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.
Type Z has two inputs, A and B, plus a precision comparison voltage, Vc, that is adjustable from 0 to +/-1V, 10V, or 100V via a ten-turn pot. It's possible to view A, -B, A-B, A-Vc, or Vc-B.
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.
With a pair of "Disconnect Signal" buttons, Type Z was the first movement toward a "Gnd" position on the input switches.
Type Z was introduced in 1960 and uses both tubes and transistors, capitalizing on each's strengths.