This was something I've heard too, way back when the motorola's had GaAS hybrids (Gallumium Arsenide or something) they suggested you pass AC before RF, and let the amps "burn in" for awhile before activating, I don't know if anyone ever actually did that ...lol All the newer mods should have silicon hybrids, that don't have a burn in issue.
This is CABL.com posting #309534. Tiny Link: cabl.co/mbsGE