Indeed the screen grid connection and voltage is suspect, but in the construction article, Phil explains that it is a "feature" not a mistake.
Quote:
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The pentode portion of the tube combines both the oscillator and modulator. The novelty of this circuit is that the pentode screen is returned to ground rather than to B+ as might be expected. The modulation input varies the pentode screen voltage about 1 volt above and below ground potential.
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I am scratching my head over that one, however.
jr