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Sounds like the thermistor is probably OK since it's not going open. Have you verified there's Boost voltage going to the height control? Should be around 600V or more.
Pin 9 of the 8BU11 is fed thru a resistor (blurry print looks like it's 100 ohms, can't read the R designation). There should be 130V on the supply end of this resistor. Is there? If there is, the resistor must be open, giving you the 0V you're getting on pin 9. Does the resistor look cooked?
There's a .01 cap from pin 9 to ground (can't read the C designation). It might be shorted. Or possibly a short in the tube.
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