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Variable Inductor 107 N


a table model consisting of a brown square brown wooden box and a black slate top panel with two coils, a rotor and a stator mounted concentrically and adjustable with two plastic tuning controls; the panel secured with fourteen screws of different kinds; the manufacture information technical details readable on the top panel

Accession Number:

Alternative Name:

Primary Materials: Wood; Slate; Plastics; Metal


Three types of markings are visible on the top panel: measurement, manufacture information, technical details.

Manufacture information reads: Variable Inductor, Type 107 N Serial No. 7815, Parallel Ind. = 1/4; Series Ind. (L) Mutual Ind. = 1/2 (L-312) mh; Max. Power: 15 watts. Nominal series connection data. Max. Cur. 0.18 a; D-C Res. 410. General Radio Co. Cambridge, Mass,, U.S.A.

Technical details: stator 1-2; rotor 3-4; Series: strap 2-3: parallel: strap 1to 3 & 2 to 4.

In addition, it is etched “MILLIHENRYS SERIES”.

Dimensions (cm): 16.5cm x 16.5cm x 22.2cm


As the position of this table model’s rotor is changed, the coupling between the two coils changes, thus causing the inductance to vary. The total inductance range is over 25:1. The maximum power is 15W.

Separate terminals are brought out for both the rotor and the stator so that they may be connected in series or in parallels as a self-inductor or used separately as a mutual inductor.



Fair condition with signs of wear including scratches on the wooden box

Associated Instruments:

Manufacturer: General Radio Company

Date of Manufacture: c. 1945-1955


Comes from the Physics Department of the University of Toronto.

Additional Information and References:

The 107 was available in 5 different versions, each covering a different range of inductances:

Model Mutual Inductance DC Resistance Self-Inductance (Series) Self-Inductance (Parallel)
107-J 0 – 10.8 uh 0.05 ohms 8 – 50 uh 2 – 12.5 uh
107-K 0 – 110 uh 0.38 ohms 80 – 500 uh 20 – 125 uh
107-L 0 – 1.1 mh 4.6 ohms 0.8 – 5 mh 0.2 – 1.25 mh
107-M 0 – 11 mh 32 ohms 8 – 50 mh 2 – 12.5 mh
107-N 0 – 110 mh 410 ohms 80 – 500 mh 20 – 125 mh


Historical Notes:

The original retail price is said to be $55.0