Thus guy is seen removing the "I" laminations, the lifting off the entire HT bobbin with relative ease.
https://www.youtube.com/watch?v=DRVlqwsIl6M
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Actually after watching it properly he safely removes the primary and filament windings and leaves the bit we want to know for another episode.
Looking at one of mine, the weld is quite superficial. More so in real life than this picture suggests, and I think a small grinder might be more suitable than a hacksaw.