potentiometers for manual dynamo control

[JonE]

Dave Mann, Malcolm Watts and others have all discussed potentiometers in old threads on the old forum allowing full manual control of the dynamo. Cornwall Club members mentioned the 'simmerstat procedure'; Dave has mentioned mini fan rheostats. I'd just like to bump the topic to find out exactly what items have been used - as cooker ring switches, the fan rheostat and Malcolm's 150W 0-5 Ohm potentiometer all seem to be different in spec.
Is anyone else using such a thing still?