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.
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
Four each No. 6 Dry Cells dated: 9-1967 (almost 45 Years old)
Each cell measures over 1 Volt.
They were very tight into the wooden box because of the
splitting and expansion.
There were three versions, the 650A, 1650A and 1650B.
Fig 1 Case in carry position
Fig 2 Case Open
Case screw visible just in front of handle pivot.
Jacks on left for external sources and detectors.
Fig 3 Inside
Remove 2 screws just in front of pivots.
Used 4 each D cells.
Fig 4 DC Ohms Measurement
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
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