Ballast tube replacement (?) Teletone TV-208
 

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.

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Thank you. I've since heard that there's a universal glass ballast, but I'm curious to know what exactly is the ID number for it?

*Update*
I looked up the Tele-Tone Ballast on the Net and was able to get an NOS TBR-104D. I see the schematic calls for a TBR-103D. Will this one be okay? Thanks.

Update - for future reference, it was confirmed that the TBR-104D is indeed different than the 103D. Payment retracted. Oh well, at least I did absolutely need one.