[Sideband]

Certainly seems like the transformer has had it. I'll guess that the original fault was the rectifier developing a cathode-heater short which theoretically would short the HT out via the heater winding. If the set was left running in this condition, the rectifier would have been glowing red hot and the transformer heater winding would have been under considerable stress resulting ultimately with insulation breakdown.

A similar problem happend with a Murphy radio I was asked to look at. This used a 7Y3 (I think) loctal based rectitfier that had developed a cathode/heater short. The transformer was completely burned out.

Looking inside the valve, it looked as if part of the cathode was burned away and I confirmed this by carefully breaking the valve open and removing the electrodes.



SB