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Kevin Wood G7BCS
Here are a few more pictures for reference:I would fix the intensity problem first if I were you.Running the tube as
bright as it looks in those pictures for any length of time will do it no
favours at all.
Check over all the components in the cathode & grid drive / DC restorer
and see if you can crack that. Then you can focus on the hum without
worrying about burning the tube.