On Monday, 5 February 2018 12:00:54 UTC, frank wrote:

Hi all,
does anyone have any very old CRT cross-reference around? I probably need to
replace an Amperex M24-302W 9" CRT on a vintage CBM PET 2001 and probably
these CRTs are unobtanium now. Maybe some old monochrome TV CRT could be
substituted?
The tube has probably a cathode to heather short. Even with the cathode lead
grounded, the screen is all white with brighter retrace lines. G1 sits at -32V
so, it's not a matter of wrong bias or something similar.
Cathode signal generated from the monitor CRT is positive and about 0V should
cutoff the beam, according to the schematics.
Might be a failure on the HV generator that gives too high voltage, I'll
measure it later (shoud be 10 KV), but I think if it was that, it would kill
the flyback transformer quickly, isn't it?
Frank

An h-k short is easily sorted with a transformer. EHT failure wouldn't get you a white raster. Cathode v normally needs to be raised to cut a tube off, not lowered.


NT