1964 Zenith 5111 comes to life!

[DaveWM]

Perhaps a tweeking of coils can help a set thats not perfect, but to go from working fine to zero color ,with nothing done in between, does not sound like spontanious slug movement.

I would stick with the basics until better knowledge has been aquired on what do to.

Start by wiggling tubes, then move on B+ checks, then plate and screen checks of the burst and chroma amp tubes.

My guess is a loose tube/bad tube/open power resistor (perhap taken out by a shorted tube).