I very carefully experimented with a Unico hybrid. It would take two days to sound its best, with significant changes at 2/4/6/8 hour marks. Even swapping hot tubes with cold, the amp otherwise fully warmed up (i.e. on for at least two days), took four hours for the sound to stabilize (and improve). I tested over several weeks, rolling my fair collection of 12AU7's. Speakers were Fostex F120A single driver augmented with electrostatic super-tweeter.
-- William
-- William