Saw this bit on the Ampex list, and was intrigued. Hadn't heard of them before.
I just received two torroidal power transformer kits... yes KITS,
from Torroid Corp of Maryland. They give you a pre-wound primary, and
instructions for putting your own secondary(ies) winding(s) onto the
core. No wire supplied for the secondary since that's load dependent.
Instructions are very complete, and there's tables to help you ensure
that your secondary will actually fit. Mylar tape to insulate the
finished winding(S) also included.
There are multiple core sizes available; you pick that when you
order. Price for an 80VA core was $30.
There is a 250v RMS voltage limitation between any two windings.
I have used the kits from both Plitron and TCM and they are both very good, BUT
they are still relatively expensive and if you want a B+ winding there are a LOT
of turns to put on. It is much cheaper to tear the secondary off an existing
toroid and wind a new one on although it can require a little cut and try work
to figure out how many winds are on the primary.