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The General Radio Impedance Bridge Page

General Radio Corporation of Massachusetts of West Concord, Massachusetts made a broad line of test equipment in the 50's, 60's and 70's. One of the most popular of their units was their impedance bridge. The 1650-A was the standard of the industry at that time. I was taught how to use it in college (MIT) in 1964. It was considered an engineering marvel.

Their first model was the 650-A shown here. It used a vacuum-tube oscillator. It was a large and heavy device. It came in a nifty wooden case.













This was a transistorized and portable version of their impedance bridge. It runs on 4 C-batteries. Since it uses a 1 kHz oscillator, the measurements at low values are pretty dubious. At higher values (say, 200 uH and up), it is pretty accurate. Within a few percent generally. It is still a useful piece of test equipment today. There are few modern equivalents. In 1966, it cost a bit over $1000.







The 1650-B was the last model of this design that General Radio made. In some ways, it was the pinnacle of this portable bridge design. They made some other desktop devices that were more precise, and more expensive, but they never made a better portable unit than this one.

Scanned General Radio Impedance Bridge Manuals

One of the most difficult parts of dealing with these old devices is finding the appropriate manuals. Without schematics and other descriptions, it is a hopeless task trying to repair or even understand these things.




Download 113MB (Watch this spot!)

General Radio 650-A Instruction Manual  This manual describes the theory and operation of the impedance bridge. It has a full set of schematics of the bridge and its companion (vacuum-tube) oscillator.

Download 138MB (Watch this spot!)

General Radio 1650-A Instruction Manual   This manual describes the theory and operation of the impedance bridge. It has a full set of schematics of the bridge and oscillator.

Download 138MB (Watch this spot!)

General Radio 1650-B Instruction Manual   This manual describes the theory and operation of the impedance bridge. It has a full set of schematics of the bridge and oscillator. This is the most complete manual of the three. It has a number of half-tone images of the interior of the unit and the construction. There are quite a few pages of instructions as to how to use bridges in their various modes of operation.

Various Scanned General Radio Manuals

Here are a number of other General Radio equipment manuals. I haven't had time to write up anything cool about the equipment, but if you need the documents, here they are. As I scan them, I'll just stack them up here.




Download 16MB

General Radio 1862-A Instruction Manual  Vacuum-tube megohmmeter.

Download 24MB

General Radio 1862-B Instruction Manual  Vacuum-tube megohmmeter.

Download 54MB

General Radio 1862-C Instruction Manual  Vacuum-tube megohmmeter.

Download 13MB

General Radio 1110-A Instruction Manual  Interpolating Frequency Standard.

Download 13MB

General Radio 1218-B Instruction Manual  Unit Oscillator 900-2000 MHz. Tuned Klystron oscillator.

Download 12MB

General Radio 1360-A Instruction Manual  Microwave Oscillator.

Download 16MB

General Radio 1362 Instruction Manual  UHF Oscillator 220-920 MHz.

Download 38MB

General Radio 1391-B Instruction Manual  Pulse, Sweep and Time Delay Generator.

Download 21MB

General Radio 1398-A Instruction Manual  Pulse Generator.

Download 49MB

General Radio 1606-A Instruction Manual  RF Bridge.

Download 29MB

General Radio 1608-A Instruction Manual  Impedance Bridge. This was the most accurate of the passive bridges. It was not portable. It was a shop-desk unit.

Download 5MB

General Radio Ganged Variacs Instruction Manual  Catalog. Has lots of technical information.

Download 5MB

General Radio V5 Variac Instruction Manual  Manual on the V5 (5-amp) variac. Has pinouts.

Download 5MB

General Radio V20 Variac Instruction Manual  Manual on the V20 (20-amp) variac. Has pinouts.

Download 10MB

General Radio Variac Catalog 1961 Instruction Manual  Catalog. Has lots of technical information.