> power supply ....for multiple preamps and thus many tubes so a much higher current demand. ....high current AC heaters be a problem or would separate lower current heater supplies be better or even dc heaters?
While good microphone(??) preamps have been built on AC heat, in a BIG project it is probably much better to go ahead and do it DC. At as high a voltage as possible (to reduce bus-wire size and rectifier losses).
Given a 5V and a 6V winding, I'd strap them for 5+6= 11.3VAC, 15.8V peak, take-away 2V for diode loss, you get 13.8V max. Taking 1V ripple for 1000uFd/1A, a 6,000uFd cap puts you near 12.6VDC, but 1V ripple around a preamp is worse than well-wired 6.3VAC. Also the ripple-current is brutal. So you should be thinking 220,000(!)uFd, 0.1 Ohms (10 Watts!), another 220,000uFd. The "0.1 Ohms" should be an array of 0.5 Ohm 5W parts so you can use more/less to get the right result (11.4V-12.8V at 12V-wired heaters; preamp tubes don't need a full 12.60V heat). Even then it is a VERY brutal build. Every *milliOhm* matters!! The PT, rectifer, and first cap have to be essentially adjacent, butted, or copper costs (and radiated EMI) will soar.
I'd even be thinking of using a *switching* supply. 12V 6A is not a huge switcher. 0.1 Ohms and 1,000uFd each side ought to take the hypersonic squeal off.