found a 1960s Philco Portable TV today at the Antique Mall!

[Electronic M]

Turn the brightness down or you will burn that line into the phosphors permanently! The reason that line is so bright is that the energy that would be dispersed over 525 lines is being concentrated on only one....The phosphor is not meant to handle that much energy hitting it! Turn the brightness all the way down (if that extinguishes the line turn it back up until the line is visible again but dim) until you fix the vertical.
Even weak tubes can produce a bright line, you will know it is a good tube once you fix the vertical.

Tubes can be an issue, but bad capacitors, and resistors are a more common cause of vertical deflection failure....I hope the vertical output transformer and yoke are good, they are not the most common cause of that type of failure, but still a possible cause, and often hard to get replacements for in many sets.