If you want 2 secondaries of say + and - 20 volts with common zero. Assuming you have the right primary and drive requirement, number of turns and gauge of wire for the secondary voltages and loads , what arrangements are permissible? Obviously a continuous run of insulated magnet wire, tapped in the centre , but what about a doubled up run, bifilar,in the same sleeving, with commoned at one end joined together for zero volts and the other end split off, one to one polarity of rectifier and one to the other. What about a bifilar run again but one end of each commoned,exterior, but the "plus" line coming from one end of one wire and the "negative" line from the other end of the other wire.
The first is out as too much bulk of sleeving and retain proper primary/secondary isolation. I'm aware that for unipolar secondaries say
0,+5V,+10V then it is permissible to run more wires/thicker wire between 0 and 5 than between 5 and 10 to reduce sleeving bulk.Is there any practical difference, at 40 to 50KHz operation, between say 10 turns of secondary wire with cross-section area A and 10 turns of quadrupled thinner wire each of area A/4. ?