All I seem to have done for the last week is take the LOPT apart and put it back together again:- I've lost track of how many times now!! Mind you, the wires are just tacked on to the terminals and the whole thing sat on the bench and connected with long wires to the set.
I suspected that the EHT leakage was due to the insulating sleeve between the overwind and the ferrite core. This was the original cause of the breakdown and I had repaired the burnt hole in it. I removed this sleeve from the overwind again and applied some varnish to the inside surface which is against the ferrite core.
Put the transformer back together again and it was much better, but not cured completely. I decided that the sleeve would have to be replaced, but it measured 17.5mm external diameter by 14mm internal. The nearest I could find on the 'net was 18mm which would need turning down- all too much trouble!
I made a temporary sleeve from some thin polycarbonate sheet, coiled up so it was several layers thick. Its natural springiness made it a very tight fit in the overwind.
That seemed to cure the problem completely, so I made a more permanent version and after a few more tests, finally reassembled the transformer properly and reinstalled it in the set.
I've got used to the variety of strange noises that the transformer emits as the valves warm up, but this time it just sat there with a rather feeble 1 Khz whine. After a few more seconds, the PL81 started to glow red. I switched off.
Why is it things that have worked for hours as a lash up, fail to work when you put them back together properly?!!
After a quick investigation, it turned out that the primary had gone open circuit between the PY81 connection and the rest of the winding
This turned out to be one of the fine lead out wires broken inside the sleeving. Luckily, it had left me an 1/8 inch stub to connect to which was very civilised of it, I thought!
I effected a repair and the thing is working happily again connected by long wires. Whether it will still work when I re- install it again, only time will tell!
Another bonus is that the EHT has gone up by about 1KV.
All the best
Nick