On Wed, 24 Feb 2016 21:15:08 +0100, Dimitrij Klingbeil wrote:

[...]

Oh, Dimitrij, I meant to say your diode replacement has made a bigger
improvement to the psu than we expected. The hissing noise has almost
gone and the power resistor now takes almost a minute and a half to reach
50'C instead of less than 15 seconds using the old incorrect BY134 diode.
I now have sufficient time to do some probing around under mains power!
First up I plan to test the rectified outputs from the long secondary
winding to see if they are anywhere near the 6V-60V range they should be.
I'll report back with the results tomorrow.
Many thanks for that!