1650-A

The General Radio 1650-A is a portable impedance bridge introduced in Catalog P (1959). It was succeeded by the 1650-B in Catalog T (1968).

The 1650 was the first GR impedance bridge to feature the "Orthonull" function, which is a mechanical link driving the DQ dial from the CRL dial through a friction clutch. (Conversely, turning the DQ dial will not turn the CRL dial.) It helps avoid the "sliding null" problem when measuring components with high losses.

The 1650-P1 Test Jig accessory was designed for the 1650-A.

Key Specifications

• Capacitance: 1 pF to 1100 μF in 7 ranges
• Inductance: 1 μH to 1100 H in 7 ranges
• Resistance: 1 mΩ to 11 MΩ in 8 ranges, AC or DC
• D (of series capacitance): 0.001 to 1 at 1 kHz, (parallel capacitance) 0.1 to 50 at 1 kHz
• Q (of series inductance): 0.02 to 10 at 1 kHz, (parallel inductance) 1 to 1000 at 1 kHz
• Basic accuracy: ±1% of full scale, ±5% for dissipation factor
• Internal oscillator: 1 kHz ±2%
• Frequency range: 20 Hz to 20 kHz (to 100 kHz with reduced accuracy)
• DC Supply: 6 V, max. 60 mA; Battery: Four D cells, current drain 10 mA (AC measurements)
• External Oscillator and Detector: Type 1210-C Unit R-C Oscillator, Type 1311-A Audio Oscillator and Type 1232-A Tuned Amplifier and Null Detector are recommended for audio measurements at frequencies other than 1 kHz
• DC Polarization: 600 V may be applied (from external source) for series capacitance measurements
• Weight: 17 pounds (8 kg) net

Links

• The GR 1650-A & 1650-B Portable Bridges @ conradhoffman.com
• US Patent 2872639, Henry P Hall, Electrical bridge and method. Filed Oct. 10, 1956; Granted Feb. 3, 1959 (describing the Orthonull feature)
• US Patent 2966257, Henry C Littlejohn, Instrument carrying case. Filed Nov. 5, 1959; Granted Dec. 27, 1960
• Henry P. Hall, A New Universal Impedance Bridge. General Radio Experimenter Volume 33, No. 3, March 1959, page 3.
• Henry P. Hall, Orthonull - A Mechanical Device to Improve Bridge Balance Convergence. General Radio Experimenter Volume 33, No. 4, April 1959, page 7.
• IET Labs Application Note, Henry Hall: Father of the Digibridge

Videos

• General Radio Genrad 1650 impedance bridge - Oscillator Circuit repair and calibration @ YouTube
• General Radio 1650-A Experimentation with Coils Capacitors and Tank circuits @ YouTube
• Vacuum Tube Audio Transformer Impedance Determined With General Radio Impedance Bridge @ YouTube

Pictures

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Internal

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  Internal view. The red jack on the bottom left is an aftermarket modification on this unit for an external +6 V supply.

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