Hornby transformer type T20

[Refugee]

I found this item looking almost mint at the flea marked for under a tenner.
It is questionable if a plug has ever been fitted as there is no sign of the cord grip having been done up and also the outside of the cable looks very clean and unused.
This does not mean the cable is any good as the rubber looks pretty brittle.
There is a small dent in the case but it did come in what looks like the bottom half of the original box.
I have it lined up for a little project that will need a modest boxed transformer so it will be fitted to a board with the other bits along side so it will not be pulled to bits.

[russell_w_b]

I thought I had one of those down the shed, but when I looked it's a Hammant and Morgan one: 2A max, 1 x 12V d.c. O/P; 1 x 12V a.c. O/P; 1 x 16V d.c. O/P.

Yours may be older than mine. I seem to remember from my childhood train set 16V a.c. being a standard a.c. accessory voltage. But I once had a Meccano motor, black stove-enamelled side-plates with the shaft protruding either side. Can't remember what voltage it took, though. It may have been 20V a.c. as well as d.c.

[Refugee]

I have got a much later Hornby one with all the paint warn off that has 15 volts AC on the accessory output. It looses the extra 3 volts across the rectifier to get 12 volts DC on the variable output.

[Cobaltblue]

SNAP!

Cheers

Mike T

[emeritus]

The Hornby T20 was for use with the 20V AC Hornby O Gauge electric trains that were available in the UK pre-war, but only available for export post-war. According the the book "The Hornby Gauge System" by Chris & Julie Graebe, the T20 was first introduced in 1932 and had a blue case. When production resumed after the war, the T20 had a Black case, and was available from 1949 to 1953, the period when electric trains were sold in Australia and elsewhere. So it seems likely that the ones illustrated in this post are of post-war manufacture.

The book mentions that in 1952 Hattons of Liverpool were advertising Hornby Electric O gauge trains, including 20V transformers, at clearance prices, so the black post-war T20's may have originated from them. Meccano France continued manufacture of O gauge electric trains in France throughout the war and well into the post-war period, but their transformers would probably have been made in France and wound for 220V. The book gives only brief details of the French electrical items.

After 1934 the operating sequence was changed from OFF/MIN/ MAX, to OFF/MAX /MIN. The reason for the change to immediate application of full voltage was to operate the reverse gear of engines fitted with automatic reverse, as the AC motors used were unidirectional.

[russell_w_b]

Originally Posted by russell_w_b

I thought I had one of those down the shed, but when I looked it's a Hammant and Morgan one...

Curiosity got the better of me and I looked down the shed. Interestingly, the rating plate (Made in England and with UK mains cable colours) says 200 - 240V 60 C/S.

[emeritus]

According to the books about Meccano products, transformers could be wound for any voltage or frequency to special order, but 240V 60Hz is an odd combination. The 12V transformer that came with my 1950's Hornby Dublo train set is stated to be suitable for 230-250V, 40 to 100Hz.

[Refugee]

Mine is clearly marked 225-250 volts and made in England.

[Refugee]

Originally Posted by emeritus

The book mentions that in 1952 Hattons of Liverpool were advertising Hornby Electric O gauge trains, including 20V transformers, at clearance prices, so the black post-war T20's may have originated from them.

That explains why I have found one that looks like a plug has never been fitted.

I have now found a freeby tape recorder so I have got another thread to start.

[Herald1360]

Check it doesn't overheat on 50Hz!


If it's engineered au point the core may start saturating with the lower mains frequency.

[Refugee]

Mine should not overheat on 50Hz as the rating says 50/60 old school cycles and they are like modern hertz.

[russell_w_b]

Originally Posted by Herald1360

Check it doesn't overheat on 50Hz!

It doesn't. I suspect some 'shorthand' has been used for the frequency rating mark. With regard to the other posters' rating plates, they make perfect sense given that the UK voltage and frequency variations in 1954 (typically) extend to include the ranges specified. I did put a PDF up on this a while back, taken from the Molloy 1954 Electrical Engineers' Handbook.

I would think the lamination material design and manufacture of a model engineering transformer to a specific, narrow frequency would prove uneconomical, given the wider frequency range of other similar-size transformers (like Emeritus' Hornby example).

[winston_1]

I had that very same T20 transformer when I was a kid in the 50s. It went with a Mecanno 20 volt motor I had. The slider contacts added a little resistance to the output but so little to make no difference.

When I got bored with Mecanno and got more interested in electrics I used it to supply individual Christmas tree bulbs in a den, used it to charge an old car battery via a home made chemical rectifier and car bulb as a limiter, and various quite dangerous things like stepping the voltage back up using another transformer.

When I was about 20 I swopped the transformer and motor for some old TVs.

[Refugee]

I have still got the one I used for my early bench power supply.
It hat 3Vac fixed and 20Vac fixed plus 12 volts DC with 4 taps that are switched.

[Trifocaltrev]

I have a collection of prewar Hornby 20v trains and have many transformers ie T20, T20A T20m T22m T6 T6A T6M T26M and TR6 all for either 200/225v or 225/250 50/60 Cycles. I also have a T20 prewar wound for 110v 40Cycles.

I suspect that many other variations exist!

Trevor.

[Refugee]

You have a big collection there.
Do you have any idea about the one in post #14?
I have got a close up of the remains of the label.

[Trifocaltrev]

I don't have the model shown in post 14# however I have a very similar one also made by Shenphone and I have the two controllers to match. My Shenphone is the same construction and crackle finish as yours, the difference being that it has an ammeter 0 -10 amps and it has 20v AC Uncontrolled, 12v DC Uncontrolled and 12v Controlled outputs.

In the Hornby range the T20, T20A T20M & T22M were all 20v AC for Hornby 20V O gauge locos and the T6, T6M, T6M & T26M were all 6v AC for the Hornby 6V range of locomotives.

The TR6 was 6v DC for the small PM locos that they made.

The T20, T20A, T6 & T6A all had resistance control and the rest were plain transformers for use with separate controls. The T22M & T26M were double the VA output of the others in order to run two locos with separate controllers from one transformer.

The Shenphone were made to run Hornby or the 12v DC Bassett Lowke range of O gauge locomotives.They date to the late 1940s to mid 1950s

Trevor.

[Refugee]

The control on mine is 4 taps on the transformer without a resistance control.
The power switch was a later addition.