112

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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. There is an unusual output coupling stage consisting of a shunt current source (6CB6). This constant current drops a constant DC voltage across series resistors in the output signal path. This gets rid of most of the DC voltage that is on present at the plate of the previous stage.

Internal photos needed.