Signedetched and white filled: .004 AIR CONDENSER / TYPE 120C SERIAL No. 170 / GENERAL RADIO CO. / CAMBRIDGE, MASS.
Inscribedin white on side: .004 AIR COND.
in black on side: CRUFT / INSTRUCTION
FunctionThe frequency of transmission or reception of a radio circuit is inversely proportional to the square root of both its capacitance and inductance. variable capacitors are one of the methods used to alter a circuit's frequency, by altering the circuit's capacitance.
Usually, variable capacitors consist of two groups of semicircular metal plates arranged in parallel. By turning the knob, the user is adjusting how much the two groups of metal plates are overlapping.
Probably 0.004 Farads.
Historical AttributesUsed for teaching at the Cruft Laboratory, Harvard University.
ProvenanceFrom the Cruft Laboratory, Harvard University.