Vintage GenRad / General Radio 1490-D Decade Inductor - 11.11H / 1mH - High Q

Up for sale is a General Radio Type 1490-D Decade Inductor, a laboratory standard for generating precise, stable inductance values. This is a foundational piece of test equipment from the most respected name in precision electronic standards.

This is the desirable later -D model, which features superior electrical characteristics compared to the earlier -B version. It is an essential tool for designing and testing filters, creating audio crossovers, conducting lab experiments, and calibrating other instruments.

The "D" is hard to read so we identified as a 1490-D based on its weight of approximately 21.4 lbs, which aligns with the 21.75 lb specification for the -D model (as opposed to the 19.25 lb specification for the earlier -B model).

Key Specifications:

• Manufacturer: General Radio (GenRad)

• Model: 1490-D

• Total Inductance: 11.11 Henries (H)

• Number of Decades: 4

• Resolution (Smallest Step): 1 millihenry (mH)

• Decade Steps:

  • Dial 1: 1 H per step

  • Dial 2: 100 mH per step

  • Dial 3: 10 mH per step

  • Dial 4: 1 mH per step

The 1490-D Advantage:

As the direct successor to the 1490-B, the 1490-D offers the same inductance range but with superior performance due to its improved molybdenum-permalloy dust cores. This results in a higher and more stable Q Factor (Quality Factor), meaning it functions as a more efficient, "ideal" inductor with lower losses—critical for precision work.