Hi Chris
Well.... The plot thickens.
Basically the output TX has 2 separate secondary windings.
I have a red / yellow winding which the red has been grounded, looks original.
Then theres another winding with blue / yellow / brown.
None of these are grounded. Also the wires are doubled up in pairs, same colour.
This would explain the lack of output as someone connected accross the grounded red on the single winding and on the blue on the other winding
I measure low resistance on the red / yellow @ 183 milliohms, then between the blue / yellow / brown 46 / 60 / 93 milliohms between them.
That all looks good, so whats what??!!
Negative F.B is taken from the brown wire.
I wonder if these 2 windings need series up together which might of been done on the rear plug when inserted?
The mullard design is differant, it has an extra ECC83.
Very similar it some respects with circuit design, some componets differant values and minus the ECC83.
Ive attached a few pics.