122
The Tektronix 122 is an external low-frequency low-level preamplifier. The low-frequency cutoff and high frequency cutoff can be selected. 40kHz is the highest cutoff.
The 122 has four stages of amplification. The first stage is a direct-coupled differential amplifier formed by both halves if a 12AX7 dual-triode tube. The second stage is a 12AU7 differential amplifier, differentially driven by the first stage. There are DC blocking capacitors between plates of the first stage and the grids of the second stage. The second stage is coupled to the third stage by capacitors, which can be switched
