Thanks Ian.
Remember the test dummy xformer is 18V regulated to 15V, the FY6600 xformer is only 15V regulated to 12V. Thought that might result in similar heat disapation.
So if an 18V xformer gives me 25Vrms / 35Vpk the 15V might be around 20.5Vrms (based on a extrapolated 29Vpk). That's unloaded.
Your spice sim won't run for me, simulate and most other things are greyed out, but my LTSpice currently has issues in Linux, might work natively in windows if I reboot.
The xformer arrived, still no FY6600. So I could end up with a rather nice audio PSU and no sig gen
Nor has the +-12V PSU kit board I ordered.
I haven't powered it up, maybe over the weekend, it looks fairly well done. The primary and secondard windings are around what looks like high temp plastic or ceramic bobbins which wrap each side of the core. The chassis protrudes up the middle, but not fully. So the windings do have separation. It's hard to see but it's not much, maybe a millimeter. That might suggest it would not have a high isolation value and could potentially arc across with a HV surge. But I'm grasping in the dark there.
Winding outputs are not polarized in any way. Same colour wire both ends, so I will need to use the meter to find the polarity for commoning.
Ordered some 63V 1000uF and 470uF caps. If I need to replace the capcitors in the +-12V and +5 regulator boards. They will also allow me to make the test xformer circuit simpler and test commoning it's two 18V secondaries.
Out of interest, my mains measures at 239V (from memory), been a while since I tested it.