Meanie wrote:

Correct. T12 are obsolete.

Thanks for confirming. The funny thing is that the only difference is the
diameter (and the wattage), so, it's odd that they're "obsolete" just
because they're a bit fatter.

What's so bad about a 40W tube versus a 32W tube?
Is the 8 watts really a big deal?

Or is there some other reason to ban "fat" tubes?

Thanks for saying that one controls outer and one controls inner.
Is that the standard setup?

Yes. The other set up would be a single four lamp ballast.

Since I think I have two bad ballasts, the single four-lamp ballast for 20
bucks is what I'm gonna get tomorrow at Home Depot (if they have it).

Correct. A T8 is supposed to be 1 inch in diameter.

I measured the T8 LED with a ruler and it was close to one inch, but the T12
was off by a lot. It was 1-3/8ths of an inch, or a T11 in diameter.

Ballasts are now becoming universal. In that, I mean, they can
accommodate voltage of 120 to 277 and they no longer have two wires of
each color. Instead, they offer one red and two blues. Each of those
wires connects with the two wires from each lamp. Thus, the single red
will connect to the two yellows, one blue will connect to two blues and
the other blue will connect to the two reds.

Hmmm... that sounds like exactly the same setup, only different colors. I
guess the colors actually "mean" something then... 'cuz color is the only
difference on the outside.

Unfortunately, inexpensive replacements usually mean cheap ballasts
which will not last long. Also keep in mind if you continue to use
fluorescent fixtures, when a lamp is burned out, it is best to replace
asap to ensure long life of the ballast. When a lamp isn't working, the
ballast continuously attempts igniting the non-working lamp and that
decreases the life of the ballast.

Thank you for that hint, as I did not know that.
They never taught me anything about this stuff in school.

Given out of 16 bulbs I took out, only about half were still working, so I'm
surprised only one ballast was outright dead (with another suspect).