Can you spot the differences?

Of course you never go into production on revision A. Lesson learned: Never use autosensing level shifters for transmission applications. They just don't have enough drive strength for a long wire. They have a very counterintuitive property when they're driving a load that's too big: they go into oscillation. When the driver cannot bring the output level above threshold before the one-shot timeout it will switch directions. Then it will try to overwhelm the driver on the Teensy (it can't) and switch directions again. Repeat.

I also had to pick different capacitors for C1 and C5. The ones I had were to big to fit into the tube. The new ones have smaller values and less voltage margin. I really hope I get away with that.

There's one more thing different. Can you spot it?