There is described an amplitude-controlled electronic device intended to generate at an output an alternating output signal of substantially constant amplitude. The roller assembly includes a rotatable roller shaft for rolling and unrolling a solar blanket and a non-rotatable protective casing which surrounds the roller shaft. The wound-field synchronous machine includes a stationary portion that includes a main armature winding and a rotating portion that includes a main field winding that receives excitation from the flux-regulated PMM. The bur can be used for abrading tooth root, gingiva, and bone structures without gingival incisions.