klystron can act as both an amplifier and oscillator whereas a reflex klystron can act as only an oscillator.

klystron needs a buncher cavity(sometimes multiple bunchers) and a catcher cavity whereas a reflex klystron needs only one cavity.

klystron bunches electrons in forward direction, whereas the other bunches in the reverse direction using a reflector plate.

klystron needs i/p signal (accelerating or deccelerating potential) whereas the other dont.

What is probably the primary advantage of the reflex klystron over the two-cavity klystron is the mechanism used to tune the device. The two-cavity klystron has mechanical tuning, but the reflex klystron is tuned electrically. And it doesn't take an electrical engineering degree for an investigator to figure out that electrical controls can be manipulated a whole bunch faster than a mechanical device.

in twt electrons are constant with rf field for long time&in klystron for short time.

in klystron electron constant with r.f field with long time& in twtare shot time.

A: It is a microwave oscillator device.

the microwave tubes that undergoes velocity modulation are klystron tubes ie, two cavity klystron.....