From what I learned by using the CR-70, a tube with air will peg the needle after advancing the cutoff control beyond a certain point. You reach the ionization point of the gas inside, and then you get full conduction. Exactly that happened with the 21AXP22 that was in my Director 21, purple neck to boot. But this one is fully variable throughout it's entire range, and the needle rises slowly as it warms up just like it should. So I'm optimistic about it, but we won't know until some HV can be applied.
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Evolution...
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