The electrons in a gyropeniotron transfer their rotational energy through the transverse migration toward the ridges or the vanes of the waveguide without any orbital bunching. A slotted waveguide (magnetron type) is used for enhanced interaction impedance at high cyclotron harmonics even with low-energy beam and for better mode control. The number of vanes required is 2(s+1) where s is the cyclotron harmonic number of the gyropeniotron interaction. We have calculated the critical current, oscillation frequency, and characteristic wave number for the excitation of absolute instability in gyropeniotron amplifiers. We found that the threshold current decreases as (alpha) increases (at fixed beam voltage) where (alpha) is the ratio of the perpendicular velocity to the parallel velocity of an electron.