Pete, I owe you a beer!
It was the one thing I didn't worry about, even though Mike (Boulevardier) drew my attention to it yesterday. Thanks to all. What a pleasure to see all the correct voltages slot into place. And it does sound good with the large OPT. I attach pic.
Since last night, I had already tried:
1. raising and lowering the value of the EL84 cathode resistor;
2. swapping the OPT secondaries, following Morgan Jones' advice on oscillation;
3. shortening the leads to the OPT (necessary anyway);
4. tried a number of different EF86s and EL84s.
This a bit of a milestone for me. With much help from members here, this non-engineer has now built all the Mullard amps in the book (5-20, 5-10, 7W stereo and now the 3-3).
David