Hi Peter,
Oh dear,
how can you put a trippler in such a rare set etc. etc. I mean they hardly ever come up for sale
Before you removed the overwind, did you rule out EHT leakage from the heater winding of the EY51 (or a gassey EY51) by using a stick diode? The heater winding has been known to leak through the paxolin to the transformer's core. Later TV24 sets (where the EHT is arranged to be slightly higher) had a ceramic ring at the top of the LOPTy to insulate the heater winding, so it must have been a problem back in the day.
I guess that if it was simply the overwind at fault, then maybe it could have absorbed so much moisture that the change in 'Q' as it was unwound was gradual, unlike with a shorted turn.
The fact that the line linearity now looks ok is a sure sign that something was wrong with the overwind. I say put the line output cover back on and no-one will know
Please see the attached horror...
Cheers
Andy