I've taken a couple of tricyclics but never transitioned from Effexor to one. They do affect multiple neurotransmitters, so maybe the switchover won't aggravate your current problems.

I know there are some forum members who take tricyclics now, so if you create a thread about the one you're going to take, you'll probably get responses. I took nortriptyline with pretty good results once, but it was a long time ago.