The tech is probably up against a not 100% provable cause. Proving it
would probably be an in shop repair. I can think of MANY good reasons he
wouldnt want to go there.
Keep in mind you want to make a good B&W first. Like John said keep the
color OFF while you troubleshoot it.
One other thing you can try. If there is a very low ohm resistor ( 1-3 ohm 1-2 w) in SERIES with the filament jump it out & see if it improves. If it
does its the CRT 99%. As with cleaning there is a tiny risk to the CRT doing this.
73 Zeno
LFOD !