Ballast tube replacement (?) Teletone TV-208

[decojoe67]

I admit that I'm a total novice when it comes to schematics, so I would appreciate if anyone could answer what is likely a simple question to you skilled guys.
Here's a PDF of the schematics:
http://www.earlytelevision.org/pdf/tele ... _90-11.pdf
I see on my chassis, what looks to be a ballast tube is marked as "M3" on the tube chart (below the "TOP VIEW" layout)
My question is that if I wanted to replace this part, what exactly do I search for? The one on the set is missing the metal cover, and although the set works okay (it's was previously recapped), it looks rather dicey.
Thank you for any and all info.