Rotary voltage controller (Bing)

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Exhibit

Rotary voltage controller (Bing)

BTMM map 030.gif
location:
Arch Three , Area 30
Classic Locomotives (display)
Shelf 3

A black circular rotary voltage controller made by Bing.

The controller consists of a disc of black (Bakelite?), with two main terminals and a silver-coloured central rotary pickup arm. Around the perimeter of the disc, just in from the edge, is a broken circular channel containing a helical coil of resistance wire connecting the two terminals, and the pickup arm makes contact with this coil at different positions when it's rotated.