OK, so I've fibbed: Its a 203-6 not 203-7
somewhat embarrassing
, but still managed to get hold of a schematic and there's really not a huge amount of difference to the general block diagram. I googled my scope and looked a the pictures and picked the one that looked closest to mine and took the PN, rather than note the model number down before I left it the other night.
HAMEG HM203-6 service manual - most of its german, but all the schma is there.
Anyway I tested some of the voltages the other night, I've made a video, just editing to length.
But the jist of it is that I've tested the heater filament voltage, the intensity control voltage, and the filament to cathode (K ?) voltage and they all appear to be as expected.
(If you look at page 13 of the PDF) I've been measuring them differentially with a cheapo-meter on the PCB on the back of the tube . So measuring between -1877V and -1900V you would expect a 23V difference - which is what I got. Along with 6.3V AC on heater filament and about 33V from intensity control pot. The focus contol is a bit tricky and need to think a bit more carefully as the control pot is part of a large string of resistors connected to -1900V and GND.
So it think the best way of measuring this is to work out the voltage expected across the focus pot and measure the wiper from one end of the pot.
your also probably thinking: "why the hell are you looking at the HV stuff first!?" - well why not, gotta start somewhere, plus it was the most easily accessible place to start! which is actually somewhat concerning: you'd expect the HV to be the LEAST accessible!
Once I get the video done I pop it up here.
cheers