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| {{GR Product
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| |model=1231-B
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| |codes=VALID,VENUS,VALOR,VIGIL,VIGOR,VILLA
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| |class=detectors amplifiers
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| |summary=Amplifier and Null Detector
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| |image=GR 1231-B Close-Up.jpg
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| |caption=General Radio 1231-B Amplifier and Null Detector
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| |series=1231
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| |introduced=1948
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| |discontinued=1959
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| |designers=
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| |manuals=
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| * [[Media:GR 1231-B Amplifier and Null Detector 634-H 05_1961.pdf|General Radio 1231-B Amplifier and Null Detector 634-H 1961]]
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| {{Catalog History}}
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| }}
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| The {{Title|General Radio 1231-B Amplifier and Null Detector}} was introduced in {{Catalog L}} and remained available through {{Catalog P}}.
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| The Type 1231-B is a combination three stage hi-gain amplifier and dual range null detector. The first stage of the amplifier uses a two step attenuator, the second stage introduces variable gain control, finally the third stage applies tuning filters and amplification. The null detector or voltmeter has two ranges using push-buttons or can be disabled. The panel meter has two scales, voltage and decibels along with a battery check function. The 1231-B is designed for battery operation or AC operation using the Type [[1261-A]] power supply. Regardless of power supply used the amplifier bias supply is provided by "Bias Cells".
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| A front panel phone jack is available for filters to apply to the amplifier.
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| Accessory filters [[1231-P2]] 60 Hz, [[1231-P3]] 400 and 1000 Hz are available to tune the amplifier to those frequencies. The Type [[1231-P5]] variable filter covers 50 Hz to 100 kHz. To adapt the 1231-B for use with a slotted line the Type [[1231-P4]] adjustable attenuator is used for standing-wave ratio measurements. Caution: When using the [[1261-A]] power supply, the 1231-A must be switched on and an external switch must be used to control the power supply.
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| ==Specifications==
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| * '''Input Impedance:''' 1 MΩ in parallel with 20 pF; alternate 10 MΩ input available
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| * '''Maximum Gain:''' Greater than 83 dB at 1 kHz with 1 MΩ load
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| * '''Null Detector Sensitivity:''' Less than 25 μV input gives 1% indication on meter at 1 kHz
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| * '''Output Impedance:''' Approximately 50 kΩ
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| * '''Maximum Output Voltage:''' 5 volts into 20 kΩ; 20 V into 1 MΩ
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| ==Links==
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| * [[Media:GR Exp 1231-B 02_1948.pdf|Experimenter February 1948 describing Type 1231-B]]
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| * [[Media:Grid Bias Cells.jpg|Bias Cell Data]]
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| ==Photos==
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| <gallery>
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| GR 1231-B Front B.jpg
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| GR 1231-B Front.jpg
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| GR 1231-B Side View.jpg
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| GR 1231-B Rear.jpg
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| GR 1231-B Bottom.jpg
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| GR 1231-B Inside Top.jpg
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| GR 1231-B Inside Left Side.jpg
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| GR 1231-B Inside Rear.jpg
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| GR 1231-B Inside Right Side.jpg
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| GR 1231-B Inside Bottom.jpg
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| GR 1231-B Inside Rear A.jpg
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| GR 1231-B Inside Rear B.jpg
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| GR 1231-B Inside Rear Left.jpg
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| GR 1231-B Inside Rear Right.jpg
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| GR 1231-B Inside Top B.jpg
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| GR 1231-B Inside Top C.jpg
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| GR 1231-B Inside Top Left.jpg
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| GR 1231-B Inside Top Right.jpg
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| GR 1231-B Bias Cells.jpg
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| </gallery>
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| [[Category:Detectors Amplifiers]]
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