1121

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The Tektronix 1121 is a 5Hz to 17MHz amplifier with gain of 100. The maximum output is 2Vpp into a 93-ohm load. The 1121 is AC coupled at the input, but DC coupled at the output. The output stage is a 12BY7A pentode, V483, biased with 33mA plate current, which gives a transconductance of about 13mS. Assuming the tube operates unilaterally, this gives an impedance of about 77 ohms at the cathode of V483. Series output resistor R486, 30 ohms, makes the output resistance of the 1121 about 107 ohms. (Why is this not 93 ohms?)

The 1121 uses a turret attenuator at the input.