Hi, folks, RR here. I have just made a 6.3 volt heater transformer from a 15 + 15 volt, 12 va general purpose transformer which I stripped out of an old knackered audio mixer. It was only possible because it had both windings wound together side by side, both wires together, I think that's what's called bifilar winding. And it has separate bobbins and it wasn't varnished, so I could easily get at the secondary winding and start unwinding it, just guessing to start with, I removed the laminations to start with but I put them back in to try it and it was still too high a voltage, about 9 volts, so I then started removing more wire carefully without removing the core this time, just threading it through the gaps at the sides and then trying it on a meter again and again until it was right and then I carefully load tested it until I got the right reading. Of course it means it is now running at just over half it's power rating but it still gives 6.3 volts at 1 amp which is more than enough for just about any colour tube. RR.