Signedon dial: GENERAL RADIO CO. / CAMBRIDGE, MA
Inscribedon base in black: 18
stamped on base: 124 B
FunctionThe frequency of transmission or reception of a radio circuit is inversely proportional to the square root of both its capacitance and inductance. Tuning coils are one of the methods used to alter a circuit's frequency, by altering the circuit's inductance.
In this particular case, the inductance of the coil (which would be part of the circuit) is changed by turning the knob, which makes one of the points of electric contact move along the coil wires, changing the effective size of the coil. Less loops and wire between the two electric contacts means a smaller inductance.
Historical AttributesThe triangle indicates its instructional use at the Physics Department, Harvard University.
ProvenanceFrom the Cruft Laboratory, Harvard University.