Many older model railway enthusiasts will remember the Hammant and Morgan line (H&M) of controllers. They were beautiful, solid, satisfying controllers to own and handle, but not very good controllers of trains, especially for shunting.
This is a Duette of the middle series, 1960s, shown with the front panel swung away. You can see the transformer, two thermal cutouts just in front of it riveted to the bottom plate. The two rectangular rectifiers (selenium?) are visible left and right of the entry point of the mains cable.
The circuit is the same as the Clipper except that there is no high-low resistance switch.
As I have said
the GaugeMaster feedback controller is the exact opposite: fabulous control, crummy interface.
This page presents a modification to the Duette that makes it into
a "Duette with Gaugemaster control characteristics".
The circuit diagram of the new Duette:
The circuit shown above operates just like a Gaugemaster feedback controller, but will do so with the rectified ac in either polarity. Reversing the polarity causes the locomotive to go in the other direction. This allows it to be wired into the Duette so that the panel knob still operates centre-off, unlike the Gaugemaster. The only modification to the Duette is that a wire must be soldered to the wiper that traverses the 50 Ohm rheostat. This wire runs to a small board carrying the above circuit, except for the 5W resistor and the 51 Ohm rheostat, and the switches and rectifiers to the left that are already inside the Duette.