3A74
The Tektronix Type 3A74 is a four-channel vertical plug-in introduced in 1963 for 560-series scopes. The bandpass is DC to 2 MHz. Each input signal passes through switchable input attenuators and then into a cathode-follower made from a 7586 Nuvistor triode. That drives a PNP differential amplifier. The output of this differential amplifier, for each of the four channels, passes through a diode-based analog signal switching network (multiplexer). The output of that multiplexer drives the output amplifier, which is part transistor, part tube. The one-hot select line signals for the multiplexer are generated by a transistor-based ring oscillator, a four-state cyclic state machine. This allows each of the input signals to be traced on the screen, one after another.