3A9
The Tektronix 3A9 is a differential amplifier plug-in introduced in 1969 for 560-series scopes. It provides a variable high-frequency cut-off from 100Hz to 1MHz. It provides a variable low-frequency cut-off from DC to 10kHz. In the case where the frequency response is set to go down to DC, the 3A9 provides a variable offset voltage. The 3A9 provides differential high-impedance voltage inputs and an AC current probe input for use with, for example, the P6021 or P6019.
The common mode rejection is 100,000:1.