Yeah, it's a fine piece of nutty professor equipment.
I'm nearly ready to wake up Frankenstein now.
And after that... World Domination! Muhaahahahahaha!
I tried it after lunch just now and it sorta works. I get a 'good' reading from a known good tube and a 'bad' reading from a tube I fried just now.
After that I opened up the unit to inspect the individual components (there's not many of them). Looks like the 330ohm load resistor has burned out. There's some scorched wires touching the resistor.
That probably explains why I get a >100% reading for a good tube, while the manual states a good tube should read about 60-80%.
Easy enough to fix tho.
I'm very happy with it.