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16EP4 is a metal cone tube, I bet it's gassy. Easy way to tell with the CR-70 is start with the cutoff knob all the way counterclockwise, flip the switch to read emission, then slowly advance the cutoff knob till it does something. If the needle slowly rises and you can control it like normal, the tube is probably good (able to display a picture anyway). If however at some point the needle pegs full scale while advancing the cutoff knob, you have a gassy tube. This is called out specifically in some B&K manuals, but not in the Sencore one. B&K call it 'gas regulator' action, whereby the gas inside breaks down at some voltage allowing full conduction at that point. If that's what you're seeing, I'm sorry but the tube is shot.
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Evolution...
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