I cut the pins at the base of the 6L6 envelope to see that area and the
ribbon that connects to the cathode tube is spark eroded to a ragged break.
This ribbon is 0.5 x 0.04mm in section, if it was copper then I make the
rupture current would be about 6 amps. Presumably failed at a weld spot so
less than that

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Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
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