GenRad 1491 series decade inductance box

The IET Labs GenRad 1491 decade inductance box is the most accurate decade inductor commercially available. The 1491, has a max inductance of 11H with a resolution of either 1mH or 100µH.

IET GenRad 1491 Decade Inductor
The decade switch has high-quality ceramic stator and-rotor members and well-defined ball-and-socket detents. All contacts are made of a silver alloy and have positive wiping action. Shielded toroidal cores are used for small mutual inductance and minimum effect from external fields.

The IET Labs, GenRad 1491 inductance decade series are convenient elements for use in wave filters, equalizers, and turned circuits throughout the range of audio and low radio frequencies. As components in oscillators, analyzers, and similar equipment, they are especially useful during the preliminary design period, when the ability to vary circuit elements over relatively wide ranges is necessary to determine optimum operating values. The 1491 Decade Inductors have values of low-frequency storage factor, Q, that are much larger than those of air-core coils.


  • Shielded toroidal cores for small mutual inductance and minimal effect from external fields
  • Sealed against moisture for long term stability
  • Excellent as a moderately precise standard of inductance .
  • High-Q, 200 and above