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General Radio 650-A
Impedance Bridge
General Radio 650-A Impedance Bridge

Available from 1935 to 1956

Catalog History
 Document Year Page
Catalog H 1935 70
Catalog J 1936 76
Catalog K1 1939 70
Catalog K2 1942 74
Catalog K3 1944 72
Catalog K4 1945 72
Catalog L 1948 76
Catalog M 1951 71
Catalog N 1954 89
Catalog O 1956 28
(All manuals in PDF format unless noted otherwise)

The General Radio 650-A Impedance Bridge was introduced in Catalog H (1935) and remained available through Catalog O (1956).

The Type 650-A is a CRL impedance bridge with a basic measurement accuracy between 1% and 2%. Its a self contained battery operated null instrument with an internal AC generator and DC potential. The internal AC generator is of the microphone hummer type similar to the Type 572-B and powered by four six inch dry cell batteries. The DC test potential is derived from same series of batteries located in a compartment at the back of the copper lined walnut case. Inductance and capacitance is measured in six ranges and resistance in seven ranges. Measurements are made using three bridge circuits, the Wheatstone, Hay and Maxwell. The recommended detector is a pair of high-impedance headphones for AC measurements. A panel galvanometer with a switchable shunt is used for DC nulls.

An accessory Type 650-P1 Oscillator-Amplifier is available providing a 1 kHz generator and a detector amplifier. See the Type 650-P1 for details.

Frederick Van Veen writes:

The most noteworthy introduction of 1933 was the Type 650-A Impedance Bridge, the work of GR engineers Horton and Field.

Priced at $1751, the 650 was one of the most successful instruments in the Company’s history, remaining in the GR catalog for the next quarter century.


  • Resistance: .001 Ω to 1 MΩ in seven ranges
  • Capacitance" 1 pF to 100 μF in six ranges
  • Dissipation Factor: .002 to 1 in two ranges
  • Inductance: 1 μH to 1 H in six ranges
  • Storage Factor: .02 to 1000 in two ranges
  • Basic Accuracy: 1% to 2% see manual
  • AC Test Frequency: 1 kHz


1About $4,100 in 2023 dollars