Was used in the HP1000 series, and I did use one ( and repaired mercury relay boards on it) that was part of a room size ATE system. Was used IIRC as one of a couple of ADC units that measured power supply voltages fed to the UUT, while the precision voltmeter ( it had a Nixie or Panaplex display, buried in the rack) did the precision readings, along with the synchro to digital converters, and the AC converters, to get the high resolution (14 bit) data.
The output is designed for transformer coupling both ends, and the input is fed to a transformer (Pulse one with a center tapped primary, and a 93R impedance secondary) that feeds a 7474 flip flop, biased so that the pulses set and reset the output, giving you the recovered data signal. IIRC 470R to Vcc, center tap to that and a 330R to GND, biasing the input nicely in the middle of "don't care" space, with the pulse amplitude alternately driving the input stage into conduction on the negative edges.
Replaced a lot of 5474 IC's in that position, they did not like being driven above Vcc on the edges, and would eventually have enough threshold shift to stop recovering the data reliably. Remove the IC, place in a test jig and it works perfectly, but you find the high threshold is now 1V or so, and the gate input current is around -5mA. We had tubes of them around, but is is a standard.