The Tektronix 5B40 is a 60 MHz timebase for 5400-series scopes
The trigger signal passes through source switching, coupling switching, and then a JFET source-follower buffer. Next, the signal is buffered by a PNP emitter-follower biased at around 5mA collector current. That provides a known (low) source impedance for driving the switch-selectable LF reject and HF reject filters. The output of the filters drives a discrete NPN differential amplifier, which drives U165, a 155-0109-01 Tek-made trigger IC.