Hello Jan, from the above i assume you know a bit (or maybe a lot) about tv technology etc, so you're able to service tv's ?
First i'd check the power supply (if the 140V is present or better, check with scope to see what happens...if the powersupply switches/trips or so).
Its easy to find this one: the big capacitor on the secondary side of the power supply.
I have serious doubts the problem is the tube, what is a likely cause is the HT transformer, this one (non original) is available for abt 45 euro and original it's abt 70 i think.
Maybe you're as lucky as i: indeed becasue it's a tube-widescreen sometimes they are quickly diagnosed ''tube broken'' but with the Avant RF32 i bought with similar behaviour it was the HT transformer....:).
Than at last: don't know if you'd ever make it to NL, for a truly broken BV3-32 (giving red picture and lines) i had a new tube here for 100,- !!
But as said: i'd take the risk, spending some time on measuring or even exchange the HT transformer, i don't think it's the tube.