The Type Z has two inputs, A and B, plus a precision comparison voltage, VC, that is adjustable from 0 to ±1 V, 10 V, or 100 V via a ten-turn pot.
The following differential amplifier can be configured to display VA, −VB, VA−VB, VA−VC, or VC−VB.
This allows DC-coupled measurements of small signals with large DC offsets.
Unlike later comparators, Type Z has separate step attenuators for each input, permitting the user to view the difference between signals of widely differing amplitudes. Unfortunately the divider resistors have no trim, so CMRR is poor except at 50mV/div.
It is also the only comparator that can handle ±100 V common mode at full sensitivity.
With a pair of "Disconnect Signal" buttons, the Type Z was the first movement toward a "GND" position on the input switches.
Maximum sensitivity is 50 mV/div, and common-mode rejection is 40,000:1 "from DC through audio frequencies".
Risetime as a general-purpose amplifier is 27 ns (13 MHz bandwidth). A side effect of Type Z's unprecedented dynamic range is that transient response is a function of signal amplitude: slew rates faster than 1V in 6ns will cause distortion due to grid current.
The Type Z uses both tubes and transistors, capitalizing on the strengths of each.
The step attenuators are turret attenuators.