Potentiometers

In the beginning, potentiometers (pots) did not resemble the shaft and cylindrical body form of today. Instead, they were made by winding fine resistive wire on an insulating bar with an ebonite disk on a slider. The disk could be moved back and forth to adjust the resistance. In early radio circuits,  a pot  was used for varying the bias voltage that was applied  to a carborundom detector.

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Model 1044 detector showing dual pots
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This is a 3986 detector/amplifier, with  one detector tube and two radio frequency tubes. Those three pots sure take up a lot of space. 
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Close up of an early potentiometer. (Museum of Science and Technology, Ottawa  photos in this table) 
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Construction
When Marconi Wireless Telegraph Company began using tubes, they needed a thick wire, low resistance, high current , variable resistor, which they called a Rheostat. These were used for varying tube filament voltage. By varying the voltage, that helped to extend the filament battery life.

Contributors and Credits:

1)  Lewis Bodkin  <05bodkin555(at)gmail,com>

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Mar 218