The Tektronix Type Z is a comparator plug-in for 500-series scopes. Its maximum sensitivity is 50mV/div, and it achieves 40,000 to 1 common-mode rejection at DC and low frequencies. Its risetime as a general-purpose amplifier is 27ns (13MHz bandwidth), but it can track a common-mode risetime of 7ns.
Unlike later comparators, it has a separate step attenuator for each input, permitting you to view the difference between signals of widely differing amplitudes. It is also the only comparator that can handle +/- 100V common mode at full sensitivity.
The Type P6023 probe, with R and C compensation, was specifically designed for Type Z.
Type Z was introduced between 1960 and 1962 and uses both tubes and transistors, capitalizing on each's strengths.