Reece, thanks for your attention to my issue. Tonight I started following circuits from the problem grids, pulling out components to test them out of the circuit, and looking closely at every solder joint.
Found a cap that may not have been grounded due to a rusty bolt. That fixed the voltage at the anode grid. Then, at 3:00 a.m., I found a resistor that tested OK out of the circuit but was apparently shorting under load. That fixed the oscillator grid.
The culprit:
