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These products
were used by amateur and professional alike to quickly determine
the value of resistors, capacitors, and inductors, the basic
building blocks of electronic circuits.
Of the many impedance bridges manufactured by General Radio,
these three are perhaps the most familiar. Many thousands of
these workhorses were sold and can still be found in ham shacks
and laboratories around the world.
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The Type
650 Impedance Bridge, the first of the series, was designed
in 1933 by R.F. Field, (M.S. Brown 1907). “Bobby” Field
joined General Radio in 1929 and designed many of GR’s
precision measuring instruments. The 650 used a “microphone
hummer” as the ac oscillator to drive the bridge circuits,
with headphones used to detect the null balance. Batteries
and a meter were used for dc balance. At $175 it was a great
seller! |
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The
Type 1650 Impedance Bridge replaced the venerable 650 in
1959. Designed by Henry P. Hall, (M.S. M.I.T. 1949) it used
transistor circuits and included a unique “Orthonull” ganging
arrangement to help avoid false nulls. This product rapidly
spread throughout the world and many are still in use. |
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The
Type 1657 Digibridge was introduced in 1976. Designed by
a team led by Henry Hall, this product was one of the first
users of a microprocessor and firmware for precision measurement.
It led to an entire family of instruments, of which the current
generation is sold by QuadTech, Inc. of Marlboro, Massachusetts
(www.quadtech.com). |
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