Humboldt State University ® Department of Chemistry
Robert A. Paselk Scientific Instrument Museum
L &N 4390 Multirange Shunt Box
Leeds & Northrup Co.
HSU Physics Department, 1960
To determine accurate current values, as when calibrating an ammeter, using a potentiometer. The current is determined via Ohm's Law by dividing the potentiometer reading by the resistance of the shunt. The multirange shunt allows the determination of currents from 0-7.5 amps, depending on which binding posts are connected in series with the current source.
There are two Bakelite terminals at the upper center of the top panel labeled "Potentiometer" with the left one also labeled "A." Eight nickel plated brass terminals are arranged across the bottom of the panel labeled: "COMMON/A/CURRENT TERMINAL; 7.5/.2; 3/.5; 1.5/1; .75/2; .3/5; .15/10; .075 AMPS/20 OHMS." The panel is held to the case with six chrome plated brass slot-head screws. The instrument has a 6 1/2 x 12 1/2" satin Bakelite top-plate, and a polished solid mahogany case and cover. It is 6" high to the top of the Bakelite plate. The case has air circulation slots at the bottom and top of the front and back panels for air circulation, as well as 32 half inch holes in the bottom of the case. There are four rubber feet which hold the case about a half inch above the ground. Condition: excellent. There is a decal on the top plate: State of California Humboldt College 30248.
A related device, a "Volt Box" is shown as item 83415 on pg. 1362 of the Central Scientific Co. Catalog J-141 (1941). Use of a multirange shunt box is described in the Directions brochure for the 7645 Student's Potentiometer from Leeds and Northrup (1960) on pg. 13.