Sorry for asking what I know in advance is going to be a stupid
question, but I tried googling and could find no information.
Normally I work on pinball machines and arcade machines, and I've
never run into this part until I was asked to work on a television set
with bad sync.

Anyways... on the sync board is what I assume to be a rectifier...
marked B12 in large letters, with the number 69 in small letters. I
can find no information online.... any ideas on what exactly this part
is, and its specs?

Thanks in advance, and sorry for the stupid question.

Gordon