Rarely do I succumb to marketing prose, but the GR folks did a fine job with their description of the 1603. My "P" catalog (April 1959) reads…
"This remarkable bridge can easily be balanced for any impedance attached to its terminals- from short circuit to open circuit, real or imaginary, positive or negative. Thus it can make not only the usual routine measurements but can also solve many difficult problems beyond the capabilities of other measuring instruments. Clearly, such versatility belongs in any laboratory where electrical impedance measurements are made."
Surely, I couldn't live without this bridge and began a search for a clean example. It was located at a dealer in Colorado, and at a rather high price. Being impatient, and having a birthday coming up, I decided to buy it, lest I not find another one in a reasonable amount of time. This was before eBay, mind you.
The bridge was in excellent shape, with the exception of the dial verniers. These had been mis-installed by someone and weren't engaging the circular plate on the back of the dials. They also needed to have their offset adjusted for proper friction. Not a difficult repair at all. Everything else was clean and in fine working order. I believe it even included a manual.
The 1603-A does exactly what GR said it would. It will measure anything. It's accuracy isn't great, but as GR said, "… the ability to get an answer of any kind is often very valuable.". The real problem is that the answer is expressed in rather inconvenient terms, the Cartesian coordinates of complex impedance or admittance. Back in the days of slide rules, I can imagine engineers avoiding this bridge in droves, and only the most mathematically savvy actually putting it to use.
Today it's a simple matter to write a computer program or a spreadsheet to do all the conversions necessary. Given that, is the bridge more useful today? In a word, no. Fascinating as the bridge is, most things I deal with happen at very low or very high values of impedance. That's where the bridge has the worst accuracy. As an example, the bridge is perfectly suited to measuring the output impedance of an amplifier or battery, as it's AC coupled. (never move the Z-Y switch when doing this) Unfortunately, these values tend to be a few ohms, and the readings, even when taken from the auxiliary dials, are crowded at the very end. I've gotten some good data on audio transducers, and can envision applications where the bridge will come in handy, but it's not something you reach for on a weekly or monthly basis. For normal component measurements (L & C), any other bridge is likely to be more accurate and certainly more convenient.
Another aspect of the bridge is the learning curve. This isn't something where you skim the manual, then make some quick measurements. It takes prior experience with traditional bridges, a careful reading of the manual, and experimentation with known impedances, to have confidence in measurements of complete unknowns. On the other hand, once you've mastered this bridge, no other bridge will intimidate you, and you'll have a better appreciation for all the forms impedance can be expressed in. Definitely recommended for any serious GR collection.
C. Hoffman
last edit August 28, 2010