How does a transistor sweep generator work?
Some triggers used Esaki diodes --- aka tunnel diiodes --- with their region of bi_stability.

Others use positive-feedback circuits, where 2 gain-devices (tubes, transistors) implement a loop. The delay around the loop, and the gain around the loop, determine the "snapiness".

With gain of 4X per device, or 16x around the loop, an input ony 1 millivolt past threshold cause 16mv after 1 loop, 256 mv after 2 loops, and 4.096 volts after 3 loops.

And 4 volts is a fine delta_V to control even vacuum tube differential pairs ( called long-tail-pairs).