1650-A

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

The 1650 has an "Orthonull" feature, which is a mechanical link driving the DQ dial from the CRL dials through a friction clutch. It helps avoid the "sliding null" insenswhen measuring components with high losses, the Orthonull feature locks the DQ dial to the CRL dial with a friction clutch. If properly adjusted, turning the CRL dial will also turn the DQ dial. But, turning the DQ dial will not turn the CRL dial. The manual describes the feature in detail, but because I didn't grasp it at first, I'll say it again. Using Orthonull, the DQ dial turns by itself in the usual fashion. The CRL dial will also drive the DQ dial at the same time. Balance the bridge in the usual way for the deepest null. Friction will be a bit higher, but the sliding null problem will be entirely avoided, thanks to Henry's very clever invention.

Specifications

Capacitance: 1 pF to 1100 μF in 7 ranges.
Inductance: 1 μH to 1100 H in 7 ranges
Resistance: 1 mΩ milliohm to 11 MΩ in 8 ranges
D: (series capacitance) 0.001 to 1 at 1 kHz, (parallel capacitance) 0.1 to 50 at 1 kHz
Q: (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)