Parasitic oscillations in an RF power amplifier may be caused by:

Parasitic oscillations in an RF power amplifier are often the direct result of a lack of neutralization. Without a neutralization circuit to cancel out the internal feedback caused by interelectrode or stray capacitance, the amplifier can easily begin to self-oscillate. Once this positive feedback loop is established, the amplifier generates radio frequency energy at unintended, unpredictable frequencies. This can cause severe interference and overheat components. Proper neutralization ensures stability by injecting a phase-inverted signal to cancel this natural positive feedback. While overdriving a stage or having poor voltage regulation can cause severe distortion, splatter, or harmonic generation, they do not inherently create the continuous feedback loop required to start a parasitic oscillation.