# 1603-A

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The **General Radio 1603-A** is a Z-Y impedance bridge introduced in Catalog O (1956) that remained available through Catalog T (1968).

Known as *the bridge that always has an answer*, its claim to fame is that it can be balanced for any impedance connected to its terminals. The 1603-A is accurate at audio frequencies from 20 Hz to 20 kHz. It requires an audio oscillator and detector for operation.

The 1603-A directly measures the quadrature components of a complex impedance Z = R + jX, or a complex admittance Y = G + jB. The unknown Z or Y may lie in any of the four quadrants of the complex plane, since this bridge can measure both positive and negative values of R and G as well as X and B.

## Specifications

**Frequency Range:**20 Hz to 20 kHz**Impedance and Admittance:**-infinity to +infinity**Accuracy (with unknown grounded):**1% (see manual)

## Links

- GR Experimenter July 1955 describing the 1603-A
- GR 1603-A @ Fred PA4TIM's page
- Genrad 1603 used to measure audio transformers by ElPaso TubeAmps @ YouTube