Drawbacks of klystron amplifiers:

• As  the oscillator frequency  changes  then  resonator frequency  also changes and the feedback path phase shift must be readjusted for a positive feedback.
• The  multicavity  klystron  amplifiers  suffer  from  the  noise  caused  because bunching is  never  complete  and  electrons arrive  at random  at  catcher  cavity. Hence  it  is not used in receivers.