This is bringing back some memories. The old soft 'lead' pencil trick. Pry open the pot - often done in situ - and scribe many lines on the carbon track with the graphite.
On this forum, on which I'm Top Anode, they are full of tricks of the trade. They are mostly from my era, where we made old kit work from war-surplus stuff.
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Young people of today don't know how to fix things. My old science master's homemade t/v was 2 1/2" green screen. And then there was the bloke that breathed life into his tires every Sunday morning with Bandages and Bostic . . .
God, old people can really be boring. 