was so long ago.

I had a very clear memory of what my first (1960s) model train controller looked like but I couldn't find anything like it in searches for Hornby controllers, and that turned out to be because it wasn't a Hornby branded unit as such, but a Triang 'P4' or 'P5', similar to the one in the attached (Web found) image.

[Aub]

I had an A2, like Graham's above, with my first Hornby Dublo 3 rail set . Must have been about 1960. Later, as more track was added, my dad got me a H&M Duette. I still have that, but not the A2.

Cheers

Aub

[emeritus]

The book "The Hornby Dublo Story" (by Michael Foster) includes extracts from letters written to the author by Mr Ronald Wyborn, ex-Chief Electrical Engineer of Meccano Ltd. He has this to say about the A2 and A3 controllers.

"The A2 and A3 Power Units provide another example of our determination to produce a quality article. The transformers which formed part of these units were designed to be strictly in in conformance with British Standards, and production testing was carried out on the most advanced equipment we could devise. .....

Awareness of this attitude towards quality must I think have gradually spread, because in the latter half of the '50's I was invited to represent the British toy industry on a permanent committee of British Standards. This was useful as it allowed me to help provide a bastion against some of the shoddy products beginning to make their appearance from abroad. It also helped me later on to obtain acceptance into the appropriate standard for a short-circuit proof transformer which I had devised and developed in an attempt to bring down cost by removing the necessity for any form of electrical protection. We had gone into production with this when later still I was also successful in getting it approved by the International Electrotechnical Commission on safety transformers at a specially convened meeting in Copenhagen. "


Does anyone know anything about this short-circuit proof transformer design? My A3 controller does have a cut-out that works on the 12V controlled output, where a bulb lights up and a cut-out operates at a current greater than about 1A, but this does not protect the 15VAC auxilliary output. My cousin managed to burn out the transformer of his contemporaneous Triang controller due to a short on its AC output.

[Radio Wrangler]

Originally Posted by emeritus

Does anyone know anything about this short-circuit proof transformer design?

Short circuit proof transformers are quite common.

Traditional electric welders frequently get short circuited as the electrode gets scratched across the work as the operator attempts to start the arc. alco, it's not uncommon for electrodes to get stuck onto the work.

This is achieved by having deliberate leakage inductance built into the welder's transformer. Usually as a movable piece of core to 'waste' some of the flux and act as a control to set the welding current.

This technology predates its use in model train controllers.

Most people don't have electric welders, but they do have microwave cookers. The magnetrons in these cookers are RF oscillators, and seen from the power supply's perspective they look like a negative resistance. They need a high voltage power supply, but it has to be current controlled to stabilise their power output. The job is done by leakage inductance designed into their transformer. This isn't enough to make the transformer completely short-proof, but it's enough to suit what the magnetron does to it.

David

[emeritus]

Thanks for the explanation, that makes sense. The curriculum included power engineering in the first two years of my electronics course at college, including transformer design, but short-circuit proof transformers were not on the syllabus.

[Radio Wrangler]

Aye, the principle is that with the flux shunt, even with the secondary shorted, the primary still has enough inductance to limit the primary current. It's a very smart idea and so subtle that if you weren't aware of it, you wouldn't know it was there.

In valve amplifier output transformers and RF transformers we bust guts to minimise leakage inductance, so it comes as a shock to find it has its uses.

Other wild transformer-y things which play games with core characteristics are magnetic amplifiers (Transductors) and fluxgate magnetometers.

David

[Techman]

Originally Posted by SiriusHardware

Triang 'P4' or 'P5', similar to the one in the attached (Web found) image.

That's exactly the power supply that I was bought as a youngster to replace the expensive to run double 6 volt lantern battery box that had originally come with the train set - I've still got them both.

The high/low red plastic switch lever unfortunately broke off early in the life of the unit. It was also used as a power supply for other things when I first started messing with electronics - not the ideal unit for such things.

[wireman]

I should have a Horby catalogue from that era but I can't find it at the moment, I can look it out if of interest. My controller (which I still have) was an H and M clipper.

[Cathovisor]

Originally Posted by emeritus

The book "The Hornby Dublo Story" (by Michael Foster) includes extracts from letters written to the author by Mr Ronald Wyborn, ex-Chief Electrical Engineer of Meccano Ltd. He has this to say about the A2 and A3 controllers.

Random thought.

Could Ronald Wyborn have been related in any way to Ekco's Chief Engineer, John Wyborn?

The A3 controller is here: https://dublonutz.blogspot.com/2016/...ontroller.html

These controllers were superseded in the Hornby 2-rail era by the "Marshal" range before finally, Rovex took over.

[emeritus]

Thanks for the A3 link.The rubber mains flex of my A3 is showing no signs of deterioration, so I have not yet needed to drill out the rivets to replace it. It has not been exposed to extreme temperature changes.

My friend had one of the later Marshall controllers. My recollection is that, rather than providing continuous adjustment, it applied power in four or five discrete steps.