General Radio GR 650-A Impedance Bridge

General Radio 1650B Impedance Bridge

Brooke Clarke 2012


General Radio GR 650-A Impedance Bridge General Radio
                  1650B Impedance Bridge

GR 650-A Bridge
    Background
    Description
GR 1650B Bridge
Patents
Related
Links

GR 650-A Bridge

Background

I have an interest in impedance measurements and this is the first impedance bridge General Radio made.  The later versions of this were the GR 1650A and GR 1650B.  This is powered by four series connected No. 6 dry cell batteries (i.e. 6 VDC).  The 650-A does not use any vacuum tubes but the 650-P Power supply does use them.


The 650-A was introduced in1933 and in 1956 the 1650A was introduced to replace it.

Description

Resistance can be measured using either DC or AC.  Capacity and Inductance are measured using the internal 1 Khz hummer.  The hummer is a carbon microphone element driven by a relay armature in a feedback loop.  It can be seen in the center front of Fig 5 and in Fig 4 with terminals marked: Batt, Hi, Low, Com and there's a second BAT terminal at the upper left of the casting.  The brown box Aerovox capacitor is connected across the Hi and Com terminals (Fig 4)
There's provision for an external AC source and an external AC detector.  These are combined in the optional 650-P that I don't have.

12" wide x 19" deep x 8"high.

Current draw is about 100 ma at 6 Volts.

Fig 1
General Radio GR
                650-A Impedance Bridge
Fig 2
General Radio GR
                650-A Impedance Bridge
Fig 3
General Radio GR
                650-A Impedance Bridge
Fig 4
General Radio GR
                650-A Impedance Bridge
Fig 5
General Radio GR
                650-A Impedance Bridge
Fig 6
General Radio GR
                650-A Impedance Bridge
Fig 7 Hummer Waveform
General
              Radio GR 650-A Impedance Bridge Hummer Waveform
Fig 8
Four each No. 6 Dry Cells dated: 9-1967 (almost 45 Years old)
Each cell measures over 1 Volt.
General Radio GR
                650-A Impedance Bridge Four each No. 6 Dry Cells dated
                Sep 1967
They were very tight into the wooden box because of the
splitting and expansion.


GR 1650B Bridge

There were three versions, the 650A, 1650A and 1650B.

Fig 1 Case in carry position
General Radio
                  1650B Impedance Bridge
Fig 2 Case Open
Case screw visible just in front of handle pivot.
Jacks on left for external sources and detectors.
General Radio
                  1650B Impedance Bridge
Fig 3 Inside
Remove 2 screws just in front of pivots.
Used 4 each D cells.
Images/GR1650B3s.jpg
Fig 4 DC Ohms Measurement
1% resistor
Color Code:
Bridge Measurement:
General Radio
                  1650B Impedance Bridge


Patents

2376394  Null-type meter and method, inclair Donald Bellamy, Gen Radio Co, 1945-05-22, - 650A Bridge?
2966257 Instrument carrying case, Henry C Littlejohn, Gen Radio Co, 1960-12-27 - case for 1650 bridge

Related

Digital Multi Meter - some have capacitance ranges
ESR and Capactance Meter - for in circuit location of bad capacitors
EVB ESR Tester
Millen 90651 Grid Dip Meter -
HP 415 VSWR Meter - can be used with a detector and slotted line to determine complex impedance
HP 4260A Universal Bridge
HP 4274A & HP 4275A LCR Meters - 4-termianl pair
HP 4328A Milliohmmeter - for low resistance measurements using an AC test signal to avoid dissimilar metal DC offsets
HP 4332 LCR Meter -
HP 4395A combined Network, Spectrum & Impedance Analyzer 0 to 500 Mhz
KS8455L2 Line Loop Tester Telephone Installers & Repairman's Meter - measures capacitance in "points" for line length and number of ringers
Stanford Research SR715 LCR Meter - the basis of the HP 4263A
TF2700 Marconi TF-2700 Universal Bridge
Z - Impedance
Zo Transmission Line Impedance (is not constant with frequency)
ZM4 - DC Resistance Bridge (battery power)
ZM-11 - Capacitance-Inductance-Resistance Bridge (AC line power)

Links

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