What are the differences between pre-transistor and transistor era jet engines?
The vibration levels on jets preclude the use of vacuum tubes. They may work if everything is fine and all rotating parts are well balanced, but once you have a defect and an out-of-balance condition, the electronics would fail quickly, just when you need their help the most. Especially the afterburner adds a lot of vibration when it works as designed already.

Earlier jet engines used hydraulics for adjusting things like compressor vane angles (litte stationary "wings" positioned between the rotating discs of the compressor, which help to convert rotational flow energy into compression) and the nozzle size. Like on piston engines, the amount of adjustment was much lower back then, and all adjustments were done mechanically.