Hammant & Morgan Duette controller : Full/Half wave & High/Low resistance switches

[Justin Smith]

I have been using an AGW double controller for my rebuilt 1970s N gauge layout, but have now ordered a Hammant & Morgan Duette off EBay. I did this partly because I find the speed separate control and Forward/Reverse switches to be "unnatural" in their operation and also because I used to have Duette back in the 70s* and I want the layout to be like it was in the 70s!
However I am unsure what the operation of the Full Wave / Half Wave switch is meant to achieve, similarly the High / Low resistance switches, does anyone know ?
Also the AGV controller has a short circuit protection (useful if I accidentally switch the points to connect a live inner and outer loop when set to opposite directions ! ) with a tell tale LED showing when it is in operation. Does the Duette have a similar feature ?

* from memory I sold it to buy a guitar !

 

[John Webb]

The Full-wave/Half-wave switch cuts out part of the rectifying circuit. In full-wave mode there are 100 pulses a second, in half-wave mode there are 50 pulses a second with a gap of 0v between them. The idea is to give a lower voltage for control of very slow speed operations, eg shunting moves.

I can't recall exactly how the High/Low resistance switch works, but that was basically to give better control of both high-current and low-current motors.

I think H&M controllers had a thermal cut-out.

You might like to look at www.handem.uk who are a specialist H&M spares and repair dealer who advertise in the model railway press.

I strongly advise a close look at the mains cable of your second-hand unit when you get it. Check there is a connection between earth and the unit's casing and that it is not an old rubber-insulated cable; if it is get it replaced with a modern plastic cable.

 

[Justin Smith]

The Full-wave/Half-wave switch cuts out part of the rectifying circuit. In full-wave mode there are 100 pulses a second, in half-wave mode there are 50 pulses a second with a gap of 0v between them. The idea is to give a lower voltage for control of very slow speed operations, eg shunting moves.

I can't recall exactly how the High/Low resistance switch works, but that was basically to give better control of both high-current and low-current motors.

I think H&M controllers had a thermal cut-out.

You might like to look at www.handem.uk who are a specialist H&M spares and repair dealer who advertise in the model railway press.

I strongly advise a close look at the mains cable of your second-hand unit when you get it. Check there is a connection between earth and the unit's casing and that it is not an old rubber-insulated cable; if it is get it replaced with a modern plastic cable.

Thanks John.
You would think the Duette controller would be protected against the sort of problem I mentioned (accidentally switching the points to connect a live inner and outer loop when they are set to opposite directions ! ), after all it's very easy to do on a layout with two circuits and a Duette is specifically designed for layouts with two circuits !

 

[ChrisT]

I used an H&M half-wave rectification unit back in the '60s as I was attracted by the claim that it would give good slow-speed running. It didn't take long to find that this wasn't the case. Whilst the locos definitely ran slower the chopping of the pulse made that slow running very clunky. As a young lad I was very disappointed and never used the unit after that.

 

[Justin Smith]

I used an H&M half-wave rectification unit back in the '60s as I was attracted by the claim that it would give good slow-speed running. It didn't take long to find that this wasn't the case. Whilst the locos definitely ran slower the chopping of the pulse made that slow running very clunky. As a young lad I was very disappointed and never used the unit after that.

There are also some reports about it burning out motors on N gauge locos ?

 

[ChrisT]

There are also some reports about it burning out motors on N gauge locos ?

It's possible but wasn't aware of that problem. I was 00 gauge at the time.

 

[Justin Smith]

Article on train controllers.
The H&M controllers (Duette and Clipper) get a slating, but that opinion is not reflected in some of the posts on this RM Web thread.

 

[John Webb]

Article on train controllers.
The H&M controllers (Duette and Clipper) get a slating, but that opinion is not reflected in some of the posts on this RM Web thread.

Interesting article you linked to, but with a glaring error. The author refers to the Powermaster as having an 'autotransformer'. It was in fact a proper transformer whose (isolated) secondary winding was tapped by the moving arm to vary the voltage. I suspect the author was confused by the 'Variac' variable output transformers which were used for controlling mains-operated equipment and which were autotransformers.

 

[Rescars]

In the dim and distant past I operated OO with a Duette. As I recall the High/Low resistance switch did nothing of consequence until I acquired a secondhand Jouef shunter. This was totally uncontrollable on the High setting, but behaved very nicely on Low.

 

[Justin Smith]

In the dim and distant past I operated OO with a Duette. As I recall the High/Low resistance switch did nothing of consequence until I acquired a secondhand Jouef shunter. This was totally uncontrollable on the High setting, but behaved very nicely on Low.

I have found similar. With some locos it has little effect, but with others it does seem to "widen" the speed control.