A few expensive small-signal components utilize two rectifier tubes, including 5AR4s; each supplying one stereo channel. This sometimes includes massive filtering capacity. OTOH, most high-end power amps have only one rectifier and much less filtering. I realize this may be for marketing purposes, to some extent, for those pre & phono amps with "over-sized" power supplies. But if there are valid reasons for this, why don't more power amps use larger a PS?