Curtis Mathes FF500M no vertical

[ha1156w]

I finally dug my CM FF500 out of storage and began to tackle its electronic ills. I have no vertical deflection although horizontal is full width. My first thought was the 6GF7 vertical osc/output tube. Are these known to fail in these sets (a reworked CTC16 I understand)? Are there other common-failure components I should go about checking?

Thank you