[wonderwrench]

If I remember right, the 75 has had issues like that. Hopefully someone else will comment on that tube further. Are you sure you have the local oscillator adjusted high, and now low of the carrier freq? Do the antenna trimmers peak?

I have not had time to work on the 620 but hope to later in the week.
"Are you sure you have the local oscillator adjusted high." I think so but I'm not sure of anything yet. "and now low of the carrier freq?" ???.
" Do the antenna trimmers peak? Yes, all trimmers act normal except the 3 RF trimmers.