Since there is a nice looking device that is in the upper right, which appears to be a triac or SCR, there will almost certainly be no tubes anywhere in that.
The nasty-looking item at bottom left is almost certainly a neon bulb. They were sometimes used in place of a "diac" in fairly old-school drives.
The diac (or the bulb) does not conduct until a certain voltage is across it. That is used with other components to set the firing point for the SCR.
I have no idea what is wrong with the drive, but the neon tube is a possible culprit. It looks as if it had too much current through it, or it is just old, since the electrode metal appears to have been evaporated and deposited on the inside of the glass.
There are very few components in that, and none of them other than the bulb are obviously showing any issues. The control potentiometer should be looked at, since it is also in the circuit with the neon bulb and the resistor and capacitor at the bottom.
Used in that way, the neon bulb is actually worked fairly hard. To trigger the SCR takes a pulse of reasonably high current, considerably more than a neon bulb normally would be carrying. That could account for the appearance.
