"shango66 on youtube does some good explanations re CRT emission problem fixing. Though I don't remember him discussing EHT boosting. "

I'll have to look into that. Nobody in their right mind would try to save an old CRT by boosting the main accelerating voltage.

First I will try the grid bias, if that does it fine, that is IF that is the problem and it isn't some other fault.

Thing is I just heard from the customer that he scope used to work, he actually found the burning -500 rectifier. There are no shorts currently, the new rectifier is doing fine in there.

But no trace.