112
The Tektronix 112 is a DC-coupled differential amplifier introduced in 1955. The voltage gain can be set from 0.5 to 5000 V/V. The frequency response is DC to 2MHz when the gain is set below 166, and DC to 1MHz for gain settings greater than that. The 121 is intended for use with the 511, 512, 514, and 524 oscilloscopes. The input impedance is 1 megohm in parallel with 47 pF. The output impedance is 8000 ohms. The amplifier's schematic and response are identical to that of a Tek 512.
The first stage is a differential amplifier using a pair of 5879 pentodes. Next is a differential amplifier using a pair of 12AU6 pentodes.
The 112 has an unusual output coupling stage. It provides output short circuit protection and shifts the common-mode DC level of the differential output to 0V. The plate voltage of the final gain stage (just before the output coupling stage) is about +150V. When enabled, the output coupling stage is a a pair of constant current sinks. It uses 6CB6 pentodes for this. This shunt current causes a constant voltage drop across output resistors, resulting in 0V at the output. The cathodes of the output coupling stage are supplied by the -150V rail, allowing them to operate as proper current sources when their plates are at 0V.
Internal photos needed.
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1955 Catalog photo
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Manual photo
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Main schematic
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Power Supply Schematic
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Calibrator Schematic
