What devices are commonly used as VHF and UHF parasitic suppressors at the input and output terminals of a transistor HF amplifier?

Explanation

A ferrite bead slipped over a transistor lead presents a loss that rises with frequency, so it damps VHF and UHF parasitic oscillation in an HF amplifier while leaving the HF signal path essentially untouched. Electrolytic capacitors are useless at VHF, a Butterworth response is a filter shape rather than a component, and a steel-core toroid would be hopelessly lossy at those frequencies.